Abstract
Titanium alloys are very attractive materials for aerospace, marine, and chemistry applications owing to their high strength, low density, and good corrosion resistance.However, the oxidation of alloys limits their use at elevated temperatures. Improving the oxidation resistance of titanium alloys has drawn much attention. In this work, two series of glass-ceramic coatings, a self-spalling coating and a anti-spalling coating, were successfully developed. The properties of oxidation resistance,microstructure, phases of the coating and binder were investigated.
The two series of coatings can protect TC4 alloy from oxidation at temperature ranging from 500 °C to 1000 0C. The coatings will serve as a perfect barrier to the inward diffusion of oxygen with the increase of the temperature. These coatings exhibited good stability after 600°C, which was beneficial to oxidation resistance at high temperatures. According to the electron probe X-ray microanalyser (EPMA) results, the coating had a tiny pollution to the alloy.For the self-spalling coating, the phase mainly consisted of AI2O3 with the temperature ranging from room temperature to 700 °C. The presence of TiO2,silicate, TiAl and SiAl compounds was revealed after 900 °C,which insured the good high temperature fluidity and stability of the coating. Moreover, it was demonstrated that properly increase the content of SiO2,Al2O3, and TiO2 was beneficial to improve oxidation resistance and service life.
For the anti-spalling coating, the phase mainly consisted of AI2O3 and Si02 with the temperature ranging from room temperature to 700 °C. SiAICa,SiAlNa, and silicate compounds appeared successively at the elevated temperature. Properly increase the content of SiO2,and AI2O3 was beneficial to improve the service life. The content of Na2O and CaO should be strictly controlled, especially that the content of Na2O can not more than 18%.
Coatings mixed with PAAS/Na2SiO3 binder and KH550 binder both provided better oxidation resistance. The PAAS/Na2SiO3 binder exhibited good stability after 700 °C, and the addition of PAAS was good for the self-spalling of coating. KH550 binder can reach a stable state after 600 °C, and coating mixed with the binder displayed a great self-spalling property.
Key Words: Titanium alloy; Glass-ceramic coating; Oxidation resistance; Spalling;Binder
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