双步球磨与放电等离子烧结Cu-Cr复合材料的组织和性能研究

发布时间：2018-08-13 19:05

【摘要】：纯铜的导电和导热性能高,是广泛应用于电工器件和导热器材的功能材料。然而,由于其强度和硬度较低,在使用过程中容易因力学性能不足而发生变形,并最终导致失效,因此大大限制了其在实际中的应用。针对以上问题,本论文以商用Cr粉作为增强相,制备Cr颗粒增强Cu基复合材料,通过双步球磨(机械研磨机械合金化)与放电等离子烧结制备高强高硬Cu-Cr复合材料,对拓宽Cu基复合材料的应用领域具有重要意义。首先,本文分别对商用Cu粉和Cr粉在干和湿两种条件下进行机械研磨处理。结果表明,两种条件下机械研磨后的Cu粉粒度均增大,湿磨能够有效抑制其颗粒的显著粗化,并使Cu粉由树枝状转变为片状粉体,而干磨则导致其严重粗化,形成粗大的球状颗粒。对于Cr粉,在两种条件下进行机械研磨均能够实现其颗粒的细化,而干磨所获得的Cr粉比湿磨更细,且干磨后Cr粉保持不规则形状,湿磨后则转变为片状粉体。采用机械研磨能够制备纳米晶Cu粉和Cr粉。与湿磨相比,干磨所获得的晶粒尺寸更小。本文对Cu粉和Cr粉的机械研磨机理进行了探究,并分析了在湿磨和干磨条件下两种金属粉末形态与结构的差异。其次,将预球磨Cu粉与原始Cr粉、原始Cu粉与预球磨Cr粉分别进行机械合金化处理,以制备Cu-8 at.%Cr复合粉末。为了进行对比,在相同实验条件下对原始Cu粉与原始Cr粉进行机械合金化处理。实验表明,相比未经预球磨处理以及单独预球磨Cu粉,单独预球磨Cr粉能够制备更细小的复合粉末,同时能获得较高的出粉率、更窄的粉末粒度分布、更小的晶粒尺寸以及更高的Cr固溶度,因此该复合粉末具有广阔的应用前景。本文深入研究了Cu-Cr复合粉末的机械合金化机制,包括形态的转变、晶粒的细化以及固溶度的变化,以分析预球磨处理对后续机械合金化过程中该复合粉末形态和结构的影响。最后,对所制备的Cu-8 at.%Cr复合粉末进行放电等离子烧结处理。采用扫描电子显微镜,透射电子显微镜和X射线衍射技术对烧结块体复合材料的组织与结构进行分析。利用压缩和维氏硬度试验表征该材料的力学性能。结果显示,相比未经预球磨处理以及单独预球磨Cu粉,单独预球磨Cr粉所制备的复合材料中Cu基体的晶粒较细小,其平均晶粒尺寸约为82 nm。该复合材料在保持一定的致密度和电学性能的前提下,具有较高的力学性能,其维氏硬度、压缩屈服强度和压缩率分别是327 HV、1049 MPa和10.4%。优异的力学性能主要是由于Cr颗粒的弥散强化、Cu基体的细晶强化以及较强的Cu/Cr结合界面。
[Abstract]:Pure copper with high conductivity and thermal conductivity is widely used as functional materials for electrical devices and thermal conductive devices. However, because of its low strength and hardness, it is easy to deform due to the lack of mechanical properties in the process of use, and ultimately lead to failure, so its application in practice is greatly limited. To solve the above problems, the commercial Cr powder was used as the reinforcing phase to prepare the cr particle reinforced Cu matrix composites. The high strength and high hard Cu-Cr composites were prepared by double step ball milling (mechanical grinding and mechanical alloying) and spark plasma sintering (SPS). It is of great significance to widen the application field of Cu matrix composites. Firstly, the commercial Cu powder and Cr powder were milled under dry and wet conditions, respectively. The results show that the particle size of Cu powder increases after mechanical grinding under both conditions. Wet grinding can effectively inhibit the obvious coarsening of Cu powder and change Cu powder from dendritic to flake powder, while dry grinding results in serious coarsening. Forming coarse globular particles. For Cr powder, the particle size can be refined by mechanical grinding under both conditions, while the Cr powder obtained by dry grinding is finer than that obtained by wet grinding, and the Cr powder keeps irregular shape after dry grinding, and changes to flake powder after wet grinding. Nanocrystalline Cu and Cr powders can be prepared by mechanical grinding. The grain size of dry mill is smaller than that of wet mill. In this paper, the mechanism of mechanical grinding of Cu powder and Cr powder is studied, and the differences of morphology and structure of the two kinds of metal powder under wet and dry grinding conditions are analyzed. Secondly, Cu-8 at.%Cr composite powder was prepared by mechanical alloying of premilled Cu powder and original Cr powder, original Cu powder and premilled Cr powder. In order to compare, the original Cu powder and the original Cr powder were treated by mechanical alloying under the same experimental conditions. The experimental results show that compared with Cu powder without pre-milling and single pre-milling, Cr powder prepared by pre-milling alone can produce smaller composite powder and obtain higher powder yield and narrower particle size distribution. Because of the smaller grain size and higher Cr solubility, the composite powder has a broad application prospect. In this paper, the mechanism of mechanical alloying of Cu-Cr composite powder is studied in depth, including morphology transformation, grain refinement and the change of solid solubility, in order to analyze the effect of pre-milling on the morphology and structure of the composite powder during subsequent mechanical alloying. Finally, the Cu-8 at.%Cr composite powder was sintered by spark plasma sintering. The microstructure and structure of sintered bulk composites were analyzed by scanning electron microscope, transmission electron microscope and X-ray diffraction. The mechanical properties of the material were characterized by compression and Vickers hardness test. The results show that the grain size of Cu matrix prepared by single premilled Cr powder is smaller than that of Cu powder prepared without or without premilling. The average grain size of Cu matrix is about 82 nm. The composite has high mechanical properties on the premise of keeping certain densification and electrical properties. Its Vickers hardness, compressive yield strength and compression ratio are 327HV1049 MPa and 10.4 MPa, respectively. The excellent mechanical properties are mainly due to the dispersion strengthening of Cr particles and the fine grain strengthening of Cu matrix and the strong Cu/Cr bonding interface.
【学位授予单位】：华南理工大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：TB331

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