Ti-50.0Ni单晶形状记忆合金组织与记忆性能研究

Investigation on Microstructure and Memory Property of NiTi Single Crystal Shape Memory Alloys

摘要:

在自制的定向凝固炉中，用带引晶器的石墨模壳制备出Ti-50.0at%Ni单晶。利用光学显微镜（OM）、扫描电镜（SEM）及其配置的能谱（EDS）仪研究合金的铸态组织，通过X射线衍射（XRD）和极图分析确定单晶晶粒取向，利用自制模具对合金的记忆性能进行评价。结果表明：试样横截面与纵截面均呈枝状晶分布特征，枝晶生长方向与定向凝固方向基本一致，未出现晶界，单晶横截面法向与[111]取向夹角为15°。由于消除了晶界对马氏体相变的不利影响，同时[111]取向是TiNi合金能获得较大可恢复应变的择优取向，与普通铸造的TiNi多晶相比，材料的形状记忆最大可恢复应变和记忆疲劳性能都得到一定提高。

Abstract:

Single crystals of NiTi (with 50.0at% Ni) were prepared in a self-designed unidirectional solidification furnace with a graphite mold shell connected with a crystal selector. Both macrostructure and microstructure of the alloy were observed by OM and SEM with EDS, the grain orientation of single crystal was determined by XRD and pole figures, and shape memory effect was evaluated by an instrument developed by ourselves. The results show that dendritic features were presented in both cross section and longitudinal section; the direction of dendrites growth were close to solidified direction; there was no obvious grain boundary observed; the angle between normal direction of cross section and [111] orientation was 15°. Compared with normal NiTi polycrystals, the maximal recoverable strain and memory fatigue property of the alloy were improved because the bad effect of grain boundary on the martensite phase transformation was eliminated, and also [111] orientation was a preferred orientation of NiTi alloy which can provide larger recoverable strain.