Vacuum Brazing of Molybdenum – Kovar and Evaluation of its Joint Strength
This paper explains the technique of vacuum brazing for joining Molybdenum and Kovar. Joining of Molybdenum and Kovar is difficult because of difference in their mechanical properties and Melting Points. Kovar is an alloy of Fe, Ni , Co (composition : Ni 29% , Co 17% , rest Iron) . Molybdenum is a refractory material and its joint with Kovar is used for high temperature applications. Various parameters affecting the vacuum brazing process , vacuum furnace and factors affecting joint strength are discussed.Vacuum brazing of Molybdenum and Kovar samples was carried out inside vacuum brazing furnace using Copper a filler material. Vacuum level of furnace hot zone was maintained better than 10-6 mbar. The joint-strength was evaluated in Universal testing machine with the help of fixtures as per AWS C 3.2 Standard for testing strength of brazed joints. Ram tensile test was conducted. Factors affecting the joint strength of brazed joints like external compressive weight, diffusion of filler material into the parent materials, surface roughness of parent materials, surface flatness have been discussed. Joint strength of 75 MPa is obtained. Failure was found at the brazed joint interface.
P. Ramesh Narayanan and S.V.S. Narayana Murty
S. Kumar et al., "Vacuum Brazing of Molybdenum – Kovar and Evaluation of its Joint Strength", Materials Science Forum, Vols. 830-831, pp. 282-285, 2015