Additively manufactured(AM)metallic materials commonly possess substantial tensile surface residual stress,which is detrimental to the load-bearing service behavior.Recently,we demonstrated that deep cryogenic treatment(DCT)is an effective method for improving the tensile properties of CoCrFeMnNi high-entropy alloy(HEA)samples fabricated by laser melting deposition(LMD),by introducing high com-pressive residual stress and deformation microstructures without destroying the AM shape.However,car-rying out the DCT in a single-step mode does not improve the residual stress gradients inherent from the LMD process,which are undesirable as the mechanical properties will not be homogeneous within the sample.In this work,we show that carrying out the DCT in a cyclic mode with repeated cryogenic cooling and reheating can significantly homogenize the residual stress in LMD-fabricated CoCrFeMnNi HEA,and improve tensile strength and ductility,compared with single-step DCT of the same cryogenic soaking du-ration.Under cyclic DCT,the thermal stress is re-elevated to a high value at each cryogenic cooling step,leading to the formation of denser and more intersecting reinforcing crystalline defects and hcp phase transformation,compared to single-step DCT of the same total cryogenic soaking duration in which the thermal stress relaxes towards a low value over time.The enhancement of defect formation in the cyclic mode of DCT also leads to more uniform residual stress distribution in the sample after the DCT.The results here provide important insights on optimizing DCT processes for post-fabrication improvement of mechanical properties of AM metallic net shapes.

Hongge Li;Wenjie Zhao;Tian Chen;Yongjiang Huang;Jianfei Sun;Ping Zhu;Yunzhuo Lu;Alfonso H.W.Ngan;Daqing Wei;Qing Du;Yongchun Zou

School of Materials Science and Engineering,Harbin Institute of Technology,Harbin 150001,China;School of Materials Science and Engineering,Dalian Jiaotong University,Dalian 116028,China;Department of Mechanical Engineering,The University of Hong Kong,Hong Kong,China;Center of Analysis Measurement and Computing,Harbin Institute of Technology,Harbin 150001,China

材料科学技术（英文版）

[1]Hongge Li;Wenjie Zhao;Tian Chen;Yongjiang Huang;Jianfei Sun;Ping Zhu;Yunzhuo Lu;Alfonso H.W.Ngan;Daqing Wei;Qing Du;Yongchun Zou-.Beneficial effects of deep cryogenic treatment on mechanical properties of additively manufactured high entropy alloy:cyclic vs single cryogenic cooling)[J].材料科学技术（英文版）,2022(20):40-51

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