【作者】 王德宝；

【导师】 吴玉程；

【作者基本信息】 合肥工业大学 ， 材料学， 2008， 博士

【摘要】 随着机械、电子以及航空航天工业的迅猛发展,迫切要求开发不仅具有良好导电(热)性、而且具有较高机械和耐磨性能,较低热膨胀系数的功能材料。铜和铜合金是传统的高导电(热)材料,但由于强度和耐热性不足,其应用范围受到很大的限制。本文以开发高性能导电(热)耐磨铜基复合材料为目标,通过成分和工艺优化,采用机械合金化(MA)、冷压成形和复压复烧工艺制备出了满足性能要求的颗粒增强Cu(-Cr)基复合材料。以寻求最佳的材料制备工艺,满足材料的高强度、高导电(热)性以及优良的摩擦磨损性能要求。通过SEM,XRD、TEM和其它实验检测仪器对粉末的机械合金化过程,复合材料的微观组织特征以及机械、物理和摩擦磨损性能进行了系统研究,为拓展新型高性能铜基复合材料的应用领域打下坚实基础。本文研究内容主要有以下几个方面:1.采用机械合金化工艺可使在固态和液态下完全互不溶的Cu-Cr系形成过饱和固溶体,并显著细化晶粒和产生严重晶格畸变。由高能球磨引起的高密度晶体结构缺陷和溶质组元化学势的降低以及晶粒细化对形成Cu-Cr过饱和固溶体起着决定作用。2.采用冷压-烧结-复压-复烧工艺对Cu-Cr合金粉末致密化过程进行研究。系统探讨了压制压力、烧结温度对相对密度的影响。研究结果表明初压和复压能显著提高材料相对密度,而复烧对提高材料的相对密度贡献不大,其作用主要体现在材料性能的改善和优化。3.通过对不同成分Cu-Cr合金性能测试,研究了成分、烧结温度和复压复烧对材料力学和物理性能的作用,同时探讨了Cu-Cr合金的增强机制。Cu-1.2wt%Cr合金的硬度、抗拉强度随着烧结温度的升高而增加,在850℃时达到峰值;当温度进一步升高时,由于析出相Cr粒子长大、粗化,与基体失去共格,使得硬度和抗拉强度又有所下降,而材料的导电(热)率则随着烧结温度的升高继续缓慢增加。合金中过饱和的Cr原子对材料强度的影响是通过沉淀强化和细晶强化来实现的。4.以SiC为增强颗粒,采用粉末冶金工艺制备了颗粒增强铜基复合材料,研究了SiC颗粒体积分数、粒度对复合材料显微组织和力学、物理、摩擦磨损性能的影响。在此基础上着重探讨了SiC颗粒粒度的变化对复合材料性能的影响。结果表明:在制备工艺相同的情况下,SiC粒度为10μm时,复合材料具有最大抗拉强度,达到265.7MPa,其断裂机制是以Cu-SiC界面处基体撕裂为主。当SiC颗粒粒度较大时(≥21μm),由于界面面积有限和增强颗粒间距过大,使得SiC颗粒增强效果有限。相对于强度的变化,复合材料的摩擦磨损特性也随SiC颗粒粒度的变化而发生明显改变。在低载荷条件下(≤120N),增大SiC颗粒粒度有助于提高材料的耐磨性,其磨损机制以磨粒磨损为主。随着载荷的增加,由于大粒度SiC颗粒易于破碎,承载作用下降,导致剥层磨损的发生。通过对复合材料物理性能研究表明:由于SiC粒度减小,复合材料单位体积Cu-SiC界面面积的增加和SiC颗粒间距的减小,都会对自由电子的运动产生阻碍作用,导致复合材导电(热)率下降。复合材料的热膨胀系数随着SiC颗粒粒度的增加而提高;同时由于SiC颗粒粒度的增加,导致材料内部的热应力提高,引起材料热膨胀系数发生突变的临界温度降低。5.采用化学沉积工艺对SiC颗粒表面包覆Cu或Ni,以改善Cu-SiC界面状况。结果表明:SiC颗粒表面经金属涂层处理提高了复合材料界面结合强度,在基体和增强颗粒之间可以有效传递载荷,使得复合材料的相对密度、硬度和拉伸性能获得提高。由于基体铜和镍镀层之间可以相互扩散,形成连续固溶层,从而使复合材料力学性能提升更为显著。在摩擦磨损过程中由于界面优化减少了SiC颗粒与基体的界面脱粘,有效地发挥承载作用,从而提高了Cu/SiC复合材料的耐磨性。6.为了结合颗粒强化和析出强化两种强化方式,以Cu-Cr合金为基体,采用SiC颗粒增强Cu-Cr合金,结果发现随着基体强度的提高,可更有效的发挥SiC颗粒对复合材料的增强作用,并改变了复合材料的断裂机制,同时材料软化温度也得到大幅度提高。7.研究了不同载荷、滑动速度和距离条件下(Cu-Cr)/SiC复合材料的摩擦磨损行为。结果表明:随着SiC颗粒含量的增加,复合材料的耐磨性能得到提高,并延缓了严重磨损的发生。当载荷和滑动速度等条件变化时,复合材料的磨损机制也发生改变,并在某一临界值附近引起磨损率的突然增加。在微缓磨损阶段磨粒磨损和氧化磨损为主要磨损机制;在严重磨损阶段因磨损面机械混合层的剥层脱落和摩擦热导致亚表层基体温升软化及对磨双方材料大量粘着转移为主要磨损机制。8.研究了(Cu-Cr)/SiC复合材料高温摩擦磨损行为,结果表明SiC颗粒的加入,可以有效提高复合材料发生严重磨损的临界温度。严重磨损发生的原因是因为温度的增加导致磨损面氧化膜破裂、脱落,磨损机制以剥层、粘着磨损为主。石墨颗粒的加入可以降低在一定温度下复合材料的摩擦系数和磨损率,改善了复合材料高温摩擦学特性。9.研究了纳米SiC颗粒对Cu-Cr合金的增强作用,结果发现在纳米SiC含量较低的情况下(0.5%-3%),复合材料硬度、抗拉强度和摩擦磨损性能随着纳米SiC颗粒增加而得到改善,而当纳米颗粒含量达到5%,则发生团聚现象,对材料力学性能产生不利影响,并导致断裂机制的改变。本文采用机械合金化工艺制备了Cu-Cr复合粉末,并开发相应的成形工艺,获得最佳工艺参数,然后采用SiC颗粒增强纯Cu和Cu-Cr合金。研究了SiC颗粒含量、粒度和基体强度对复合材料性能的影响。同时通过化学沉积工艺对Cu/SiC复合材料进行界面优化,并探索其对复合材料性能的作用。系统地研究了复合材料在室温和高温环境下的摩擦磨损行为,分析其微观磨损机理。初步探讨了纳米SiC颗粒对Cu-Cr合金性能的增强作用及机制。本论文的研究结果对研制开发新型耐磨铜基复合材料和丰富材料摩擦学有着重要的理论和现实意义。更多还原

【Abstract】 With the development of electronic, mechanical, aeronautic and aerospace industries, requires imperative demand of developing functional materials with not only high electrical conductivity, thermal conductivity, and excellent mechanical properties, wear-resistant, low coefficient of thermal expansion. Copper and copper alloys are the traditional high-conductivity, thermal conductivity materials, but because of lack of strength and heat-resistant Performance, its application is greatly restricted.In this thesis, to developing copper matrix composites with high electrical conductivity, thermal conductivity and good wear-resistant as the objective, the components of the composite systems and the preparation technique were designed. SiC particles reinforcement of Cu(-Cr)matrix composites were fabricated by mechanical alloying (MA)plus cold pressure forming and repressing and resintering process to find the best fabrication process and meet the high-strength, high-conductivity and excellent wear-resistant properties. The mechanical alloying process of powder and composites microstructure, mechanical, physics, wear and tribological properties were systematically observed and analyzed by means of SEM, XRD, TEM, and other test instruments.All of these works lay a solid foundation for development the utilization area of novel advanced wear-resistant copper matrix composites. The works include the following aspects:1. Cu (-Cr) supersaturated solid solutions were prepared by mechanical alloying, whereas such a binary system is known to be immiscible in solid and liquid state. The crystalline of Cu-Cr alloy powders were significantly refined and lattice strain were have serious lattice distortion during MA process. This suggests that the high density crystal defects, solute elements chemical potential decreasing and crystalline refinement due to MA may play a critical role on the supersaturated solid solution of Cr in Cu.2. Densification Process of Cu-Cr alloy powders was studies by means of cold pressing-sintering- repressing-resintering method. The influence of different pressure and temperature on the relative density was discussed systematically. The results showed that pressing and repressing can significantly improve the relative density, however, resintering did not evidently contribute to the relative density, and its main role reflected in the performance improvement and optimization.3. Through to test the different composition Cu-Cr alloys properties to analyze the influence of composition, temperature and repressing-resintering on the alloys mechanical and physical properties. Hardness and tensile strength of Cu-1.2wt%Cr alloy increased with the rising sintering temperature, and reached the peak value when 850℃and it decreased with further temperature rising due to Cr particles growth and coarsening, electrical conductivity and thermoconductivity slowly increase with the increase of sintering temperature. Over-saturated Cr atoms are the dominant factors accounting for strengthen by precipitation and grain refinement strengthening.4. Cu/SiC composites were fabricated by powder metallurgy. The effect of SiC volume fraction and sizes on the mechanical properties, physical, wear properties and microstructure of composites were investigated. On this base, the influence of various sizes reinforced particles on the properties of composites was investigated. The results indicated that under the same preparing parameters, the composites with SiC particle for 10μm possess the highest ultimate tensile strength, beyond 265.7MPa, and their breakage is due to tearing of matrix near Cu-SiC interface. Composites with large particle (≥21μm) possess finite strength owing to interfacial area limited and the space between SiC particles larged. Compared with tensile strength varying, the friction and wear properties of Cu/SiC composites obviously differ with the size of SiC changing. When the applied load was lower 120N, the bigger SiC are helpful to improve the wear resistance of Cu/SiC composites. However, composites reinforced with larger SiC particulates increase the counterpart steel wear rate, and wear mechanism is mainly abrasion. When the applied load increased, because larger size SiC particles mashed, the load carrying capacity decreased, which lead to delamination wear occurring. Because the SiC particle size reduced, Cu-SiC interfacial area increased and space between SiC particles increased, which impede the movement of electronic effects, leading to electrical conductivity and thermoconductivity decreased. The coefficient of thermal expansion composites increases with enhancing particle size. With the increasing in SiC particle size, the thermal stress trend to be improved and critical temperature with causing the coefficient of thermal expansion catararophe droped.5. SiC particles were coated Ni or Cu film by electroless deposition to modify Cu-SiC interfaces. The effects of modification different metals(Cu, Ni)on SiC particles surface on the interfacial bonding were investigated. The results indicate that the interface of composites is compact, improves interfacial bonding strength and loads can be transferred effectively between matrix and SiC by the surface modification with Cu and Ni. Therefore, the densification, bulk hardness and tensile properties of composites are improved. Matrix and coating Ni atoms can diffuse each other to form continual a film of solid solution, which is in favor of improving mechanical properties of composites. In the course of friction and wear, SiC particles effectively play the role of load carrying capacity and thereby improving the tribological properties.6. In order to combine particulate reinforcement with precipitation reinforcement, SiC particle were used to be fabricated Cu-Cr matrix composites. As a result, SiC particle can be more effective enhancing composites strength with the improvement of Cu-Cr matrix strength, and change the mechanism of the fracture, while softening temperature had large increased.7.The wear behavior of (Cu-Cr)/SiC composites under different loads、sliding velocities and distances was studied. The results showed that the wear resistance properties of composites increased with volume fraction of SiC particles, and delayed severe wear to hanppen. The wear mechanism of (Cu-Cr)/SiC composites changed with the extrinsic factors, such as load, sliding velocity and distance. The wear rate may increase abruptly at certain critical values. In the mild wear stage, the main wear mechanism was abrasion and oxidation wear. In the severe wear stage, mechanically mixed layer was detached and composites was softened by the frictional heat, and therefore massive materials transfer resulted in the abrupt increase of wear rate.8. The elevated-temperature wear behaviors of SiC particulate reinforced Cu-Cr matrix composites were studied. The results indicated that the critical temperature to occurring serious wear was increased effectively by the addition of SiC. Along with temperature elevation, the oxide film cracked and fell off from worn surface, leading to serious wear, and wear mechanism is mainly delamination and adhesive. The wear rate and friction coefficients of composites were reduced by further addition of Gr, improving the tribological characteristic in elevated-temperature environment.9. The nanometer SiC particles reinforced (Cu-Cr)/SiC composites were investigated. The results indicated that the hardness, tensile strength, electrical conductivity and friction and wear properties of composites were improved with the increase of nanometer SiC particles content when nanometer SiC particles was lower(0.5vol%-3vol%). When nanometer SiC particles content was 5vol%, the nano-particles were agglomerated, which would be harmful to the mechanical properties and lead to fracture mechanism of composites changing. In this thesis, Cu-Cr powders were fabricated by mechanical alloying, and developed forming techniques,obtained the best forming parameters.SiC reforcement Cu and Cu-Cr matrix composites, and the influence of different content, sizes of SiC particles and matrix strength on the properties of composites were investigated. The interface of Cu/SiC was optimized by electroless deposition, and the effects of interfacial modifying on the properties were stuied.The friction and wear behaviors of the composites under room-and elevated-temperature conditions were studied systematically, and micro-wear mechanism were analyzed. The reinforcement mechanism and strengthening effect of nano-SiC particles on Cu-Cr alloy was also studied elementarily. It is of great significances in theory and practice to develop the new type of wear-resistant copper matrix composites and to enrich the tribological research.更多还原