Method of diffusion bonding and brazing of materials

Abstract

A diffusion and brazing method of bonding honeycomb core material to its facing sheets wherein the core and facing sheets have a predetermined configuration and either the facing sheets or the core edges have had deposited thereon a laminate formed of diffusion bridge or braze alloy material. First, the faying surfaces of the facing sheets and the core are positioned together with the core located between the facing sheets to form the assembly. Secondly, a male plug is inserted into the interior of the assembly wherein the dimensions of the male plug are slightly smaller than the interior dimensions of the asembly and wherein the male plug is formed from a metal having a thermal coefficient of expansion greater than that of the material of the facing sheets and core. Thirdly, the combined male plug and the assembly of the previous step is inserted into a container having an open top surface wherein the height of the container is greater than the height of the assembly and wherein the width of the container is greater than the width of the assembly thereby forming a chamber surrounding the assembly within the container. Next, the chamber is filled with pellets of ceramic, graphite or the like selected size at least to the height of the assembly to produce a positive pressure against the surface of the outer facing sheet due to their weight thereby subjecting the faying surfaces to sufficient pressure to maintain position and alignment for joining. Following this, the container and all the items placed in it in the previous two steps are heated, a protective atmosphere may be required for materials such as titanium or titanium base alloy, from ambient temperatures to a higher temperature wherein diffusion or brazing occurs. The elevated temperature is held lower than the melting point or beta transus of any of the metals involved in the process and, while this heating is continuing, the expansion of the male plug will be exerting kinetic pressure against the interior of the assembly and the pellets located within the chamber will be transferring a portion of this pressure against the outer surface of the predetermined configuration while the lack of a confining surface against the pellets from the top of the chamber allows the level of the pellets to rise and fall as a safety valve against undue pressures being exerted against the walls of the assembly. The temperature is held for a sufficient length of time to enable bonding of the materials. Lastly, the temperature is lowered by a predetermined cooling period to ambient, the protective atmosphere is maintained during cooling where required.