Effect of crystal quality on twinning stress in Ni–Mn–Ga magnetic shape memory alloys
Effect of crystal quality on twinning stress in Ni–Mn–Ga magnetic shape memory alloys
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DOI：
10.1016/j.jmrt.2021.07.081
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发表时间：
2021-09
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影响因子：
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通讯作者：
D. Musiienko;Frans Nilsén;Andrew Armstrong;M. Rameš;P. Veřtát;R. Colman;J. Čapek;P. Müllner;O. Heczko;L. Straka
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作者：
D. Musiienko;Frans Nilsén;Andrew Armstrong;M. Rameš;P. Veřtát;R. Colman;J. Čapek;P. Müllner;O. Heczko;L. Straka
低孪生应力（TS）是铁磁马氏体中磁性形状记忆功能的先决条件。我们比较了Ni 50 Mn 28 Ga 22（标称at.%）单晶从四个不同的生产商，以揭示晶体质量上的TS的影响。在逆马氏体转变附近，TS通常较低，约为1 MPa，而不管高达1.7°的镶嵌度和高达2at.%的化学成分偏差的Mn。纯的I型和II型孪晶界出现在具有平滑化学成分梯度的晶体中。相应的温度依赖性TS遵循普遍的线性趋势，I型孪晶的斜率为−0.045 MPa/K，II型孪晶的斜率为−0.001 MPa/K，后者的TS可低至2 K。在具有剧烈局部化学偏差的晶体中，I型/II型孪晶混合晶界的中间斜率为−0.023 MPa/K。我们的结论是，晶体质量间接影响TS的大小，通过其对孪晶界的字符的影响。在马氏体相变温度附近，这种效应很弱，而在低温下很强。
Low twinning stress (TS) is a prerequisite for magnetic shape memory functionality in ferromagnetic martensites. We compare Ni50Mn28Ga22(nominal at.%) single crystals from four different producers to reveal the effect of crystal quality on the TS. Near the reverse martensite transformation, the TS is generally low, about 1 MPa, regardless of mosaicity of up to 1.7° and chemical composition deviations of up to 2 at.% of Mn. Pure type I and type II twin boundaries occur in crystals with smooth chemical composition gradients. The corresponding temperature dependences of TS follow universal linear trends with the slopes of −0.045 MPa/K for type I twins and −0.001 MPa/K for type II twins, enabling a very low TS down to 2 K for the latter. An intermediate slope of −0.023 MPa/K appears for mixed type I/type II twin boundaries in a crystal with sharp local chemical deviations. We conclude that the crystal quality affects the magnitude of the TS indirectly, through its impact on the character of the twin boundaries. The effect is weak near the martensite transformation temperature and strong at low temperatures.