Design of Low Cost High Performance Powder Metallurgy Titanium Alloys: Some Basic Considerations

Abstract

The inexpensive hydrogenated–dehydrogenated (HDH) titanium powder made from the Kroll sponge titanium provides a cost-affordable basis for powder metallurgy (PM) Ti alloy development. The design targets we hope to achieve are low feedstock cost (< $25/kg) including all alloying elements; low fabrication cost based on cold compaction and pressureless sintering, and wrought grades of properties of Ti-6Al-4V in the as-sintered state. Relevant issues are considered. These include alloying with inexpensive elements such as Fe and Si, grain size control during heating, isothermal sintering and cooling, chemical homogeneity of as-sintered microstructure, and simultaneous scavenging of oxygen and chlorine. In addition, it is proposed that achieving 6% of tensile elongation will be adequate for most PM Ti applications, compared to PM steels (normally < 2%), PM aluminium alloys (mostly < 4%) and the requirements for wrought Ti-6Al-4V armour plates (≥ 6%). This will allow the use of HDH Ti powder that contains relatively high oxygen (~0.35wt.%) and direct more efforts towards improving other properties.