TEM Characterization of Aged Ti-5Al-2.5Sn Powder Metallurgy Alloys with Si and with Ge Additions
Titanium alloys produced by the powder metallurgy (PM) techniques are of interest because of the potential cost savings and property enhancement above that possible by conventional ingot metallurgy approaches. In the present program the Ti-5Al-2.5Sn alloy, an all alpha system, is being studied as a model PM titanium alloy. Alloying additions of Si and Ge, which normally result in coarse precipitate regions in cast and wrought material because of their low solubility, have been made. The PM products circumvent the ingot problem because segregation is avoided and precipitates are retained in solution by either the rapid quench rate (pre-alloyed powder) or homogeneous mixing (elemental blend approach). The resulting product displays structures and behavior which differ from conventional Ti-5Al-2.5Sn product. To date Ti-5Al-2.5Sn PM alloys with 0.5 Si and with 1.0Ge w/o have been prepared by an elemental blend/cold compact/sinter process, followed by Hot Isotatic Pressing (HIP'ing). Subsequently specimens were aged at 1000°F (540°C) for 3, 66, and 500 hours in order to precipitate silicides and germanides. Thin foils were then prepared and characterized using TEM and STEM techniques.