2020 Volume 61 Issue 3 Pages 430-437
The previous study indicated powder metallurgy (PM) Ti-64 alloys with oxygen showed the increment of not only their tensile strength but elongation. This study investigated the elongation improvement mechanism of Ti-64 alloys with oxygen atoms. The mix of Ti-64 alloy powder and TiO2 particles (0∼0.4 mass%) was used as starting materials and consolidated by spark plasma sintering (SPS). The following heat treatment in vacuum was applied to sintered materials. β transus temperature increased by oxygen addition because it was one of α-phase stabilizer elements. Prior-β grains size and aspect ratio of α-Ti grains were changed by heat treatment conditions. For example, Ti-64+O alloys after heat-treated at β-phase temperature range showed acicular α-Ti grains with a large aspect ratio (6.1∼7.0) although those with heat treatment at α+β-phase temperature had α-grains with a small aspect ratio of 3.3∼4.0. These grain morphology changes strongly depended on the temperature of heat treatment, not oxygen contents. In addition, the latter materials indicated high elongation (16∼17%) compared to the former with 9∼10%. When Ti-64+O alloy specimens after tensile test were analyzed by SEM-EBSD, Kernel average misorientation (KAM) maps showed many plastic strains induced in small aspect ratio α-Ti grains.
This Paper was Originally Published in Japanese in J. Jpn. Soc. Powder Powder Metallurgy 65 (2018) 699–706.