Ti-22Al-25Nb合金鍛后熱處理過程中的組織演變Microstructure evolution of as-forged Ti-22Al-25Nb alloy during heat treatment

調(diào)查了鍛造態(tài)的Ti-22Al-25Nb金屬間化合物合金在930~1 010 ℃固溶、空冷，并在750 ℃和870 ℃分別時(shí)效4 h和24 h后的顯微組織演變特點(diǎn)。結(jié)果表明：在α₂+β/B2+O三相區(qū)的930 ℃→1 010 ℃不同溫度下固溶處理，鍛造態(tài)的Ti-22Al-25Nb合金顯微組織中的O相分別呈無規(guī)則的長透鏡狀(其長寬比＜10)、短棒狀和球狀，α₂相依附在O相邊緣。當(dāng)固溶處理溫度較低(930 ℃)，在750 ℃時(shí)效時(shí)，隨著時(shí)效時(shí)間的延長，析出的O相條變粗，有序的B2相轉(zhuǎn)變成無序的β相，且體積增加；在870 ℃時(shí)效時(shí)，除有條狀O相析出外，還有O+B2相混合物存在，隨著保溫時(shí)間延長至24 h，析出的魏氏O相條粗化并趨向均勻，而O+B2相混合物消失；當(dāng)固溶處理溫度較高(1 010 ℃)時(shí)，在750 ℃時(shí)效伴隨有胞狀反應(yīng)，O相以塊狀形態(tài)從B2晶粒中不連續(xù)析出；在870 ℃時(shí)效，析出的O相條的長寬比減小，且隨著時(shí)間的延長，O相變粗并逐漸球化，B2晶界處的B2相條增厚并有部分聚集成塊的趨勢(shì)。

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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