Carbon fiber-reinforced carbon and silicon carbide (C_f/C–SiC) composites have garnered substantial attention because of their superior mechanical properties at elevated temperatures. In the present work, the tribological properties of 2.5D C_f/C–SiC against silicon nitride under dry friction over a wide temperature range, ranging from room temperature (RT) to 800 °C, are studied with a pin-on-disc tribometer, and the microstructure is characterized via a 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 °C, the friction coefficient clearly increases with increasing 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 °C, 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 °C, 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 the tribological behavior and wear mechanism of C_f/C–SiC at elevated temperatures.

Significant advancements in ultra-precision machining technology have forced a re-examination of the spindle perpendicularity errors’ impact on the milled surface quality at the micro-nano scale. In this paper, a method of spindle precision adjustment is proposed to enhance surface finish quality. Sensitive errors in the machining process are identified using multi-body kinematic theory, with the milling process serving as an example. A two-degree-of-freedom (2-DOF) rotation platform is designed, optimized, and fabricated. The platform’s static model is established based on elastic beam theory and verified by finite element analysis. Structural parameters are optimized via the response surface method in combination with the Pareto front. Experimental results reveal the effects of spindle speed, voltage amplitude, vibration frequency, cutting depth, and feed rate on the platform’s modulation performance. The static modulation experiment shows that the perpendicularity error between the spindle and the guideway can be reduced from 92.5 μrad to 0.25 μrad. Finally, milling experiments show that the surface quality can be improved by 37.6% after spindle modulation.

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.