Papers by Author: Jiu Jun Xu

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Authors: Jun Jie Chang, Xing Guo Wang, Ying Chun Shan, Jiu Jun Xu
Abstract: The capability of Rayleigh wave to be used as a tool for the evaluation of CVD DLC coating layer has been presented in this paper. One uncoated specimen and two CVD DLC coated specimen has been used. The dispersion curves of group velocity of leaky Rayleigh wave were measured. The dispersion curve of uncoated specimen shows that the group velocities were same at different frequencies, as there is no coating layer affecting the group velocities at different frequencies. There are distinct different between ‘sound’ specimen and ‘bad bonding’ specimen as the ‘bad bonding’ specimen show unevenness on its dispersion curve.
Authors: Ying Chun Shan, Feng Zhu, Chun Long Guan, Jiu Jun Xu, Liang Wang, Xiao Guang Han
Abstract: Aluminum nitride thin film has been deposited on transparent SiAlON substrate by reactive magnetron sputtering. X-ray photoelectron spectroscopy patterns and raman spectra were used to analysis the phase composition of the thin film, and the surface morphology of the thin film was observed by atomic force microscope, which reveal that AlN thin film with smooth surface and columniform microstructure was formed. The fourier transform infrared spectral of the SiAlON substrate and SiAlON/AlN composition structure indicate that the AlN thin film has high transmittance above 99%, it is to say that the AlN thin film is transparent, and it nearly have no affect on the infrared transmittance of the SiAlON substrate.
Authors: Lie Shen, Liang Wang, Jiu Jun Xu, Ying Chun Shan
Abstract: The fine grains and strain-induced martensite were fabricated in the surface layer of AISI 304 austenitic stainless steel by shot peening treatment. The shot peening effects on the microstructure evolution and nitrogen diffusion kinetics in the plasma nitriding process were investigated by optical microscopy and X-ray diffraction. The results indicated that when nitriding treatments carried out at 450°C for times ranging from 0 to 36h, the strain-induced martensite transformed to supersaturated nitrogen solid solution (expanded austenite), and slip bands and grain boundaries induced by shot peening in the surface layer lowered the activation energy for nitrogen diffusion and evidently enhanced the nitriding efficiency of austenitic stainless steel.
Authors: Ying Chun Shan, Jiu Jun Xu, Xiao Dong He, Ming Wei Li
Abstract: A 2D kinetic Monte Carlo (KMC) simulation has been applied to study the microstructure of Ni-Cr film deposited by physical vapor deposition (PVD) for variable incident angle. In the KMC method, two phenomena were incorporated: adatom-surface collision and adatom diffusion, the interaction between atoms was described by embedded atom method and jumping energy was calculated by molecular statics calculations, initial location of adatom was located by Momentum Scheme. The results reveal that there exists critical incident angle, which is 35˚ for Ni-Cr thin film. When incident angle is less than 35˚, incident angle have less affect on surface roughness factor and packing density, compact films with smooth surface are obtained, their surface roughness factor is bellow 1.12 and packing density is more than 99.6%. However, when incident angle is more than 35˚, surface roughness factor increases quickly and packing density decreases sharply with incident angle increasing: surface roughness factor increase to 1.5 and 2.3 for incident angle of 45˚ and 60˚ respectively, packing density is below 99% and 96% accordingly. Which reveal that the self-shadowing effect emphasizes with incident angle increasing when the incident angle is more than 35˚.
Authors: Ying Chun Shan, Guang Wang, Hui Ye, Xiao Guang Han, Jiu Jun Xu, Jiang Tao Li
Abstract: Dense Y3+-dopted α-SiAlON/BN composition ceramics was fabricated by hot pressing at 1900 °C for 60 min, and flextural strength at room and 1000 °C was investigated through three-point bending test. The results show that h-BN contribute to the densification of powder body, but h-BN have little affect on the key temperature region of sintering densification of α-SiAlON ceramics. When content of BN is lower, which didn’t affect on the phase transformation of α-SiAlON, but when content of BN is higher, besides of major phase α-SiAlON, a little of β-SiAlON was also formed. For the α-SiAlON/BN composite ceramics content of 20 wt.% h-BN, the higer flexural strength( room-temperature and 1000 °C) were abtained, the formation of β-SiAlON should be an important resonon for the higher strentgh, more important is , whose flexural strength at 1000 °C is higher 50 MPa than at room temperature, the differnce of thermal properties between SiAlON and BN should contribute to the improve of high-temperature flextural strength.
Authors: Zhi Hui Chen, Jiang Tao Li, Jiu Jun Xu
Abstract: Yttrium aluminum garnet (YAG) nanopowders were synthesized by n-amyl co-precipitation method. Transparent YAG ceramics were achieved by sintering the green body at 1800°C and then 1600°C for ten hours with TEOS as sintering additive. The transmittance of the sample was 75% at visible wavelength of 800nm.
Authors: Ying Chun Shan, Hui Ye, Jiu Jun Xu, Jiang Tao Li
Abstract: The single-phase Y-α-sialon ceramics with highly optical transmittance were produced by hot pressing starting mixtures of Si3N4, AlN, Al2O3 and Y2O3 at 1900 °C for 0.5 h in a nitrogen atmosphere. The resultant sialon shows very high optical transparency in the near infrared wavelength region, about 70% for 0.8 mm thickness. In addition to highly transmittance, the Y-α-sialon also show high hardness (19 GPa) and well fracture toughness (4 MPa•m1/2), which attribute to the compound microstructure of uniform, equiaxed grain with a grain size of 2 μm and small aspect ration elongated α-sialon (<2) with a length no more than 5 μm. The high transparent was attribute to the uniform dense microstructure and pure single-phase α-sialon.
Authors: Yang Li, Liang Wang, Jiu Jun Xu, Ying Chun Shan
Abstract: The nitriding of AISI 316L stainless steels has been carried out at anodic potential in a space enclosed by an active screen that consists of two cylinders with different diameter. These two cylinders made up a hollow cathode in a discharge system. Nitriding experiments were carried out on AISI 316L stainless steel at 450°C for times ranging from 1 to 24h in ammonia atmosphere. The intensity of electron bombardment on the surface of sample was low due to the anodic sheath, the disadvantages attached to conventional plasma nitriding were completely avoided. The phase composition, the thickness and the surface topography of the nitrided layer, as well as its hardness, were investigated by X-ray diffraction, scanning electron microscopy and a micro-hardness tester. The surface microhardness values and the thickness of the hardened layers increased as the nitriding time increased. Tribology properties of the untreated and nitrided 316L stainless steel have been investigated using a ball-on-disc tribometer with AISI52100 ball as the counterface. The results showed wear resistance of the AISI 316L stainless steels were greatly increased by anodic nitriding, owing to the strengthening effect of expanded austenite formed in the modified surface layer.
Authors: Jiu Jun Xu, Ying Chun Shan, Jiang Tao Li, Yong Ge Cao
Abstract: Large scale translucent yttrium-doped α-sialon (80 mm in diameter) with the composition of Y0.4Si9.6Al2.4O1.2N14.8 (m=1.2 and n=1.0) was prepared by two-steps hot pressing sintering (first heating to 1850 °C holding for 30 min, then continue heating to 1900 °C holding for 30 min) at 25 MPa in nitrogen, and the optical property was approached over the wavelength range 900-5000 nm. The results showed that dense sample was obtained and its assemblage only consisted of single α-sialon phase. The large scale sialon had uniform and higher infrared transmittance property. The maximum infrared transmittance for 1.0 mm thick specimen could reach 66% at 3200 nm. It is attributed to the dense, uniform, equaxed microstructure. In addition to high optical transmission property, the sample showed higher hardness of 20 GPa and better fracture toughness of 5 MPa•m1/2.
Authors: Jiu Jun Xu, Ying Chun Shan, Jiang Tao Li, Qin Ji Song
Abstract: Multi-step hot pressing sintering was adopted to prepare Y-SiAlON (Y0.4Si9.6Al2.4O1.2N14.8) at 1950°C for 60 min under 25 Mpa in nitrogen atmosphere, and the microstructure was studied. The phase assemblages, microstructures and densification of the sintered samples were discussed in detail. In order to contrast to multi-step sintering, one step sintering also was adopted. The results reveal that single-phase α-SiAlON with elongated grain pattern is formed in the multi-step sintering specimens, because of holding at low temperature in multi-step sintering is helpful to reduce the kinetics of crystal growth, the mount of elongated grain in multi-step sintering samples is more than that of in one step sintering ones.
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