Densification mechanism of fine Ni-20Cr powder during pulsed electric current sintering

Microstructure observation and kinetic analysis were conducted on fine Ni-20Cr powder (spherical shape and 5 mu m in average particle diameter) to understand the sintering mechanism of fine metallic powder during pulsed electric current sintering (PECS). Insulation of the sample during PECS was carried out to investigate the influences of pulsed electric current passing through the sample. Temperature at the sample/die interface was measured as sample temperature. Pulsed electric current did not influence densification. The microstructure observation revealed that the necks between particles had very small curvature radius, which means the neck formation by compressive deformation of particles owing to creep. As results of the kinetic analysis of the densification, the creep rate of fine Ni-20Cr powder was two digits larger than the extrapolated values of the steady-state creep on PECS of coarse Ni-20Cr powder and creep tests reported previously. The larger creep rate of fine Ni-20Cr powder during PECS may be influenced by not only smaller grain size of powder particles but also contribution of the initial creep, which was faster than the steady-state creep.