陰極電弧放電離子被覆抗蝕性鋅鎳合金鍍膜的研究

A Study on the Corrosion-Resistant Cathodic Arc Plasma Deposited Zn-Ni Coating by using Alloy Target

鑑於抗蝕鋅鎳合金鍍膜的使用日益廣泛，卻存在著電鍍製程的環境相容性以及潛在氫脆所衍生之問題，故本研究乃嘗試以真空鍍膜技術取代電鍍，採用高沉積速率的陰極電弧放電離子被覆法在AISI 304不銹鋼基材上被覆鋅鎳合金鍍膜，並觀察鍍膜表面及截面形態、分析鍍膜組成及晶體結構。另進行動電位極化試驗量測鍍膜試片在3. 5 wt% NaCl溶液中的腐蝕電位及腐蝕電流值。藉此評估陰極電弧放電離子被覆法製備鋅鎳合金鍍膜之可行性。研究結果發現，Zn73Ni27為脆性靶材，臨界靶電流極小。在艙內低工作壓力下靶面電弧呈現單點離化並緩慢移動，容易造成靶材過熱熔化導致剝落。在提高工作壓力後，則靶面電弧轉成多弧且快速移動，靶材離子通量變大，較適宜用於鍍膜沉積。以Zn73Ni27為靶材可被覆在AISI 304不銹鋼表面形成鍍膜，其主相為γ-Zn21Ni5和γ1-Zn3Ni，所得膜厚約2-3 µm。鍍膜表面有許多的微粒附著於鍍膜表面。鍍膜組成元素為Zn87Ni13，顯示鍍膜中的鋅含量高於靶材中的鋅含量。動電位極化試驗結果顯示：鍍膜能夠提供適度的陰極防蝕。雖然如此，Zn73Ni27合金靶在放電被覆過程中有容易碎裂的問題，有待克服。

In considering the popularly used corrosion-resistant Zn-Ni alloy coatings by electro plating, the environmental compatibility and hydrogen embrittlement problems are generally encountered. Cathodic arc plasma ion plating technology capable of high-speed deposition seems to be an alternative of electroplating. In this study, such a process was chosen to deposit Zn-Ni alloy coatings on AISI 304 stainless steel. The coating surface and cross sectional view of the deposited alloy coatings were observed, and the film composition and crystal structure of Zn-Ni alloy coatings was analyzed. Potentiodynamic polarization experiment was carried in aerated 3.5 wt%sodium chloride electrolyte to evaluate the feasibility of corrosion protection for the Zn-Ni alloy coatings deposited by cathodic arc plasma ion plating. Experimental results show that target Zn73Ni27 is brittle and its critical arc current is very small. At low working pressure the slow-moving single arc spot on the target surface induced local overheating on target, and caused chipping near target edge. When the working pressure was increased, the arc was split into multiple spots. The spots may move more rapidly on the target surface thus emitting higher ion flux suitable for Zn-Ni alloy depositing. The major phases in the deposited film are γ-Zn21Ni5 and γ1-Zn3Ni, and the thickness of the deposited film is about 2-3 m, with many microparticles on the film surface. The chemical composition of the Zn-Ni alloy film is Zn87Ni13 with Zn composition higher than that of the target source. The results of potentiodynamic polarization experiment show that Zn-Ni film increases the corrosion resistance. A problem of brittle failure of the target Zn73Ni27 during coating is pending.