采用超高温度梯度真空区熔法定向凝固制备了Ni2MnGa晶体, 改变晶体生长速度、温度梯度和熔区长度, 获得了平直的固-液生长界面, 制备出Ni2MnGa单晶. 用光学显微镜观察了Ni50Mn29Ga21晶粒的竞争生长过程. 制备的定向凝固试样无宏观成分偏析. X射线衍射分析仅显示四方结构马氏体Ni2MnGa 400峰和004峰, 晶体生长轴向择优取向为立方奥氏体<100>方向. 采用差式扫描量热分析(DSC)和热重法(TG)分别测定试样中不同部位的相转变温度和Curie温度. 在稳定生长区, 沿轴向马氏体相变温度在10 ℃左右变化, 而Curie温度几乎没有变化. 这进一步表明采用该方法制备的Ni2MnGa晶体沿轴向成分 均匀, 且马氏体相变温度一致.
The crystals of Ni2MnGa were prepared by high temperature gradient zone-melting unidirectional solidification. Through altering the growth velocity, the temperature gradient and the zone-melting length, a flat solid-liquid interface can be obtained, and a single crystal was successfully prepared. The crystal growth competition was observed in Ni50Mn29Ga21 alloy. No obvious composition macro-segregation was detected. In X-ray diffraction pattern only 400 and 004 peaks of the tetragonal martensitic structure appear, showing the preferred orientation along <100> of the high-temperature cubic austenite Ni2MnGa. DSC and TG methods were applied to describe the distributions of the martensitic transition temperature and Curie temperature along the solidified axis of the Ni50Mn29Ga21, no obvious change for Curie temperature and about 10℃ increase for the martensitic transition temperature were observed, further indicating the homogeneity of the composition along the growth axis.
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