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 by field assisted hot pressing (FAHP) for between 600 and 1200 s at temperatures between 725 and 1070 °C and the resulting microstructures were compared. The average powder diameters ranged between 50 and 100 μm, where both the B-containing powders and resulting FAHP compacts contained elongated B-rich needles. The microstructure in the FAHP compacts depended on the processing temperature. For processing temperatures less than or equal to 960 °C, porosity was evident on the FAHP compact, where greater porosity was observed with decreasing temperature. Processing temperatures greater than or equal to 980 °C resulted in minimal porosity and three-phase microstructures containing a mixture of the orthorhombic, α2, 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 °C for 4 h using hot isostatic pressing (HIP). For both HIP and FAHP processing, the B-containing compacts exhibited finer prior-BCC grain sizes. Compositional analysis of the B-rich phase within the Ti–22Al–26Nb HIP compact suggested that it could be the B27 orthorhombic structure with a B2TiNb stoichiometry. Overall, FAHP was shown to be a viable powder metallurgy processing technique for intermetallic Ti2AlNb based intermetallic alloys.