选区激光熔化成形Inconel 718合金孔隙缺陷的研究

Pore Defects of Inconel 718 Alloy Fabricated by Selective Laser Melting

目的研究选区激光熔化成形Inconel 718合金的孔隙缺陷,对缺陷进行科学分类并探究其形成机制,建立熔池溅射特征与缺陷形貌的对应关系,优化工艺参数,抑制缺陷产生。方法采用扫描电子显微镜(SEM)、能量色散X射线光谱仪(EDX)分别对Inconel 718粉末的显微组织和化学成分进行观测,使用数字视频显微镜分析成形件内部缺陷,利用高速摄像机拍摄金属液滴的动态飞溅过程,并定量分析溅射特征参数。结果随着激光功率的增大,能量密度升高,总的溅射数量增大,孔隙数量增多;当扫描速度增大时,能量密度降低,总的溅射面积减小,孔隙尺寸变小。当缺陷的圆度Circ≥0.731或纵横比AR≤1.368时,缺陷形貌由不规则向规则演变。当能量密度E=95.24 J/mm^3时,相对致密度达到99.94%。经测量,所有样品的孔隙率和孔隙尺寸的平均值分别为2.249%和2.774μm^2。结论孔隙缺陷可分为不规则的匙孔缺陷和规则的气孔缺陷两类,存在发生演变的圆度/纵横比门槛值。熔池震荡引起溅射特征变化,对应产生不同形貌特征的缺陷。减小激光功率和增大扫描速度可降低能量密度,使熔池震荡程度减弱,从而抑制缺陷产生,提高成形件的相对致密度。

The work aims to study the pore defects of Inconel 718 alloy fabricated by selective laser melting and scientifically classify the defects and explore the formation mechanism and then establish the corresponding relationship between the sputtering characteristics of the molten pool and the defect morphology to optimize the process parameters to inhibit the formation of defects.The microstructure and chemical composition of Inconel 718 powder were observed with scanning electron microscope(SEM)and energy dispersive X-ray spectroscopy(EDX),respectively.A digital video microscope was used to analyze the internal defects of the forming parts.The dynamic spatter process of metal droplets was filmed by high speed camera and the sputtering characteristic parameters were quantitatively analyzed.As the laser power increased,the energy density,the total number of sputtering drops and the number of pores al so increased.However,when the scanning speed increased,the energy density,the total sputtering area and the pore size decreased.Moreover,when the circularity of the defect was Circ≥0.731 or the aspect ratio of the defect was AR≤1.368,the defect morphology changed from irregular to regular.At the energy density E=95.24 J/mm^3,the relative density reached 99.94%.The average values of porosity and pore size of all samples were 2.249%and 2.774μm^2,respectively.Pore defects can be divided into two types:irregular keyhole defects and regular stomatal defects.There are evolving circularity/aspect ratio thresholds.The sputtering characteristics change due to the shock of the molten pool,which corresponds to the defects with different morphologies.Decreasing the laser power and increasing the scanning speed can reduce the energy density and weaken the shock degree of the molten pool,thus inhibiting the formation of defects and increasing the relative density of the formed parts.