| 摘要: | 銅及銅合金因具有優良的耐腐蝕性、易加工性、高熱傳導性、高導電性及在低、常溫及中高溫時優良的機械性質等，故已廣泛應用於電子電路的零件及耐磨耗材料。 金屬基複合材料可以結合基材及添加相的優點，以獲得所需的材料性質，如較佳的強度、剛性及耐磨耗性等，其中又以添加顆粒強化相之複合材料因具備較佳的等向性，故常被應用。不過，複合材料常因第二相的存在，導致腐蝕性質的劣化。此外，若材料在腐蝕的環境下進行磨耗，會受到磨耗與腐蝕的交互作用，常導致材料嚴重的損失，亦即，磨耗腐蝕的性質與單獨磨耗或腐蝕性質有相當大的差異。 本論文主要目的係選擇粉末冶金之熱壓法製造銅基複合材料，添加四種不同顆粒(碳化矽、石墨、碳化鎢、鈷)之強化相，期能獲得高緻密度的銅基複合材料，並進一步研究不同複合材料磨耗及腐蝕性質。本研究對添加相的選擇為：碳化矽及碳化鎢可增加材料硬度、石墨可作為磨耗潤滑劑、而鈷則有抗震效果。 本論文採用兩種方式來探討乾磨耗性質，一種是用來回式磨耗試驗機評估添加碳化矽及石墨的銅基複合材料；另一種則使用轉輪磨耗(block-on-ring)方式研究添加碳化鵭及鈷的銅基複合材料。實驗結果顯示，銅/碳化矽複合材料雖硬度較高，其磨耗性質却比純銅差，此外，加入石墨至銅基地中雖大幅降低複合材料硬度，但因為石墨具潤滑效果，反而提升銅/碳化矽/石墨複合材料抗磨耗性。另一方面，添加碳化鎢的銅基複合材料不但硬度提高，同時也表現較好的抗磨耗性質；而添加鈷可進一步提昇磨耗性質。 除了磨耗性質的探討外，本論文並研究銅基複合材料添加不同的顆粒後對腐蝕性質的影響。腐蝕性質測定則分別運用靜態浸漬法測量腐蝕重量損失及電化學法測量腐蝕性質及分析腐蝕機構，腐蝕溶液採用3.5wt%氯化鈉溶液。實驗結果顯示，添加碳化矽使腐蝕重量損失較純銅增加，再添加石墨使重量損失持續增加，此乃因添加相與基地介面易產生間隙腐蝕及添加相與基地間因電位差產生伽凡尼腐蝕所造成。另外，添加碳化鎢的複合材料產生孔蝕使腐蝕性質變差，然而同時添加碳化鎢及鈷則使複合材料重量損失比純銅少，此乃因材料表面形成鈍化膜可扺抗腐蝕；此外，經電化學實驗證明加入第二相至銅基地中將使腐蝕性質變差(腐蝕電流增加)，主要的原因亦由於局部腐蝕及伽凡尼腐蝕的影響，導致材料耐腐蝕性質惡化。同時，材料鈍化膜的破裂亦為影響腐蝕性質因素之一。 為了進一步探討磨耗與腐蝕的交互影響，使用銅/碳化鎢/鈷複合材料進行腐蝕環境下(模擬海水)的磨耗試驗，結果發現當處於陰極電位(相對於開路電位)時的磨耗，腐蝕幾乎没發生作用，使得銅基複合材料磨耗損失仍以機械磨耗為主；然而在陽極電位時，由於磨耗與腐蝕產生加成作用，材料磨耗損失隨著外加陽極電位增加而急遽增加。 Copper and copper alloys are well known for a combination of good corrosion resistance in a variety of environments, excellent workability, high thermal and electrical conductivities, and attractive mechanical properties at low, normal and moderately elevated temperatures. Copper and copper alloys thus are widely used in the electronic application and bearing materials. Metal matrix composites combine the advantages of the matrix and reinforcement to obtain the required properties, to increase strength, toughness and anti-wear. Among them, the composites incorporated with particles reinforcement, owing to better isotropic behaviors, were mostly used as bearing materials. However, the presence of foreign phase in composites often results in a worse corrosion behavior. Furthermore, in a wear and corrosion coexistence environment, the composites in general experience severe wear loss. This is due to the synergic effect of wear and corrosion which are more complicated than wear or corrosion alone. The main object of this thesis is to adopt a hot pressing process, a powder metallurgy route, for manufacturing Cu metal matrix composites (Cu MMCs) with four additional particulates, i.e., SiCp, graphite, WCp and Cop. The experimental results verify the method can acquire high densification, sound composites. The wear performance of Cu MMCs was studied using two different wear examinations associated with two different composites in this study. The Cu/SiCp/graphite composites uses a reciprocal (back and forth) wear machine while the Cu/WCp/Cop composites uses a block-on-ring wear tester. The sliding tests were performed under ambient conditions and without lubricant. Selection of foreign particles is based on the fact that SiC and WC phases can improve the bulk hardness of composites, graphite is commonly used in bearing Al matrix composites acting as a lubricant, and Co is helpful to increase shock resistant. Traditionally, harder composites exhibit better wear resistance due to their capability to endure contact load from being plastic deformation. By using different wear tests, the harder Cu/SiCp and Cu/WCp composites, indicate different results. The former get worse wear resistance than pure copper, while the later better do. Although graphite lowers hardness of composite, it increases wear resistance since graphite phase can lubricate a contact surface during friction. Besides, the addition of a Cop phase is also beneficial for improving wear resistance of Cu/WCp/Cop composites. In this work, the corrosion test also executed to identify corrosion behavior after particles were incorporated into a copper matrix. The corrosion measurement in this study includes static weigh loss immersed in a corrosive solution and potentiodynamic polarization. The corrosive solution used in this examination was unified as 3.5 wt. % NaCl at pH 6.7 (simulative sea water). The electrochemical measurements were carried out using a three electrode system. Experimental results demonstrate that the static corrosive wear loss of Cu/SiCp/graphite increases, meanwhile, that of Cu/WCp/Cop composites decreases. Additionally, the mixing of particles into copper matrix depressed the anti corrosion behavior of Cu MMCs. The worse corrosion behavior of Cu MMCs can be explained mainly owing to the local corrosion (crevice and pitting) and the galvanic corrosion, while the influence of broken passive films can be referred to another factor. The synergistic effect of wear and corrosion was also studied. The test was adopted by taking Cu/WCp/Cop composites for wearing in the same 3.5 wt. % NaCl solution at pH 6.7. The corrosion potential effect on the loss of composites can be concluded as follows: Cu/WCp/Cop composites exhibit a very small wear corrosion rate at a cathodic potential (relative to OCP) because corrosion seems negligible and mechanical wear dominates wear loss of the composites. However, at an anodic potential, the wear corrosion rate dramatically increases with an increase of applied potential owing to a synergistic effect of wear and corrosion. |
