Papers by Keyword: Diamond

Abstract: Many efforts have been directed to the micro structure and performance evaluation of Electroplated Diamond Film. The indentation method has become extensively utilized in the evaluation of materials’ mechanical. Nano indentation devices, such as MTS-XP, are very useful, but on the other hand, are not affordable for many research institutions. This paper presents an effective and economic method for testing and evaluating micro-cracking performance of Electroplated Diamond Film on Instron 5848 MicroTester by considering the relative hardness values, and the need to evaluate the maximum strength for brittle materials in practical applications. The design of the test system, the evaluation methods, the test results, and the discussions are presented.

Abstract: Wide band gap semiconductors have been attracted as the material for fabricating power switching devices to obtain lower power conversion loss in high voltage circuit, and to operate harsh environment of high temperature. This paper focuses on diamond as the wide band gap semiconductor material and elucidates the dynamic characteristics in switching operation. To this end, Schottky barrier diode (SBD) is fabricated with p type diamond semiconductor and static I-V characteristics is evaluated. Then, the switching operation of diamond SBD is demonstrated, and forward current dependency of the recovery phenomena is characterized. The diamond SBDs show superior fast switching capability with low reverse recovery current, which is inherent in uni-polar switching device.

Abstract: In order to obtain stable and homogeneous diamond-Ni-P composite electroless plating, dispersants were selected by determining the height of emulsion in the colorimetric cylinder after standing different time.The structure,elemental contents and properties of the diamond-Ni-P composite electroless plating coating were investigated by SEM and EDS. Experimental results show that OP-10 of 50mL•L^-1 and softex kw of 1g•L^-1 have better dispersing effect to diamond powder of 1g•L^-1 in water. This composite electroless plating solution can keep stable for more than twelve or eight hours respectively at 85°C. While in the electroless plating solution, Softex kw of 1g•L^-1 has better dispersing effect and can be stable for more than two hours at 85°C. The diamond powder grains in the composite coating are homogeneous and the content of carbon is 2.261 wt% under the certain amount of the selected dispersant. When the content of diamond was 5g•L^-1 in the solution, the diamond powders were dispersed non-homogeneously in plating and cluster phenomena were appeared. The composite electroless plating coating consists of amorphous Ni-P and diamond powder. Its hardness and porosity are similar to those of the electroless plating Ni-P coating. The wear-resisting is improved greatly,which is 2.6 times of electroless plating Ni-P or 2 times of that after heat treatment at 400°C for one hour.

Abstract: Diamond polycrystalline composites with some different elements were prepared by HPHT (high pressure and high temperature). The dependence between emission energy and excitation energy was characterized by PL technique. The results showed that the photoluminescence of diamond polycrystalline composites was not affected by additives, only related to the excitation. The emission wavelengths of composites decreased with excitation, at the same time, emission peaks shifted to high energy region and the peak width at half-height decreased relatively. The energy of emission had a linear relationship with that of excitation. The emission band peak location shifted from 1.57 (790nm) to 1.97eV (628nm) as the excitation wavelength changed from 2.34 (530nm) to 2.95eV (420nm). Emission intensity decreased linearly with the decrease of excitation energy intensity. However, this linear dependence disappeared as excitation wavelength was below 400nm.

Abstract: This paper first analyzes the characteristics of holding strength of ceramic adhesive to diamond grains within vitrified abrasives grinding wheel, subsequently put forwards a calculating method of holding strength based on the data of the samples tensile strength test and fractography analysis. The holding strength mechanical model and the mathematic model are presented in this paper, which is figured out by load strength analyzing and idealized assumptions. Considering the holding strength computational complexity a set of software was designed to calculate the strength with the Excel data sheets exported from the tensile strength test and micro image analysis. Its flow diagram was shown in this paper.

Abstract: In order to develop new generation brazed Diamond grinding wheels, the joining experiments of Diamond super abrasive grains and medium carbon steel using the powder mixture of Ni-Cr alloy as active brazing alloy are carried out via laser in an argon atmosphere. The relevant characteristics of the special powder mixture, the microstructure of the interfacial region, which are both the key factors for determining the joining strength among the Diamond grains, the filler layer and the steel substrate, are investigated extensively by means of scanning electron microscope (SEM) and energy dispersion spectrometer (EDS), as well X-ray diffraction (XRD) analysis. The formation mechanism of carbide layers was discussed. All the results indicate that high strength bonding between diamond grits and the steel substrate has been successfully realized because the chromium in the Ni-based alloy segregated preferentially to the surface of the diamond to form a chromium-rich reaction product Cr3C2, and the bond between the alloy and the Diamond was established through the reaction product.

Abstract: Diamond nanoparticles (NPs), grown by chemical vapor deposition (CVD), have been characterized by utilizing AFM, SEM, and Raman spectroscopy. AFM and SEM data show increase in NPs size with growth period, ranging from about 20 nm for 15 min to 200 nm for 105 min growth. The Raman spectra show a sharp line at around 1332 cm-1, which is characteristic of diamond structure. We analyze the Raman spectra by using optical phonon confinement in nm-size crystals and discuss the resulting data for NP sizes.

Abstract: The nickel coatings and electroplated diamond tools were fabricated with ultrasonic and without ultrasonic condition. Hardness and adhesive strength of nickel coatings were tested. Diamond grains on tool substrate were observed with microscope. Al2O3 ceramic was machined with fabricated electroplated diamond tools to compare material removal rate and grinding ratio. Experimental results show that high hardness can be obtained under the effect of ultrasonic during tool fabrication processes. Ultrasonic agitation can make grain dense and guarantee nice contact between substrate and coating. With ultrasonic power of 200W, nickel coating presents highest values of hardness and adhesive strength. High grain density of diamond tool can be obtained. During buildup processes, some buildup time is needed to obtain enough thickness of nickel coating before ultrasonic agitation is applied. Grinding ratios of diamond tool with ultrasonic during buildup processes were better than without ultrasonic. The diamond tool fabricated with ultrasonic agitation presents better cutting ability. During tool fabricating processes, the reasonable application of ultrasonic agitation is very important.

Abstract: The main causes of segment failure of diamond saw blade are studied in this paper. The segment material, the microstructure and the wear resistance of saw blade material were studied with scan electronic microscope, energy disperse spectroscopy, hardness meter, optical microscope. The results shows that the addition of alloying elements could refine grains, improve the holding force of matrix to diamond, enhance wear resistance of matrix to diamond, and decrease wear coefficient about 20%.

Abstract: For obtaining materials with high thermal conductivities and suitable thermal expansion coefficient for thermal management applications, diamond/Al composites were fabricated by the low-cost pressureless metal infiltration. The resulting composites exhibited thermal conductivities as high as 518.7 W/m•K and thermal expansion coefficient as low as 4.61×10-6/K friendly matching with semiconductors materials like Si or GaAs. The diamond particles were not only well embedded, but also uniformly distributed in the metallic matrix along with SEM observations of the composites. Fractograph of the composites illustrated that aluminum matrix fracture was the dominant fracture mechanism and the stepped breakage of diamond particles indicated strong interfacial bonding between diamond and the Al matrix. The Si skeleton with coralline morphology in the interface between diamond and the matrix were found to play a role of bridge in the interfacial structure and result in distinctive interfacial bonding. Also a little content of Al4C3 were realized to have positive effect on the improved thermal conductivities for promoting interfacial bonding between aluminum and diamond. In addition, the excellent mechanical behavior of the composite was illustrated. The results shows a superior Young’s modulus of 286 GPa compared with traditional thermal management materials and relatively high bending strength of 306MPa.