针对激光选区熔化(selective laser melting, SLM)制造K4202合金复杂金属零件在航空航天等领域的应用需求, 以K4202合金粉末为材料, 研究了该合金的SLM成形工艺、成形态和热处理后的显微组织和力学性能. 结果表明, K4202合金SLM成形试样显微组织由树枝晶和等轴晶构成, 树枝晶生长方向多与熔池边界近似垂直. 固溶+时效处理后, 由于再结晶的发生, SLM成形所形成的树枝晶结构完全消失, 同时晶界和晶内有金属碳化物析出. 时效处理后的组织与SLM成形态相比, 变化并不明显, 其树枝晶结构保存较完整, 晶界处同样有碳化物析出. SLM成形试样的拉伸性能优于传统铸造方法, 通过固溶+时效处理和时效处理, 试样的屈服强度、抗拉强度均提升显著, 但塑性下降明显, 其中时效处理后的拉伸强度最高.

As a cast nickel base superalloy, K4202 is mainly used in aircraft engines due to its high strengths at elevated temperatures, excellent resistance to hot corrosion and favorable weldability. K4202 alloy is usually fabricated by the conventional casting method and mechanical processing, along with macro-segregation and excessive tool wear. As one of the most promising additive manufacturing technologies, selective laser melting (SLM) is able to manufacture high-performance and complex components. According to the requirement of selective laser melting manufactured metal parts with complex structures in aerospace and other fields, K4202 alloy was used as material for SLM in this research and the forming technology, microstructure and mechanical properties of SLMed and heat-treated samples were studied. The results show that the microstructure of samples formed by SLM is composed of dendrites and isometric crystal. The growing direction of dendrites is nearly perpendicular to melt pool traces in most cases. The dendrite structures disappear completely after solution+ageing heat treatment on account of recrystallization and metal carbide precipitates in grains and at grain boundaries. The precipitates are able to improve the strength of the grain boundary due to the pinning effect. The microstructure has no significant changes after ageing heat treatment, but carbide precipitates at grain boundaries as well. The microhardness of SLM samples is uniform on cross section and vertical section. After solution+ageing and ageing heat treatment, there is a significant improvement on the microhardness. The mechanical properties for as-fabricated samples are superior to those of the cast K4202. Besides, the yield strength and tensile strength increase clearly after heat treatments and the mechanical properties is the highest after ageing heat treatment. This is because of the precipitation of γ' strengthening phases. However, the obvious decrease in the ductility occurs at the same time.