Pulsed laser deposition of hydroxyapatite-diamondlike carbon multilayer films and their adhesion aspects

We have developed a layered hydroxyapatite/diamondlike carbon/functionally gradient diamondlike carbon-silver/titanium carbide/titanium carbonitride/titanium nitride composite film using pulsed laser deposition. A diamondlike carbon interlayer between a hydroxyapatite coating and the Ti-6Al-4V alloy can serve several purposes, including preventing corrosion of Ti-6Al-4V alloy, overcoming poor adhesion between the hydroxyapatite coating and the titanium oxide surface, and reducing inflammation at the implant/tissue interface. Titanium nitride, titanium carbonitride (TiC _x N _y ), titanium carbide and functionally gradient diamondlike carbon-silver layers were used to improve the adhesion of diamondlike carbon films to Ti-6Al-4V alloy. We envision several potential medical applications for these multilayer materials, including use in orthopedic and dental devices.     

Nucleation and growth of diamond films on aluminum nitride by hot filament chemical vapor deposition

Nucleation and growth of diamond films on aluminum nitride (ALN) coatings were investigated by scanning electron microscopy, Raman spectroscopy and scratch test. ALN films were grown in a magnetron sputtering deposition. The substrates were Si(111) and tungsten carbide (WC). Chemical vapor deposition (CVD) diamond films were deposited on ALN films by hot filament CVD. The nucleation density of diamond on ALN films was found to be approximately 10⁵ cm⁻², whereas over 10¹⁰ cm⁻² after negative bias pre-treatment for 35 min was −320 V, and 250 mA. The experimental studies have shown that the stresses were greatly minimized between diamond overlay and ALN films as compared with WC substrate. The results obtained have also confirmed that the ALN, as buffer layers, can notably enhance the adhesion force of diamond films on the WC.     

Pulsed laser deposition of functionally gradient diamondlike carbon–metal nanocomposites

Diamondlike carbon thin films possess atomic smoothness, chemical inertness, and hardness properties close to those of diamond. Unfortunately, these films exhibit poor adhesion to metals and polymers used in medical prostheses. This paper presents the processing and characterization of diamondlike carbon–copper, diamondlike carbon–silver, diamondlike carbon–silicon, and diamondlike carbon–titanium nanocomposite films with enhanced adhesion to Ti–6Al–4V alloy substrates. Silver forms nanoparticle arrays within the diamondlike carbon matrix in diamondlike carbon–silver nanocomposite films. On the other hand, titanium forms layers of titanium carbide within the diamondlike carbon matrix in diamondlike carbon–titanium nanocomposite films. These films were characterized using electron energy loss spectroscopy, transmission electron microscopy, Raman spectroscopy, Rutherford backscattering spectrometry, nanoindentation, wear testing, and scratch adhesion testing. Diamondlike carbon–metal nanocomposite films have numerous potential medical applications, including use on the surfaces of medical prostheses.     

Adhesion at diamond-metal interfaces: a chemical composition perspective

Diamond films were chemically vapor deposited (CVD) on titanium, tungsten, molybdenum, copper and aluminum oxide substrates. In these studies, the interface formed between diamond and the substrate was exposed by mechanically deforming the metal substrate or diamond film to cause film delamination. The observed degree of adhesion for these interfaces can be ranked in the order: Ti » Al₂O₃ (thin films) > Cu > W » Mo. For highly adherent films, delamination procedures were carried out under controlled conditions in order to preserve the integrity of the interfacial species. The exposed interfaces were characterized by X-ray photoelectron spectroscopy (XPS), scanning Auger microscopy (SAM), scanning electron microscopy (SEM) and Raman microprobe spectroscopy. We find that substantial interfacial reaction layers exist at all interfaces except in the diamond-copper system and are composed of both oxides and carbides of the native substrate. Variations in the relative concentration of these species and the distribution throughout the reaction layer also were observed for the different substrates. We believe that both the chemical composition and morphology of the interface influence the adhesion properties of the diamond coating. Correlated investigations of the interfacial surfaces reveal that fracture of the diamond-metal interface occurs discretely at the diamond nucleation plane or within a reaction layer near the diamond interface. We discuss each of these findings in light of qualitative observations of adhesion and suggest avenues for improving the adhesion of diamond films.     

The effect of a buffer layer on the structure and the performance of cutting-tools for ZrWN films that are deposited using DCMS and HIPIMS

This paper determines the optimal settings for the deposition of ZrWN nitride films using reactive direct current magnetron sputtering (DCMS) and high-power impulse magnetron sputtering (HIPIMS), with pure Zr and W metal targets and Ar plasma and N₂ reactive gases. The materials tested as buffer layers are metal tungsten (W) and tungsten nitride (WN) thin films. Using a Taguchi method, this study determines the effect of deposition parameters for the buffer layer (W DC power, substrate bias, N₂/(N₂+Ar) flow rate and substrate temperature) on the structural and mechanical properties, and the dry machining performance of cutting-tools for multilayer ZrWN/W and ZrWN/WN/substrates. In the confirmation runs using grey Taguchi analysis, there is an improvement of 32.31% and 13.38% in surface roughness and flank wear, respectively. The films are characterized using X-ray diffraction (XRD), atomic force microscopy (AFM), scanning electron microscopy (SEM), transmission electron microscopy (FEI-TEM) and a nanoindenter. The TEM pattern for the ZrWN films shown corresponds to the (111), (200) and (220) planes of the face-center-cubic phase. Pretreatment of a tungsten carbide tool uses oxygen plasma etching to enhance the adhesion of the multilayer ZrWN/WN coating. Compared with coatings that are deposited using DCMS, the samples that are deposited using HIPIMS exhibit a higher film density and a smoother surface. In the HIPIMS mode, the XRD diffraction peaks of the films are sharper and more intense, which indicates an improvement in crystallinity.     

Rhenium alloys as ductile substrates for diamond thin-film electrodes

Molybdenum–rhenium (Mo/Re) and tungsten–rhenium (W/Re) alloys were investigated as substrates for thin-film, polycrystalline boron-doped diamond electrodes. Traditional, carbide-forming metal substrates adhere strongly to diamond but lose their ductility during exposure to the high-temperature (1000 °C) diamond, chemical vapor deposition environment. Boron-doped semi-metallic diamond was selectively deposited for up to 20 h on one end of Mo/Re (47.5/52.5 wt.%) and W/Re (75/25 wt.%) alloy wires. Conformal diamond films on the alloys displayed grain sizes and Raman signatures similar to films grown on tungsten; in all cases, the morphology and Raman spectra were consistent with well-faceted, microcrystalline diamond with minimal sp² carbon content. Cyclic voltammograms of dopamine in phosphate-buffered saline (PBS) showed the wide window and low baseline current of high-quality diamond electrodes. In addition, the films showed consistently well-defined, dopamine electrochemical redox activity. The Mo/Re substrate regions that were uncoated but still exposed to the diamond-growth environment remained substantially more flexible than tungsten in a bend-to-fracture rotation test, bending to the test maximum of 90° and not fracturing. The W/Re substrates fractured after a 27° bend, and the tungsten fractured after a 21° bend. Brittle, transgranular cleavage fracture surfaces were observed for tungsten and W/Re. A tension-induced fracture of the Mo/Re after the prior bend test showed a dimple fracture with a visible ductile core. Overall, the Mo/Re and W/Re alloys were suitable substrates for diamond growth. The Mo/Re alloy remained significantly more ductile than traditional tungsten substrates after diamond growth, and thus may be an attractive metal substrate for more ductile, thin-film diamond electrodes.     

Gradient layers of boron-doped diamond on titanium substrates

For the deposition of well-adhesive, low-doped diamond layers on titanium substrates a gradient layer is designed. At first a highly boron-doped diamond layer is deposited, which shows good adhesion to the titanium substrate, followed by a low-boron-doped diamond layer on the surface.The boron-doped diamond layers were deposited on titanium stretch metal substrates by the hot-filament CVD method. It is shown that with increasing boron content during diamond deposition above 6000 ppm B/C the intermediate Ti(C,B) layers becomes very thin and so at high-boron concentrations no problem with layer adhesion occurs. These Ti(C,B)-layers formed during diamond deposition were investigated by standard metallographic preparations. To form a diamond gradient layer on the highly boron-doped diamond the boron content was reduced and a low-doped diamond layer was deposited.Electrochemical cyclic voltammetric measurements show that the lower boron contents at the diamond surface provide better electrochemical properties. These layers show extraordinary electrochemical properties in respect of the gained hydrogen and oxygen overvoltage.     

Effect of titanium metal in the prenucleation of ultrananocrystalline diamond film growth at low substrate temperature

Ultrananocrystalline diamond (UNCD) film is usually grown in methane–argon plasma unlike methane–hydrogen plasma conventionally used to deposit microcrystalline diamond film. The prenucleation and growth mechanism of these two types of diamond films are different as well. The present study introduces titanium metal powder during ultrasonication of silicon substrate to enhance the nucleation density of UNCD. A titanium thin film was also used at the interface to find the effect of metal on the growth of diamond film. The nucleation density of as-grown film was estimated from the FE-SEM images. After 20 min of growth, nucleation density reaches to 10¹¹/cm² on a surface pretreated by titanium mixed nanodiamond powder. Raman study was carried out for qualitative analysis of different carbon phase present in the UNCD films. X-ray photoelectron spectroscopy (XPS) was used to understand the growth mechanism by detecting the formation of carbon phase and metal carbide formation at the surface after stopping the growth at different time intervals.     

Deposition of cubic boron nitride films on diamond-coated WC:Co inserts

Cubic boron nitride (cBN) thin films were deposited on diamond-coated tungsten carbide (WC) cutting inserts using electron cyclotron resonance (ECR) microwave plasma chemical vapor deposition (MPCVD). The effects of gas flow rate and substrate bias on the phase composition and structure of the BN films deposited on diamond surfaces were studied. It was revealed that both the cubic phase formation and the selective etching of hexagonal phase were controlled by modulating the hydrogen and boron trifluoride flow rate ratio. By the trial and error method the gas flow rate ratio and substrate bias voltage were optimized. Moreover the phase composition of the BN film was found to be affected by the thickness of diamond buffer layer and interrelated to the effective substrate bias. The hardness of the resulting cBN films reached the value of 70 GPa. In the synthesized coatings, the diamond beneath renders the best mechanical supporting capacity while the top cBN provides the superior chemical resistance and extreme hardness. The cBN/diamond bilayers deposited on WC inserts may serve as universal tool coatings for machining steels and other ferrous metals.     

Interfacial processing and adhesion of diamond,diamond-like,and TiN films on metallic and polymeric substrates

Diamond, diamond-like, and titanium nitride (TiN) films have extremely desirable chemical, electrical, and mechanical properties for a variety of applications ranging from corrosion- and erosion-resistant coatings to electronics packaging of microelectronic devices. However, many of these applications are limited by the poor adhesion of these films to metal and polymer substrates. The adhesion of a film is determined primarily by internal stresses in the film, thermal and lattice mismatch, and most importantly by interfacial bonding. We have developed methods based on mechanical interlocking, chemical bonding, grading of interatomic potentials, and the multilayer discontinuous thin films approach to control stresses and strains in thin films. A substantial improvement in adhesion and wear properties is obtained by using these methods selectively. We review issues related to the adhesion of diamond, diamond-like carbon, and TiN films on metal and polymeric substrates.     

Ceramic Coatings on Ceramic Substrates by Liquid Metal Transfer

A variety of ceramic coatings have been put on ceramic substrates by the molten metal transfer technique. In the diffision coating process a reactant metal dissolved in a molten "transfer agent" metal reacts with a substrate to form the coating. Titanium dissolved in molten tin has been reacted with silicon carbide, aluminum nitride, and silicon nitride substrates to produce titanium carbide and titanium nitride coatings, respectively. Similarly tantalum metal has been reacted to form carbide or nitride coatings. The unreacted tin is finally removed by decantation followed by acid leaching.     

Adherent and low friction nano-crystalline diamond film grown on titanium using microwave CVD plasma

The use of titanium alloys for aerospace and biomedical applications could increase if their tribological behavior was improved. The deposition of an adherent diamond coating can resolve this issue. However, due to the different thermal expansion coefficients of the two materials, it is difficult to grow adherent thin diamond layers on Ti and its metallic alloys. In the present work microwave plasma chemical vapor deposition (MWPCVD) was used to deposit smooth nano-crystalline diamond (NCD) film on pure titanium substrate using Ar, CH₄ and H₂ gases at moderate deposition temperatures. Of particular interest in this study was the exceptional adhesion of approximately 2 μm-thick diamond film to the metal substrate as observed by indentation testing up to 150 kg load. The friction coefficient, which was measured with a cemented carbide ball of 10 mm diameter with 20 N load, was estimated to be around 0.04 in dry air. Morphology, surface roughness, diamond crystal orientation and quality were obtained by characterizing the sample with field emission electron microscopy (FE-SEM), atomic force microscopy (AFM), X-ray diffraction (XRD) and Raman spectroscopy, respectively.     

Morphological study of thin films: Simulation and experimental insights using horizontal visibility graph

We studied the morphological nature of various thin films such as silicon carbide (SiC), diamond (C), germanium (Ge), and gallium nitride (GaN) on silicon substrate Si(100) using the pulsed laser deposition (PLD) method and Monte Carlo simulation. We, for the first time, systematically employed the visibility algorithm graph to meticulously study the morphological features of various PLD grown thin films. These thin-film morphologies are investigated using random distribution, Gaussian distribution, patterned heights, etc. The nature of the interfacial height of individual surfaces is examined by a horizontal visibility graph (HVG). It demonstrates that the continuous interfacial height of the silicon carbide, diamond, germanium, and gallium nitride films are attributed to random distribution and Gaussian distribution in thin films. However, discrete peaks are obtained in the brush and step-like morphology of germanium thin films. Further, we have experimentally verified the morphological nature of simulated silicon carbide, diamond, germanium, and gallium nitride thin films were grown on Si(100) substrate by pulsed laser deposition (PLD) at elevated temperature. Various characterization techniques have been used to study the morphological, and electrical properties which confirmed the different nature of the deposited films on the Silicon substrate. Decent hysteresis behavior has been confirmed by current-voltage (IV) measurement in all the four deposited films. The highest current has been measured for GaN at ～60 nA and the lowest current in SiC at ～30 nA level which is quite low comparing with the expected signal level (μA). The HVG technique is suitable to understand surface features of thin films which are substantially advantageous for the energy devices, detectors, optoelectronic devices operating at high temperatures.     

Tribological properties and cutting performance of boron and silicon doped diamond films on Co-cemented tungsten carbide inserts

Boron and silicon doped diamond films are deposited on the cobalt cemented tungsten carbide (WC-Co) substrate by using a bias-enhanced hot filament chemical vapor deposition (HFCVD) apparatus. Acetone, hydrogen gas, trimethyl borate (C₃H₉BO₃) and tetraethoxysilane (C₈H₂₀O₄Si) are used as source materials. The tribological properties of boron-doped (B-doped), silicon-doped (Si-doped) diamond films are examined by using a ball-on-plate type rotating tribometer with silicon nitride ceramic as the counterpart in ambient air. To evaluate the cutting performance, comparative cutting tests are conducted using as-received WC-Co, undoped and doped diamond coated inserts, with high silicon aluminum alloy materials as the workpiece. Friction tests suggest that the Si-doped diamond films present the lowest friction coefficient and wear rate among all tested diamond films because of its diamond grain refinement effect. The B-doped diamond films exhibit a larger grain size and a rougher surface but a lower friction coefficient than that of undoped ones. The average friction coefficient of Si-doped, B-doped and undoped diamond films in stable regime is 0.143, 0.193 and 0.233, respectively. The cutting results demonstrate that boron doping can improve the wear resistance of diamond films and the adhesive strength of diamond films to the substrates. Si-doped diamond coated inserts show relatively poor cutting performance than undoped ones due to its thinner film thickness. B-doped and Si-doped diamond films may have tremendous potential for mechanical application.     

Growth and Adhesion Enhancement of Diamond Films Deposited on Steel Substrates by a Cr–N Interlayer

Diamond film deposition onto iron-based substrates by chemical vapor deposition methods is complicated by the formation of black carbon or graphitic soot on the substrate surface prior to diamond nucleation and growth, by fast diffusion of carbon into the iron substrate, and by poor adhesion of the deposited film. These complications suggested the use of a buffer layer between the deposited diamond film and the iron-based substrate. We review different methods used to improve the adhesion of diamond film to steel substrates. In particular we describe in detail our own studies which involve the use of a Cr-N interlayer. The use of a chromium nitride interlayer has been found to improve significantly the adhesion of diamond films deposited on ferrous substrates. This is achieved by hindering diffusion processes of carbon and iron, very stable mechanical and chemical bonding between the interlayer and the diamond film, and good adhesion of the interlayer to the steel substrate. We also report on our studies related to residual stress present in the films, as well as a correlation between the interlayer properties and adhesion strength of deposited films.     

Growth and characterization of diamond films on TiN/Si(100) by microwave plasma chemical vapor deposition

Polycrystalline diamond films were deposited on silicon (100) substrate by microwave plasma chemical vapor disposition (MPCVD) using ~ 300 nm thick <001> textured titanium nitride (TiN) films as buffer layer which were prepared by radio-frequency reactive sputtering. The diamond/TiN films were characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and Raman spectroscopy. The results show that no apparent change can be observed for the <100> oriented TiN buffer layers after MPCVD even with a negative bias voltage applied onto the substrates.     

Bilayered coatings of BN/diamond grown on Si3N4 ceramic substrates

Cubic boron nitride (c-BN) is a well known material to be used in machining of ferrous metallic alloys, namely as a coating. However, in most practical cases, there is a lack of adhesion to the substrate material. In this work, BN coatings were deposited by magnetron sputtering on silicon nitride (Si₃N₄) ceramic substrates using an intermediate layer of CVD microcrystalline (MCD) or nanocrystalline diamond (NCD). The goal was to improve the c-BN content by using diamond interlayers, and to optimize film adhesion to the substrate by employing such ceramic, which is known to provide very high adhesion strength to CVD diamond. The BN/NCD/Si₃N₄ combination demonstrated to be unique regarding the absence of delamination at both the BN/diamond and diamond/substrate interfaces, also providing the highest c-BN phase content.     

Influence of internal diffusion barriers on carbon diffusion in pure titanium and Ti–6Al–4V during diamond deposition

Diamond coatings were deposited on pure titanium and Ti–6Al–4V, at a temperature in the range of 600–750 °C, in a microwave plasma from CH₄/H₂ and CO/H₂ mixtures. The influence on carbon diffusion of different intermediate layers, especially tungsten, niobium, titanium nitride and pure titanium previously deposited on titanium alloys by physical vapor deposition (PVD) is reported. These intermediate layers are always composed of at least two sub-layers: (1) an internal diffusion barrier and (2) an external titanium layer that allows some carbon diffusion to be maintained. After diamond deposition, X-ray diffraction (XRD) analysis and scanning electron microscopy (SEM) observations coupled with energy-dispersive X-ray (EDX) analysis of the final multilayer systems allow us to determine the diffracting phases, their lattice parameters and the efficiency of the different barriers. The carbon diffusion coefficients in the titanium carbide phase and in the α-titanium solid solution are deduced from an experimental study carried out on pure titanium with or without an underlying diffusion barrier. The results are compared to the carbon diffusion in Ti–6Al–4V alloy. This work permitted us to calculate the carbon concentration profiles in both pure titanium and Ti–6Al–4V substrates.     

Diamond coatings for micro end mills: Enabling the dry machining of aluminum at the micro-scale

We show that thin diamond coatings can dramatically enhance the performance of micrometer-scale cutting tools. We present a new approach for coating 300 μm diameter tungsten carbide (WC) micro end mills using a tailored seeding method and hot filament chemical vapor deposition (HFCVD) to obtain uniform, conformal, and continuous diamond coatings less than 2 μm in both thickness and grain size. The performance of the uncoated and coated tools has been evaluated by dry machining channels in 6061-T6 aluminum. The test results demonstrate far lower tool wear and breakage, much lower adhesion of aluminum to the tool, and significantly lower cutting forces for the coated tools. The coatings achieve a more predictable surface finish and enable dry machining at high speeds (40,000 rpm) with little or no burr formation. The improved performance of the coated tools is a result of the superior tribological properties of fine-grained diamond against aluminum, specifically low friction, low adhesion, and low wear of the film. Since the coating allows machining without lubricants and essentially eliminates metal burrs, this approach can reduce the environmental impact of micro-machining processes and offers greatly improved performance for micro and meso-scale manufacturing applications.     

Surface acoustic wave properties of natural smooth ultra-nanocrystalline diamond characterized by laser-induced SAW pulse technique

Diamond is one of the best SAW substrate candidates due to its highest sound velocity and thermal conductivity. But conventional diamond films usually express facet structure with large roughness. Ultra-nanocrystallined diamond (UNCD) films grown in a 2.45 GHz IPLAS microwave plasma enhanced chemical vapor deposition (MPECVD) system on Si (100) substrates in CH₄-Ar plasma possess naturally smooth surface and are advantageous for device applications. Moreover, highly C-axis textured aluminum nitride (AlN) films can be grown by DC-sputtering directly on UNCD coated Si substrate. However, properties of UNCD films are much complex than microcrystalline diamond films, that is because this is a very complex material system with large but not fixed portion of grain boundaries and sp²/sp³ bonding. Properties of UNCD films could change dramatically with similar deposition condition and with similar morphologies. A simple and quick method to characterize the properties of these UNCD films is important and valuable. Laser-induced SAW pulse method, which is a fast and accurate SAW properties measuring system, for the investigation of mechanical and structure properties of thin films without any patterning or piezoelectric layer.