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An K.,Taiyuan University of Technology | Liu X.-P.,Taiyuan University of Technology | Li X.-J.,The Ningbo Branch of Ordnance Science institute of China | Zhong Q.,Taiyuan University of Technology | And 3 more authors.
Rengong Jingti Xuebao/Journal of Synthetic Crystals | Year: 2015

According to the demand of high-power MPCVD device, a novel model of high-power MPCVD reactor for diamond films deposition was introduced. HFSS was preliminary used for size optimization in all parts of the device. COMSOL was used to simulate the electric filed and the plasma distribution when the gas was dissociated under high pressure and power, COMSOL was also used to verify the in and out way of the gas. The new reactor with the proposed geometry was constructed. The experiment of large-area diamond film was deposited under high pressure and power with the new reactor. The simulated and experimental results show that the reactor exhibit excellent focusing capability after the structure optimization. Meanwhile the electric field strength is larger than the similar unit reported by others. The plasma and reactant gas were evenly distributed only on the substrate. The plasma is isolated with the quartz window by the middle cavity, which effectively protects the quartz window from the etching of plasma. By using our new reactor, the deposition of high quality and large-area diamond films with high growth rate under high power and gas pressure can be obtained. ©, 2015, Rengong Jingti Xuebao/Journal of Synthetic Crystals. All right reserved.

Li X.,Central South University | Song Y.,Central South University | Ni P.,The Ningbo Branch of Ordnance Science institute of China | Liu F.,Central South University
Jinshu Xuebao/Acta Metallurgica Sinica | Year: 2015

To solve such problems as sensitivity to noise and low accuracy of grain size evaluation using traditional ultrasonic time-domain attenuation method, an ultrasonic nondestructive evaluation model based on multiscale attenuation coefficient was proposed. The distribution of time-scale of ultrasonic energy was obtained by means of wavelet transformation, then to calculate the distribution of attenuation coefficient with scale, and to make a comprehensive analysis of attenuation characteristics of various scales. After the weighted multi-scale ultrasonic attenuation coefficient was defined, a multi-scale ultrasonic attenuation evaluation model was established on the basis of combination of optimal dimension and normalized weight distribution strategy designed by particle swarm optimization. 304 stainless steel was used in the test. The distribution of attenuation coefficient with scale shows that ultrasonic wave of small scales attenuates fast, presenting the frequency characteristics of ultrasonic attenuation among high scattering materials. Following increase of the sample grain size, ultrasonic attenuation of all scales was intensified significantly. Test results show that the sound velocity method, the traditional evaluation method and the proposed method have maximum systematic errors of +12.57%, +5.85% and -1.33%, respectively. With these 3 methods, evaluation results of the sample with a mean grain size of 103.5 μm measured by metallographic method are (110.4±7.8), (98.2±6.6) and (101.7±3.9) μm, respectively, showing that the presented method can not only reduce the systemic error, but also can effectively control the random error by constant Q filtering properties of wavelet transformation. This model can be extended to grain size evaluation of other metals. © Copyright.

Yu S.,Taiyuan University of Technology | An K.,Taiyuan University of Technology | Li X.,The Ningbo Branch of Ordnance Science institute of China | Shen Y.,Taiyuan University of Technology | And 4 more authors.
Hongwai yu Jiguang Gongcheng/Infrared and Laser Engineering | Year: 2013

Polycrystalline diamond films were prepared by using H2-CH4 as the source gas in a newly developed ellipsoidal cavity type MPCVD reactor. The influence of CH4 concentration on the diamond growth and quality was studied in this paper. On the basis of the above research, large area optical grade free-standing diamond film was prepared. Surface and cross-sectional morphology as well as the quality of the diamond films were examined by scanning electronic microscopy and Raman spectroscopy. Furthermore, the infrared transmittance of the samples was measured by Fourier transform spectrometry. The results show that the growth rate of the diamond films increases with the increase of CH4 concentration. However, when the CH4 concentration is increased to certain level, the diamond growth rate will no longer increase. High quality diamond films can be prepared when the CH4 concentration is between 0.5%-2%. The results prove that high quality optical grade diamond films can be obtained by this newly developed ellipsoidal cavity type MPCVD reactor.

Hu H.-W.,Changsha University of Science and Technology | Li X.-B.,Central South University | Yang Y.,Central South University | Ni P.-J.,The Ningbo Branch of Ordnance Science institute of China | Tong L.-J.,Central South University
Zhongnan Daxue Xuebao (Ziran Kexue Ban)/Journal of Central South University (Science and Technology) | Year: 2012

An automatic method of inspecting porosity in CFRP (Carbon fiber reinforced plastic) with complex surface by ultrasonic was presented. Through-transmission mode was used to obtain ultrasonic signals of CFRP test blocks with given porosity, and phase-unwrapping method was used to calculate the test blocks phase velocity, and an ultrasonic inspection model based on the relation between phase velocity and porosity was established. The 3D surface data of CFRP with complex surface were obtained by ultrasonic measurement, and then the inspection path was planned after the CAD model had been reconstructed. A multi-degree-of-freedom manipulator was used to acquire ultrasonic signals of CFRP with complex surface, and its porosity was calculated according to the ultrasonic inspection model presented. In order to verify the validity of the presented method, microphotography was used to get the porosity of CFRP with complex surface after block slitting and polishing. The results show that the porosity inspected by the ultrasonic method is in good agreement with that obtained by microphotography.

Hei H.,Taiyuan University of Technology | Ma J.,Taiyuan University of Technology | Li X.,The Ningbo Branch of Ordnance Science institute of China | Yu S.,Taiyuan University of Technology | And 3 more authors.
Surface and Coatings Technology | Year: 2015

In this paper, bi-layer (SiC+diamond) coatings were synthesized on 0.8-mm-diameter cemented carbide micro-end mills. The influences of SiC interlayers and diamond coatings on the morphologies, phase composition and fracture strength were investigated. The cutting performance of the bi-layer (SiC+diamond) coated tools was validated by dry cutting of aluminum alloys. The results indicated that the binder Co reacted with SiC to form cobalt silicides (i.e., Co2Si and CoSi), suggesting that the SiC interlayer suppressed the deleterious effects of Co, successfully. Neither the presence of the SiC interlayer nor the bi-layer coatings reduced the fracture resistance of the tools. The workpieces had a better surface finish after being cut by the coated tools than those cut by the uncoated tools. This result indicated that the bi-layer (SiC+diamond) coated tools exhibited better cutting performance than the uncoated tools. Thus, SiC interlayers were demonstrated as a suitable option for adherent diamond coatings on the cemented carbide components and cutting tools. © 2014 Elsevier B.V.

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