BT25钛合金连续冷却转变曲线研究

Study on Continuous cooling transformation diagram of BT25 titanium alloy

摘要:

采用膨胀法测得BT25钛合金在不同冷却速度下的线膨胀曲线，同时用分段冷却方法证明了此膨胀曲线能够准确反映BT25钛合金在不同冷却速度时的相变过程，并结合物相分析（XRD）、扫描电镜（SEM）和显微硬度分析，获得了合金的连续冷却转变曲线( CCT 曲线)，研究了冷却速度对BT25钛合金相变组织演变规律的影响。结果表明:当冷速小于C1(1~3 ℃?s-1) 时，相变组织为魏氏组织；冷速大于C2(50 ~100 ℃? s-1)时，组织为α"马氏体；冷速在C1 ~ C2时，组织为魏氏组织和α"的混合物。并且随着冷却速度的增加，魏氏组织含量减少，而α"含量增加。合金硬度随冷却速率的增加而增加。

Abstract:

The expanding curves of BT25 titanium alloy under different cooling rates was investigated using dilatometry method. It was proved that the expansion method was able to measure accurately phase transformation of BT25 titanium alloy at different cooling rates. The continuous cooling transformation ( CCT ) diagram of this alloy was obtained by means of X ray diffractometry ( XRD), scanning electron microscopy(SEM) and micro-hardness。As well as the effect of cooling rate on microstructure evolution was investigated .The results showed that the Widmanstaten structure is obtained at the cooling rate of less than C1 (1~3 ℃?s -1); therefore, α" phase is generated at the cooling rate of greater than C2 (50 ~100 ℃?s -1) ; The microstructure consists of Widmanstaten structure and α" at the cooling rate from C1 to C2. With the cooling rate decreases, the quantity of Widmanstaten structure increases and the quantity of α" phase decreases in this microstructure. The micro-hardness of BT25 alloy decreases as the cooling rates decreasing.