- 學位論文
利用陰極電弧離子製程披覆Cr(N, O) / CrN 複合鍍膜之微結構及特性研究
Study on microstructure and characteristics of Cr(N,O) /CrN duplex coatings deposited by cathodic arc ion plating processes
摘要
本研究以陰極電弧離子製程披覆CrN單層鍍膜及Cr(N,O)/CrN複合鍍膜於AISI M2工具鋼上，變化腔體中之O2/N2流量比，分別以X光繞射儀(XRD)、掃瞄式電子顯微鏡(SEM)、歐傑電子光譜儀(AES)、X光電子光譜儀(XPS)及穿透式電子顯微鏡(TEM)，觀察鍍膜微結構及組織型態；鍍膜特性分析方面以熱分析(TGA/DTA)、水接觸角(Contact angle of water)、附著性(Adhesion)、硬度(Hardness)、磨耗性(Wear)、沖蝕(Erosion)及抗腐蝕(Corrosion)性，來探討鍍膜性質的變化及影響。從低掠角XRD與TEM平面繞射影像分析得知利用陰極電弧離子製程披覆之CrN單層鍍膜，鍍層本身由柱狀晶結構所組成，其微結構主要包含CrN及Cr2N，而在Cr(N,O)/CrN複合鍍膜中則有有CrN、Cr2O3及其他化合物相的存在(如CrO、Cr2N)。熱分析中觀察發現CrN單層鍍膜約在600℃開始氧化，而在表面生成氧化鉻(Cr2O3)相；由SEM影像觀察表面型態與AES元素分析中發現Cr(N,O)/CrN複合鍍膜約在800℃左右，除了出現顆粒狀之形貌外，其表面應該有Cr3C2或Cr2O3的生成。研究發現以陰極電弧離子製程披覆之鍍膜皆有微粒之產生，且過多的氧氣會導致靶材的毒化(Poison)情形加速，也會增加微粒及孔洞的數量進而影響表面特性，因此不論是氧氣流量或沈積時間的增加，都會造成表面微粒及微坑數目的增加。在鍍膜特性探討方面發現，不論是維克氏硬度或奈米硬度，各種Cr(N,O)/CrN複合鍍膜硬度皆比單層鍍膜CrN來的高，應與鍍層之晶粒結構及鍍層間殘留應力有關；附著性試驗發現CrN具有良好之附著性，但隨著氧氣流量的增加，由於硬度高、低熱膨脹係數、韌性較低及高內應力等因素造成Cr(N,O)/CrN複合膜層之附著性降低；計算鍍膜彈性係數得知當H/E越高，會有較小應變累積量，故其抗磨耗性佳，因此本實驗之CAIP製程中添加氧氣後，除提高奈米硬度值外，各種製程條件之Cr(N,O)/CrN複合鍍膜其H/E值都比CrN鍍膜來的高，高H/E值同樣在Cr(N,O)/CrN複合鍍膜中提供較低之塑性應變量，因此鉻氧化物的生成有助於增加膜層的磨潤性。沖蝕結果顯示CrN鍍膜及Cr(N,O)/CrN複合鍍膜對於低角度(30˚)之沖蝕可具有較高之耐沖蝕能力，雖對於高角度沖蝕仍易被破壞。就整體沖蝕行為而言，鍍膜對於低角度之沖蝕可具較高之耐沖蝕能力，但高角度沖蝕仍易被破壞，如能增加鍍膜附著性與硬度及韌性，則可有效地增加耐沖蝕性；在抗腐蝕行為研究上發現不論是極化試驗、酸鹼溶液浸泡試驗、鹽霧試驗中皆可知Cr(N,O)/CrN複合鍍膜較CrN單層鍍膜之抗腐蝕性好；對A356鋁熔液熱熔損試驗來說，Cr(N,O)/CrN複合鍍層的結構設計具有減少連續性孔隙的優點，可以減少鋁液滲透至基材的機率，達到改善耐腐蝕的能力，因此Cr(N,O)/CrN複合鍍膜比CrN單層鍍膜更具有明顯的減緩鋁液侵蝕之效果。
並列摘要
This research is focused on the effects of various O２/N2 gas flow on the CrN and Cr (N, O)/CrN coating properties using cathodic arc ion plating technology. With X-ray and TEM, column structures were found in the CrN coating layer microstructures, which include CrN and Cr2N. Contrastingly, there were CrN, Cr2O3, and other compounds in the Cr (N, O)/CrN duplex coating layer. Upon analysis, we found oxidation of CrN and Cr2O3 phase formation on surface at the temperature of 600℃. At around 800C, there were formation Cr3C2 and Cr2O3 particles on the coating surface as seen by the SEM and AES. Generally, cathodic arc ion plating will produce micro-particles. However, excess oxygen flow will accelerate the target poisoning resulting in increased micro-particles and voids. Our result indicates that this phenomenon occurs when there is/are increased oxygen flow and/or increased deposition time. Upon analysis by Vickers and nano-indenter hardness test, we found the Cr (N, O)/CrN duplex coating layer has higher hardness than CrN coating layer because of its microstructure and residual stress. CrN has excellent adhesion, however, as oxygen flow increases, the adhesion of Cr (N, O)/CrN duplex coating layer decreases. This phenomenon occurs because of high hardness, low expansion coefficient, low toughness, and high residual stress of the Cr (N, O)/CrN duplex coating layer. After calculating for the Young’s modulus (E), we found that as the value of the Hardness/Young’s modulus (H/E) ratio increases, the residual strain decreases, resulting in better wear resistance. After addition of oxygen, not only the nano-indenter hardness increases, but all of the Cr (N, O)/CrN duplex coating also have higher H/E ratio than CrN coating. High H/E ratio indicates lower plastic strains in the Cr (N, O)/CrN duplex coating; therefore, the production of chromium oxide on the surface will help the wear properties of the coating layer. Moreover, the erosion results show that both the CrN coating layer and Cr (N,O)/CrN duplex coating layer has high erosion resistance for low angle (30°), but low erosion resistance for large angle. If one can increase the adhesion, hardness, and toughness of the coating layer, then one can effectively increase the coating layer’s erosion resistance. Results from the polarization test, alkali/acidic solution dipping test, and the salt spraying test indicates that the Cr (N, O)/CrN duplex coating layer has higher anti-corrosive properties than the CrN layer. For A356 aluminum emersion test, Cr (N, O)/CrN duplex coating layer has better anti-corrosive property because of its duplex layer microstructure. The specific microstructures of Cr (N, O)/CrN duplex coating layer decrease the probability of molten aluminum filtration into the substrate.