Diamond Coatings Research Articles

Scratch adhesion evaluation of diamond like carbon coatings with alternate hard and soft multilayers

A series of four diamond like carbon coatings comprising alternating soft and hard layers was prepared by closed field unbalanced magnetron sputtering. A constant bias voltage of −40 V was used for soft layer deposition, while the hard layers were deposited at different bias voltages for different coatings in series. A uniform hard-to-soft layer thickness ratio of approximately 1:1.33 was maintained for all four coatings. Cross-sectional transmission electron microscopy of the coatings confirmed that these diamond like carbon coatings indeed exhibited distinct soft and hard layers. Moreover, increasing bias voltage during hard layer deposition also increased the residual stress in these coatings. The coatings were also subjected to scratch testing to determine the effect of increasing bias voltage on the scratch toughness. Scratch cracking mechanism changed from chevron tensile cracking at low bias voltages to buckle spallation at higher bias voltages. All the coatings exhibited substrate exposure at high normal loads beyond the upper critical load. The scratch crack propagation resistance parameter was reduced by ∼1.5 times when the bias voltage was increased to −140 V. It was demonstrated that coatings deposited at a hard layer bias voltage of −100 V demonstrated the best combination of mechanical properties, including the plastic deformation resistance (H3/E2 ratio) and elastic strain to failure (H/E ratio).

Hot-filament CVD diamond coatings for optical applications

The demand for highly scratch resistant transparent coatings is motivated by the industrial sector of consumer goods for example for the protection of displays, touch-screens, watches, and all kinds of optical instruments. In a wide variety of applications, scratch-free and highly wear-resistant surfaces are the enabling factor for improvement of lifetime and thus sustainability of the products. Diamond with its unique properties such as the highest known hardness, low thermal expansion coefficient and chemical resistance (to acids and bases) [1,2] has outstanding potential for optical applications [3]. The use of thin ultrahard diamond layers with adapted optical properties is expected to enhance the resistance against abrasive wear to a new level. At Fraunhofer IST large-area Hot-Filament Chemical Vapor Deposition (HFCVD) processes have been developed [4,5] and now utilized for depositing highly uniform and transparent diamond coatings on optical components with sizes of up to 200 mm × 200 mm. The use of single-layer diamond coatings is investigated as well as the integration of diamond films into multilayer film stacks combining anti-reflective properties with mechanical stability (strength). Four-layer anti-reflective coatings (Si3N4/SiO2/Diamond/SiO2) entirely deposited with hot-filament/hot-wire processes and their optical and mechanical performance will be presented.

Effect of doping level on residual stress, coating-substrate adhesion and wear resistance of boron-doped diamond coated tools

Boron doping can change the basic properties of diamond coatings prepared by the hot filament chemical vapor deposition (HFCVD) method, including residual stress, coating-substrate adhesion and wear resistance. However, the specific effect of boron doping level on the properties of diamond coatings and the mechanism needs further investigation. In the present study, the tungsten cemented carbide (WC-Co) material is selected as the substrate to deposit boron-doped diamond coatings with different doping levels ranging from 0 to 15,000 ppm. To elaborate the influences of doping level on the boron-doped diamond (BDD) coatings, microstructure, surface roughness, grain orientation, nanohardness, Raman spectral, Kernel Average Misorientation (KAM) and Rockwell indentation of diamond coatings are characterized, then friction tests and milling experiments are conducted on all specimens. The results indicate that the appropriate doping level of 8000 ppm can change the grain orientation to (110) orientation, guarantee diamond quality and hardness, reduce the residual stress, minimize the coefficients of friction (COF) and improve the tool life. Raman and KAM analysis demonstrate that the specimen generates suitable tensile stress in the diamond lattice and offsets the compressive stress of the coating to obtain the lowest residual stress and the highest coating-substrate adhesion strength. Friction test results illustrate that the specimen has the best wear resistance because the grain with (110) orientation has high hardness and low COF. In addition, milling experiments illustrate that the specimen has the best machining life due to the combination of good coating-substrate adhesion and wear resistance, with a tool life of 355 min, which is 29.6 % longer than the machining life of the undoped diamond coated tool.

Promising directions in studying and using polycrystalline diamond coating

The paper deals with the study of promising areas for obtaining and using thin diamond and carbon-containing coatings. The retrospective and current situation in distributing inventions protected by patents over the countries and companies and the role of Russian companies and scientific organizations in this process are analyzed. It is concluded that it is necessary to stimulate national applicants in order to maintain positive trends in patenting in the national market and abroad.

Influence of Size and Content on the Wear Resistance of Induction Brazing Diamond Coating in Air

Influence of Size and Content on the Wear Resistance of Induction Brazing Diamond Coating in Air

Comparison of Enamel Surface Roughness between Light-cured and Self-cured Composites used in Orthodontic Bonding by using Atomic Force Microscopy

Introduction: Debonding is a procedure of removing orthodontic attachments along with the entire residual adhesives from the surface of enamel following orthodontic treatment completion. The objective of the orthodontists should be to restore the surface of enamel as closely as possible to natural enamel without inducing iatrogenic injury and with minimal loss of enamel structure. Bonding of brackets on enamel involves surface etching, application of primer, and adhesive. All these steps involve the risk of damaging the enamel surface and changing its original morphology. Upon completion of orthodontic treatment, the debonding procedure followed by residual resin removal further damages the enamel, producing scratches, cracks, grooves, removal of fluoride-rich external enamel layer, and increasing the enamel roughness. The rough enamel surface inhibits proper cleaning and thus invites plaque deposition, bacterial retention, stain formation, and thus dampening the aesthetic appearance of the teeth. Restoring the enamel to its original morphology is a challenge. A variety of mechanical methods have been proposed to achieve satisfactory resin removal with least possible enamel damage following bracket debonding. The Enhance finishing and Pogo polishing system (Dentsply, Milford, USA) is also widely used and is made up of polymerized urethane dimethacrylate resin, aluminium oxide, silicon dioxide, and fine diamond powder. Methods: The sample of 50 tooth extracted for orthodontic purpose was procured as per the inclusion criteria. Buccal surfaces of teeth on the area where bracket is bonded and then debonding is done. After residual resin removal with Enhance system finishing and polishing bur. Measurements for each specimen were measured and mean was calculated and evaluated with the help of Atomic Force Microscopy (Baseline roughness data). Result: Self cure composite gives relatively lesser surface roughness when compared to light cure composites. Conclusion: The study shows that the self cure adhesive gives the smoother enamel surface when compared to the tooth treated with light cure adhesive after debonding and finishing and polishing.

Bonding of orthodontic ceramic brackets: Optimal conditioning method of lithium disilicate restorations

Introduction. According to the data obtained from the American Orthodontic Society survey conducted in 2015, the number of adult patients that requested orthodontic treatment increased from 14% to 27% between 2010 and 2014. Because of the increased age of the patients, fixed orthodontic treatment is expected to be performed on restored teeth, including all ceramic restorations. The objectives of the present study were to evaluate the influence of different surface treatments on the bond strength of ceramic brackets to lithium disilicate ceramic and to determine the mode of fracture. Material and method. 45 ceramic rectangular specimens were obtained from lithium disilicate CAD/CAM blocks which were divided in five groups according to the performed surface conditioning method: 1. grinding with a fine diamond bur (control group); 2. sandblasting with 29 ?m alumina (Al2O3); 3. etching with 4% hydrofluoric acid (HF); 4. sandblasting followed by conditioning with a universal primer - silanization (Al2O3 + S); 5. HF acid etching followed by silanization (HF + S). Shear bond strength test was performed after storing the samples in water bath for 7 days. All of the fractured samples were analyzed with optical microscope to determine the type of fracture. Results. HF acid etching followed by silanization performed the highest bond strength of 8.03 MPa, while sandblasting followed by silanization - 6.69 MPa. Mechanical surface conditioning with either HF acid etching or sandblasting resulted in significantly lower bond strength (2.65 MPa and 1.51 MPa respectively). Mainly adhesive mode of fractures was noticed after sandblasting and silanization, indicating minor chance of damaging the ceramic restoration after debonding, at the end of the orthodontic treatment, unlike the ceramic specimens in the Group 5 (HF + S) with 42.8% mixed and 14.4% cohesive fractures; 100% adhesive fractures were observed after mechanical treatments. Conclusion. According to the SBS test results and fracture type, sandblasting followed by the application of a universal primer can be considered as an adequate method for conditioning the lithium disilicate ceramic restorations before the bonding of ceramic orthodontic brackets.

Effect of Substrate Pretreatment Process on the Cutting Performance of Diamond-Coated PCB Micro-Milling Tools

Diamond coatings were deposited on PCB (printed circuit board) carbide milling tool substrates under various schemes of acid and alkali pretreatment by hot filament chemical vapor deposition (HFCVD). Scanning electron microscopy and X-ray coating analysis were used to examine the surface morphology of the milling tools and the impact of de-cobalt from the substrate surface after pretreatment. Milling experiments were carried out to study the cutting performance of diamond-coated PCB micro-milling tools under various pretreatment processes. The results show that abrasive wear, coating flaking, and cutting-edge chipping are the main failure forms of coated PCB milling tools. The substrate pretreatment process with 20 min of alkali etching followed by 20 s of acid etching allows the diamond-coated micro-milling tools to produce the best film-substrate adhesion and substrate strength. These milling tools also have the longest service lives and are suitable for the high-speed cutting processing of PCB.

Technology Features of Diamond Coating Deposition on a Carbide Tool

The production of carbide tools with polycrystalline diamond coatings, which are used for processing modern carbon composite materials, includes a number of technological techniques that ensure reliable adhesion of the coating to the substrate. This review examines these features of substrate-surface pretreatment to improve adhesion, which includes chemical etching, mechanical hardening, modification by ion beams, plasma treatment and application of buffer layers between the substrate and the coating. This review also discusses the advantages and disadvantages of the most common methods for obtaining polycrystalline diamond coatings using hot filament and deposition of coatings from microwave plasma.

Synthesis, characterization and cutting performances of gradient gradual changing (GGC-) MCD/SMCD/NCD/UNCD diamond coatings with tailored interfacial integrity on CFRP drilling tools

Drilling holes is a common mechanical processing method in the high-precision machining of carbon fiber reinforced plastic (CFRP) material. Diamond coatings can be deposited on the drilling tools to enhance the tool life and improve the machining quality. However, traditional multilayer diamond coatings, such as MCD/NCD etc., easily suffer from interfacial separation in actual applications due to the sharp interfaces of diamond layers. Novel gradient gradual changing (GGC-) structure without clear interfaces is applied to tailor the architecture of diamond coatings, which can lead to superior interfacial integrity and the reduction of sp2 phase content at the transition between distinct diamond layers. Various diamond films, containing monolayer diamond films (MCD, SMCD, NCD, UNCD) and gradient gradual changing multilayer diamond films (GGC-MCD/SMCD/NCD, GGC-MCD/SMCD/NCD/UNCD), were fabricated on WC-Co samples. The deposition of tailored gradient gradual changing coating interfacial architecture can be accomplished by controlling the linear variation of carbon concentration and gas pressure simultaneously. The complementary characteristics of high coating-substrate adhesive strength, superior frictional and wear resistance, good interfacial integrity and favorable crack propagation resistance are concentrated on GGC-MCD/SMCD/NCD and GGC-MCD/SMCD/NCD/UNCD coatings compared to monolayer MCD, SMCD, NCD and UNCD coatings. Moreover, because of the existence of UNCD layer, GGC-MCD/SMCD/NCD/UNCD coating performs lower surface roughness, frictional coefficient and higher surface smoothness than GGC-MCD/SMCD/NCD coating. Besides, the cutting performances in high-speed drilling experiments of CFRP laminates using different types of diamond coated drilling tools were compared systematically, showing that the dominant wear modes are abrasive wear and adhesive wear, and the GGC-MCD/SMCD/NCD/UNCD coated drilling tool exhibits the longest tool lifetime and best machining quality because of the overall interfacial integrity and high surface smoothness.

Key Challenges in Diamond Coating of Titanium Implants: Current Status and Future Prospects.

Over past years, the fabrication of Ti-based permanent implants for fracture fixation, joint replacement and bone or tooth substitution, has become a routine task. However, it has been found that some degradation phenomena occurring on the Ti surface limits the life or the efficiency of the artificial constructs. The task of avoiding such adverse effects, to prevent microbial colonization and to accelerate osteointegration, is being faced by a variety of approaches in order to adapt Ti surfaces to the needs of osseous tissues. Among the large set of biocompatible materials proposed as an interface between Ti and the hosting tissue, diamond has been proven to offer bioactive and mechanical properties able to match the specific requirements of osteoblasts. Advances in material science and implant engineering are now enabling us to produce micro- or nano-crystalline diamond coatings on a variety of differently shaped Ti constructs. The aim of this paper is to provide an overview of the research currently ongoing in the field of diamond-coated orthopedic Ti implants and to examine the evolution of the concepts that are accelerating the full transition of such technology from the laboratory to clinical applications.

Outstanding Bio-Tribological Performance Induced by the Synergistic Effect of 2D Diamond Nanosheet Coating and Silk Fibroin.

Due to their excellent biocompatibility, outstanding mechanical properties, high strength-to-weight ratio, and good corrosion resistance, titanium (Ti) alloys are extensively used as implant materials in artificial joints. However, Ti alloys suffer from poor wear resistance, resulting in a considerably short lifetime. In this study, we demonstrate that the chemical self-assembly of novel two-dimensional (2D) diamond nanosheet coatings on Ti alloys combined with natural silk fibroin used as a novel lubricating fluid synergistically results in excellent friction and wear performance. Linear-reciprocating sliding tests verify that the coefficient of friction and the wear rate of the diamond nanosheet coating under silk fibroin lubrication are reduced by 54 and 98%, respectively, compared to those of the uncoated Ti alloy under water lubrication. The lubricating mechanism of the newly designed system was revealed by a detailed analysis of the involved microstructural and chemical changes. The outstanding tribological behavior was attributed to the establishment of artificial joint lubrication induced by the cross binding between the diamond nanosheets and silk fibroin. Additionally, excellent biocompatibility of the lubricating system was verified by cell viability, which altogether paves the way for the application of diamond coatings in artificial Ti joint implants.

Microcrystalline diamond film evaluation by spectroscopic optical coherence tomography

This study has focused on the microcrystalline diamond film (MCD) thickness evaluation. For this purpose, optical coherence tomography (OCT) enhanced by spectroscopic analysis has been used as a method of choice. The average thickness of the tested layer was about 1.5 µm, which is below the standard 2-point OCT resolution. In this case, the usefulness of the spectroscopic analysis was confirmed for the evaluation of the thickness changes in the submicrometer range. Full Text: PDF ReferencesM.D. Drory, J.W. Hutchinson, "Diamond Coating of Titanium Alloys", Science, 263 (1994). CrossRef J. Wang, J. Zhou, H.Y. Long, Y.N. Xie, X.W. Zhang, H. Luo, Z.J. Deng, Q. Wei, Z.M. Yu, J. Zhang, Z.G. Tang, "Tribological, anti-corrosive properties and biocompatibility of the micro- and nano-crystalline diamond coated Ti6Al4V", Surf. Coat. Technol., 258 (2014). CrossRef P.A. Nistor, P.W. May, F. Tamagnini, A.D. Randall, M.A. Caldwell, "Long-term culture of pluripotent stem-cell-derived human neurons on diamond – A substrate for neurodegeneration research and therapy", Biomaterials, 61 (2015). CrossRef C.A. Love, R.B. Cook, T.J. Harvey, P.A. Dearnley, R.J.K. Wood, "Diamond like carbon coatings for potential application in biological implants—a review", Tribol. Int., 63 (2013). CrossRef P. Strąkowska, R. Beutner, M. Gnyba, A. Zielinski, D. Scharnweber, "Electrochemically assisted deposition of hydroxyapatite on Ti6Al4V substrates covered by CVD diamond films — Coating characterization and first cell biological results", Materials Science and Engineering: C, 59 (2016). CrossRef T.S. Ho, P. Yeh, C.C. Tsai, K.Y. Hsu, S.L. Huang., "Spectroscopic measurement of absorptive thin films by Spectral-Domain Optical Coherence Tomography", Opt. Express 22, 5 (2014). CrossRef N. Bosschaart, T.G. van Leeuwen, M.C.G. Aalders, D.J. Faber, "Quantitative comparison of analysis methods for spectroscopic optical coherence tomography", Biomedical Opt. Express 4, 11 (2013). CrossRef F.E Robles, C. Wilson, G. Grant, A. Wax, "Molecular imaging true-colour spectroscopic optical coherence tomography", Nat. Photonics 5, 12 (2011). CrossRef A.F. Fercher, W. Drexler, C.K. Hitzenberger, T. Lasser, "Optical coherence tomography - principles and applications", Rep. Prog. Phys. 66, 239 (2003). CrossRef A.M. Kamińska, M.R. Strąkowski, J. Pluciński, "Spectroscopic Optical Coherence Tomography for Thin Layer and Foil Measurements", Sensors 20, 19, (2020). CrossRef M. Kraszewski, M. Strąkowski, J. Pluciński, B.B. Kosmowski, "Spectral measurement of birefringence using particle swarm optimization analysis", Appl. Opt. 54, 1 (2015). CrossRef

Tribological Performance of Microcrystalline Diamond (MCD) and Nanocrystalline Diamond (NCD) Coating in Dry and Seawater Environment

In the present study, the tribological properties of diverse crystalline diamond coating with micro (MCD) and nanometer (NCD) sizes, fabricated by the microwave plasma chemical vapor deposition (MPCVD) method, are systematically investigated in dry and seawater environments, respectively. Owing to the SiO2 lubricating film with extraordinary hydrophilicity performance by a tribochemical reaction, the average friction coefficient (COF) and wear rate of NCD coating under seawater decreased by 37.8% and 26.5%, respectively, comparing with in dry conditions. Furthermore, graphite would be generated with the increment of surface roughness. Graphite transformed from the diamond under high contact pressure. Thus, with the synergism between SiO2 lubricating film with extraordinary hydrophilicity performance and graphite, the corresponding COF and wear rate of MCD would be further decreased by up to 64.1% and 39.5%. Meanwhile, various characterizations on morphology, spectra, and tribological performance of the deposited diamond coating were conducted to explore the in-depth mechanism of the enhanced tribological performance of our NCD and MCD coatings in the extreme under seawater working conditions. We envision this work would provide significant insights into the wear behavior of diamond coatings in seawater and broaden their applications in protective coatings for marine science.

Polycrystalline Diamond Coating on Orthopedic Implants: Realization and Role of Surface Topology and Chemistry in Adsorption of Proteins and Cell Proliferation.

Polycrystalline diamond has the potential to improve the osseointegration of orthopedic implants compared to conventional materials such as titanium. However, despite the excellent biocompatibility and superior mechanical properties, the major challenge of using diamond for implants, such as those used for hip arthroplasty, is the limitation of microwave plasma chemical vapor deposition (CVD) techniques to synthesize diamond on complex-shaped objects. Here, for the first time, we demonstrate diamond growth on titanium acetabular shells using the surface wave plasma CVD method. Polycrystalline diamond coatings were synthesized at low temperatures (∼400 °C) on three types of acetabular shells with different surface structures and porosities. We achieved the growth of diamond on highly porous surfaces designed to mimic the structure of the trabecular bone and improve osseointegration. Biocompatibility was investigated on nanocrystalline diamond (NCD) and ultrananocrystalline diamond (UNCD) coatings terminated either with hydrogen or oxygen. To understand the role of diamond surface topology and chemistry in the attachment and proliferation of mammalian cells, we investigated the adsorption of extracellular matrix proteins and monitored the metabolic activity of fibroblasts, osteoblasts, and bone-marrow-derived mesenchymal stem cells (MSCs). The interaction of bovine serum albumin and type I collagen with the diamond surfaces was investigated by confocal fluorescence lifetime imaging microscopy (FLIM). We found that the proliferation of osteogenic cells was better on hydrogen-terminated UNCD than on the oxygen-terminated counterpart. These findings correlated with the behavior of collagen on diamond substrates observed by FLIM. Hydrogen-terminated UNCD provided better adhesion and proliferation of osteogenic cells, compared to titanium, while the growth of fibroblasts was poorest on hydrogen-terminated NCD and MSCs behaved similarly on all tested surfaces. These results open new opportunities for application of diamond coatings on orthopedic implants to further improve bone fixation and osseointegration.

Growth of Nitrogen Incorporated Ultrananocrystalline Diamond Coating on Graphite by Hot Filament Chemical Vapor Deposition.

This article shows the results of experiments to grow Nitrogen incorporated ultrananocrystalline diamond (N-UNCD) films on commercial natural graphite (NG)/Cu anodes by hot chemical vapor deposition (HFCVD) using a gas mixture of Ar/CH4/N2/H2. The experiments focused on studying the effect of the pressure in the HFCVD chamber, filament-substrate distance, and temperature of the substrate. It was found that a substrate distance of 3.0 cm and a substrate temperature of 575 C were optimal to grow N-UNCD film on the graphite surface as determined by Raman spectroscopy, SEM, and TEM imaging. XPS analysis shows N incorporation through the film. Subsequently, the substrate surface temperature was increased using a heater, while keeping the substrate-filament distance constant at 3.0 cm. In this case, Raman spectra and SEM images of the substrate surface showed a major composition of graphite in the film as the substrate-surface temperature increased. Finally, the process pressure was increased to 10 Torr where it was seen that the growth of N-UNCD film occurred at 2.0 cm at a substrate temperature of 675 C. These results suggest that as the process pressure increases a smaller substrate-filament distance and consequently a higher substrate surface temperature can still enable the N-UNCD film growth by HFCVD. This effect is explained by a mean free path analysis of the main precursors H2 and CH3 molecules traveling from the filament to the surface of the substrate The potential impact of the process developed to grow electrically conductive N-UNCD films using the relatively low-cost HFCVD process is that this process can be used to grow N-UNCD films on commercial NG/Cu anodes for Li-ion batteries (LIBs), to enable longer stable capacity energy vs. charge/discharge cycles.

Noncarious cervical lesions: Morphology and progression, prevalence, etiology, pathophysiology, and clinical guidelines for restoration.

To synthesize the literature regarding noncarious cervical lesions (NCCLs) and propose clinical guidelines when lesion restoration is indicated. A PubMed search was performed related to NCCL morphology, progression, prevalence, etiology, pathophysiology, and restoration. NCCLs form as either rounded (saucerlike) depressions with smooth, featureless surfaces that progress mainly in height or as V-shaped indentations that increase in both height and depth. Prevalence ranges from less than 10% to over 90% and increases with age. Common locations are the facial surfaces of maxillary premolars. They have a multifactorial etiology due to personal habits such as excessive horizontal toothbrushing and consumption of acidic foods and drinks. Occlusal factors have been identified as contributing to the prevalence of NCCLs in some studies, whereas other studies indicate there is no relationship. The concept of abfraction has been proposed whereby mechanical stress from occlusal loading plays a role in the development and progression of NCCLs with publications supporting the concept and others indicating it lacks the required clinical documentation. Regardless of the development mechanism, demineralization occurs and they are one of the most common demineralization diseases in the body. Treatment should be managed conservatively through preventive intervention with restorative treatment delayed until it becomes necessary due to factors such as lesion progression, impact on patient's quality of life, sensitivity, poor esthetics, and food collection may necessitate restoration. Composite resins are commonly used to restore NCCLs although other materials such as glass ionomer and resin-modified glass ionomer are also used. Sclerotic dentin does not etch like normal dentin and therefore it has been recommended to texture the dentin surface with a fine rotary diamond instrument to improve restoration retention. Some clinicians use mechanical retention to increase retention. Beveling of enamel is used to increase the bonding area and retention as well as enhance the esthetic result by gradually creating a color change between the restoration and tooth. Both multistep and single-step adhesives have been used. Dentin etching should be increased to 30 seconds due to the sclerotic dentin with the adhesive agent applied using a light scrubbing motion for 20 seconds but without excessive force that induces substantial bending of a disposable applicator. Both flowable and sculptable composite resins have been successfully used with some clinicians applying and polymerizing a layer of flowable composite resin and then adding an external layer of sculptable composite resin to provide enhanced resistance to wear. When caries is present, silver diamine fluoride has been used to arrest the caries rather than restore the lesion. Noncarious cervical lesions (NCCLs) form as smooth saucerlike depressions or as V-shaped notches. Prevalence values as high as 90% and as low as 10% have been reported due to habits such as excessive toothbrushing and an acidic diet. Occlusal factors have been proposed as contributing to their presence but it remains controversial. Publications have both supported and challenged the concept of abfraction. They are one of the most common demineralization diseases in the body. Conservative treatment through prevention is recommended with restorative treatment delayed as long as possible. When treatment is needed, composite resins are commonly used with proposed restorative guidelines including texturing the sclerotic dentin, beveling the enamel, potential use of mechanical retention, 30 seconds of acid etching, and use of either multistep or single-step adhesives in conjunction with a light scrubbing motion for 20 seconds without excessive force placed on disposable applicators.

Microstructure, mechanical properties and reciprocating wear properties of diamond grits-reinforced NiCrBSi composite coatings on 42CrMo

In this study, diamond grits-reinforced wear-resistant NiCrBSi composite coatings with diamond exposed to the air (Sample I) and embedded in the coating (Sample II) were prepared on 42CrMo steel by vacuum cladding technique. Moreover, a post-heat treatment was performed to restore the weakened substrate. The surface morphology, interfacial microstructure, mechanical properties and reciprocating wear properties of the coated samples, as well as the post-heat-treated samples, were investigated. Besides, the wear mechanism was discussed. On both the coatings, flaky and prismatic structure and rectangular precipitates around diamond grits were chromium carbides. The cross-sectional morphology and EDS results showed that a metallurgical bonding interface was developed by the apparent element diffusion between the cladding layers and the 42CrMo steel substrates, which was beneficial for ensuring their bonding strength. Both the NiCrBSi/diamond composite coatings could significantly improve the wear resistance of 42CrMo steels. The wear resistance of Sample I and Sample II were 7.7 times and 5.3 times heavier than that of the original substrate, respectively. The abrasive, adhesive, and oxidative wear occurred during the friction-wear tests, in which the abrasive wear was dominant. In addition, the dominant wear mechanism of 42CrMo steel was adhesive wear. After the post-heat treatment, the weakened properties of 42CrMo steel were restored due to the phase transformation from lath martensite and ferrite to lamellar pearlite and ferrite. Further, the treated 42CrMo steel achieved higher properties than the original substrate and retained the excellent wear properties of the surface composite coating.

Gas-Jet Synthesis of Diamond Coatings from a H2+CH4+Ar Mixture Activated in a Microwave Discharge

Gas-Jet Synthesis of Diamond Coatings from a H2+CH4+Ar Mixture Activated in a Microwave Discharge

INTERFACE MODIFICATION OF SUBSTRATE FOR ENHANCING ADHESIVE STRENGTH OF CVD DIAMOND COATING BY SOLID PARTICLES

The strong adhesive strength is essential for the widespread applications of diamond coating in the mechanical field. In this paper, a novel method combining conventional chemical vapor deposition (CVD) diamond technique with solid particles was proposed to modify the interface material properties of substrate to improve the adhesive strength of the diamond coating. Prior to deposition, wet dispersion was adopted to uniformly distribute solid particles on the substrate, with which the diamond coatings with the WC, TiC and BN particles embedded at the interface were fabricated on Co-cemented tungsten carbide (WC-Co) substrate. In addition, the pure diamond coating was also fabricated for comparison. The as-deposited diamond coatings were characterized by scanning electron microscopy (SEM), atomic force microscopy (AFM), energy dispersive X-ray spectroscopy (EDS) and Raman spectroscopy. The results indicated that the diamond coating with TiC exhibited the highest residual stress, which may be due to the larger lattice mismatch between TiC and diamond as compared to WC and BN. The indentation test suggested that WC and BN particles were favorable for the improvement of the adhesive strength and the crack resistance of diamond coating, while this phenomenon was not observed in the diamond coating with TiC particle. This might be caused by the large lattice parameter, high lattice mismatch, and high thermal expansion coefficient mismatch of TiC as compared with diamond. Furthermore, the lattice parameter of additional particles might be an important factor to determine whether or not the adhesive strength of diamond coating can be enhanced, because it determined the compressive stress or tensile stress generated inside diamond coating. Hence, interface modification of substrate by dispersing the solid particles with low lattice parameter or similar material properties of diamond may be an effective and convivence approach to improve the adhesive strength of the diamond coating.