Showing papers in "Surface & Coatings Technology in 2009"

Effect of nanoparticles on the anticorrosion and mechanical properties of epoxy coating

Abstract: Homogeneous epoxy coatings containing nanoparticles of SiO 2 , Zn, Fe 2 O 3 and halloysite clay were successfully synthesized on steel substrates by room-temperature curing of a fully mixed epoxy slurry diluted by acetone. The surface morphology and mechanical properties of these coatings were characterized by scanning electron microscopy and atomic force microscopy, respectively. The effect of incorporating various nanoparticles on the corrosion resistance of epoxy-coated steel was investigated by potentiodynamic polarization and electrochemical impedance spectroscopy. The electrochemical monitoring of the coated steel over 28 days of immersion in both 0.3 wt.% and 3 wt.% NaCl solutions suggested the beneficial role of nanoparticles in significantly improving the corrosion resistance of the coated steel, with the Fe 2 O 3 and halloysite clay nanoparticles being the best. The SiO 2 nanoparticles were found to significantly improve the microstructure of the coating matrix and thus enhanced both the anticorrosive performance and Young's modulus of the epoxy coating. In addition to enhancing the coating barrier performance, at least another mechanism was at work to account for the role of the nanoparticles in improving the anticorrosive performance of these epoxy coatings.

Suspension and solution thermal spray coatings

Abstract: The emerging methods of coating deposition by suspension and solution thermal spraying are described. The liquid suspensions of fine powders and liquid precursors are injected into flames and/or jets generated in the torches. The formulation and stability of suspensions as well as the methods of fine powders synthesis are briefly described. Typical solutions, being often the liquid organo–metallics are also briefly described. An important problem of injection of liquids into jets and flames is then presented. Two principal modes of injection, used at present, are outlined, i.e.: (i) atomization; and, (ii) injection of a continuous jet. Subsequently, the phenomena occurring in flames and plasma jets are discussed and the major differences to these occurring during conventional spraying are stressed up. The build up of coatings starting from the impact of fine particles on the substrate is described and typical microstructures of suspension and solution sprayed coatings are shown. Some properties of the sprayed coatings, including mechanical, electrical, chemical, and thermophysical ones are collected and presented. Finally, the emerging applications of coatings are shown and the possible future applications are discussed.

Characterisation of discharge events during plasma electrolytic oxidation

Abstract: A study has been made of the electrical characteristics and optical emission spectra exhibited when discharge events take place during plasma electrolytic oxidation processing. Both conventional and small area experimental arrangements have been employed, allowing detailed measurement of durations, and temporal distributions, as well as such characteristics as charge transfer, and power. Individual discharges are of short duration, typically tens to hundreds of microseconds, but there is a strong endency for themto occur in cascades that commonly last between several ms and several tens of ms. The composition, temperature and electron density of the plasma formed during PEO processing are inferred from characteristics of the emission spectra. This confirms that there are two distinct regions of plasma; a lower density peripheral region at ~3500 K, and a higher density core at ~16,000±3500 K. The implications of these results are considered in terms of the interpretation of different types of experimental measurement, and attention is also briefly given to how such behaviour might relate to the mechanisms of growth.

Characterization of AC PEO coatings on magnesium alloys

Abstract: Optical emission spectroscopy, fast video imaging and coating characterization are employed to investigate AC plasma electrolytic oxidation (PEO) of magnesium alloys The findings revealed initiation and gradual increase in the number of discharges after 2–4 ms of each anodic pulse once a critical voltage was reached No discharges were observed during the cathodic half-cycles The lifetimes of discharges were in the range of 005–4 ms A transition in the voltage-time response, accompanied by a change in the acoustic and optical emission characteristics of discharges, was associated with the development of an intermediate coating layer with an average hardness of 270–450 HV 005 The coatings grew at a rate in the range 40–75 µm min − 1 , depending on the substrate composition Regardless of the substrate, the coatings consisted of MgO and Mg 2 SiO 4 , with incorporation of alloying element species Electrolyte species were mainly present in a more porous layer at the coating surface, constituting 20–40% of the coating thickness A thin barrier layer consisting of polycrystalline MgO was located next to the alloy The corrosion rate of the magnesium alloys determined using potentiodynamic polarization in 35 wt% NaCl was reduced by 2–4 orders of magnitude by the PEO treatment

CuO–cotton nanocomposite: Formation, morphology, and antibacterial activity

Abstract: Copper oxide nanoparticles were synthesized and subsequently deposited on the surface of cotton fabrics using ultrasound irradiation. Optimization of the process resulted in a homogeneous distribution of CuO nanocrystals, 15 nm in size, on the fabric surface. The antibacterial activities of the CuO–fabric composite were tested against Escherichia coli (Gram negative) and Staphylococcus aureus (Gram positive) cultures. A significant bactericidal effect, even in a 1% coated fabric (%wt.), was demonstrated.

The use of Al–Al2O3 cold spray coatings to improve the surface properties of magnesium alloys

Abstract: Pure Al and 6061 aluminium alloy based Al2O3 particle-reinforced composite coatings were produced on AZ91E substrates using cold spray. The strength of the coating/substrate interface in tension was found to be stronger than the coating itself The coatings have corrosion resistance similar to that of bulk pure aluminium in both salt spray and electrochemical tests. The wear resistance of the coatings is significantly better than that of the AZ91 Mg substrate, but the significant result is that the wear rate of the coatings is several decades lower than that of various bulk Al alloys tested for comparison. The effect of post-spray heat treatment, the volume fraction of Al2O3 within the coating and of the type of Al powder used in the coatings on the corrosion and wear resistance was also discussed.

A comparative study of titanium nitrides, TiN, TiNbN and TiCN, as coatings for biomedical applications

Abstract: A strategy used to reduce wear of the ultra high molecular weight polyethylene (UHMWPE) component of orthopedic joint implants has been to coat the metallic part with a hard ceramic layer. The advantage of this procedure is to reduce both wear and ion release of the metal while keeping a high mechanical resistance. In the present study, the performance of three titanium nitride coatings: TiN, TiNbN, and TiCN for biomedical applications was assessed in terms of their surface properties and cytotoxicity. The morphology, chemical composition, and wettability were determined through atomic force microscopy (AFM) imaging, X-ray photoelectron spectroscopy (XPS) and contact angle measurement, respectively. The tribological behaviour of the coatings rubbing against UHMWPE in lubricated conditions was investigated using a pin-on-disk apparatus. Albumin adsorption on the three coatings was studied with a quartz crystal microbalance with dissipation (QCM-D) and AFM scratching. Cytotoxicity was determined both in direct or indirect contact of the cells with the coating materials. The results demonstrate that the three coatings have similar surface properties and are not cytotoxic. TiNbN seems to have the best tribological performance in the presence of albumin, although albumin adsorption is slightly higher on TiN.

Aluminum composite reinforced with multiwalled carbon nanotubes from plasma spraying of spray dried powders

Abstract: Homogenous dispersion of carbon nanotubes (CNTs) in micron sized aluminum silicon alloy powders was achieved by spray drying. Excellent flowability of the powders allowed fabrication of thick composite coatings and hollow cylinders (5 mm thick) containing 5 wt.% and 10 wt.% CNT by plasma spraying. Two phase microstructure with matrix having good distribution of CNT and CNT rich clusters was observed. Microstructural evolution has been explained using single splat and the infiltration of CNT clusters by liquid metal. Partial CNT surface damage was observed in case of the 10 wt.% CNT coating due to CNT mesh formation and smaller size of spray dried agglomerate. Increase in the elastic modulus and improvement in the yield strength and elastic recovery properties due to CNT addition was observed by nanoindentation.

Formation and corrosion behavior of Fe-based amorphous metallic coatings by HVOF thermal spraying

Abstract: coatings with a composition of Fe(48)Cr(15)Mo(14)C(15)B(6)Y(2) were prepared by means of high velocity oxygen fuel (HVOF) thermal spraying under different conditions. Microstructural studies show that the coatings present dense layered structure and low porosity with a fraction of nanocrystals precipitated. The porosity and fraction of the coatings decrease as the kerosene and oxygen flow increase within the parameter range examined. Corrosion behavior of the amorphous coatings was investigated by electrochemical measurement. The results show that the coatings are spontaneously passivated with wide passive region and low passive current density in 3.5% NaCl. 1 N HCl and 1 N H(2)SO(4) solutions. and exhibit an excellent ability to resist localized corrosion. However, the corrosion resistance of the coatings decreases in 1 N NaOH solution with lower transpassive potential and passive region. In addition, the optimal spraying parameter improves the corrosion resistance of the amorphous coatings obviously due to the proper proportion of porosity and amorphous fraction. (C) 2009 Elsevier B.V. All rights reserved.

Tribological investigation of adaptive Mo2N/MoS2/Ag coatings with high sulfur content

Abstract: Adaptive nanocomposite Mo2N/MoS2/Ag coatings were deposited on Inconel and silicon substrates by magnetron sputtering with individual targets of Mo, MoS2 and Ag. The tetragonal β-Mo2N structure in addition to Ag and MoS2 phases were detected using X-ray diffraction. The elemental composition of the coatings was investigated using Auger electron spectroscopy. The tribological properties of the coatings were studied at room temperature (RT), 350, and 600 °C against Si3N4 balls. The lowest friction coefficients that were obtained were 0.4, 0.3, and 0.1 at RT, 350 °C, and 600 °C, respectively. The average friction coefficient was maintained at 0.1 for more than 300,000 cycles at 600 °C due to the formation of lubricious silver molybdate phases at the contact surfaces. Three types of silver molybdate phases were detected by both X-ray diffraction and micro-Raman spectroscopy in the wear tracks, namely, Ag2Mo4O13, Ag2Mo2O7 and Ag2MoO4 depending on the Mo and Ag contents in the coatings. The superior performance of all three compounds is due to their layered structure with weaker Ag–O bridging bonds. These relatively weak bonds may shear or even break easily at high temperatures to account for the observed friction reduction.

Photocatalyst of TiO2/ZnO nano composite film: Preparation, characterization, and photodegradation activity of methyl orange

Abstract: The TiO 2 /ZnO nano composite film with atomic ratios of Ti/(Ti + Zn) of 100%, 75%, 50%, 25%, and 0% was successfully prepared via sol–gel process from directly mixing TiO 2 /ZnO sol followed by heat treatment at 500 °C for 2 h in air. The SEM observation and the XRD measurement revealed that the microstructural morphology and the crystallization behavior of the composite film were essentially related to the atomic ratio of Ti/(Ti + Zn). The UV irradiated degradation of MO solution using the composite film as catalyst showed a linear tendency of the photocatalytic activity of the film against the value of Ti/(Ti + Zn). An exception to photocatalytic activity was observed for the film with Ti/(Ti + Zn) of 75%, which has been attributed to the poor crystallization of the film. Heat treatment with 5 h was applied to the film and better crystallization was achieved for the film. Consequently, a substantial improvement of the photocatalytic activity for the film was finally achieved.

Design and performance of AlTiN and TiAlCrN PVD coatings for machining of hard to cut materials

Abstract: Machining of hard to cut materials such as hardened steels and high temperature strong aerospace materials is a challenge of modern manufacturing. Two categories of the aluminum-rich TiAlN-based Physical Vapor Deposited (PVD) coatings, namely AlTiN and TiAlCrN, are commonly used for this area of application. A comparative investigation of the structural characteristics, various micro-mechanical properties, oxidation resistance and service properties of the both coatings has been performed. Crystal structure has been studied using High Resolution Transmission Electron Microscopy (HR TEM). Electronic structure has been investigated using X-ray Photoelectron Spectroscopy (XPS). Micro-mechanical properties (microhardness, plasticity index, impact fatigue fracture resistance) have been evaluated using a Micro Materials Nano-Test System. Short-term oxidation resistance has been studied at 900 °C in air. The tool life of the coating was studied during ball nose end milling of hardened H 13 tool steel as well as end milling of aerospace alloys such as Ni-based superalloy (Waspalloy) and Ti alloy (TiAl6V4). It was shown that the set of characteristics that control wear performance strongly depend on specific applications. For machining of hardened tool steels, when heavy loads/high temperatures control wear behavior, the coating has to possess a well-known combination of high hot hardness and improved oxidation resistance at elevated temperatures. To achieve these properties, crystal structure for TiAlN-based coatings should be mainly B1, and elemental composition of the coating should ensure formation of strong inter-atomic bonds such as Al–Cr metal-covalent bonds in the TiAlCrN coating. Nano-crystalline structure with grain size of around 10–30 nm enhances necessary properties of the coating. In contrast, for machining of aerospace alloys, when elevated load/temperature combined with intensive adhesive interaction with workpiece material results in unstable attrition wear with deep surface damage, the coating should possess a different set of characteristics. Crystal structure for TiAlN-based coatings is basically B1; but due to a high amount of aluminum, the AlTiN coating contains AlN domains. The coating has a very fine-grained nano-crystalline structure (grains sized around 5 nm). Electron structure of energy levels indicates formation of metallic bonds. This results in plasticity increase at the cost of hot hardness reduction. The surface is able to dissipate energy by means of plastic deformation (instead of crack formation) and in this way, surface damage is reduced.

Effects of nitrogen content on structure and mechanical properties of multi-element (AlCrNbSiTiV)N coating

Abstract: AlCrNbSiTiV metallic and nitride films were deposited by reactive radio-frequency unbalanced magnetron sputtering. The composition, microstructure and mechanical properties of the coatings deposited at different nitrogen flow rates were evaluated. The deposited AlCrNbSiTiV metallic film has an amorphous structure. The nitride films, regardless of the nitrogen flow ratio, were found to have only an FCC structure register on the XRD profiles. A Stoichiometric nitride ratio, i.e. (Al,Cr,Nb,Si,Ti,V) 50 N 50 is attained for a nitrogen flow ratio ( R N ) of 10% and higher. At the lowest nitrogen flow ratio there is a preferred (200) orientation; however the films become less textured at higher nitrogen flow ratios. Nano-grained structures are obtained for all flow ratios, with grain sizes ranging from 8.7 to 12.3 nm. At the highest nitrogen flow rates the coatings have a compressive stress of around 4.5 GPa. The (Al,Cr,Nb,Si,Ti,V) 50 N 50 nitride coatings have both a high hardness and elastic modulus of 41 and 360 GPa, respectively. The maximum H / E ratio occurs at a nitrogen flow ratio of 20%.

Influence of curing temperature, silica nanoparticles- and cerium on surface morphology and corrosion behaviour of hybrid silane coatings on mild steel

Abstract: This work is aimed at developing and investigating silane based organic–inorganic hybrid coatings possessing unique properties, which can be used to improve the performance of steel structures subjected to marine corrosion. These silane based sol–gel coatings were prepared by dip coating planar samples of mild steel in solution of an organically modified silica sol made from hydrolysis and polycondensation of tetraethylorthosilicate (TEOS) and methyltriethoxysilane (MTES) in acid catalysis condition. Crack-free coatings were obtained on curing at 200 °C. On increasing the curing temperature to 400 °C, however, cracks developed in the plain organic–inorganic hybrid coatings. This observation was consistent with the visual observations where appearance of the coated specimen changed from colourless metallic to brownish grey on curing from 200 °C to 400 °C temperature. The coatings were further modified using SiO 2 nanoparticles and cerium. The effect of change in the – temperature as well as – composition on the microstructural properties of the coatings was determined using optical microscopy, scanning electron microscopy and atom force microscopy. Additionally, Attenuated Total Reflectance–Fourier Transform Infrared Spectroscopy (ATR/FTIR) was carried out to show the formation of the Si–O–Si structural backbone of the hybrid material with the organic CH 3 group incorporated into the silica network. The corrosion protection performance of these coatings was examined using potentiodynamic polarisation technique and electrochemical impedance spectroscopy in aerated 3.5 wt.% NaCl solution. The polarization curves and corrosion resistance as measured by the bode plots suggested that the plain hybrid coatings offer good protection against corrosion. However, the SiO 2 and cerium modified nano hybrid coatings exhibited superior performance to that displayed by plain hybrid coatings.

Fabrication of super-hydrophobic surfaces for enhanced stone protection

Abstract: In the current study, we demonstrate that the modification of a commercial siloxane protective composition by the addition of silica nanoparticles substantially enhances its protective efficiency and renders the treated stone surface super-hydrophobic and self-cleaning. The extent of surface hydrophobization depends on nanoparticle concentration and reaches a maximum value of ~ 160° at 1% w/v of nanoparticles for the case of white Greek marbles (Naxos, Pentelic and Thassos) treated with the modified composition. The investigation of the surface morphology by scanning electron microscopy (SEM) reveals the presence of micron-sized protrusions (10–100 μm in diameter) formed by nanoparticle aggregates consolidated by the siloxane polymer. The diameter and surface density of the protrusions depend on nanoparticle concentration. The developed nanostructure of the protrusions was observed by atomic force microscopy (AFM). The nano-dimensions of the silica particles are essential for the superhydrophobization of the treated marble surfaces. In the case of micron-sized silica particles that were mixed with siloxane and were applied accordingly on similar white Greek marbles, the superhydrophobic effect was not achieved and the observed water contact angles were substantially lower. In the event that hydrophobicity is not the sole parameter of optimal stone and stone-monuments protection, other important parameters, such as water vapor permeability, water capillary absorption and stone color alterations, were also investigated and their dependence on nanoparticle concentration was established.

Growth of intermetallic layer in the aluminide mild steel during hot-dipping

Abstract: Mild steel was coated by hot-dipping in a molten aluminum bath. The growth behavior in the intermetallic layer after various times of immersion in the hot-dip at 700 °C was analyzed by electron backscatter diffraction (EBSD). The results showed that the aluminide layer consisted of an outer aluminum topcoat, minor FeAl 3 and major Fe 2 Al 5 , respectively. From another perspective, Fe 2 Al 5 possessed a tongue-like morphology, which caused the corresponding serration-like morphology of the steel substrate. The Fe-Al/steel substrate interface of the Fe 2 Al 5 phase, after removal of the steel substrate, displayed a columnar structure growing toward the steel substrate, implying that Fe 2 Al 5 grew at a rapid rate along the diffusion direction. Moreover, the EBSD results revealed the Fe 2 Al 5 phase was not only composed of columnar grains, but also possessed fine grains clustered around the peaks of the serration-like steel substrate.

Synthesis and characterization of self-cleaning cotton fabrics modified by TiO2 through a facile approach

Abstract: Self-cleaning fabrics have been successfully prepared by depositing and grafting TiO 2 nanoparticles via an aqueous sol process at low temperature. SEM, HRTEM, ATR-IR and XRD have been adopted as the characterization techniques. Anatase TiO 2 nanoparticles were well developed in size of 3–5 nm. These TiO 2 -coated cotton fabrics possessed distinct self-cleaning properties, such as bactericidal activity and photocatalytic decomposition of dyes. The photocatalytic activity of the treated fabrics was fully maintained upon several numbers of photodegradation cycles. And the prepared TiO 2 -coated cotton fabrics inhibited obviously the growth of bacteria both in the liquid Luria–Bertani Medium (LBM) and on the solid LBM.

Elaboration of Al2O3/PTFE icephobic coatings for protecting aluminum surfaces

Abstract: In order to protect aluminum ground wires and phase conductors of overhead power lines against ice adhesion and excessive accretion, for ensuring safe and reliable power transmission during winter periods, a new coating with icephobic characteristics and satisfactory mechanical properties was developed. The method consisted in depositing an extremely adherent poly(tetrafluoroethylene) or PTFE coating on an Al2O3 underlayer produced by anodisation in either a phosphoric or an oxalic acid electrolyte. PTFE impregnation was carried out at low temperature (320 °C) and coating adhesion was assessed using tape and bend tests. These treatments resulted in highly hydrophobic surfaces with water contact angles lying between 130° and 140°. Ice shear stress was reduced by almost 2.5 times, and the PTFE coatings remained active after several ice shedding events. Morphologies and chemical compositions were studied using scanning electron microscopy, energy dispersive X-Ray analysis, as well as Fourier Transform Infra Red and X-Ray photoelectron spectroscopy.

Progress in the Development of Adaptive Nitride-Based Coatings for High Temperature Tribological Applications

Abstract: Adaptive tribological coatings were recently developed as a new class of smart materials that were designed to adjust their surface chemical composition and structure as a function of changes in the working environment to minimize friction coefficient and wear between contact surfaces. This paper provides an overview of the current research developments in this field, including: (1) Chameleon nanocomposite coatings which are produced by depositing a multi-phase structure whereby some of the phases provide mechanical strength and others are lubricious; (2) Micro- and nano-textured coatings which consist of hard nitride films with highly ordered micropores and nanopores that are subsequently filled with solid lubricants using various techniques such as lithography, reactive ion etching, laser texturing, pulsed air arc treatment, and ceramic beads as placeholders for sputter deposition; and, (3) Carbon and nitride nanotubes that are filled electrochemically with solid lubricants. The frictional and wear properties of the above three classes of newly developed adaptive structures, tested in various controlled environmental conditions (temperature, humidity), will be discussed in detail.

The effect of saccharin addition and bath temperature on the grain size of nanocrystalline nickel coatings

Abstract: Nanocrystalline nickel coating was synthesized by direct current electrodeposition from a Watts bath at the current density of 100 mA/cm 2 and pH = 4. The effect of saccharin addition (0–10 g/l) and bath temperature (45–65 °C) on the average grain size of the deposits was investigated by XRD technique. The results showed that the average grain size decreased from 426 nm to 25 nm as the saccharin concentration increased from 0 to 3 g/l, while further increase in saccharin concentration had no significant effect. Theoretical model also indicated a non-linear function for dependence of grain size on saccharin concentration, which was in accordance with experimental results. The experimental results showed that the increases in the bath temperature had no considerable effect on the average grain size of the deposits. A theoretical formula was also established for the temperature dependence of the grain size.

A study of the antimicrobial and tribological properties of TiN/Ag nanocomposite coatings

Abstract: TiN/Ag coatings with varying silver contents have been deposited by pulsed magnetron sputtering. The films were characterised in terms of structure and composition using scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX) and X-ray diffraction (XRD). The tribological properties of the coatings were assessed by thrust washer wear testing, which showed a marginal reduction in friction coefficient with increasing silver content against a steel counterface. Zones of inhibition were used to determine the extent of silver ion release from the nanocomposite materials, and a NBT (nitro-blue tetrazolium) redox dye was used in an assay to determine the antimicrobial effectiveness of the surfaces following incubation. The microorganisms tested were Pseudomonas aeruginosa and Staphylococcus aureus. Whilst no zones of inhibition were observed on any of the surfaces, for the NBT assays, after incubation, the silver containing coatings revealed a significant reduction in the number of viable cells of both microorganisms, compared to a ‘pure’ TiN surface.

Pilot scale sonochemical coating of nanoparticles onto textiles to produce biocidal fabrics

Abstract: The pilot installation is designed for the scale up of sonochemically assisted coating of textile fabrics with various kinds of nanoparticles. The installation can coat up to 50 m of continuous cotton fabric per run with CuO or ZnO nanoparticles. The structure and morphology of the metal oxides adhering to the fabric on the coated cotton have been characterized by XRD and HR SEM, and shown to be nanocrystalline oxides (~ 10–20 nm in size). The coating is homogeneous, stable and retains its biocidal properties through at least 20 washing cycles. The CuO–cotton bandages demonstrated good antimicrobial properties against E. coli bacteria.

A novel phosphate conversion film on Mg–8.8Li alloy

Abstract: [Song, Yingwei; Shan, Dayong; Chen, Rongshi; Zhang, Fan; Han, En-Hou] Chinese Acad Sci, State Key Lab Corros & Protect, Inst Met Res, Shenyang 110016, Peoples R China.;Song, YW (reprint author), Chinese Acad Sci, State Key Lab Corros & Protect, Inst Met Res, 62 Wencui Rd, Shenyang 110016, Peoples R China;ywsong@imr.ac.cn

Characterization and frictional behavior of nanostructured Ni–W–MoS2 composite coatings

Abstract: Fil: Cardinal, Maria Fernanda. TENARIS Research and Development Centre; Argentina. Consejo Nacional de Investigaciones Cientificas y Tecnicas; Argentina

Corrosion behavior of ZrN/Zr coated biomedical AZ91 magnesium alloy

Abstract: Magnesium alloys are potential materials in biodegradable hard tissue implants. However, their fast degradation rates in a physiological environment constitute the main limitation for their applications. In this work, a ZrN/Zr bilayered coating is deposited on AZ91 magnesium alloy using a filtered cathodic arc deposition system. The ZrN/Zr bilayered structure buffers the serious mismatch between the substrate and ZrN coating thus improving film adhesion. The composition of the coating is evaluated by X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). The electrochemical behavior of the coated alloy is systematically studied by means of potentiodynamic polarization test and electrochemical impedance spectroscopy (EIS). Our results disclose that the corrosion resistance of the coated alloy is significantly improved.

Coating optimisation for high speed machining with advanced nanomechanical test methods

Abstract: Advanced nanomechanical testing has been used to evaluate key factors influencing tool life (1) a plasticity index (PI, the plastic work done/total work done during indentation), at room and elevated temperature (2) hot hardness and (3) fatigue fracture resistance, and determine their relative importance in different cutting applications. The optimum combination of hardness and toughness/plasticity to minimise wear and extend the life of coated WC–Co cutting tools was found to vary with the severity and nature of the cutting conditions. For interrupted cutting the plasticity index is critical, with high values (i.e. not extremely high H/E) resulting in extended tool life. Elevated temperature nanoindentation showed decreasing hardness and increasing PI with temperature. In high-speed turning hot hardness is the dominant factor whilst for interrupted cutting high hot hardness should be combined with improved plasticity for longer tool life. A novel test technique nano-impact, was used to simulate the interrupted contact (and cyclic loading) conditions occurring in milling applications and evaluate the fatigue fracture resistance of coated tools. It was able to successfully rank coatings in terms of tool life in end milling and reproduce the evolution of tool wear in the cutting test. In elevated temperature nano-impact testing the probability and extent of fracture during the test decreased at elevated temperature, consistent with the higher PI. Results from the advanced nanomechanical tests can be used in combination to predict which coatings have longer life in severe cutting conditions.

The laser-assisted cold spray process and deposit characterisation

Abstract: Laser-assisted Cold Spray (LCS) is a new coating and fabrication process which combines the supersonic powder beam found in Cold Spray (CS) with laser heating of the deposition zone. LCS combines some advantages of CS: solid-state deposition, high build rate and the ability to deposit metals onto a range of substrates, with reduced operating costs which arise from not using a gas heater and replacing helium with nitrogen as the process gas. A system has been developed to impact metallic powder particles onto a substrate which is locally heated using a diode laser. A pyrometer and control system are used to record and maintain impact site temperature. In this study,

Ion energy and mass distributions of the plasma during modulated pulse power magnetron sputtering

Abstract: article i nfo Modulated pulse power (MPP) sputtering is a variation of high power pulsed magnetron sputtering (HPPMS) that overcomes the rate loss issue and achieves enhanced plasma ionization through modulation of the pulse shape, intensity, and duration. In this study, the principle and characteristics of MPP/HPPMS technique are first introduced. An electrostatic quadrupole plasma mass spectrometer installed parallel to the target surface has been used to examine the plasma properties, including time averaged ion energy and mass distributions of the positive ions, generated during sputtering a metal Cr target in pure Ar and Ar/N2 atmospheres using MPP and continuous dc power sources in a closed field unbalanced magnetron sputtering system. It was found that the MPP plasma exhibits a low ion energy peak at 1-2 eV and a short ion energy tail with the maximum ion energy affected by the peak current and power utilized on the cathode. A significantly increased numbers of single and double charged Cr and Ar ions were identified in the MPP plasma as compared to the dc plasma in pure Ar. The number of ions (ion flux) increased when the peak target power and current were increased. Besides single and double charged Cr, Ar and N ions, N3 + ,N 4 + , CrN

Predictive modeling and experimental results for residual stresses in laser hardening of AISI 4140 steel by a high power diode laser

Abstract: A predictive model for residual stresses induced in a laser hardened workpiece of AISI 4140 steel with no melting has been developed and experimentally verified. A transient three-dimensional thermal and kinetic model is first solved to obtain the temperature and solid phase history of the workpiece, which is then sequentially coupled to a three-dimensional stress model to predict residual stresses. The phase transformation strains are added to the thermal strains at each time step during the heating and cooling cycles to obtain the resultant residual stresses in the workpiece. The importance of considering phase transformation has been explained through the comparison of the magnitudes of residual stresses with and without the inclusion of phase transformation kinetics. The model predicted strong compressive residual stresses of about 200 MPa in the heat affected zone due to austenite-to-martensite transformation. The predictions matched well with the X-ray diffraction measurements.

Improvement in water and oil absorbency of textile substrate by atmospheric pressure cold plasma treatment

Abstract: Cold plasma, an ionized mixture of gases with bulk temperature near the room temperature, can be safely used for surface modification of textile substrates. Plasma treatment can change surface hydrophilicity of the textile substrates by forming hydrophilic groups or can clean the surfaces by etching out top layers. With an aim to improve water absorbency of the textile substrates, nylon and polyester fabrics were treated continuously in an atmospheric-pressure-glow-discharge-plasma produced in presence of different gases. After plasma treatment, time taken in spreading a water droplet over a pre-defined area was found to decrease significantly. As expected, the chemical changes brought about by plasma, increased the surface energy of both nylon and polyester fabrics. However, the rate of oil absorption (a hydrophobic fluid) was also found to increase to a great extent. Spreading time for mustard oil droplet over a specified area was observed to decrease significantly from 152 s in an untreated fabric to 52 s in He plasma treated fabric for nylon, whereas, it decreased from 28.6 min in untreated fabric to 2.8 min in the treated fabric for PET samples. The effect of plasma treatment on the rate of oil absorbency was further confirmed for cotton fabrics, where the time for oil absorbency decreased from 59.5 s in the untreated sample to 30.4 s in the treated sample. The atomic force microscopy (AFM) analysis of the treated fabrics revealed the formation of nano-sized channels on their surfaces. The samples, after plasma treatment, showed only a marginal drop in their mechanical properties.