Failure analysis of an Ag-Mg-Ni reed in a relay in aircraft applications

Abstract

The relays used in aviation electronic equipment are required to have extremely high reliability. Due to strong shock and vibration in the service process, premature failure of reeds in aviation relays is a common problem. Nonetheless, limited published investigations focus on reed failures. In this study, a reed in a force-balanced aviation relay was investigated, which comprised of internally oxidized Ag-Mg-Ni alloy. The fracture and microstructural investigation of the failed reed were conducted systematically, and the microhardness of the reed was also measured. The results indicated that the intergranular fracture occurred in the failed reed, and the failure of the reed was caused by severe Ni segregation. Abnormally large grains and remarkable difference in grain size for the core regions were observed in the failed reed, and the overall hardness of the failed reed was lower than the technical specification. The results indicated that Ni segregation led to inhomogeneous microstructure. In addition, secondary particles in the fracture surface were identified as Ni particles and oxides of Ni. Numerous nanoparticles were distributed in the grain boundaries, which led to intergranular brittle fracture of the reed. This study provides guidance on the evaluation of microstructure and failure analysis for Ag-Mg-Ni reeds.