Y.P. Ma

Study on the Effects of Substrate Grain Size on Diamond Thin Films Deposited on Tungsten Carbide Substrates

Three sets of Co-cemented tungsten carbide (94 wt.%WC-6wt.%Co) blades with different average grain size (0.5, 1.5 and 3 μm) were used as substrates. After usual acid etching and scratching with diamond powders, H2 gas etching decarburization by microwave plasma and cleaning in an ultrasonic bath of acetone solution, substrates with different WC grain size were placed in the electron aided hot filament chemical vapor deposition (EACVD) reactor to fabricate diamond thin films. Scanning electron microscopy (SEM), X-ray diffraction (XRD), Raman spectroscopy, indention tests and surface scanning profilometer showed that substrate grain size plays an important role in determining the performance of diamond films deposited on the tungsten carbide substrates such as film adhesive strength, film surface roughness and diamond film quality. The related conclusions were beneficial to the optimization of CVD diamond process and also to the metallurgical process of tungsten carbide.

Adhesive strength of CVD diamond thin films quantitatively measured by means of the bulge and blister test

Large advancement has been made in understanding the nucleation and growth of chemical vapor deposition (CVD) diamond, but the adhesion of CVD diamond to substrates is poor and there is no good method for quantitative evaluation of the adhesive strength. The blister test is a potentially powerful tool for characterizing the mechanical properties of diamond films. In this test, pressure was applied on a thin membrane and the out-of-plane deflection of the membrane center was measured. The Youngs modulus, residual stress, and adhesive strength were simultaneously determined using the load-deflection behavior of a membrane. The free-standing window sample of diamond thin films was fabricated by means of photolithography and anisotropic wet etching. The research indicates that the adhesive strength of diamond thin films is 4.28±0.37 J/m^2. This method uses a simple apparatus, and the fabrication of samples is very easy.

Study on Critical Ductile Grinding Depth of Nano ZrO2 Ceramics by the Aid of Ultrasonic Vibration

The crack extension course and ductile removal mechanism of nano ZrO2 ceramics were analyzed in this paper. On the basis of contrast tests with or without ultrasonic vibration, the influences of critical ductile grinding depth on grinding forces and surface quality were studied by dynamometer, SEM and AFM in different grinding condition. The reason for the increase of the critical grinding depth was discussed based on the analysis of grinding force and ultrasonic vibration course. At last, the formation mechanism of surface topography observed by AFM in ductile domain was analyzed. The research indicated that ultrasonic machining could obtain nano finished surface with high efficient.

Studies on the Performance of Diamond Thin Films with Different Tungsten Carbide Substrates

In order to make sure the details of influences of grain size on the performance of diamond thin film, different trademarks of tungsten carbide tools with different scales of substrate grain size were selected. Scanning electron microscopy (SEM), Raman spectroscopy, indention tests and surface scanning profilometer showed that WC grain size played an important role in determining the performance of diamond films deposited on the tungsten carbide substrates. Therefore, an appropriate combination of pretreatments, substrate grain size and deposition parameters should be selected. The tribological pin-on-disc tests have been conducted. The quantitative relations between the friction coefficient and the surface roughness were investigated. The experimental results have shown that the surface roughness of diamond coatings has appreciable influences on the friction coefficient, especially on the initial friction. There exists an optimal value of surface roughness of diamond-coated tools with regard to cutting tool life.

Mechanical properties of diamond thin films quantitative measured by means of blister test

Abstract In recent years, large strides have been achieved in understanding nucleation and growth of chemical vapour deposition diamond, but there is still not a good method of how to determine the adhesive strength, residual stress and elastic modulus of diamond thin films accurately. The blister test method which can obtain adhesive strength, elastic modulus and residual stress of thin films in a single test is very economical and practical, so it has expansive foreground in quantitative evaluation mechanical properties of thin films. By means of electron enhanced hot filament chemical vapour deposition, diamond films were deposited on silicon slice (100), and a free standing window sample of diamond thin films was fabricated by means of photolithography and anisotropic wet etching in this research. Using a self-designed bulge equipment, the membrane bulge height under differential pressure was measured by laser interferometry system, and then fitted by least squares procedure, the elastic modulus, residual stress and adhesive strength of diamond thin films were obtained. The apparatus of blister test is available readily and is not limited by the shape of substrate, so it can measure the mechanical properties of diamond coated tool with complicated shape, and it has provided an effective means for precisely measuring the mechanical properties of other thin films.

Measurement of Elastic Modulus and Residual Stress of Diamond Thin Films

Despite great advancements in diamond thin film growth and deposition techniques, determination of the residual stress and Young’s modulus for diamond films has continued to be a challenge. The bulge test is a potentially powerful tool for characterizing the mechanical properties of diamond film. In a bulge tester, pressure is applied on a thin membrane and the out-of-plane deflection of the membrane center is measured. The Young’s Modulus and the residual stress are simultaneously determined by using the load-deflection behavior of a membrane. By means of electron-enhanced hot filament chemical vapor deposition (HFCVD), a diamond film was deposited on silicon slice (100), and the free-standing window sample of diamond thin films was fabricated by means of photolithography and anisotropic wet etching. The deflection of the membranes is measured using a laser interferometry system. The elastic modulus and residual stress were measured using a self-designed bulge equipment. In addition, the distortion of diamond thin films under different pressure was simulated using finite element analysis and the contrast was made with experimental data. The research indicated that the Young’s Modulus of diamond thin films is 937.8GPa and the residual stress is -10.53MPa. The elastic modulus and the residual stress coincide with the report in the literature and the value tested by X-ray diffraction, respectively. This method uses a simple apparatus, and the fabrication of samples is very easy, and it has provided an effective means for precise measure the mechanical properties of other thin films.

Synthesis of nanocrystalline diamond films on smooth WC-Co cemented carbide substrates

Nanocrystalline Diamond Films (NDFs) are deposited on WC-Co cemented carbide substrates by the bias-enhanced hot filament Chemical Vapour Deposition (CVD). A new pretreatment method is performed to diffuse boron into WC-Co substrate without surface roughening of smooth substrates. The new CVD processes are used to enhance the secondary nucleation, reduce the grain size of nandiamond and promote the growth of NDFs by appropriately increasing acetone concentration, lowering the reactive gases pressure and adding Ar gas in the reactive gases. Research results show that the boronization pretreatment can result in the formation of the stable cobalt boride compounds on the substrate surface, thus effectively ensure the adhesion of smooth diamond films. NDFs consist of nanocrystalline diamond with grain sizes range from 20 to 60 nm. The surface roughness of NDFs is measured at Ra < 50 nm. The diamond-coated drawing dies with these NDFs show obvious effect in the practical application.

Study on Surface Quality of Nano ZrO2 Ceramics in Grinding by the Aid of Ultrasonic Vibration

Nano ceramics possesses excellent mechanical property and physical characteristics in contrast to conventional engineering ceramics, so it has tremendous application prospect. Adopting ultrasonic composite processing we describe the influences of grinding speed, grinding depth, wheel granularity and no-spark grinding times on the surface roughness of nano ZrO2 ceramics. By means of SEM and AFM the surface character and critical ductile grinding depth of nano ZrO2 ceramics in the condition of conventional and ultrasonic grinding are also discussed. At last, the residual stress of surface and crystalline phase transformation under the condition of conventional grinding and ultrasonic vibration grinding were analyzed by X-ray diffraction. The research indicated that ultrasonic vibration grinding could obtain nano finished surface with high efficiency. The residual stress of nano ZrO2 ceramics surface is determined much by different grinding styles.

Resin Bonded CBN Grinding Wheel Dressing by Laser — Simulation and Experiment

Due to the large difference in thermal properties of the resin and the abrasive grits, the laser-assisted dressing technology is of great interest for grinding wheel preparation. From a viewpoint of thermal induced material removal mechanism, a numerical method was presented to simulate the laser dressing process. The numerical simulation results could reveal the relations between the laser parameters and the groove formation. The overlap coefficient was introduced for practical application. Simulation for the variation of the number of active grinding points was also made for non-uniform wheel topography. Based on the numerical modeling, the suitable grinding^wheel surface topography can be achieved through the laser-assisted dressing technology. The comprehensive researches on the laser-assisted dressing process control, grinding wheel topography reconfiguration by 3D laser scanning technology and analyses of grinding temperature were made. A series of grinding tests with the laser-assisted dressed grinding wheel and mechanically dressed grinding wheel were conducted for comparison. The results proved the feasibility of laser-assisted dressing for resin bonded superabrasive grinding wheels and revealed the importance of choosing appropriate laser dressing parameters.

Deposition of Smooth Diamond Films with High Adhesive Strength on WC-Co Inserts and Their Cutting Performance in Turning GFRP

Deposition processes of conventional diamond films and smooth fine-grained diamond films on cemented tungsten carbide inserts (SCMT120408-HR, 6wt. %Co) in the hot filament chemical vapor deposition (HFCVD) apparatus were investigated. A novel combined pretreatment of Murakami’s reagent, acid etching and microwave plasma decarburization in Ar-H2 gas was carried out. The adhesive strength of the films to the substrates, diamond-coated tool wear and surface roughness of the workpiece were further studied by turning glass fiber reinforced plastics (GFRP) cylindrical bars. Scanning electron microscopy (SEM), X-ray diffraction (XRD), energy dispersive X-ray spectroscopy (EDX), and Raman spectroscopy were employed to characterize the substrates and diamond films subjected to different pretreatments and deposition processes. Optical microscope and surface scanning profilometer were utilized to monitor the evolution of tool wear and surface roughness of the workpiece respectively during the cutting test. The experimental results showed that the novel combined pretreatment was more effective in enhancing the adhesive strength of diamond films to the substrate. Fine WC interlayer generated during the initial stage of the diamond film deposition played an important role in improving the adhesion. Diamond coated tools subjected to such pretreatment demonstrated up to 6 times longer tool life than uncoated ones. Varied parameter deposition process produced smooth fine-grained diamond films, which led to remarkably lower surface roughness of the workpiece in turning GFRP