选区激光熔化成形TiC/Inconel 718复合材料热物理机制研究

Thermal-Physical Mechanisms during Selective Laser Melting of TiC/Inconel 718 Composites

摘要:

建立了TiC/Inconel 718复合材料体系选区激光熔化三维有限元模型，在考虑了相变潜热，热传导/对流/辐射多重传热机制和随温度变化的热物性参数条件下，使用ANSYS二次开发语言APDL实现了高斯激光热源的移动，并利用“生死单元”完成了多层多道的能量加载。研究表明：温度变化率与工艺参数 (激光功率和扫描速度) 存在正对应关系，最高可达7.03×106 °C/s。当扫描速度过快 (300 mm/s) 或激光功率过低 (50 W) 时，获得的熔池温度低 (1991 °C)，液相存在时间过短 (0.29 ms)，而且液相量少，粘度大，不利于液相金属在粉末间隙中的铺展和润湿，易于在制件中形成不规则孔洞，增加制件孔隙率；在优化的工艺参数下：P = 100 W, v = 100 mm/s，重熔深度 (15.1 μm)、重熔宽度 (35.0 μm)、液相存在时间 (1.2 ms)、熔池最高温度 (2204 °C) 和温度变化率均较为合适，易于获得冶金结合良好的SLM制件。对TiC/Inconel 718混合粉末进行了选区激光熔化实验，验证了模拟结果的正确性。

Abstract:

A three dimensional finite element model was established to simulate the selective laser melting (SLM) of TiC/Inconel 718 composites. Latent heat of phase change, multiple heat transfer mechanisms and temperature-dependent thermal physical properties were considered. The movement of Gaussian laser source and the application of energy of multi-layers and multi-tracks were realized using APDL secondary development language. The results indicated that there was a positive corresponding relationship between the rate of temperature change and processing parameters (laser powers and scan speeds). The maximum of the rate of temperature change was 7.03×106 °C/s. A high scan speed (300 mm/s) or a low laser power (50 W) yielded an extremely short liquid lifetime (0.29 ms) and low temperarure (1991 °C), resulting in the formation of a small amount of liquid phase with a relatively high viscosity. This phenomenon was detrimental for the wettaility of the liquid phase among the pores of powders, causing the appearance of irregular pores and the attendant high porosity in SLM-produced parts. The combination of a laser power of 100 W and a scan speed of 100 mm/s contributed to achieve a sound metallurgical bonding between the neighboring layers and tracks, due to the appropriate remelted depth (15.1 μm), remelted width (35.0 μm), the rate of temperature change, the liquid lifetime (1.2 ms) and maximum temperature (2204 °C) of molten pool. The selective laser melting experiments on a TiC/Inconel 718 powder mixture were carried out and simulation results were verified to be correct.