Organised by Metallwerk Plansee in the picturesque Austrian Tyrol, the Plansee Seminar (3–7 June, Reutte, Austria) comes around just once every four years. Metallwerk Plansee was one of the pioneers of powder metallurgy, and its seminars encourage the interchange of ideas at the highest levels of science and technology.
In five hectic days, well over a hundred papers are crammed into nineteen regular oral, ‘special interest’ oral and poster sessions, cunningly devised so that those with an interest only in refractory metals OR hard materials will miss nothing, whilst those with an interest in both (like myself) are constantly be faced with problems of selection and a need to be in two places at the same time.
This preview feature is based on advance abstracts and therefore subject to change. Only the “key” author is identified here, also expected to be the presenter. The headings are those employed by the Seminar organisers for the relevant sessions and the papers are reviewed in their order in the advance programme. This installment, covering the first group of poster contributions on hardmetals, is both a “taster” for those attending and, for those interested but unable to be present, encouragement to obtain the full papers when published by Plansee.
The Plansee Seminar takes place from 3–7 June, 2013 in Reutte, Austria.
Applications
Tribological behaviour of hardfacing materials in PWR environment, W.-J. Chitty, AREVA, France
Hardfacing materials are employed in Pressurised Water Reactors (PWRs) in order to improve wear resistance of some components. Not only does this wear threats component efficiency and service life, but it also could raise safety issues.
For these applications, materials withstand relatively aggressive environmental conditions: high pressure and temperature (300°C, 150 bar) in water containing boric acid and lithium hydroxide. This peculiar environment induces specific tribological properties of these materials that have to be qualified in PWR conditions.
Hence, wear behaviour of cobalt base and nickel base hardfacing materials obtained by Hot Isostatic Pressing (HIP) are compared in air at different temperatures based on experiments on a pin-on-disk tribometer and in PWR conditions with an impact-sliding motion on a specific tribometer developed by AREVA. An interest is also given on the relationship between the manufacturing process of Stellite® 6 and its tribological properties.
Applications of PM hard materials to scrapers of railway machines, C. Besleaga, Econet Prod Bucharest, Romania
In the frameworks of railway infrastructure, the various forms of wear phenomena have a significant share. The objects of this paper are the scrapers from the ballast cleaning railway machines. These scrapers work in an intensive stress and wear regime. The metallic powder from very hard alloys and specific technologies of powder metallurgy were used for manufacturing the active part of the scrapers' bolts, and also a charge with very hard alloys powders by laser melting on the body of the bolt, in the adjacent zone of the active part, to decrease the wear intensity. For establishing the very hard alloys powders and charge zones, FEM simulations were performed on the models and also experimental research was done (on site) in various work conditions. We established the optimal shapes of the scrapers and of the zones, (of) the sizes and types of powder from the charge zones through melting with laser technology to increase the lifespan. This paper is addressed to the fields of powder metallurgy, road infrastructure or mining.
Design optimisation of complex shaped cutting tool systems on the examples of a lightweight crankshaft milling cutter and a lightweight turn chasing wheel system, A. Hosp, CERATIZIT Austria GmbH, Austria
Increasing demands with respect to time-to-market issues and total-cost efficiency in high-performance cutting applications for complex-shaped parts such as milling of crankshafts for automotive applications nowadays require an interdisciplinary engineering approach regarding the interaction between design, development and prediction of the system behaviour with the aid of numerical analyses. In the present contribution this is addressed to a lightweight internal milling cutter and a lightweight turn chasing wheel system, respectively. Both of them are built up modularly via a multiple cartridge system clamped onto wheel shaped tool bodies by an innovative X-Lock system for milling and screws for turning, respectively. A mechanical 3D finite element based modelling approach accounting for assembling as well as cutting loads is applied to the full part assemblies aiming at minimisation of load induced deflections as well as mechanical stressing of the individual components. Real-scale field tests verify the numerically obtained results, thus, enabling the derivation of functional dependencies between material, geometrical design, assembling load, and operational load parameters, respectively. As a result novel tool designs are developed showing improved structural rigidity, reduced time for tool handling and minimised costs in technical application.
High performance ultrafine cemented carbides and its application, C. Wei, Beijing University of Technology, China
Recently, we have developed a rapid and complete route to prepare ultrafine cemented carbides, which integrates in-situ synthesis of WC-Co composite powder and sinter-HIP. By the in-situ reduction and carbonisation reactions of pretreated nanoscale WO2.9, Co3O4 and carbon black powders, the WC-Co composite powder with ultrafine particle size was synthesised. The composite powder was densified by the sinter-HIP technique. The prepared cemented carbides bulk has homogeneous and ultrafine microstructure, particularly the material has excellent combined mechanical properties with the Vickers hardness of HV30 1580, fracture toughness of 14.5 MPa.m1/2 and transverse rapture strength of 4720 MPa. The mechanisms for the enhancement of the properties were proposed based on the grain size distribution, binder phase characteristics and WC/Co orientation relationship. The prepared ultrafine cemented carbides have been manufactured into the cutting tools, which exhibit outstanding properties as compared with the materials produced by some other techniques. It shows that the present route has distinctly important potential to industrialisation and wide applications.
Modelling, Characterisation and Testing
An innovative nondestructive method for the inspection of brazed cutting tools, W. Tillmann, Technical University Dortmund, Germany
The increasing importance of cemented carbides is based on their ability to significantly improve the wear resistance and durability of many cutting tools. In case of the low cost manufacturing of bulk products such as saw blades, a fast and stable joining technology is needed to fix saw teeth on a steel blade. Brazing is a suitable technology due to the possibility of joining different materials like cemented carbides and steel. Even though this technology has been investigated for many years, failures like chipped teeth as a result of insufficient joints cause a premature breakdown of the tool. It is almost impossible to detect these failures during a visual inspection of the saw blade after brazing.
In this paper, the authors present their first results to apply an innovative, nondestructive method for the inspection of cemented carbide joints. In particular, the measurement of the electric resistance could help to solve the problem of producing joints with a high bonding quality.
Tribological profile of binderless niobium carbide, W. Mathias, BAM Federal Institute for Material Research and Testing, Germany, Germany
The unlubricated (dry) friction and wear behaviour of alumina (99,7%) mated against binderless niobium carbide (NbC) rotating disks under the type of motions of unidirectional sliding (0,03 m/s to 7 m/s) and oscillation (f= 20 Hz, dx= 200 mm, 2/50/98% rel. humidity, n= 105/106 cycles) will be shown. The microstructure and mechanical properties are also presented.
Thanks to the tribological database TRIBOCOLLECT of BAM; the obtained tribological data will be benchmarked with different ceramics, cermets and thermally sprayed coatings.
The estabished tribological profile revealed a strong position of NbC under tribological considerations and for closed tribosystems against traditional references, like WC, Cr3C2, (Ti,Mo)(C,N), etc..
Correlation of WC grain size distribution to hardness and coercivity, T. Persson, Seco Tools AB, Sweden
This study presents the correlation of WC (tungsten carbide) grain sizes and grain size distributions to coercivity and hardness with a fixed amount of Co binder. 14 samples of WC-7wt%Co-0.28wt%Cr have been investigated. The matrix of samples contains a large variety of mean WC grain sizes and WC grain size distributions. The coercivity and the hardness have been related to the area fractions of the grain sizes. EBSD has been used to evaluate the WC grain size.
Main conclusions are that in cemented carbides, with a fixed amount of Co binder:
- Coercivity is decided by the fine fraction of the WC grains.
- Hardness is decided by the mean WC grain size.
- There is no standardized analyzing method in use today that gives information about the largest WC grains.
The implications for coercivity as a quality measurement, used to approximate the mean WC grain size in cemented carbide, depends on the ability to predict the WC grain size distribution, e.g. the stability of the raw material and the production process. If one can expect that the grain size distribution is predictable, it is possible to estimate the mean grain size from the coercivity measurements. If, however, the grain size distribution cannot be considered predictable (due to e.g. milling, sintering or the raw material) it is questionable to use coercivity as a quality measurement.
The corrosion behaviour of WC-TiC-Co cemented carbides in alkaline solutions, N. Lin, Central South University, China
The effect of increasing titanium carbide (TiC) content on the corrosion behaviour of WC–10 wt% Co hardmetals was investigated in 1 M sodium hydroxide (NaOH) alkaline solution. Increasing TiC content makes the open circuit potential (OCP) in the test solutions more positive than the base alloy. Increasing TiC led to nobler free-corrosion potential value and decreasing corrosion current density. XRD results showed that the addition of TiC can reduce the corrosion of WC in the sodium hydroxide solution. SEM and X-Ray Photoemission Spectroscopy demonstrated that titanate formed in the surface films of the TiC content specimens in sodium hydroxide alkali.
Microstructure analysis and mechanical properties of nbc-co/ni/cu/fe3al cemented carbides, S. Huang, Katholieke Universiteit Leuven, Belgium
NbC has a high hardness (19.6 GPa) and melting temperature (3600°C), and is used as a grain growth inhibitor in WC-Co cemented carbides. In the present study, the influence of different binders on the sintering ability, microstructure and mechanical properties of NbC-matrix cemented carbides was investigated. The binders are Co, Ni, Fe3Al or Cu. The powder mixtures were sintered in the solid state by spark plasma sintering and in the liquid state by conventional vacuum sintering. The binders not only affected the densification but also the microstructure and mechanical properties. A limited NbC grain growth was found in the NbC-Cu and NbC-Fe3Al materials, whereas rapid grain growth occurred in the Co and Ni bonded NbC. A detailed microstructural analysis was conducted by electron probe microanalysis. Mechanical properties, such as Vickers hardness and indentation toughness were compared.
On the formation mechanism of TaC/TaNbC aggregation in WC-Co cemented carbides, J. Qu, Zhuzhou Cemented Carbide Cutting Tools Co., Ltd., China
The formation of TaNbC aggregation in WC-Co hardmetal when the content of TaNbC is about less than 0.5wt% can be easily found, resulting in nonuniform distribution of Co phase and aggregation of TaNbC phase in local zone. However, the formation mechanism of TaNbC aggregation is still uncertain. To further investigate the mechanism, temperature sintering experiments of WC-Co-TaNbC alloys (1200~1450°C) were conducted, and the microstructure evolution of TaNbC were exhibited by SEM/EDS. The results indicated that when the sintering temperature is above 1350°C, TaNbC started to be aggregated. With the increase of the sintering temperature, the aggregation area increased obviously. Besides, the results demonstrated that TaNbC aggregation were sensitively dependent on their content. The lowest additional content of TaNbC with disperse distributed in WC-Co alloy are their saturation solid solubility in Co phase. The formation of TaNbC aggregation is related to their nucleation and growths in cooling. Fast cooling can alleviate or even eliminate the TaNbC aggregation.
Fatigue behaviour of cemented carbide based forming tools, K. Andreas, University of Erlangen-Nuremberg, Germany
The increased demand for manifold industrial goods requires superior manufacturing techniques. In the field of steel products cold forging has gained importance for the last sixty years. Within cold forging the tool takes a key role as it determines accuracy and efficiency of forming process. Aside from tool construction, the choice of tool material has a decisive influence on tool life [ ]. Forming tools have to sustain heavy loads. For processes with high demands regarding wear resistance, cemented carbides are often used as tool materials. The forming process requires a certain profile of material properties with high hardness but also sufficient fracture toughness. In order to guarantee a certain amount of fracture toughness high Co-cemented carbides are applied in cold forging industry. However, due to the brittleness of cemented carbides fatigue is one of the major limits of tool life. Within the paper the fatigue behaviour of the grades G55 and G45C is investigated in a model test under laboratory conditions. The results show higher fatigue strength of G45C compared to G55. Since the surface integrity has a fundamental influence on the fatigue behaviour also different machining strategies for preparation of specimens were investigated. In this context the process chain “grinding + polishing” gains higher fatigue strength compared to the process combination “EDM + polishing”.
Fatigue behaviour of a WC-Ni cemented carbide, J.M. Tarragó, Universitat Politècnica de Catalunya, Spain
Nickel is one of the materials most commonly used as a binder alternative to cobalt in cemented carbides. However, knowledge on mechanical properties and particularly on fatigue response of nickel-base cemented carbides is relatively scarce. In this study, the fatigue behaviour of a fine grained WC-Ni cemented carbide is assessed. In doing so, fatigue crack growth (FCG) behaviour and fatigue limit are determined, and the attained results are compared to corresponding fracture toughness and flexural strength. An analysis of the results within a fatigue mechanics framework permits to validate FCG threshold as the effective fracture toughness under cyclic loading. Experimentally determined data are then used to evaluate the fatigue sensitivity of the studied material. Additionally, fracture modes under monotonic and cyclic load condition are assessed. Clear differences in fractographic features are discerned and discussed.
Structural determination of (Cr,Co)7C3, B. Kaplan, Sandvik Coromant R&D Materials and Processes, Sweden
Chromium is one of the most well-known WC grain growth inhibitors in cemented carbides. It is thus vital to understand and to be able to thermodynamically model the prevailing phase equilibria in the WC-Co-Cr system. To do this it is important that the lower order systems, such as the Co-Cr-C system, are correctly described. Previous investigations have shown that the M7C3 (M=Cr,Co,W) phase is the first carbide to form when Cr is added in excess to the WC+fcc-Co/liquid+graphite phase field. However, the exact structure of this phase has not been investigated and there are many proposed structures already for the binary Cr7C3 carbide, ranging from trigonal, via hexagonal to orthorhombic symmetry. Recent investigations show that the hexagonal structure belonging to the P63mc space group is the stable structure at 0 K. In the present study the binary Cr7C3 carbide and a mixed M7C3 carbide are investigated. The structures of both carbides and preferential positions for Co atoms in the mixed carbide are determined by XRD measurements in combination with ab initio calculations and Rietveld refinement.
In situ reduction of vanadium oxide to nano vanadium carbide, M. Mahajan, Thapar University, India
Among all the transition metal carbides, vanadium carbide (VC) is extremely hard refractory ceramic. Because of its excellent mechanical properties and high temperature strength, it is being used for different industrial applications. Currently, its applications in fuel cells as a catalyst, energy storage materials and as grain–growth inhibitor have increased its demand. Moreover, these properties get further enhanced when its size reduced to nano range. In the present work, we report single - step synthesis of nano vanadium carbide (VC) produced by autogenic pressure. This enables the reduction to occur even at low temperature (800°C) as compared to conventional route followed in industries. The process parameters to synthesise nano vanadium carbide by thermo – chemical route have been optimised to get good quality product. Our basic requirement of these is to have uniform particle size. The phase, degree of crystallinity, size and morphology and surface area of the synthesised powder was studied by using X-ray diffraction (XRD), high resolution transmission electron microscope (HRTEM) and Brauneur-Emmette-Teller (BET). This is a unique process and save energy and manpower as conventional processes requires high temperature (> 1400°C) and multi-step synthesis route.
Mechanical strength of WC-Co: influence of temperature, microstructure and testing configuration, Y. Torres, Universidad de Sevilla, Spain
This work focuses on assessing the effect of temperature and test configuration on the mechanical behaviour of WC-Co cemented carbides with different binder mean free path (λCo). Mechanical strength was measured at different temperatures (200, 400 and 500°C) in 4-point bending on bar-shaped specimens and using biaxial testing on disc-like specimens (ball-on-three-balls). Results were compared with strength measurements at room temperature under the same loading and environmental conditions. A universal bending machine was coupled to a tubular furnace which allowed testing in different atmospheres. Fractographic detailed analyses were conducted in broken specimens for each testing condition. Differences in strength are discussed based on a linear elastic fracture mechanics model and Weibull statistics, taking into account the effect of temperature on the crack growth resistance of the WC-Co material.
Micro facets at WC/Co interfaces in VC-doped WC-Co alloys with a variation of carbon content, T. Yamamoto, Nagoya University, Japan
We investigated WC/Co interface structural change in VC-doped WC-Co alloys by HRTEM, STEM and EDS from a view point of the carbon activity of the alloys. Carbon activity of the alloys is ranged in a two phase region consisting of WC and Co-based phases without any graphite and η phases. WC grain size varies in the ranged carbon activity. WC grain size increases at higher carbon activity while it decreases at lower carbon activity. By observing WC/Co interfaces at atomic scales, we found WC/Co interface structure largely changes with a variation of the carbon activity. At lower carbon activity, very fine micro steps are formed as we have already reported. In contrast, flat WC/Co interfaces appear at high carbon activity. The variation of WC/Co interface structure is closely related to a change in the step flow mechanism on the surface of WC grains. In the presentation, we would like to show the carbon activity dependency of the detail atomic structures at WC/Co interfaces in VC-doped WC-Co alloys with by HRTEM, STEM and EDS.
Effect of binder content on fracture toughness KIc of cermet and cemented carbide, T. Ogura, Fuji Die Co., Ltd., Japan
Fracture toughness (KIc) of Ti(C,N)-Ni base cermet is well known to be inferior to that of WC-Co base cemented carbide at a given hardness and/or a given binder-metal volume content (Vb). In order to elucidate this mechanism, the effects of Vb on KIc, crack propagation path and its deflection were investigated for two sample series of Ti(C,N)-base cermets and two sample series of WC-base cemented carbides whose binder metal were Ni and Co for each material. The results were as follows: (1) KIc at 0vol%Vb, i.e., KIc of hard-phase itself was low in cermets compared with that in cemented carbides, and it was greatly noted that KIc difference between two kinds of materials widened with increasing Vb, (2) The contiguity of hard-phase grain was considerably larger in cermets, (3)The crack propagated preferentially through hard-phase grain inside and hardly through hard-phase grain/binder-metal matrix phase interface in cermets, compared with in cemented carbides, (4) The degree of crack deflection was smaller in cermets, probably due to these three facts (1)-(3). These four facts (1)-(4) suggested that the contribution of binder-metal matrix phase to crack-tip blunting and plastic deformation energy during the crack propagation, i.e., crack propagation resistance, was smaller in cermets. Thus, the KIc -inferiority of cermets could be attributed to the lower KIc of hard-phase itself, such crack propagation path and deflection caused by both lower fracture strength and larger contiguity of hard phase grain.
Creep behaviour of hardmetals with alternative binder alloys at elevated temperatures, C. Buchegger, Vienna University of Technology, Austria
For characterising the creep behaviour of hardmetals a device analogous to a three-point bending test was constructed. The apparatus consists of a vertical silica tube which is enclosed by two stainless steel flanges. The inner parts are fabricated of graphite which is creep resistant at the test temperatures. The creep rate is measured in real time by a laser distance sensor. The setup was tested successfully for temperatures up to 800°C. The creep of hardmetals with alternative Fe/Co/Ni and Fe/Ni binder alloys was determined and compared to a conventional WC-Co grade. At temperatures between of 600 and 725°C the creep rate was measured for various stress levels in a range of 0.4 – 1.2 GPa. From these data creep parameters were estimated by a semi-empirical model. Activation energies between 235 and 320 kJ/mol were determined. The evaluated Norton exponents of 3 – 6 indicate power-law creep at the testing conditions.
Multiscale modelling of mechanical performance of P/M microstructures, A. Laukkanen, VTT Technical Research Centre of Finland, Finland
A multiscale method for computational evaluation of performance of P/M microstructures with respect to mechanical and wear properties is presented. The method is implemented as a PSPP (processing, structure, properties, performance) approach in such a manner that a systematic holistic analysis originating from material manufacturing process up to component performance can be completed, demonstrating the feasibility of a specific material selection. The numerical methodology relies on image based recognition of material microstructure and generation of a statistically equivalent discrete numerical model consisting of microstructure morphology and defects, such as pores and cracks. In this manner the microstructural features can be used as a basis for component material tailoring and optimisation. The method is applied to a hot isostatically pressed (HIP) Cr2O3 material, which is generally known its poor sinterability in air. This limits the applicability of this otherwise promising material, which has high melting temperature and good elevated temperature oxidation resistance. The modelling work is accompanied and enabled by material testing and characterisation work. The implications to component performance are illustrated via a case study.
Material characterisation using positrons: new opportunities for industry, J.-M. Rey, CEA SACLAY and Posithot, France
Recent developments made in fundamental sciences have lead to the availability of compact, non radioactive, intense positrons sources. These new devices provide slow positron production rates up to one tenth of the rate available on a nuclear power plant, offering new opportunities for surface testing, interface and near surface defect analysis. The analysis principles based on positron annihilation and the innovative devices developped by the Posithot company will be presented, as well as application examples of these techniques.
Correlation of impact/wear behaviour to physical properties of WC-Co mining grades, T. Jewett, Global Tungsten & Powders Corp., USA
Development of advanced hardmetal mining and oil field grades for tri-cone drill bits requires insight into the strata-drilling insert interactions not available with traditional laboratory equipment. In order to bridge the gap between laboratory equipment and full scale drilling rigs, a modified impact wear testing apparatus was constructed at GTP-Towanda. Initial tests revealed the wear rates to be dependant on several grade properties, such as; the amount of cobalt, sintered hardness and average WC grain size. The observed wear mechanism was pure wear, which did not change based on the hub speed, media loading or media type. In order to elicit a response on the degree of toughness it was necessary to augment the media load with a single WC-Co sintered insert. In doing so, the wear mechanism changed from primarily abrasive wear to impact dominated wear. After developing suitable testing parameters, several standard grades from Ceratizit were tested in both the abrasive and impact modes. Results of the testing show good correlation between the observed wear and the sintered physical properties.
Analysis of the tribological behaviour of WC-Ni-Co-Cr hardmetals in contact with steel at high temperatures, J.M. Sánchez-Moreno, CEIT-Centro de Estudios e Investigaciones, Spain
The densification, microstructure and wear properties of WC-Ni-Co-Cr alloys were analysed for different metallic contents and Ni/Co ratios. Shrinkage is characterised by successive accelerations and decelerations, a behaviour related to the dissolution kinetics of the Cr3C2 particles added to the powder mixtures. New ? phases found in low carbon sintered specimens present diamond type crystalline structures with stoichiometries close to W4M2C (with M=Ni, Co, Cr). Finally, a “pin on block” tribometer was used to study the wear behaviour in contact with steel at high temperatures and pressures (120 MPa and 800ºC). In general, wear resistance increases with hardness, which depends mainly on the metallic content of the alloy for a given WC grain size. Thus, cemented carbides with 15 wt.% of metallic content exhibit lower mass losses than those with 25 wt.% of metal. Nevertheless, when compositions with the same metallic content are compared, those based on Ni-Co-Cr binders exhibit higher wear resistance than those based on Co, which is related to their oxidation resistance. Friction coefficients are lower for the compositions with higher metallic content, probably due to the formation of continuous oxide tribofilms with potential lubricating ability.
Parallel beam glancing X-ray diffraction: a new technique for measuring surface residual stresses, J.M. Sánchez-Moreno, CEIT-Centro de Estudios e Investigaciones, Spain
Parallel beam glancing X ray diffraction is a technique specially suited for measuring residual stresses of hard coatings on hardmetal substrates. This diffraction geometry avoids the issues due to the strong overlapping between the coating and the substrate diffraction peaks. These results are compared to those obtained with the sin2? technique. The elastic moduli of the different coatings, required for the calculation of the residual stresses, have been obtained from nanoindentation experiments.
In-situ mechanical characterisation of WC-Co hardmetals using micro-beam testing, M. Trueba, CEIT and TECNUN, Spain
Mechanical properties and reliability of hard metals depend on the behaviour of the hard phases, binders and their interfaces. In the last years, important progresses have been made developing predictive models for the material behaviour as a function of the microstructure but reliable information on the mechanical properties of the different phases and interfaces is still lacking. In this work we propose an approach to characterise the local mechanical behaviour of hard metals based on testing micro-beams. Micro-cantilever beams have been machined with an FIB (Focused Ion Beam) and tested at a nanoindenter. Beams with different geometries, with or without a pre-notch, have been machined at different locations within the hard metal. The influence of the relative crystallographic orientation and the beam axis on the load-displacement records has been studied. Experimental results along with numerical analysis on the stress state are presented. The approach presented, combined with modelling, is a powerful tool to gain understanding on the mechanisms controlling hard metals mechanical behaviour.
Micro-defects in ground tungsten carbide revealed by (sub-)surface investigations, E. Fisslthaler, Graz Centre for Electron Microscopy, Austria
Cutting tools for mechanical machining such as turning, milling, drilling, etc. are typical applications for Tungsten Carbide compounds. Consequently, enhancing the quality of the cutting material and therefore the lifetime of the tool is an issue of major interest. Many investigations were done about the honing process of cutting edges, and about the difference between ground and as sintered surfaces. The results concerning the different surfaces are ambiguous, and still there is only little knowledge about possible influences of grinding the hard metal surfaces on causing defects on the µm scale.
In this study, cross section investigations of two samples of a Tungsten Carbide compound – one as sintered, one ground – are presented and compared with respect to microstructure and defects possibly originating from the grinding process. The application of contact-free sectioning methods assures conclusive investigations of the immediate subsurface region via Scanning and Transmission Electron Microscopy, backed by X-ray diffraction measurements and atomic force microscopy.
It was found that the grinding process creates defects and significantly alters the first few microns of the surface.
Advanced cross-sectional characterisation of hard coatings, M. Tkadletz, Materials Centre Leoben Forschung GmbH, Austria
Characterisation of hard coatings with thicknesses of a few microns is often based on measurement techniques yielding averaged material data without depth information. Since this conventional approach is not sufficient for the development of advanced coating materials, depth-dependent characterisation methods have been carried out to illuminate the evolution of coating structure and properties with film thickness for chemical vapor deposited α- and κ-Al2O3 coatings on cemented carbide with a TiCN interlayer. Coating microstructure was characterised by electron back-scatter diffraction on cross-sections prepared by a focused ion beam, demonstrating the evolution of individual grains and their texture. Residual stresses were determined using X-ray nano-beam synchrotron experiments on cross-sectional slices in transmission mode. To measure hardness and Young´s modulus, nanoindentation experiments were performed on cross-sections as well as on the coating surface. Using these techniques, a fundamental understanding of the interaction between microstructure and mechanical properties can be established, providing the basis for a knowledge-based design of advanced hard coatings.
Surface engineering, powder, PM processes and recycling
Violet tungsten oxide’s in-situ reduction technology for the preparation of ultrafine grained WC-Co hardmetals, C. Wu, China National R&D Centre for Tungsten Technology, China
The sintered WC-Co hardmetals with ultrafine grain sizes (≤0.5 μm), which possess optimised properties such as hardness and toughness, are the preferred materials for the efficient tools. In spite of only 15-year production history of the ultrafine grained hardmetals, China has become the largest producer of these materials, thanks to the invention of the preparation technology of ‘violet tungsten oxide’s in-situ reduction’. The development of preparation technology of ultrafine grained hardmetals and raw materials in China was systematically introduced and reviewed. The sets of technologies of ‘violet tungsten oxide’s in-situ reduction’ were focused on, mainly the aspects of contents, principles and advantages. The high quality of those ultrafine grained hardmetals was derived from the ultrafine tungsten carbide powders produced by these technologies, for these powders were characterised with single phase, uniform particle size and high crystallinity. The production equipment supporting these technologies was also discussed.
Study on brush wear and processing efficiency of brush mechanical polishing, W. Zeng, Zigong Cemented Carbide Co.,Ltd, China
According to different installation ways of a brush, brush mechanical polishing equipments can be divided into two categories: horizontal wheel brush and vertical disc brush polishing machines. In the paper, motion mode of the brush is analysed, processing efficiency of the brush is higher in the entrance face than in the exit face, brush wear is investigated in the view of brush media, effects of hardness of materials (including elastic coefficient, diameter, length), working temperature and humidity on the wear rate of the brush are analysed. Based on the formula D=WL3/0.1473Ed4N, the larger the brush filament diameter is ,the higher the hardness is, and the greater the wear rate is. The longer the brush filament is, the lower the hardness is. Keeping other factors constant except the hardness of the brush filament, for the same materials, the harder the filament is, the faster the wear is. The wear rate is increased as the temperature is raised, whereas the wear rate is reduced as the humidity is increased. However, under atmospheric environment, the humidity is increased with rising temperature, effects caused by two changes can be counteracted with each other. It is pointed out that by a comparision of the processing efficiency of two equipments, the horizontal wheel brush is suitable for the cutting edge passivating treatment of carbide turning inserts, while the vertical disc brush is suitable for the surface polishing treatment of cemented carbide cutting inserts.
The synthesis of borides of refractory and rare earth metals by reduction-distillation, A. Mukherjee, Bhabha Atomic Research Centre, India
The synthesis of borides of group IV, V and VI refractory metals as well as the rare earths lanthanum, neodymium, europium and yttrium starting from their compound intermediates by a novel reduction-distillation process has been investigated. The process, carried out at temperatures in the range 1000-1500°C under dynamic argon flow, comprises of reduction and in-situ separation of the reduction products by distillation. The thermodynamic basis of the process and experimental results on practical application to the synthesis of borides of selected metals are presented in this paper. Both oxides and halides have been used as the start materials for synthesis and boron and aluminum as the reducing agents.
Magnetic characteristics of nanocarbon of different modifications, G. Bogatyreva, ISM - V.Bakul Institute of Superhard Materials, National Academy of Sciences of Ukraine, Ukraine
During last years many studies proved promising using nanocarbon in medicine as platform for target delivery of drugs in magnetic resonance tomography and magnetically controlled local hyperthermia as well as in the electronics to create sensor devices. In this context it is important to have data of magnetic properties of nanocarbon.
The target of this work is study of magnetic properties of nanocarbon materials: carbon nanotubes produced by methane pyrolysis and nanodiamonds produced by detonation of explosives ("dry" and "wet" methods of synthesis) with follow-up special chemical treatment.
The studies have been carried out by magnetometric analysis with oscillating magnetometer 7404 VSM (Lake Sore Cryotronics, Inc., USA) in magnetic fields up to 13 000 Oe. The device sensitivity is 10-7 emu. Measurement range of magnetic moment is 10-7 - 10+3 emu. It makes possible to measure magnetic moment of samples weighing only a few milligrams. Weight of the samples was measured using electronic microbalance AB135-S/FACT with autocompensation (METTLER TOLEDO, Switzerland). Sensitivity of the balance is 10-5 grams.
The results of study have been shown that coercitivity of nanocarbon samples varies from 26 to 160 Oe, saturation magnetic moment varies from 0.08 to 0.28 emu/g. Nanodiamonds and carbon nanotubes are ferromagnetic materials, its magnetic properties can be controlled by special chemical treatment.
New analytical computer-based methods of diagnostics of characteristics of powders of superhard materials, G. Bogatyreva, ISM - V.Bakul Institute of Superhard Materials, National Academy of Sciences of Ukraine, Ukraine
New analytical computer-based methods of diagnostics of grain number in 1 carat of powder of superhard material (SHM), number and average value of edge angles of cutter bits of the grains have been developed.
The first method is based on advanced extrapolation-affine 3D simulation of spatial shape of grain with application of mathematical apparatus of affine space transformation. Special computational algorithms of engineering of extrapolation-affine 3D simulation of spatial shape of grain ensure getting final result with miscalculation not exceeding 7%.
Analytic definition of number (n) and average value of edge angles of cutter bits (F) of grains of SHM powder is carried out by solution of combined transcendental equations. Initial data for solution of this problem are shape factor (f) and roughness (R) of grains of abrasive powder. Shape factor describes degree of roundness of grain projection, it expresses by formula: ratio of square of actual perimeter of grain projection to area of grain projection multiplied by 4pi.
Roughness expresses through formula: ratio of actual perimeter of grain projection to convex perimeter. Both characteristics are diagnosed by modern devices of automated diagnostics of morphometric characteristics of abrasive powders. Experimental check of suggested method has been shown close coincidence of calculation and experimental data.
Developed new methods are provided with special software support; it simplifies and intensifies process of generating of high valid data of values of diagnosed characteristics.
Influence of process parameters on microstructure and density of an ultrafine WC-6Co hardmetal produced by spark plasma sintering (SPS), M. Zivcec, IWM RWTH Aachen, Germany
In spark plasma sintering (SPS) processing the process parameters as pressure, heating rate, sintering temperature and holding time need to be set to get optimised material properties. The achievement of dense hard metals with a homogeneous distribution of the Co phase and low WC-grain growth during sintering is the target of an optimal combination of parameters.
WC-6 Co samples were consolidated by SPS using various sintering parameters. A systematic study about the variation of these parameters and their influence on the material properties is presented.
Starting with a parameter combination that gives 99.8 % of theoretical density the maximum sintering temperature was stepwise reduced. In the following studies the heating rate and the holding time were varied independently of each other for each holding temperature. The influence of the parameters was defined by measuring the change of the density and by analyzing microstructural images. Additionally the influence of the pressure was determined at one sintering temperature. The significance of the process parameters to the material densification is going to be discussed.
Use of mechanically induced self-sustaining reactions in the design of cermets based on complex transition metal carbonitrides, E. Chicardi, Instituto de Ciencia de Materiales de Sevilla (US-CSIC), Spain
Cermets based on titanium carbonitride are used as coatings in cutting tools instead of cemented carbides due to their better mechanical behaviour and chemical stability at high temperature. Usually, the ceramic components are obtained by carbothermal reduction from metal transition oxides. After the liquid phase sintering, the ceramic grains show the characteristic core-rim microstructure.
It is reported that the use of complex transition metal carbonitrides as raw materials previous sintering allows controlling the ceramic phase composition and microstructure and modulating the final properties. It would also be possible obtaining cermets without the core-rim microstructure avoiding the presence of the interface between the core and rim that generates residual stresses and crack propagation.
We propose the mechanochemical MSR (Mechanically Induced Self-Sustaining Reaction) method to synthesise directly and simply complex transition metal carbonitrides starting from elemental powder blends using N2 as reactive gas. This raw ceramic material was applied to develop cermets (TixTa1-xCyN1-y - Co) with and without the core-rim microstructure. By varying the nature and composition of starting elements, the microstructure and properties were modulated.
Thermal compression treatment of WC-Co and TiC-VC-NbC-WC-Ni-Cr hard alloys, H. Kramar, Ternopil Ivan Pul'uj National Technical University, Ukraine
Hard alloys on the basis of tungsten and titanium carbides are still the most effective instrumental materials. Their properties can be improved by using new technological approaches - thermal compression treatment (?CT), in particular. The aim of the work was to research ?CT influence on microstructure and mechanical properties of WC - 10Co and TiC - 5VC-5NbC-5WC-18(Ni - Cr) hard alloys. The alloys sintered by standard technology were subject to TCT at the temperature 1370?, argon pressure 3,0 ?Pa during 75 minutes. Decreasing of porosity, increasing of medium size carbide grains in 30% and appearance of separate recrystallized grains of 12...15 μm sizes were noticed for ultrafine WC - Co alloy after TCT. Thus, the transverse rupture strength increases in 20% and fracture toughness decreases in 6,5% comparing with untreated alloys. Considerable increase of carbide grains in TiC based alloys was not available. Unlike the WC based alloys, fracture toughness increased in 11,5%, that is explained by the change of size descriptions of carbide rim and redistribution of carbides and binder metals.
Influence of milling conditions in processing of submicron to near-nano WC/Co powders, B. Caspers, H.C. Starck GmbH, Germany
In the presented work the influence of different milling media on particle size distribution after milling, pressing behaviour and shrinkage as well as coercive force of the sintered hardmetals is analysed. WC powders from near nano size of ~ 100 nm up to submicron size (0.8 µm FSSS) are investigated in an alloy consisting of 90 wt% WC (including 1 wt% Cr3C2) and 10 wt% Co.
The results show that the pressing behaviour strongly depends on the grain size of the WC powder and on the milling media. While for submicron WC powders the influence of the milling media is only limited for near nano sized powders the difference in shrinkage for different milling media is significant. As a consequence the right choice of the milling media is gaining importance when processing near nano sized WC powders.
Hard alloys production during vacuum sintering of nanometric tungsten carbide-cobalt composition, Y. Blagoveshchenskiy, IMET RAS, Russia
The process of vacuum sintering of tungsten carbide-cobalt composites with or without grain size inhibitors is investigated. The average grain size of pure tungsten carbide is 40-60 nm. The influence of process parameters such as temperature and time hold on the structure and porosity obtained hard alloy is studied. The accurate regulation of carbon content in tungsten carbide make possible to avoid the appearance of double carbide (eta-phase) as well as abnormal grain growth in material structure even on the solid-phase sintering. The quantity of submicronic pores forming during sintering of such powders can be sharply decreased under hold in vacuum at the temperature below start of sample displacement. The possibility of saving of considerable part of carbide particles in the structure less than 100 nm in diameter is shown. Obtained hard alloys have higher Vickers hardness and fracture strength on 25-30%.
Compaction process of pure tungsten carbide by spark plasma sintering, V. Chuvildeev, NIFTI UNN, Russia
In this work the sintering process of nanometric tungsten carbide for the aim of high mechanical properties production by spark plasma sintering was investigated.
Spark plasma sintering (SPS) was carried out in the equipment Dr. Sinter Model-625 supplied by SPS SYNTEX INC., Japan. Tungsten carbide nanopowders with average grain size 50-60 nm were sintered in the temperature range of 1400-1950 °C without time hold. The heating rate was from 25 to 2400°/min.
It was shown that near-theoretical density of pure tungsten carbide could be achieved at the temperature of sintering 1800°C and 500°C/min heating rate. The average grain size of samples obtained at 1400°- 1800°C was from 90 to 150 nm. The samples obtained at high heating rate have high hardness and possess better combination of such property as hardness/viscosity. The hardness of WC was HV 3180 and fracture strength was K1C=5,2 with high density sintered at 1800°C, 2400°C/min.
Short-term recycling technique for tungsten carbides scraps, X. Liu, Beijing University of Technology, China
A short-term recycling technique for tungsten carbides scraps is proposed, which contains the oxidation and reduction-carbonisation procedures. The effect of the oxidisation process on the phase constitution and chemical compositions in the reaction products of metal oxides was studied. The optimised parameters for the reduction-carbonisation process was obtained to synthesise the recycled WC-Co composite powder. The recycled WC-Co powder was applied to fabricate the cemented carbides bulk materials, and the microstructures and properties of the resultant WC-Co bulk materials were characterised. The results show that the prepared WC-Co bulk materials by the recycled powders have pure phase constitution, homogeneous microstructure and good mechanical properties. In addition to the high quality of the recycled WC-Co powder products, the present recycling technique has advantages of low energy cost, environment-friendly and high potential of industrialisation.
Hydrogen reduction of tungsten oxides: alkali additions and their interaction on the metal nucleation process, T. Zimmerl, Wolfram Bergbau und Hütten AG, Austria
It is known that the addition of alkali compounds influences W particle growth during the reduction of tungsten oxide using hydrogen. Literature exists but the mechanism and mode of interaction remain unclear. To improve understanding of the reduction process, lithium, sodium and potassium compounds were added to a highly pure tungsten oxide prior to reduction, and interrupted reduction experiments were carried out at 750 °C. The resulting powders were investigated by metallographic and chemical means, X-ray diffraction, SEM and EDX analysis.
The experiments showed that intermediately formed tungsten bronzes play an important role in the early stages of reduction. In addition it is demonstrated that the kinetics of the reduction sequence differs significantly between doped and undoped tungsten oxide powders, as demonstrated by the on-line measurement of reaction water in the hydrogen process gas.
The results help to understand how the presence of alkali compounds effects the reduction of tungsten oxides.
Incorporation of titanium, tantalum, and vanadium into the hexagonal WC lattice, A. Pasquazzi, Vienna University of Technology, Austria
Based on our earlier work on the formation of a hexagonal (W,Cr)C mixed crystal carbide, the formation of (W,Me)C (Me=Ti, Ta, V, V+Cr) solid solutions was studied in the temperature range of 1450°C to 1950°C. A two step carburisation procedure was used for their preparation: In a first step, (W,Me)2C was formed, which in a second carburisation step was then transformed into the (W,Me)C carbide.
Experimental and theoretical study of the grain growth process of wc-co nano composites, A. Kumar, Sri Guru Granth Sahib World University, India
The present work describes the experimental as well as theoretical aspects of grain growth process of different tungsten carbide-cobalt (WC/Co) nano composites sintered using liquid phase sintering (LPS). The composites were prepared using tungsten carbide nano particles synthesised by solvo-thermal process and commercially available cobalt nano particles as binder material for these particles. Sintering parameters; temperature, time and binder composition were varied to study the grain growth process. In these composites no grain growth inhibiters was used. Sintered composites were analysed using scanning electron microscope (SEM) and x-ray diffraction (XRD). The microstructural examination showed that the grain growth occurred through coalescence. The XRD analysis showed that no ‘η’ phase or any other unwanted phases were present in all the sintered composites. A theoretical model is developed on analysing the microstructure of the composites.
Special Interest: Hardmetal powder production and recycling
Review of the hardmetal recycling market and the role of the zinc process as a recycling option, T. Karhumaa, Tikomet Oy, Finland
Recycling in the hardmetal industry has greatly gained in popularity since 2005 due to the increase in tungsten prices. The recent developments in hardmetal recycling, the various recycling options and their market shares in Europe are reviewed and the future outlook is discussed.
A significant new development in recent years has been the emergence of the zinc process as a new recycling option. The basics of the zinc process are reviewed and the current position of the zinc process in the recycling market is discussed.
Both lab and production scale experiments were carried out where WC-Co zinc reclaim powders were blended with virgin raw materials and the effect of such additions on the processing of powders and properties of sintered hardmetal were analysed. Results of both laboratory and production scale tests are shown and discussed.
The results show that the WC-Co zinc reclaim powders when added in the right amounts and processed properly have no negative effect on the properties of sintered hardmetal.
Based on the results various applications for zinc reclaim powders are discussed
Numerical simulation of organic binder decomposition during thermal debinding, T. Kraft, Fraunhofer Institute for Mechanics of Materials IWM, Germany
In several powder technological processing routes debinding of green parts can be critical due to possible damage formation. Especially large parts or very dense compacts in combination with higher thermal heating rates are vulnerable. In this paper we present a model which describes the chemical decomposition of organic binders and the consequential development of an internal gas pressure. It includes the combined Maxwell-Stefan and Knudsen diffusion and the seepage flow of multiple gaseous reaction products through a porous body. The model is implemented into the finite element program ABAQUS. The internal stresses developing due to this gaseous overpressure during decomposition are shown for some simple examples. Predicting these stresses can indicate critical temperature regions and help to optimise debinding conditions.
Effect of WC material properties and milling parameters on the grain size and sintering behaviour of coarse WC powder, A. Johansson, Seco Tools AB, Sweden
The wet-milling and sintering behaviour of two coarse WC powders was studied experimentally. Microscopy, laser light scattering, BET adsorption isotherms, X-ray powder diffraction, and magnetic coercivity measurements were used to quantify the effect of material and process parameters on the evolution of the WC grain size distribution throughout the process chain. Analysis of the results showed that the WC grain size reduction with increasing milling time is characterised by a power-law behaviour. The evaluation of the effect of several process parameters on milling efficiency could be facilitated by the use of simple scaling factors. In addition, the correlation between WC grain size after ball-milling and after sintering was investigated.
Property changes induced in submicron WC through various final milling techniques, R. Cook, Global Tungsten & Powders Corp., USA
Milling techniques vary in both the energy and mechanism applied to powder samples. Due to these variations, powder properties and the resulting sintered properties change accordingly. This study looks at these changes by comparing a wide variety of commonly employed milling operations including ball milling, attritor milling, pin milling and rod milling as applied to sub-micron WC. A wide range of physical, chemical and sintered properties are examined to see changes due to milling in sub-micron WC and WC+Co. From these studies certain attributes such as densities, particle size distributions and sintered shrinkage changes can be directly modeled by the milling time and type, however each mill style (combination of impact and shear) has a different phenomenological response.
Rim-nitrided WC powder: preparation, properties and use for hardmetals, M. Wetzel, TU Bergakademie Freiberg, Germany
Nitrogen uptake of commercial WC powders of different grain size was studied by high-pressure nitridation (≤ 200bar N2). The nitrided powders were characterised by XRD, chemical analysis, SEM, TEM and for their grain-size distribution. Interestingly, it was found that a perceptible amount of nitrogen dissolves in WC. As the diffusion rate of N in WC is extremely slow, nitridation occurs in the outermost rim of the WC particles. Upon appropriate nitridation conditions the powders are even purified with respect to the oxygen level and do not show particle growth.
Sintering experiments were performed with these powders for a possible use in the preparation of hardmetals. It turned out that nitrogen can retard low temperature grain growth and thus hardmetals of reduced grain size can be obtained. Mass-spectrometric delubing experiments showed that the powders loose nitrogen upon sintering. If the employed powder particles have a steep N gradient (essentially a nitrogen-rich fringe area) no porosity remains in the hardmetals, contrary that of powders with uniform nitrogen distribution with a similar overall nitrogen content.
Analysis of WC with increased Ta doping, J. Weidow, Chalmers University of Technology, Sweden
Tungsten and tantalum metal powders were co-carburised to yield a mixture of cubic and hexagonal carbide. The carburisation was made through a two-step carburisation process with (W,Ta)2C powder as an intermediate product. X-ray diffraction analysis showed that the lattice parameters of the hexagonal phase in the fully carburised powder were larger than those of pure WC indicating the formation of a mixed crystal carbide, (W,Ta)C. The powder with the largest lattice parameters was investigated in detail. A method to produce atom probe tomography specimens of this powder was developed. The atom probe tomography measurement showed the Ta solubility expressed as Ta/(Ta+W) to be as high as 0.086 (i.e. about 8.6 at%). In addition, it was found with electron backscatter diffraction that the (W,Ta)C grains had a large fraction of Σ2 grain boundaries as well as a small fraction of what was suggested as Σ4 grain boundaries.
Special Interest: Hardmetal trends in processing
Thermal spraying – a technology for hardmetal coating solutions, L.-M. Berger, Fraunhofer Institut IWS, Germany
Thermal spray processes represent an important and rapidly growing group of surface modification technologies, it is the only surface technology allowing to produce hardmetal coating solutions. It it thus complementary to sintering technology and applicable to large parts.
The contribution reviews the development of these coatings, including the different processes and the feedstock materials, and presents the technical possibilities of state-of-the-art coating solutions. Hardmetal coatings are based also mostly on WC, but also on Cr3C2. Cubic hard phases based on TiC represent an alternative. Specifics of the hardmetal compositions for coatings (large Cr3C2 addition, high binder contents) are considered. The need of fundamental research is outlined for understanding the specifics of the metallurgical reactions during the spray processes, e.g.the formation and properties of (W,Cr)2C. The microstructure-property relationships are discussed in dependence of the feedstock powder properties and the specifics of the spray processes applied. Besides the traditional use as wear resistant coatings, new applications, such as service under contact loading is envisaged.
Development of a HVOF WC based thick coating, J. He, Global Tungsten & Powders Corp., USA
To protect from severe wear, gas/oil and other mining industries need very thick wear-resistant layers, currently produced by PTA techniques. It is known that HVOF thermal spray coatings have advantages over PTA and plasma coatings in wear resistance, based on its microstructure formed at lower temperatures and higher particle velocities. This work will present the microstructure and mechanical property of WC-10%Ni HVOF thick coatings of up to 1,000 μm. The coating were produced using both densified and non-densified thermal spray powders. The thick coatings were sprayed on both rotating and still substrates. The resulting microstructure is comparable to the typical HVOF coatings with no cracks or large voids either in the coatings or near interface between coating and substrate. Thick coatings have the same level of porosity (less than 0.5%), microhardness (~1030HV300) and bond strength (~ 10 ksi) as the corresponding normal HVOF coatings in the 100 to 300 µm range.
Rapid synthesis of ultrafine WC-Co cemented carbides, X. Song, Beijing University of Technology, China
Recently we have developed novel routes to prepare in a rapid way the ultrafine WC-Co cermets, which have potential applications in the industrial fields. One is the rapid synthesis of the WC-Co composite powder with controllable particle size by in situ reduction-carbonisation reactions using metal oxides and carbon black as the raw powders. The powder products, which have advantages in the pure phase constitution, uniform particle size distribution and homogeneous distribution of the binder phase, are available as the high-performance coating materials, as well as the sintering powders for the preparation of the cermet bulks. The second is a one-step route for synthesising the cermet bulks through reaction sintering in a spark plasma sintering system. This route is applicable to prepare the dense nanocrystalline cermet bulks and is feasible to be developed as a net-forming fabrication technique for certain cermet products. Along with the development of the preparation methods, the mechanisms of the rapid synthesis have been studied, and the prospects concerning the applications of the techniques are proposed.
Characterisation of gas reactions during ceramic and hardmetal production, T. Gestrich, Fraunhofer Institute IKTS Dresden, Germany
Gas reactions are critical steps during the thermal treatment for the production of hard materials like hardmetals (e.g. WC-Co) or ceramics (e.g. Liquid Phase Sintered SiC). Thermogravimetry (mass changes), Differential Scanning Calorimetry (caloric effects) and Mass Spectrometry (gas analysis) are suitable methods to study gas reactions. Thermodilatometry (length changes) can give valuable additional information. It is shown how gas reactions are influenced by grain size, grain growth inhibitors, and amount or composition of binder phase respectively. Through kinetic analysis of thermoanalytical results it is possible to predict the thermal behaviour for any temperature-time profile or special mass change behaviour. This knowledge can be used to avoid problems like por osity which influence important properties of the sintered material, such as the strength and / or the carbon balance. The created process knowledge may lead to a better cost efficiency, to stabilisation of properties and improvement of technology.
On the interaction of alumina during sintering of cemented carbides, A. Bicherl, Wolfram Bergbau und Hütten AG, Austria
Even today sintering of certain cemented carbide parts is carried out in push-type furnaces under hydrogen atmosphere. In this case the parts are embedded in a coarse-grained alumina/carbon fill. Other grades are sintered in vacuum on a graphite tray coated by a fine suspension of alumina.
During the sintering sequence the oxygen partial pressure within the heating zone is significantly reduced through the presence of carbon, and a partial carbothermic decomposition of alumina takes place, resulting in an up-take of aluminium in the binder phase during sintering.
It is demonstrated, that both temperature and atmosphere determine the amount of aluminium in solution. Under extreme sintering conditions even the formation of intermetallic phases can be observed. The amount of aluminium is measured as a function of temperature and respective alloy system (Co-, Ni-, or Fe-base), and the influence of dissolved aluminium on subsequent cooling and the properties of the parts will be discussed.
Selective laser sintering of tungsten carbide inlays for local wear protection of injection moulding tools, H. Koehler, BIAS - Bremer Institut für angewandte Strahltechnik, Germany
Materials of tools for injection moulding like steel 1.2343 need to withstand different types of wear. Typically tool wear varies locally, i.e. it is increased dramatically on spots of injection. Hence, inserts of wear resistant material are used in such areas. The selective laser sintering/melting process was chosen to produce near net shape parts out of a variety of materials. The highly wear-resistant alloys WC-Co 83/17 and WC-Co 88/12 were chosen to be generated on steel substrates. Major challenge was the determination of process parameters to meet desired densities and avoid cracking. The influence of process parameters and weld trajectories on the density was investigated. It was found that the key to achieve densities of >95% through the complete specimens was the combination of comparatively low scanning speed, large beam diameter and checker board shaped weld trajectories where the single boards were to be made with overlap. Inserts fulfilled the requirements for brazing to the tool steel 1.2343. The complete process chain of generating and joining wear protective inlays could be realised.