MECHANISMS OF LIQUID-PHASE SINTERING IN IRON-COPPER POWDER COMPACTS.

When iron copper powder compacts were liquid-phase sintered in a dilatometer, three stages of dimensional change were observed: (I) rapid shrinkage, attributed to rearrangement, (II) rapid expansion, dominated by liquid penetration of grain boundaries, and (III) shrinkage initiated by agglomeration and sustained by solid state sintering mechanisms. No significant shrinkage could be attributed to solution-precipitation effects. During stages I and II, complete wetting (dihedral angle phi less than equivalent to 0) prevailed. It is argued that solid-liquid interfacial energy is lowered by a concentration of oxygen in the liquid at solid-liquid interfaces, associated with diffusion of copper across the interfaces. When the iron locally nears saturation with copper (end of Stage II), oxygen no longer segregates, gamma //S//L and phi greater than 0 prevails. The effects of several sintering variables are examined and discussed.