bluuebunny/crossref_metadata_2025 huggingface dataset:
On the effect of preoxidation on nitriding kinetics
Authors: Friehling P.B. , Somers M.A.J.
Published: May 2005

Oxidation of ferritic surfaces prior to gaseous nitriding has been reported to lead to improved compound layer thickness uniformity and enhanced nitriding kinetics. The present work considers the nucleation and growth of a model compound layer on pure iron and, using previous experimental and theoretical results reported in the literature, puts forward two hypotheses to explain the effects of preoxidation on compound layer formation. It is proposed that the nucleation of iron nitrides is enhanced by the presence of an iron oxide layer, and that the growth of an iron nitride layer proceeds faster after preoxidation owing to a higher nitrogen content in the part of the compound layer closest to the surface.
Joint second prize low pressure pack sublimation: Newly developed zinc coating process
Authors: Walton A. , Speight J.D. , Harris I.R.
Published: May 2005

The LPPS process has been developed to coat Nd–Fe–B magnets and related alloy powders. The process is similar to sherardising, except that the coating chamber is static and evacuated to a moderate vacuum (10-1 torr). Compared to sherardising, LPPS achieves lighter coloured coatings and enhanced coating uniformity and has the ability to coat reactive ferrous materials such as Nd–Fe–B magnets. The corrosion protection provided by LPPS zinc is equivalent to that obtained with conventional sherardising. Using SEM, XRD, and SIMS analysis, the mechanism for both sherardising and LPPS has been shown to be the interaction of zinc vapour with ferrous substrates to form Fe–Zn intermediate phases (δ, ξ, and γ). At a given temperature, the zinc vapour pressure, chamber pressure, surface preparation of the component, and substrate material have been found to influence the rate of layer growth and final intermediate phase mixtures. Activation energy and thermodynamic analysis suggest that in galvanising, galvannealing, sherardising, and LPPS, Fe–Zn phase formation is dominated by the inward diffusion of zinc. For LPPS zinc coated Nd–Fe–B magnets, the same mechanism applies and leads to a complex mixture of (Nd–Fe–B)–Zn phases. The ‘black zinc’ layers seen occasionally with sherardising and LPPS have been shown to be associated with residual oxygen present in the deposition chamber. Black zinc surfaces have high optical absorbance as a result of their finely divided nature. Recent work on extending LPPS to coat magnet powders is also presented.
Shortlisted laser surface coating of TiC on H13 die steel: Effects on corrosion and errosion behaviour
Authors: Pirzada D. , Baburaj E.G. , Govindaraju R. , Froes F.H.
Published: May 2005

Coatings and surface treatments are being extensively used to increase the service life of die casting dies by reducing molten metal corrosion and erosion of the die. Owing to their excellent corrosion and abrasion resistance, refractory ceramic coatings are particularly suitable for coating die casting dies, and titanium carbide can provide significant resistance to molten aluminium corrosion and erosion. Technologies currently in use for applying such coatings include physical vapour deposition, plasma spraying, and ion implantation. Laser surface engineering is a very attractive technique because of its flexibility, non-equilibrium processing capabilities (involving high solidification rates in the range 103–108 K s-1), and ability to produce metastable phases and increase the solid solubility limit beyond the equilibrium phase diagram. Coatings thus produced are metallurgically bonded, which provides better substrate adhesion. The effects of the grain size of laser coated TiC coatings and of laser surface treatment itself on corrosion and erosion behaviour of H13 die steel in molten Al casting alloy A390 were investigated in the present study. The corrosion rate is accelerated by turbulence and by an increase in melt temperature. A significant improvement in corrosion resistance was achieved for H13 steel coated with TiC. Finer grain size and use of laser shock processing contribute to improved corrosion and erosion resistance of steel in molten aluminium. Based on metallographic and energy dispersive spectrometry studies, the effectiveness of the coatings along with possible reasons for their behaviour are discussed.
Shortlisted substrate ion etching in combined steered cathodic arc–ubm deposition system: Effects on interface architecture, adhesion, and tool performance
Authors: Schönjahn C. , Lewis D.B. ,   Münz W.-D., Petrov I.
Published: May 2005

In PVD processes, substrate cleaning by ion etching prior to deposition is a key step in achieving good film adhesion, which is essential for all coating applications. The substrate surface is generally cleaned by bombarding it with metal or gas ions, extracted from a cathodic arc or glow discharge plasma respectively, by negatively biasing the substrate. This alters substrate surface chemistry, topography, and microstructure and affects subsequent film growth and adhesion. The present study involved Cr ion bombardment of steel and tungsten carbide at bias voltages Ub of -600 and -1200 V as well as ion etching in an Ar glow discharge at Ub = -1200 V. Ion etching was followed by reactive unbalanced magnetron deposition of TiAlN based coatings. The microstructure and microchemistry of the interface region was investigated by XTEM and STEM–EDX analysis. After Ar ion pretreatment the presence of a low density substrate surface region was observed. This surface promotes the nucleation of randomly oriented grains leading to competitive growth with small column size and open boundaries. Interfaces generated after Cr ion bombardment at Ub = -600 V exhibit a local Cr deposition layer which leads also to competitive growth. In contrast, Cr ion bombardment at Ub = -1200 V results in the removal of around 100 nm of substrate material, providing a clean surface, and local epitaxial growth is observed. The different interface architecture is reflected by the critical loads obtained in scratch testing of 3·5 μm thick TiAlCrYN coatings deposited on tungsten carbide, ranging from 33 N for Ar bombardment to 141 N achieved by Cr ion bombardment at Ub = -1200 V. Cr ion pretreatment at Ub = -600 V results in a critical load of 68 N. The influence on the lifetime of coated tungsten carbide tools is also discussed.
Surface modification of tial based intermetallics by pressure nitriding
Authors: Bryar J.C. , Jacobs M.H. , Ashworth M.A.
Published: May 2005

Two TiAl based intermetallic alloys, Ti–48Al–2Mn–2Nb and Ti–45Al–2Mn–2Nb + 1 at.-%TiB2, were nitrided at high gas pressures using a conventional hipping facility under a range of process conditions. Detailed microstructural characterisation indicated that pressure nitriding produces a compound TiN–Ti2 AlN layer on the alloy surface. The growth of these titanium rich nitrides results in the formation of an aluminium rich, single phase γ-TiAl diffusion layer immediately below the compound layer. Partitioning of the alloying elements (Mn and Nb) is observed in the region immediately below the compound layer. The presence of a thin (<0·5 μm) layer of AlN has been identified on the surface of as nitrided specimens. The influence of process parameters on the growth rate and morphology of the compound layer has been determined. The compound layer formed on Ti–45Al–2Mn–2Nb+ 1 at.-%TiB2 was generally thinner than that formed on Ti–48Al–2Mn–2Nb following nitriding under identical conditions.
Mechanical properties of multilayer pvd Ti/TiB2 coatings
Authors: Berger M. , Larsson M.
Published: May 2005

To obtain from a tribological perspective acceptable PVD coatings of covalently bonded materials, such as borides and oxides, it is essential to control and often reduce the very high compressive stresses which develop during coating growth, since such stresses not only reduce coating adhesion but also limit film thickness. A possible way to obtain lower stress levels could be to utilise multilayer coatings, that is to combine the stressed material with a more ductile material in a layered structure. In the present study a highly stressed PVD TiB2 material was layered with ductile Ti. The multilayer period, i.e. the combined thickness of one Ti lamella and one TiB2 lamella, and the lamellar thickness ratio of the two phases were varied in order to evaluate their influences on some important mechanical properties and on the abrasive wear resistance of the Ti/TiB2 coatings. The coatings were deposited using magnetron sputtering of TiB2 and electron beam gun evaporation of Ti. To evaluate the coating phase composition X-ray diffraction was used. Mechanical and tribological properties were examined by nanoindentation (hardness and modulus), beam deflection (residual stress), scratch testing (cohesion and adhesion), and dimple grinding (abrasive wear resistance). Hardness, Young's modulus, compressive residual stress, and abrasive wear resistance were found to increase with the fraction of TiB2 in the coatings, and an inverse relation was found for the critical normal load obtained in scratch tests, i.e. cohesion/adhesion decreased with increasing TiB2 fraction. The investigation showed that a hybrid PVD technique combining electron beam evaporation of Ti and magnetron sputtering of TiB2 can be used to produce coatings with increased fracture toughness, decreased residual stress, and relatively high hardness as compared to homogeneous PVD TiB2. It was also found that the yield/fracture strength of Ti was insufficient, i.e. it could not accommodate the level of stress generated in the TiB2 phase. Therefore, by choosing another material with higher yield/fracture strength than Ti it is believed that the properties of the multilayer coating could be improved even further.
Comparison of tribological properties of metal–metal and metal–cermet couples under lubricated and dry conditions
Authors: Neville A. , Kollia-Rafailidi V.
Published: May 2005

The focus of this paper is on the determination of friction, wear, and film forming characteristics in conventional metal–metal couples and in cermet–metal couples. The tribological behaviour of a WC–Co based cermet applied by the HVOF process to a carbon steel substrate has been investigated in contact with cast iron, and this behaviour has been compared with carbon steel–cast iron couples. A mineral oil, a mineral oil containing zinc dialkyldithiophosphate (ZDDP), and a fully formulated lubricant were used for lubrication. The results show that the behaviour of the lubricant, in terms of its film forming and friction behaviour, is critically dependent on the load. The oil containing ZDDP shows a very significant increase in its ability to form a boundary film as the load increases.
Characterisation of nicr flame and plasma sprayed coatings for use in high temperature regions of boilers
Authors: Higuera Hidalgo V. , Belzunce Varela J. , Martínez de la Calle J. , Carriles Menéndez A.
Published: May 2005

Nickel–chromium coatings have been plasma sprayed onto a stainless steel surface in order to protect it from the high temperature and erosive conditions encountered in power plant boilers. Microstructure, porosity, and microhardness of the coatings have been studied. High temperature oxidation behaviour was studied in an atmosphere similar to service conditions used in power plant, and thermal fatigue tests were performed in an experimental combustion chamber. Finally, adhesion between the steel substrate and NiCr coating was evaluated by means of tensile tests. The results obtained are discussed with particular reference to the evolution of microstructure owing to thermal effects and coating deposition method.
High temperature nanoscale mechanical property measurements
Authors: Smith J.F. , Zheng S.
Published: May 2005

A depth sensing indentation instrument widely used for measuring the small scale mechanical properties of thin films and surfaces has been modified for operation at elevated temperatures. The essential feature permitting this development is the vertical orientation of the specimen, which allows the heated zone to be placed above the high sensitivity displacement transducer. In the present work, small scale hardness and elastic modulus measurements were performed on glass, gold, and single crystal silicon at room temperature and 200°C. The results show that at 200°C the hardness and elastic modulus of soda lime glass and gold are lower than at room temperature, as anticipated. In contrast, indentation testing of Si(100) at 200°C produced a similar hardness value to that obtained at room temperature, although the modulus was again reduced, from 140·3 to 66·0 GPa. In addition, the well known ‘pop out’ event, which is observed during unloading of a silicon indentation at room temperature, disappeared at 200°C.
First prize deep case hardening of titanium alloys with oxygen
Authors: Boettcher C.
Published: May 2005

In order for such engineering components as bearings and gears to withstand the high Hertzian contact stresses encountered in service, deep case hardening is necessary. Oxygen diffusion (OD) and thermal oxidation (TO) techniques have been successfully applied to the low strength Ti–6Al–4V alloy to develop a deep hardened case and a thin, hard, wear resistant surface layer. These techniques have been used to produce homogeneous, composition controlled, and highly reproducible alloyed surface layers in the Ti–6Al–4V alloy. It was the objective of the present investigation to develop and apply the novel duplex OD–TO surface treatment to the high strength titanium alloy Timet550. The higher strength of Timet550, compared with Ti–6Al–4V, would have the advantage of increasing the bending strength of a component under load. Various oxidation and diffusion treatments were carried out to optimise the OD–TO process and consequently a post-diffusion heat treatment was developed to maximise the depth and hardness of the OD case for Timet550. The surface layers were characterised using XRD, GDS, and SEM, which revealed a rutile surface with an oxygen rich case. The loadbearing capacities of duplex treated Timet550 specimens were evaluated using friction monitored scratch tests and a wheel on block Amsler wear tester. It was found that the OD, heat treated, and TO processed Timet550 specimens had the greatest loadbearing capacity.
Manufacture of RP tools with high quality surface finish using high temperature epoxy resin and electroless nickel plating
Authors: Tay F.E.H. , Haider E.A. , Rahman M. , Lee J.Y. , Ong T.E.H.
Published: May 2005

Rapid tooling is gaining increasing attention in the manufacturing sector, especially for the development of new products, owing to its distinctive characteristics. Rapid prototyping techniques can be used in this prospective manufacturing area to produce tooling either directly or indirectly. Although powder metal based rapid prototyping systems are considered most effective for rapid tooling, the requirements for injection moulding are not yet fully attained. In the present study, rapid tooling produced by direct laser sintering of metal powder has been investigated with the aim of improving its quality for industrial acceptance. High temperature epoxy resin was used to fill the pores to improve compressive strength, and electroless nickel plating was employed to enhance hardness, conductivity, ductility, lubricity, wear, and abrasion resistance without affecting dimensional accuracy. Results demonstrate that these techniques possess significant potential for rapid tool production.
Crater wear mechanisms of tin coated high speed steel tools
Authors: Lim C.Y.H. , Lim S.C. , Lee K.S.
Published: May 2005

This paper examines the crater wear characteristics of TiN coated high speed steel tool inserts during dry turning of steel workpieces over a wide range of machining conditions. Scanning electron microscopy shows that cracking and attrition of the TiN coating on the rake face result in coating loss soon after machining begins. The subsequent wear of the exposed high speed steel substrate occurs via attrition, diffusion, and high temperature shear. A wear mechanism map linking the observed crater wear mechanisms to machining conditions reveals that transitions from one dominant mechanism to another may be related to variations in measured tool wear rates.
Wear resistance of JIS SKD61 tool steels with Cr based coatings
Authors:   Chiu L.-H.,   Yang C.-F.,   Liu P.-M.
Published: May 2005

The wear behaviour of three chromium based metallic and compound coatings on a JIS SKD61 (AISI H13) tool steel has been investigated. Hard chromium, chromium nitride, and chromium carbide coatings were applied to the SKD61 steel using electroplating, cathodic arc plasma deposition, and thermoreactive diffusion respectively. Microstructures, crystal structures, and chemical compositions of the coated materials were examined using SEM, XRD, and GDOS. The microhardnesses of the hard chromium, chromium carbide, and chromium nitride coatings were found to be 943, 1667, and 2148 HV respectively. Results of wear tests showed that the hard chromium coating, with the highest friction coefficient and a low hardness value, exhibits the lowest wear resistance. The wear resistance of the chromium carbide and chromium nitride coated SKD61 steels was excellent: these coatings are very hard, with either strong cohesion bonding between the coating and the substrate or low friction coefficient.
Surface oxidation of steels at low oxygen pressure and elevated temperature: Impact on gas nitriding
Authors: Haase B. , Stiles M. , Dong J.
Published: May 2005

Low alloy steels are covered with a thin oxide layer containing Fe3O4 adjacent to the metal and Fe2O3 at the interface with the atmosphere. It can be shown by means of modern surface analysis techniques that such layers are usually less than 10 nm thick. The formation of Fe3O4 is held to be a precondition for the formation of Fe2O3, the latter being responsible for corrosion protection and the slight passivity of iron and low alloy steels. Passivity can be significantly increased by increased chromium concentration, which in the case of stainless steels means by chromium contents exceeding 13 wt-%. Stainless steels form an oxide layer at the surface enriched in chromium oxides (Cr2O3). When this layer is formed spontaneously near room temperature, it too is thinner than 10 nm. At elevated temperatures, for example during heating in a nitriding furnace to 500 or 600°C, oxide layers tend to grow fast when oxygen is present, even at low partial pressure. The result is oxide layers which are at least an order of magnitude thicker than oxide layers formed at room temperature, their thickness depending not only on oxygen partial pressure but also on kinetic parameters such as heating rate and time. Experimental investigations have been carried out to study the formation of oxide layers at a range of temperatures and oxygen partial pressures, and to see how this impacts on subsequent nitrogen uptake in an ammonia atmosphere. The objective of the investigation was to explain contradictory and irreproducible results in practical gas nitriding and, more generally, in heterogeneous surface treatment processes in gas atmospheres at elevated temperatures.
Bodycote international prize paper competition: Joint second prize tinitron process for low pressure nitriding of titanium and its alloys
Authors: Foi R. , Deramaix C. , Atale O. , Jacquot P.
Published: May 2005

Titanium has been known for nearly 200 years and in mineral form is the fourth most commonly occurring element. Although titanium is such a common element, the pure metal is still expensive. Nevertheless, titanium is being more and more extensively used in a wide range of applications, from aerospace components to leisure products. In fact the main drawback of titanium, despite its cost, is that it usually needs additional treatments to enhance its wear resistance capabilities. These treatments are usually expensive, which limits their use to high added value parts. The Tinitron process is a gaseous treatment giving excellent wear resistance to titanium parts at the lowest possible cost for a wide range of applications. This thermochemical treatment is based on nitrogen diffusion into titanium without the use of a plasma. The diffusion of nitrogen creates a compound layer of TiN+Ti2 N and a diffusion layer of Ti(N) underneath. As the treatment is based on diffusion there are no adhesion problems. The compound and diffusion layers harden the surface of the material and the compound layer increases its wear resistance. Furthermore, the treatment is performed under vacuum at low pressure, thus minimising gas consumption and environmental impact. Tinitron permits homogeneous bulk treatment of complex shaped parts (grooves, holes, etc.) and it can be used in the medical field as the process is 100% biocompatible. Finally, Tinitron is less expensive than standard titanium surface treatments.
Surface oxidation of aluminium nitride thin films
Authors: Watanabe Y. , Hara Y. , Tokuda T. , Kitazawa N. , Nakamura Y.
Published: May 2005

Two types of aluminium nitride thin films were prepared on silicon substrates by ion beam assisted deposition; one had columnar microstructure and the other granular microstructure. Surface oxidation was performed on both films by annealing them at 900°C for 5–120 min and the effect of film microstructure on oxidation behaviour was studied. X-ray diffraction studies showed that aluminium oxynitride phase was formed in granular films after annealing for 60 min, whilst this oxidised phase was hardly observed in columnar films. Depth analysis by X-ray photoelectron spectroscopy revealed that oxygen diffusion occurred more readily in the granular microstructure than in the columnar. Observations using an atomic force microscope indicated that the surface average roughness increased with annealing time. It was therefore concluded that granular AlN films can be more easily oxidised than columnar films.
Formation of β-C3N4 grains by sputtering
Authors: Wei J. , Hing P.
Published: May 2005

If β-Si3 N4 and β-C3 N4 have the same structure they might be expected to be mutually miscible, giving rise to silicon carbon nitride (SiCN), which has potential industrial applications. SiCN films were deposited onto Si (100) substrates by unbalanced magnetron sputtering. Reactive deposition was performed using graphite and silicon targets in an argon–nitrogen plasma. The growth kinetics of the films are discussed. The films were characterised by X-ray photoelectron spectroscopy, Fourier transform infrared spectroscopy, and scanning electron microscopy. The N2 fraction in the gas mixture has a major influence on the deposition rate and composition of the films: a high N2 fraction results in increased deposition rate and N/(C + Si) and C/(N + Si) ratios. The SiCN films are mainly amorphous. XPS and FTIR spectra show the existence of Si–N, C–N single, C=N double, and C≡N triple bonds. Almost no Si–C bonding is found in the films.
Growth of SiCN films by magnetron sputtering
Authors: Wei J. , Gao Y. , Zhang D.H. , Hing P. , Mo Z.Q.
Published: May 2005

If β-Si3 N4 and β-C3 N4 have the same structure they might be expected to be mutually miscible, giving rise to silicon carbon nitride (SiCN), which has potential industrial applications. SiCN films were deposited onto Si (100) substrates by unbalanced magnetron sputtering. Reactive deposition was performed using graphite and silicon targets in an argon–nitrogen plasma. The growth kinetics of the films are discussed. The films were characterised by X-ray photoelectron spectroscopy, Fourier transform infrared spectroscopy, and scanning electron microscopy. The N2 fraction in the gas mixture has a major influence on the deposition rate and composition of the films: a high N2 fraction results in increased deposition rate and N/(C + Si) and C/(N + Si) ratios. The SiCN films are mainly amorphous. XPS and FTIR spectra show the existence of Si–N, C–N single, C=N double, and C≡N triple bonds. Almost no Si–C bonding is found in the films.
Preparation of fluorinated amorphous carbon nitride films by magnetron sputtering
Authors: Yokomichi H.
Published: May 2005

Fluorinated amorphous carbon nitride (a-C1-x Nx : F) films were prepared by magnetron sputtering to reduce the C≡N bonding configuration and the dangling bond density, while increasing the optical bandgap over that of amorphous carbon nitride (a-C1-x Nx) and hydrogenated amorphous carbon nitride (a-C1-x Nx : H) films. The structural, optical, and defect properties of these films were investigated by infrared absorption, X-ray photoelectron spectroscopy, ultraviolet–visual spectroscopy, and electron spin resonance (ESR) measurements. No IR peaks due to C≡N bonding were observed for the a-C1-x Nx : F films, indicating that the amount of C≡N bonding decreased with the incorporation of fluorine atoms. Furthermore, IR signals due to the Raman G band were not observed in any of the films, although the Raman D band was observed for all of them. In addition, the IR spectra revealed that CF2 bonding dominated over CF bonding. These results can be explained in terms of a decrease in structural dimension owing to fluorine incorporation and a ‘perfect’ amorphous structure that has no graphite crystalline region. The dangling bond density, peak to peak line width, g values of the ESR spectra, and optical bandgap for a-C1-x Nx : F films were smaller than those for a-C : F films.
Gelling induced autophobicity effects in multilayer sol–gel coating systems
Authors: Tan S.N. , Zeng X. , Fokkink B.
Published: May 2005

Dewetting phenomena in silica dioxide multilayer sol–gel systems were studied. A second layer of coating was found to dewet and form domains on top of the first coating rather than forming a continuous film. To promote wetting of the first coating by the second, the application of three surface treatment techniques (thermal treatment, post-surface condensation in high pH solution, and surface oxidation by oxygen plasma) to the first coating was investigated. These treatments result in high surface energy hydrophilic surfaces onto which subsequent smooth and continuous coatings can be applied. However, the time interval between treatment of the first coating and application of the second coating (the ‘aging’ time) was found to affect the wettability of the first applied layer. With increasing aging time, the surface energy decreases, resulting in a more hydrophobic surface. A detailed study of water contact angles with aging time after the three surface treatments supports the hypothesis that the observed ‘autophobicity’ is due to migration of the residual hydrophobic ethoxy chains from the bulk of the coating to the surface, which consequently results in a more hydrophobic surface.
Metal surface investigation by scanning probe microscopy
Authors: Thornton J.T.
Published: May 2005

Metallic materials are widely used in the fabrication of devices and structures because of their wide range of useful physical properties, such as conductivity and formability. As the need for the fabrication of microscopic structures increases, more importance is being attached to the investigation of metal surfaces on the submicro-and nanometre scale. Scanning probe micros copy (SPM) has become an increasingly useful tool for the investigation of metallic structures owing to its ability to perform three-dimensional measurements on the nanometre scale as well as to investigate the material properties. As a result of its versatility, there are a large number of ways in which SPM can be applied to the study of metallic surfaces. This paper presents an overview of some of the more common SPM techniques used for investigations of metal surfaces.
High pressure reactive plasma spray synthesis of titanium nitride based coatings
Authors: Valente T. , Carassiti F. , Suzuki M. , Tului M.
Published: May 2005

The term thermal spray covers a wide range of fabrication methods for surface engineering applications. A very promising thermal spray process involves the production of protective coatings or freestanding components by reactive plasma spray (RPS) techniques. Using reactive gases such as nitrogen or methane it is possible to synthesise hard nitride and carbide phases in reactive metals such as Ti, Cr, and Al. In this investigation RPS was used to produce composite titanium nitride/titanium coatings. Commercially pure titanium powders were used as raw materials and sprayed in a nitrogen atmosphere at up to 300 kPa. The process was carried out by means of a controlled atmosphere plasma spray system, allowing spraying in the pressure range 10–400 kPa. The effects of chamber pressure, plasma gas composition, and spraying distance on the scope of the expected reactions were evaluated. Phase analysis, measurements of nitrogen content and Vickers microhardness, and metallographic investigation of the as sprayed coatings revealed that titanium hard phases were synthesised during spraying and became embedded in the titanium matrix. High pressure significantly enhanced nitride formation (Ti2 N, TiN, TiN1–x) in the titanium matrix. Microhardness values up to 1433 HV0·3 were obtained, with maximum nitrogen content of about 11·1 wt-%. Studies on sprayed particles showed that TiN was the dominant phase formed during flight, suggesting that diffusion processes play an important role in the substrate. Compared with pure titanium deposits, coatings produced by RPS are much harder and have better tribological properties.
Plasma deposition of polymer films on pmma powders using vacuum fluidisation techniques
Authors: Chityala A. , van Ooij W.J.
Published: May 2005

Thin organic films were deposited on polymethylmethacrylate powder particles by combining the techniques of plasma polymerisation and vacuum fluidisation. The treated powders were characterised by scanning electron microscopy, energy dispersive X-ray analysis, and time of flight secondary ion mass spectrometry. The primary objective of the investigation was to demonstrate the efficacy of the two techniques in combination for modifying the surface properties of particulate materials.
Pretreated al substrates for better adhesion with silicone RTV adhesive sealant
Authors: Lucena M. , Clarson S.J.
Published: May 2005

Adhesion in peel’ tests were performed to determine the average peel strength and adhesion characteristics of silicone RTV sealant deposited on aluminium substrates pretreated by plasma deposition using hexamethyldisiloxane and hexamethyldisilazane as monomers and argon and oxygen as carrier gases. Chemically prepared films of SiO2 were also deposited on the aluminium substrates from tetraethylorthosilic ate and tetramethylorthosilicate solutions. Test specimens were prepared following the ASTM C794–93 specification. The average peel strength necessary to peel the silicone sealant from the aluminium substrate was shown to be increased by pretreatment, however the extent of the improvement was dependent on the type and duration of pretreatment performed. Although the average peel strength was increased and the adhesion characteristics were improved, no record of 100% cohesive failure was obtained. A mixed failure mode (adhesive and cohesive) was observed in many cases.
Silane based pretreatments for automotive steels
Authors: Sundararajan G.P. , van Ooij W.J.
Published: May 2005

Previous papers have reported on various silane based pretreatments which can replace the phosphate and chromate based systems currently used for corrosion protection of metals in applications where such metals are used in the unpainted or powder painted state. The present paper reports for the first time on the performance of silane based pretreatments in automotive systems. On electrogalvanised steel, hot dip galvanised steel, and aluminium alloys (Al 6061, Al 6111), the silanes bis-(trimethoxysilylpropyl)amine (bis-amino silane) and bis-(triethoxysilylpropyl)tetrasulphide (bis-sulphur silane) were found to provide excellent corrosion protection in conjunction with the electrocoat ED-5000 (PPG Industries Inc.). On cold rolled steel, a mixture of the above two silanes provided corrosion protection comparable to the currently used zinc phosphate system. The corrosion performance of automotive steels pretreated with silanes has been compared with that of zinc phosphated steels using a variety of tests including the GM scab test, electrochemical impedance spectroscopy, and N-methyl pyrrolidone adhesion tests. The silane films have also been characterised by reflection–absorption infrared spectroscopy.
Emergence of chemical and electrochemical processes in surface engineering
Authors: Gabe D.R.
Published: May 2005

The new century opens with a large stock of available coating process technologies, among which are old (electroplating) and new (physical vapour deposition, PVD) techniques. While electroplating may have some disadvantages, its proven technology is of primary importance, which is demonstrated by a number of large, continuing applications. By contrast, the cost and operating disadvantages of PVD will ensure that it maintains a small specialist niche in the coating technology spectrum.
Mechanisms of coating failure as demonstrated by scratch and indentation testing of TiN coated HSS
Authors: Larsson M. , Olsson M. , Hedenqvist P. , Hogmark S.
Published: May 2005

In situ monitoring of acoustic emission during scratching and indentation in combination with post-test light optical and scanning electron microscopy were used in order to evaluate the dominant coating failure mechanisms for TiN coated high speed steel. During scratching, six different coating failure mechanisms could be distinguished, i.e. cracks parallel with the scratch channel, semicircular cracks within the scratch channel, external transverse cracks, cohesive chipping, adhesive spalling, and complete breakthrough of the coating within the scratch channel resulting in substrate exposure. During indentation, four different types of coating failure could be distinguished, i.e. circular cracks within the indentation, radial cracks outside the indentation, cohesive chipping, and adhesive spalling. The influence of coating thickness, substrate hardness, and substrate surface topography on the coating failure mechanisms is very complex and depends on the type of contact, i.e. static or dynamic, contact load, etc. However, the results show that indentation testing enables a more appropriate method for the evaluation of the intrinsic fracture resistance of the coating material and coating/substrate adhesion as compared with scratch testing. In contrast, scratch testing, simulating the contact condition between an asperity sliding on a flat, is preferably used for evaluating the load carrying capacity of a coating/substrate composite. It can also be used in order to find the optimum substrate surface roughness for coated components used in various sliding applications.
Protective coatings for non-oxide ceramics
Authors: Bellosi A. , Esposito L.
Published: May 2005

Protective coatings for non-oxide ceramics have a great potential for reducing oxidation under hot oxidising conditions. In the present paper a technique to coat silicon nitride and silicon carbide ceramics with a glass layer is proposed. The composition of the coating is in the Al2O3–SiO2–Y2O3 system and is close to the composition of the grain boundary phase of the two dense materials. At the processing temperature, that was slightly higher than the glass softening temperature, the glass coating wet both Si3 N4 and SiC and promoted strong adhesion with the ceramic without the formation of any new weak compounds. The coatings are different for Si3 N4 and SiC based systems, especially across the original ceramic/glass interface. In the case of silicon nitride, the grains at the interface that were in direct contact with the glass dissolved until the glass became saturated with nitrogen. Then the Si3 N4 grains moved from their original position towards the free glass surface. The extent of dissolution and consequent grain removal was influenced by the sintering aids used to densify the silicon nitride, and in particular by the refractoriness of the secondary phase that they formed. In silicon carbide based systems, the attractive force between the grains is stronger than in silicon nitride. As a consequence, at the processing temperature the liquid glass coating wet the SiC well but did not affect its microstructure because there was no driving force for glass penetration even after long treatments.
Nitrogen doping of amorphous DLC films by rf plasma dissociated nitrogen atom surface bombardment in a vacuum
Authors: Ogwu A.A. , Magill D. , Maguire P. , McLaughlin J. , McCullough R.W. , Voulot D.
Published: May 2005

Interpretations of recent (1999) theoretical first principles calculations in the literature based on the density functional theory using the local density approximation has led to suggestions that a low energy nitrogen surface bombardment of amorphous carbon films should lead to a reduction in the work function of the films. By applying a low energy nitrogen flux generated by a nitrogen plasma source to the surface of amorphous diamondlike carbon (DLC, a-C : H) films prepared by plasma enhanced chemical vapour deposition (PEVCD) in a vacuum, relatively high non-bonded nitrogen doping levels have been observed compared with DLC films prepared by other methods reported in the literature. The amorphous DLC films have been characterised by X-ray photoelectron spectroscopy and Raman spectroscopy before and after nitrogen bombardment. This novel processing route is expected to have an impact on residual stress relief and the field emission properties of amorphous DLC.
Influence of secondary phase on residual stress of plasma sprayed glass coatings
Authors: Bao Y. , Gawne D.T. , Zhang T. , Qiu Z. , Zhang K.
Published: May 2005

The behaviour of glass coatings during thermal spray deposition is fundamentally different from that of metal and ceramic coatings because quench stresses can berelaxed during spraying. However, the expansion coefficient mismatch between the coating and the steel substrate remains an important source of residual stress and this paper investigates the effect of incorporating an alumina second phase into the glass to reduce the mismatch. Real time measurements on the deflection of coated specimens during spraying show that the residual stress can be reduced to zero by controlling the second phase content. The results also show that substantial temperature variations may be developed across large substrates during spraying as a consequence of the scanning action. These variations can affect the residual stress owing to the thermally activated nature of the stress relief and the marked sensitivity of glass properties to temperature. This research indicates that the pattern of residual stress developed in glass coatings is complex and will depend upon the substrate dimensions and the process operating conditions.
Investigation of nitrogen diffusion during laser heating of titanium
Authors: Yilbas B.S. , Shuja S.Z.
Published: May 2005

Titanium alloys find wide application in industry despite their poor wear resistance. One of the alternative methods to improve the surface properties of titanium alloys is the laser gas alloying process. The modelling of the laser assisted nitrogen diffusion process minimises experimental costs and gives insight into the diffusion process. In the present study, nitrogen diffusion into titanium as a result of laser heating is considered. A transient heat transfer analysis based on the Fourier theory is carried out and a closed form solution taking into account the phase change process is introduced. The diffusion coefficient obtained from a previous study is employed when computing the nitrogen concentration inside the substrate. In order to investigate the effect of laser parameters on the diffusion process five pulse lengths with the same energy content are considered. It is found that the influence of the pulse length on the nitrogen concentration is considerable and its effect on the diffusion coefficient is significant.
High temperature oxidation studies of yttrium implanted pure iron and various steels
Authors: Caudron E. , Buscail H.
Published: May 2005

Yttrium implanted and unimplanted pure iron, extra low carbon steel, low manganese steel, and low manganese–carbon steel were analysed at 700°C and under an oxygen partial pressure PO2 of 0·04 Pa for 24 h to show the effect of yttrium implantation on high temperature oxidation resistance. Specimen oxidation weight gains were studied by thermogravimetry, and structural analyses were carried out by in situ high temperature X-ray diffraction (XRD) with the same experimental conditions. The aim of this paper is to show that the initial nucleation stage of the main compounds induced by oxidation at high temperature depends on the initial specimen composition and the surface treatment (yttrium implantation). The results obtained by in situ high temperature XRD will be compared with those from thermogravimetry for a better understanding of the weight gain curves observed during oxidation tests. This study is a fundamental approach which demonstrates the improved corrosion resistance of yttrium implanted specimens at high temperature.
Electrochemical synthesis of polyaniline–polypyrrole composite coatings on carbon fibres in aqueous toluene sulphonate solution
Authors: Iroh J.O. , Rajagopalan R.
Published: May 2005

Polyaniline and polypyrrole were codeposited electrochemically on carbon fibres under potentiostatic conditions. Electropolymerisation was carried out by varying the applied potential and the feed ratio of monomers. The progress of electropolymerisation was monitored by weight gain analysis and infrared spectroscopy. The thermal stability of the coatings was determined by using thermogravimetric analysis and differential scanning calorimetry. Characteristic behaviour of polyaniline and polypyrrole can be deduced from the weight gain plots. Formation of polyaniline–polypyrrole composite coatings was further confirmed by the presence of characteristic peaks for polyaniline and polypyrrole in the infrared spectra. Thermal analysis also revealed the behaviour of the composite. Composite coatings composed of polyaniline and polypyrrole were formed at applied potentials of <1·0 V. Polypyrrole is preferentially formed at 1·5 V. Scanning electron micrographs were also used to illustrate the composite behaviour.
Surface topography of pulsed current gas metal arc clads
Authors: Rajasekaran S.
Published: May 2005

Clad surface quality in the pulsed current gas metal arc welding (GMAW-P) process is mainly influenced by the pulse parameters. Selection of the most suitable combination of pulse parameters is very difficult owing to the complex interdependence of the parameters on the pulsed current. Therefore the effect of pulse parameters on clad surface characteristics has been studied for different types of droplet detachments, namely background detachment, one droplet detachment per peak, two droplet detachments per peak, and three droplet detachments per peak. The most suitable type of droplet detachment for cladding, using a 1·2 mm diameter ER 5356 filler metal, has been selected on the basis of measuring the surface characteristics of the clad using a computerised measuring system based on a linear variable differential transformer. One droplet detachment per peak was considered to be capable of providing a smoother clad surface than the other types of droplet detachment. The peak energy was found to be low for the background detachment.
Effect of secondary processing on EDM surfaces
Authors: Ramasawmy H. , Stout K. , Blunt L.
Published: May 2005

A traditional practice in the die and mould making industry is to hand polish finally the part as a finishing operation irrespective of the type of primary machining process used in its manufacture (e.g. milling, electrodischarge machining, etc.). However, a possible alternative when die sinking using electrodischarge machining (EDM) is to electrochemically polish the surface. Hence, the surface resulting after the EDM process will be a combination of two processes (the former and the latter), and as a consequence the surface will reflect the way in which these processes interact with each other. The aims of this paper are to examine how the two processes in sequence affect the surface topography of the finished component, and to study the effects of the current density employed in the electrochemical polishing process. The primary set of three-dimensional surface parameters recently revised at the University of Huddersfield was used as a basis to characterise the surface produced by the combined processes. The paper also illustrates which three-dimensional parameters are more sensitive to the machining processes variables, and which can therefore be used to characterise the results of the dual process.
Thin layer activation for on line measurement of rocker pad scuffing
Authors: Hoffmann M. , Macchi G. , Horstmann W. , Arroja F. , Stroosnijder M.F.
Published: May 2005

Despite its benefits, the use of thin layer activation (TLA) is limited owing to the restricted number of dedicated facilities available and to the unfamiliarity with the technique. The purpose of this paper is to familiarise a wider audience with the TLA technique for engine wear testing. For this the anti-scuffing properties of three different engine oils were evaluated by measuring the scuffing on one rocker pad on line during engine operation using TLA. The results illustrate that TLA offers the possibility of evaluating the scuffing of rocker pads on line with a high degree of precision, thus providing a deeper scientific understanding of material degradation processes than with conventional techniques.
Wear behaviour of HVOF thermally sprayed WC–14Co–3Cr coatings
Authors: Staia M.H. , Carrasquero E.
Published: May 2005

The present study describes the tribological properties of thermal sprayed WC–14Co–3Cr (wt-%) coatings produced by using the high velocity oxyfuel (HVOF) deposition process. The coatings have been characterised with respect to their chemical composition and microstructural features (SEM-EDX) and roughness (profilometry). Experiments using a tribometer (pin on disk configuration) under non-lubricating conditions have been performed with the aim of determining the wear resistance of these coatings. To ensure reproducibility of the wear tests, the coated samples have been ground to an average superficial roughness Ra of 0·230 μm. Steel balls of AISI 1086, 6 mm in diameter, were tested against coated and uncoated samples. The morphology of the wear tracks on both pins and discs was characterised using SEM and three-dimensional profilometry. An average friction coefficient of 0·596 and average wear rate of 1·21 × 10-4 mm3 Nm-1 werefound for the tribological pair AISI 1086 pin/ WC–14Co–3Cr coated disc. For this pair a mixed wear mechanism of both abrasive and adhesive wear was observed for the pin with unidirectional material transfer from the pin toward the coating.
Fractal dimension: Measure of coating quality
Authors: Oliva A.I. , Anguiano E. , Aguilar M.
Published: May 2005

Fractal analysis recognises that the concepts of length and area for irregular objects are not absolute, but depend on the measurement scale. In the present work, three-dimensional topography of different surfaces has been measured by scanning tunnelling microscopy (STM) and atomic force microscopy (AFM) tech niques. In particular, gold and aluminium thin films grown by evaporation techniques on silicon substrates have been studied. Fractal analysis by the frequency method was used to characterise the quality of the surfaces. The films were prepared with thickness from 30 up to 2000 nm. It was observed that the low and high frequency components of the roughness depend strongly on film thickness. Moreover, at small thickness two different fractal components in the surface roughness can be observed, which implies that low thickness coatings follow a dynamic completely different from that for high thickness. In conclusion, it has been established that fractal analysis can be used to characterise thin film surface coatings and to determine the coating type obtained.