CoNi基合金力学行为与变形机制的原位探究

In situ investigation of mechanical behavior and deformation mechanism of CoNi-based alloys

采用真空电弧熔炼、高温锻造及室温拔丝技术制备了Co_(62)Ni_(38)与Cr_(8)Co_(62)Ni_(30)(原子百分比)两种合金丝材。利用拉伸实验表征了两种合金的力学行为,利用穿透式广角X射线衍射技术原位追踪了合金变形过程中晶格参数与相结构演变。随后根据原位X射线衍射数据计算了两种合金的层错能与相变自由能,并与力学行为及变形机制建立联系。结果表明,Cr元素添加使合金屈服强度、抗拉强度、均匀伸长率及加工硬化率同时提升。原位X射线衍射结果表明Co_(62)Ni_(38)合金变形过程中未发生相变,Cr_(8)Co_(62)Ni_(3)0合金变形过程中发生应力诱发马氏体相变,且Cr_(8)Co_(62)Ni_(3)0合金层错能相比Co_(62)Ni_(38)合金下降约18%,相变自由能下降约42%。综上,Cr元素添加产生了固溶强化效应,有效降低了合金的层错能与相变自由能,促进应力诱发相变,使加工硬化率显著提高,从而明显改善合金的力学性能。

Two alloy wires,Co_(62)Ni_(38)and Cr_(8)Co_(62)Ni_(3)0(atomic percentage),were prepared using vacuum arc melting,high-temperature forging and room temperature wire drawing techniques.Mechanical behavior of the two alloys was characterized by tensile tests,and the evolution of lattice parameters and phase structure of the alloys during deformation was explored by in situ using penetrating wide-angle Xray diffraction technology.Subsequently,the stacking fault energy and the free energy difference between the FCC and HCP phases of the two alloys were calculated based on in-situ X-ray diffraction data,and a relationship was established with their mechanical behavior and deformation mechanism.The results show that the addition of Cr element increases the yield strength,tensile strength,uniform elongation and work hardening rate of the alloy simultaneously.The in-situ X-ray diffraction results show that no phase transformation occurs during the deformation process of the Co_(62)Ni_(38)alloy,but stress-induced martensitic transformation occurs during the deformation process of the Cr_(8)Co_(62)Ni_(3)0 alloy.The stacking fault energy of the Cr_(8)Co_(62)Ni_(3)0 alloy decreases by about 18%compared to the Co_(62)Ni_(38)alloy,and the free energy difference between the FCC and HCP phases decreases by about 42%.In summary,the addition of Cr element has produced a solid solution strengthening effect,effectively reducing the stacking fault energy and phase transformation free energy of the alloy,promoting stress-induced phase transformation,significantly improving the work hardening rate,and thus significantly improving the mechanical properties of the alloy.