Effects of interface formation kinetics on the microstructural properties of wear-resistant metal–matrix composites

Hard-particle metal–matrix composites (MMC) are generally used to increase the lifetime of machinery equipment exposed to severe wear conditions. Depending on the manufacturing technology, dissolution reactions of hard phases undergo different temperature/time profiles during processing affecting the microstructure and mechanical properties of the MMCs. Therefore, quantification of the carbide dissolution effects on the microstructure and micro-mechanical properties is the key to success in the development and optimisation of MMCs. Dissolution kinetics of WC/W2C in Ni-based matrices were determined in the liquid-sintering with a well-defined temperature/time profile. Microscopic evaluation of the samples showed two intermediate layers between matrix and carbides. The layer thicknesses were quantitatively determined using image analysis. A kinetics relationship was used for modelling the interface layer growth as a function of processing time, temperature and Cr-addition. Furthermore, the micro-mechanical properties of the intermediate layers were examined using nanoindentation. Based on the chemical composition and the hardness of the intermediate layers, formation of mixed Ni- and W-carbides and/or borides on the interface microstructures was indicated. Results showed that the chemical composition and the micro-mechanical properties were almost constant within all the detected layers in the interface zone between matrix and carbides, indicating that the microstructure gradients were most dependent on the intensity of the MMC processing.

Research highlightsThe dissolution reaction kinetics and the formation of intermediate layers of tungsten carbides in Ni–(Cr)–B–Si matrices were studied in liquid-phase sintering with well-defined temperature/time relationship. ▶ The internal intermediate layer formation, close to the original primary tungsten carbide showed diffusion-controlled kinetic (∼t0.5), whereas the outside layer thickness formation, proportional to the processing time (∼t), was formed by the subsequent eutectic reaction of the Ni–(Cr)–B–Si matrix with the WC/W2C component. ▶ Cr-addition in the matrix highly influences the inner layer thickness caused probably by increasing the C-diffusion rate, whereas the outer layer thickness was not dependent on the initial Cr-content in the matrix. Generally, the Cr-addition in the Ni-based matrix increased the hardness and elastic modulus of the intermediate phases along the carbide/matrix interface. ▶ The different microstructure gradients are depended mainly on the interface growth kinetics. ▶ The intermediate layers are hard phases (carbides, borides or carbo-borides). ▶ The hardness of the carbide/matrix interface area is significantly lower as the hardness of the original primary tungsten carbides.