Materials science and engineering of hydrogen-induced shear transformation in hydrogen absorbing materials

形变孪晶的激活对提高镁合金的加工性能是必不可少的，但其激活机制尚未得到充分的认识。已知当晶粒尺寸减小到纳米量级时，变形孪晶的激活是困难的。在孪晶形核临界体积存在的假设下，通过确定形变模式从孪晶向滑移转变的临界体积，研究了形变孪晶的形核尺寸。当微米级尺寸的Mg单晶沿沿着a轴方向压缩时，观察到{11 - 21}上的孪晶。如果试样尺寸进一步减小到亚微米量级，则观察到{11 - 23}上的滑移而不是{11 - 21}上的孪生。在Mg-Zn-Y系统的LPSO单晶中观察到类似的行为。因此，在这些合金中孪晶的临界体积被确定为约1微米。

The activation of deformation twinning is indispensable to promote the workability of Mg and its alloys, but their activation has not been well understood. The activation of deformation twinning is known to be difficult when the grain size is reduced down to the orders of nano-meters. On the assumption of the existence of critical volume for twin nucleation, we have investigated nucleus sizes for deformation twinning through the determination of the critical volume for the transition in deformation modes from twinning to slip. When single crystals of Mg of the size of micron-meter order are compressed along the a-axis direction, twinning on {11-21} is observed. If the specimen size is further reduced down to sub-micron orders, slip on {11-23} id observed to operate instead of twinning on {11-21}. The similar behavior is observed in LPSO single crystals of the Mg-Zn-Y system. The critical volume for twinning in these alloys is thus determined to be about 1 micrometer.