Characterization of silicon carbide joints fabricated using SiC particulate-reinforced Ag-Cu-Ti alloys

CVD silicon carbide was brazed to itself using two Ag-Cu-Ti braze alloys reinforced with SiC particulates to control braze thermal expansion and enhance joint strength. Powders of the braze alloys, Ticusil (composition in wt%: Ag-26.7Cu-4.5Ti, T-L: 900 degrees C) and Cusil-ABA (Ag-35.3Cu-1.75Ti, T-L: 815 degrees C) were pre-mixed with 5, 10 and 15 wt% SiC particulates (similar to 20-30 mu m) using glycerin to create braze pastes that were applied to the surfaces to be joined. Joints were vacuum brazed and examined using optical microscopy (OM), field emission scanning electron microscopy (FESEM), energy dispersive spectroscopy (EDS) and the Knoop hardness test. The SiC particles were randomly distributed in the braze matrix and bonded to it via reaction with the titanium from the braze alloy. Titanium together with Si and C segregated at the particle/braze interface, and promoted nucleation and precipitation of the Cu-rich secondary phase on particle surfaces. The Si-Ti-C-rich reaction layers also formed at the interface between CVD SiC substrate and the braze alloy. The loss of Ti in the reaction with SiC particulates did not impair either the bond quality or the thickness of the reaction layer on the CVD SiC substrate. Microhardness measurements showed that the dispersed SiC particulates lowered the braze hardness by depleting the braze matrix of Ti. Theoretical calculations indicated the CTE of the braze to decrease by nearly 45-60% with the incorporation of about 45 vol% SiC. (C) 2012 Elsevier Ltd and Techna Group S.r.l. All rights reserved.