Carbon fiber reinforced carbon and silicon carbide composites (C_f/C-SiC) have garnered substantial attention due to their superlative mechanical properties at elevated temperatures. In the present study, the tribological properties of 2.5D C_f/C-SiC against silicon nitride under dry friction over a wide temperature spectrum, ranging from room temperature to 800 °C, are studied by a pin-on-disc tribometer, and the microstructure is characterized by variety of methods. The results underscore that 600 °C marks a pivotal juncture where the tribological properties of C_f/C-SiC undergo a notable shift. Below 600 ℃, the friction coefficient demonstrates a clear increase with rising temperature, paired with minimal wear. For this temperature range, the main wear mechanisms are minor oxidation wear and slight abrasive wear. In contrast, above 600 ℃, a slightly lower, fluctuating plateau is observed in the friction coefficient. This is attributed to the accumulation of wear debris, the cyclical formation and breakdown of the friction film, and the softening of the friction surface. For temperatures above 600 ℃, the wear mechanism transitions into a state characterized by the concurrent presence of adhesive wear, abrasive wear, and severe oxidative wear. This study provides an in-depth understanding of tribological behaviors and wear mechanism of C_f/C-SiC at elevated temperatures.

Vibration-assisted grinding is one of the most promising technologies for manufacturing optical components due to its efficiency and quality advantages. However, the damage and crack propagation mechanisms of materials in vibration-assisted grinding are not well understood. In order to elucidate the mechanism of abrasive scratching during vibration-assisted grinding, a kinematic model of vibration scratching was developed. The influence of process parameters on the evolution of vibration scratches to indentation or straight scratches is revealed by displacement metrics and velocity metrics. Indentation, scratch and vibration scratch experiments were performed on quartz glass, and the results showed that the vibration scratch cracks are a combination of indentation cracks and scratch cracks. Vibration scratch cracks change from indentation cracks to scratch cracks as the indenter moves from the entrance to the exit of the workpiece or as the vibration frequency changes from high to low. A vertical vibration scratch stress field model is established for the first time, which reveals that the maximum principal stress and tensile stress distribution is the fundamental cause for inducing the transformation of the vibration scratch cracking system. This model provides a theoretical basis for understanding of the mechanism of material damage and crack propagation during vibration-assisted grinding.