Thermal induced nanovoid evolution in the vicinity of an immobile austenite-martensite interface

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In this paper, thermal induced nanovoid evolution in the vicinity of an immobile austenite (A)-martensite (M) interface is studied. The phase field approach (PFA) to martensitic phase transformation (PT) is presented and the coupled Ginzburg-Landau (GL) and mechanics equations are solved to resolve an A-M interface. Then, the solution is stopped when the interface reached its finite width under thermal loading to keep the interface immobile. Next, the PFA for nanovoid evolution is presented and the coupled Cahn-Hilliard (CH) and mechanics equations are solved for the sample consisting of the obtained immobile A-M nanostructure. As a novelty, the mobility coefficient and the formation energy of nanovoids are considered phase dependent. The finite element method and the COMSOL code are used to solve the coupled GL and mechanics equations for single martensitic variant PTs as well as the coupled CH and mechanics equations for nanovoid evolution. The presented models and the numerical procedure are verified with the existing analytical and experimental data. The effect of the phase dependent energy barrier and the mobility coefficient of nanovoids, the transformation strain and the A-M interface width size on the nanovoid evolution is in detail investigated and the nanovoid structures and stress fields are presented. Mainly, the obtained nanostructures show that the nanovoids which appear at the interface grow only in martensite while they are suppressed in austenite, resulting in an oval shape for the nanovoids. Also, the nanovoids which appear in the martensite away from the interface and move toward it are suppressed at the interface. No nanovoid formation is found in austenite. The obtained results agree with the existing experimental data. The current model and the results can help for a better understanding of nanovoid evolution in different neighboring phases and the effect of different PT characteristics on the nanovoid evolution. Thus, they can be used to build the model for the interaction of nanovoids and the PT at the nanoscale.