Precipitates Generation Mechanism and Surface Quality Improvement for Aluminum Alloy 6061 in Diamond Cutting

To improve the surface quality for aluminum alloy 6061(Al6061) in ultra-precision machining, we investigated the factors affecting the surface finish in single point diamond turning(SPDT)by studying influence of the precipitates generation of Al6061 on surface integrity and surface roughness.Based on the Johnson-Mehl-Avrami solid phase transformation kinetics equation, theoretical and experimental studies were conducted to build the relationship between the aging condition and the type, size and number of the precipitates for Al6061. Diamond cutting experiments were conducted to machine Al6061 samples under different aging conditions. The experimental results show that, the protruding on the chip surface is mainly Mg_(2)Si and the scratches on the machined surface mostly come from the iron-containing phase(α-, β-AlFeSi).Moreover, the generated Mg_(2)Si and α-, β-AlFeSi affect the surface integrity and the diamond turned surface roughness. Especially, the achieved surface roughness in SPDT is consistent with the variation of the number of AlFeSi and Mg_(2)Si with the medium size(more than 1 μm and less than 2 μm) in Al6061.

Effect of surface modification on the radiation stability of diamond ohmic contacts

The ohmic contact interface between diamond and metal is essential for the application of diamond detectors.Surface modification can significantly affect the contact performance and eliminate the interface polarization effect.However,the radiation stability of a diamond detector is also sensitive to surface modification.In this work,the influence of surface modification technology on a diamond ohmic contact under high-energy radiation was investigated.Before radiation,the specific contact resistivities(ρc)between Ti/Pt/Au-hydrogen-terminated diamond(H-diamond)and Ti/Pt/Au-oxygenterminated diamond(O-diamond)were 2.0×10^(-4)W·cm^(2) and 4.3×10^(-3)Wcm^(2),respectively.After 10 MeV electron radiation,the ρc of Ti/Pt/Au H-diamond and Ti/Pt/Au O-diamond were 5.3×10^(-3)W·cm^(2)and 9.1×10^(-3)W·cm^(2),respectively.The rates of change of ρc of H-diamond and O-diamond after radiation were 2550%and 112%,respectively.The electron radiation promotes bond reconstruction of the diamond surface,resulting in an increase in ρc.

Generating micro/nanostructures on magnesium alloy surface using ultraprecision diamond surface texturing process

The lightness and high strength-to-weight ratio of the magnesium alloy have attracted more interest in various applications.However,micro/nanostructure generation on their surfaces remains a challenge due to the flammability and ignition.Motivated by this,this study proposed a machining process,named the ultraprecision diamond surface texturing process,to machine the micro/nanostructures on magnesium alloy surfaces.Experimental results showed the various microstructures and sawtooth-shaped nanostructures were successfully generated on the AZ31B magnesium alloy surfaces,demonstrating the effectiveness of this proposed machining process.Furthermore,sawtooth-shaped nanostructures had the function of inducing the optical effect and generating different colors on workpiece surfaces.The colorful letter and colorful flower image were clearly viewed on magnesium alloy surfaces.The corresponding cutting force,chip morphology,and tool wear were systematically investigated to understand the machining mechanism of micro/nanostructures on magnesium alloy surfaces.The proposed machining process can further improve the performances of the magnesium alloy and extend its functions to other fields,such as optics.

SURFACE ROUGHNESS PREDICTION MODEL FOR ULTRAPRECISION TURNING ALUMINIUM ALLOY WITH A SINGLE CRYSTAL DIAMOND TOOL

A surface roughness model utilizing regression analysis method is developedfor predicting roughness of ultra-precision machined surface with a single crystal diamond tool. Theeffects of the main variables, such as cutting speed, feed, and depth of cut on surface roughnessare also analyzed in diamond turning aluminum alloy. In order to predict the optimum cuttingconditions during process planning. A lot of experimental results show that the model can predictthe surface roughness effectively under a certain cutting conditions.

Tool Wear and Its Effect on Surface Roughness in Diamond Cutting of Glass Soda-lime

For the technology of diamond cutting of optical glass, the high tool wear rate is a main reason for hindering the practical application of this technology. Many researches on diamond tool wear in glass cutting rest on wear phenomenon describing simply without analyzing the genesis of wear phenomenon and interpreting the formation process of tool wear in mechanics. For in depth understanding of the tool wear and its effect on surface roughness in diamond cutting of glass, experiments of diamond turning with cutting distance increasing gradually are carried out on soda-lime glass. The wear morphology of rake face and flank face, the corresponding surface features of workpiece and the surface roughness, and the material compositions of flank wear area are detected. Experimental results indicate that the flank wear is predominant in diamond cutting glass and the flank wear land is characterized by micro-grooves, some smooth crater on the rake face is also seen. The surface roughness begins to increase rapidly, when the cutting mode changes from ductile to brittle for the aggravation of tool wear with the cutting distance over 150 m. The main mechanisms of inducing tool wear in diamond cutting of glass are diffusion, mechanical friction, thermo-chemical action and abrasive wear. The proposed research makes analysis and research from wear mechanism on the tool wear and its effect on surface roughness in diamond cutting of glass, and provides theoretical basis for minimizing the tool wear in diamond cutting brittle materials, such as optical glass.

Electrochemical incineration of dimethyl phthalate by anodic oxidation with boron-doped diamond electrode

The anodic oxidation of aqueous solutions containing dimethyl phthalate （DMP） up to 125 mg/L with sodium sulfate （Na2SO4） as supporting electrolyte within the pH range 2.0-10.0 was studied using a one-compartment batch reactor employing a boron-doped diamond （BDD） as anode. Electrolyses were carded out at constant current density （1.5-4.5 mA/cm^2）. Complete mineralization was always achieved owing to the great concentration of hydroxyl radical （-OH） generated at the BDD surface. The effects of pH, apparent current density and initial DMP concentration on the degradation rate of DMP, the specific charge required for its total mineralization and mineralization current efficiency were investigated systematically. The mineralization rate of DMP was found to be pH-independent and to increase with increasing applied current density. Results indicated that this electrochemical process was subjected, at least partially, to the mass transfer of organics onto the BDD surface. Kinetic analysis of the temporal change of DMP concentration during electrolysis determined by High Performance Liquid Chromatography （HPLC） revealed that DMP decay under all tested conditions followed a pseudo first-order reaction. Aromatic intermediates and generated carboxylic acids were identified by Gas Chromatography- Mass Spectrometry （GC-MS） and a general pathway for the electrochemical incineration of DMP on BDD was proposed.

Enhancement of surface wettability via micro-and nanostructures by single point diamond turning

Studies on surface wettability have received tremendous interest due to their potential applications in research and industrial processes. One of the strategies to tune surface wettability is modifying surface topography at micro-and nanoscales. In this research, periodic micro-and nanostructures were patterned on several polymer surfaces by ultra-precision single point diamond turning to investigate the relationships between surface topographies at the micro-and nanoscales and their surface wettability. This research revealed that single-point diamond turning could be used to enhance the wettability of a variety of polymers, including polyvinyl chloride(PVC), polyethylene 1000(PE1000), polypropylene copolymer(PP) and polytetrafluoroethylene(PFTE), which cannot be processed by conventional semiconductor-based manufacturing processes. Materials exhibiting common wettability properties(θ≈ 90°) changed to exhibit "superhydrophobic" behavior(θ > 150°). Compared with the size of the structures, the aspect ratio of the void space between micro-and nanostructures has a strong impact on surface wettability.

Synthesis and characterization of p-type boron-doped IIb diamond large single crystals

High-quality p-type boron-doped IIb diamond large single crystals are successfully synthesized by the temperature gradient method in a china-type cubic anvil high-pressure apparatus at about 5.5 GPa and 1600 K. The morphologies and surface textures of the synthetic diamond crystals with different boron additive quantities are characterized by using an optical microscope and a scanning electron microscope respectively. The impurities of nitrogen and boron in diamonds are detected by micro Fourier transform infrared technique. The electrical properties including resistivities, Hall coefficients, Hall mobilities and carrier densities of the synthesized samples are measured by a four-point probe and the Hall effect method. The results show that large p-type boron-doped diamond single crystals with few nitrogen impurities have been synthesized. With the increase of quantity of additive boron, some high-index crystal faces such as {113} gradually disappear, and some stripes and triangle pits occur on the crystal surface. This work is helpful for the further research and application of boron-doped semiconductor diamond.

Surface graphitization analysis of cerium-polished HFCVD diamond films with micro-raman spectra

The etching technique using Ce is a convenient and fast method for polishing and shaping diamond films. In this study, the influence of polishing parameters such as polishing temperature and time on the surface crystallinity and phase composition of diamond films was thoroughly investigated via the analysis of Raman spectra such as FWHM and ID/IG. Moreover, the issue on the graphitization of diamond after polishing with Ce was further researched through the detailed study of the depth distribution of Raman data including FWHM and ID/IG, and a result completely different from the hot-iron metal polished ones was obtained. The results showed that polished diamond films had considerably higher diamond content than those before polishing, and not a bit of graphitization was found in the polished ones, owing to a higher solubility of carbon in rare earth metal Ce than that in transition metals, and the original crystallinity of the films polished with Ce did not deteriorate.

Investigation of Surface Micro Waviness in Single Point Diamond Fly Cutting

Single point diamond fly cutting is widely used in the manufacture of large-aperture ultra-precision optical elements. However,some micro waviness( amplitude about 30 nm,wavelength about 15 mm) along the cutting direction which will decrease the quality of the optical elements can always be found in the processed surface,and the axial vibration of the spindle caused by the cut-in process is speculated as the immediate cause of this waviness. In this paper,the analytical method of dynamic mesh is applied for simulating the dynamic behavior of the vertical spindle. The consequence is then exerted to the fly cutter and the processed surface profile is simulated. The wavelength of the simulation result coincides well with the experimental result which proves the importance of the cut-in process during the single point diamond fly cutting.

Surface Free Energies and Morphologies of Chemical Vapor Deposited Diamond Films

We have calculated the surface free energies of the chemical vapor deposited diamond crystals during the preparation process,using the model that a fraction of carbon dangling bonds on the growth surface are saturated by hydrogen.The results show that the surface free energies of the three most energetically favored crystal planes,i.e.(100),(110)and(111),can be used to interpret the changes of predominant facets in the surface morphology from{100}to{111}with increasing substrate temperature.In chemical vapor deposition conditions,it is found that the growth surfaces of diamond are more stable than that of graphite.

Texturing and evaluation of concrete pavement surface:A state-of-the-art review

Concrete pavement is accompanied by two major functional properties,namely noise emission and friction,which are closely related to pavement surface texture.While several technologies have been developed to mitigate tirepavement noise and improve driving friction by surface texturization,limited information is available to compare the advantages and disadvantages of different surface textures.In this study,a state-of-the-art and state-of-thepractice review is conducted to investigate the noise reduction and friction improvement technologies for concrete pavement surfaces.The commonly used tests for characterizing the surface texture,skid resistance,and noise emission of concrete pavement were first summarized.Then,the texturing methods for both fresh and hardened concrete pavement surfaces were discussed,and the friction,noise emission and durability performances of various surface textures were compared.It is found that the next generation concrete surface(NGCS)texture generally provides the best noise emission performance and excellent friction properties.The exposed aggregate concrete(EAC)and optimized diamond grinding textures are also promising alternatives.Lastly,the technical parameters for the application of both diamond grinding and diamond grinding&grooving textures were recommended based on the authors'research and practical experience in Germany and the US.This study offers a convenient reference to the pavement researchers and engineers who seek to quickly understand relevant knowledge and choose the most appropriate surface textures for concrete pavements.

Preparation of Diamond-like Carbon Films on the Surface of Ti Alloy by Electro-deposition

In this paper, diamond-like carbon (DLC) films were deposited on Ti alloy by electro-deposition. DLC films were brown andcomposed of the compact grains whose diameter was about 400 nm. Examined by XPS, the main composition of the filmswas carbon. In the Raman spectrum, there were a broad peak at 1350 cm^(-1) and a broad peak at 1600 cm^(-1), which indicatedthat the films were DLC films.

Deposition of Diamond-Like Carbon on Inner Surface by Hollow Cathode Discharge

A cylindrical hollow cathode discharge （HCD） in CH4/Ar gas mixture at pressure of 20-30 Pa was used to deposit diamond-like carbon （DLC） films on the inner surface of a stainless steel tube. The characteristics of the HCD including the voltage-current curves, the plasma im- ages and the optical emission spectrum （OES） were measured in Ar and CHn/Ar mixtures. The properties of DLC films prepared under different conditions were analyzed by means of Raman spectroscopy and scanning electron microscopy （SEM）. The results show that the electron exci- tation temperature of HCD plasma is about 2400 K. DLC films can be deposited on the inner surface of tubes. The ratio of sp3/sp2 bonds decreases with the applied voltage and the deposition time. The optimizing CH4 content was found to be around CH4/Ar =1/5 for good quality of DLC films in the present system.

Multiple enlarged growth of single crystal diamond by MPCVD with PCD-rimless top surface

We report the simultaneous enlarged growth of seven single crystal diamond(SCD) plates free from polycrystalline diamond(PCD) rim by using a microwave plasma chemical vapor deposition(MPCVD) system. Optical microscope and atomic force microscope(AFM) show the typical step-bunching SCD morphology at the center, edge, and corner of the samples. The most aggressively expanding sample shows a top surface area three times of that of the substrate. The effective surface expanding is attributed to the utilization of the diamond substrates with(001) side surfaces, the spacial isolation of them to allow the sample surface expanding, and the adoption of the reported pocket holder. Nearly constant temperature of the diamond surfaces is maintained during growth by only decreasing the sample height, and thus all the other growth parameters can be kept unchanged to achieve high quality SCDs. The SCDs have little stress as shown by the Raman spectra. The full width at half maximum(FWHM) data of both the Raman characteristic peak and(004) x-ray rocking curve of the samples are at the same level as those of the standard CVD SCD from Element Six Ltd. The nonuniformity of the sample thickness or growth rate is observed, and photoluminescence spectra show that the nitrogen impurity increases with increasing growth rate. It is found that the reduction of the methane ratio in the sources gas flow from 5% to 3% leads to decrease of the vertical growth rate and increase of the lateral growth rate. This is beneficial to expand the top surface and improve the thickness uniformity of the samples. At last, the convenience of the growth method transferring to massive production has also been demonstrated by the successful simultaneous enlarged growth of 14 SCD samples.

CHEMICAL PRETREATMENTS OF THE SURFACE OF WC-15wt%Co WITH DIAMOND COATINGS

Diamond films were deposited on the cemented carbide WC-15%Co substrates by a hot-filament chemical vapor deposition (HF CVD) reactor. The substrate surfaces were chemically pretreated by the following two-step etching method: first using Murakami reagent for 1-3 min, and second using an HNO3:HCl=1:1 solution for 10-40 min. It is indicated that the Co content of the substrate surfaces could be reduced from 15% to 0.81-6.04% within the etching depth of 5-10μm, the surface roughness of the substrates was increased up to Ra=1.0μm, and the substrates hardness was decreased from 89.0 HRA to 83.0 HRA after the two-step etching. It is observed that the morphologies of the diamond films on the WC-15%wt Co substrates emerge in various shapes. The indentation testing shows that the good adhesion between diamond film and the substrate after HF CVD deposition could be obtained.

Effects of Surface Pretreatment on Nucleation and Growth of Ultra-Nanocrystalline Diamond Films

The effects of different surface pretreatment nmthods on the nucleation and growth of ultra-nanocrystalline diamond （UNCD） fihns grown from focused microwave Ar/CHa/H2 （argon- rich） plasma were systematically studied. The surface roughness, nucleation density, mierostruc- ture, and crystallinity of the obtained UNCD films were characterized by atomic force microscope （AFM）, scanning electron microscopy （SEM）, X-ray diffraction （XRD）, and Raman spectroscopy. The results indicate that the nucleation enhancement was found to be sensitive to the different sur- face pretreatment methods, and a higher initial nucleation density leads to highly smooth UNCD films. When the silicon substrate was pretreated by a two-step method, i.e., plasma treatment followed by ultrasonic vibration with diamond nanopowder, the grain size of the UNCD films was greatly decreased： about 7.5 nm can be achieved. In addition, the grain size of UNCD films depends on the substrate pretreatment methods and roughness, which indicates that the surface of substrate profile has a ＂genetic characteristic＂.

Diamond machining of sinusoidal grid surface using fast tool servo system for fabrication of hydrophobic surface

Ultra-precision diamond machining with piezoelectric-assisted fast tool servo (FTS) was used to produce various free-form surfaces.A low cost,rapid and large area fabrication of uniform hydrophobic surface at room temperature which transfers the FTS fabricated sinusoidal grid surface to the flat film with UV-moulding process was described.A piezoelectric-assisted FTS with high band width of 2 kHz,travel range up to 16 μm and the compact mechanism structure was designed for the sinusoidal grid surface machining and the dynamic performance testing of FTS was described in detail.Machining results indicate that the dimensions of sinusoidal grid change with the variation of the FTS machining condition.Wetting properties of UV-moulded surface were evaluated,the best contact angle was measured to be 120.5° on the sinusoidal grid surface with profile wavelength of 350 μm and peak-to-valley amplitude of about 16 μm.

Effect of Krypton Addition on Electron Cyclotron Resonance-Radio Frequency Hybrid Oxygen Plasma for Patterning Diamond Surfaces

Electron cyclotron resonance radio frequency （ECR-rf） hybrid krypton-diluted oxygen plasmas were used to pattern the surfaces of diamond films with the assistance of a physical mask, while optical emission spectroscopy was employed to characterize the plasma. It was found that with krypton dilution the etching rate decreased, and also the aspect ratios of nanotips formed in micro-holes were significantly modified. The oxygen atomic densities were estimated by oxygen atom optical emission and argon actinometry. Under a microwave power of 300 W and rf bias of-300 V, the absolute density of ground-state oxygen atoms decreased from 1.3×10^12 cm^-3 to 1.4×10^11 cm^-3 as the krypton dilution ratio increased to 80%, accompanied by the decrease in the plasma excitation temperature. It is concluded that oxygen atoms play a dominant role in diamond etching. The relative variations in the horizontal and vertical etching rates induced by the addition of krypton are attributed to the observations of thicker nanotips at a high krypton dilution ratio.

Synthesis of Boron-doped Diamond/Porous Ti Composite Materials——Effect of Carbon Concentration

Highly boron-doped diamond films were deposited on porous titanium substrates by hot filament chemical vapor deposition technique. The morphology variation of highly boron-doped diamond films grown on porous titanium substrates was investigated, and the effects of carbon concentration on nucleation density and diamond growth were also studied. The continuous change of surface morphology and structure of diamond film were characterized by scanning electron microscopy. The structures of diamond film and interlayer were analyzed by X-ray diffraction. The quality of boron-doped diamond film was confirmed by visible Raman spectroscopy. The experimental results reveal that surface morphology and quality of boron-doped diamond films are various due to the change of carbon concentration. The thickness of intermediate layer decreases with the carbon concentration increasing.