Initial stage of liquid phase sintering: liquid reaction and particle growth in W–Ni–Fe–(Co)

Abstract

The initial stage of liquid phase sintering, involving liquid reaction and particle growth, has been investigated under microgravity in experiments using tungsten heavy alloys for short periods of time (8-14 seconds). The influence of different factors, such as alloy composition, plastic deformation, and non-equilibrium conditions, have been evaluated. During the liquid phase sintering of tungsten heavy alloys at about 1470°C, the liquid matrix penetrates the tungsten particle agglomerates. A fraction of the tungsten particles goes into solution in the liquid phase and the original tungsten powder size will initially be reduced. At the same time, the agglomerates of tungsten particles are effectively separated. In a second stage, larger particles grow in equilibrium with the matrix while pure tungsten particles are dissolved into the matrix. When equilibrium is reached, the tungsten particles start to grow in the liquid Ni-Fe-W matrix phase in accordance with the Ostwald ripening pro-a c b d cess. A theoretical treatment of the particle solution a powder mixture; b liquid formation; c liquid penetration; and growth during these stages is proposed. d particle separation The addition of iron and cobalt to the W-Ni system 1 Illustration of initial stage of LPS showing liquid (dark) reduces the rate of penetration and growth. Non-equipenetration of particle agglomerates (white) and librium conditions during the formation of a liquid separation of particles phase have a marked effect on the tungsten particle separation. Milling of the tungsten powder increases the initial growth of tungsten particles. PM/0942 The aim of this work is to evaluate how parameters, The authors are at the Royal Institute of Technology, such as alloying elements, non-equilibrium conditions, Department of Production Engineering, Casting of milling of the tungsten powder, and deformation of the Metals, S-100 44 Stockholm, Sweden. Manuscript powder during compaction, influence the initial part of the

Computer simulation of solution and growth processes during the initial stage of liquid phase sintering of tungsten heavy metal

“…The initial stages of LPS have been studied experimentally (Fig. 1), by Antonsson and Ekbom [7]. It was established that the reactions, which occur immediately after the matrix melts, are very rapid.…”

“…To further evaluate these initial reactions they have been divided into 3 stages: (1) dissolution, (2) dissolution and growth and (3) ripening. Expressions to describe these stages have been suggested [7]. Of course these stages overlap and occur successively as the melt penetrates the agglomerates of solid particles.…”

“…The initial part of LPS with the reaction between the melting matrix and the particles can thus be divided into 3 stages, as was suggested by Antonsson and Ekbom [7].…”

“…Several of our investigations of the initial stages, during the first 1-14 s, of LPS of this system have been performed under microgravity and have been reported previously [4][5][6][7]. Particle growth under microgravity has also been evaluated by German et al [8].…”

Tungsten grain separation during initial stage of liquid phase sintering

“…In a series of papers [8][9][10][11] the penetration of the molten W/Ni/Fe matrix into the tungsten grains and agglomerates has been treated by the authors. This paper will analyse and present a theoretical explanation to the mechanisms behind the separation and dispersion of the tungsten grains.…”