Bonding of Steels using Thermal Spray Coatings

A new method for the bonding of metals is proposed. The method includes thermal spray coatings of a self-fluxing alloy on the bonding surfaces. The bonding of mild steels, which had been spray-coated with nickel base alloy powders, was attempted at 1253-1333 K for 60 s-10.8 ks mainly in Ar gas without any bonding pressure except the dead load of test pieces themselves. The bonding region showed satisfactory metallographic structures, but only a few pores were observed. The tensile strength of the bonded joints was over 310 MPa for an optimum bonding condition. The similar tensile strength was also obtained in the bonding atmospheres of the air and a vacuum (1.33×10−2 Pa) as well as in Ar gas. Fractures occurred mostly in the diffusion zone in the bonding region where small voids were located. It is assumed that these voids might be the unbonded spots at the initial interface between the mild steel and the spray coatings.