Ni52Mn24Ga24单晶中取向内应力的热动力学计算

测量了Ni₅₂Mn₂₄Ga₂₄单晶样品在磁场加载和未加载情 况下马氏体相变时的相变应变.分析结果表明：用提拉法生长单晶时在晶体内部引入了单一取向的内应力，该取向内应力可诱导马氏体变体择优取向，从而导致马氏体相变时产生大的相变应变.从理论上计算了该内应力的大小.另外，对样品在马氏体态单纯磁诱导应变的热动力学研究，表明取向内应力在马氏体态依然存在. 关键词： 马氏体相变 磁感生应变 内应力

Thermodynamic calculation of the oriented internal stress in single crystals of Ni52Mn24Ga24

The internal stress in single crystals of Ni₅₂Mn₂₄Ga_{2 4} has been calculated based on the balance equation and the experimental data on transformation strains with or without bias field. It was found that the residual oriented internal stress caused by the directional solidification during the crystal growth plays an important role in achieving the reorientation of the variants, and resulting in a large transformation strain.Furthermore, according to Maxwell equation and Ullako's thermal dynamic model, the theoretical value of magnetic-field-induced strains and internal stress at different temperatures in martensite was calculated based on a best fitting of the strain curves versus the bias field. Compared with the experimental observation, the availability of various models has been discussed.