激光选区熔化GH3536镍基高温合金的微观组织和晶体取向

Microstructure and Crystal Orientation of Nickel-based Superalloy GH3536 by Selective Laser Melting

采用激光选区熔化方法(selective laser melting,SLM)制备了高致密度GH3536镍基高温合金,分析了激光选区熔化成形GH3536合金显微组织和晶体取向。结果表明:随着激光能量密度的升高,成形试样的致密度先升高后降低,当激光能量密度为180~230 J·m^-1时,致密度达到99.55%以上,组织存在着明显的各向异性,垂直于构建方向的组织呈"棋盘状"形貌,晶粒大多数为等轴晶(长宽比为1.83)且得到了细化(dmean=11.23μm),尤其熔池搭接区域晶粒更加细小(5μm)以下),而平行于构建方向为"鱼鳞状"形貌,大多数为柱状晶(长宽比为2.83),晶粒直径较大(dmean=2596μm)。同时SLM成形GH3536镍基高温合金存在明显的择优取向,横截面上晶粒具有较强的<100>取向,垂直于构建方向和平行于构建方向均为立方织构{100}<001>。此外SLM凝固成形中晶粒生长对晶粒内晶体取向演变有着显著影响,横截面变形晶粒内的晶体取向变化不明显,纵截面变形晶粒内的晶体取向变化比较明显,这是由于SLM成形具有极高的温度梯度和极快的冷却速率(105 K/s),导致晶粒的生长方向垂直于熔池的固液界面且沿着温度梯度的反方向生长,固液界面处温度梯度沿构建方向的分量大于其他方向的分量,晶粒沿构建方向生长较快。

High density GH3536 Ni-based superalloy block specimens were prepared by selective laser melting(SLM),and the micro structure and crystal orientation of GH3536 alloy were analyzed.The results show that with the increase of laser energy density,the density of the formed sample increases at first and then decreases.When the laser energy density is 180~230 J·m^-1,the density reaches above 99.55%.The structure has obvious anisotropy,the microstructure perpendicular to the construction direction presents a checkerboard morphology,and most of the grains are equiaxed(the length-diameter ratio is 1.83)and are refined(dmean=11.23μm).In particular,the grain size in the lap area of molten pool is relatively finer(less than 5μm).Parallel to the construction direction is the fish scale morphology,most of which are columnar crystals(the length-diameter ratio is 2.83),with a larger grain diameter(dmean=25.96μm).Simultaneously,SLM processed GH3536 Ni-based superalloy has obvious preferential orientation.On the cross section,the grain has a strong<100>orientation,which is cubic texture{100}<001>when it is perpendicular to or parallel to the construction direction.In addition,grain growth in SLM solidification has a significant effect on the evolution of crystal orientation in grains,the crystal orientation in the deformed grain of the longitudinal section does not change obviously,while the crystal orientation in the deformed grain of the longitudinal section changes obviously,which is due to the extremely high temperature gradient and rapid cooling rate(105 K/s)of SLM.