旋转加速喷丸表面纳米化工业纯铝和纯铜的制备工艺与性能研究

发布时间：2018-05-30 12:23

本文选题：纳米晶 + 超细晶　；参考：《南京理工大学》2015年硕士论文

【摘要】：在金属材料的三大失效方式中(断裂、腐蚀和摩擦磨损),摩擦磨损直接发生与金属的表面,而疲劳断裂和腐蚀也是首先起始于材料的表面。因此,通过诸多化学和物理方法来改变材料表面的组织结构或成分以满足工程使用所需要的性能(表面改性)一直是材料科学与工程的重要领域之一。本论文利用自行设计的旋转加速喷丸处理设备(RASP),对工业纯铝纯铜和纯铜两种材料进行了表面纳米化处理：在材料表面通过机械变形而获得了一定厚度的纳米晶和超细晶结构表层,并通过改变工艺参数,获得不同性能的材料,并将正交试验设计和和实验结果相结合,最终获得最佳生产工艺参数。并利用金相显微镜、XRD、TEM等测试技术分析细晶化表面的微观组织与显微结构特征,对比探讨了两种材料的细化机理。此外,运用便携式粗糙度仪、硬度测试仪对处理样品表面性能进行了测定。具体实验结果如下：1、工业纯铝和纯铜经过RASP处理后,表面区域均产生了强烈的塑性变形,使表面粗晶晶粒发生了明显的细化,纯铜材料表层形成了纳米晶,并随着距离表层深度的增加,塑性变形区的晶粒从纳米晶逐渐增大至超细晶再增大到粗晶,纯铝表层形成了超细晶,也形成了沿表面至基体的晶粒尺寸的梯度分布。对于纯铜材料,弹丸直径越大,晶粒细化效果越好。对于纯铝,弹丸能量越高(与弹丸直径、速度和处理时间有关),表面粗糙度和表层硬度越大,细化效果越明显。但如果弹丸能量过高(比如处理时间为60min),超细晶粒因发生动态再结晶而长大,并使得硬度降低。2、微观结构观测发现,纯铝的晶粒细化是通过位错的不断积累和反应完成：变形首先在粗晶晶粒内部形成高密度的位错缠结和位错墙,进一步的位错积累使位错缠结和位错墙先演变成小角度亚晶界,并随之变成大角度亚晶界和大角晶界,形成等轴状取向随机的超细晶组织。纯铝的位错细化机制是由其高的层错能决定的。3、对于纯铜,在高速变形条件下,粗晶晶粒被高密度的孪晶分割成层片状,随后位错运动使层片折断而进一步将其细化成取向随机的等轴纳米晶。在应变速率较低时,纯铜的晶粒细化机理等同于纯铝的细化机理：先由位错积累形成等轴状位错胞,进而形成亚微晶和纳米晶。铜的这一细化特征是由其中等层错能所决定。应变速率较高时,变形方式主要是机械孪生；而应变速率较低时,变形方式以位错滑移为主。
[Abstract]:In the three failure modes of metallic materials (fracture, corrosion and friction wear), friction and wear are directly related to the surface of the metal, and fatigue fracture and corrosion are also the first to start from the surface of the material. Therefore, it is one of the important fields of material science and engineering to change the structure or composition of the material surface by a variety of chemical and physical methods to meet the performance (surface modification) required for engineering use. In this paper, the surface nanocrystals of industrial pure aluminum copper and pure copper were prepared by using the rotating accelerated shot peening equipment designed by ourselves. The nanocrystals and nanocrystals were obtained by mechanical deformation on the surface of the materials. The surface layer of ultrafine crystal structure, By changing the process parameters, the materials with different properties are obtained, and the orthogonal experimental design is combined with the experimental results to obtain the best production process parameters. The microstructure and microstructure of the fine crystalline surface were analyzed by means of metallographic microscope (TEM) and X-ray diffraction (TEM), and the refining mechanism of the two materials was compared and discussed. In addition, the surface properties of the treated samples were measured by a portable roughness tester and a hardness tester. The specific experimental results are as follows: 1. After RASP treatment of industrial pure aluminum and pure copper, the surface area of pure aluminum and pure copper has produced strong plastic deformation, resulting in obvious refinement of coarse crystal particles on the surface, and nanocrystals formed on the surface of pure copper materials. With the increase of the depth from the surface to the surface, the grain size in the plastic deformation zone gradually increases from nanocrystalline to ultrafine grain and then to coarse grain, and the superfine grain is formed on the surface of pure aluminum, and the gradient distribution of grain size is formed along the surface to the matrix. For pure copper material, the bigger the projectile diameter is, the better the grain refinement effect is. For pure aluminum, the higher the projectile energy is (related to the diameter, speed and treatment time of the projectile), the greater the surface roughness and surface hardness are, the more obvious the refining effect is. However, if the projectile energy is too high (for example, the treatment time is 60 mins, the ultrafine grain grows up because of dynamic recrystallization, and the hardness decreases by 0.2, the microstructure observation shows, The grain refinement of pure aluminum is accomplished by the continuous accumulation and reaction of dislocation: firstly, high density dislocation entanglement and dislocation wall are formed in coarse grain, and further dislocation accumulation causes dislocation entanglement and dislocation wall to evolve into small angle subgranular boundary first. And then the large angle subgranular boundary and the large angle grain boundary are formed, and the uniform axis orientation random ultrafine crystal structure is formed. The mechanism of dislocation refinement of pure aluminum is determined by its high stacking fault energy. Then the dislocation movement breaks the laminates and further refines them into randomly oriented equiaxed nanocrystals. When the strain rate is low, the grain refinement mechanism of pure copper is equivalent to that of pure aluminum: firstly, equiaxed dislocation cell is formed from dislocation accumulation, and then sub-microcrystalline and nanocrystalline are formed. This fine feature of copper is determined by the equal-stacking fault energy. When the strain rate is high, the deformation mode is mainly mechanical twinning, while when the strain rate is low, the dislocation slip is the main deformation mode.
【学位授予单位】：南京理工大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：TG668

【引证文献】