Experimental brazing filler alloys have been developed containing tem¬perature depressants which have been volatilized during the brazing of stain¬less steel leaving joints of high remelt temperature. The mechanisms by which remelt temperature is increased have been studied for the range of alloys investigated which contained nickel, chromium, germanium, iron, lithium, and phosphorus. The two main mechanisms are (i) dissolution of the base metal in the filler metal and diffusion of constituents of the filler metal into the base metal and (ii) volatilization of the filler metal con¬stituents.nIt has been shown theoretically and experimentally that in order for re¬melt temperature to increase there must be solid solubility of the diffusing or volatile element in the filler alloy. Although compositional changes may result from either mechanism, a remelt temperature change does not necessarily occur. The degree to which a compositional change affects remelt temperature is proportional to the solid solubility.nIn this program, vacuum pumping was the more efficient apor-removal method among several discussed and investigated. Furthermore, under vacuum the surface-area-to-volume ratio of the filler alloy becomes less rate-controlling due to boiling. Boiling, however, causes porosity in the joint.nOf the alloys investigated a 61% Ni-39% in alloy exhibited the greatest remelt temperature rise due to volatilization alone, whereas a 94% Ni-6% P responded only to dissolution and diffusion to exhibit the largest rise in remelt temperature due to this mechanism. Ni-Cr-In-Ge alloys exhibited a substantial rise in remelt temperature due to the operation of both mecha¬nisms. This alloy and the binary Ni-In alloy can be considered practical al¬loys for high-temperature usage.nA direct effect of metallic vapors on wetting and flow of the filler al¬loy was observed and subsequently discussed with respect to their influence on surface tension relationships. It has been' shown that in the presence of metal vapors, discoloration of the base metal, wetting, flow, and skull for¬mation of the filler alloy are functions of the rate and quantity of metal vapor removal.
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