选区激光熔化<strong>René 88DT</strong>高温合金的晶粒组织及冶金缺陷调控

doi:10.11900/0412.1961.2020.00143

金属学报

2021, Vol. 57

Issue (2): 191-204 DOI: 10.11900/0412.1961.2020.00143

研究论文

本期目录 | 过刊浏览

选区激光熔化René 88DT高温合金的晶粒组织及冶金缺陷调控

刘健¹^,², 彭钦¹^,², 谢建新¹^,²(

)

^1.北京科技大学新材料技术研究院北京 100083
^2.北京科技大学材料先进制备技术教育部重点实验室北京 100083

Grain Structure and Metallurgical Defects Regulation of Selective Laser Melted René 88DT Superalloy

LIU Jian¹^,², PENG Qin¹^,², XIE Jianxin¹^,²(

)

^1.Institute for Advanced Materials and Technology, University of Science and Technology Beijing, Beijing 100083, China
^2.Key Laboratory for Advanced Materials Processing, Ministry of Education, University of Science and Technology Beijing, Beijing 100083, China

引用本文:

刘健, 彭钦, 谢建新. 选区激光熔化René 88DT高温合金的晶粒组织及冶金缺陷调控[J]. 金属学报, 2021, 57(2): 191-204.
Jian LIU, Qin PENG, Jianxin XIE. Grain Structure and Metallurgical Defects Regulation of Selective Laser Melted René 88DT Superalloy[J]. Acta Metall Sin, 2021, 57(2): 191-204.

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摘要:

采用OM和SEM对选区激光熔化René 88DT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René 88DT合金的选区激光熔化制备参数。

关键词 ：选区激光熔化, René 88DT高温合金, 晶粒组织, 冶金缺陷, 制备参数

Abstract：

Columnar grain and hot crack restrict the performance of laser melting deposited René 88DT 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 René 88DT 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 affect the 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 René 88DT superalloys are low heat input and 67° scan vectors rotation based on the forming quality and service conditions.

Key words： selective laser melting René 88DT superalloy grain structure metallurgical defect processing parameter

收稿日期: 2020-05-06

ZTFLH:

TN249

基金资助:中央高校基本科研业务费项目(FRF-TP-18-092A1)

作者简介: 刘健，男，1989年生，博士

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https://www.ams.org.cn/CN/10.11900/0412.1961.2020.00143 或 https://www.ams.org.cn/CN/Y2021/V57/I2/191

图1 René 88DT高温合金粉末形貌

表1 选区激光熔化成形实验参数、形成的缺陷类型及缺陷密度

图2 不同层间扫描转角成形示意图(a) 0° (b) 67° (c) 90°

图3 选区激光熔化René 88DT高温合金试样的缺陷形貌(a) No.1, P=200 W (b) No.2, P=250 W (c) No.5, P=400 W(d) No.6, V=720 mm/s (e) No.3, V=960 mm/s (f) No.9, V=1200 mm/s(g) No.10, A=0° (h) No.11, A=67°

图4 选区激光熔化René 88DT高温合金No.5试样中的裂纹形貌(a) low magnification(b) morphology showing the boundary of deposition track (dash line)(c) high magnification of cracks

表2 选区激光熔化成形René 88DT高温合金试样EDS分析结果 (mass fraction / %)

图5 采用不同层间扫描转角制备的René 88DT高温合金试样XOZ面沉积道形貌(a) 0° (b) 67° (c) 90°

图6 采用不同层间扫描转角制备的René 88DT高温合金试样晶粒组织(a-c) 0° (d-f) 67° (g-i) 90°

图7 采用不同激光功率制备的René 88DT高温合金试样XOZ面沉积道形貌及沉积道深宽比和底部曲率半径随激光功率的变化关系

图8 选区激光熔化René 88DT镍基高温合金试样中的未熔化粉末形貌

图9 采用不同激光功率制备的René 88DT高温合金试样晶粒组织(a-c) 200 W (d-f) 300 W (g-i) 400W

图10 采用不同扫描速率制备的René 88DT高温合金试样XOZ面沉积道形貌及沉积道深宽比和底部曲率半径随扫描速率的变化关系

图11 采用不同扫描速率制备的René 88DT高温合金试样晶粒组织(a-c) 720 mm/s (d-f) 960 mm/s (g-i) 1200 mm/s

图12 选区激光熔化René 88DT镍基高温合金No.3试样显微组织

图13 沉积道的深宽比和底部曲率半径随选区激光熔化体能量密度(E)的变化关系

图14 不同热输入条件下René 88DT高温合金试样的枝晶生长及晶粒形成规律

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