A Study of Sintering Using Hot-Stage Electron Microscopy

Abstract

Hot-stage electron microscopy has been used to study the sintering of b.c.c. (Fe) and f.c.c. (Fe–Ni) powders in the size range 0·005–0·2 μm, where the particles are transparent to 100 kV electrons. The observations show that in the absence of an external load dislocations play no part in sintering, even in the earliest stages of neck growth. The sphere–sphere model is employed to calculate the total climbing forces (elastic plus chemical) acting on dislocations, and elasticity theory is applied to determine the principal and maximum shear stresses generated at the weld-neck of sintering particles. Only dislocations lying very close to the grain boundary can move to the neck or the grain boundary and so contribute to neck growth. However, the maximum shear stresses generated in sintering are too small to nucleate new dislocations and it is thus concluded that neck growth is controlled solely by diffusional processes.