A comparison of field assisted hot pressing and hot isostatic pressing for gas atomized Ti-22Al-26Nb(at.%) and Ti-22Al-26Nb-5B(at.%) powders

Abstract

Ti-22Al-26Nb(at.%) and Ti-22Al-26Nb-5B(at.%) compacts were processed from gas atomized prealloyed powders byfield assisted hot pressing (FAHP) for between 600 and 1200 s at temperaturesbetween 725 and 1070 degrees C and the resulting microstructures were compared. The average powder di-ameters ranged between 50 and 100 mm, where both the B-containing powders and resulting FAHPcompacts contained elongated B-rich needles. The microstructure in the FAHP compacts depended onthe processing temperature. For processing temperatures less than or equal to 960 degrees C, porosity wasevident on the FAHP compact, where greater porosity was observed with decreasing temperature.Processing temperatures greater than or equal to 980 degrees C resulted in minimal porosity and three-phasemicrostructures containing a mixture of the orthorhombic, a2, and body-centered-cubic (BCC) phases, where longer processing times led to microstructural coarsening. The microstructures of the FAHP compacts were compared to those from compacts consolidated at 1027 degrees C for 4 h using hot isostatic pressing (HIP). For both HIP and FAHP processing, the B-containing compacts exhibited finer prior-BCCgrain sizes. Compositional analysis of the B-rich phase within the Tie22Ale26Nb HIP compact suggested that it could be the B27 orthorhombic structure with a B2TiNb stoichiometry. Overall, FAHP wasshown to be a viable powder metallurgy processing technique for intermetallic Ti2AlNb based inter-metallic alloys.