熱處理對超細晶Ti-55511近β鈦合金顯微組織和力學(xué)性能的影響Effect of heat treatment on microstructure and mechanical properties of ultra-fine grained Ti-55511 near β titanium alloy

采用熱軋制備晶粒尺寸為0.1~0.5 μm的超細晶Ti-55511近β鈦合金，利用SEM和TEM等研究熱處理工藝對超細晶合金顯微組織和力學(xué)性能的影響。結(jié)果表明，在350~650 ℃的溫度條件下，合金強度和硬度隨溫度的升高呈現(xiàn)先增高后降低的趨勢，在450 ℃時達到峰值強度1486.09 MPa；在450 ℃退火時，隨著退火時間的延長，合金強度首先急劇上升至1536 MPa后趨于穩(wěn)定，伸長率呈現(xiàn)先增加后下降的趨勢；合金在退火過程中主要經(jīng)歷動態(tài)回復(fù)過程，未發(fā)生明顯的粗化長大現(xiàn)象，晶粒尺寸均小于1 μm。動態(tài)回復(fù)過程在消除加工硬化的同時促進了晶界/相界的穩(wěn)定化，增強細晶強化作用；退火過程中發(fā)生α→α₂和β→ω→α相變過程，第二相粒子彌散強化效應(yīng)增強。但是當(dāng)?shù)诙嗔Ｗ映叽缭龃笾烈欢ǔ潭葧r，會顯著降低合金的塑性。退火過程中合金力學(xué)性能的變化與強化機制的作用有關(guān)。

The ultra-fine grained (UFG) Ti-55511 near β titanium alloy with grain size of 0.1-0.5 μm was prepared by hot rolling. The effects of heat treatment on the microstructure and mechanical properties were investigated by SEM and TEM. The results indicate that both the strength and hardness of the alloy increase firstly and then reduce with increasing the heat treatment temperature from 350 ℃ to 650 ℃. The peak strength of 1486.09 MPa appears at 450℃. The strength dramatically reaches 1536 MPa and then becomes stable with prolonging the holding time when heat-treated at 450 ℃. While the maximum elongation increases firstly and then decreases. During the annealing process the dynamic recovery occurs in the alloy and the grain size remains smaller than 1 μm. The dynamic recovery stimulates the grain refinement effect by eliminating the hardening process and improves the stability of the grain boundary/phase boundary. The phase transitions of α→α₂ and β→ω→α enhance the second phase particle dispersion effect during the annealing process. However, the ductility of alloy significantly decreases when the second phase particles grow up to a certain size. The mechanical property evolution during annealing process is mainly related to the effect of strengthening mechanisms.

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