Phase Transformation during the Continuous Cooling in Near α Titanium Alloy Ti60

摘要:

研究了近α型Ti60钛合金自β单相区连续冷却至室温过程的相转变规律，冷却速率控制在80 ℃?s-1至0.1 ℃?s-1范围内。采用膨胀法原位分析了冷却过程中β→α′马氏体转变和β→α扩散型转变的起止温度及动力学特征，并观察对比了不同冷却速率下显微组织特征。在超过50 ℃?s-1的快冷条件下，原始β相约在910 ℃快速转变为细小针状α′马氏体，并且没有残余。在马氏体内部发现大量的位错以及层错，证明转变过程伴随有晶格畸变。在5 ℃?s-1的慢冷条件下，α相在β晶内和晶界都有形核，而在低于1 ℃?s-1时，α相仅在晶界形核，透射电镜下发现α片层间仍残留少量β相，而在片层内部α相发生了有序转变，形成α2相。冷却速率决定了连续冷却过程中同素异构的相转变机制以及生成相的内部结构

Abstract:

The phase transformation mechanism of near α titanium alloy Ti60 was investigated during the continuous cooling from β phase field, at the cooling rate from 80 oC?s-1 to 0.1 oC?s-1. The initial and final temperatures and kinetics of the β→α′ and β→α diffusion type transformations were analyzed by a dilatometric method. Over the cooling rate of 50 oC?s-1, the original β phase rapidly transformed to α′ martensite at 910 oC in the form of acicular platelets without any β phase left. A great amount of dislocations and stacking faults were found inside the marten site. Under cooling rate of 5 oC?s-1 , α phase nucleates along the grain boundary as well as inside the grain, while at the cooling rate below 1 oC?s-1, the nucleation occurred only along the grain boundary. A small amount of retained β phase was observed along the α platelet boundary under TEM, while the ordering transformation of α phase occurred inside the platelet, resulting in forming of α2 phase. Therefore, the cooling rate determines the alloy phase transformation mechanism and the inner structure of product phase