Role of Dislocations on Martensitic Transformation and Microstructure Through Molecular Dyanmic Simulations
Abstract
Martensitic transformation underlies the phenomena of super-elasticity within shape memory alloys and the production of advanced steels. Experimentation has demonstrated that this process is strongly influenced by defects and microstructural changes. With simulations granting up to an atomic-level understanding as to the impact that grain-boundaries and precipitates have upon the solid-to-solid phase transformation. Yet the role that dislocations partake on the martensitic transformation and its microstructures remains unclear or disputed.Therefore, we utilize large-scale molecular dynamics (MD) simulations to study the forward and reverse transformation of martensitic material modeled after Ni63Al37shape via thermal cycling loading. The simulations indicate that dislocations retain martensite well above the martensite start temperature and behave as nucleation sites for the martensite. We found that a reduction in dislocation density with cycle correlated with a decrement in the Ms and As transition temperatures, in agreement with experiment. It was found that competing martensite variants could develop stable domains as dislocation density reduced sufficiently that resulted in multi-domain structures. Furthermore, the critical nuclei size of martensite variant was able to be extracted from our results.
Degree
M.Eng.
Advisors
Strachan, Purdue University.
Subject Area
Energy|Computer science|Engineering|Thermodynamics
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