電漿化學氣相沈積矽化物於氮化鈦被覆鋼材之耐蝕性

Corrosion Resistance of The Titanium Nitride Coated Steel by Using Plasma Enhanced Chemical Vapor Deposited Silicon Compound Layer as a Top Coat

鑑於以電漿化學氣相沈積法可得非晶質、針孔少的透明薄膜，本研究乃利用此法分別以類氧化矽和類碳化矽為頂層以求改善被覆氮化鈦之鋼鐵基材的耐蝕性，並探討二者之影響因素及行為。腐蝕試驗的評估是在3.5%氯化鈉水溶液中進行交流阻抗測試，並輔以鹽霧試驗及耐候試驗以印證電化學試驗對於耐蝕性評估的準確性。結果顯示，兩種頂層被覆皆可提昇試片之耐蝕性，其成長與腐蝕行為類似，皆為一電漿聚合反應，鍍層中的化學鍵結型式並非單一，且隨被覆參數改變而改變，這可歸因於自由基一分子反應和離子－分子反應競爭的結果。因此除了頂層的膜厚影響耐蝕性之外。以類氧化矽為頂層的決定性參數為CO2/SiH4流量比，以類碳化矽頂層的決定性參數為放電功率的大小。藉著被覆參數的調整使鍍層以自由基－分子反應進行成長形成的類高分子顆粒及較高的成長速率，可得較高的膜電阻，使低碳鋼試片之極化電阻從175Ω·cm2或僅被覆氮化鈦之數kQ·cm2提昇到數百kΩ·cm2，經由鹽霧試驗和耐候試可確認高膜電阻的試片耐蝕性較佳。經過頂層被覆之試片，基本上可以滿足透明度的要求，並能保持氮化鈦鍍層之原色，在某些條件下肉眼視之，試片顏色較暗，並有干涉波紋，所幸做為頂層所需倶備的透明度之最佳範圍恰好落於耐蝕性之最佳範圍。

An attempt of using plasma enhanced chemical vapor deposited SiO2 or Sic as a top coat to improve the corrosion resistance of titanium nitride coated steel was made. Coating parameters were changed to reveal the influence on A.C. impedance behavior, salt spray corrosion resistance and atmospheric corrosion resistance. Experimental results showed that both top coats promoted corrosion resistance of titanium nitride coated steel. Growth behavior of both top coats was similar to each other and was a plasma polymerization process that was dominated by the radical-molecule reaction and ion-molecule reaction depending on the coating parameters. CO2/SiH4 ratio was found to be the most influential parameter on the corrosion resistance of SiO2 top coated speciments while it was R.F. power in the case of SiC top coated specimens. By optimizing coating parameters, e.g. SiO2 deposition at a lower CO2/SiH4 ratio or SiC deposition at a moderate R.F. power, a nodule rich film with high film resistance and the subsequent higher corrosion resistance was obtained. Microstructure observation and chemical state analysis suggested that the nodules obtained via rad-icalmolecule reaction was responsible for the higher corrosion resistance. Both top coated specimens remained basically gold yellow color with some exceptions, darker and appearing of interference strips, at extreme coating parameters.