单晶Ni_(52)Mn_(24)Ga_(24)的磁感生应变和磁增强双向形状记忆效应

铁磁性Heusler合金Ni2 MnGa是近年开发的磁控制功能材料 ,已发现该材料结合马氏体相变可以产生大磁致伸缩 (磁感生应变 )和磁控制形状记忆效应两种应用功能。用磁悬浮冷坩埚提拉设备沿 0 0 1]方向生长了组分为Ni52 Mn2 4 Ga2 4 的单晶。室温时沿该单晶样品 0 0 1]方向加磁场 ,在该方向获得了 - 0 6 %的大磁感生应变。当磁场方向垂直于 0 0 1]方向时 ,样品在 0 0 1]方向的磁感生应变值为 0 5 %。同时该单晶样品在室温附近还具有可由磁场增强和控制的双向形状记忆效应。无磁场作用时 ,降低温度 ,样品在发生马氏体相变时 ,在 0 0 1]方向产生1 2 %的收缩形变。随后升高温度 ,反马氏体相变时样品以同样的应变量膨胀 ,恢复到原来的形状 ,显示了特有的无需外应力协助的自发的双向形状记忆效应。其温度滞后只有 10℃。如果在样品的 0 0 1]方向加一个偏磁场 ,其形状记忆的应变量随磁场的增强而增大。在磁场为 1 2T时可达 4%。而当磁场转向 10 0 ]方向时 ,形状记忆的应变可以改变符号。本文指出产生大磁感生应变和磁增强双向形状记忆效应的关键是马氏体变体的择优取向。

Magnetic-Field-Induced Strain and Field-Enhanced Two-Way Shape Memory Effect in Ni_(52)Mn_(24) Ga_( 24) Single Crystals

Ferromagnetic Heusler alloy Ni 2MnGa has been invested as a new magnetic field control actuator material. The results show that such material combined with the martensitic transformation can produce field controlled shape memory effect and magnetic filed induced strain(MFIS). A single crystal of Ni 52 Mn 24 Ga 24 was grown in 001] direction of the cubic parent phase by the Czochralski method. At room temperature, a large MFIS of about -0.6% was obtained in the growth direction with field applied along 001] direction. Moreover, stress free and two way thermoelastic shape memory, with 1.2% recoverable strain and 10K temperature hysteresis, was also obtained in Ni 52 Mn 24 Ga 24 at around room temperature. The strain can be enhanced more than three times, up to 4.0% with a bias field of 1.2T applied along the 001] direction. It indicates that the preferentially orientation of martensitic variants is the crucial term for achieving large MFIS and field enhanced two way shape memory effect in this material.