Deposition of copper coatings on internal aluminum contact surfaces by high-energy plasma spraying

The deposition of functional coatings for various purposes on internal surfaces of devices and equipment is highly requested in a wide variety of production areas. In the electric power industry, there is a problem of combining a copper‑aluminum contact pair in the conical terminals of vacuum switches with the possibility of providing a low contact resistance and a high tightening torque or compression force, respectively. In this work, it is proposed to use high-energy plasma spraying for reliable combining copper and aluminum by Cu plasma spraying onto the inner conical Al contact surfaces. For this, a unique configuration of a high-energy plasma accelerator has been developed, which ensures producing and uniform spraying of Cu material in a single short-term working process (less than 1 ms). The dependence of the amount of deposited Cu material on the value of the specific supplied energy has been established to ensure the deposition of coating with a thickness not less than 40 μm and porosity from 3 to 8%. Also, the process implementation at increased supplied energy is found to provide the Cu and Al combination with a fourfold decrease in the contact resistance in comparison with the classical method of their connection. In addition, the high-energy plasma spraying results in forming an intermediate layer between copper coating and aluminum substrate containing intermetallic phases of Al4Cu6 and Cu3Al2. This layer is characterized by increased microhardness (up to 6–12 GPa) and provides high adhesion (more than 2000 MPa) due to hydrodynamic mixing of Cu and Al.