Influence of oxygen impurity content on transient liquid phase sintering behaviour of Cu–Ni powders

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The oxygen content of a Cu powder has a significant influence on the transient liquid phase sintering (TLPS) behaviour of a Cu–Ni powder mixture. For Cu with low oxygen content, interdiffusion occurs between the Cu and Ni powders during heating and melting of the Cu phase. This interdiffusion leads to isothermal solidification of the Cu rich liquid and full TLPS behaviour. For Cu with a high oxygen content, a displacement reaction at the Cu/Ni interface occurs. Under certain conditions, this reaction leads to the formation of a continuous NiO layer over the Ni powder surface. This prevents Cu/Ni interdiffusion and wetting of the Ni particles by the molten Cu, thus eliminating the possibility for a TLPS process. Analysis of the results, indicate that the extent of NiO layer formation depends on oxygen content of the Cu, the composition of the powder mixture and the Ni particle size.