离焦量对3D打印18Ni-300马氏体时效钢组织和力学性能的影响

Influence of Defocusing Distance on Microstructure and Mechanical Properties of 3D-Printed 18Ni-300 Maraging Steel

采用激光选区熔化(SLM)工艺打印18Ni-300马氏体时效钢零件,研究了正离焦量对18Ni-300成型零件打印质量和力学性能的影响规律。结果表明:当离焦量较小(+1.5 mm)时,功率密度过高,导致熔池内部产生湍流,熔道表面出现明显的球化现象,成型试样内部出现较大的孔隙缺陷,力学性能下降,拉伸断口呈准解理断裂特征;随着离焦量增加,功率密度减小,光斑和熔道随之变宽,改善了试样的性能,试样的拉伸断裂机制转变成塑性断裂;当离焦量为+2.5 mm时,功率密度适中,熔道之间形成了良好搭接,内部组织均匀,增强了层间结合,试样的硬度和抗拉强度分别为37.7 HRC和1215 MPa;当离焦量增加至+3 mm以上时,熔道之间的搭接率过大,出现过度堆叠现象,功率密度过低,光斑穿透力减弱,影响了层间结合,试样性能下降。

Herein,18Ni-300maraging steel parts were printed using selective laser melting process to examine the influence of positive defocusing distance on the printing quality and mechanical properties of 18Ni-300forming parts.Results show that the power density is too high for a small defocusing distance(+1.5mm),causing turbulence in the molten pool and obvious spheroidization is observed on the molten channel surface.Moreover,large pore defects appear inside the formed sample,the mechanical properties deteriorate,and the tensile fracture shows quasi-cleavage fracture characteristics.With an increase in the defocusing distance,the power density decreases and the spot and melting channel become wider,which improves the properties of the samples.Thus,the tensile fracture mechanism transforms into plastic fracture.For+2.5mm defocusing distance,the power density is moderate,weld channels are well formed,internal structure is uniform,and interlayer bonding is enhanced.The hardness and tensile strength are 37.7 HRC and 1215 MPa,respectively.When the defocusing distance increases to more than+3mm,the overlap ratio between the melt channels is too large and the over stacking phenomenon occurs.Furthermore,the power density is too low and the spot penetration force is weakened,thereby affecting the interlayer bonding and decreasing the sample performance.