In order to improve the quality of diamond coatings, this paper combined the chemical etching and buffer layers to deal with cemented carbide with cobalt (Co) content of 8%. Diamond coatings were prepared with hot filament chemical vapor deposition (HFCVD). The surface morphology, quality and wear property were explored by using scanning electron microscopy, X-ray diffraction, laser Raman spectrometer, and friction and wear tester. Compared to the sample with no pretreatment, samples after pretreatment have better surface morphology. There are no obvious impurities as well. Diamond crystals are uniform and compact. Friction and wear test indicated that the friction coefficient is lower than 0.1. Samples after pretreatment are much lower and steady among them. The sample using tungsten(W)-molybdenum(Mo) layer has the best surface morphology and the lowest friction coefficient. The result shows that the pretreatment combined the chemical etching and buffer layers cannot only act as the diffusion barrier, but also can improve the adhesion between substrate and diamond coatings. The effect of composite buffer layer is better than single metal buffer layers.

Diamond films were deposited on silicon nitride (Si₃N₄) substrates with three different roughnesses using the method of hot-filament chemical vapor deposition (HFCVD). The tribological properties of the film were studied by changing the deposition time, deposition distance, and methane (CH₄) concentration. The friction coefficient, delamination threshold load, and wear rate of the diamond films were tested and calculated using the reciprocating friction and wear test under dry friction conditions. The results show that, when the deposition time is 12 h, the bonding force of the film is the lowest and the friction coefficient is the largest (0.175, 0.438, and 0.342); the deposition distance has little effect on the friction performance. The friction coefficients (0.064, 0.107, and 0.093) of nano-diamond films (NCD) prepared at a 40 sccm CH₄ concentration are smaller than those of micro-diamond films (MCD) prepared at a 16 sccm CH₄ concentration. The load thresholds before delamination of R_a 0.4 μm substrate diamond film are as high as 40 N and 80 N, whereas the diamond films deposited on R_a 0.03 μm substrates have lower wear rates (4.68 × 10⁻⁴ mm³/mN, 5.34 × 10⁻⁴ mm³/mN) and low friction coefficients (0.119, 0.074, 0.175, and 0.064). Within a certain load range, the deposition of a diamond film on a R_a 0.03 μm Si₃N₄ substrate significantly reduces the friction coefficient and improves wear resistance. Diamond film can improve the friction performance of a workpiece and prolong its service life.

Bearing as the core components of high-grade CNC machine tools, with the constant change of internal clearance of bearing wear increasingly aggravated, spindle rotation accuracy reduced. In this paper, the idea of control variable method is used to explore the dynamic change of bearing clearance from different speeds and different radial loads. Starting with the dynamic model of bearing vibration, the theoretical model of rolling bearing with five degrees of freedom is established in this paper. The interaction force between steel shaft and ceramic bearing inner ring is calculated by Runge-Kutta method with elastic wall thickness ring theory, and the reduction of radial clearance of bearing is obtained. Therefore, a dynamic model of ceramic bearing considering the extrusion force of ceramic bearing inner ring is proposed. At the same time, the vibration test of steel shaft-all-ceramic bearing is designed and carried out. The test results show that under the same load, the higher the rotating speed, the shorter the time for the bearing-rotor system to reach temperature stability, and the root mean square of ceramic bearing-rotor system is obviously reduced. At the same speed, the greater the load, the more obvious the root mean square increase of the bearing-rotor system.