Influence Of The Rmomechanical Treatment On The Microstructure And Properties Of A High Temperature Titanium Alloy For Short-Term At 650-700℃

High temperature titanium alloy has heat resistance, good creep resistance, good lasting high strength, which makes it widely used in aerospace materials. Its special service environment requires that the material has high temperature tensile strength and high temperature stability and fracture toughness.In this paper, the deformation heat treatment process to eliminate the crystal defects, improve the alloy grain size, micro structure, the volume fraction of the case, to obtain a good comprehensive mechanical properties.The ingot of Ti-Al-Sn-Zr-Mo-Nb-W-Si high temperature alloy was prepared by induction skull melting(ISM) in a water cooler cooper crucile.The three kinds of forgings which were multidirectional forging with two fires,forging going along with the radial and multidirectional forging with one fire.The sheet of a thickness of 3mm was rolling based on the radial forging. The micro structure of the plate was composed of needle alpha+ transformation beta+grain boundary alpha phase, and the micro structure of the forging were composed of lamellar alpha and beta phase transition. AT 650℃, The high temperature strength of the plate and the unidirectional forging exceeded 780Mpa, but the elongation rate was low, which was between 5%-8%.The tensile strength of sheet at room temperature is higher of 47.7Mpa than that of unidirectional forging, At 700℃, the tensile strength of unidirectional forging was 630.87Mpa. The room temperature tensile strength of multidirectional forging was more than 1230Mpa, the elongation rate is greater than 4.3%, but the high temperature strength was low, the high temperature strength of 700℃ was under 440Mpa.By the way of differential scanning calorimetry,continuous heating-up technique and calculating,the transformation point was concluded at 1010℃. According to the phase transition point, the heat treatment process of the alloy is established, and the solid solution temperature of the alloy is 960℃, 980℃,1000℃, and the solution temperature is 1020℃. Aging temperature: 650℃,700℃,750℃.The changes of short-time high temperature titanium alloy’s micro structure were researched after solid solution and aging by EDS and X-ray diffraction (XRD) on the phase composition of the alloy in the two-phase region heat treatment, and the influence of the solution temperature, solution time, cooling method and aging temperature on the micro structure and phase structure of the alloy were discussed. The results showed that heat treatment in the two-phase region, the duplex micro structure composed by alpha, beta micro structure transformation was obtained; single-phase region got the widmanstatten structure. With the solid solution temperature rising, reduced the volume fraction of primary alpha phase, increased in size, in the dynamic recrystallization and lamellar alpha phase in the vicinity of the original beta grain boundaries, or different orientation of lamellar alpha photographs interfascicular equiaxed, the transformed beta tissue increased. The cooling rate had a significant impact on the organization. The effect of solid solution time was not obvious. After aging, the temperature increased, the secondary alpha phase coarsened.Performance and micro structure of the two phase heat treated were analysised. The results showed that After heat treatment, the elongation at room temperature and high temperature of the plate and the unidirectional forging were improved obviously, and the elongation was increased to 21.77% at 650℃. Multidirection forging’s high temperature strength were improved, At 700℃, the highest strength reached 630Mpa. the change of plastic was consistent with the change of the volume fraction of the primary alpha phase.and the strength was consistent with the quantity of volume fraction of the primary alpha phase With a number of large size of the primary and secondary acicular alpha alpha, the alloy strength and plasticity to achieve the best matching. One fire and multidirection forging was in the best at room temperature tensile properties, tensile strength was 1247.54Mpa, elongation was 5.61%. The sheet was at the best tensile strength, tensile strength was 821.59Mpa and elongation 15.02% at 650℃ after 1000 C 1hAC+650 C 2hAC. Two fire times the multidirection forging after 980 C 1hAC+650 C 2hAC was in the best at 700℃, tensile strength 633.22Mpa, elongation was 34.04%.