Ti-6Al-4V熱浸鋁及其高溫腐蝕特性

The hot-dip Aluminizing of Ti-6Al-4V and its High temperature Corrosion Characteristics

本研究使用Ti-6Al-4V（Ti64）於720℃~820℃熱浸純鋁，探討熱浸機制及熱浸鋁塗層對Ti64高溫腐蝕之作用。結果顯示，熱浸鍍之TiAl3層厚度不隨熱浸溫度與時間而有顯著變化。由於鈦與液態鋁形成TiAl3後體積大幅縮小，因此TiAl3層中的TiAl3顆粒（晶粒）均為Al所包覆。當熱浸後之Ti64再升溫到高於鋁熔點以上，晶粒間Al（l）快速沿晶與Ti64底材反應，再因體積收縮而使鋁化層呈現多孔之形貌。此多孔鋁化層之形貌於單純高溫氧化環境，因TiAl3有很好的抗氧化性，雖然是孔洞形貌，但仍僅有少量的氧化增重。但在Na2SO4-V2O5熱腐蝕，熔融腐蝕鹽沿孔洞滲入，快速破壞鋁化層侵蝕合金底材。若Ti64熱浸鋁後先於鋁熔點溫度以下持溫擴散，較緩慢的固體擴散以及較小的體積收縮，可以獲得較緻密的TiAl3層，大幅提升Ti64的抗熱腐蝕性。

In this study,Ti-6Al-4V (Ti64) was hot-dippure aluminum at 720℃~820℃to explore the hot-dip mechanism and the effect of hot-dip aluminum coating on hot corrosion. The results show that the thickness of the TiAl3layer did not change significantly with the hot-dip temperature and time. Since the volume of TiAl3formed by titanium and liquid aluminum is greatly reduced, the TiAl3particles (grains) in the TiAl3layer are covered by Al. When the Ti64 after hot dipping heats up to above the melting point of aluminum, the Al(l)rapidly reacts along the grain with the Ti64 substrate, and the aluminized layer appears porous due to volume shrinkage. The morphology of this porous aluminized layer is a simple high-temperature oxidation environment. Although TiAl3forms witha porous morphology, there is still only a small amount of oxidation weight gain, sicnce TiAl3has good oxidation resistance. However, in Na2SO4-V2O5hot corrosion, molten salt penetrates along the pores, which leads to a rapid destruction of the aluminized layer and corrosion of the alloy substrate. If Ti64 is hot-dipaluminum and then diffuses below the melting point of aluminum, the coatinghas a slower solid diffusion and smaller volume shrinkage, which leads to a more compact TiAl3layer and aimprovementof thermal corrosion resistance of Ti64.