Microstructure and mechanical properties of high Nb containing TiAl alloy parts fabricated by metal injection molding

Metal injection molding (MIM) process was applied to fabricate parts of high Nb containing TiAl alloys with a nominal composition of Ti-45Al-8.5Nb-0.2W-0.2B-0.02Y (at.%), and the effects of sintering parameters on their microstructures and mechanical properties, as well as the fractographies after tensile tests were investigated. Results show that for sintering of the alloy in vacuum, effective densification took place in the temperature range 1460-1480 °C. Sintering at too high a temperature or too long a time will result in distortion or warpage of the sintered body or coarsening of the lamellar colony. When the optimum sintering parameters (1480 °C, 2 h) were chosen, the alloy with the relative density of 96.2% was obtained. The microstructure was homogenous and fine-grained near lamellar structure, consisting of α2/γ lamellar colonies with an average size of 60 μm, small amounts of β phase, few boride rods and yttrium oxide precipitates. Its compressive strength, compressibility, ultimate tensile strength and plastic elongation were 2839 MPa, 34.9%, 382 MPa and 0.46%, respectively. At tensile tests, translamellar fracture was the predominant mode and the microcracks often originated from pores and the interfaces of borides/matrix and β phase/matrix.