退火温度对冷变形Ti_(50)Ni_(45)Cu_5形状记忆合金马氏体相变及力学性能的影响

Martensitic Transformation Characteristics and Properties of Deformed Ti_(50)Ni_(45)Cu_5 Shape Memory Alloy with Annealing

使用透射电镜(TEM),动态热机械分析(DMA)以及示差扫描量热法(DSC)等测试方法对固溶态25%冷变形Ti_(50)Ni_(45)Cu_5合金400℃/1 h,500℃/1 h,600℃/1 h,700℃/1 h退火态的组织结构,马氏体相变特征以及力学性能进行分析,并在实验中对比使用DSC与DMA两种测试方法用于马氏体相变测试。结果表明,随着退火温度升高,Ti50Ni45Cu5合金的强度、硬度降低,塑性升高,400℃/1 h退火态合金有最高的强度和硬度,分别为996 MPa和HV 280,700℃/1 h退火态合金有最好的延伸率27.8%。随着退火温度升高,合金的马氏体相变温度因为合金内位错密度降低,孪晶晶界减少及内应力减少,逐渐从54.5℃下降至37.7℃。400℃/1 h,500℃/1 h,700℃/1 h退火态合金均发生B19-B19'马氏体相变,而600℃/1 h退火态合金由于Ti3Ni4相的析出B2-B19'马氏体相变转变为B2-B19-B19'两步马氏体相变。两步马氏体相变的B2-B19相变部分和B19-B19'相变部分均在DMA模式测试出,而DSC模式只检测出B2-B19相变部分,DMA模式更适合于本实验测试马氏体相变。

The microstructures, transformation characteristics and mechanic properties of 25% cold-deformed supersaturated Ti50Ni45Cu5 alloys annealed at 400 ℃/1 h, 500 ℃/1 h, 600 ℃/1 h, 700 ℃/1 h were mainly investigated by transmission electron microscope （TEM） , dynamic mechanical analyzer （DMA） and differential scanning calorimeter （DSC）. According to the experimental results, with annealing temperature increasing, the strength and hardness decreased, while the ductility increased. Specimens annealed at 400 ℃/1 h exhibited the maximum tensile strength 996 MPa and the maximum hardness HV 280, and specimens annealed at 700 ℃/ 1 h exhibited the maximum elongation 27.8%. With annealing temperature increasing, the transformation temperatures decreased from 54.5 to 37.7 ℃ due to the reducing of dislocation density and internal stresses. The B19-B19＇ martensitic transformation occurred in the specimens annealed at 400 ℃/1 h, 500 ℃/1 h, 700 ℃/1 h, while B2-B19-B19＇ two-step martensitic transformation occurred in the specimen annealed at 600 ℃/1 h due to the precipitation of Ti3Ni4. The B2-B19 transformation and the B19-B19＇ transformation of two-step martensitic transformation were both detected in DMA method, in contrast that only B2-B19 transformation was detected in DSC method. It indicated that DMA method was suitable for martensitic transformation measurement in the experiment.