高温热变形条件下Ni-Ti形状记忆合金的微结构演变

Microstructure evolution of NiTi based shape memory alloys under high temperature deformation

采用真空感应法炼制了不同氧、碳含量的NiTi和NiTiNb形状记忆合金 .分析研究了合金的微观组织、相结构以及高温热变形对合金微观组织的影响 ,重点研究和探讨了合金微观结构在高温热变形过程中的演变规律 .确定了合金组织中TiNi基体相、Nb相及在晶界形成的氧化物和碳化物的形变特点 .结果表明 ,合金中C、O含量决定其组织中碳化物和氧化物的形态和含量 ,高温热变形时 ,TiNi基体相和Nb相粒子均产生较大塑性变形 .当合金中氧和碳含量较高时 ,氧化物和碳化物在变形时碎裂 ,在组织中的分布比铸态更均匀 .在本文研究的氧、碳含量的范围内 ,氧化物和碳化物的存在对合金的力学性能 ,如拉伸强度、延伸率等影响不大 .

Ni-Ti and Ni-Ti-Nb alloys were produced by melting in high frequency vacuum induction furnace. The microstructures and effect of high temperature deformation on the microstructure were investigated. We focus attention on the microstructure evolution of alloys under high temperature deformation. The deformation characteristics of the Ni-Ti matrix, Nb-rich phase, and oxides and carbides were determined. It is indicated that the morphology and amount of oxide and carbide in the microstructure are closely dependent on the content of impurities(C,O). During high temperature deformation, the oxide and carbide are crushed upon substantial plastic deformation, especially in the case of high oxygen or/and carbon content. In the range O and C content of present study, the oxide and carbide exhibit little influence on the mechanical properties of the NiTiNb shape memory alloys.