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Theoretical considerations, experimentally established facts, and elementary estimates lead to the conclusion that the initial stage of the sintering process may be accompanied by plastic deformation, while a later stage is controlled by diffusion-dislocation flow, in which mass transport responsible for growth of the contact neck takes place under conditions of self-consistency of the dislocation loop generation and dissolution processes. This article is concerned only with monocrystalline objects, but the conclusions arrived at in it can be extended also to real polycrystalline systems. This will necessitate regarding the structural elements of a polycrystal as obstacles to dislocation motion characterized by different degrees of penetrability. An opportunity will thus arise in particular to obtain fuller information on the initial stage of sintering of powder compacts, which are characterized by high sintering activity.

The results of model experiments confirm the validity of the hypothesis that the plastic flow of material in the contact zone is a consequence of conservative motion of dislocations in the contact region. Before the capacity for mass transport by this mechanism and hence its contribution to “activity” can be reliably assessed, it will be necessary to examine the problem of possible dislocation multiplication in the peripheral zone of the contact. At present we can only assert that this capacity is not less than that due to dislocations linked with the previous history of a material. Under conditions of a model experiment this capacity is determined by the density of dislocations generated in the vicinity of the crack mouth during cleavage. In the case of ideally brittle fracture this density might prove to be equal to zero.

A description is given of the correct procedure for processing results of model sintering experiments for the purpose of finding coefficients of self-diffusion. It is shown that the large quantity of published data on X vs t relationships has been processed without taking into account the strong influence of the initial stage of rapid contact growth, which is followed by a stage of slow growth, on the value of D determined from the X vs t relationship.