Ti-22Al-25Nb合金锻后热处理过程中的组织演变Microstructure evolution of as-forged Ti-22Al-25Nb alloy during heat treatment

调查了锻造态的Ti-22Al-25Nb金属间化合物合金在930~1 010 ℃固溶、空冷，并在750 ℃和870 ℃分别时效4 h和24 h后的显微组织演变特点。结果表明：在α₂+β/B2+O三相区的930 ℃→1 010 ℃不同温度下固溶处理，锻造态的Ti-22Al-25Nb合金显微组织中的O相分别呈无规则的长透镜状(其长宽比＜10)、短棒状和球状，α₂相依附在O相边缘。当固溶处理温度较低(930 ℃)，在750 ℃时效时，随着时效时间的延长，析出的O相条变粗，有序的B2相转变成无序的β相，且体积增加；在870 ℃时效时，除有条状O相析出外，还有O+B2相混合物存在，随着保温时间延长至24 h，析出的魏氏O相条粗化并趋向均匀，而O+B2相混合物消失；当固溶处理温度较高(1 010 ℃)时，在750 ℃时效伴随有胞状反应，O相以块状形态从B2晶粒中不连续析出；在870 ℃时效，析出的O相条的长宽比减小，且随着时间的延长，O相变粗并逐渐球化，B2晶界处的B2相条增厚并有部分聚集成块的趋势。

The microstructure evolution of as-forged Ti-22Al-25Nb alloy was investigated during 930-1 010 ℃ for 1 h solution treatment, air cooling, followed aging at 750 ℃ and 870 ℃ for 4 h and 24 h, respectively. The results show O phases evolution from a lenticular fashion to short bar and to spheric shape as solution temperature increasing in as-forged Ti-22Al-25Nb alloy. For as-forged alloy solution-treated at lower temperature, O precipitates get coarse gradually with elongation aging time, and the volume fraction of ordered B2 phase transiting into disordered β phase increases during aging at 750 ℃. At 870 ℃ aging, except O precipitates, there is O+B2 phase mixture. With aging time elongating to 24 h, O precipitates get coarse and tend homogeneous, O+B2 phase mixture vanishes simultaneously. For as-forged alloy solution-treated at higher temperature, it is accompanied by a cellular reaction at 750 ℃ aging. At 870 ℃ aging, the aspect ratio of O precipitates gets small. With the age time increasing, O phases get coarse and spheroidal. This makes B2 phases at B2 grain boundaries have trend of gathering into block.

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