Papers by Keyword: Single Crystal Diamond

Abstract: Single crystal diamond is widely used in high-tech fields for its remarkable performance on mechanics, calorifics, optics, acoustics, etc. High-quality diamond surface with small roughness and low scathe are required in these applications. However, the extreme hardness and high chemical inertness of diamond result in severe processing difficulties. Chemical mechanical polishing (CMP) is a promising processing method which can obtain super-smooth and low-damage diamond surface. Oxidant is a key issue for CMP of single crystal diamond. In this study, five different oxidants were used to polish diamond samples. The results indicated that Fenton reagent was an appropriate CMP oxidant and a super-smooth diamond surface of Ra 2.4 nm was achieved by using Fenton reagent in CMP.

Abstract: Single point diamond tools are commonly used for ultraprecision machining. At high cutting speeds, frictional contact and local heat may cause material damage to the diamond tool. The diamond crystal is softened and its mechanical strength decreases with the increase in temperature. Plastic deformation of diamonds was recently reported in some experimental studies. In this work, a molecular dynamics (MD) simulation was implemented to predict the deformation of single crystal diamond at various temperatures. Diamond is brittle at room temperature, however, it starts to exhibit plastic dislocation at a temperature above 1200 K under a confining pressure. The condition in ultraprecision machining is indeed a temperature gradient distribution at the tool tip, between the maximum temperature at the tool-workpiece interface and the average temperature at the core. The simulation results predicted that diamond deformed plastically under the gradient between 1500K and 860K. It is surprising that secondary cracks were resulted from the gradient, as comparing to a single slip obtained in an evenly distributed temperature. Bond dissociation nucleated the fractures along the (111) shuffle planes, perfect dislocation merely occurred in the hot zone and sp³-to-sp² disorder at the cool zone. The temperature gradient created a lattice mismatch and nucleated the secondary cracks. The results give an insight that a catastrophic fracture and local material damage can occur at a diamond tool tip at the cutting temperature above 1200 K, due to softening and graphitization.

Abstract: In this paper, the cutting performance of cemented carbide with ultrafine particles using single crystal diamond for tool material in die and mold manufacturing is investigated. The flat work is done using spiral for tool pass. The flat work is divided into small area and middle area. The spiral pitch in addition to depth of cut is changed in flat work. The tool wear is also estimated from form deviation by measuring surface form before and after machining. These results showed that ductile mode cutting was possible and the tool wear could be estimated from surface form. The tool wear was large in proportion to both the depth of cut and cutting length.

Abstract: A new process was proposed. The disadvantage of of using brown alumina grinding wheel to grinding and lapping surface was studied in the analysis. The diamond facing tool was designed and manufactured with the solution of the key technique of the critical technical of single crystal diamond’s material selecting, grinding, welding. The face cutting parameters: “V”, “f” and “ap” were measured by experiment and academic analysis. Tt can fully meet the quality requirements of stainless steel valve flap’s surface used by one valve machinery factory; meanwhile the productivity was increased by a factor of 15, with overcoming the disadvatange of grinding and lapping valve flap’s surface.

Abstract: Homoepitaxial diamond layers were grown on commercial 3.5 x 3.5 x 1.2 mm3 HPHT synthetic type Ib (100) single crystal diamond plates using a DC Arc Plasma Jet CVD operating at gas recycling mode. The effects of substrate temperature and CH4/H2 ratio on the surface morphology, the growth rate and the quality of the synthesized diamond have been studied using optical microscopy and Raman spectroscopy. With no intentional nitrogen added, the growth rate up to 12.3µm/h has been obtained in the single crystal diamond sample deposited at 1000 °C with CH4/H2=0.625%, exhibiting relatively smooth surface morphology without any growth hillocks nor non-epitaxial crystallites, and presenting the typical feature of the epitaxial step-flow growth. The full width at half maximum (FWHM) of the Raman spectra was 2.08 cm-1, which was close to that of the natural type IIa single crystal diamond.

Abstract: In this thesis, the new process will proposed which using diamond profile boring to boring 8-shaped hole in intermediate stainless steel plate of synthetic fiber gear pump. Academic analysis was made for gear pump’s flow rate, and analysis was made for the disadvantage of using brown alumina grinding wheel to grinding 8-shaped hole in intermediate plate’s internal surface. The critical technical of single crystal diamond’s material selecting, grinding, welding were solved, and diamond profile boring was designed and manufactured. We confirmed the boring parameters: “”, “” and “” through experiment and academic analysis. The qualified intermediate stainless steel plate with 8-shaped hole was using in one spinning factory; we conquered the grinding hole’s disadvantage and productivity is increasing 15 times.

Abstract: The ultra-precision polishing assisted by the ultraviolet rays irradiation was performed to achieve the atomic-scale planarization of the single crystal diamond substrates. This polishing method is a novel and simple polishing method characterizing by a quartz disk and an ultraviolet irradiation device. The principle three crystal planes of the diamond substrate were polished by this method. The polished surfaces were evaluated by an optical interferometric profilers (Wyko), an atom force microscope (AFM) and LEED (low-energy electron diffraction). The surface roughness of the polished diamond substrates was evaluated as 0.2 ~ 0.4 nmRa in (100), (110) and (111) crystal planes. The LEED (low-energy electron diffraction) patterns indicated the almost perfect crystallographic structure without the residual processed strain beneath the polished surface. In this paper, the optimum polishing condition to achieve the atomic-scale planarization of the diamond substrates has been investigated by the evaluation of LEED patterns, Wyko and AFM images. The mechanismof the ultraviolet rays assisted polishing is discussed in detail.