Characterizing and understanding the microstructure evolution in CuSil (BAg-8) brazed monel joints through instrumented indentation

摘要

Microstructure evolution in CuSil (BAg-8) brazed beryllium (S-200F) to Monel 400 joints were investigated. Titanium dihydride (TiH{sub}2) was used as a wetting enhancment agent for the beryllium. Metallographic evaluations coupled with advanced characterization tools including scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS) were used in completely characterizing the observed phases. Various physical, chemical, and metallurgical inhomogeneities were detected in the system. Extensive elemental segregation and intermetallic phase formation was detected in the braze microstructure. In addition to segregation of copper and silver, large quantities of titanium were also detected in the braze microstructure. Formation of the 8(Cu-Be) intermetallic phase, accompanied by interfacial cracking, was detected on the beryllium surface. Nickel diffusion was observed out of the Monel into the CuSil braze. Instrumented indentation was used in conjunction with the microstructural evaluations to characterize differences in the mechanical properties of the various phases in the braze microstructure. This tool is useful in understanding the overall mechanical response of the system.