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Ultra-fine WC/Co composite powders were prepared by electroless plating in this study. The Co layers with an average thickness of 50–100 nm were uniformly and completely covered on raw WC particles with a diameter of 0.3–0.5 µm. The influences of electroless plating conditions on the composites were investigated. The Co layer covering on WC particles was controlled by the content of CoSO 4 ·7H 2 O, pH value and bath temperature. With increasing the content of CoSO 4 ·7H 2 O up to 25 g/L, both the weight gain and the plating rate markedly increased. However, when the content of CoSO 4 ·7H 2 O further increased to 30 g/L, while the weight gain displayed a slight decrease, the plating rate continued to increase moderately. Moreover, with the increase of pH value from 9.5 to 11, both the weight gain and the reaction time decreased. Furthermore, the plating rate exhibited an exponential relationship with the bath temperature. When the pH value, bath temperature and the concentration of CoSO 4 ·7H 2 O are 10, 80 °C and 25 g/L respectively, the weight gain of Co-coated WC composite powders is 185.1 mg/g.

Due to excellent chemical stability, high rigidity, superior corrosion and wear resistance, aluminum oxynitride (AlON) has been considered as one of most promising candidate ceramic materials in high-performance structural, advanced abrasives and refractory fields. However, it usually exhibited relatively low flexural strength and poor fracture toughness. The study is aimed to develop silicon carbide (SiC) and zirconium nitride (ZrN) nano-particulate reinforced AlON composites with improved mechanical properties and fracture resistance via a hot-press sintering process. It was found that the addition of ZrO 2 nanoparticles would be transformed into ZrN during sintering. Due to the pinning effect of SiC and ZrN nano-particles positioned at grain boundaries of micro-sized AlON particles, the presence of SiC and ZrN nano-particles resulted in the reduction of both porosity and grain size, and a change of fracture mode from intergranular cracking in AlON to intragranular cracking in composites. With presence of 8 wt% SiC and 5.2 wt% ZrN nano-particles, the relative density, microhardness, Young’s modulus, flexural strength and fracture toughness increased. Different toughening mechanisms including crack bridging, crack branching and crack deflection were observed, thus effectively increasing the crack propagation resistance and leading to a considerable improvement in flexural strength and fracture toughness.

Aluminum oxynitride (AlON) exhibits excellent stability, chemical and mechanical properties. Corrosion resistance to molten steel is an important performance index of ceramic refractories. While silicon carbide (SiC) particles have been proven to improve the mechanical properties and thermal shock resistance of AlON ceramic, the corrosion of AlON and SiC–AlON composites by molten steel were unknown. The aim of this investigation was to evaluate the corrosion resistance to molten steel and identify the underlying mechanisms of AlON ceramic and 8 wt% SiC–AlON composites at the temperature of 1550 °C for 30 min. Due to the reaction between AlON and molten steel, a solid product of Al 2 O 3 is detected in the corrosion region. Besides, some round shaped pores form and increase toward the sample surface in the corrosion region. The thickness of corrosion region of AlON ceramic is about 150 μm, indicating that the AlON ceramic has an excellent corrosion resistance to molten steel. However, the corrosion resistance of 8 wt% SiC–AlON composites to molten steel can be characterized with a penetrated depth of approximately 250 μm. This is mainly attributed to the thermal dissociation of SiC and the reaction between SiC and molten steel.

Aluminum oxynitride (AlON) has been considered as a potential ceramic material for high-performance structural and advanced refractory applications owing to its excellent stability and mechanical properties such as high rigidity and good chemical stability. Thermal shock resistance is a major concern and an important performance index of refractories and high-temperature ceramics. While zirconium nitride (ZrN) particles have been proven to improve mechanical properties of AlON ceramic, the thermal shock behavior has not been evaluated yet. The aim of this investigation was to identify the thermal shock resistance and underlying mechanisms of hot-pressed 2.7% ZrN–AlON composites by a water-quenching technique over a temperature range between 225 °C and 275 °C. The residual strength and Young's modulus after thermal shock decreased with increasing temperature range and thermal shock times due to large temperature gradients and thermal stresses caused by abrupt water-quenching. The presence of nano-sized ZrN particles exhibited a positive effect on the improvement of both residual strength and critical temperature difference of AlON ceramic due to the toughening effects, the higher thermal conductivity of ZrN, the refined grain size and the reduction of porosity. Different toughening mechanisms including crack deflection, crack bridging and crack branching were observed during thermal shock experiments, thus effectively enhancing the crack initiation and propagation resistance and leading to a considerable improvement in thermal shock resistance in the ZrN–AlON composites.