摘要
采用OM和SEM对选区激光熔化René88DT高温合金显微组织进行了表征,分析了制备参数对晶粒组织及冶金缺陷的影响。结果表明,制备参数可以影响合金凝固过程中胞状枝晶的择优生长方向,进而影响晶粒的形貌和尺寸。在低热输入以及67°层间扫描转角条件下,不同取向的枝晶相互竞争生长,使试样的组织呈现近等轴晶;采用高热输入以及0°层间扫描转角制备的试样,因其枝晶能够跨越多个沉积层连续外延生长而形成了柱状晶组织。采用90°层间扫描转角制备的试样晶粒组织为柱状晶,但其长径比低于0°层间扫描转角制备的试样,且由于金属蒸气烟尘的遮蔽作用导致试样在相互垂直的扫描方向上产生了各向异性。试样内部的冶金缺陷主要为低熔点共晶液化所导致的沿晶界分布的凝固裂纹,等轴晶组织阻碍凝固裂纹的扩展能力远高于柱状晶组织,后者裂纹密度是前者的22倍。考虑成形质量及服役条件,67°层间扫描转角以及较低的热输入是适合René88DT合金的选区激光熔化制备参数。
Columnar grain and hot crack restrict the performance of laser melting deposited René88 DT superalloy when applied to turbine disks,requiring equiaxed grain to improve the fatigue property.Selective laser melting can fabricate material with low composition segregation,reduced defects,and equiaxed or near-equiaxed grains due to the fast cooling rate and vastly varied local heat flow direction during processing.In this study,a selective laser melted René88 DT was fabricated under variable processing parameters.The formation mechanism and control methods of grain structure and metallurgical defects were investigated.Results showed that changing the processing parameters can affectthe preferred growth direction of crystal;thus,affecting the grain morphology and size.Processed with low heat input and 67°scan vectors rotation between deposited layers,cellular dendrites with different orientations grow competitively with each other,leading to the formation of near-equiaxed grains.The cellular dendrites can grow epitaxially across multiple deposited layers due to high heat input and 0°scan vector rotation,forming columnar grains.The columnar grains with a relatively low aspect ratio can be fabricated with 90°scan vectors rotation.However,anisotropy exists between the two orthogonal scanning directions due to the shielding effect of metal vapor dust.The primary defects in specimens are solidification cracks along grain boundaries caused by remelting of low-melting-point eutectic.Specimens with equiaxed grains showed much better ability in preventing solidification cracks from propagation than that with columnar grains.The defect density in the columnar grains is about 21 times higher than the equiaxed grains.Suitable processing conditions for selective laser melted René88 DT superalloys are low heat input and 67°scan vectors rotation based on the forming quality and service conditions.
作者
刘健
彭钦
谢建新
LIU Jian;PENG Qin;XIE Jianxin(Institute for Advanced Materials and Technology,University of Science and Technology Beijing,Beijing 100083,China;Key Laboratory for Advanced Materials Processing,Ministry of Education,University of Science and Technology Beijing,Beijing 100083,China)
出处
《金属学报》
SCIE
EI
CAS
CSCD
北大核心
2021年第2期191-204,共14页
Acta Metallurgica Sinica
基金
中央高校基本科研业务费项目No.FRF-TP-18-092A1。
