Displacive transformation as pathway to prevent micro-cracks induced by thermal stress in additively manufactured strong and ductile high-entropy alloys  

增材制造高强韧高熵合金中基于切变型相变的微裂纹抑制机理

作　　者：Rui-di LI Peng-da NIU Tie-chui YUAN Zhi-ming LI 李瑞迪;牛朋达;袁铁锤;李志明(中南大学粉末冶金国家重点实验室,长沙410083;中南大学材料科学与工程学院,长沙410083)

机构地区：[1]State Key Laboratory of Powder Metallurgy,Central South University,Changsha 410083,China [2]School of Materials Science and Engineering,Central South University,Changsha 410083,China

出　　处：《Transactions of Nonferrous Metals Society of China》2021年第4期1059-1073,共15页中国有色金属学报（英文版）

基　　金：financial support of the National Natural Science Foundation of China (51505166,51971248);the Huxiang Young Talents Project (2018RS3007,2019RS1001);the Innovation-Driven Project of Central South University,China (2020CX023);Science and Technology Project of Hunan Province (2020GK2031)。

摘　　要：The micro-cracking behaviors of two high-entropy alloys(HEAs) of the FeMnCoCrNi family prepared by selective laser melting were systematically studied. Residual stresses were also analyzed by X-ray diffraction technique. Results show that the equiatomic FeMnCoCrNi HEAs with a relatively stable single-phase face-centered cubic(FCC) structure suffered from micro-cracking with residual tensile stress after laser melting. In contrast, the metastable non-equiatomic Fe MnCoCr HEAs with reduced stacking fault energy are free of micro-cracks with residual compressive stress at various volumetric energy densities(VEDs). The displacive transformation from the FCC matrix to the hexagonal close-packed(HCP) phase during cooling prevents the micro-cracking via consuming thermal stress related internal energy. Further, the displacive transformation during tensile deformation contributes to the higher strength and ductility of the metastable dual-phase HEA compared to that of the stable single-phase HEA. These findings provide useful guidance for the design of strong, ductile, and crack-free alloys for additive manufacturing by tuning phase stability.研究选区激光熔化增材制造FeMnCoCrNi体系高熵合金的微裂纹行为,并采用XRD技术对激光打印后样品表面的残余应力进行分析。结果表明,经激光打印后等原子比FeMnCoCrNi高熵合金显示为稳定的单相面心立方(FCC)结构,出现残余拉应力,并产生微裂纹。相比之下,具有低层错能的非等原子比亚稳FeMnCoCr高熵合金在各种激光能量密度下均出现残余压应力,且无微裂纹形成。在激光熔化后的冷却过程中,亚稳高熵合金中发生的从FCC基体相到密排六方(HCP)相的切变型相变消耗了激光打印过程中的热应力,从而抑制微裂纹的产生。此外,相比于单相稳定高熵合金,亚稳高熵合金在拉伸变形过程中马氏体相变也有助于提高其抗拉强度和延展性。这些结果为增材制造领域设计开发高强、高韧、无裂纹的合金提供有益参考。

关 键 词：selective laser melting high-entropy alloys phase transformation MICRO-CRACKING residual stress 

分 类 号：TG139[一般工业技术—材料科学与工程]