Plasma formation during electric discharge (50 V) through conductive powder compacts

Despite the large amount of research on Electric Current Assisted Sintering (ECAS) processing, this paper presents the first direct evidence of plasma formation during ECAS. Atomic emission spectroscopy revealed that Spark Plasma Sintering (SPS) under typical conditions (<10 V applied across the sample) does not generate a plasma when the electric current flows across conductive particles (e.g., ZrB2, W). The formation of plasma cannot be excluded in the case of other ECAS techniques employing higher voltages. We report the in-situ observation of plasma under pressureless conditions, in a flowing argon atmosphere and when a voltage of 50 V is applied across a 1 mm thickness loose compact of electrically conductive powder. The plasma formation produced surface cleaning as confirmed by the oxygen spectral emission lines, and high temperature localized melting (Tm ≈ 3683 K) as confirmed by microstructural analysis. The developed approach has the potential to further understand the mechanisms operating during ECAS.