Showing papers in "Surface & Coatings Technology in 1997"

Tribology of diamondlike carbon and related materials: an updated review

Abstract: Diamondlike carbon (DLC) has been studied for many years as a wear-resistant material with low friction coefficient. Its tribological behavior is strongly affected by the tribotesting environment and is controlled by tribochemical effects, which may in turn be dependent on the technique used for the deposition of the films. New variations of DLC films, with various dopings, and new deposition methods have been investigated in recent years. The paper presents an updated review of the tribological properties of DLC and related materials, and discusses the mechanisms suggested for the explanation of the wear and friction behavior of these materials.

Industrial applications of CrN (PVD) coatings, deposited at high and low temperatures

Abstract: Industrial applications of CrN (PVD) coatings are entering an expanding but selective range of mass manufactured goods. They may be prepared as single, low and high temperature CrN coatings and double TiN+CrN coatings. In this work, depositions of CrN at high temperatures were performed by a low voltage thermionic arc in a BAI 730M apparatus, while at low temperatures (below 250 °C), the plasma-beam sputtering process in a SPUTRON apparatus was used. We studied the following critical parameters that influence the quality of the coatings and applied the performance tests used in industrial practice: adhesion and scratching coefficient, microhardness, surface topography, oxidation and corrosion resistance. The performance tests were made with the assistance of technicians as well as in 12 Slovenian factories. CrN coatings were deposited at 480 °C for wear and corrosion protection in cold forming and cutting of copper in commutator manufacturing, in forming of aluminium components in automotive production and for surface improvement of moulds (made of H11 steel) in Al-Si die casting under pressure. Deposition temperatures of 180–220 °C, obtained in the SPUTRON apparatus, were required to improve cold forming tools made of alloyed tool steels (e.g. D2 and D3). The lowest obtainable temperature of 140 °C in the SPUTRON gave a CrN coating of high quality for practical use. These coatings were used to protect electrodeposited and electropolished nickel moulds (models) in artificial teeth production. Double TiN+CrN coatings were used as a highly abrasive resistant coating in the production of rotors (in the electromotor industry), and in cold forming and forging in mass manufacturing of screws. The results and performance tests were compared with the available data, mostly published on forming, milling, deep drawing of copper, nickel and titanium and their alloys, and on die casting of aluminium and Al-alloys.

Friction control of diamond-like carbon coatings

Abstract: The friction reduction of contacting surfaces in relative motion may be achieved through the use of solid lubricant coatings. The control of friction and wear through diamond-like carbon (DLC) coatings strongly depends on both the environmental conditions and the nature of the coating, as determined by the deposition process. The paper presents and discusses friction results linking the structure and composition of DLC coatings prepared by PACVD and varying precursor and bias, with physical and mechanical properties and tribological behavior in controlled environments. The wide range of the friction coefficients observed, from less than 0.01 to more than 0.5, and the different mechanisms involved are explained by the effects of the deposition process and tribological parameters.

XPS studies of MoS2 formation from ammonium tetrathiomolybdate solutions

Abstract: Preparation of MoS 2 by acidification of ammonium tetrathiomolybdate solution has been studied by X-ray photoelectron spectroscopy (XPS). The precipitates formed from the solution are mainly composed of MoS 3 , the Mo 3d chemical shift of which is approximately 4.2eV. Heat treatments of the above product at 450 and 850°C, in a vacuum of 1.33 × 10 −4 Pa, lead largely to formation of MoS 2 , with typical chemical shifts of abouth 1.2eV. The MoS 2 formed consists of nano-sized, crystalline particles of hexagonal (2H-type) structure. The validity of MoS 2 formation by this route is confirmed by comparative study, namely the decomposition of ATT solids under the same respective heat treatment conditions. Apart from these main aspects, origins of minor XPS peaks are also considered.

Metal plasma immersion ion implantation and deposition : a review

Abstract: Metal plasma immersion ion implantation and deposition (MePIIID) is a hybrid process combining cathodic arc deposition and plasma immersion ion implantation. The properties of a metal plasma produced by vacuum arcs are reviewed and the consequences for MePIIID are discussed. Different version of MePIIID are described and compared with traditional methods of surface modification such as ion beam assisted deposition (IBAD). MePIIID is a very versatile approach because of the wide range of ion species and energies used. At one extreme case, films are deposited with ions in the energy range 20–50 eV, and at the other extreme, ions can be implanted with high energy (100 keV or more) without film deposition. Novel features of the technique include the use of improved macroparticle filters; the implementation of several plasma sources for multi-element surface modification; tuning of ion energy during implantation and deposition to tailor the substrate-film intermixed layer and structure of the growing film; simultaneous pulsing of the plasma potential (positive) and substrate bias (negative) with a modified Marx generator; and the use of high ion charge states.

Corrosion and protection characteristics of zinc and manganese phosphate coatings

Abstract: The corrosion and protection characteristics of zinc and manganese phosphate coatings in aqueous solutions are investigated by means of physical methods and electrochemical measurements. The results show that the insulation property of zinc phosphate coating is better than that of manganese phosphate, but the porosity of the former is inferior to that of the latter. The anodic current of coated samples decreases and polarization resistance increases compared to the substrate. The corrosion of phosphated steel exhibits the characteristics of no diffusion in acidic solution, a finite-length diffusion in neutral medium, and a semi-infinite diffusion in alkahne solution. Chemical dissolution is the primary form in the failure of phosphate coatings, which is induced by the electrochemical corrosion of the substrate. The protection ability of phosphate coatings mainly depends on their barrier performance.

Microstructure and oxidation-resistance of Ti1 − x − y −zAlxCryYzN layers grown by combined steered-arc/unbalanced-magnetron-sputter deposition

Abstract: Cation-substituted Ti 1 − x − y −z Al x Cr y Y z N alloys, with y = 0.03 and z = 0.02, have been shown to offer greatly enhanced high-temperature oxidation resistance compared to presently used TiN and Ti 1 − x Al x N films. Layers (3 μm thickness) were deposited by unbalanced magnetron sputter deposition onto austenitic stainless steel and M2 high-speed steel substrates which had been ion etched in situ using a steered Cr-metal-ion cathudic arc discharge at an Ar pressure of 6 × 10 −4 mbar (0.45 mTorr). The metal ion-etching promoted initial local epitaxy on individual substrate grains while the overall film texture evolved through competitive growth to (111) in Ti 0.44 Al 0.53 Cr 0.03 N alloys and (200) in Ti 0.43 Al 0.52 Cr 0.03 Y 0.02 N. Although Ti 0.44 Al 0.53 Cr 0.03 N layers exhibited a columnar microstructure similar to that previously observed in Ti 1 − x Al x N alloys, the addition of 2 mol% YN resulted in significant grain refinement giving rise to a more equiaxed structure. The Knoop microhardness of Ti 0.43 Al 0.52 Cr 0.03 Y 0.02 N alloys was HK 0.025 = 2700 kg mm −2 compared to 2400 kg mm −2 for Ti 0.44 Al 0.53 Cr 0.03 N. The onset of rapid oxidation, as determined from thermo-gravimetric measurements, ranged from ≈ 600 °C for TiN to 870 °C for Ti 0.46 Al 0.54 N to 920 °C for Ti 0.44 Al 0.53 Cr 0.03 N to 950 °C for Ti 0.43 Al 0.52 Cr 0.03 Y 0.02 N.

Microstructural evolution in pulse plated nickel electrodeposits

Abstract: Square-wave cathodic current modulation was used to electrodeposit ultra-fine-grained nickel from an additive-free Watts bath. The influence of pulse parameters, namely, pulse on-time, off-time and peak current density on the grain size, surface morphology and crystal orientation was determined. The study showed that an increase in peak current density resulted in considerable refinement in crystal size of the deposit. The crystal orientation progressively changed from an almost random distribution at the lowest peak current density of 400 mA cm −2 to a strong (200) texture at a peak current density of 1600 mA cm −2 . At constant peak current density and off-time, the crystal size of the deposit was found initially to decrease with pulse on-time before it started to increase with further increase in on-time. The crystal orientation progressively changed from an almost random distribution at the shortest on-time of 1 ms to a strong (200) fibre texture at an on-time of 8 ms. An increase in the pulse off-time at constant on-time and peak current density resulted in a progressive increase in crystal size. However, the crystal orientation remained unaffected with increasing off-time.

Influence of environmental parameters on the frictional behavior of DLC coatings

Abstract: It was shown in our previous studies that diamond like carbon (DLC) films possess low friction coefficient (ƒ) and excellent wear resistance. The reduction in ƒ was found to be consistent with a ‘wear-induced graphitization’ mechanism of the DLC structure proposed recently by Liu and Meletis (J. Mater. Sci., 32 (1997) 3491). A recent study showed that operational parameters (sliding velocity and loading level) influence the tribological behavior of DLC film through control of the kinetics of the graphitization process. The objective of the present study was to investigate the influence of environmental parameters (humidity and temperature) on the tribological behavior of DLC film and test the wear-induced graphitization mechanism. Ion-beam deposition was utilized to deposit DLC on a SiC substrate. Pin-on-disk experiments were conducted by varying humidity (0%, 40% and 100%) and temperature (−10 °C and 25 °C). As-deposited DLC and wear debris was characterized by transmission electron microscopy. It was found that lower humidity increases the graphitization rate more than likely due to the reduction in the effect by the water molecules. A decreased graphitization rate was observed at lower temperature and higher humidity, and can be attributed to suppression of temperature rise at ‘hot spots’. The present findings are consistent and further support the wear-induced graphitization mechanism.

Phase transition of pseudobinary Cr–Al–N films deposited by magnetron sputtering method

Abstract: Phase transition of pseudobinary Cr 1− x Al x N was investigated by synthesizing Cr–Al–N films using a reactive magnetron sputtering method. It was found that the crystal structure of the pseudobinary Cr–Al–N films changes from B1 (NaCl) type to B4 (wurtzite) type at the AlN content between 67 mol% and 75 mol%. The critical composition for the transition from B1 to B4 shows good agreement with the composition (77 mol% AlN) predicted by the two band parameters. The crytallinities of the Cr–Al–N films with B1 type structure became higher with increasing content of CrN and the lowest crystallinity was observed in the B4 type Cr–Al–N films with the AlN content around 75 mol%, which is very close to the critical composition for B1/B4 phase transition.

Influence of substrate roughness and coating thickness on adhesion, friction and wear of TiN films

Abstract: We have studied the effect of substrate surface roughness and coating thickness on the adhesion and tribological behaviour of TiN deposited by reactive ion plating on steel substrates. Three coating thicknesses (1.5, 3 and 5 μm) and three substrate surface finishes ( R a = 0.02, 0.15 and 0.35 μm) were tested. Scratch tests show that coatings on substrates with a poor surface finish show worse adhesion than on those with a smooth surface. Sliding friction tests were conducted with a pin-on-disc tribometer. The pin was a ball of 100C6 steel or alumina. The results show that adhesion takes place at the TiN coating/steel interface followed by metal transfer onto the ceramic. Wear of the steel increases with increasing TiN coating thickness and substrate surface roughness. Adhesion also occurs when TiN is in sliding contact against alumina. The latter did not suffer any wear while the TiN coating suffered adhesive wear. Large TiN transfer was detected on alumina. The results show that, for a given coating thickness, the wear of the coating is as important as the roughness of the substrate is high. In addition, the coating thickness of 3 μm shows better resistance to wear compared to the two other thicknesses.

Characterization of sputter-deposited chromium nitride thin films for hard coatings

Abstract: CrN and Cr 2 N thin films were deposited on silicon, quartz, HSS-steel and carbon substrates by rf reactive magnetron sputtering. The phase and texture were determined by X-ray diffraction analysis. The chemical composition was measured by electron probe microanalysis. Atomic force microscopy revealed a finely grained morphology. The nitrogen content in the sputtering gas influences the film composition and morphology. At N 2 partial pressure below 20% (0.08 Pa) of the total pressure (0.67 Pa) the hexagonal Cr 2 N phase is present, while above 40%, the cubic CrN phase only is observed. Thin films grown at high substrate temperatures (T s ≥400 K) exhibit larger grain sizes of up to 20 nm. The real and imaginary parts of the dielectric function were determined by spectroscopic ellipsometry in the photon energy range of 1.5 to 5.0 eV. The core levels and the valence band were analyzed using X-ray photoelectron spectroscopy. The degree of ionicity of the Cr-N bonding increases continuously with the N 2 partial pressure promoting the CrN phase. Hardness values of 2950 HV for Cr 2 N films and 1800 HV for CrN films were obtained by microindentation,

Conventional and new approaches towards the design of novel superhard materials

Abstract: We present recent results on the preparation of stoichiometric C 3 N 4 and its hardness which is far below the theoretically expected value. A comparison with the turbostratic substoichiometric CN 0.2–0.35 films prepared by Sundgren et al. shows the dominant importance of the microstructure. Based on some general rules a concept for the design of thermodynamically stable superhard nanocrystalline composite materials is presented and verified experimentally on three systems: nc-TiN/a-Si 3 N 4 , nc-VN/a-Si 3 N 4 and nc-W 2 N/a-Si 3 N 4 . Hardness of about 5000 kg mm −2 (about 50 GPa) or more and a high elastic modulus of 550 GPa were found in all these systems.

Pulsed laser deposition of diamond-like carbon wear protective coatings : a review

Abstract: Pulsed laser deposition (PLD) is an emerging technology, which has recently produced diamond-like coatings (DLC) for protection against sliding wear. In this review, the characteristics of PLD that govern the growth of wear resistant DLC coatings are identified, including laser pulse energy density and wavelength, target material and substrate temperature. Attention is given to the mechanical, tribological and wear properties of hydrogen-free DLC and hydrogenated H:DLC coatings produced by laser ablation of graphite and polycarbonate targets, respectively. Mechanisms of friction and wear of these coatings are discussed with emphasis on the formation of an sp2-rich transfer film inside wear tracks. The DLC coatings have hardnesses of up to 70 GPa, friction coefficients about 0.1 and wear rates several orders of magnitude lower than ceramic coatings. The incorporation of DLC into advanced coating architectures to improve wear protection at high contact loads is discussed, including composite DLC/H:DLC coatings, functionally gradient Ti-TiC-DLC coatings, and multilayer Ti-DLC nano-composites for wear protection at high contact loads. These advanced coatings have increased toughness and prevent DLC cracking and delamination under contact pressures above 1 GPa. The potential of PLD DLC in wear protection applications is highlighted in the conclusion.

Clean diffusion coatings by chemical vapor deposition

Abstract: An experimental program was undertaken to identify diffusion coating impurities introduced by standard aluminizing processes and to evaluate the impact of those impurities on oxidation resistance of the resultant Pt aluminide coating. IN-738 tabs and foils were platinum-electroplated, and then aluminized using three different processes: high-activity pack cementation, high-activity CVD and low-activity CVD. The results suggest that aluminizing processes which involve aluminum bearing alloys in the coating retort with H 2 or H 2 /HCl gas at high temperature can contaminate the diffusion coating during deposition. CVD low-activity aluminizing (coating gas generated at low temperature outside the coating chamber from 99.999% Al) did not introduce any coating impurities. In addition, the data indicates that harmful impurities from the IN-738 substrate (sulfur, boron and tungsten) and the electroplating process (phosphorus) were removed from the coating during deposition. The CVD low-activity Pt aluminide coating was the ‘cleanest’ in the study, and it exhibited the best high-temperature oxidation resistance of the coatings considered. It can be concluded that trace elements in diffusion coatings from the superalloy substrate and/or the aluminizing process can adversely effect the oxidation resistance of those coatings, and that CVD low-activity aluminizing yields cleaner coatings than other commercially available aluminizing techniques.

Polymer surface modification by plasma source ion implantation

Abstract: The plasma source ion implantation technique has been used to improve the wetting property of polymer surfaces. The modified polymer surfaces were evaluated with a contact angle meter to note the change of water contact angles and their variations with time. The oxygen-implanted samples showed extremely low water contact angles of 3° compared with 79° of unimplanted ones. Furthermore, the modified surfaces were relatively stable with respect to aging under ambient conditions. Time-of-flight secondary-ion mass spectrometry(TOF-SIMS) and scanning auger electron spectroscopy were used to analyze the implanted surfaces. From TOF-SIMS analysis it was found that oxygen-containing functional groups had been formed on the implanted surfaces. On the other hand, the CF 4 -implanted samples turned out to be more hydrophobic than unimplanted ones, giving water contact angles exceeding 100°. The experiments showed that plasma source ion implantation is a very promising technique for polymer surface modification, especially for large area treatment.

The tribological properties of MoS2/metal composite coatings deposited by closed field magnetron sputtering

Abstract: MoS2 coatings deposited by closed field magnetron sputtering are dense and adherent and have certain superior tribological properties compared to coatings deposited by other techniques. The properties can be further improved by the co-deposition of small amounts of metal with the MoS2. The results of scratch adhesion, pin-on-disc and reciprocating wear tests are reported and compared to those from earlier coatings. A number of practical applications are given and, in particular, large improvements in the performance of cutting tools are reported.

Characteristics of the liquid flame spray process

Abstract: Liquid flame spraying (LFS) is a new thermal spray process. Liquid feedstock is injected and atomized in an oxygen-hydrogen flame where the liquid phase is evaporated and thermochemical reactions are completed to produce fine particles. Production of nanoparticles requires a thorough understanding of the process. Therefore, various process stages were studied; i.e., the atomization of liquid feedstock, and characterization of the flame and flame-droplet interactions. Experimental techniques included laser diffraction anemometry for droplet size distribution, laser doppler velocimetry for particle velocity, pulsed laser Rayleigh back scattering for flame temperature and Schlieren photography for flame structure. Atomization is optimized with an organic solvent, such as isopropanol, nebulized with hydrogen gas at a high flow rate. Liquid droplets injected into the flame are subjected to a maximum temperature of 2600°C and are accelerated to about 160 m s−1. The flame length can be controlled by flame velocity and the solvent type. Water produces a shorter flame whereas ispropanol extends the flame. Injection of the aerosol produces a “pencil-like” region which does not experience turbulence for most of the flame length. Experimentation with manganese nitrate and aluminium isopropoxide or aluminium nitrate showed conversion to a

Surface analysis of chemically-etched and plasma-treated polyetheretherketone (PEEK) for biomedical applications

Abstract: Surface modifications of polyetheretherketone (PEEK) made by chemical etching or oxygen plasma treatment were examined in this study. Chemical etching caused surface topography to become irregular with higher roughness values R a and R q . Oxygen plasma treatment also affected surface topography, unveiling the spherulitic structure of PEEK. R a , R q and surface area significantly increased after plasma treatment; topographical modifications were, nonetheless, moderate. Wetting angle measurements and surface energy calculations revealed an increase of wettability and surface polarity due to both treatments. XPS measurements showed an increase of surface oxygen concentration after both treatments. An O:C ratio of 3.10 for the plasma-treated PEEK surface and 4.41 for the chemically-etched surface were determined. The results indicate that surface activation by oxygen plasma treatment for subsequent coating processes in supersaturated physiological solutions to manufacture PEEK for biomedical appiications is preferable over the chemical etching treatment.

Degradation of the platinum aluminide coating on CMSX4 at 1100 °C

Abstract: The interdiffusion behaviour of a Pt-aluminide coating on CMSX4 was investigated in air at 1100 °C for up to 600 h. During exposure, platinum and aluminium in the coating diffused inward into the CMSX4 substrate while nickel in the substrate of CMSX4 diffused outward into the coating. For the Pt-aluminide coating, the increase of Ni and decrease of Al resulted in a phase transformation from β -(Pt,Ni)Al to γ′ (Ni 3 Al) and γ (Ni,Pt), Pt diffusion into the CMSX4 substrate caused the formation of a Re, W, Cr and Mo enriched TCP phase in the γ′ matrix at the interdiffusion zone,

Plasma-enhanced chemical-vapour-deposition of thin films by corona discharge at atmospheric pressure

Abstract: A corona discharge (also called dielectric barrier discharge or silent discharge) near or at atmospheric pressure was used for the deposition of organic and inorganic thin films at low temperatures. Inorganic SiOx thin films were deposited with tetramethylsilane (TMS, Si[CH3]4) or tetraethylortosilicate (TEOS, Si[OC2H5]4) in oxygen-containing atmospheres. In inert argon/nitrogen atmospheres, TMS formed amorphous plasmapolymerlike hydrogenated silicon carbon coatings (a-SiC:H). Hydrocarbons like methane (CH4), ethine (C2H2) or propargyl alcohol (HC2CH2OH) as monomers lead to polymer-like amorphous hydrogenated carbon coatings (a-C:H). With tetrafluoroethene (C2F4) teflon-like carbon coatings (a-C:F) were deposited. Surface energies between 16 and 66 mN m−1 on silicon and between 16 and 62 mN m−1 on polypropylene were obtained depending on the film composition.

Corrosion resistance and microstructure of electrodeposited Zn and Zn alloy coatings

Abstract: The nature of electrodeposited zinc coating corrosion inhibition by alloying with Fe group metals is not fully understood, because it depends on several factors including the microstructure. The crystallographic texture and lattice cell parameters were determined for nonchromated Zn, Zn-Co, Zn-Fe and Zn-Ni coatings, deposited from alkaline baths, and the results have been used to explain the observed differences in their corrosion behaviour in aerated chloride solutions and in neutral salt spray tests. The presence of Ni or Co in the zinc matrix increases the Zn coating corrosion resistance, while Fe has no effect. It has been suggested that the lower Zn-Ni alloy corrosion rate is due to the predominant presence in this layer of crystallographic planes with a higher packing density. The lower Zn-Co alloy corrosion rate compared with that of Zn and Zn-Fe has been associated with the lower values of its lattice cell parameter c/a (axial ratio).

The evolution of oxidation stresses in zirconia thermal barrier coated superalloy leading to spalling failure

Abstract: The evolution of the stresses in the aluminum oxide formed beneath a zirconia thermal barrier coating during high-temperature oxidation has been measured from the piezospectroscopic shift in the R-line photoluminescence from Cr 3+ impurities incorporated into the growing aluminum oxide scale. The early stages of oxidation are associated with concurrent phase transformations in the aluminum oxide leading to the stable alpha-alumina phase. On the basis of microstructural observations and the broadening of the luminescence lines, it is suggested that spalling failure occurs as a result of linking together of localized decohesion of the oxide/bond-coat interface, a process accelerated by moisture enhanced sub-critical crack growth at the interface.

Thermal stability and oxidation resistance of TiAlN/CrN multilayer coatings

Abstract: TiAlN/CrN multilayer films with superlattice characteristics were deposited onto M2 high-speed steel and 304 stainless steel by reactive unbalanced magnetron sputtering involving three TiAl targets and one Cr target The wavelength of the multilayer structures (ranging from 24 nm to 48 nm) and Cr content (from 10% to 30%) was controlled by varying the power supplied to the Cr target (P Cr ) from 2 kW to 12 kW These coatings were then heated in an ambient atmosphere at temperatures ranging from 500 to 1000 °C and for times up to 16 h Breakdown of the multilayer structure was studied using such techniques as hardness measurements, X-ray diffraction (XRD) and cross-sectional TEM (XTEM) The results show that both the multilayer structure and hardness can be maintained for as long as 16 h at 700 °C This was found to be independent of the Cr content (multilayer wavelength) of the coatings Oxidation behaviour involving isochronal thermogravimetric analysis (TGA), XRD and SEM revealed that all coatings exhibited weight gains of as little as 5% of that of TiN under similar conditions at 1000 °C The resistance to oxidation was found to be dependent on the Cr content, with the greatest effect occurring in the P Cr = 12 kW samples Two very distinct regimes of oxidation were observed Up to approximately 900 °C, the rate of oxidation was very low (approximately 02 gm 2 in the case of the P Cr = 4 kW samples and 01 gm −2 in the case of the P Cr = 12 kW samples) Above this temperature, the oxidation rates increased markedly for all samples, with that of the P Cr = 12 kW being the least severe

The oxidation behaviour of HVOF thermal-sprayed MCrAlY coatings

Abstract: A new high velocity oxygen fuel (HVOF) spraying process to produce MCrAlY coatings was developed and optimized. The HVOF sprayed MCrAlY coatings were isothermally oxidized at 950 °C and 1050 °C in air as well as in different oxidizing atmospheres (synthetic air, He-10% O2 and He-10% synthetic air). The oxidation behaviour of HVOF-sprayed coatings is compared with that of VPS coatings. Under the chosen oxidation conditions, which assure a high oxygen partial pressure, the oxidation kinetics of the two coatings are very different, i.e. the oxidation rate of the HVOF sprayed coating is considerably lower than that of the VPS coating. In the present paper, this observation is explained by the presence of finely divided α-Al2O3 particles in the HVOF-sprayed coating, which are formed during spraying. The Al2O3 probably hinders the grain boundary diffusion of the elements. As a consequence, the oxide scale growth is very low. This effect is more evident at high temperature. The as-sprayed coating as well as the oxidized coatings were examined by optical microscopy, X-ray diffraction, scanning electron microscopy and transmission electron microscopy to study the appearance and the composition of the oxide scales and the phase transformations in the MCrAlY coating.

Use of low-energy, high-current electron beams for surface treatment of materials

Abstract: This article describes the characteristics of original sources of low-energy (10–45 keV), high-current (up to 50 kA) electron beams of microsecond duration, designed for the surface thermal treatment of materials. Under the action of this type of beam, graded structures are formed which may impart improved physicochemicai properties and strength to the surface layers. This permits the use of these beams for improving the strength and electrochemical properties of pieces and tools, and for increasing the electric strength of vacuum insulation. Some technological operations, such as the deposition and removal of coatings and surface alloying, can be realized in the intense evaporation mode.

Enhanced corrosion resistance of duplex coatings

Abstract: A series of electrochemical tests have been carried out to investigate the corrosion behaviour of physically vapour deposited TiN, CrN and (TiAl)N coatings on plasma nitrided En40B steel. Surface and subsurface characterisation before and after corrosion testing were performed using scanning electron microscopy (SEM) and energy-dispersive X-ray analysis (EDX). The experimental results indicate that all three duplex coating systems possess superior corrosion resistance over the individually plasma nitrided or PVD coated En40B steel, highlighting the importance of the iron nitride subsurface in determining the corrosion resistance of duplex coating systems. It is also demonstrated that among these three duplex coating systems, the corrosion resistance increases in the order of TiN/PN, CrN/PN and (TiAl)N/PN. The critical potentials corresponding to the onset of transpassive behaviour for both the CrN/PN and the (TiAl)N/PN duplex coating systems are above the practical potential range (

Adherent diamond-like carbon coatings on metals via plasma source ion implantation

Abstract: Various techniques are currently used to produce diamond-like carbon (DLC) coatings on various materials. Many of these techniques use metallic interlayers, such as Ti or Si, to improve the adhesion of a DLC coating to a ferrous substrate. An alternative processing route would be to use plasma source ion implantation (PSII) to create a carbon composition gradient in the surface of the ferrous material to serve as the interface for a DLC coating. The need for interlayer deposition is eliminated by using a such a graded interface. A PSII approach has been used to form adherent DLC coatings on magnesium, aluminum, silicon, titanium, chromium, brass, nickel and tungsten. A PSII process tailored to create a graded interface allows deposition of adherent DLC coatings even on metals that exhibit a positive heat of formation with carbon, such as magnesium, iron, brass and nickel.

Cathodic arc sources and macroparticle filtering

Abstract: Cathodic arc sources of metallic plasma are used widely in surface modification technologies: deposition of the different functional coatings, ion implantation and combinations of these processes. Possibilities for the extraction of the high ionized plasma flow and high ion current of practically all electroconducting materials as well as the design simplicity and the reliability of this technique allow the use of the cathodic arc sources (with macroparticle filtering or without it) in machine-building, electronic, automobile, aircraft and other branches of industry. A review report on more than 25 years of the development history of cathodic arc sources and macroparticle filtering (for separation of the plasma flow from the neutral atoms and macroparticles) is presented. Arc sources with the plane and the cylindrical evaporation surfaces, with the magnetic control and without it are considered. Different designs of the cathodic arc sources as well as their advantages and disadvantages are analyzed. The most effective and simple technique for separation and focusing of plasma flow are the devices where the control of plasma flow (created by arc sources) is carried out by means of plasma optical methods. Using plasma optical principles it is possible to control the electric field structure and plasma motion changing magnetic field configuration. The different designs of the magnetic separators, the focusing and the scanning systems are considered. The advantages and disadvantages of these plasma optical systems and their possibilities are described.

Magnetron-sputtered superhard materials

Abstract: Superhard materials such as nanocrystalline cubic boron nitride (c-BN) and β -silicon carbide ( β -SiC) as well as amorphous boron carbide (B 4 C) and highly tetrahedral amorphous carbon (ta-C) are produced by radio frequency (RF) unbalanced magnetron sputtering in combination with intense ion plating in a pure argon discharge. As a result of energy and mass analysis the film-forming fluxes Φ n consist of sputtered atomic target components and the plating flux Φ Ar + of argon ions. Subplantation, ion-plating-induced increase of surface mobility and substrate-temperature-induced crystallisation are the three main parameters affecting the formation of superhard phases with strong covalent bonding. Knock-on subplantation allows the formation of B 4 C with hardness up to 72 GPa at a flux ratio Φ Ar + / Φ n of 3 for a plating energy of 75 eV. Also c-BN and ta-C can be produced with similar parameters. In the case of SiC, densification is diminished by preferential sputtering of Si and consequently stochiometry and hardness are adversely affected. However, intense ion plating with a low ion energy of 25 eV and small film-forming fluxes shift the temperature of the phase transition from amorphous to nanocrystalline β -SiC from the usual value of >900 °C to about 420 °C. Furthermore, investigations of the formation of superhard materials in the ternary system boron–carbon–nitrogen are reported.