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Chen Y.,University of Windsor | Nie X.,University of Windsor | Leyland A.,University of Sheffield | Housden J.,Tecvac Ltd. | Matthews A.,University of Sheffield
Surface and Coatings Technology | Year: 2013

A cyclic inclined impact-sliding test was operated in an unlubricated, ambient environment and Hank's balanced salt solution (HBSS) to study the contact fatigue wear behavior of DLC and TiN biomedical coatings on relatively soft but corrosion resistant Ti alloy (Ti6Al4V) and hard but corrodible AISI M2 steel as model systems. The test was designed to simulate coating wear under combined impact and sliding motion. In each impact-sliding cycle, the forces comprised a dynamic impact load, Fi (140N) and a "pressing" load, Fp (300N). As expected, both coatings performed better on hard M2 substrates than Ti substrates under ambient test conditions. In the HBSS-lubricated solution test conditions, no obvious corrosion degradation occurred when either the bonding layers or substrates were Ti-based; instead, the solution provided a lubricating effect and enhanced coating performance. When the bonding layer for the DLC coating case was Si-based, it could not prevent crack propagation into the substrate after a certain number of test cycles. The crack opening allowed the HBSS solution to contact the substrates, which should only cause a minor problem when the substrate was a corrosion-resistant Ti alloy. However, when the substrate was corrodible M2, a severe corrosion-induced weakening of the interface occurred. When the coating bonding layer was a Ti layer (within the TiN coating), it could function to some extent as a corrosion and crack barrier to protect the M2 steel from interface degradation. Thus, a corrosion-resistant bonding layer and its ability to impede extension of cracking under cyclic dynamic loads can have a positive influence on the coating performance when the substrate has inferior anti-corrosion properties. © 2013 Elsevier B.V.


Wang L.,University of Windsor | Northwood D.O.,University of Windsor | Nie X.,University of Windsor | Housden J.,Tecvac Ltd. | And 3 more authors.
Journal of Power Sources | Year: 2010

In this study, the contact resistance (CR) and electrochemical properties of TiN, CrN and TiAlN electron beam physical vapor deposition (EBPVD) coatings and their stainless steel 316L (SS316L) substrate were investigated in a simulated proton exchange membrane (PEM) fuel cell environment. The potentiodynamic polarization corrosion tests were conducted at 70 °C in 1 M H2SO4 purged with either O2 or H2, and the potentiostatic corrosion tests were performed under both simulated cathodic (+0.6 V vs. Ag/AgCl reference electrode purged with O2) and anodic conditions (-0.1 V vs. Ag/AgCl reference electrode purged with H2) for a long period (4 h). SEM was used to observe the surface morphologies of the samples after corrosion testing. All the TiN-, TiAlN- and CrN-coated SS316L showed a lower CR than the uncoated SS316L. While the corrosion performance of the coatings was dependent on the cathodic and anodic conditions, the CrN coating exhibited a higher (in the anodic environment) or similar (in the cathodic environment) corrosion resistance to the uncoated SS316L. Thus, the CrN-coated SS316L could potentially be used as a bipolar plate material in the PEM fuel cell environment. Although the EBPVD process greatly reduced number of pinholes in the coatings compared to other plasma enhanced reactive evaporations, future research efforts should be directed to eliminate the pinholes in the coatings for long-term durability in fuel cell applications. © 2010 Elsevier B.V. All rights reserved.


Grant
Agency: European Commission | Branch: FP7 | Program: MC-ITN | Phase: FP7-PEOPLE-2011-ITN | Award Amount: 3.37M | Year: 2012

The main aim of the ENTICE proposal is to provide professional development in the multidisciplinary field of ENgineering Tribochemistry and Interfaces for IC Engines, capable to develop the new generation of clean and energy-efficient engines. It aims to train the next generation of researchers to work in diverse teams, to cross disciplinary and sectoral boundaries and apply advanced communication and information technologies to work across many scales of time and space. Detailed project objectives are: 1. To provide scientific and professional development to a highly motivated group of early stage researchers (ESRs) to address a number of key interdisciplinary research issues of great importance to the future of transport industries. 2. To facilitate and support scientific and professional development of two experienced researchers (ERs) to enable them to become the research leaders in two challenging interdisciplinary research areas. 3. To disseminate the knowledge and products developed through scientific research to industry, policy makers and the wider academic community for maximum impact of the research. 4. To initiate a sustainable long-term research, training and educational collaboration between the partners involved. Here we propose the development of a training network that brings together some of the key active research groups in Europe, with a leading international reputation, in complementary areas relevant to the fields of tribochemistry and interface design. A number of leading industrial companies, comprising of SMEs and LEs, will engage in training and facilitate the Transfer of Knowledge (ToK) to and from the industrial partner through research programmes for 12 ESRs and 2 ERs. The training programme proposed comprises two key elements; generic training to cover aspects of training required for future research leaders in academia and industry and on-the-job training which will include specialised project-specific skills and development.


Cassar G.,University of Sheffield | Banfield S.,University of Sheffield | Banfield S.,Tecvac Ltd. | Wilson J.C.A.B.,Tecvac Ltd. | And 3 more authors.
Surface and Coatings Technology | Year: 2011

Sequential triode plasma oxidation and nitriding have been used to provide enhanced load support for physical vapour deposited (PVD) hard coatings. The diffusion process has been designed to maximise process efficiency and coating adhesion, thereby significantly improving the tribological properties of the Ti-6Al-4V alloy - particularly at high contact pressures. This has been demonstrated using unlubricated linear reciprocating-sliding ball-on-plate wear tests and micro-scratch adhesion testing. Also, surface micro-profilometry, nano/micro-indentation hardness testing, scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX), X-ray diffraction (XRD), and glow-discharge optical emission spectroscopy (GDOES) data are presented to corroborate the effect of the several plasma diffusion processes and duplex diffusion/coating combinations discussed here. The results presented show that the novel processing technique developed permits the use of oxygen diffusion in order to obtain relatively large case depths in shorter treatment times without compromising the adhesion strength of subsequently deposited PVD layers. © 2011 Elsevier B.V.


Cassar G.,University of Sheffield | Banfield S.,University of Sheffield | Banfield S.,Tecvac Ltd. | Avelar-Batista Wilson J.C.,Tecvac Ltd. | And 3 more authors.
Wear | Year: 2012

In this paper micro-abrasion wear testing is used to evaluate the wear resistance of triode plasma diffusion-treated, single-layered TiN-, CrAlN-, and WC/C-coated and duplex-diffusion and coated Ti-6Al-4V under uniform three-body rolling abrasion. Nanoindentation, Knoop microhardness, mechanical surface profilometry, optical microscopy, scanning electron microscopy and atomic force microscopy, were used to characterise the surfaces under investigation. Optimum testing conditions for rolling abrasion were established by varying the test parameters and resultant severity of contact. Very low normal loads and high volume fractions of particles in the abrasive slurry are necessary to obtain predictable and reproducible results. Relatively coarse SiC abrasive particles, having a mean diameter of around 3μm, appear more suitable for micro-abrasion testing of the samples investigated, compared to finer Al 2O 3 particles. Problems associated with the measurement of the scar volume and subsequent calculation of the wear rate for hard coatings deposited on relatively soft metals like titanium are identified, and suitable testing and measurement techniques are suggested. Three-dimensional wear scar maps generated by mechanical stylus profilometry were used to measure the wear volumes. Under the test conditions used, wear coefficients can be determined from perforating and non-perforating tests, although perforating tests provide more consistent results. Triode plasma diffusion treatments, plasma-assisted (PA) PVD TiN and PAPVD CrAlN can reduce the specific wear rate of Ti-6Al-4V, while PACVD-based WC/C coatings do not provide suitable protection against abrasive wear. The combination of triode plasma oxynitriding diffusion treatments and PVD coatings to create duplex treatments can also lead to further reductions in the coating wear coefficient when compared to non-duplex coatings deposited on non-pretreated substrates. © 2011 Elsevier B.V.


Cassar G.,University of Sheffield | Wilson J.C.A.-B.,Tecvac Ltd. | Banfield S.,University of Sheffield | Banfield S.,Tecvac Ltd. | And 3 more authors.
Wear | Year: 2010

Triode plasma nitriding was used in conjunction with electron-beam plasma-assisted physical vapour deposition of TiN and CrAlN to enhance the wear resistance of Ti-6Al-4V titanium alloy. Linear reciprocating-sliding ball-on-plate wear tests were performed to assess the tribological performance of the treated alloy. Wear volumes were correlated to changes in coefficient of friction, which is often indicative of breakdown of the surface treatment. Debris generated during wear testing was characterised using scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX), X-ray diffraction (XRD) and laser diffraction for particle size analysis. Surface micro-profilometry and SEM were used to characterise the wear scars. The results obtained indicate that, in order to assess the relative improvement in wear behaviour attained by using surface treatments it is insufficient to compare linear wear rates alone. A clear comparison is only possible if testing is carried out in steps of increasing sliding distance, until the treated/deposited layers have been completely removed. Also, it is shown that the number of repeated tests necessary to evaluate clearly the treatment and/or coating can vary substantially, depending on the observed test progression; typically this necessitates the greatest number of repeats around the point of wear at which the ball counterface contact area is in transition from the treatment layer(s) to the substrate bulk. The inherent variability in wear performance under linear ball-on-plate reciprocating-sliding is correlated to debris generation, changes in relative humidity - and the resultant wear mechanisms involved. © 2010 Elsevier B.V. All rights reserved.


Cassar G.,University of Sheffield | Avelar-Batista Wilson J.C.,Tecvac Ltd. | Banfield S.,University of Sheffield | Banfield S.,Tecvac Ltd. | And 4 more authors.
International Journal of Fatigue | Year: 2011

The effect of triode-plasma enhanced low-pressure oxygen and/or nitrogen diffusion treatments, either as a single process or in conjunction with plasma-assisted physical vapour deposition (PAPVD) on Ti-6Al-4V has been studied under rotating-bending fatigue testing. Following the diffusion treatment, samples exhibit a hardened case, more than 30 μm deep. Semi-logarithmic S-N plots are used to demonstrate and compare the significant changes in fatigue resistance obtained from each process. Fractography and residual stress measurements show that, compared to annealed samples, the fatigue strength of the diffusion-treated samples was superior; although the result changed depending on the processing parameters and microstructure of the substrate material. Also, unsupported and mechanically uncompliant ceramic coatings, such as TiN, promote the initiation of multiple crack sites, which lead to premature failure of the Ti-alloy substrate and a consequent reduction in endurance limit. © 2011 Elsevier Ltd. All rights reserved.


Llanes Leyva C.A.,Federal University of Minas Gerais | Godoy C.,Federal University of Minas Gerais | Bozzi A.C.,Federal University of Espirito Santo | Avelar-Batista Wilson J.C.,Tecvac Ltd.
Surface and Coatings Technology | Year: 2011

Ultra-low carbon (ULC) steels exhibit low yield strength and excellent formability. Plasma Assisted Physical Vapor Deposition (PAPVD) is a potential coating method for enhancing the strength at the surface of these steels [1]. However, when deposited onto low strength alloys PAPVD coatings may undergo premature failure if the substrate plastically deforms under heavy load. Extra load support is usually required for hard coatings to perform satisfactorily. Combined treatments involving plasma nitriding and PAPVD coating have been used to improve the load-bearing capacity of hard films [2]. This work describes the characterization and micro-abrasive wear behavior of Ti-stabilized ULC steels after surface modification by D.C Triode Plasma Nitriding (DC-TPN) and sequential coating with CrAlN by Electron Beam Plasma Assisted Physical Vapor Deposition (EB-PAPVD). Ti-ULC steel, plasma nitrided Ti-ULC steel and Ti-ULC duplex system were characterized by SEM, EDS, XRD analyses, micro-hardness and instrumented indentation hardness measurements, and stylus profilometry. Micro-abrasive wear tests were performed in fixed-ball configuration up to 1350 revolutions using SiC abrasive slurry and a 25mm diameter - AISI 52100 steel ball. Micro-abrasion mechanisms are presented and discussed. Nitrided steel and duplex systems were, respectively, 2.6 and 3.5 times harder than the untreated Ti-ULC steel. Wear coefficient of nitrided steel was 36% lower than that of the parent Ti-ULC steel. Regression analyses were used to calculate substrate (ks) and coating (kc) wear coefficients for the duplex system, the latter being 6.5 times lower than that of the nitrided steel. Coating thickness (3μm max.) was determined from inner and outer diameter measurements of the wear scars. Results indicate that it is feasible to manufacture duplex Ti-ULC steel via PAPVD, as significant improvements in wear resistance were recorded for both nitrided and duplex-treated steels. Duplex treatment clearly was the most effective method to enhance the wear resistance of ULC steels. © 2011 Elsevier B.V.


Cassar G.,University of Sheffield | Banfield S.,University of Sheffield | Banfield S.,Tecvac Ltd. | Avelar-Batista Wilson J.C.,Tecvac Ltd. | And 3 more authors.
Surface and Coatings Technology | Year: 2012

In this paper dynamic ball-on-plate impact wear testing is utilised to evaluate the intrinsic fatigue strength of the surface of triode plasma diffusion treated, single-layered TiN-, CrAlN-, and WC/C-coated and duplex diffusion treated/PVD-coated Ti-6Al-4V. The test is used to assess the resistance of surfaces to dynamic, high-cycle loading caused by the repeated impact of a cemented carbide ball. The subsequent observation and comparison of the wear craters produced (and their measured volumes) was used to identify which diffusion treatment (or treatment/coating combination) provided the most marked reduction in contact-induced deformation and overall improvement in wear behaviour. A combination of nanoindentation, Knoop hardness microindentation, scratch adhesion, stylus profilometry, optical microscopy, scanning electron microscopy, energy-dispersive X-ray spectroscopy and atomic force microscopy test and evaluation methods, was used to characterise the surfaces under investigation. Experimental results revealed that triode plasma diffusion treatments can provide exceptional improvements in the impact fatigue resistance, particularly when the diffusion process has been designed to maximise the resultant hardened case depth. Also, amongst the three coatings tested, PVD CrAlN was found to be the most suitable for applications involving such dynamic impact loading. Finally, the results presented show that an appropriate sequential triode plasma oxidation and nitriding diffusion pretreatment, in combination with a hard and tough PVD ceramic coating, can provide a significant reduction in surface impact wear when compared to either plasma diffusion treatments alone, or PVD ceramic coatings deposited on non-pretreated Ti-alloy substrates. © 2011 Elsevier B.V.


Cassar G.,University of Sheffield | Avelar-Batista Wilson J.C.,Tecvac Ltd. | Banfield S.,University of Sheffield | Banfield S.,Tecvac Ltd. | And 3 more authors.
Surface and Coatings Technology | Year: 2012

In this study, triode plasma oxidation (TPO) has been used to improve the tribological characteristics of Ti-6Al-4V. The effect of TPO on ball-on-plate reciprocating-sliding, impact, and micro-abrasion wear resistance of this alloy is investigated. Surface micro-profilometry, nano-/micro-indentation hardness testing, scratch-adhesion testing, scanning electron microscopy (SEM), atomic force microscopy (AFM), glancing-angle X-ray diffraction (GAXRD), and glow-discharge optical emission spectroscopy (GDOES) data is presented to corroborate the effects of the oxidation process. 'Traditional' thermal oxidation processes were used to benchmark this novel treatment. Following TPO treatment at 700°C for only 4h, a hard (exceeding 11GPa) and well-adhered oxide layer, composed of mixtures of the anatase and rutile polymorphs of TiO 2, was formed at the surface of the Ti-alloy. This layer is accompanied by a much larger oxygen-solution strengthened zone which creates a gradual chemical and mechanical gradient from the hard oxide 'compound layer' into the ductile substrate core. The various wear testing methods employed revealed excellent wear resistance of the TPO-treated alloy-compared both to the untreated alloy and to conventional, thermally oxidised samples. © 2012 Elsevier B.V.

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