Modification mechanism of Cu–Al alloy with pre-cladded Al/AlY layers treated by plasma nitriding: Experiments and first-principles calculations

The improvement in the properties of aluminum bronze alloys after nitriding is limited due to the immiscibility of nitrogen atoms with the copper matrix. To address this issue, a Cu-Al intermetallic compound prelayer is used, and the rare earth element Y is introduced to facilitate the diffusion of nitrogen atoms, thereby significantly enhancing the surface properties. The aluminum bronze alloy samples pre-cladded Al/AlY layers were obtained by low-temperature plasma nitriding, and the microstructure and properties of the composite modified layers were investigated. The results showed that a composite modified layer containing rich AlN→rich Cu 9 Al 4 →rich Al 6 Cu 6 Y was formed on the surface of Cu-Al alloy. The layer was closely bonded to the substrate and had no obvious defects. Compared to pre-cladded with Al, the thickness of the modified layer increased. By comparing with the modified layer, the pre-cladded AlY and nitrided sample exhibited the best comprehensive properties. This mainly depended on the concentration and distribution of N element in the modified layer. The results of first principles calculation confirmed that the addition of rare earth element Y could significantly reduce the solubility energy of N atom and greatly promote the nitriding process. Therefore, the concentration of nitride in the composite modified layer was increased, the grain was refined, and the final comprehensive performance was improved.