Effect of Cr and Nb on the phase transformation and pore formation of Ti-Al base alloys

understand the effect of composition on the pore formation during sintering at low and high temperatures. Ti-Al base alloys with nominal compositions of Ti52Al48, Ti50Al48Cr2, Ti50Al48Nb2 and Ti48Al48Cr2Nb2 are prepared by the conventional elemental powder metallurgy route. The sintering of mixed powders was carried out at 600 degrees C (low-temperature sintering below the Al melting point) and 1200 degrees C (high-temperature sintering). Al-rich intermetallic compound TiAl3 was primarily formed during low-temperature sintering while Ti-rich intermetallic compound Ti3Al was formed during high-temperature sintering. The phase transformations increase the overall porosity and pore size of alloys to a similar extent regardless of the alloy composition during the low-temperature sintering. However, large differences in the pore size and pore volume distribution occur depending on the composition of Ti-Al alloys during high-temperature sintering. Chromium and niobium do not affect the formation of Kirkendall voids and thus show a similar void formation behavior at 600 degrees C, but affect the void agglomeration behavior to a different extent due to the different diffusion activities at 1200 degrees C. (C) 2017 Elsevier B.V. All rights reserved.