Joining of Carbon‐Carbon Composites by Graphite Formation

Abstract

Joining of carbon‐carbon (C‐C) composites by graphite formation, using manganese, magnesium, and aluminum interlayers, has been investigated. The process involved the formation of a metal carbide by chemical reaction between the metal interlayer and the composite, followed by the decomposition of the carbide and evaporation of the metal at elevated temperatures. The maximum bonding temperature in these experiments was 2200°C. Bonding of composite specimens occurred when manganese or a powder mixture of aluminum and graphite was used as interlayers. Attempts to join C‐C pieces using a magnesium interlayer were unsuccessful. The double notch shear strengths of the joints produced using Mn interlayers were very low and ranged from 0.15 to 1.61 MPa at test temperatures of 1200° and 1400°C. The interlayer, after completion of the joining operation, consisted, in most cases, only of graphite. The joints produced with aluminum plus graphite interlayers were even weaker, with strength values of 0.11 MPa or less. The presence of aluminum could be detected in some of these joints, suggesting incomplete dissociation of Al 4 C 3 at the maximum bonding temperature of 2150°C.