As additive manufacturing/3D printing (AM) has grown rapidly over the last several years, interest in titanium and titanium alloy powders has increased dramatically. This has been reflected in the number of presentations on titanium powders related to AM in recent PM conferences. The publication of the POWDERMET2017 conference proceedings in Advances in Powder Metallurgy & Particulate Materials – 2017 gives an opportunity to include some of the presentations it was impossible to report in previous articles due to conflicting session schedules.
It would seem that titanium alloys and AM are made for each other: Ti-base materials possess exceptional strength/weight and corrosion properties but have faced an up-hill battle when used in conventional processes due to very high extraction and fabrication costs. The infamous “buy-to-fly” ratio often quoted in relation to aerospace components was the starting point in a paper by Eric Bono, Carpenter Technology Corporation, USA, discussing costs in additive manufacturing. He illustrated this by reference to the sequence of steps in the manufacture of an aerospace spar by forging and machining, during which a 48 kg billet resulted in a 2 kg finished part – for a buy-to-fly ratio of 21. “With expensive materials such as Ti and nickel-base superalloys it doesn’t take long for machining and material waste to add up to more value than the actual part is worth”. There is a strong incentive to switch to AM even though the starting material (atomized powder) is so much more expensive (than wrought billet). Bono went on to discuss the details of the cost factors involved in producing gas atomized powders for use in AM. The large difference in price for the same alloy in powder form versus billet has drawn much attention even though powder represents only about 20% of total AM production cost. He went on to analyze the factors comprising the cost of manufacture for gas-atomized powders, currently the most common type used in AM. These factors were: particle size distribution and chemistry requirements, as well as quantity. Gas atomization produces a wide range of particle sizes from 500 μm on down. Dividing the size ranges into three segments: 0–45, 46–106, and 107–500 μm, the 0–45 μm segment is produced in the smallest quantities of the three (Table 1). Unfortunately, this segment is the one most in demand, for laser-bed printing as well as for MIM applications. This creates an imbalance between the size ranges of gas-atomized powders and the current market, resulting in increased cost of powders to compensate for the unsaleable material. Bono saw no easy solution to this dilemma. Non-standard or customized powder chemistry was another important cost factor because of the need to clean out the production equipment between grades. Greater use of industry standards could help reduce costs. Finally, increased demand for a narrow particle size distribution exacerbated the imbalance and pushed up the cost.
This article appeared in the November–December 2017 issue of Metal Powder Report.
