Effects of composition and sintering time on liquid phase sintered Co-Cu samples in microgravity

Twelve Co-Cu powder compact samples with different liquid volume fractions were processed during microgravity liquid phase sintering on a suborbital sounding rocket and three Space Shuttle missions. The processing times ranged from 2.5 minutes to 66 minutes. The samples exhibited dimension stability after sintering. Microstructural evolutions such as densification, dihedral angle, contact per grain and grain growth rates, indicated a dependency on Cu composition and sintering time. Grain growth analysis showed a diffusion-controlled grain growth mechanism. The diffusional layer was found in a microgravity processed 70vol%Co-Cu sample. A mechanism that explains the transient nature of this diffusion layer is proposed and used to explain the results at other processing times. Agglomeration and coalescence of particles were observed in this study, and the grain size distributions were in agreement with LSEM model, which incorporates the effect of higher solid volume fraction and particle coalescence. Analysis of the samples also revealed considerable pore formation and metamorphosis. Unlike the Fe-Cu samples, in which pore breakup was found, pore filling and coarsening dominate in all Co-Cu samples. The evolution of these parameters has been used to enhance the understanding of driving forces that contribute to the pore metamorphosis during liquid phase sintering in the Co-Cu system under microgravity.