Tungsten Copper Electrode Sintering Mechanism and Densification II

Viewed from the diagram, the particle with deep color, cladded internal is tungsten (W), and the external particles in white is copper (Cu), the particles contacts by point. In the solid-phase state, the shrinkage of powder takes up 1/3 shrinkage of total volume. Generally, tungsten copper W-Cu powder does not shrink in the solid-phase state. However, if the temperature rises up to or exceeds copper recrystallization temperature during the copper powder sintering, it will remarkably sintering in solid-phase.

In addition, tungsten grain of tungsten copper nano composite powder is disperse at the beginning, basically Cu phase contacts with each other. Therefore, some related researchers propose that Cu solid-phase sintering at the temperature lower than copper liquid is the main mechanism of sintering densification, and the internal tungsten grains cladded in Cu blocks out the sintering process to some extent.

Picture a to picture c shows that due to the diffusing and flowing effect of copper liquid, the contact area of particles is expanding, the internal gas is extruded so that the compact densification. Tungsten particles close to each other and in contact gradually under the action of the flow of fluid passing copper will eventually gather and grow up under the influence of interfacial tension.

Picture a is the initial status of compact, which powder is disperse and the contact of particles is point with small contact area, the small tungsten grain inside of Cu phase is separated by the larger Cu grain; Picture b shows that with the increasing sintering temperature gradually, the tension of diffusion of surface atoms and surface tension force it to flow to the contact, the contact area expands, the pores shrinks and the internal tungsten grain cladded by Cu phase get close, gathers and grows up by the flowing copper liquid and interfacial energy; Picture c, with the temperature increasing further, the contact area is becoming larger, the pore is shrinking to ball-shaped, tungsten grain is gathering and composed of the larger grain, which blocks out copper solid-phase sintering further.