表面Ni及Ni-Al鍍層對Ti-6Al-4V合金抗高溫氧化之研究

Effects of Surface Platings by Ni and Ni-Al on High-Temperature Oxidation Behavior of Ti-6Al-4V Alloy

本研究主要探討商用鈦合金Ti-6Al-4V （Ti-64）在施以表面Ni及Ni-Al改質後，於700 ~900℃空氣條件下的高溫氧化行為。其中，表面改質可分別為單純電鍍Ni [Ti-64（Ni）]及電鍍鎳加滲Al [Ti-64（NA）]兩種。研究結果顯示，Ti-64（Ni）在700℃時仍遵守抛物線律，而在800 ~ 900℃呈現直線律，但Ti-64（NA）在各溫度之氧化動力學皆遵守抛物線律。Ti-64（Ni）在700℃氧化主要生成NiO，此時鍍Ni層具有保護基材的作用；但當溫度上升至800 ~ 900℃時，氧化生成物則主要是TiO2，顯示鍍Ni層已失去保護作用。而Ti-64（NA）在700 ~ 800℃下生成保護性良好之α-Al2O3氧化物，但在900℃條件下卻生成α-Al2O3及TiO2兩種混合氧化物。

The effects of various Ni-Al surface modifications on the high temperature oxidation behavior of Ti-6Al-4V(Ti-64) alloy were studied over the temperature range of 700 ~ 900 ℃ in air. Two different Surface modifications were adopted in the study, including the pure electro-plating Ni [Ti-64(Ni)] and the pre-Ni plating followed by the aluminizing treatment [Ti-64(NA)]. The results showed that the oxidation kinetics of Ti-64(Ni) followed a parabolic rate law at 700 ℃, but linear kinetics were observed at 800 ~ 900 ℃. In addition, the oxidation kinetics of the Ti-64(NA) alloy followed a parabolic-rate law throughout the entire temperature range of interest.
The scales formed on the surface-modified Ti-64 alloys were strongly dependent on coating composition and temperature, consisting of an exclusive NiO at 700 ℃ for Ti-64(Ni), while an exclusive TiO2 was present at 800 ~ 900 ℃. On the other hand, the scales formed on the Ti-64(NA) consisted of an exclusive α-Al2O3 at 700 ~ 800 ℃, while both α-Al2O3 and TiO2 were detected at 900 ℃.