The effects of free surfaces on martensite microstructures: 3D phase field microelasticity simulation study

The phase field microelasticity approach to coherent phase transformations is extended to the case of a finite sample with free surfaces. The 3D simulation model is based on numerical solution of exact elasticity equation. No ad hoc assumptions on the microstructure morphology along evolution path are made. It is used to investigate the effects of free surfaces on multi-variant martensitic transformations in AuCd and FeNi alloys. The simulation shows that formation of free surfaces changes the martensite microstructures mostly in the surface layers, the thickness of these layers being commensurate with the size of martensite domains. It also shows that the free surfaces affect the microstructures of the high-symmetry FeNi more significantly than that of the low-symmetry AuCd because the latter has more orientation variants and can achieve better stress accommodation.