中文摘要：

对锻造态的粉末冶金Ti-45Al-7Nb-0.3W（摩尔分数，%）合金进行后续热处理，研究热处理时间和热处理温度对合金组织演变的影响，利用扫描电镜及透射电镜对合金显微组织进行观察。结果表明：在1230-1260℃温度区间热处理可消除锻造态合金的少量β相。在该温度区间进行等时热处理时，随着热处理温度的升高，α晶粒和γ晶粒迅速长大，γ相体积分数急剧减小，且α晶粒趋于等轴化。合金在1260℃进行等温热处理时，热处理时间由0.5 h延长至6 h，α晶粒和γ晶粒迅速长大，γ相体积分数降低，继续延长热处理时间，显微组织没有明显的变化。通过计算可知，1260℃下α晶粒尺寸的极限值约为0.54 Dγ/Vγ（Dγ为γ晶粒尺寸；Vγ为γ晶粒体积分数）。

英文摘要：

Powder metallurgy Ti-45Al-7Nb-0.3W （mole fraction, %） alloy was canned-forged and then heat-treated. The effects of heat treatment time and temperature on the alloy microstructure evolution were studied. The microstructures of as-forged alloy and heat-treated alloy were investigated by scanning and transmission microscopy. The results demonstrate that a fewβ grains in as-forged alloy are eliminated during heat treatments in the temperature range of 1230-1260℃. Isochronal annealing experiments show that theα grain size andγ grain size rapidly increase with increasing the temperature, while the volume fraction ofγ phase steeply decreases andα grains become equiaxial. Isothermal annealing experiments at 1260℃ for 0.5-6 h reveal a sharp increase ofα grain size andγ grain size with time. Meantime, the volume fraction ofγ phase decreases. The microstructure of alloy shows no significant change during prolonging the annealing time. By calculation, the extremeα grain size at 1260℃ is approximately 0.54Dγ/Vγ （Dγ is short forγ grain size andVγ is short or the volume fraction ofγ phase）.