Molecular Dynamics Simulation Of Martensitic Phase Transformations In Cu-Al-Ni Alloy

Martensitic phase transformation (MT) denotes a class of first-order, non-diffusive transformation in materials with high symmetry at high temperature (called austenite) subjected to a quenching or applied stress. On the phase interface, austenite undergoes a displacive atomic motion, resulting a low symmetry product----martensite. The most typical application of MT is the strengthening of steel, and that of shape memory alloy and super-elastic materials. The Cu-Al-Ni alloy studied in the work is such a typical material capable of undergoing martensitic phase transformation.Due to either the fast transformation or the difficulty to trace the motion on the interface in MT, the method of molecular dynamics simulation is applied in this work to accomplish this goal. This method can give all the details of the transformation thus making itself an effective way to patch the cons of traditional experiment.This thesis first reviews the current research status, and then gives a broad view of the molecular dynamics. After that, the MT behavior in copper-based alloys, especially in Cu-Al-Ni is summarized. Based on the crystallography theory of MT, we cast a matlab package to construct the spatial configuration of austenite and austenite-twinned martensite. We also give a set of MEAM (modified embedded-atom method) parameters for Cu-Al-Ni based on literature work and our own investigation. The testing of the parameter set against the physical constants show that the set is a reasonable construction.Based on the above work, the thermo-elastic and stress-induced MT in Cu-Al-Ni are investigated. Simulations under a uni-temperature loading and a cyclic temperature loading are conducted. The transition temperature range for thermo-elastic MT in Cu-Al-Ni are determined. We also observe the surface roughening and torsion during the MT and inverse MT. The stress-induced MT is successfully observed too.The output of the current work can be used to study the high-speed propagation of interface motion in MT in the future.