Adhesion Strength Of Diamond Films Research Articles

Study of Tribological Properties of Textured Boron-Doped Diamond Film under Water Lubrication

To explore the effects of different surface textures and boron doping on the surface friction properties of diamond film, cemented carbide tools were provided with elliptical and groove textures using laser technology. Undoped diamond (UDD), boron-doped un-textured diamond (BDUTD), boron-doped elliptical textured diamond (BDETD), and boron-doped grooved textured diamond (BDGTD) films were prepared by bias-enhanced hot filament chemical vapor deposition (BEHFCVD). The effects of different surface texture and lubrication conditions on the tribological properties of diamond coated tools were studied by TBT-M5000 ball-on-disk friction tester. The surface morphology, film quality, adhesion strength and residual material composition of diamond films were characterized by SEM, Raman, Rockwell hardness tester and EDS, respectively. The results show that boron-doped can effectively improve the film quality and the existence of texture further improves the adhesion strength of diamond film. Under water lubricated condition, the average friction coefficients of UDD and BDGTD film are 0.1426 and 0.123, respectively. The wear rate of the steel ball corresponding to BDGTD film shows excellent anti-friction performance, which is 1.37 × 10−8 mm3 / Nm. From the wear morphology, the UDD film pair has the largest wear diameter, which is 1.536 mm. The steel ball corresponding to BDGTD film has the smallest wear diameter, which is 1.258 mm. Compared with the other three films, the wear of UDD film is the most serious and BDGTD film shows the best wear morphology, this is due to the fact that texture can promote the lubricant to enter the friction contact surface, make the contact surface fully lubricated and can collect wear debris.

Fabrication and performance of boron doped textured diamond coated tool

ABSTRACTBoron doped diamond (BDD) film is deposited on two types of texture cemented carbide inserts by hot filament vapour deposition (HFCVD) method. The surface morphology and composition of boron doped textured diamond (BDTD) film are characterized by scanning electron microscopy and Raman spectroscopy, respectively. And the influence of different texture shape parameters on adhesion strength and cutting performance of BDTD film tools are analysed by an indentation test and milling test, respectively. The results showed that the texture has a significant effect on grain growth and quality of the diamond film. In addition, texture can further enhance the adhesion strength of diamond film. The adhesion strength of BDTD film is better than that of BDD films. Concurrently, the boron doped groove textured diamond (BDGTD) film tool has longer tool life and a better cutting performance than the other three kinds of diamond film tools due to its suitable texture shapes.

Sandblasting induced stress release and enhanced adhesion strength of diamond films deposited on austenite stainless steel

We firstly used sandblasting to treat austenite stainless steel and then deposited a Cr/CrN interlayer by close field unbalanced magnetron sputtering on it. After that, diamond films were prepared on the interlayer. It is found that the sandblasting process induces phase transition from austenite to martensite in the surface region of the stainless steel, which decreases thermal stress in diamond films due to lower thermal expansion coefficient of martensite phase compared with that of austenite phase. The sandblasting also makes stainless steel’s surface rough and the Cr/CrN interlayer film inherits the rough surface. This decreases the carburization extent of the interlayer, increases nucleation density and modifies the stress distribution. Due to lower residual stress and small extent of the interlayer’s carburization, the diamond film on sandblast treated austenite stainless steel shows enhanced adhesion strength.

Adhesion strength of diamond films on heat-treated WC–Co cutting tools

The adhesion strength and deposition behavior of diamond films with different grain size onto heat-treated WC–Co cutting tool inserts were investigated. The diamond film was deposited on WC–6%Co cutting tool inserts by the hot-filament chemical vapor deposition method, with H 2/3% CH 4 mixed gas. The N 2 gas was incorporated in the mixed gas to refine the grain size of the deposited diamond film (nanocrystalline diamond: NCD). Pores were observed in the interface region between the micrometer-size diamond film (MCD) and the WC–Co cutting tool insert. This suggested that the growth of diamond grains on top of elongated WC grains, which was induced by heat treatment to improve the adhesion strength of the deposited film, hindered the deposition of diamond in the valley area between the elongated WC grains. By contrast, in the case of the NCD film with a grain size of less than 50 nm obtained by addition of N 2 gas, no pores were observed, due to the fact that the refined diamond grains filled the interface region regardless of the existence of the elongated WC grains. The adhesion strength of the NCD film was likely to be greater than that of the MCD film on the heat-treated WC–Co cutting tool insert, which was explained by the full coverage with small diamond grains at the rough interface region.

Adhesion improvement of the diamond film in diamond-coated WC–Co insert prepared with AC substrate bias

The grain size of diamond film deposited on WC–Co insert can be reduced by AC substrate bias during deposition, which enables a smooth surface finish of a workpiece during machining process. However, the adhesion of diamond film deposited on WC–Co insert became poor due to AC bias application, which was attributed to the increased surface Co content. To maintain adhesion strength while achieving grain size refinement by AC-biased growth, a certain thickness of diamond layer grown without bias was introduced as a buffer layer. The AC bias was applied after diamond deposition of 8 and 15 μm in thickness without bias and the total thickness of the diamond film was controlled to be around 20 μm. The adhesion strength of diamond film for the diamond-coated WC–Co insert prepared with AC bias, measured by indentation technique, was greatly improved by the adoption of diamond buffer layer deposited without bias.

Characterization of diamond adhesion on micro-grain WC–Co substrates using Brinellindentations and micro-Raman spectroscopy

In this study, we investigate the adhesion of diamond coatings deposited on0.8 µm WC–10% Co substrates using chemical vapour deposition (CVD).Polycrystalline diamond films were deposited using (i) constant methane(CH4) flow, at 3 and 4.5 sccm,and (ii) modulated CH4 flow at 4.5 and 3 sccm for 8 and 10 min, respectively. ConstantCH4 flow into the vacuum chamber during diamond CVD is the conventionalapproach to deposit diamond onto a range of substrate materials. The timedCH4 modulations are an integral part of our recently proposed process called time-modulatedCVD (TMCVD). The coating adhesion was characterized using indentation tests employinga Brinell indenter. In this study, we employ three indentation loads: 294, 490 and 612.5 N.In addition, micro-Raman spectroscopy was used to (i) characterize the deposited films fordiamond-carbon phase purity and (ii) determine the biaxial stresses in the coating samples.In this paper, we correlate the adhesion strength of diamond films to biaxial stresses.No lateral cracking occurred in diamond films deposited by the TMCVD process after a294 N load indentation. This result coupled with the complementary stress calculationsindicates a higher film–substrate adhesion in time-modulated films. Our findings suggestthat at higher indentation loads the response from and the behaviour of the substrate needto be considered in determining the coating adhesion strength. The TMCVDprocess promotes secondary nano-sized diamond crystallites during the highertimed methane modulations. It is expected that the mechanical interlock at thefilm/substrate interface is higher for film coatings deposited using TMCVD, thusresulting in the improved adhesion of the time-modulated coating on WC–Co.

Evaluation of the adhesion strength of diamond films brazed on K-10 type hard metal

The coating of cutting tools with diamond films considerably increases the tool performance due to the combination of the unique tribological properties of diamond with the bulk properties of the substrate (toughness). The tool performance, however, is strongly related to the adhesion strength between the film and the substrate. In this work our main goal was to propose and to test a procedure, based on a tensile strength test, to evaluate the adhesion strength of a diamond wafer brazed on a hard metal substrate, taking into account the effect of the brazing temperature and time. The temperature range studied was from 800 to 980 °C and the brazing time ranged from 3 to 40 min. The obtained results could be used to optimize the costs and time required to the production of high performance cutting tools with brazed diamond wafers.

Adhesion improvement of diamond coating on silicon nitride substrate

Abstract Adherent diamond coating on sintered silicon nitride substrate was prepared by a microwave plasma enhanced chemical vapor deposition (CVD) in the CO and H 2 reactant system. The substrate was pretreated in a hot and strong acid solution and microflawed ultrasonically with diamond grains suspended in ethanol. The effects of diamond-like carbon (DLC) interlayer on the adhesion strength of diamond film was investigated in relation to the formation of the graded texture and characteristic C–C bonding varied from substrate side to diamond film. The DLC interlayer was grown by RF plasma enhanced CVD in the CH 4 –H 2 system. Adhesion strength of the diamond film were evaluated by a compression topple test and the subsequent observation of the fractured surface. Adhesion was found to increase considerably by the insertion of DLC layer, which would relax the residual stress in the interfacial region between diamond film and substrate. Actual cutting test by milling the Al–20 wt%Si alloy work revealed an excellent long tool life in using a thick diamond coated specimen inserted with DLC interlayer.

Effect of plasma etching on adhesion strength of diamond film : Z.Kesong et al. (Guangzhou Research Inst. of Non-Ferrous Metals, Guangzhou, China.)

Effect of plasma etching on adhesion strength of diamond film : Z.Kesong et al. (Guangzhou Research Inst. of Non-Ferrous Metals, Guangzhou, China.)

Characteristics and applications of steel bonded cermets: H. Annuka et al. (Tallinn Technical University, Tallinn, Estonia.)

One of the expected applications of diamond coatings is in cutting tools for non-ferrous metals and alloys such as Al-Si and non-metals such as hard carbons etc. However, the poor adhesion strength of diamond films must be improved for practical use in cutting.In this study, sintered tungsten carbide (WC) without cobalt metal was used as the substrate and the effect of surface decarburization of the substrate to improve the adhesion strength of diamond films was investigated. Surface decarburization and diamond coating were carried out using a microwave plasma chemical vapour deposition apparatus. Good adhesion was obtained by surface decarburization of the substrate before diamond coating. From the results of observations by scanning electron microscopy and transmission electron microscopy, the improvement in the adhesion strength can be considered to be due to an increase in the contact area between the film and the substrate by generation of fine WC grains on the surface of the substrate, with the film embedded in the shape of a wedge at the fine WC grain boundaries. The coated insert demonstrates a very small steady wear without film flaking when milling a hard carbon compared with the large amount of wear exhibited by uncoated cemented carbides.

Characterization and adhesion strength of diamond films deposited on silicon nitride inserts by d.c. plasma jet chemical vapour deposition

Abstract Diamond films have been deposited on silicon nitride and cemented carbide inserts using the d.c. plasma jet chemical vapour deposition (CVD) technique. The morphologies and structures of the diamond films were characterized by scanning electron microscopy (SEM) and Raman spectroscopy. It was found that some of the diamond films deposited on WC-8%Co cemented carbide inserts peeled off immediately after shutting off the plasma torch owing to the large thermal stress accumulated inside the diamond films; this was caused by the different thermal expansion coefficients of diamond and cemented carbide inserts as well as the rapid heating and cooling rates in the d.c. plasma jet CVD process. In contrast, diamond films deposited on silicon nitride inserts, at deposition times ranging from 10 min to 3 h, showed no evidence of flaking even under severe thermal shock, since the similar thermal expansion coefficients of diamond and silicon nitride greatly reduce the thermal stress inside the diamond films. However, further indentation test results under loads of 31.25, 60 and 100 kgf revealed that almost all of the diamond films deposited on silicon nitride inserts spalled around the indentation centres even under a 31.25 kgf load (the lowest limit of the apparatus). This may be caused by the low toughness of the silicon nitride inserts. As a result, cracks initiated by the indentation load in the substrate propagate rapidly and cause chipping and loss of silicon nitride as well as the diamond film.

Investigation of adhesion of diamond films on Mo, W and carburized W substrates

Abstract A four-factor, three-level, fractional factorial experiment design was used to investigate systematically the influences of substrate pretreatment, deposition parameters, residual stress and substrate material on the adhesion strength of diamond films produced by a microwave plasma CVD process. The experimental results revealed that pretreatment of the substrates with diamond powder scratching was necessary for growing continuous diamond films on Mo, W and carburized W substrates. Statistical analysis showed that the substrate pretreatment had strong influences on film adhesion and, in particular, that the films on the substrates pretreated with Murakami's reagent demonstrated improved adhesion. The methane concentration in the hydrogen/methane gas source had significant effects on the diamond crystallite size and film surface morphology. Neither methane concentration nor deposition temperature in the ranges studied, however, showed significant influences on film adhesion. The total residual stress in the film was shown to be affected by substrate material and deposition temperature. The high mean residual tensile stress in the films deposited on pure W substrates was probably responsible for the poor film adhesion observed in this case. The decrease of the total stress in the films on carburized W substrates correlated well with the improved film adhesion. Carburization of the W substrates before diamond film deposition appeared to lessen the intrinsic stress in the film due to a better structure match between the diamond and tungsten carbide, thus enhancing film adhesion.

Adhesion and Young's Modulus of CVD Diamond Thin Films Grown Over Various Substrates

ABSTRACTDiamond films were deposited by microwave plasma CVD using H2 and CH4 gas mixture over various substrate materials such as Si, Pd, Be, Cu, Mo, AIN, SiO2, Si3N4, Al2O3, Sapphire, Quartz, Ni-base alloys, single crystal Ni, boron nitride, and Ti. We have used a Z-axis pull stud test to determine adhesion strength of diamond film to some of the substrates. Our observations on the adhesion of diamond films to the above substrates are reported. A method will be described to evaluate Young's modulus of CVD diamond films using fabricated diamond cantilever beams.

Morphologies and adhesion strength of diamond films deposited on WC6%Co cemented carbides with different surface characteristics

Diamond films were deposited on YG 6(WC6%Co) cemented carbides with different surface characteristics using hydrogen and ethyl alcohol as the feed gases in a hot filament assisted chemical vapour deposition system. The synthesized diamond films were examined by scanning electron microscopy, X-ray diffraction and Raman spectroscopy. It was found that cobalt near the surface of cemented carbides was very detrimental to diamond deposition and the surface characteristics of substrates had a strong influence on the diamond-substrate adhesion. Grinding test results showed that the adhesion strength of diamond to the lapped substrates of smooth surface micro-topographies was very poor and the films flaked severely during the grinding process. However, the diamond films demonstrated good adhesion to substrates with rough surface micro-topographies.

Adhesion strength of diamond film on cemented carbide insert

We have been studying diamond coatings on cemented carbide for cutting tool applications. To improve the adhesion strength of diamond film, a cemented carbide insert which contains a metal belonging to group 4a or 5a was heat treated before coating. A thin solid solution layer, which contains a large amount of this metal but no cobalt, was formed on the surface of the heat-treated carbide insert. The diamond film deposited onto the heat-treated insert showed a high adhesion strength, because the surface of the solid solution layer was very rough. The cutting performance of the diamond-coated insert was almost the same as that of a sintered diamond insert.

Improvement on adhesion strength of diamond film on cemented carbide by heated intermediate layer

Recently, we have obtained good adhesion strength between diamond film and an ISO K-type insert, which is the most common type of cutting inserts for Al and AlSi alloys, by heating the intermediate layer which is affixed to the insert. The heat treatment caused the migration of some metal component of the intermediate layer to the surface region and improved the adhesion strength between the diamond and the substrate. The cutting life and performance of a diamond-coated ISO K-type insert with heat treatment of intermediate layer were equal to those of a polycrystalline diamond insert.

Adhesion Strength of Diamond Films to Cutting Tool Materials Markedly Improved

Adhesion Strength of Diamond Films to Cutting Tool Materials Markedly Improved

Formation of functionally gradient diamond films

Abstract To improve the adhesion strength of diamond films, we developed a deposition process for functionally gradient diamond film. The film has an intermediate composition gradient layer consisting of diamond synthesized using d.c. plasma jet chemical vapor deposition and plasma-sprayed material. Diamond film is synthesized by spraying a plasma jet of hydrogen and methane onto a water-cooled substrate. The intermediate layer is formed by feeding powdered materials to the plasma for diamond synthesis. The composition gradient can be controlled by changing the powder feed rate. Tungsten carbide powder and molybdenum powder were plasma-sprayed at the same time during diamond synthesis. The formation of the mixture of diamond and plasma-sprayed materials was observed by electron probe microanalysis. X-ray diffraction and Raman spectroscopic analysis showed that the intermediate layer did not contain graphite. The adhesion strength of the diamond film with an intermediate layer exceeded 150 kg cm−2.

The improvement of the adhesion strength of diamond films

One of the expected applications of diamond coatings is in cutting tools for non-ferrous metals and alloys such as Al-Si and non-metals such as hard carbons etc. However, the poor adhesion strength of diamond films must be improved for practical use in cutting. In this study, sintered tungsten carbide (WC) without cobalt metal was used as the substrate and the effect of surface decarburization of the substrate to improve the adhesion strength of diamond films was investigated. Surface decarburization and diamond coating were carried out using a microwave plasma chemical vapour deposition apparatus. Good adhesion was obtained by surface decarburization of the substrate before diamond coating. From the results of observations by scanning electron microscopy and transmission electron microscopy, the improvement in the adhesion strength can be considered to be due to an increase in the contact area between the film and the substrate by generation of fine WC grains on the surface of the substrate, with the film embedded in the shape of a wedge at the fine WC grain boundaries. The coated insert demonstrates a very small steady wear without film flaking when milling a hard carbon compared with the large amount of wear exhibited by uncoated cemented carbides.

Quantitative adhesion strength measurement of diamond coatings

Various adhesion measurement methods for hard coatings have been studied. However, not one has yet been established for use with a superhard coating such as diamond. This study proposes an adhesion tester which can determine quantitatively the adhesion strength of diamond films coated, e.g. on WCCo alloy substrates using the thermal CVD method. The tester comprises a scraping blade of tungsten carbide which is moved along the interface between the coating and the substrate; the scraping force is measured so as to provide the adhesion strength. Finally, the quantitative adhesion strength values thus determined were compared with the adhesion strength qualitatively determined with the shearing test in which the diamond-coated tool tip was mounted in the shearing die set. The results show that the adhesion strength values obtained either qualitatively or quantitatively relate well with each other, thus providing the usefulness of the present adhesion testing method for diamond films.