Influence of processing conditions on the carbide/matrix interface in sintered composite layers

Metal matrix composite (MMC) coatings composed of nickel-based matrices and tungsten carbides (WC/W2C) are frequently used to solve problems of reduced life time under severe abrasive and corrosive conditions. The influence of processing conditions on the carbide/matrix interface was studied in the liquid-sintering process with a well defined temperature/time profile. Evaluation of the sintered samples by optical microscopy (OM) showed formation of an interface layer between matrix and carbides. SEM/EDS analysis indicated the formation of mixed Ni- and W-rich carbides on the interface microstructures. XRD measurements revealed the formation of Ni3B. The layer thicknesses were determined quantitatively by OM-image analysis. The hardness profiles across the interface were examined by nanoindentation. Furthermore, scratch tests were performed for the characterisation of carbide bonding in the matrix and evaluation of the influence of the interface layer on the single abrasion behaviour of the MMC samples. s show that the carbide/matrix bonding and the single abrasion behaviour were dependent on the gradient of the micro-mechanical properties. Increasing processing temperature or time increased the hardness gradient and consequently decreased the bonding between carbide and matrix. Additions of chromium and iron in the matrix powder caused an improvement of the bonding and the abrasion behaviour under 2-body-condition of the MMC samples.