Development and Characterization of CuCr Composite Coatings & Thin Films as Contact Materials for Vacuum Interrupters

Abstract

CuCr composites are widely used as high-performance contact materials in medium voltage Vacuum Interrupters, especially in switching applications up to 145kV. These composites exhibit exceptional properties, including high conductivity, excellent hardness, and superior arc-erosion resistance compared to other solid solution copper alloys. To enhance the manufacturing efficiency of traditional composite manufacturing methods, this study explores two coating techniques: 1) CuCr cold spray, which produces coatings with lower Cr content, and 2) Vacuum Arc Plasma Deposition (VAPD), which produces films with high Cr content. While recent research has shown promising results in arc-erosion behavior and overall breakdown performance with nanostructured composites, conventional methods for producing CuCr composites are limited in achieving nanometer sized microstructures. The proposed VAPD technique produces nanostructured CuCr films, as it achieves atomic scale mixing, and also offers the opportunity to explore non-equilibrium microstructures that are challenging to obtain using current production methods. The current study is structured into three parts. In Part 1, CuCr coatings are produced using cold-spray deposition, where deposition pressures are adjusted to manipulate critical velocities of depositing powders. This impacts a coating’s internal porosity and conductivity, both of which are critical for contact material applications. The microstructures of the cold-sprayed CuCr coatings are analyzed, and properties such as residual stresses, hardness, and conductivity are measured. The breakdown performance of these coatings is established by comparison with bulk CuCr composites produced through traditional manufacturing methods. Part 2 explores VAPD CuCr films produced with co-deposition technique by varying Cu/Cr cathode currents. Higher ion-fluxes result in Cu-self sputtering phenomena, leading to compositional non-uniformity across the films. The coatings developed through VAPD exhibit a sub-micron layered Cu-Cr structure, attributed to high adatom mobility and phase separation of the immiscible elements on a sub-micron scale. SRIM calculations are performed to validate the high sputtering yield of Cu from the films under the bombardment of high energy Cu and Cr ions. Part 3 focuses on producing CuCr films using single composite cathode with 65% Cr content, achieved through a pressure-less infiltration technique. The deposition process is carried out under different substrate biasing conditions to study the effects of incident ion energies on microstructure, compositional uniformity, and film density. The hardness and electrical properties of the films are measured. Finally, the vacuum breakdown performance of the CuCr films is established and compared against traditional bulk composites with similar compositions. This study contributes to a comprehensive understanding of CuCr coatings and films, especially on various sub-micron and nanoscale CuCr microstructures that can be obtained, their corresponding properties, and breakdown performance. The findings hold promise for advancements in producing high-performance contact materials.