316 L stainless steel samples were built vertically (VB) and horizontally (HB) by selective pulsed laser melting. The microstructure of the as-fabricated samples was investigated using a range of characterisation techniques and the properties evaluated by tensile testing. It was found that at a relatively low laser power (200 W) pores evolved from lack-of-fusion pores to keyhole pores with increased laser exposure time. Correspondingly, the porosity level decreased first and then increased with exposure duration. Increased laser power led to minimisation of porosity. The porosity type and level did not cause significant influence on tensile properties in the current case. With increased energy density, the microstructure changed from a fine dispersive fan-like grain structure gradually into a coarse vertically grown columnar grain structure, leading to increased <100> texture along the building direction. With the latter microstructure, the VB samples show much higher yield strength and ultimate tensile strength but lower elongation than their HB counterparts, leading to development of mechanical anisotropy. The mechanical anisotropy was strongly associated with grain movements through different dominant deformation mechanisms in different building directions, i.e., the VB samples deformed mainly by grain elongation via dislocation slipping whereas the HB samples deformed by grain rotation through massive twinning and slipping. With the refined fan-like grain structure, grain rotation was heavily involved in both HB and VB samples, which was beneficial for reduction in mechanical anisotropy. The extent of mechanical anisotropy decreased with decreased laser power and exposure time, paving the way for reducing mechanical anisotropy in this material.

通过选择性脉冲激光熔化，垂直（VB）和水平（HB）构建316 L不锈钢样品。使用一系列表征技术研究了所制造样品的微观结构，并通过拉伸测试评估了其性能。已经发现，在相对较低的激光功率（200 W）下，随着激光暴露时间的增加，孔从缺乏融合的孔演变为锁孔。相应地，孔隙率水平随着暴露时间的延长而先降低然后升高。激光功率的增加导致孔隙率最小化。在当前情况下，孔隙率类型和含量对拉伸性能没有明显影响。随着能量密度的增加，微观结构从细分散的扇状晶粒结构逐渐变为垂直生长的粗大柱状晶粒结构，导致沿建筑物方向增加<100>纹理。对于后一种微观结构，VB样品显示出比HB对应物高得多的屈服强度和极限抗拉强度，但伸长率却较低，导致机械各向异性的发展。机械各向异性与在不同建筑方向上通过不同的主要变形机制与晶粒运动密切相关，即，VB试样主要是由于位错滑移而主要由晶粒伸长引起变形，而HB试样则通过大量孪晶和滑移而因晶粒旋转而变形。由于具有精细的扇状晶粒结构，HB和VB样品都大量参与了晶粒旋转，这有利于降低机械各向异性。