Effect Of Elements Al,O And Heat Treatment On Microstructure And Tensile Properties Of Cast Ti₃Al Alloy

Ti3Al based alloy has a low density, high specific strength and excellent high temperature performance, which is ideal material for aviation, spacecraft, lightweight high-temperature structural materials in future, but low room temperature ductility limit its application, so improving Ti3Al alloy’s room temperature tensile properties has become a research emphasis in recent years.This paper studied the effect of elements Al and O on the microstructure and room temperature tensile properties of cast Ti3Al alloy; developed a variety of heat treatment to explore the influence of the solution temperature, solution time, cooling rate and aging on the microstructure and tensile properties at room temperature; used argon tungsten pulsed arc welding to repair Ti3Al precision castings and evaluated the effect of welding on the properties of the original casting.The study shows:Within the range of18.5-21at.%, the Al content increases, the amount and size of0.2phase increases. When the Al content is between18.5-20.5at.%, the room temperature strength decrease and elongation increase significantly with the Al content increase; from20.5at.%to21at.%Al, the room temperature strength and elongation of the alloy does not change obviously. Within the range of0.068wt.%to0.15wt.%, the content of O increases, the morphology, distribution and volume percentage of the primary α2phase, small secondary α2/O phase and the B2phase do not change significantly; the strength of the alloy increases, the overall trend of the elongation is to reduce, only in the presence of intermediate volatility.When the cooling method is air cooling and water quenched after solution treatment, Ti-22Al-15Nb-1Mo alloy’s room temperature phase is the primary α2phase and the B2phase, as the solution temperature increases, the morphology of primary α2phase has no significant change, but the volume percentage increases; while furnace cooling, Ti-22Al-15Nb-1Mo alloy’s room temperature phase is the primary α2phase, secondary α2/O phase and B2phase, the primary α2phase and secondary α2/O phase crude in the furnace cooling process, as the solution temperature increases, the volume percentage of the primary α2phase and secondary α2/O phase has no significant change, but increases roughening. Aging in (α2+O) two-phase region, with increasing aging temperature and aging time, the volume percentage and size of secondary α2/O phase increase; in (α2+B2+O) region, with the the aging temperature and aging time increases the volume percentage of secondary α2/O phase decrease but size increases.1020℃/1h, with the decrease of the cooling rate, the room temperature strength of Ti-22Al-15Nb-1Mo alloy is lowered, the elongation increases. When slow cooling with the way of wrapping cotton insulation, the solution temperature and solution time have no significant effect on the room temperature strength and elongation of Ti-22Al-15Nb-1Mo alloy. Aging at different temperature after1020℃/1h/SC solution treatment, the room temperature strength of Ti-22A1-15Nb-1Mo alloy first increases and then decreases, the elongation first decreases and then increases.The fusion zone of homogeneous Ti-22Al-15Nb-1Mo joint after the1020℃/1h/SC heat treatment is mainly composed of α2phase and B2phase, it has a very narrow welding heat affected zone which has similar microstructure with base material; homogenous joint is easy to produce micro-cracks at the grain boundaries of the fusion zone, so the tensile properties of the joint are poor. The fusion zone of heterogeneous Ti-6A1-4V joint after the1020℃/1h/SC heat treatment is mainly composed of a phase and β phase, it has a very narrow welding heat affected zone which has similar microstructure with base material; the tensile properties of the joint are excellent.