Analysis of ceramic-metal braze alloy systems by EPMA

Abstract

The development of advanced material systems for brazing silicon nitride-based ceramics to various metallic substrates (e.g. Incoloy 909 Fe-based superalloy) depends strongly upon the structural and chemical nature of a number of interfaces (ceramic-braze and braze-metal) as well as on the braze microstructure. Such systems are being considered for joining ceramic rotors to metal shafts in automotive applications. Coatings may be deposited on the ceramic surface prior to brazing to promote braze adhesion and wetting. These materials further complicate the resulting microstructure of the system.Electron probe microanalysis can play a substantial role in the elucidation of the resulting braze microstructures since both phase morphology, distribution, and chemistry may be obtained. Here, a PY-6 silicon nitride ceramic was brazed to Incoloy 909 by using a Mo interlayer brazed between the two materials, Figure 1. The braze is a Au-5Ni-2Pd solid solution system and was used as a 50 μm thick foil. Brazing was accomplished by holding the specimen at 1080 °C for 10 min in a vacuum furnace. A cross-section for EPMA analysis was obtained by normal metallographic methods. All EPMA data were collected using a JEOL JXA-840 coupled with a Noran 5402 EDS system. Digital, background-subtracted maps (256x256, 0.1 s/point) were collected using “IPP” software.