Effect of Al/Cr Composite Coating on Hot Corrosion Resistance of Ti2AlNb Alloy

The work aims to improve the hot corrosion resistance of Ti2AlNb alloy in high-temperature corrosion environment. Al/Cr composite coating was designed and fabricated on Ti2AlNb alloy by double-glow plasma chromizing and magnetron sputtering. Morphologies and phase composition of the coating before and after corrosion were analyzed. Meanwhile, the hot corrosion behavior of the coated samples in Na2SO4 was studied at different temperature (750, 850 and 950 °C). Al/Cr composite coating was uniform and compact, and could be bonded with the substrate well, with the thickness of about 73 μm. This protective coating could be divided into 4 layers, including Al deposition layer, Al/Cr alloy layer, Cr deposition layer and Cr diffusion layer from outer to inner, respectively. After the corrosion test in Na2SO4 at different 表面失效及防护 第 49 卷 第 2 期 李阳等:Al/Cr 复合涂层对 Ti2AlNb 合金抗热腐蚀性能的影响 ·193· temperature, the coating had a lower weight loss than the substrate. Under the condition of 750~850 °C corrosion test in Na2SO4, the coated sample had a small mass change, and the weight gain was only 0.525 mg/cm2 at 850 °C. While, the mass loss of the coated sample reached 73.571 mg/cm2 after 950 °C molten-salt hot corrosion for 40 h. The cross-section of the sample had obvious spallation, suggesting that the hot corrosion resistance of Al/Cr composite coating was degenerated. The hot corrosion resistance of the samples with Al/Cr coating is better than that of the substrate. Al/Cr composite coating has good corrosion resistance in 750~850 °C Na2SO4 salt, while the resistance decreases at higher temperature. The good corrosion resistance of coating in Na2SO4 salt environment is attributed to the formation of mixed oxidation film dominated by Al2O3 and Cr2O3, which effectively prevents the invasion of oxygen and corrosive media from the outside into the substrate.