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首页> 外文会议>15th European workshop on modern developments and applications in microbean analysis, 7th meeting of the International Union of Microbean Analysis Societies >DIRECT OBSERVATION OF a-b TWIN LAMINATE IN MONOCLINIC FIVE-LAYERED MARTENSITE OF Ni-Mn-Ga MAGNETIC SHAPE MEMORY SINGLE CRYSTAL
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DIRECT OBSERVATION OF a-b TWIN LAMINATE IN MONOCLINIC FIVE-LAYERED MARTENSITE OF Ni-Mn-Ga MAGNETIC SHAPE MEMORY SINGLE CRYSTAL

机译：Ni-Mn-Ga磁性形状记忆单晶单斜晶五层马氏体中a-b双叠层的直接观察

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Magnetically induced reorientation (MIR), one of the magnetic shape memory effects, hinges on extremely low twinning stress or high mobility of particular types of twin boundaries. Only by fulfilling this condition the twin microstructure can be manipulated by magnetic field [1]. The extreme easiness of twin boundary motion is very puzzling and particular hierarchical structure of twinning may play the important role in high mobility. Certain twin hierarchy occurs naturally to fulfil the compatibility conditions on interfaces. The compatible twin microstructure in Ni--Mn-Ga was predicted from the elastic theory of martensite. Ni-Mn-Ga martensite is slightly monoclinic with c/α ≈ 0.94, b/α ≈ 0.995 and monoclinic distortion y= 90.3°. This allows five different twinning systems, of which the most important is a-c twinning as it provides the reorientation. The interface between these twins is called twin boundary and can be of Type I and II. The stress to move twin boundary, i.e., twinning stress, is exceptionally low of a few tenths of MPa for Type II, and about 1 MPa for Type I twin boundary [2]. Full hierarchy of twinning including a-b twin laminate was directly observed by optical and scanning electron microscopy (SEM) in the vicinity of macroscopic, mobile a-c twin boundary in five-layered monoclinic (10M) martensite of Ni_(50)Mn_(28)Ga_(22) single crystals exhibiting MIR [3]. The submicron a-b twin laminate was identified by backscattered electrons (BSE) in SEM [4]. Figure 1 shows BSE images of a-b laminate terminating straight on Type I (Fig. 1 left) and by laminate branching on Type II (Fig. 1 right) twin boundary in agreement with the model.
机译：磁性形状记忆效应之一的磁感应重定向（MIR）取决于极低的孪生应力或特定类型的孪晶边界的高迁移率。只有满足这种条件，孪晶的微观结构才能被磁场控制[1]。孪晶边界运动的极端容易性令人费解，孪生的特殊层次结构可能在高迁移率中起重要作用。为了满足接口上的兼容性条件，自然会发生某些孪生层次结构。根据马氏体的弹性理论预测了Ni-Mn-Ga中相容的孪晶组织。 Ni-Mn-Ga马氏体为单斜晶，c /α≈0.94，b /α≈0.995，单斜应变y = 90.3°。这允许五个不同的孪生系统，其中最重要的是a-c孪生，因为它提供了重新定向。这些双胞胎之间的界面称为双胞胎边界，可以是I型和II型。移动孪晶边界的应力，即孪晶应力，对于II型非常低，仅为十分之几MPa，而对于I型双边界则约为1 MPa [2]。通过光学和扫描电子显微镜（SEM）在Ni_（50）Mn_（28）Ga_（）的五层单斜晶（10M）马氏体的宏观，可动的ac孪晶边界附近直接观察到包括ab双叠层的孪晶的完整层级。 22）单晶具有MIR [3]。亚微米a-b孪晶层压板是通过SEM中的反向散射电子（BSE）鉴定的[4]。图1显示了与模型一致的a-b层压板的BSE图像，该B-层压板直接终止于I型（图1左），并在II型（图1右）双边界处终止了层压板。

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