Cu-Mn和Cu-Ni系列合金的疲劳变形行为及其微观机制：层错能和短程有序的综合影响

Two kinds of face centered cubic (FCC) Cu-Mn and Cu-Ni alloys with high stacking fault energy (SFE) are selected as the target materials in the present research project. For the Cu-Mn alloy, the SFE almost keeps unchanged but the degree of short range order (SRO) increases with increasing content of Mn, while for the Cu-Ni alloy, both of SFE and SRO degree increase with increasing content of Ni. A series of coarse-grained and ultrafine-grained Cu-Mn and Cu-Ni alloys with different contents of Mn and Ni (5 – 20 at%), respectively, will be prepared. The plastic deformation behavior and micro-mechanisms of these alloys will be examined under uniaxial tension at different strain rates, focusing on the relationship between strength and plasticity. High-cycle and low-cycle fatigue deformation and damage behaviors as well as the relevant micro-mechanisms of these alloys will be systematically investigated under stress-amplitude-controlled tension-compression loads and plastic-strain-amplitude-controlled tension-tension loads, respectively. Combined with the quantitative characterizations of SRO degree of these alloys with the aid of electric resistivity measurements and diffuse neutron scattering experiments, new reasonable composite parameters will be put forward in an attempt to reflect synthetically the influencing actions of two factors, i.e., SFE and SRO, and the micro-mechanisms for the competitive effects of SFE and SRO on the unaxial and fatigue deformation and damage behaviors of Cu-Mn and Cu-Ni alloys will thus be clearly revealed as a general rule. In a word, the present research project makes important theoretical and practical senses to the deep-going understanding of the fatigue deformation and damage mechanism of FCC alloys, and it is expected to provide some valuable references for strengthening and toughening of FCC alloy as well as for the improvements in their fatigue properties.

本项目拟选取的研究对象为高层错能Cu-Mn和Cu-Ni两种面心立方（FCC）合金，其中：Cu-Mn合金的层错能随Mn含量增加基本不变，而短程有序度增高；Cu-Ni合金的层错能和短程有序度均随Ni含量增加而升高。制备出不同Mn和Ni含量（5–20 at%）的粗晶和超细晶Cu-Mn和Cu-Ni系列合金样品，研究它们在不同应变速率下单向拉伸变形的强塑性行为及微观机制；研究它们在恒应力幅控制和恒塑性应变幅控制下的拉-拉高周疲劳和拉-压低周疲劳变形与损伤行为及其微观机制。再结合电阻率测试法和中子或X射线漫散射技术定量表征合金短程有序度，试图提出能综合反映出“层错能”和“短程有序”两种内在影响因素的合理复合参量，全面系统地揭示两者对Cu-Mn和Cu-Ni合金单向与疲劳变形与损伤行为竞争性影响的一般性规律及微观机理，为深入理解FCC合金材料的疲劳变形与损伤机理、及其强韧化与疲劳性能改善提供有益的参考。

本项目系统研究了“短程有序（SRO）与层错能（SFE）竞争”对Cu-Mn和Cu-Ni合金单向、疲劳力学性能的影响规律及其微观机理，澄清了面心立方（FCC）合金中“SRO”对塑性变形微观机制的关键性影响。得到以下主要创新性研究结果：(1) 对于较高SFE的Cu-Mn合金，在单向或循环载荷下，SRO随Mn含量的单方面增加可有效抑制位错交滑移的开动，导致位错滑移机制由波状滑移转变为平面滑移。具有高度滑移可逆性的平面滑移的形成，显著改善了合金的加工硬化能力和抵抗疲劳损伤能力，因此Cu-Mn合金表现出良好的强塑性匹配和改善的疲劳性能（包括拉-拉和拉-压疲劳）。单向拉伸变形过程中，在高SFE的Cu-Mn合金中可观察到明显的形变孪晶，这有异于“形变孪晶是低SFE材料微观变形机制的典型特征”这一普遍认识；(2) 对于高SFE的Cu-Ni合金，在变形初期，SRO的增加可有效促进位错平面滑移，引起加工硬化能力的提高；随着变形程度增加，SRO被运动的位错逐步消耗，波状位错滑移主导了塑性变形机制。基于这种竞争性机制，随Ni含量增加，Cu-Ni合金的强度和拉-拉疲劳性能得到改善，但拉-压疲劳性能甚至出现下降趋势；(3) SRO的引入有利于Cu-Mn合金在剧烈塑性变形（SPD）下形变孪晶的形成，促进晶粒的进一步细化。SPD制备出的超细晶Cu-15at%Mn合金表现出较好的强塑性匹配；(4) SRO的增加有效抑制了位错的湮灭速率，从而减弱了Cu-Mn合金拉伸力学性能“越小越弱”的尺寸效应；(5) Cu-Mn和Cu-Ni合金中SRO的增加降低了发生动态应变时效的温度区间，增强了动态应变时效行为，从而削弱了温度升高对其拉伸强塑性带来的不利影响。. 上述结果深入揭示了SRO和SFE对Cu-Mn和Cu-Ni合金单向、疲劳变形与损伤行为竞争性影响的一般性规律及微观机理，为FCC合金的强韧化与疲劳性能改善提供了重要的理论和实验基础。基于项目研究，共发表SCI学术论文30余篇，在重要学术会议上做邀请报告16次，培养博士生2名和硕士生9名。较好地执行并完成了项目的研究计划。