FCC结构和HCP结构金属表面机械研磨过程的比较

发布时间：2018-05-14 06:38

本文选题：表面纳米化 + 表面合金化　；参考：《太原理工大学》2016年硕士论文

【摘要】：近年来,具有优异的力学性能和独特的微观结构的纳米材料已经成为人们的研究热点。材料表面纳米化是在材料表面制备出具有一定厚度的纳米结构表层,通过改变其组织结构以及应力状态,使材料的整体力学性能得到改善的方法。表面机械合金化(SMA)技术来源于表面纳米化技术,是表面强烈塑性变形(SPD)的另一分支领域,是在进行表面机械研磨的同时引入不同于基体的成分,形成具有纳米梯度结构的复合表面,以满足材料表面多样性的要求。本文通过实验对比FCC结构金属(Cu)和HCP结构金属(Mg)机械研磨过程中参数配比问题,并探讨其表面纳米化和合金化过程的区别,以及期望制备出表面性能更好的纳米结构层,研究了合金化过程中原子扩散的问题。(1)由于纯铜和纯镁晶体结构不同,并且其层错能也不同,导致塑性变形过程机理也不相同,纯铜变形机理包括(a)位错缠结和位错墙在原始粗晶以及细化胞中演变、(b)形成小角度亚晶界、(c)小角度亚晶界转化为大角度亚晶界及纳米晶三个步骤,位错机制对塑性变形过程起主要贡献;纯镁变形机理包括(a)应力应变诱发孪晶结构形成、(b)孪晶间的交互作用发展为位错的缠结、(c)动态再结晶过程三个步骤,塑性变形过程初期以孪生交互机制为主,随着应力应变持续作用,位错机制对变形过程起主要作用。(2)在相同纳米化体系中,弹丸尺寸增大对纳米化效果起促进作用,塑性变形层厚度增加,纳米晶尺寸减小。特别是纯镁基体,8 mm的弹丸作用下,表层择优取向面发生变化,由原先的(101)晶面择优变为(002)晶面和(101)晶面共同择优。(3)在相同纳米化体系中,smat时间增长对纳米化效果(深度及晶粒大小)起促进作用,塑性变形层厚度明增加,纳米晶尺寸减小,晶格畸变严重。(4)将表面纳米化法和表面机械合金化法结合,在纯cu、纯mg表面得到均匀、连续的ni涂层和cu-ni、mg-ni复合涂层。这一种新的方法对原位形成表面复合涂层提供了实验指导。(5)经过表面纳米化预处理30min的cu板、mg板合金化效率明显高于未处理过的cu板、mg板,合金化4h后,预处理的样品ni涂层厚度可以分别达到40μm和60μm,分别是未预处理样品的8和6倍。涂层的厚度、均匀性和连续性随合金化时间延长而提高。(6)经过表面合金化后样品表面硬度得到很大的提高,纯铜样品表面硬度从98hv提高到280hv,提高2.8倍;纯镁样品表面硬度从45hv提高到340hv,提高7.5倍。(7)涂层的形成主要经历了三个阶段:粉体与基体机械结合、形成冷焊层和互扩散(扩散)过程。并且经过预处理后,基体表层发生严重的塑性变形,导致表层呈现凹凸不平的形貌,表面积增大,表面硬度提高,促进合金涂层形成。(8)在塑性变形过程中,原始粗晶由于应力应变作用发生严重扭折,细化,晶粒之间存在大量晶界特别是三岔晶界,晶粒内部存在大量位错线等缺陷。(9)在塑性变形过程中,由于晶界、位错等缺陷增多,局部温度升高,Ni以原子的形式在纯铜、纯镁基体中扩散。
[Abstract]:In recent years, nanomaterials with excellent mechanical properties and unique microstructures have become a hot spot of research. The surface nanocrystallization of materials is a method to improve the overall mechanical properties of the material by changing the structure and stress state of the surface of the material with a certain thickness. Surface mechanical alloying (SMA) technology is derived from surface nanoscale technology. It is another branch of surface strong plastic deformation (SPD). It is introduced into a composite surface with a nano gradient structure to meet the requirements of the material surface diversity. In this paper, a comparison of FCC is made in this paper. The problem of parameter ratio in mechanical lapping of structural metal (Cu) and HCP structure metal (Mg), and the difference between the surface nanoscale and alloying process, as well as the preparation of the nano structure layer with better surface properties, the problem of atomic diffusion in the process of alloying. (1) the structure of pure copper and pure magnesium is different and its layer is wrong. The mechanism of plastic deformation process is different, and the deformation mechanism of the plastic deformation is different. The deformation mechanism of pure copper includes (a) dislocation entanglement and dislocation wall in the original coarse grain and refined cell. (b) formation of small angle subgrain boundary, (c) small angle subgrain boundary into large angle subgrain boundary and nanocrystalline step, dislocation mechanism plays the main contribution to the plastic deformation process. The mechanism of pure magnesium deformation includes (a) the formation of stress strain induced twin structure, and the interaction between (b) twins develops into dislocation entanglement, (c) the dynamic recrystallization process of (c), the early stage of the plastic deformation process is twin interaction mechanism, with the continuous action of stress and strain, the dislocation mechanism plays a major role in the deformation process. (2) in the same nanometer In the system, the size of the projectile increases to the nanocrystalline effect, the thickness of the plastic deformation layer increases and the size of nanocrystalline decreases. Especially the pure magnesium matrix, under the action of 8 mm projectiles, the preferential orientation surface of the surface changes from the original (101) crystal surface to (002) crystal surface and (101) crystal surface together. (3) in the same nanoscale system, s The time growth of mat promotes the nanocrystalline effect (depth and grain size), the thickness of the plastic deformation layer increases, the size of the nanocrystalline decreases, and the lattice distortion is serious. (4) the surface nanocrystallization and the surface mechanical alloying method are combined, the pure Cu, the pure Mg surface is uniform, the continuous Ni coating and the Cu-Ni, Mg-Ni composite coating. The method provides experimental guidance for the in-situ surface composite coating. (5) after the surface nanocrystalline pretreatment of 30min Cu plate, the alloying efficiency of the Mg plate is obviously higher than that of the untreated Cu plate. After the Mg plate and the alloying 4h, the thickness of the pre treated sample Ni coating can reach 40 Mu and 60 u respectively, respectively, 8 and 6 times of the untreated samples. The thickness of the coating, respectively. The uniformity and continuity increased with the alloying time. (6) the surface hardness of the sample was greatly improved after the surface alloying. The surface hardness of pure copper samples increased from 98hv to 280hv, and increased by 2.8 times. The surface hardness of pure magnesium samples increased from 45hv to 340hv, up to 7.5 times. (7) the formation of the coating mainly experienced three stages: powder and base The cold welding layer and diffusion (diffusion) process are formed by body mechanical combination. And after pretreatment, the surface of the matrix has serious plastic deformation, which leads to uneven surface appearance, the surface area increases, the surface hardness is increased, and the alloy coating is promoted. (8) during the plastic deformation process, the original coarse grain is serious due to the stress and strain effect. There are a large number of grain boundaries, especially the three fork grain boundaries, and there are a large number of dislocation lines in the grain. (9) in the process of plastic deformation, due to the increase of grain boundary, dislocation and other defects, the local temperature increases, and Ni diffusion in pure copper and pure magnesium matrix in the form of atoms.

【学位授予单位】：太原理工大学
【学位级别】：硕士
【学位授予年份】：2016
【分类号】：TG580.68

【参考文献】