Diamond Coatings

Interface delamination is the major failure mode of
diamond-coated carbide tools in machining. On the other hand, coating cracking is possibly accompanied during a tribological process that induces the delamination phenomenon. However, such an influence between the two failure behaviorshas not been investigated in a quantitative way to better understand and design diamond coating tools.
In this study, a three-dimensional (3D) indentation model
combiningcohesive interactions and extended finite element
method (XFEM)was developed to investigate the diamond coating, carbide-substrate interface behavior with the
incorporation ofcoating cracking. The cohesive interaction was
based on a cohesive zone model(CZM) with a bilinear tractionseparation law. XFEM was applied to the coating domain to model cracking in the diamond coating with a damage criterion of the maximum principal stress. Deposition stresseswere also included to investigate theireffect on the coating delamination
and fractures. The model was implemented in finite element
(FE) codes to analyze the cone crack in brittle coatings, as well
as the interface delamination of diamond coated carbide tools.
The XFEM model was validated by the indentation testing data
from literature in crack initiation and propagation in brittle
materials. FE results from the indentation on diamond-coated
tools showthat the interface delamination size and loading force
become smaller whencoating fracturesareincorporated in the
model, and the deposition stresses will increase the initial crack radius and the critical load for delamination in diamond coatings.

The goal of this research is to enhance the diamond-coated cutting tool performance through fundamental understanding of the interface adhesion of chemical vapor deposition (CVD) diamond-coated tungsten carbide cutting tools. CVD diamond-coated cutting tools have the advantages of superior tribological properties and low cost in fabrications compared to polycrystalline diamond tools. However, the applications of diamond-coated tools are limited by interface delamination. Therefore, it is necessary to not only accurately detect interface delamination events, but also understand the delamination behavior affected by coating fractures.
The primary objectives of this research are: (1) to utilize acoustic emission (AE) signals for wear monitoring of diamond-coated tools in machining, (2) to develop a finite element (FE) model of indentation for investigating the interface adhesion related to coating-substrate system parameters, (3) to combine micro-scratch testing and FE sliding model to assess the interface cohesive characteristics, and (4) to investigate the interface delamination considering coating cracking by developing a 3D indentation/sliding model using the extended finite element method (XFEM).
The research methods include: (1) machining test A359/SiC-20p composite with an acoustic emission sensor, (2) finite element (FE) modeling and analysis of indentation and sliding with different configurations, and (3) scratch testing on diamond-coated tools. The major results are summarized as follows. (1) The short-time Fourier transform method has a potential for monitoring diamond coating failures. (2) In scratch testing, the tangential force and AE signal intensity vary significantly when the coating delamination critical load is reached. (3) Increasing the coating elastic modulus will reduce the delamination length and a thicker coating tends to have greater resistance to the interface delamination. (4) Coating cracking will decrease the interface delamination size, while the deposition stress will increase the delamination radius and critical load of interface failures.
The contributions of this study include the following. (1) This study correlates the AE frequency response during machining with diamond-coated tool failures. (2) A cohesive zone model has been incorporated in FE modeling of indentation and scratch processes on a diamond-coated tool in evaluating coating adhesion with interface characteristics. (3) XFEM models of indentation and scratch simulations on a diamond-coated tool with an embedded cohesive layer are developed to simultaneously study coating cracking and interface delamination.
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In this paper, we present numerical simulations of the residual stresses developed between diamond coatings and Ti-6Al-4V substrates when using chemical vapour deposition technique. The large difference in thermal expansion coefficients of diamond and titanium alloys results in high residual stresses in the diamond film. This could lead to interfacial cracking and material failure. The finite element method was used to simulate the cooling process of diamond films at various thicknesses and deposited at temperatures ranging from 600 °C to 900 °C. The influence of different parameters such as temperature, film thickness, material characteristics, geometry and edge effects are investigated for different case geometries. The film debonding and cracking is discussed and numerical results are compared with existing experimental and numerical results. Finally, some propositions are made to enhance the experimental process in order to reduce the residual stress intensities and the possible material degradation.

Diamond coated cutting tools have been pursued as a cost-effective substitute to
brazed polycrystalline diamond (PCD) tools in applications such as machining high-strength and
lightweight materials. However, coating delamination has been known as the major failure mode
of diamond coated tools, which terminates tool life prematurely. Once delamination failure
occurs, the tool substrate often subjects to severe abrasive wear leading to catastrophic tool
failures that imparts the part quality and interrupts machining operations. Hence, accurate
detections and forecasts of coating delamination events can prevent production loss and assist
process planning. In this study, the characteristics of acoustic emission (AE) signals when
machining a high-strength aluminum alloy and a composite using diamond coated cutting tools
were investigated. The AE signals were analyzed in both time and frequency domains at various
machining conditions and different cutting times. It was found that AE root-mean-square values
decrease considerably once coating delamination occurs. The results also indicate a correlation
between the tool condition and fast Fourier transformation (FFT) spectra of AE raw data. In
addition, the machining experiments implied that it may be feasible to use AE signals to monitor
the condition of diamond coated tools during machining. The fast Fourier transformation (FFT)
spectra of AE data along cutting time generally show decreased intensity for low frequency
peaks, but increased intensity for high frequency peaks. In addition, the AE FFT spectra of subdivided
time zones during one cutting pass may clearly indicate the coating failure transition,further research by using short-time Fourier transform (STFT) method show that during the
coating failure pass, a clear sharp increase of amplitude ratio (value change over one) of
high/low frequency occurs along the cutting time, thus, it can be suggested that the applied STFT
method has a potential for diamond coating failure monitoring. However, for coating failure
associated with a smaller tool wear (VB less than 0.8 mm), the amplitude ratio plot from the
STFT analysis may not clearly show the failure transition.

Coating failures due to delaminations are the primary lifelimiting criteria of diamond-coated tools in machining. Process
monitoring to capture coating failures is thus desired to prevent from poor part quality and possible production disruption.
Following previous studies of AE signal analysis for diamond coating failure monitoring in machining applications, this
research applied a short-time Fourier transformation (STFT) method to capture the coating failure transition during cutting.
The method uses sub-divided signal segments, in a continuous manner, for the fast Fourier transform (FFT) analysis and computes the amplitude ratio of high vs. low frequencies as a function of cutting time during a cutting pass.
The results show that during the coating failure pass, a clear sharp increase of amplitude ratio (value change over one)
of high/low frequency occurs along the cutting time. On the other hand, the amplitude ratio only exhibits a certain low range
fluctuations in other passes, e.g., initial cutting and prior to failure passes. Thus, it can be suggested that the applied STFT
method has a potential for diamond coating failure monitoring. However, for coating failure associated with a smaller tool
wear (less than 0.8 mm flank wear-land width), the amplitude ratio plot from the STFT analysis may not clearly show the failure transition.

Residual stresses in diamond coatings grown on WC-Co substrate have been investigated by X-ray diffraction (XRD) method. Nano-diamond coatings were deposited by microwave plasma-enhanced chemical vapor deposition technique (MP-CVD). To measure residual stress, we tried different peak selection and instrument setting mode (χ mode and ω mode). For getting reliable residual stress value, sin2ψ-method with omega-tilting mode (χ=0) was employed. The
(311) plane of CVD diamond was used with tilting angle (ψ) from -40 to 40 degrees. A compressive stress of 1.65GPa was obtained by linear fitting the mean d-spacing values of
positive and negative tilting. The occurrence of “ψ-splitting” demonstrates the existence of non-zero shear stress normal to the surface.

The progresses in the magnetic media technology
brought to the application of liquid lubricant films on
diamond-like carbon (DLC) coatings. Hard surfaces are
typically lubricated with fluorinated or perfluorinated organic
compounds, such as perfluoropolyethers (PFPE) (1). Many
attempts have been done to obtain a stable layer of PFPE
lubricant on the DLC surface by dip-coating or by vapour
deposition so as to minimize any friction and wear (2, 3).
Diamond-like carbons are formed by an amorphous mixture
of sp3 and sp2 hybridized carbon atoms with hydrogen atoms
incorporated in the structure (a-C:H DLC). We have established
a specific methodology for the straight-forward introduction
of perfluorinated groups with carbon-carbon bond formation
on a variety of unsaturated materials (4-8). Indeed, by using
this methodology, perfluorinated radicals can directly bond
to the sp2 sites of the DLC structure avoiding any spacer, that
usually decreases both thermal and chemical stabilities of the
resulting fluorinated layers.

The effectiveness of a plasma-deposited, diamond-like carbon (DLC) coating on aluminium alloy based surgical instruments is investigated. Surgical instruments must satisfy a number of important criteria including biocompatibility, functional performance, sterility and cleanability, structural integrity, and fatigue resistance. The integrity of the DLC layer and the diffusion barrier properties are of paramount importance due to biocompatibility considerations of the underlying aluminium metal. We investigate the optimisation of the coating with incorporation of silicon and variation in negative self bias, and highlight the design and manufacture of a lightweight laparoscopic assist instrument from aluminium alloy coated with diamond-like carbon, which has been used successfully in the clinical environment to improve operations such as cholecystectomy (gall bladder removal) and exploratory techniques for the diagnosis of cancer.


DLC; diamond-like carbon; silicon; silicated carbon; silicon carbide; amorphous carbon; a-C; medical devices; diffusion barrier; impact resistance; biomedical; laparoscopy; keyhole surgery; surface; topography; thin films; properties; PECVD; PACVD; nanotechnology

Integration of lead zirconate titanate (PZT) thin film on diamond substrate offers a great deal of potential for the application of multifunctional devices under extreme conditions. However, fabrication of perovskite PZT thin films on diamond substrate without a buffer layer has not been realized to date. We report for the first time on the successful deposition of PZT thin film directly on a diamond substrate without any buffer layer using the pulsed-laser deposition technique. The perovskite phase was realized only under specific growth conditions. X-ray diffraction and Raman studies confirmed the perovskite phase. The ferroelectric behaviour of the deposited PZT thin film was confirmed using piezo response microscope phase image and ferroelectric hysteresis loop.

This paper investigates the effects of different surface pretreatments on the adhesion and performance
of CVD diamond coated WC–Co turning inserts for the dry machining of high silicon aluminum alloys.
Different interfacial characteristics between the diamond coatings and the modified WC–Co substrate
were obtained by the use of two different chemical etchings and a CrN/Cr interlayer, with the aim to
produce an adherent diamond coating by increasing the interlocking effect of the diamond film, and
halting the catalytic effect of the cobalt present on the cemented carbide tool. A systematic study is
analyzed in terms of the initial cutting tool surface modifications, the deposition and characterization
of microcrystalline diamond coatings deposited by HFCVD synthesis, the estimation of the resulting
diamond adhesion by Rockwell indentations and Raman spectroscopy, and finally, the evaluation of the
dry machining performance of the diamond coated tools on A390 aluminum alloys. The experiments
show that chemical etching methods exceed the effect of the CrN/Cr interlayer in increasing the diamond
coating adhesion under dry cutting operations. This work provided new insights about optimizing the
surface characteristics of cemented carbides to produce adherent diamond coatings in the dry cutting
manufacturing chain of high silicon aluminum alloys.

Extremely smooth (6 nm RMS roughness over 4 lm2), thin (100 nm), and continuous ultrananocrystalline diamond (UNCD) films
were synthesized by microwave plasma chemical vapor deposition using a 10 nm tungsten (W) interlayer between the silicon substrate and the diamond film. These UNCD films possess a high content of sp3-bonded carbon. The W interlayer significantly increased the initial diamond nucleation density, thereby lowering the surface roughness, eliminating interfacial voids, and allowing thinner UNCD films to be grown. This structural optimization enhances the films’ properties and enables its integration with a wide variety of substrate materials.

2006 Elsevier B.V. All rights reserved.

Integration of lead zirconate titanate (PZT) thin film on diamond substrate offers a great deal of potential for the application of multifunctional devices under extreme conditions. However, fabrication of perovskite PZT thin films on diamond substrate without a buffer layer has not been realized to date. We report for the first time on the successful deposition of PZT thin film

We report a novel all-hydrocarbon molecular rectifier consisting of a diamantane-fullerene conjugate.  By linking both sp3 (diamondoid) and sp2 (fullerene) carbon allotropes, this hybrid molecule opposingly pairs negative and positive electron affinity moieties. The morphology and single-molecule conductances of self-assembled diamantane-fullerene domains on Au(111), probed by low-temperature scanning tunneling microscopy and spectroscopy, reveal a large rectifying response of the molecular constructs.  This specific electronic behavior is postulated to originate from the electrostatic repulsion of diamantane-fullerene molecules due to positively-charged terminal hydrogen atoms on the diamondoid interacting with the top electrode (scanning tip) at various bias voltages.  Density functional theory computations have been performed on the diamantane-fullerene hybrid in order to scrutinize the electronic and vibrational spectroscopic fingerprints of this unique molecular structure.