Metallurgical Engineering

Argon plasma treatment techniques on steel and effects on diamond-like carbon structure and delamination

by Benjamin Jones

BJ Jones, L Anguilano, JJ Ojeda
Diamond and Related Materials 20 (2011) 1030-1035
DOI: 10.1016/j.diamond.2011.06.004 (available online 23rd June 2011)

We demonstrate alteration in diamond-like carbon (DLC) film structure, chemistry and adhesion on steel, related to... more We demonstrate alteration in diamond-like carbon (DLC) film structure, chemistry and adhesion on steel, related to variation in the argon plasma pretreatment stage of plasma enhanced chemical vapour deposition. We relate these changes to the alteration in substrate structure, crystallinity and chemistry due to application of an argon plasma process with negative self bias up to 600 V.

Adhesion of the DLC film to the substrate was assessed by examination of the spallated fraction of the film following controlled deformation. Films with no pretreatment step immediately delaminated. At 300 V pretreatment, the spallated fraction is 8.2%, reducing to 1.2% at 450 V and 0.02% at 600 V. For bias voltages below 450 V the adhesion enhancement is explained by a reduction in carbon contamination on the substrate surface, from 59 at.% with no treatment to 26 at.% at 450 V, concurrently with a decrease in the surface roughness, Rq, from 31.5 nm to 18.9 nm. With a pretreatment bias voltage of 600 V a nanocrystalline, nanostructured surface is formed, related to removal of chromium and relaxation of stress; X-ray diffraction indicates this phase is incipient at 450 V. In addition to improving film adhesion, the nanotexturing of the substrate prior to film deposition results in a DLC film that shows an increase in sp3/sp2 ratio from 1.2 to 1.5, a reduction in surface roughness from 31 nm to 21 nm, and DLC nodular asperities with reduced diameter and increased uniformity of size and arrangement. These findings are consistent with the substrate alterations due to the plasma pretreatment resulting in limitation of surface diffusion in the growth process. This suggests that in addition to deposition phase processes, the parameters of the pretreatment process need to be considered when designing diamond-like carbon coatings.

Research highlights

► Diamond-like carbon (DLC) film texture and chemistry, as well as adhesion, are affected by argon plasma pretreatment ► Two mechanisms for adhesion improvement on steel, cleaning (low energy) and nanostructuring (high energy) ► DLC adhesion improved by three orders of magnitude, with nanotextured, nanocrystalline, reduced stress substrate surface ► Changes in film surface morphology and sp2/sp3 ratio linked to substrate surface diffusivity

Keywords: Diamond-like carbon; plasma enhanced CVD; surface structure; delamination; morphology; interface; PECVD; plasma CVD; metal; steel; texture; aromatic; XRD; XPS; SEM; AFM; amorphous carbon; amorphous hydrogenated carbon; a-C; a-C:H

Archive version available at http://bura.brunel.ac.uk/handle/2438/5633
Definitive version available at: http://dx.doi.org/10.1016/j.diamond.2011.06.004

Factors affecting the accuracy of high resolution electron backscatter diffraction when using simulated patterns.

by T Ben Britton

T. B. Britton, C. Maurice, R. Fortunier, J.H. Driver, A.P. Day, G. Meaden, D.J. Dingley, K. Mingard and A.J. Wilkinson published in Ultramicroscopy (2010)

High resolution EBSD directly compares electron backscattering patterns (EBSPs), generated in a scanning electron... more High resolution EBSD directly compares electron backscattering patterns (EBSPs), generated in a scanning electron microscope, to measure relative strain and rotation to a precision of 10E−4 in strain and 10E−4 rad (0.006°) in rotation. However the measurement of absolute strain and rotation requires reference EBSPs of known strain and orientation (or a far-field region of known strain). Recent suggestions of using simulated EBSPs with known strain show much promise. However accurate measurement of the experimental geometry (pattern centre) is required. Common uncertainties of 0.5% in pattern centre result in uncertainty of 10E−3 in strain state. Aberrations in the compact lenses used for EBSP capture can also result in image shifts that correspond to strains/rotations of ±10E−3 between experimental and simulated EBSPs. Simulated EBSPs can be generated using dynamical or kinematic models (or a combination of the two). The choice in simulation model has a significant effect on the measured shifts, particularly at zone axis and high structure factor bands, due to large intensity variations, and for simple kinematic simulations can result in the measurement of rogue shifts and thus erroneous strain measurements. Calibrant samples of known strain provide a method of measuring the experimental geometry but imprecise stage movement combined with the high depth of field in the SEM could also result in uncertainties in strain of 10E−3.

Effect of Particle Coating on Matrix-Reinforcement Bonding

by Shaiful Rizam Shamsudin

Potentiodynamic Polarization of Mg-0.22 Ca Alloys Containing Minor Element of Aluminium

by Shaiful Rizam Shamsudin

Effect of Colloidal SIO2 Content on the Morphology of Coated Ceramic Particles

by Shaiful Rizam Shamsudin

Rapid analysis of copper ore in pre-smelter head flow slurry

by Neil Lawrence

Copper laden ore is often concd. using flotation.  Before the head flow slurry can be smelted, it is important to... more Copper laden ore is often concd. using flotation.  Before the head flow slurry can be smelted, it is important to know the concn. of copper and contaminants.  The concn. of copper and other elements fluctuates significantly in the head flow, requiring modification of the slurry prior to smelting.  A rapid, real-time anal. method is needed to support on-site optimization of the smelter feedstock.  A portable, battery-operated X-ray fluorescence spectrometer was utilized to det. the copper and contaminant concn. in a head flow suspension at the slurry origin.  The method requires only seconds and is reliable for copper concns. of 0.2-25% (as CuSO4), typically encountered in such slurries.