Study On Solidification Crystallization Of Laser Melting Coating Based On Phase - Field Method

Laser melting injection is a novel surface enhancement technology, It is suitable forpreparing gradient transition composite coating with wear, corrosion and high temperatureresistance and so on. In the laser melt injection process, melt injection layer’s microstructureand distribution of enhanced particle play a decisive role for melt injection layer’sperformances and lifespan. So studying the melt injection layer’s microstructure can helpcontrol the properties of material and design reasonable parameters, to promote theapplication of laser melt injection technology. This paper use the phase-field method to studydendrite growth during the laser melting Injection molten pool solidification processes,simulate the influence of convection, particles distribution and external factors on themicrostructure, and lay a foundation for predicting the performance of laser melt injectioncoating.Based on the pure substance Wheeler model, it built a magnesium alloy phase fieldmodel by introducing a concentration field parameters. It simulated the influence ofundercooling on the microstructure combined with physical parameters of materials, todetermine the value of parameters. Multi-grain phase-field model was built based on theprinciple of random lattice method, Studied the process of multi-grain dendrites growth andthe influence of temperature gradient and cooling rate on the morphology of dendrites growth,reproduced the interference effect between the inner region of dendrites; Temperaturegradients made each dendrite size gradually increases along the direction of heat flow;Cooling rates led dendrite growth rate to become larger, dendrite arms became coarse andappeared the phenomenon of merger and coarsening between dendrite arms.Based on the multi-grain phase-field model, it built a phase field model by coupling withflow field to study the influence of convection on multi-dendrites growth. The study showedthat, melt flow could impact the dendrite growth by changing the distributions of temperatureand concentration of dendrites. In the convection，the upstream side of dendrites was scouredby melt while the scouring action of downstream side was weak, led to temperature boundarylayer of the upstream side of dendrites become thinner while the downstream side’s becomethicker, made the actual undercooling of the dendrites’ upstream side become bigger and thedendrites growth faster, while the actual undercooling of the dendrites’ upstream side becamesmaller and the dendrites growth became slower, resulted the dendrite arms of the dendrites’upstream side more developed while the dendrites’ upstream side degenerate. With convection velocity increasing, this phenomenon is more obvious.The larger the particles volume fraction, the bigger the sphere of action of particles, thegreater the influence on the dendritic morphology. The smaller the particles size, the wider thedistribution area the greater impact on dendritic morphology under certain volume fraction. Inthe study of the influence of temperature gradient, cooling rate, convection and enhancedparticles on the multi dendrites growth morphology, the influence of enhanced particles ondendritic morphology regularity was the greatest.