Quasi-crystalline (QC) materials, especially Al-Cu-Fe-based systems, have attracted considerable attention due to their unique properties, such as high hardness, low friction coefficient, and good corrosion resistance. The application of QC coatings to metal substrates can significantly improve their performance in aggressive environments, particularly at high temperatures.
In this paper, the behavior of the Al–Cu–Fe–Cr QC coating formed on a titanium alloy by plasma spraying was investigated during cyclic oxidation in an air atmosphere at a temperature of 700 °C. Cyclic tests included heating the samples to a given temperature, holding for a certain time, and subsequent cooling to room temperature.
The phase composition and microstructure of the coating before and after oxidation were studied using X-ray phase analysis and scanning electron microscopy. It was shown that during cyclic oxidation, an oxide layer consisting mainly of aluminum and titanium oxides is formed on the coating surface. The formation of the oxide layer leads to a change in the phase composition of the CC coating and its degradation.
Thermal stability of the quasicrystalline Al–Cu–Fe–Cr coating is characterized by a slight increase in weight at temperatures of 650°C and 800°C. No separation of the coating from the titanium alloy was recorded during oxidation. After oxidation, aluminum oxide is formed on the surface of Al–Cu–Fe–Cr.
The quasi-crystalline Al–Cu–Fe–Cr coating was created using the low-pressure plasma spraying method. The formation of the quasi-crystalline Al–Cu–Fe–Cr structure directly depends on the annealing temperature. The initial Al–Cu–Fe–Cr coating consists of a mixture of quasi-crystalline and crystalline components.
During heat treatment, with increasing temperature, the content of the icosahedral phase first increases and then decreases, while the amount of crystalline phases decreases and the decagonal quasicrystalline phase increases. Application of the quasicrystalline Al–Cu–Fe–Cr coating improves the resistance of titanium alloys to cyclic oxidation.
Evaluation of oxidation kinetics showed that the process obeys a parabolic law, which indicates a diffusion mechanism of oxide layer growth. The introduction of chromium into the composition of the CC coating helps to increase its resistance to oxidation due to the formation of a protective layer of Cr2O3.
The obtained results allow us to evaluate the prospects of using Al–Cu–Fe–Cr QC coatings to protect titanium alloys from high-temperature corrosion.
Author: Chungen Zhou, Fei Cai, Huibin Xu, Shengkai Gong
Institute: Department of Materials Science and Engineering, Beijing University of Aeronautics and Astronautics, Beijing, 100083, People’s Republic of China