Microstructural Development and Mechanical Properties of PM Ti-45Al-2Nb-2Mn-0.8 vol.% TiB2 Processed by Field Assisted Hot Pressing

A gamma-TiAl intermetallic alloy, Ti-45Al-2Nb-2Mn (at.%)-0.8 vol.% TiB2, has been processed from gas atomized prealloyed powder by field assisted hot pressing (FAHP). An initial analysis of the prealloyed powder helped on the understanding of the intermetallic sintering behavior. Atomized powder consisted of alpha metastable phase that transformed into alpha(2)+gamma equilibrium phases by thermal treating. Different powder particle microstructures were found, which influence the microstructure development of the FAHP gamma-TiAl material depending on the sintering temperature. Duplex, nearly lamellar and fully lamellar microstructures were obtained at the sintering temperatures above 1000 degrees C. Lower consolidation temperatures, below 1000 degrees C, led to the formation of an Al rich phase at powder particle boundaries, which is deleterious to the mechanical properties. High compressive yield strength of 1050 MPa was observed in samples with FAHP duplex microstructures at room temperature. Whereas nearly lamellar and fully lamellar microstructures showed yield strength values of 655 and 626 MPa at room temperature and 440 and 425 MPa at 750 degrees C, respectively, which are superior in comparison to similar alloys processed by other techniques. These excellent properties can be explained due to the different volume fractions of the alpha(2) and gamma phases and the refinement of the PM microstructures.