The applicability of P/M processing can be extended by joining different segments together. One of the recent innovations in joining P/M components is the sinter joining process, where bonding takes place simultaneously with sintering.
The process has been reported to produce strong bonding and to be cost effective. In this study, the behavior of sinter joining between P/M compact and wrought material has been studied by fitting and joining ring shaped compact of $Fe-Fe_3P$ mixed powder to cylinder shaped low carbon steel.
The results are as follows;
1) It was found that shrinkage of the compact during sintering was the most important factor affecting the bonding strength.
2) The mechanism of sinter joining between P/M compact and wrought steel is similar to that of diffusion bonding of wrought steel.
3) The bonding strength was increased as the phosphorus content in the compact increased. This is due to the fact that phosphorus enhances sintering, and in turn causes higher shrinkage, by promoting formation of α phase, in which self diffusivity of Fe is about 100 times higher than in γ phase.
4) The bonding strength was increased with sintering temperature and sintering time. It is, however, noted that the effect of sintering temperature is greater than that of sintering time.
5) Investigation of the fracture surfaces of specimens showed two types of fracture modes, fracture at the imperfect joint and fracture at the base metal. Higher bonding strengths were obtained when the fracture occured at the base metal.
6) In order for the fracture at the base metal to occur, the grain must grow to cross the original interface between P/M compact and wrought steel. So trans-interfacial grain growth is one of the requirements for the optimum bonding in sinter joining.
