Simulation Of The Microstructure Evolution Of Pure Metal During Laser Cladding Using Phase-field Method

As one of the new technologies in surface modification, laser cladding has lots ofadvertages including high efficiency, low cost, small heat-affected zone andpollution-free. Laser cladding technology has been widely applied in industry, such asmould manufacture, laser direct manufacturing and biomedical manufacturing.However, the organization of the mechanical properties and the crack of lasercladding layer were difficult to control, which was a great barrier of the application oflaser cladding technique. It is well known that the mechanical properties of thecladding layer and the service life of parts are determined by the microstructure andgrain morphology of laser cladding layer. Therefore the understanding of theformation of the microstructure in the cladding is able to control the mechanicalproperties and cracks of the cladding layer, design the reasonable process parameters,and promote the popularization and application of laser cladding.In this thesis, grain morphology, mechanism and model of grain formation areinvestigated based on the theory of metal solidification and the method of grainsimulation. The main work was done as follows:1. The formation mechanism of laser cladding and the morphology of laser meltpool were studied and analyzed. Based on the thermal theory,the thermal model oflaser cladding was established using mobile Gaussian heat source. The conduction,convection, heat radiation were taken into consideration during laser cladding.Thethermal distribution of laser cladding was simulated.2. Based on the thermal field model of laser cladding and the basic principle ofthe phase field, the diffusion phase field model of pure metal was derived by couplingmicrostructure simulation model namely phase field model with macro temperaturefield equation. The external temperature and internal phase-field were coupled. Theeffect of phase-field parameters on grain growth was analyzed.3. The goveming equations of phase-field models were discretized using thefinite diffbrence method. The computational program to simulate the microstructureevolution of laser cladding was programmed by using Microsoft Visual C++6.0software. The grain morphologies of different locations in laser molten pool weresimulated using pure nickel metal. The results show that the grain morphologies ofdifferent locations in the molten pool were also different.4. The laser cladding experiments were carried out using pure nickel as testmaterial. The reasonable and feasible of the phase model were verified by comparing grain morphology obtained from the simulation results with the experimental results.