Cu-based Composites Fabricated By Selective Laser Melting: Simulation And Experiments

A melting and solidification mathematical model under stationary or moving laser beams atvarious laser powers P and scan speeds V was established to simulate the selective laser melting ofcopper-tungsten powder system. The transient temperature and velocity field as well as the forcesacting on tungsten particles were obtained, and the metallurgy behavior in the laser-powderinteraction zone was analyzed. The results indicated that when the laser power P ranged from600Wto900W, the value of field synergy angle θ decreased from50°to0°, implying the enhancement ofheat transfer from laser center to edge of molten pool. Under the condition of a stationary laser beam,P≥800W, or for a moving laser beam, η=16kJ/m, there existed the second flow on around thetungsten particles, leading to the formation of pressure acting on the tungsten particle induced by thepressure difference. As the included angle of attractive force and pressure was acute angle, tungstenparticles tended to form small-scaled rim structure and the rearrangement rate was limited,accordingly tending to form segregation structure. Otherwise, tungsten particles tended to formlarge-scaled rim structure and the rearrangement was efficient, contributing to the formation ofhomogeneously distributed structure.Simulation of temperature distribution and densification process of selective laser meltingWC/Cu composite powder system has been performed, using a finite volume method (FVM). Thetransition from powder to solid, the surface tension induced by temperature gradient, and themovement of laser beam power with a Gaussian energy distribution are taken into account in thephysical model. The effect of the applied linear energy density (LED) on the temperature distribution,melt pool dimensions, behaviors of gaseous bubbles and resultant densification activity has beeninvestigated. It shows that the temperature distribution is asymmetric with respect to the laser beamscanning area. The center of the melt pool does not locate at the center of the laser beam but slightlyshifts towards the side of the decreasing X-axis. The dimensions of the melt pool are in sizes ofhundreds of micrometers and increase with the applied LED. For an optimized LED of17.5kJ/m, anenhanced efficiency of gas removal from the melt pool is realized, and the maximum relative densityof laser processed powder reaches96%. As the applied LED surpasses20kJ/m, Marangoni flow tendsto retain the entrapped gas bubbles. The flow pattern has a tendency to deposit the gas bubbles at themelt pool bottom or to agglomerate gas bubbles by the rotating flow in the melt pool, resulting in ahigher porosity in laser processed powder. The relative density and corresponding pore size andmorphology are experimentally acquired, which are in a good agreement with the results predicted by simulation.It shows that the metal flow on the surface of melt pool is radially outward, while as the appliedLED surpasses20kJ/m, the typical direction of the melt flow accordingly disappears and becomesconsiderably disordered. The maximum velocity magnitude is found in the surface vicinity rather thanin the center of the melt pool. The turbulent intensity and the revolutions increase with the appliedLED. For an optimized LED of17.5kJ/m, the turbulent intensity and the revolutions are260and208,respectively, leading to the efficient rearrangement of WC particles and resultantly obtaining ahomogeneous distribution of WC particles. At the meantime, the WC particles are subject to theForces and the opposite direction force gravity force, giving rise to impeding the formation of severeaggragation of WC particles.