Abstract
In present study, a quantitative analytical approach has been taken to evaluate means to protect copper alloys (nickel silvers) against surface discoloration under the exposure of high temperatures. The aim is to propose future direction to further improve the surface protection against oxidation for nickel silver plates. Two approaches have been taken: one is to apply surface coating, another is to refine the subsurface grain structure in the bare substrate. Samples of nickel silver (C7521 and C7701) with and without surface coatings were exposed to 300°C and 350°C, respectively, for lOmin. Tested samples were then subjected to spectral colorimeter studies; phase identifications were carried out by XRD. In addition, the coating procedures were carefully studied in order to determine the optimal processing parameters for yielding the maximum protection. In conclusions, coating thickness does not affect the resistance against discoloration, pre-treatment of the substrate surfaces as well as the concentration and soak time of the anti-discoloration solutions can greatly influence the performances of the entire system against the occurrence of surface discoloration. ©2009 The Thermoelectrics Society of Japan.