Papers by Author: Wen Yue

Abstract: The stability of SiC and SiO₂ in helium with little water vapor is studied in this paper in order to confirm whether they can service as anti-oxidation layers on the surface of fuel elements of high temperature gas-cooled reactor (HTR) under water-ingress accident. Through thermodynamic analysis, it is found that the influence factor controlling the critical temperature of passive oxidation for SiC in He-H₂O is the partial pressure of H₂O; the critical temperature of passive oxidation for SiC increases with the partial pressure of H₂O. The influence factors controlling the critical temperature of decomposition for SiO₂ are the partial pressure of H₂O and the amount of H₂O in gas for 1 mol SiO₂, the critical temperature of decomposition for SiO₂ increases with the partial pressure of H₂O while it decreases with the amount of H₂O in gas for 1 mol SiO₂. SiO₂/SiC composite coating is more suitable than SiC coating in He-H₂O with little H₂O.

Abstract: The combination of diamond-like carbon (DLC) coatings and fluid lubrication is an efficacious method to improve the performance and service life of the friction-pairs working under the severe conditions, but the synergistic effect of DLC coatings and lubricant additives have not been clearly unveiled. The synergistic effect of Cr-doped DLC coatings with different Cr content and the lubricant additives of ZDDP, MoDTC, and T307 on the wear of DLC-coated stainless steel sample was studied, and it was found that the wear resistance of DLC-coated stainless steel sample can be further improve by the combination of DLC coatings and fluid lubrication; doping DLC coatings with Cr at an optimum level is beneficial for the wear resistance of DLC-coated stainless steel sample lubricated by PAO, PAO+ZDDP or PAO + MoDTC, but DLC coatings with a moderate Cr content is harmful to the wear resistance of DLC-coated stainless steel sample lubricated by PAO+T307. The synergistic effect of T307 and undoped DLC coatings or Cr-doped DLC coatings with a Cr content of 23.3 % is the best, while the three studied lubricant additives are harmful for the wear resistance of DLC coatings with a Cr content of 2.4 %.

Abstract: Si-C-N-O amorphous films were fabricated at about 800°C by pyrolysis of poly- vinylsilazane precursor films in a vacuum oven under N₂ flow. The polymer precursor films were prepared onto Si wafers by spinning from a solution of the polymer. The compositions of the as-prepared films were confirmed by X-ray diffraction, Fourier transformation infrared spectroscopy, and x-ray photoelectron spectroscopy. SEM analysis indicated that the films can be formed with thickness more than several micrometers, and very smooth surfaces. Such films will be promising in application of protecting equipments in high-temperature, corrosive and wear environments.

Abstract: The electrical properties of ZnO-Pr6O11-based varistors, which composed of (98.5-x)mol% ZnO +0.5mol% Pr6O11 +1.0mol% Co3O4 +xmol% Cr2O3 (x=0.0, 0.25, 0.5, 1.0, 2.0), were investigated as a function of sintering temperature in the range of 1250-1400°C for 2 h. At the same sintering temperature, the nonlinear exponents increased with the increase of Cr2O3 doping amount no more than 0.5mol%, but decreased with more Cr2O3 doped. With the same doping level of Cr2O3, the samples' varistor voltage decreased with the sintering temperature increased; and the samples' nonlinear exponents increased first with the sintering temperature increased to 1300 °C, but decreased when the temperature increased further. Conclusively, the electrical properties of ZnO-Pr6O11-Co3O4- Cr2O3 varistors were strongly affected by the sintering temperature and the doping level of Cr2O3, and the samples, doped with 0.5 mol% Cr2O3 and sintered at 1300 °C, exhibited the optimum nonlinear performance.

Abstract: This work investigated the wear behavior of cemented carbide cermet YG8B under different concentrations of abrasive slurries using a modified ASTM B611 wet sand rubber rimmed wheel test system with a load of 225 N. The angular sand abrasives involved in carborundum, corundum and silica with particle size of about 350 μm, and were dispersed into water with different mass fractions. It was found that, with increasing sand concentration in slurry, the wear loss of the cermet samples increased, and with the increase of duration time, the wear loss of the cermet samples also increased. Under the same conditions, the cermet samples presented the biggest wear loss with carborundum as abrasive. On the basis of the observations on the worn surfaces by scanning electron microscope and 3D white-light interfering surface profiler, the wear mechanism of the cermet samples was proposed, which includes in extensive plastic deformation, groove, fracture and pullout.

Abstract: Ti-doped DLC films were synthesized from C2H2 and Ti by ion beam deposition and magnetron sputtering, and the influence of Ti target current on the structures and the friction coefficients of Ti-doped DLC films were studied by SEM, AES, XPS, a ball-on-disk friction tester. The Ti content in Ti-doped DLC films is below 1at% when Ti target currents rise up to 3.5 A; but when Ti target current exceeds 3.5 A, Ti content in the films is obviously increased with increasing Ti target current. Ti-doped DLC films have a smooth dense surface with several particles dispersed in it and the surface morphology deposited with different Ti target currents is similar. With the augment of Ti target current, the ratio of sp3-C to sp2-C is almost a constant first, and then an obvious rise followed by an abrupt decrease is found; but only when Ti target current is above 5A, the ratio of TiC-C to sp2-C is obviously increased with Ti target current. The lowest friction coefficients are obtained for the Ti-doped DLC films with the highest ratio of sp3-C to sp2-C and a low ratio of TiC-C to sp2-C.