The SPS process is based on the electrical spark discharge phenomenon: a high energy, low voltage spark pulse current momentarily generates spark plasma at high localized temperatures, from several to ten thousand ℃ between the particles resulting in optimum thermal and electrolytic diffusion. SPS sintering temperatures range from low to over 2000 ℃ which are 200 to 500 ℃ lower than with conventional sintering. Vaporization, melting and sintering are completed in short periods of approximately 5 to 20 minutes, including temperature rise and holding times.

The SPS process concentrates high energy pulses at the point of intergranular bonding offering significant improvements over conventional hot-press and hot isostatic press sintering. Now, a look at the mechanism of neck formation during the SPS process. We have already explained under Principles that when spark discharge appears in the gap between the particles of a material, a local high temperature state of several to ten thousand ℃ momentarily occurs. This causes vaporization and the melting of the surfaces of the powder particles during the SPS process; constricted shapes or “necks” are formed around the contact area between the particles. These necks gradually develop and plastic transformation progresses during sintering, resulting in a sintered compact of over 99% density.