Titanium Powder and Compacts

Titanium is very reactive, forming very stable oxides and nitrides. Unlike many metals, titanium is capable of dissolving its own surface oxides at sintering temperatures. Consequently, these oxides do not have to be reduced through the use of a reactive atmosphere. The formation of additional oxides should be avoided; consequently, the use of high vacuum or high-purity inert gas atmosphere is common practice.

Titanium sponge fines used for P/M parts typically range from -80 to -100 mesh. Sodium-reduced sponge fines contain -0.23% residual sodium chloride entrained in the particles. Although it is impossible to remove this residual salt by leaching, some salt usually is liberated at high temperatures and condenses in cooler parts of the sintering system.

Sponge fines can be compacted at room temperature in rigid dies or isostatically pressed in elastomeric tooling. Due to the reactive nature of titanium, admixed lubricants are not used, but die-wall lubrication is required with rigid dies. The irregular particle shape of sponge fines provides compacts with excellent green strength, and green densities can range from 60 to 85%, the latter at die pressures of 552 MPa (40 tsi) or isostatic pressures of 414 MPa (60 ksi).

When additional sintered strength is required, alloying powders can be elemental or master alloys; in the case of Ti-6Al-4V, for example, a master alloy powder of 60Al-40V is frequently used. Sponge fine powders exhibit strengthening from sintering at temperatures as low as 1000 °C (1830 °F), but higher temperature and sufficient time must be used when alloying powders are added to allow for complete interdiffusion and to obtain the strengthening benefit of the alloy additions. Temperatures in the range of 1200 to 1260 °C (2200 to 2300 °F), with holding times of 1 to 4 h, are sufficient to homogenize admixed alloy powders.

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