超细晶Cu-Al合金的高周疲劳性能研究

发布时间：2018-02-11 05:27

本文关键词： 搅拌摩擦加工超细晶层错能高周疲劳疲劳损伤　出处：《沈阳工业大学》2017年硕士论文　论文类型：学位论文

【摘要】：强度和硬度是材料的基本力学性能,而疲劳性能则是材料能否进入实际工程应用的最终判据。与传统材料相比,超细晶材料表现出了良好的强度和硬度,然而传统的严重塑性变形(SPD)工艺得到的超细晶在提高材料强度的同时大大降低了材料的塑性,而且在疲劳变形过程中极易发生局部变形从而导致疲劳裂纹过早地萌生和扩展,大大降低了其疲劳性能,限制了这种新型材料的使用范围。而新型的搅拌摩擦加工(FSP)技术制备出的超细晶具有独特的微观组织特性使超细晶材料得到了良好的强塑性匹配。层错能是面心立方金属的一个重要参量,决定了位错滑移的方式,从而对疲劳变形有重要影响。因此,本文选取具有不同层错能的Cu-Al合金为研究对象,利用FSP技术在辅助水冷却的条件下成功制备出超细晶,对其常规力学性能和高周疲劳性能进行了深入研究,主要研究结论如下:FSP超细晶Cu-Al合金呈等轴再结晶状态,位错密度比较低,高角晶界比例较高并引入大量的孪晶界。降低层错能,改变了超细晶Cu-Al合金的晶粒细化机制,从而减小了超细晶的晶粒尺寸;而且高角晶界和孪晶界的增加,有助于超细晶在提高强度的同时增大材料的均匀延伸率,使超细晶获得良好的强塑性匹配。与等通道转角挤压(ECAP)超细晶铜相比,FSP超细晶铜具有更高的疲劳强度和疲劳比。ECAP超细晶铜的疲劳损伤表现为大尺度剪切带和晶粒严重粗化,而FSP超细晶铜特有的均匀微观组织结构抑制了大尺度剪切带的形成和晶粒的长大,其疲劳损伤以挤出为主。在超细晶Cu-Al合金中,降低层错能可以提高超细晶材料的疲劳强度,抑制位错的交滑移,从而抑制了疲劳过程中的再结晶和晶粒的长大,少量的剪切带也在晶粒内部产生。特别是在低应力下,疲劳表面不会出现大尺度的挤出现象,疲劳裂纹主要沿晶界萌生。
[Abstract]:The strength and hardness are the basic mechanical properties of the material, while the fatigue property is the final criterion of whether the material can be applied in practical engineering. Compared with the traditional material, the ultrafine grained material shows good strength and hardness. However, the superfine grains obtained by the traditional severe plastic deformation (SPD) process not only increase the strength of the material, but also greatly reduce the plasticity of the material. Moreover, local deformation is easy to occur in the process of fatigue deformation, which leads to the premature initiation and propagation of fatigue cracks. The fatigue performance is greatly reduced. The application range of the new material is limited, and the ultrafine crystal prepared by the new friction stir processing (FSPs) technology has unique microstructure characteristics, which makes the ultrafine crystal material get a good strong plastic match. The stacking fault energy is the surface center. An important parameter of cubic metals, Therefore, the Cu-Al alloy with different stacking fault energy was selected as the research object, and the ultrafine grain was successfully prepared by FSP technology under the condition of auxiliary water cooling. The conventional mechanical properties and high cycle fatigue properties of the superfine Cu-Al alloy were studied. The main conclusions are as follows: the superfine Cu-Al alloy exhibits equiaxed recrystallization state and low dislocation density. The high angle grain boundary ratio is higher and a large number of twin boundaries are introduced. The reduction of stacking fault energy changes the grain refinement mechanism of ultrafine grain Cu-Al alloy, thereby reducing the grain size of ultrafine grain, and the increase of high angle grain boundary and twin grain boundary, It helps to increase the strength of the ultrafine crystal and increase the uniform elongation of the material. Compared with ECAP ultrafine crystal copper, FSP ultrafine crystal copper has higher fatigue strength and fatigue ratio. The fatigue damage of ECAP ultrafine crystal copper shows large scale shear band and serious grain coarsening. The uniform microstructure of FSP ultrafine crystal copper inhibits the formation of large scale shear band and grain growth, and its fatigue damage is dominated by extrusion. In ultrafine grained Cu-Al alloy, reducing stacking fault energy can improve the fatigue strength of ultrafine grained material. The intersecting slip of dislocation is restrained, thus the recrystallization and grain growth in fatigue process are restrained, and a small amount of shear band is also produced in the grain. Especially under low stress, there is no large-scale extrusion phenomenon on the fatigue surface. Fatigue cracks mainly occur along grain boundaries.
【学位授予单位】：沈阳工业大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TG146.11

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