THREE DIMENSIONAL TRANSIENT FINITE ELEMENT ANALYSIS FOR SOLIDIFICATION MICROSTRUCTURE AND THERMAL STRESSES IN MULTI-PASS LASER AIDED DMD PROCESS

摘要

Despite enormous progress in Laser Aided Direct Metal/Material Deposition (DMD) process many issues concerning the adverse effects of process parameters on the stability of variety of properties and the integrity of microstructure have been reported. Traditional solidification theories as they apply to castings or related processes are inappropriate in describing solidification in high energy beam processes involving significantly greater cooling rates. A complete model that provides a quantitative relationship between process parameters, temperature history, phase transformation kinetics, solidification parameters such as temperature gradient, growth rate, resultant interface undercooling, and the thermal residual stresses along with the deposited material microstructure is highly desirable. The focus of this paper is the solute transport in multi-pass DMD process, especially the coupling of the process scale transport with the transport at the local scale of the solid-liquid interface. This requires modelling of solute redistribution at the scale of the secondary arm spacing in the dendritic mushy region. This paper is an attempt towards a methodology of finite element analysis for the prediction of solidification microstructure and macroscopic as well as microscopic thermal stresses in this process. The computer simulation is based on the metallo-thermo-mechanical theory and finite element analysis for coupled temperature, solidification, phase transformation and stress/strain fields, and compared with experiments to verify the model.