Active Brazing Alloy Containing Carbon Fibers for Metal–Ceramic Joining

Abstract

The addition of 8.4 vol% short metal‐coated carbon fibers to an active brazing alloy increased the debonding strength of metal/ceramic joints by 18% to 28%. The carbon fibers helped to strengthen the brazing alloy and to decrease slightly the thermal stress at the brazing interface. The carbon fibers were either uniformly distributed in the brazing layer or concentrated near the ceramic side of the metal/ ceramic brazing interface. The latter resulted in a lower thermal expansion in the part of the brazing filler near the ceramic arid gave superior joints such that the debonding occurred in the part of the brazing filler without carbon fibers. The titanium in the active brazing alloy was segregated at the interfaces between the brazing filler and the ceramic, between the brazing filler and the metal (steel), and between the carbon fibers and the matrix of the brazing filler. The amount of titanium at the interface between the brazing filler and the ceramic was smaller when carbon fibers were present in the brazing filler. Titanium segregation at the fiber–matrix interface was also observed when bare carbon fibers instead of metal‐coated fibers were used. The bare carbon fibers gave joints comparable in quality to the metal‐coated carbon fibers. The carbon fibers also served to lower the cost of the brazing material.