激光功率与扫描速度对选区激光熔化钴铬合金组织性能的影响

目的 明确选区激光熔化钴铬合金中激光线能量密度、激光功率和激光扫描速度对成形件组织、性能的影响，探究优化工艺参数的方法。方法 基于ANSYS有限元软件模拟选区激光熔化过程中熔池尺寸的基础上，通过金相显微镜分析了熔池尺寸和显微组织，电子背散射衍射分析了晶粒尺寸，使用力学试验机和洛氏硬度计研究了试样的力学性能。结果 随着线能量密度降低，成形件的熔池尺寸、晶粒大小、冷却速度和力学性能降低。但在激光线线能量密度为0.242 J/mm的条件下，扫描速度为1 200 mm/s时成形试样的致密度为98.7%，抗拉强度为867 MPa，延伸率为6.5%，其力学性能均高于扫描速度为950 mm/s时成形的试样，与线能量密度更高的0.263 J/mm成形条件下250 W+950 mm/s的成形试样力学性能相近。结论 激光线能量密度是影响选区激光熔化钴铬合金熔池尺寸和组织性能的关键因素，但熔池尺寸与激光线能量密度没有线性关系。相同的线能量密度下，增加激光扫描速度，有利于获得大的熔池尺寸和冷却速度，提高成形件的致密度和降低晶粒尺寸，最终使成形件力学性能提高。

Effect of Laser Power and Scanning Speed on Microstructure and Properties of Co-Cr Alloy by Selective Laser Melting

It is an advanced manufacturing technology by direct metal laser melting. The important characteristic of the SLM technology is that it can produce parts with high geometrical dimensional accuracy, the forming parts have brilliant mechanical properties, and the relative density of the parts is close to 100%. However, the energy density cannot accurately reflect the relationship between scanning speed and molten pool size in process parameter optimization of SLM. This article studies the effect on SLM cobalt-chromium alloy of linear energy density and process parameter. Firstly, a suitable range of process parameters of linear energy density is selected, then the scanning speed is increased by fix the linear energy density for the process parameter optimization, and finally, the melt pool size is calculated by commercial finite element software ANSYS simulation under each process parameter to analyze the effect on process parameters of the molten pool size. The molten pool size obtained from the numerical simulation is analyzed to obtain the appropriate scan spacing, and the process parameters are imported into EOS M290 for specimens forming. The SLMed specimens are sandpapered and polished, and the porosity defects of the parts are observed by metalloscope, and the relative density of the parts are calculated by Imagepro software. After etch, the SLMed parts are analyzed by micrographs to determine the molten pool overlap and size under different process parameters. The variation of sub-cellular and grain size with process parameters is analyzed using FE-SEM and EBSD. The tensile strength and elongation of the SLMed specimens are tested by universal testing machine. The hardness of the SLMed specimens is tested using Rockwell hardness tester and five-point tests are collected to reduce the error. Finally, the cooling rate under different process parameters is analyzed by commercial ANSYS software again. Results showed that the molten pool size and the cooling rate decreased with the linear energy density, which result in inferior to relative density and grain sizes of the SLMed parts, and led to a decrease in the mechanical properties of the SLMed parts. At the same linear energy density of 0.242 J/mm, the densities of 98.7%, tensile strengths of 867 MPa, and elongation of 6.5% were higher for the specimens with scanning speed of 1 200 mm/s than that of scanning speed at 950 mm/s. The molten pool size and grain size of the forming parts with high scanning speed are higher than that of low scanning speed forming parts at the linear energy density of 0.242 J/mm, and the high scanning speed mechanical properties are similar to those of the specimens with 250 W+950 mm/s at a higher linear energy density of 0.263 J/mm. With the investigated the relationship between parameters and molten pool size, the linear energy density seemed to have direct effect on the molten pool size and mechanical properties of SLMed cobalt-chromium alloys, but there is no linear relationship between the molten pool size and the linear energy density. At the same linear energy density, higher scanning speed exhibited the better molten pool size, cooling rate, relative density, grain refinement, and ultimately succeeded in the mechanical properties.