Brazing of carbon-carbon composites: Filler metals and techniques for brazing carbon carbon composite to metals

Carbon-Carbon composites are attractive for use at high temperature because of their high strength, modulus, chemical stability and resistance to activation by radiation. These properties make them ideal for many aerospace and nuclear applications. In the Tokamak nuclear fusion reactor, the C-C composites are a candidate material for the armor tiles of the reactor's first wall and diverter structures.; In these applications, the C-C composite must be joined to itself and to metals. Developing a method for joining C-C composites to metals such as stainless steel (SS) and refractory metals (Nb, Zr, Mo and W) is one of the most difficult challenges to be overcome.; The research described in this dissertation has led to the invention of a new brazing filler metal from the Cu-Mn-Ti system and the development of a brazing process for joining C-C composites to metals. The newly invented brazing filler metal compositions, with controllable melting points ranging from 800-920{dollar}spcirc{dollar}C has excellent wettability on both C-C composites and metals (stainless steel, Nb, Mo, W, and Zr). Sound joints of C-C composite/metal were produced using the brazing filler metal and the specially developed brazing processes. The composition of the Cu based brazing filler metal Cu-Mn-Ti is 15-25% Mn, 8-14% Ti, with minor elements Sn, Si and Ni (total {dollar}<{dollar} 6%). A patent on this brazing composition is currently being pursued by RCT incorporated as an agent for Auburn University.; The C-C composite/metal joints were brazed in a vacuum chamber (1 {dollar}times{dollar} 10{dollar}sp{lcub}-4{rcub}{dollar}-10{dollar}sp{lcub}-6{rcub}{dollar} torr) at brazing temperatures of 850-950{dollar}spcirc{dollar}C using a holding time ranging from 2 to 10 mins. The shear strength of the resulting joints was between 15-20 MPa.; Finite element analyses were used to predict the residual stress distribution in the brazed joints. Theoretical predictions were confirmed by interlayer experiments.; The brazed joints were studied using optical and scanning electron microscopy (SEM) to examine the microstructure and fractured brazed joints. The results showed 100% bonding was obtained using the developed braze metal and brazing procedure.