热轧对Ti_(50)Ni_(50-x)Al_x(x=1,2,4)形状记忆合金微观组织、相变和力学性能的影响

Effect of Hot-rolling on Microstructures,Phase Transformation and Mechanical Properties of Shape Memory Alloys Ti_(50)Ni_(50-x)Al_x(x=1,2,4)

形状记忆合金的相变和力学性能受机械加工过程影响明显。在850℃下将Ti50Ni50-xAlx(x=1,2,4)形状记忆合金轧制成为板材。采用扫描电镜、透射电镜和X射线衍射对合金的微观结构研究表明:合金由NiTi相和Ti2Ni相组成,Al元素在Ti2Ni相中的固溶度比在TiNi相中高。差示扫描量热分析和电阻-温度测试表明:随着Al元素原子分数的增加,合金R相变和马氏体相变温度均下降,而两个相变之间的温度差增大。经850℃轧制以后,合金中Ti2Ni相减少,NiTi相中Al元素增加,从而使合金R相变和马氏体相变温度进一步降低,两个相变之间的温度差进一步增加,同时提高了合金的室温塑性。

The phase transformations and mechanical properties of shape memory alloys are remarkably affected by mechanical processing.In this study shape memory alloys Ti50Ni50-xAlx（x=1,2,4） are rolled into a plate at 850 ℃.The microstructures of the alloys are investigated by scanning electronic microscopy,transmission electron microscopy and X-ray diffraction.The results show that the alloys are composed of NiTi and Ti2Ni phases and the solid solubility of Al in the latter is higher than that in the former.The differential scanning calorimetry and electric resistance vs temperature measurements indicate that with the increasing Al content both the R and martensitic transformation temperatures decrease,and the temperature difference between the two transformations is enlarged.After hot-rolling at 850 ℃,the volume ratio of the Ti2Ni phase in the alloy decreases and the solid solubility of Al in the NiTi phase increases.Furthermore,the hot-rolling induces the decrease of R and martensitic transformation temperatures and the increase of their transformation temperature difference as well as the improvement of plasticity of the alloys at room temperature.