Papers by Author: Fang Hong Sun

Abstract: Carbon fiber reinforced plastics (CFRP) is difficult to machine because of the extremely abrasive nature of the carbon fibers and its low thermal conductivity. CVD diamond films have many excellent properties such as wonderful wear resistance, high thermal conductivity and low friction coefficient, therefore depositing diamond films on the surface of drills is thought to be an effective way to elongate the lifetime of drills and improve the cutting performance. In this study, diamond films are deposited on the WC-Co drill using hot filament chemical vapor deposition (HFCVD) method. The results of characterization by the scanning electron microscope (SEM) and Raman spectrum indicate that the fabricated CVD diamond coated drill is covered with a layer of uniform and high-purity diamond films. The cutting performance of as-fabricated CVD diamond coated drill is evaluated in dry drilling CFRP, comparing with the uncoated WC-Co drill. The results demonstrate that the CVD diamond coated drill exhibits much stronger wear resistance. Its flank wear is about 50μm after drilling 30 holes, about one-third of that of WC-Co drill. Machining quality of the exit and internal wall of drilled holes shows better surface finish obtained by coated drill, which suggests that CVD diamond coated tool has great advantages in drilling CFRP.

Abstract: Silicon carbide (SiC) is a promising material for fabricating wire compacting dies due to its advantages of light weight and even high wear resistance over the tungsten carbide, which currently is the most popular material used to produce compacting dies. In present study, a layer of CVD diamond film is deposited on the interior-hole surface of compacting dies using the hot filament chemical vapor deposition (HFCVD) method, following by a surface polish process, aiming at further elongating the lifetime of compacting dies and improving the surface quality of produced wires. The characterization of both as-deposited and polished CVD diamond films is employed by scanning electron microscopy (SEM), surface profiler, Raman spectroscopy and X-ray diffraction (XRD) spectroscopy. Furthermore, the performance of as-fabricated CVD diamond coated compacting dies is examined in the real production process. The results exhibit that the as-deposited CVD diamond films are homogeneous and their surface finish is significantly smoothened after the surface polish process. As compared with the conventional compacting dies, the working lifetime of the diamond coated SiC compacting dies can be increased by a factor of above 15 and in the course of processing, copper stranded wires with high surface quality and uniform sectional area can be obtained.

Abstract: Diamond-coated drawing dies are considered as ideal drawing dies for their unique characteristics, such as high hardness, wear resistance and low friction. In order to utilize the superior characteristics of diamond coatings towards improving the drawing performance, the nonlinear FEM simulation is used to simulate the whole stainless steel tube hollow sinking process, with 2D axi-symmetric elastic-plastic element. Based on the simulation results, the distributions of the axial stress and radial stress are analyzed, the influence of parameters of drawing dies on the diameter shrinkage is investigated. Optimal die parameters are obtained.

Abstract: Thin diamond films are deposited on commercial tungsten carbide micro ball end mill by using hot filament chemical vapour deposition (HFCVD) technique. Raman spectrum results confirm the high purity of sp³-carbon bond diamond of as-deposited films. The scanning electron microscope (SEM) investigation exhibits continuous fine grained diamond films are uniformly deposited on micro ball end mill. Milling of graphite is chosen to check the cutting performance of fabricated diamond coated micro ball end mill. For the sake of comparison, milling test is also carried out using uncoated micro ball end mill under the same cutting parameters. The milling test results show that the tool life of diamond coated micro ball end mill is about 10 times than that of uncoated one, which may attribute to high hardness, wear resistance, low sticking to graphite of deposited diamond films and strong adhesive strength between them and substrate surfaces.

Abstract: In this investigation, conventional microcrystalline diamond (MCD) and boron doped diamond (BDD) films are deposited onto commercially available cemented tungsten carbide (WC-Co) Ball-nose endmills by using hot filament chemical vapour deposition (HFCVD). The quality and properties of the as-deposited diamond film are characterized by field emission scanning electron microscope (FESEM) and Raman spectroscopy. Milling tests of graphite materials using MCD, BDD coated and uncoated tool are carried out. Experiment results reveal that BDD films possess higher adhesive strength to the substrate than that of MCD films, and the BDD coated mills allow to be given smaller flank wear and longer tool life, when compared with MCD coated and uncoated WC-Co tools. Cutting performances of WC-Co mills in graphite milling are greatly improved by BDD coating, and typically more than 10 times the tool life is obtained. The research results are of great significance for high efficiency and quality machining of graphite materials.

Abstract: The substrate temperature has great influence on the growth rate and quality of diamond films by hot filament chemical vapor deposition (HFCVD). In order to deposit polycrystalline diamond films of uniform thickness over large areas and improve the growth rate of diamond films, the substrate temperature uniformity need to be further improved. Thus three-dimensional finite volume simulation has been developed to predict substrate temperature distribution, and optimize the deposition parameters like the size and arrangement of filaments which have a profound effect on the substrate temperature. Based on the simulation results, the optimum parameters of diamond deposition are found. Subsequently, experiments of depositing diamond films on silicon (100) wafers are done when the deposition parameters are fixed at optimum values gained from the simulation results. According to the results of scanning electron microscopy (SEM) and Raman spectroscopy, the thickness and quality of diamond films are homogeneous, which validate that the simulated deposition parameters are conducive to fabricate the high quality diamond films.

Abstract: The high quality micro diamonds with the euhedral diamond faces are fabricated by hot filament chemical vapor deposition technique (HFCVD). The high pressure and high temperature (HPHT) single crystal diamonds in size of 1 μm are used as seeds. In order to disperse the diamond seeds uniformly on a silicon wafer, the photoresist solution with diamond seeds are performed on the silicon wafer by a spin coater machine. The high substrate temperature and low acetone concentration are employed for decreasing the nucleation rate and accelerating the growth rate. The morphology and quality of the micro diamonds are observed and analyzed by SEM and Raman spectroscopy. After 4 hours of the deposition, the surface imperfections of the diamond seeds have disappeared completely, and the euhedral diamond faces with (111) and (100) begin to emerge. Subsequently, 8 hours of deposition leads to a final average size of approximately 4 μm. The micro diamonds have very high quality, and the surfaces appear flat and smooth in this stage. The results indicate that it is an effective way to eliminate the defects of the HPHT micro diamonds and develop high quality diamonds with well-defined morphology by HFCVD technique.

Abstract: In present study, a novel deposition method combining conventional hot filament chemical vapor deposition (HFCVD) method and surface polishing is adopted to deposit the micro/nano-crystalline multilayered ultra-smooth diamond (USCD) film on the cobalt cemented tungsten carbide (WC-Co) cutting inserts. The scanning electron microscopy (SEM) image shows that the deposited USCD film exhibits an ultra-smooth surface, whose surface roughness (R_a) is measured as ~95.7 nm using surface profilometer. The characterization of Raman spectroscopy and X-ray diffraction (XRD) further confirms that the grain size of USCD film is down to the nanometer scale. Furthermore, dry turning tests using Al/SiC-MMC as workpiece are conducted to examine the cutting performance of as-fabricated USCD coated inserts, comparing with uncoated WC-Co inserts, MCD and DLC coated inserts. The results show that the USCD coated insert exhibits much longer lifetime than other inserts, whose effective cutting length is as long as 190 m, nearly two times more than that of DLC and MCD coated inserts, and 5 times more than that of uncoated WC-Co inserts. The excellent wear resistance and ultra-smooth surface of USCD films is supposed to play determinate role on elongating the lifetime of WC-Co cutting insert.

Abstract: The tribological performance of conventional microcrystalline diamond (MCD) film and diamond-like carbon (DLC) film is investigated comparatively under water lubricating condition. The MCD and DLC film are deposited on cobalt cemented tungsten carbide (WC-Co) substrate using the hot filament chemical vapor deposition (HFCVD) method and the vacuum arc discharge with a graphite cathode respectively. Scanning electron microscopy (SEM), white light interferometer, and Raman spectra are employed to characterize as-deposited MCD and DLC samples. The friction tests are carried out on a ball-on-plate reciprocating friction tester, where the sliding process is conducted under water lubricating condition. Silicon nitride, tungsten carbide, ball-bearing steel and copper are used as counterpart materials. The results indicate that DLC film always exhibits lower friction coefficient than MCD film under water lubricating condition, except the case of sliding against the silicon nitride, in which DLC film is worn out very rapidly and thus leads to the high friction coefficient. The wear resistance of DLC film under water lubricating condition is significantly poorer than that of MCD film. While sliding against silicon nitride, tungsten carbide, ball-bearing steel and copper, its wear rate is calculated as 3.67´10^-7 mm³N^-1m^-1, 9.31´10^-9 mm³N^-1m^-1, 3.54´10^-7 mm³N^-1m^-1, and 4.97´10^-8 mm³N^-1m^-1 respectively. Comparatively, no measurable wear track can be found on the worn surface of MCD films.

Abstract: Carbon fiber reinforced plastics (CFRP) have been widely used for manufacturing spacecraft, aircraft and automobile structural parts in aerospace and automotive industries. However, CFRP is a kind of hard machining materials and conventional tungsten carbide drills always experience severe tool wear, and thus short lifetime in the CFRP drilling process. In this paper, the CVD diamond films are deposited on the surface of cobalt cemented tungsten carbide (WC–Co) drills using hot filament chemical vapor deposition (HFCVD) method. Scanning electron microscope (SEM) is adopted to investigate the surface morphology of as-fabricated CVD diamond coated drills, additional analysis using Raman spectrum also indicates the high purity of sp3 phase of as-deposited diamond film. Furthermore, the machining performance of as-fabricated CVD diamond coated drills is examined in drilling the CFRP, comparing with the uncoated WC-Co drills. The chisel edge and primary cutting edge wear of drills are studied using the tool microscope. The results show that as-fabricated CVD diamond coated drills exhibit a much elongated lifetime than that of uncoated WC-Co drills, and also smoother surface finish of machined holes, which is supposed to be attributed to the excellent wear resistance and satisfied adhesive strength between the as-deposited diamond films and drills.