Microstructure and mechanical properties of an extruded γ-TiAlMoSi alloy

Two samples of a two phase γ/α2-Ti52Al46.8Mo1Si0.2 alloy have been extruded with the reduction ratio in the cross section of 7:1 at 1250°C and the ratio 12.5:1 at 1300°C. Mechanical tests have been performed in the temperature regime from 20 to 1000°C. The sample extruded at 1250°C possesses a microstructure with γ and α2 grains with grain sizes of less than 3 μm and coarser single-phase γ grains 10–40 μm in size. The alloy exhibits an excellent balance of ductility and strength. At room temperature the yield strength is 720 MPa, the elongation to failure is ϵpl=3.0%. The ductility rapidly increases and the yield stress strongly decreases with temperature increases above 700°C. The alloy extruded at 1300°C has a similar microstructure as the alloy extruded at 1250°C, but lamellar grains exist near the rod axis. The yield strength of this alloy is higher within the considered temperature range, but its ductility is reduced (YS=807 MPa, ϵpl=2.6% at room temperature). The loss in yield strength with increasing temperature of the 7:1 extruded TiAlMoSi alloy is much more pronounced than that of the 12.5:1 extruded TiAlMoSi alloy for temperatures higher than 600°C.