Numerical Simulation of Thermal Behavior of Inconel 718 Coating Prepared by Pulsed Laser Cladding and Its Effect on Microstructure
As a new green and environment-friendly material preparation technology, laser cladding technology expands the use of Inconel 718 alloy materials, but the non-equilibrium solidification process of cladding pool is often accompanied by the segregation of elements such as Nb and Mo, finally forming Laves phase. At the same time, the high-heat laser input is easy to coarsen the dendritic structure and reduce the mechanical properties of the coating. For this reason, the work aims to investigate the evolution mechanism of solidification heat transfer behavior of Inconel 718 alloy coating under pulsed laser to explore the effects of pulsed laser on element segregation, microstructure and mechanical properties of the coating, so as to provide a theoretical basis for optimizing the quality of Inconel 718 cladding coating.The effects of physical parameters with temperature, pulsed laser heat source, powder transmission form and phase transformation latent heat during solidification on the solidification thermal behavior of the coating were comprehensively considered, and the heat transfer model of pulsed laser cladding was established. Laser cladding experiments were carried out by a fiber laser (wavelength 1070 nm and spot diameter 3 mm) and a six-degree-of-freedom series manipulator. After the test, the WEDM equipment was used to prepare the specimen along the longitudinal and transverse direction of the cladding layer. After polishing, the specimen was etched by Kalling's 2 etching agent (5 g CuCl2+100 mL HCl+100 mL C2H5OH) for 10 seconds. The microstructure and morphology of the coating were analyzed by VHX-2000 electron microscope, and the reliability of the numerical model was verified. The phase analysis of the pulsed laser coating was carried out by a diffractometer (D8/advance) at a scanning speed of 2 (°)/min and a diffraction angle of 10°-80°. The hardness of the coating prepared by two laser modes was tested by microhardness tester (DUH-211) (test load 1000 mN, material Poisson's ratio 0.3 and maintenance time 10 s), and the effect of pulsed laser on the microstructure and mechanical properties of Inconel 718 coating was investigated.The numerical simulation results showed that the cooling rate, temperature gradient and solidification rate of pulsed laser coating were higher than that of CW laser coating, the dendrite growth of pulsed laser coating was fine and the elements of No and Mo were dispersed. The microstructure existed in the form of plane crystal, cellular dendrite, columnar dendrite and equiaxed dendrite from bottom to top. The volume fraction of Laves phase in the coating was reduced to 2.93％. Under the action of fine grain strengthening and solid solution strengthening, the average microhardness of the coating increased to 307HV0.1.The numerical simulation results of thermal behavior of pulsed laser coating are consistent with the law of rapid solidification of Inconel 718 coating. The numerical model is reliable. The high cooling rate and high temperature gradient formed by pulsed laser can inhibit the segregation of Nb and Mo elements in Inconel 718 alloy coating, disperse and refine γ dendrite structure, and reduce the volume fraction of Laves phase. The microstructure improves the mechanical properties of the coating under the action of fine grain strengthening and solid solution strengthening.
laser claddingInconel 718pulsed lasernumerical simulationmicrostructure and properties
万方数据
维普
