Interfacial adhesion characteristics of nanocrystalline and microcrystalline diamond coatings deposited on tungsten carbide (WC-Co) substrates were studied and analysed using a scratch tester. Coating failure events and critical point loads were identified by acoustic emission, tangential force measurement and image analysis carried out on the scratch track. In this respect, enhanced scratch resistance properties were observed in microcrystalline diamond (MCD) coating in comparison to nanocrystalline diamond (NCD) coating. Significant difference in critical loads for adhesive failure was observed for MCD and NCD coatings. These loads were 42 N and 20 N for MCD and NCD coatings, respectively. The reason for these two distinctly different adhesive characteristics was attributed to the microstructure of the respective coatings. The surface morphologies at critical failure point and wedge spallation regions of the scratch tracks were completely different for NCD and MCD coatings. Critical point regions were analysed by Raman stress mapping to study the scratch induced residual stresses in the strained diamond flakes and deformed coating of the scratch track. In this respect, high tensile stresses were observed in the regions of critical failure. This behaviour is strongly dependent on magnitude of stress and nature of deformation during the scratch test of NCD and MCD coatings. © 2014 Elsevier B.V. All rights reserved.

Mamidanna Sri Ramachandra Rao

Department Of Physics

Chittu R. Kumaran

B. Ramamoorthy

ADHESION CHARACTERISTIC

CRITICAL FAILURE POINT

CVD diamond

MICROCRYSTALLINE DIAMOND

NANOCRYSTALLINE DIAMONDS

RAMAN MAPPING

SCRATCH TEST

TUNGSTEN CARBIDE (WCCO)

Adhesion

Diamond cutting tools

Diamonds

Mapping

Residual stresses

tungsten carbide

Coatings

IIT Madras is a public technical and research university located in Chennai, Tamil Nadu. Founded in 1959, it is recognised as an Institute of National Importance.

IIT Madras has been ranked as the top engineering institute in India for four years in a row by the National Institutional Ranking Framework of the MHRD

It currently offers undergraduate, postgraduate and research degrees across 16 disciplines in Engineering, Sciences, Humanities and Management. About 596 faculty belonging to science and engineering departments and centres of the Institute are engaged in teaching, research and industrial consultancy.

IIT Madras

Diamond and Related Materials

The microscale characteristics of gray and black shale samples collected from two different locations of Singrauli coalfield, Madhya Pradesh, India were investigated using scratch tester and Raman stress mapping. The failure events were analyzed for the entire scratch track. The areas of critical point were identified based on the acoustic emission, tangential force measurement along with characterization methods Scanning Electron Microscopy (SEM) and Raman spectroscopy. The SEM studies at the critical points indicate the failure in black and gray shale are completely different. The critical points are analyzed by confocal Raman spectroscopy for measuring the Raman spectral shifts and Raman stress mapping. The Raman spectra of disordered D band are used for quantifying the stress in the entire scratch track. Micro scratch test performed in different directions along with critical point regions of black and gray shale is compared. Raman spectral shifts of D band are measured and compared for the strained regions. This reveals the 2D Raman imaging of black and gray shale as a proxy for characterizing the stress inversion. Correspondingly the Raman peak intensity ratios along with full width at half maximum (FWHM) were calculated for the critical regions. © 2017 Elsevier B.V.

International Journal of Coal Geology

Microscale assessment of 3D geomechanical structural characterization of gondawana shales

The microscale interfacial characteristics of coal are studied based on the analysis of mechanical behavior of individual elements contributing to coal heterogeneity with respect to high volatile bituminous A of coal, from Singrauli coal field, Madhya Pradesh, India. Micro-scale delineation of elastic plastic properties of coal by grid micro-indentation test and fracture toughness was accomplished by micro-scratch test on collotenite maceral. Micro-scratch test was performed in different directions on and critical points of failure were diagnosed by measuring acoustic emissions and tangential force. The 3D heterogeneity of coal is studied based on the damages at certain point of loads known as critical points with respect to distribution of macerals derived from coal petrography. Damages were observed at higher critical loads on samples collected from 332.9-335.6 m depth compared to 329.7-330.9 m depth samples owing to less heterogeneity and increased compaction. Raman stress mapping at critical points of scratch track revealed a spectral shift due to stress inversion. Shift from 1576-1593 cm-1 for graphite band (G), and from 1344-1357 cm-1 for disordered Carbon (D) band indicate the nature of stress and the deformation occurred for coal bulk sample. Raman spectra variation for maceral collotelinite is studied and compared with coal bulk samples behaviour a shift from 1574-1597 cm-1 for G, and from 1346-1356 cm-1 for D. © 2015 Elsevier B.V.

Implications of the 3D micro scale coal characteristics along with Raman stress mapping of the scratch tracks

In the present experimental study, wear performance of the diamond coated cutting tools with various coating architectures was studied by turning Al m-30%SiCp metal matrix composite material. Chemical vapor deposited (CVD) diamond can be classified into nanocrystalline diamond (NCD) and microcrystalline diamond (MCD) that are known for their distinct characteristics. Diamond coatings with three different coating architectures were deposited for the machining study; (i) mono-layer MCD coating (MCD/WC-Co), (ii) dual-layer composite diamond coating (NCD/MCD/WC-Co) and (iii) dual-layer graded composite diamond coating (NCD/transition-layer/MCD/WC-Co). Wear performance of the diamond coated (3 architectures), uncoated and commercial TiN coated tools was evaluated and compared by conducting high speed machining tests. Superior wear performance of the diamond coated tools was clearly evident from the tool wear measurements. The poor tool life (t &lt; 1 min) of the uncoated and TiN coated tools was attributed to the abrasive action of the hard SiC reinforcement particles. Dual-layer graded composite diamond coated (t = 14.7 min) and mono-layer MCD coated (t = 13.5 min) tools showed superior machining performance in comparison to that of the dual-layer composite diamond coated tool (t = 9.8 min). Dual-layer graded composite diamond coatings deposited with the concept of transition-layer are the prospective tool coatings for high performance machining applications due to their top-layer nanocrystallinity and enhanced interfacial integrity. © 2014 Elsevier Ltd.

International Journal of Refractory Metals and Hard Materials

High wear performance of the dual-layer graded composite diamond coated cutting tools

Cross-sectional structural characteristics of the CVD diamond coatings deposited on the tungsten carbide (WC-Co) substrates were analysed using Raman imaging technique. The grain size of the nanocrystalline diamond (NCD) coatings was observed to deviate from the nanocrystallinity with increasing thickness and exhibited the surface characteristics of microcrystalline diamond (MCD). However, thick diamond coatings with surface nanocrystallinity is the key requirement for load-bearing tribological applications. Tribological tests have clearly indicated the significance and need for the top-layer nanocrystallinity. Graded composite diamond coatings with an architecture of NCD/transition-layer/ MCD/WC-Co are potentail candiadates to realize thick diamond coatings with top-layer nanocrystallinity. Residual stresses along the cross-section of the graded composite diamond coatings were analysed using Raman imaging technique, which confirmed the improved interfacial integrity of the graded composite diamond coatings. © 2013 Elsevier B.V.

Applied Surface Science

Graded composite diamond coatings with top-layer nanocrystallinity and interfacial integrity: Cross-sectional Raman mapping

The stability of diamond thin films grown by hot filament CVD (HFCVD) upon thermal treatment was studied using Raman imaging. By adapting two different surface pretreatments, continuous microcrystalline diamond (MCD) thin films (grain size: 100-400 nm; cross-sectional thickness: ~300 nm) as well as thin film with isolated and coalesced diamond particles (particle size: 400-600 nm; cross-sectional thickness: ~200-300 nm) were grown. The thermal stability of isolated diamond particles and continuous MCD films annealed in air at atmospheric pressure was analyzed by Raman imaging. For Raman imaging, Raman spectra were collected over an area of 85 × 85 μm using 532 nm laser (Nd:YAG) before and after thermal treatment. It was observed that the isolated diamond particles were stable for 1 h at ~750 C, whereas for the same annealing duration, continuous MCD films grown under the same HFCVD condition were completely oxidized at 700 C. From these results and analysis, the reason for the higher oxidation rates in the case of MCD and nanocrystalline diamond films is discussed. © 2013 Springer Science+Business Media Dordrecht.

Journal of Nanoparticle Research

Effect of temperature on the stability of diamond particles and continuous thin films by Raman imaging

In this work, integrated composite diamond (ICD) coatings have been achieved with top layer nanocrystallinity, low friction coefficient and enhanced integrity. ICD coatings were deposited on chemically treated tungsten carbide (WC-Co) substrates using hot filament chemical vapour deposition technique. Nanocrystalline diamond (NCD) layer was deposited over microcrystalline diamond (MCD) layer with a coating architecture of NCD/transition layer/MCD/WC-Co. Graded transition layer thickness of ∼ 1 μm was realized by controlling the process parameters such as methane concentration and chamber pressure in order to integrate the MCD and NCD layers. Integrity of the coatings was examined by the cross-sectional studies. Structural and microstructural characteristics of ICD coatings were compared with those of MCD coatings. The measured average nanohardness of ICD coating was ∼ 96 GPa. A low and stable friction coefficient of ∼ 0.06 was observed for ICD coatings against silicon nitride (Si3N4). ICD coatings were anticipated to exploit the advantages of both NCD and MCD coatings and these coatings can be promising candidates for various mechanical applications. © 2012 Elsevier Ltd. All rights reserved.

Growth and characterization of integrated nano- and microcrystalline dual layer composite diamond coatings on WC-Co substrates

Surface and Coatings Technology

Coating thickness and interlayer effects on CVD-diamond film adhesion to cobalt-cemented tungsten carbides

Wear

A multilayer approach for enhancing the erosive wear resistance of CVD diamond coatings

Adhesion characteristics of nano- and micro-crystalline diamond coatings: Raman stress mapping of the scratch tracks

Journal	Data powered by TypesetDiamond and Related Materials
Publisher	Data powered by TypesetElsevier Ltd
ISSN	09259635
Open Access	No