First-principles study of the effect of aluminum content on the elastic properties of Cu-Al alloys

CuAl alloy is an important host material for abradable sealing coatings, and its aluminum content has a significant effect on the performance of the coatings. In this article, the mechanical properties of Cu-Al binary alloys at finite temperatures were investigated using the first-principles calculation based on density functional theory. Cu-Al disordered alloys were modeled using the special quasi-random structure. The Al content of the alloys were 0 at%, 3.125 at%, 6.250 at%, 9.375 at%, 12.500 at%, 15.625 at% and 18.750 at%, respectively. Their mechanical properties at 0 K, 300 K and 870 K were investigated in combination with quasi-harmonic approximation. The results showed that the mechanical stability, shear modulus, Young's modulus, and bulk modulus of the alloy performed a decreasing trend with increasing Al content at 0 K. With the increase of temperature, all the above properties showed a decreasing trend. The shear modulus, Young's modulus and bulk modulus of the alloy with 18.750 at% Al content at 870 K decreased by 21.2%, 21.4% and 23.0%, respectively, compared with those at 0 K. With the increase of Al content, B/G ratio first decreased and then increased. The experimental results showed that the trend of those mechanical properties with Al content was consistent with the calculated results. The secondary phase appeared when the Al content is 18.850 at% in the experiment, which made an inflection point in the trend of the alloy properties. Considering the abradability and erosion resistance of the sealing coating, the Al content in the range of 15.625-18.750 at% with single alpha phase is more suitable for practical applications.