The effect of surface treatments on the brazing of iron-based powder metal compacts

Powder metallurgy (P/M) parts may be difficult to braze because molten filler metal may infiltrate porous compacts resulting in voids in the joint area. The influence of base material composition and brazing parameters on infiltration and joint filling have been studied on compacts of a pure iron powder and an alloyed powder (Fe-1.75Ni-1.5Cu-0.5Mo-0.5C). The filler metal was AWS/ANSI BNi-8. The effect of brazing temperature, filler metal amount, and compact density has been established on as-sintered compacts, as well as on compacts that were surface modified by coining, lapping and grit-blasting. Lapping and grit-blasting resulted in fully closed surface pores, making the brazing operation comparable to that of brazing fully dense parts. Coined and as-sintered compacts, with open pores, resulted in increased infiltration, but by using compacts with higher densities and a brazing temperature just above the liquidus temperature of the filler metal, the infiltration was reduced due to isothermal solidification. In this way, good-to-acceptable joints can be obtained. The results were the same with either of the base metals studied.