HOT CORROSION RESISTANCE OF Cr_(1-x)Al_xN COATINGS ON A Ti_3Al BASED ALLOY IN DEPOSITED(Na_2SO_4+K_2SO_4) MOLTEN SALT AT 800℃

Cr_(0.82)Al_(0.18)N and Cr_(0.53)Al_(0.47)N coatings were deposited on a Ti_3Al based alloy by reactive magnetron sputtering method.Hot corrosion of these two coatings in 75 mass%Na_2SO_4+25 mass%K_2SO_4 molten salt at 800℃was performed in a Setsys 16/18 thermoanalyzer.The phase compositions of the corrosion products were identified by X-ray diffractometer(XRD).Both the surface and cross-sectional morphologies of the samples were observed by a scanning electron microscope(SEM).The results showed that both Cr_(0.82)Al_(0.18)N and Cr_(0.53)Al_(0.47)N can reduce the hot corrosion rate of the Ti_3Al based alloy and their hot corrosion resistance decreases with increasing aluminum content;the main corrosion products of the coatings are Cr_2O_3 andθ-Al_2O_3 and the amount ofθ-Al_2O_3 in the corrosion products is proportional to the Al content in the coating.The better hot corrosion resistance of Cr_(0.82)Al_(0.18)N coating can attribute to the high stability of Cr_2O_3 in the molten salt.