Simulation of heat-affected zone microstructure during laser processing.

摘要

The mechanical properties of a weldment are significantly influenced by its heat affected zone (HAZ) microstructure. An understanding of the latter is thus essential for predicting and realizing the mechanical properties of a weldment. However, traditional analysis of the microstructure involves metallographic examination, which is both destructive and time consuming. To enhance the capability for non-destructive and real time microstructural prediction, a dimensionalized Monte Carlo-based computer simulation methodology has been developed for two and three dimensional simulations of the evolution of grain structure in the steep temperature gradient environment of the HAZ as arises during laser processing.; A triangular lattice and a cubic lattice were employed for the two-dimensional and three-dimensional simulations, respectively. In either case, 99.9% Ni was the reference material used. Large matrices, consisting of 200 x 200 sites with 100 possible grain orientations, were used for the two-dimensional simulation to obtain a detailed evolution of the grain structure. Temperature histories obtained using Omega type K thermocouples were substituted into the simulation. Both the grain size distribution and the grain topology throughout the HAZ showed reasonable agreement with existing experimental results. The difference in average grain size for the 1000 kW welding experiment on nickel was 27 and 10 {dollar}mu m{dollar} at depths of 2.52 and 1.26 mm below the specimen surface in the plane located at the center of the weld and along the welding direction.; The three-dimensional simulations were based on a matrix consisting of 100 x 100 x 100 sites with 50 possible grain orientations. Temperature histories were obtained using Rosenthal's point heat source model. The analyses of the number of grain edges and the distribution of grain size for isothermal simulations show good agreement with experimental results from the literature. The results of the heat affected zone (HAZ) grain topology analyses show that a grain structure with a varying average grain size has a different topology from the normal distribution because of the temperature variation in the matrix.