Microstructure Study And Numerical Simulation Of Ni Based Alloy Fabricated By Laser 3D Printing

As an advanced digital manufacturing technology, 3D Printing fabricated threedimension solid by jointing material lay by lay. Laser 3D Printing technology is a hot research area of 3D Printing. With lot of advantages such as high material utilization, high manufacturing flexible, low processing cycle, without being limited by the size of part and so on, it is especially suitable to fabricate low production volume and complex parts and it has a broad application foreground in selected industries, particularly the aerospace, medical, automotive, marine, nuclear power and other fields. At the moment, there are many inadequate in the theory about Laser 3D Printing. With a large of thermal stress in 3D Printing sample, it is easy to have cracks. In bad condition, the 3D Printing sample will collapse.80Ni20Cr alloy samples and Inconel 718 alloy samples were produced by Laser Melting Deposition, and microstructure of samples were characterized by SEM, OM, XRD and TEM in order to analyze formation mechanism of internal defect and growth situation of grains. Mechanical properties were tested by Vickers hardness tester and universal testing machine. Combining with the microstructure, reasons of different mechanical properties in samples produced by different process were studied.The moving heat source model in the process of laser melting deposition was established, and the temperature field of Inconel 718 alloy in laser melting deposition process was simulated by ANSYS, including the temperature field distributions and morphologies of single-channels printed at different process. Moreover, temperature field distribution and morphology in single layer which was printed at the process parameters for P = 500 w, v = 5 mm/s, lap at a rate of 20% were also simulated. Combining with the experimental result, the forming reasons of defects in the sample were analyzed.The results showed that combination property of layer-layer orthogonal printing samples, which presented fine microstructure characteristics, was superior to the one of layer–layer synthetic printing samples. The microstructure of alloy components presented small lamellar grains and columnar grains, and columnar grains grow along laser deposition direction. The composition of the alloy components is Ni-Cr solid solution based Ni solvent. The tensile strength of the sample produced by layer-layer orthogonal process was 410 MPa and the micro hardness was 406 HV 0.2. The tensile failure form of the sample included transgranular fracture and intergranular fracture, while sample produced by layer-layer synthetic process expressed mainly intergranular fracture.The width and height of single-channel produced by Laser 3D Printing increased with the increase of laser power, decreased with the increase of laser scanning speed. With the increase of laser power, the porosity of the printing samples were reduced from 2.6% to 1.3%, samples were more dense. Cracks on the samples were mainly concentrated in the bottom of the sample. In the thin-wall sample, it was easy for cracks to grow along the height deposition direction and become macrocrack, while in the cube sample, it was hard to grow across the different layer and almost has no possible becoming macrocrack. The main grains in the side of cube sample were columnar grains which were out of order.By the finite element simulation of laser melting deposition process, it was found that the simulation results were well matched with the experiments results. With the increase of laser power, the molten pool became larger and the single channel became wider and higher, and melting-coagulation time in center single-channel became longer. With the increase of scanning speed, the single channel became more narrow and short, and cooling speed in single-channel center became faster. The simulation results of single-layer deposition process showed that the laser energy had a certain lag, and flare front-end powder was difficult to melt. When laser move to the corner, the laser beam energy was easy to focus and formed a bulge on the corner. At the overlap of two singlechannels, the temperature in the molten pool was low and the powder did not melt completely, which might cause pore and sunken.