Diffusion processes in the sintering of nickel alloy powders with spherical particles under pressure

Abstract

Hot gasostatic pressing and subsequent annealing at 1200‡C result in the formation of 160–200-Μm diffusion zones between particles, which extend over practically the whole particle widths. During sintering under conditions of hot hydrostatic pressing, which is characterized by a shorter period of annealing at any given temperature and pressure, the widths of the diffusion zones after sintering and annealing attain 50–65Μm. The optimum diffusion zone width in the sintering of particles making good contact with one another (pure and even surfaces) is about 30–40Μm. However, the presence of oxides, carbide phases, and more complex compounds on the surfaces of particles substantially increases the optimum width of this zone. In such a case the optimum width is determined by the need for diffusion to cross interparticle contacts with diffusion-inhibiting barriers. In view of this, for particles of the nickel alloys investigated the optimum diffusion zone width may be taken to be ∼100Μm. At this width there are no areas in which the diffusion zone width is less than 40Μm, i.e., the minimum thickness at which strong bonds can be expected to form between particles.