热轧对CoCrNi中熵合金微观组织和性能的影响
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摘要
为了研究热轧(高于再结晶温度)过程中CoCrNi中熵合金组织与性能的演变,在不同温度下(900℃和1 100℃)轧制,制备不同厚度的板材。采用X射线衍射仪、金相显微镜、维氏硬度仪和万能试验机分别对板材进行物相组成分析、组织形貌分析以及力学性能分析。研究结果表明:热轧过程中无第二相析出;热轧会使晶粒被压扁、拉长、转动和破碎,形成亚晶粒与板织构,通过动态再结晶过程完成了由树枝晶向等轴晶组织的全部转变,且相同下压量下1 100℃热轧后晶粒尺寸大于900℃热轧后晶粒,说明高温会促进晶粒长大;冷轧CoCrNi合金的显微硬度可达520 HV,900℃或1 100℃热轧其显微硬度不到300 HV,且断后延伸率明显增加,说明热轧可以改善合金内部缺陷,且无明显的加工硬化现象,从而优化其力学性能。
In order to study the evolution of the structure and properties of CoCrNi medium-entropy alloy during hot rolling(above the recrystallization temperature),plates of different thickness were prepared by rolling at different temperatures(900 ℃ and 1 100 ℃).Their phase composition,morphology and mechanical properties were analyzed by using an X-ray diffractometer,metallographic microscope,vickers hardness tester and universal testing machine.The results show that there was no second phase precipitation during hot rolling and that hot rolling caused the grains to be flattened,elongated,rotated and broken, forming sub-grains and plate texture,and completing the transformation from the dendrite to the equiaxed structure through dynamic recrystallization process.The grain size after hot rolling at 1 100 ℃ was larger than that after hot rolling at 900 ℃ at the same rolling reduction,suggesting that high temperature can promote grain growth.The microhardness of cold-rolled CoCrNi alloy was as high as 520 HV,and the microhardness of hot-rolled CoCrNi alloy was less than 300 HV at 900 ℃ or 1 100 ℃,and the elongation increased obviously after fracture,showing that hot rolling can improve the internal defects of the alloy without obvious work hardening phenomenon,thus optimizing its mechanical properties.
In order to study the evolution of the structure and properties of CoCrNi medium-entropy alloy during hot rolling(above the recrystallization temperature),plates of different thickness were prepared by rolling at different temperatures(900 ℃ and 1 100 ℃).Their phase composition,morphology and mechanical properties were analyzed by using an X-ray diffractometer,metallographic microscope,vickers hardness tester and universal testing machine.The results show that there was no second phase precipitation during hot rolling and that hot rolling caused the grains to be flattened,elongated,rotated and broken, forming sub-grains and plate texture,and completing the transformation from the dendrite to the equiaxed structure through dynamic recrystallization process.The grain size after hot rolling at 1 100 ℃ was larger than that after hot rolling at 900 ℃ at the same rolling reduction,suggesting that high temperature can promote grain growth.The microhardness of cold-rolled CoCrNi alloy was as high as 520 HV,and the microhardness of hot-rolled CoCrNi alloy was less than 300 HV at 900 ℃ or 1 100 ℃,and the elongation increased obviously after fracture,showing that hot rolling can improve the internal defects of the alloy without obvious work hardening phenomenon,thus optimizing its mechanical properties.
引文
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[7] WU Z,BEI H,OTTO F,et al.Recovery,Recrystallization,Grain Growth and Phase Stability of a Family of FCC-structured Multi-component Equiatomic Solid Solution Alloys[J].Intermetallics,2014,46:131.
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[9] ZHAO Y,YANG T,TONG Y,et al.Heterogeneous Precipitation Behavior and Stacking-Fault-Mediated Deformation in a CoCrNi-Based Medium-Entropy Annoy[J].Acta Materialia,2017,138:72.
[10] STEPANOV N D,SHAYSULTANOV D G,YURCHENKO N Y,et al.High Temperature Deformation Behavior and Dynamic Recrystallization in CoCrFeNiMn High Entropy Alloy[J].Materials Science & Engineering A,2015,636:188.
[11] SHAHMIR H,HE Y Y,LU Z P,et al.Effect of Annealing on Mechanical Properties of a Nanocrystalline CoCrFeNiMn High-entropy Alloy Processed by High-pressure Torsion[J].Materials Science & Engineering A,2016,676:294.
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