Spark plasma sintering behaviour of copper powders having different particle sizes and oxygen contents

Two different copper powders with different initial oxygen contents (H = high, L = low) were milled and spark plasma sintered to obtain nanosized bulk copper. The characteristics of the milled powders were analysed together with their behaviour in sintering. Spark plasma sintering was carried out at 950 degrees C for 1 min, applying a pressure of 30 MPa at 700 degrees C. The consistent difference observed between the two powders is related to the much lower particle size of powder H and its consequent higher surface oxidation. It was observed that even if the finer particle size should lead to a faster and better densification, the much higher oxide amount predominates, slowing down the sinterability of the powder. Moreover, during the sintering process, a higher electrical resistance was measured for powder H due to its higher surface (particle -particle contact area) and oxide content. The degassing process occurring on sintering, caused by the decomposition of the stearic acid used as a process control agent in ball milling, is also markedly influenced by the powder particle size, showing an anticipated decomposition in sample H due to the higher reactivity of this powder. (C) 2015 Elsevier B.V. All rights reserved.