Effect of mechanical processing and heat treatment of powders on their sinterability characteristics linked with their method of manufacture

Abstract

It has already been established that the method of manufacture of a powder, including any intermediate operations such as milling and annealing, affects its sintering kinetics. This influence, hereafter called the "heredity effect," manifests itself under different conditions of sintering with different powders, and may be reflected in results of technological and theoretical investigations. Because of this, the "heredity" phenomenon deserves more detailed study, even if only within the framework of a phenomenological description. The specific densification characteristics of a powder of a certain origin manifest themselves most vividly during sintering with a rapid rise in temperature ("temperature jump") between two isothermal periods. During the temperature rise period the rate of pore volume reduction at first sharply (sometimes extremely sharply) grows and then rapidly decreases to a quasiequilibrium level characteristic of the temperature of the second isothermal step. Mechanical and thermal actions on powders and semifinished products which substantially alter their stereological properties (particle size, shape, and structure) and also their degree of work-hardening have no effect on the relative rate growth ~/v ~ (dv/dT). (i/v), where v is the pore volume and T time, in a temperature jump with a constant temperature--time The rate growth expressed as (~/v)m:(~/v) i remains within the usual limits typical of a powder of a given origin [here (~/v) m and (v/v)i are the rates of reduction in unit pore volume at the maximumand before the jump, respectively].*