Optimization Of MEAM Potential Of CuALNi Alloy And Analysis Of Constitutive Relations In Martensitic Transformation

Nowadays, applications of Shape Memory Alloy(SMA) become more and morepopular in many areas. It is based on the martensitic transformation (MT) under thetemperature and stress environment change. However, lack of experimental capabilitiesconstraints deeper understanding of the details and mechanism of MT. This obstructs thedevelopment of SMA. Thus, advancing in the mechanism of MT becomes one of themost important issues in solid transformation field.To obtain details of MT, this work apply molecurlar dynamics method (MD) tosimulate the MT and the reverse MT of CuAlNi alloy. The potential is optimized, andthe strain in obtained martensites calculated. Finally, combing the atomistic stress，wegain the more understanding of constutive relations of MT.This thesis concerns three parts of work:(1) Computation of elastic constants by a new deformation-fluctuation methodunder finite temperatures. Based on literature work, the new method improves vastly onaccuracy, applicability and computational speed, especially for complicated many-bodypotentials. This method is widely used in the potential parameter optimization.(2) MEAM potential parameter optimization of ternary alloy CuAlNi. MEAMpotential is semi-empirical and contains a large selection of adjustable parameters. Forbetter simulation of forward and inverse martensitic transformation of CuAlNi, asoftware incorporating Genetics Algrorithm is developed to optimize the parameter.They are applied in the simulations of thermal-elastic and stress-induced martensitictransformation in CuAlNi. Microstructures of stacking faults and twins are obtained, aswell as the hysteresis.(3) Analysis ofconstitutive relations in martensitic transformation. A micro-analysisof local deformation gradient and thus strain is developed for the stacking fault basedmicrostructures. With the atomistic stress, the analysis of constitutive relations inmartensitic transformation is completed.The method developed and the results obtained in this thesis will promote theresearch of mechanism of martensitic transformation.