Papers by Keyword: Twinning Mode

Abstract: This paper investigated the twinning mode in a homogenized Mg-10Gd-2Y-0.5Zr ingot compressed at 300 oC and 1 s-1 using transmission electron microscopy observation and schematic method. Details about the primary twinning mode was studied based on the minimum sear criterion by comparing the values of the four major twinning modes in the magnesium alloys. The results show that the twins are formed first by {10-11} primary twinning being step characteristics, and then the secondary twins are formed later around the step by {10-12}secondary twinning. The results also show that the XRD Rietveld refinement method is an effective means to obtain the lattice parameter and to calculate the twinning shear that has important effect on the primary twinning mode in a h.c.p alloy.

Abstract: A three-dimensional phase field model applicable for the B2-B19′ martensitic phase transformation of NiTi alloys was developed to predict the twinning modes in the B2-B19′ transition. The phase field simulation results showed that by taking into account the transformation induced elastic strain, the martensite variants were self-accommodated and sheared along the specific interface in the entire transition stage for reducing the elastic energy, whether the formed interface between the variants belongs to twinning plane could be determined by calculating the minimum value of long range elastic interaction energy, Bpq. Through comparison with the existing analytical solutions, it is demonstrated that the phase field model can be used to predict the type I twinning modes in the B2-B19′ phase transition with good precision.