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The dry sliding wear behaviour of a high carbon martensitic stainless steel (HCMSS) consisting of ~ 22.5 vol% of chromium (Cr)- and vanadium (V)-rich carbides processed by electron beam melting (EBM) has been captured. The microstructure consisted of martensite and retained austenite phases with a homogeneous distribution of sub-micron-sized V-rich and micron-sized Cr-rich carbides, leading to relatively high hardness. The CoF decreased ~ 14.1% with increasing load in the steady-state, due to the material transferred from the wear track over the counterbody. The wear rate of the HCMSS compared to martensitic tool steel processed in the same manner, and it was nearly identical under low applied load. The dominant wear mechanism was removal of the steel matrix through abrasion, followed by the oxidation of the wear track, while three-body abrasive wear occurred with increasing load. A plastically deformed zone beneath the wear track was revealed through cross-sectional hardness mapping. Specific phenomena occurred with increasingly aggressive wear conditions were described with carbide cracking, pull-out of V-rich carbides and matrix cracking. This study revealed the wear performance of the additively manufactured HCMSS, which could pave the way for producing components for wear-related applications ranging from shafts to plastic injection moulds via EBM. [ABSTRACT FROM AUTHOR]

Adhesive bonding is a key joining technique for aluminium alloy components in the automotive industry. Plasma Electrolytic Oxidation (PEO) is an emerging surface treatment for the protection of metal alloys including those of aluminium. This work set out to assess the adhesive bond strength and behaviour of PEO coated aluminium alloy AA6060-T6. Thin (15 to 25 μm) oxide coatings were produced on AA6060-T6 by Plasma electrolytic Oxidation (PEO) in phosphate and silicate-phosphate electrolytes. The coatings were characterised extensively, then adhesively bonded in lap-shear joints and loaded to failure under tensile mode to evaluate the bond strength of adhesively bonded coated samples. Surface fracture analysis was carried out to determine the failure modes of the lap-shear joints. The failure mechanism and strength of the coated joints was compared to the characteristic features of the coatings, in an attempt to identify governing properties. It was found that PEO coatings could withstand high loading; however, the strength of the bonded joints was governed by the cohesive strength of the oxide layers. All coatings produced in the phosphate and thicker coatings produced in the silicate-phosphate electrolyte ultimately experienced cohesive failure within the oxide region. Thinner silicate-phosphate coatings electrolyte displayed a favourable failure mechanism with fracture occurring within the adhesive, which highlights the possibility of PEO technique to be used for adhesively bonded aluminium alloy parts. • PEO coatings of varying thickness were produced on AA6060-T6 samples in Phosphate and Silicate/Phosphate electrolytes. • PEO coated samples were adhesively bonded with a heat cured epoxy resin and subjected to lap shear testing to failure. • Thinner Si/P coatings produced in 3 mins exhbited superior bond strength. • Thicker Si/P coatings and Coatings produced in a P electrolyte failed cohesively within the oxide coating. • Fracture in thicker 5 min Si/P coatings generally propogated through the dense inner alumina region of the coating. [ABSTRACT FROM AUTHOR]

Plasma electrolytic oxidation (PEO) has attracted significant attention as a promising eco-friendly technology for the deposition of ceramic-like oxide coatings with superior wear- and corrosion resistance as well as biomedical, catalytic, magnetic, dielectric and optical properties. However, the industrial implementation of PEO has been hindered by a poor understanding of the mechanisms underlying plasma-assisted electrochemical coating formation. This study compares the characteristics of PEO processes on different valve metals in a dilute aqueous solution of NaOH and Na 2 SiO 3 under pulsed unipolar and bipolar polarisation conditions. The focus is given to the influence of the nature of the valve metal on the transition to the soft sparking regime characterised by reduced energy consumption whilst yielding sintered coating materials enriched with crystalline phases. In-situ dynamic voltammetry analysis was employed to study the effects of the net current ratio and local negative charge injection using diagnostic pulses embedded in the polarisation signal. It has been demonstrated that soft sparking is a characteristic feature of valve metals such as Mg, Al, Zr and Ta that form insulating surface oxides with negligible electronic conductivity, whereas Ti and Nb form semiconducting oxides, which do not exhibit a characteristic voltage drop, although some features of spark softening were detected. This generalisation paves a way for implementation of a model known as 'digital twin' to the rational design of the PEO processes for deposition of the functional ceramics. [Display omitted] • Unipolar and bipolar plasma electrolytic oxidation compared for six metals. • Reverse polarisation leads to soft sparking on metals forming a dielectric oxide. • Cathodically induced changes promote planar energy dissipation in the active zone. • The soft sparking induction period relates inversely to the oxide isoelectric point. • Electronic conductivity in semiconducting oxides inhibits soft sparking. [ABSTRACT FROM AUTHOR]

The limited choice of metallic alloys suitable for additive manufacturing restricts the possibilities for new design strategies and improved materials performance in demanding applications. We applied plasma electrolytic oxidation to improve the performance of 3D printed and cast AlSi12 alloy substrates. A silicate alkaline electrolyte and a combined current mode were used. Coatings were characterised by XRD and SEM analyses and microhardness tests. Produced coatings feature microhardness level of 300–600 HV 0.2 , which is 3–5 times higher than the original alloy, extending the mechanical properties of 3D printed articles. The features in electrochemical behaviour of Al Si alloys with the same elemental composition, but different microstructural state, are explained by means of individual electrochemical responses of aluminium and silicon phases. • PEO of 3D printed AlSi12 alloy in silicate electrolyte • Unipolar anodic pre-treatment facilitate breakdown initiation • The size of Si grains affects stability during transition to soft sparking • Behaviour of alloy is accounted for electrochemical response of Si and Al phases. [ABSTRACT FROM AUTHOR]

A nanoporous and large surface area (∼800 m2/g) graphene-based material was produced by plasma treatment of natural flake graphite and was subsequently surface decorated with platinum (Pt) nano-sized particles via thermal reduction of a Pt precursor (chloroplatinic acid). The carbon-metal nanocomposite showed a ∼2 wt% loading of well-dispersed Pt nanoparticles (<2 nm) across its porous graphene surface, while neither a significant surface chemistry alteration nor a pore structure degradation was observed due to the Pt decoration procedure. The presence of Pt seems to slightly promote the hydrogen sorption behavior at room temperature with respect to the pure graphene, thus implying the rise of "weak" chemisorption phenomena, including a potential hydrogen "spillover" effect. The findings of this experimental study provide insights for the development of novel graphene-based nanocomposites for hydrogen storage applications at ambient conditions. Image 1 [ABSTRACT FROM AUTHOR]

Lattice inhomogeneities, i.e. nitrogen interstitial-induced hexagonal-close-packed martensite (HCP-ε N) and shear bands, can form in face-centred cubic nitrogen-expanded austenite (FCC-γ N) synthesised on Fe-Cr-Mn and Fe-Cr-Ni austenitic stainless steel (ASS) using triode-plasma nitriding (TPN). Homogenous elemental distribution between HCP-ε N and FCC-γ N supports the displacive shear transformation mechanism proposed for a high-Mn, low stacking fault energy ASS under nitrogen interstitial-induced deformation. While resulting from transformation-induced plasticity, HCP-ε N exhibits similar lattice expansion behaviour to the parent FCC-γ N. However, inhomogeneous elemental distributions in the shear bands formed in γ N layers on a 400°C TPN-treated high-Ni ASS indicate local migration of substitutional elements. Image, graphical abstract [ABSTRACT FROM AUTHOR]

Understanding charge transfer at strongly polarised gas-evolving electrodes is crucial for the development and control of Contact Glow Discharge Electrolysis (CGDE), a method of interest in a wide range of applications spanning from biochemistry to materials engineering. Since the pioneering work of Kellogg in 1950, the transition from conventional electrolysis to the CGDE regime has been generally associated with excessive ohmic heating at the working electrode, disregarding basic principles of electrochemical kinetics. Here we attempt to address this controversy by investigating of a CGDE process at a Fe-13%Cr anode in aqueous solutions of (NH 4) 2 SO 4 using an original method of in-situ impedance spectroscopy combined with voltammetric, gravimetric, chemical analysis and optical emission spectroscopy techniques. The study reveals three characteristic relaxation processes representing charge transfer through the surface oxide-hydroxide layer, the presence of which is confirmed by Glow Discharge Optical Emission and Raman Spectroscopies, and adsorption-desorption behaviour which we identify with oxo- and peroxo-intermediates of the oxygen evolution reaction (OER) coupled with anodic metal dissolution. We explain the transition to CGDE by the OER pathway change from direct recombination of two terminally coordinated oxides to a single-site route involving early peroxide formation. This change triggers electrochemical luminescence which proceeds via a co-reactant mechanism involving fragments of metastable peroxide structures and metal cations at the active sites on the anode surface that produce electrically excited intermediates prone to radiative relaxation. Our results undermine existing CGDE theories whilst emphasising common bases in behaviour of conventional and plasma-assisted electrochemical systems, thus providing far-reaching implications for understanding, development and practical use of electrolytic plasma processes. Image 1 • In-situ impedance spectroscopy used to study Contact Glow Discharge Electrolysis. • Equivalent circuit of anodic CGDE process with Fe-13%Cr electrode is proposed. • 3D surface oxide with adsorbed oxo and peroxo species affects charge transfer. • CGDE onset is caused by the change in pathways of oxygen evolution reaction. [ABSTRACT FROM AUTHOR]

Thermal spraying, an important industrial surface manufacturing process in sectors such as aerospace, energy and biomedical, remains a skill intensive process often involving multiple trial runs impacting the yield. The core research challenge in digitalisation of thermal spraying process lies in instrumenting the manufacturing platform as the process includes harsh conditions, including UV Rays, high-plasma temperature, dusty chemical environment, and spray booth inaccessibility. This paper introduces a novel application of machine learning to the acoustic emission spectra of thermal spraying. By transitioning from the amplitude-time domain to a Fourier-transformed frequency-time domain, it is possible to predict anomalies in real-time, a crucial step towards sustainable material and manufacturing digitalization. Our experimental results also indicate that this method is suitable for industrial applications by generating useful data that can be used to develop Visual Geometry Group (VGG) transfer learning models to overcome the traditional limitations of convoluted neural networks (CNN). [ABSTRACT FROM AUTHOR]

• A remote atmospheric pressure plasma (APP) was developed to modify PLA nonwovens. • Rapid and polymeric textile-friendly APP process for immobilizing carboxyl groups. • Improved hydrophilicity and stability on PLA without damaging the substrate. • Enhanced hydroxyapatite (HAp) bioceramic deposition efficiency on functionalized PLA. • Increased proliferation ability of MC3T3-E1 cells on HAp-deposited PLA nonwovens. When adopting polylactic acid (PLA) nonwoven for bone tissue engineering scaffolds, the inert and hydrophobic nature of PLA leads to poor biocompatibility and osteoconductivity, and limits the efficiency of applying bioceramic coatings, such as hydroxyapatite (HAp), for surface functionalization. To tackle these issues, a remote atmospheric pressure plasma (APP) system using a bespoke Pyrex chamber and acrylic acid monomer was designed and employed to functionalize the PLA via depositing carboxylic acid functional groups onto its surface. The remote APP showed being polymeric textile-suitable with an improved efficiency on not only immobilizing carboxylic acid functional groups on the PLA nonwoven than conventional systems but also the alternate soaking process for HAp deposition. Being compared with the neat PLA, the plasma-functionalized PLA exhibited a more hydrophilic surface (from 130.49 ± 1.28° to 117.40 ± 2.53°) with a 30-day stability (from 117.40 ± 2.53° to 119.40 ± 0.75°) and showed better biocompatibility (136 % to the neat PLA) with MC3T3-E1 mouse embryonic osteoblast cells after HAp deposition. The presence of carboxylic acid functional groups and HAp (Ca/P ratio of 1.7) was also identified using X-ray photoelectron spectroscopy, Fourier-transform infrared spectroscopy and a scanning electron microscope with energy dispersive X-ray analysis. [ABSTRACT FROM AUTHOR]

Abstract The increasing demand for high-performance lightweight metallic materials is driving an interest in Plasma Electrolytic Oxidation (PEO) as one of the most promising techniques for surface engineering of Mg. In order to enable smart and multifunctional performance, it can be beneficial to incorporate into ceramic PEO coatings nanocontainers to carry appropriate active and functionalising agents. In situ incorporation of nanocontainers is challenging since their integrity may be compromised by plasma discharge assisting coating formation. We studied incorporation of halloysite nanotubes (HNTs) as potential nanocontainers into forsterite, Mg 2 SiO 4 , formed during PEO processing of AM50 alloy at the frequency range of 100–5000 Hz. Detailed analysis of the coating microstructure, chemical and phase composition carried out by Scanning Electron Microscopy/Energy Dispersive X-ray Spectroscopy, Transmission Kikuchi Diffraction and X-ray Diffraction enabled evaluation of a pattern of surface temperature evolution during current pulses underpinning the PEO process. Transient analysis revealed that at pulses longer than 10−4 s, the surface heating becomes affected by the metal substrate acting as a heat sink. As the pulse duration approaches 10−3 s, raising surface temperature and increasing thermal gradients across the coating cause crystallisation of forsterite and grain growth towards the surface; this triggers thermally induced degradation and decomposition of HNTs adsorbed on the surface. In contrast, at short pulse durations (2 × 10−5 s), the energy released is insufficient to induce forsterite crystallisation and incorporated HNTs are retained in their original tubular structure. Due to the fine porosity and good structural integrity, such coatings show enhanced corrosion resistance in saline solution. Strong correlations between surface thermodynamic conditions and evolution of coating microstructure disambiguate the fundamental mechanisms underlying incorporation of nanoparticles into growing PEO coatings, thus creating the basis for efficient design of PEO processes and development of novel smart and multifunctional coatings with potential applications in many industrial sectors. [ABSTRACT FROM AUTHOR]

Abstract Plasma electrolytic oxidation (PEO) is an attractive technology for improving resistance to wear, heat and corrosion of aluminum alloys. PEO results in a hard, well-adhered alumina ceramic coating with a morphology which is graded from a dense region near the substrate interface to a porous outer region. Such properties mean that PEO can be an ideal underlying layer for the application of solid lubricants which can be entrapped in outer pores and provide reservoirs for the tribological contact lubrication. This study investigates the fretting wear behavior and adaptive mechanisms for a PEO-produced alumina surface of about 11–12 GPa hardness with a top layer of an MoS 2 /Sb 2 O 3 /C chameleon solid lubricating coating, the composition of which was designed to self-adapt in variable humidity environments for friction and wear reduction. Coupons of AA 6082 alloy were coated by the PEO process and then were over-coated by a burnishing process with a MoS 2 /Sb 2 O 3 /C chameleon coating to prepare a duplex coating combination. The coated surfaces were investigated using nanoindenation, Raman spectroscopy and scanning electroscopy and were then subjected to fretting wear tests against steel and alumina balls with variable amplitude (0–100 μm) and loads (10–100 N) in both humid air and in dry nitrogen environment conditions. The tests demonstrated low friction coefficients, considerable reduction in critical amplitude for the stick-slip transition, and self-adaptive tribological behavior in cycled environment tests. Friction coefficients of the order of 0.10–0.15 in humid air and 0.06–0.09 in dry nitrogen were recorded and linked with the surface self-adjustment from graphite to MoS 2 lubrication, respectively, which was confirmed by Raman spectroscopy. The studies demonstrate the effectiveness of the PEO/chameleon duplex coating system for the friction reduction of and fretting wear in the gross-slip regime, as well as significantly reducing the critical amplitude of stick-slip transition for fatigue wear mitigation. Highlights • Cost effective duplex PEO/chameleon (MoS 2 /Sb 2 O 3 /C) coating on Al alloy was produced • Chameleon lubricant was embedded in PEO porosity surface with burnishing process • Hexagonal MoS 2 and graphite phase lubrication in fretting contact was confirmed by Raman spectroscopy • PEO/chameleon coating reduces critical amplitude for fatigue prone stick-slip fretting regime • PEO/chameleon coating has low friction and fretting wear in humid and dry conditions [ABSTRACT FROM AUTHOR]

The facile, rapid and bulk production of composite materials consisting of carbon nanostructures doped with metal-based compounds has been a significant challenge for various research areas where such types of materials can be applied, including catalysis, energy storage and water purification. In this work, a carbon foam‑aluminum fluoride composite (C-AlF 3 ) was developed by adopting a combustion synthesis approach, which is an attractive alternative to wet chemical methods usually employed for such purposes. The flame ignition and combustion of a solid-state mixture comprising a fluoropolymer and nano-sized Al powder leads to the formation of a porous carbon foam network doped with dispersed cubic-like AlF 3 nanoparticles (100 to 500 nm in size), as observed by high-resolution microscopy methods. Selective area electron diffraction and X-ray diffraction studies revealed a rhombohedral α-AlF 3 crystal structure for these embedded particles, while micro-Raman spectroscopy indicated typical carbonaceous features for the foamy matrix. The C-AlF 3 composite also showed a combination of micro-, meso- and macro-porous characteristics (i.e. pore sizes in the nanometer scale) based on the analysis of N 2 sorption data collected at 77 K. The findings of this study provide useful insights for further research on carbon-based nanocomposite materials prepared via direct combustion synthesis routes. [ABSTRACT FROM AUTHOR]

CrCuAgN PVD nanocomposite coatings were produced using pulsed DC unbalanced magnetron sputtering. This investigation focuses on the effects of post-coat annealing on the surface morphology, phase composition and nanostructure of such coatings. In coatings with nitrogen contents up to 16 at.%, chromium exists as metallic Cr with N in supersaturated solid solution, even after 300 °C and 500 °C post-coat annealing. Annealing at 300 °C did not obviously change the phase composition of both nitrogen-free and nitrogen-containing coatings; however, 500 °C annealing resulted in significant transformation of the nitrogen-containing coatings. The formation of Ag aggregates relates to the (Cu + Ag)/Cr atomic ratio (threshold around 0.2), whereas the formation of Cu aggregates relates to the (Cu + Ag + N)/Cr atomic ratio (threshold around 0.5). The primary annealing-induced changes were reduced solubility of Cu, Ag and N in Cr, and the composition altering from a mixed ultra-fine nanocrystalline and partly amorphous phase constitution to a coarser, but still largely nanocrystalline structure. It was also found that, with sufficient Cu content (>12 at.%), annealing at a moderately high temperature (e.g. 500 °C) leads to transportation of both Cu and Ag (even at relatively low concentrations of Ag, ≤3 at.%) from inside the coating to the coating surface, which resulted in significant reductions in friction coefficient, by over 50% compared to that of the substrate (from 0.31 to 0.14 with a hemispherical diamond indenter, and from 0.83 to 0.40 with an alumina ball counterface, respectively). Results indicate that the addition of both Cu and Ag (in appropriate concentrations) to nitrogen-containing chromium is a viable strategy for the development of ‘self-replenishing’ silver-containing thin film architectures for temperature-dependent solid lubrication requirements or antimicrobial coating applications. [ABSTRACT FROM AUTHOR]

Formation of the high-temperature α-Al 2 O 3 phase during Plasma Electrolytic Oxidation of aluminium at ambient bulk temperatures has been previously attributed to local microdischarge events providing multiple melting-solidification cycles in micro-volumes of the surface oxide layer. In this work, it is demonstrated that the α phase can be formed even if the microdischarge is fully suppressed under specific processing conditions. Oxide layers produced in the post-sparking anodising mode were studied by FIB, TEM, EBSD, EDS and GDOES techniques to reveal microstructural and chemical evolutions that accompany the γ to α alumina transition. Our results provide strong evidence that the α phase can form spontaneously in regions of oxide with the appropriate temperature, grain size and impurity distributions in the γ-Al 2 O 3 matrix that allow sufficient mobility of α/γ grain boundaries. Ionic migration within the oxide and hydrothermal dissolution/precipitation in the associated microporous network that facilitate species mobility at the grain boundaries allow the critical temperature for activation of γ→α transition to be reduced. Overall, it is suggested that oxide layer growth can be considered in terms of a relatively simple Plug Flow Reactor model. This can help predict the phase transition kinetics depending on key processing parameters such as current density and frequency of pulse polarisation, thus enabling optimum control of coating microstructure for specific application requirements. [Display omitted] [ABSTRACT FROM AUTHOR]

The paper discusses a methodology for the equivalent circuit design for the plasma electrolytic oxidation (PEO) process from the voltage and current waveform transients recorded during pulsed bipolar PEO treatment. Joint analysis of the coating morphology and the electric transients enabled the proposal of an equivalent circuit with elements corresponding to characteristic parts of the system — electrolyte, porous and dense coating layers, showing different behaviours at anodic and cathodic polarisations of PEO. Two thresholds based on the sparking voltage for a positive pulse and on the minimal resolved current for a negative pulse were introduced to draw the boundaries for the application of the circuit structures. The simplest equivalent circuit corresponds to lower positive and negative pulse voltages ( U p < 526 V, U n < 20 V); it comprises a linear parallel RC branch corresponding to the thinnest coating in series with the electrolyte resistance. For higher negative voltages ( U p < 526 V, U n > 20 V), the anodic and cathodic branches become separated due to different coating behaviour under positive and negative polarisations. The RC branch represents the anodic behaviour of a thinner porous single layer coating, and the RL branch describes the cathodic response. For higher positive and negative voltages ( U p > 526 V, U n > 20 V), the PEO microdischarges become stronger, and the anodic branch evolves into two RC loops connected in series in order to represent heterogeneity developed in the coatings containing porous outer and dense inner regions. The fact that the equivalent circuit elements evolve with the coating growth enables assessment of the coating thickness in-situ during the PEO treatment. Finally, the equivalent circuit modelling methodology can contribute towards design of advanced PEO equipment with power supplies optimised to the electrolyser properties depending on the treatment conditions and with diagnostic instruments providing in-situ estimates of the coating properties. [ABSTRACT FROM AUTHOR]

This paper investigates niobia/silica mixed oxide thin films deposited by reactive pulse-DC/RF magnetron co-sputtering of Nb and Si metal targets at room temperature. The reactive gas flow during the sputtering processes was either controlled by direct mass flow rate (i.e. constant reactive gas flow) or by an active feedback process control system. 61% and 137% higher deposition rates of Nb 2 O 5 and SiO 2 layers, respectively, were obtained using the latter technique as compared to constant reactive gas flow. Films exhibited bulk or near-bulk density. All mixture films produced in this study had an amorphous structure. A volume law of mixtures was used to determine the coating composition. It is shown that the fraction of SiO 2 or/and Nb 2 O 5 has a linear dependency on sputter target power density. On this basis, rugate filter coating designs can be easily deposited, where refractive index gradually varies between that of pure Nb 2 O 5 and pure SiO 2 . Substantially less inhomogeneity of coating mixtures was found in films produced using a reactive sputtering process with feedback-control. [ABSTRACT FROM AUTHOR]

To prevent overheating of high-power electronic devices, effective cooling and thermal management is a key issue. Owing to the extraordinarily high thermal conductivity of graphene structure in nature, an approach for growth of carbon nano-coating with multiplex layer architecture on copper foil by using high power impulse magnetron sputtering (HiPIMS), as an alternative to the conventional chemical vapor deposition process, is reported for heat-spreading purposes. For successful deposition, a high peak current of 600 A with a short pulse of 30 μs at a relatively low substrate temperature of 600 °C was applied. Moreover, growth mechanisms without and with applying copper for Cu/carbon (Cu/C) nano-coating periodic deposition are revealed and discussed. Based on the measurement results using Angstrom's method, under optimum deposition time, the HiPIMS prepared carbon nano-coating with multiplex layer architecture, which contains in-plane-oriented multilayer graphene structure and the following out-of-plane-oriented turbostratic graphene structure, can enhance the heat spreading ability of the copper foil, reaching a thermal diffusivity value of 1.05 cm2/s. For Cu/C nano-coating periodic deposition, copper can act as catalyzing ingredient to inhibit amorphous carbon formation and promote the crystalline graphene-like structure growth, resulting in a further increase in the thermal diffusivity up to 1.21 cm2/s, twice that of the bare copper foil. [ABSTRACT FROM AUTHOR]

In this study, we investigated the microstructural evolution, surface hardening and general corrosion properties of a precipitation-strengthened Inconel 718 Ni-superalloy after triode-plasma nitriding (TPN) at low treatment temperatures of 400–450 °C (i.e. thermodynamic paraequilibrium conditions) and a high treatment temperature of 700 °C. At low treatment temperatures, apart from the formation of nitrogen-expanded austenite (γ N) from the high-Cr γ matrix, the pre-existing γ′ and γ″ intermetallic nano-precipitates appear to exhibit different nitriding responses. The spheroidal N-modified γ′ (or γ′ N) precipitates were 'slightly-expanded', leading to slightly shifted XRD peaks, i.e. 2-theta angles of ~0.2° from γ substrate (111) and ~0.5° from γ substrate (200). In contrast, N-modified γ″ (or γ″ N) could experience substantial lattice expansion close to that of the γ N matrix. With increasing treatment temperature, nitride formation started as additional nano-sized precipitates (e.g. ~3–6 nm diameter as observed at 450 °C) and grew into laths (e.g. ~5–10 nm thick and ~15–30 nm wide as observed at 700 °C). Without changing core microstructure/properties, surface nitrogen modification and hardening were obtained on alloy 718 after TPN (e.g. from ~486 HV 0.025 to ~1212 HV 0.025 after TPN at 400 °C). No degradation of corrosion performance was observed for the nitrogen-supersaturated surface after TPN at 400 °C. However, the 450 °C TPN-treated surface showed a slightly increased current density in the anodic region, which can be associated with early-stage nitride formation. The significantly deteriorated corrosion performance after TPN treatment at 700 °C is due to pronounced nitride formation and segregation of substitutional alloying elements. • Triode plasma nitriding of a precipitation-strengthened corrosion-resistant Ni-superalloy, Inconel 718 • Significant anisotropic XRD peak shifts from lattice expansion of high-Cr matrix (and most likely high-Nb γ″). • A "slightly-expanded" phase corresponds to spheroidal high-Al γ′ N. • A "dotted" and a "woven" nitride precipitation morphology at 450 °C and 700 °C, respectively • Hard surface layers without altering core microstructure/hardness [ABSTRACT FROM AUTHOR]

The soft sparking regime of Plasma Electrolytic Oxidation (PEO) of valve metals attracts increasing attention as it enables a better process control with improved energy efficiency and coatings with enhanced performance to be obtained. Here, the discharges softening phenomenon was characterised by evaluation of changes in electrical signal, composition of gaseous products and morphology of the metal-oxide interface in PEO coatings on Al. The coatings were formed using two electrical regimes retarding or promoting soft sparking conditions. Harmonic analysis of PEO process has been performed using independent evaluation of the positive and negative half-waves of polarisation signal. The composition of gas evolved during the PEO process was evaluated by a quantitative gas analyser. Coatings were characterised by scanning and transmission electron microscopy with energy dispersive spectroscopy and small area electron diffraction. It was found that discharge softening is accompanied with a decrease in oxygen evolution rate, an increase in equivalent capacitance of anodic process as well as structural and compositional changes near the metal-oxide interface. The experimental findings provide further support to the explanation of discharge softening phenomenon by narrowing the active zone at the metal-oxide interface due to intercalation of hydrogen species into anodic alumina under cathodic polarisation. Such mechanistic understanding allows rational regime selection, in-situ process control and optimisation of the coating properties to be performed that paves the way to intellectual manufacturing approach based on careful process monitoring in operando. [ABSTRACT FROM AUTHOR]

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

Abstract: This paper demonstrates a new method to grow nano-structured TiO2 over a plasma electrolytically oxidised titanium surface. Microstructural characterisation by employing a variety of transmission electron microscopy techniques was carried out to explore the nano-scale structural changes due to the alkaline and thermal treatments. Photovoltaic performance was measured and this revealed the effect of microstructural changes. Such coatings can be considered potential candidates for the electrode material in a dye-sensitised solar cell (DSSC). The experimental results show that a titania layer with a 3D network ‘nano-flaky’ surface can be successfully prepared. The obtained nano-flakes are around 100 to 200nm across and have a thickness of less than 10nm. These completely cover the outermost surface as well as the inner pores and voids. The formed nano-flaky structure is amorphous and provides a larger surface area for dye absorption to increase the efficiency of assembled DSSC. Thermal annealing treatment causes the transformation of the amorphous nano-flakes into anatase nano-crystallites and further enhances the photovoltaic efficiency of the assembled DSSC. [ABSTRACT FROM AUTHOR]

Abstract: Titanium dioxide (TiO2) films have been prepared using physical vapor deposition (PVD) processes for several decades. It is often considered as a material for applications such as photocatalysis, self-cleaning and antimicrobial purposes. However, numerous questions regarding the growth behavior and microstructure remain unanswered. This study aims to clarify, using microstructural characterization techniques and optical emission spectroscopy (OES), the conditions under which rutile or anatase phase constituents appear in films deposited by PVD arc ion plating (AIP), to give a better understanding of TiO2 films deposited using different deposition processes. The experimental results show that the calculated free energy for rutile phase growth is lower than for anatase, and that the rutile phase grows preferentially if thermodynamically satisfactory oxygen supply (in terms of oxygen partial pressure) is present, although less activation energy is required for anatase growth. However, OES studies reveal that, with further increased oxygen partial pressure and extended deposition time, oxidation occurring at the cathode surface generates a higher amount of neutral titanium atoms and, consequently, the metastable anatase phase grows. Detailed TEM microstructural characterization of the deposited TiO2 films in this study also explicitly shows that films identified as XRD amorphous actually contain very fine rutile nanocrystallites within the amorphous structure, whereas films revealed by XRD as composed predominantly of the anatase phase are actually as a consequence of later growth, preceded by rutile growth in the initial stage. [Copyright &y& Elsevier]

Abstract: An arc ion plating (AIP) system was used to deposit anatase TiO2 thin films with photocatalytic and antimicrobial properties. This study aims to evaluate the properties and performance of such films, including surface hardness, adhesion, abrasive wear resistance and corrosion protection. The experimental results show that film hardness and scratch adhesion reach maximum values of 679.6 HV and 21.2 N, respectively. Film quality is strongly influenced by the degree of crystallinity, which is in turn affected by both deposition time and oxygen partial pressure. The wear resistance of the TiO2 coatings can be closely correlated to the film adhesion, however all films impart significantly higher resistance to abrasive wear than that of the uncoated surface. On the other hand, TiO2 coatings on stainless steel give rise to an increased (less negative) corrosion potential and decreased corrosion current in a sodium chloride solution. Overall, AIP-TiO2 film can however provide satisfactory protection for stainless steel. [Copyright &y& Elsevier]

Mg 2 SiO 4 coatings were formed on cp-Mg by Plasma Electrolytic Oxidation (PEO) using electrical regimes based on sawtooth anodic current pulses with extended ascending or descending segments (ramps). Voltage, current and light emission signals were simultaneously acquired to derive and analyse the evolution of system current and discharge population density during PEO process, while optical emission spectroscopy was employed for identification of plasma species. Coating morphological characterisation was carried out using Scanning Electron Microscopy. Phase composition was identified by X-ray diffraction. The corrosion performance was evaluated with Electrochemical Impedance Spectroscopy at various periods of exposure to corrosive media (0.5 wt% NaCl). It was shown that the application of sawtooth pulses allowed the controlling of microdischarge characteristics and coating morphology in both pulsed unipolar and reversed current regimes. Results further demonstrate that the application of anodic sawtooth pulses with the negative ramp facilitated defect healing during coating formation leading to production of more uniform PEO coatings with lower porosity and a slower degradation rate of magnesium substrate. A steady decay in the coating resistance with immersion time provides a possibility for controlling magnesium degradation and thereby for optimisation of component lifetime in applications where predictable Mg dissolution rate is required, such as sacrificial anodic protection of metallic structures and resorbable biomedical implants. • The quality of PEO coatings is modified by sawtooth pulse current regimes with controlled positive or negative anodic ramp. • Applying sawtooth waveforms with positive ramps refined the coating morphology. • Negative ramps introduced a defect healing effect reducing coating porosity and roughness. • Corrosion resistance of refined coating was proved to be better by EIS measurement. [ABSTRACT FROM AUTHOR]

Recent progress in additive manufacturing (AM) enables the development of novel cemented carbides for specifically wear-related applications. However, the available literature on their tribological performance is very limited. The present work aims to reveal the friction and wear performance of AM-produced cemented carbides consisting of a cobalt (Co) matrix and ∼65 vol % of tungsten (W) and chromium (Cr) -rich carbides through dry reciprocating wear tests under different conditions (counterbodies: alumina and hardened AISI 52100 steel balls; loads 10 N and 30 N), in-situ scratch wear testing, post-test microscopy, and laser profilometry. The dominant wear mechanism was abrasion against alumina and adhesion against steel through the removal of the Co matrix, along with surface oxidation and tribolayer formation. The coefficient of friction increased by 11.9% with increasing load against steel, whereas it remained the same against alumina, indicating a bearing effect due to the oxidation of the wear track. The specific wear rate increased by 7.3% against alumina with increasing load, while it sharply decreased by 56.4% against steel, presumably due to surface strain-hardening. The in-situ scratch wear testing under a scanning electron microscope revealed degradation of the Co matrix and carbides network over time. These observations provided evidence of tribolayer formation and strain-hardening of the Co matrix. The present paper contributes to understanding the tribological behaviour of AM-produced CrC-rich WC-Co cemented carbides, which are promising for innovative and longer-lasting mining and machine tools. [Display omitted] • The CoF against steel was approximately two times higher than alumina. • The surface degradation was visualised using surface maps and wear track profiles. • The wear mechanisms changed specifically depending on the counterbody. • Abrasion, adhesion, and oxidation of the removed matrix were the main mechanisms. • Tribolayer formation and strain-hardening of the matrix were shown. [ABSTRACT FROM AUTHOR]

Low-temperature plasma nitriding has been widely studied and applied, in enhancing the wear performance of austenitic stainless steels (ASSs) without losing corrosion resistance. In this work the wear and corrosion behaviours of two specialty ASSs, i.e. Staballoy® AG17 (Fe-17Cr-20Mn-0.5N, in wt%) and RA330® (Fe-19Cr-35Ni-1.2Si, in wt%), were evaluated – and compared to AISI 304 – before and after low-temperature triode plasma nitriding (TPN) at 400 °C and 450 °C. A nitrogen interstitially-supersaturated expanded austenite layer (γ N) was developed for all three ASSs after TPN treatment at 400 °C, which led to a) an approximately 4-fold increase in surface hardness, b) a reduction in specific wear rate of at least 2 orders of magnitude in unlubricated dry-sliding, and c) an improved resistance to pitting in 3.5 wt% NaCl aqueous solution. Large numbers of 'linear defects' (identified in TEM studies as strips of HCP-ε N) were seen in the γ N -AG17 layer, that could be correlated to comparatively higher surface hardness and better wear resistance. Several slip/shear bands were also seen in the γ N -330 layer, where short-range Cr-segregation could occur, leading to localised corrosion. More importantly, after TPN treatment at 450 °C, alloys AISI 304 and AG17 presented a deterioration in corrosion performance, whereas good corrosion performance was maintained for alloy RA330. Redistribution of Si (in preference to Cr) was revealed in γ N -330 after TPN treatment at 450 °C, whereby Si-alloying at a significantly higher level than in the other two alloys investigated appears (in addition to the high Ni content in alloy 330) to be beneficial in delaying CrN precipitation, and thus in maintaining the good corrosion performance of γ N after nitriding at low-to-intermediate temperatures. [ABSTRACT FROM AUTHOR]

Duplex coatings comprising MoS 2 /Sb 2 O 3 /graphite layer burnished on top of plasma electrolytically oxidised AA6082 alloy enhanced fretting wear resistance against alumina and steel whilst reducing friction from ~0.6 ... 0.9 to ~0.08 ... 0.1 in dry nitrogen and humid air. Transitions to stick-slip (~3 μm), partial slip (5–10 μm) and gross slip (>10 μm) showed an order of magnitude improvements over single-layer PEO coatings. In the latter mode, high initial contact pressures (~1.1 GPa) with steel counterpart under oxidising atmosphere increased friction due to generation of Fe/Al/Cr oxides/hydroxides in the contact region, leading micro-cracking in PEO coating followed by fatigue damage of aluminium substrate. Reducing contact pressure <1 GPa, retained topcoat lubricating behaviour, high wear resistance and eliminated fatigue damage after 104 cycles. • Fretting behaviour of duplex chameleon/PEO coatings on Al at 1 GPa contact pressure. • MoS 2 /Sb 2 O 3 /graphite topcoat reduces stick-slip transition by an order of magnitude. • Realignments of MoS 2 and graphite provide low friction in dry and wet environments. • Steel counterface oxidation in wet air increases friction and wear of the topcoat. • Increased friction at high contact pressure induces damage in both PEO coating and Al. [ABSTRACT FROM AUTHOR]

Advances in additive manufacturing present the opportunity to design tool steels with higher carbon contents than previously possible with conventional manufacturing. A new class of carbide-rich tool steels with 8 % , 20 % and 25 % volume fraction carbides has been developed using electron beam melting. Reciprocating ball-on-plate dry wear tests were performed to investigate the macro tribological performance of these materials. In-situ scratch wear tests were also performed to assess wear degradation effects at a more fundamental level. The main macro wear mechanism was oxidation with adhered iron oxide islands in all carbide-rich tool steels and the sliding of oxide particles caused three body abrasive wear in the lowest carbide containing material. Surface material removed from the counterbody and formed adhesive iron oxide islands over the oxidized carbide-rich tool steel surface. The compacted oxide islands initially formed at the edges of embedded carbides and then evolved to encompass the entire wear scar. The wear damage was assessed quantitatively through laser profilometry. The lowest wear damage was observed in the 20 % carbide tool steel which also had the lowest coefficient of friction on moving average of 0.52 ± 0.01 compared to the 8 % and 25 % carbide tool steel having on moving average 0.66 ± 0.03 and 0.61 ± 0.03 respectively. In-situ scratch wear tests revealed the potential plastic deformation mechanism of the matrix underneath the oxide film. The deformed matrix of 20 % carbide tool steel generated limited wear debris at the interface of the tribo-system and this is surmised to provide better wear and friction performance among the materials considered. Image 1 • Oxidative wear with adhered iron oxide islands was the main macro mechanism for all carbide-rich tool steels. • The increased carbide content and matrix strengthening shifts the micro mechanism from microcutting to microplowing. • The 20% carbide tool steel produced limited debris and this is surmised to provide better wear and friction performance. [ABSTRACT FROM AUTHOR]

CrCuAgN coatings with a wide range of Cu and Ag contents (combined values in the range of <10 at% to >50 at%) were prepared on AISI316L stainless steel coupons by closed-field unbalanced magnetron sputtering (CFUBMS). After the deposition process, the coated coupons were annealed at 300 °C and 500 °C, respectively. The transport behaviour of Cu and Ag in selected CrCuAgN coatings was then investigated by conventional and high-resolution transmission electron microscopy (HR-TEM), energy-filtered (EF)TEM elemental mapping, and scanning (S)TEM with EDX elemental mapping. Results showed that the aggregation of both Cu and Ag are detachment-limited, rather than diffusion-limited. The co-existence of Cu with Ag in a PVD metallic coating was found to be beneficial in promoting Ag transport to the coating surface, resulting not from the anticipated "intergranular network channels" of Cu, but from a much higher detachment rate of Cu than Ag. This study verified that CrCuAgN coatings with desired composition and nanostructure can be obtained via coating/process design, providing a controllable precipitation rate of Ag (via adjusting Cu content) for practical applications. Image 1 • CrCuAgN coatings with a wide range of Cu and Ag contents were prepared for investigation on their transport behaviour. • The aggregation of both Cu and Ag are found to be detachment-limited, rather than diffusion-limited. • Cu was found to be beneficial in promoting Ag transport, resulting from the much higher detachment rate of Cu. • For the Cr-Cu-Ag-N system, coatings with desired specific nanostructures can be obtained via coating/process design. [ABSTRACT FROM AUTHOR]

Refractory High-Entropy Alloys (RHEAs), such as NbMoTaW, MoNbTaVW, HfNbTaZr, Re 0.1 Hf 0.25 NbTaW 0.4 , Nb 40 Ti 25 Al 15 V 10 Ta 5 Hf 3 W 2 , Ti x NbMoTaW (x = 0, 0.25, 0.5, 0.75 and 1), and 3d transition metal HEAs such as Al 10.3 Co 17 Cr 7.5 Fe 9 Ni 48.6 Ti 5.8 Ta 0.6 Mo 0.8 W 0.4 have demonstrated superior performance compared to traditional superalloys, particularly in high-temperature applications for engine components. However, the development of these alloys often depends on critical raw materials (CRMs) such as Ta, W, Nb, Hf, and others. The reliance on critical raw materials (CRMs) not only generates substantial emissions during recycling processes but also imposes considerable risks across global supply chains, hindering the pursuit of Net-zero ambitions. In this pioneering work, we unveil an inventive approach to inversely predict novel multicomponent alloy compositions, meticulously crafted to eliminate CRMs while achieving hardness levels comparable to those of CRM-containing multi-principal element alloys (MPEAs). A robust machine learning (ML) model was developed using a computational database of 3,608 entries, covering unary and binary materials from the Thermo-Calc 2024a software. Among various ML models, the Extra Trees Regressor (ETR) exhibited superior performance and was integrated with metaheuristic optimization techniques to identify novel MPEA compositions. The Cuckoo Search Optimization (CSO) method produced reduced-CRM MPEAs that closely matched Thermo-Calc predictions, with an error margin below ± 20%. To assess the efficacy of these reduced-CRM MPEAs, we compared the hardness of newly synthesized MPEA with CRM-containing counterparts reported in the literature, particularly those with high-risk critical raw materials like Niobium (Nb) and Tantalum (Ta). For example, the CoCrFeNb 0.309 Ni alloy, which includes CRMs Nb and Co exhibits a Vickers hardness of 480 HV. In contrast, our proposed composition, Ti 0.01111 NiFe 0.4 Cu 0.4 achieves a comparable hardness of 488 HV without using a CRM. Our objective was not to develop high hardness alloy but to facilitate the development of reduced-CRM multi-principal element alloys (R-CRM-MPEAs). We validated our computational approach through the experimental synthesis of an FCC-phase alloy, Al 6.25 Cu 18.75 Fe 25 Co 25 Ni 25 . Thermo-Calc evaluation and ML model predictions of the Vickers hardness showed excellent agreement with the experimental hardness values, which lends credence to our approach. In conclusion, this study provides a robust framework for accelerating the discovery of novel R-CRM-MPEAs, effectively addressing challenges related to supply chain vulnerabilities, import dependence, and related environmental concerns., Competing Interests: Declarations. Competing interests: The authors declare no competing interests. Content of the publication: During the preparation of this work, the author(s) used AI assistance toimprove the readability and language of the manuscript. The authorsreviewed and edited the final content and took full responsibility for thecontent of the published article., (© 2025. The Author(s).)

This paper reports a study involving the formation of a self-assembled polymeric monolayer on the surface of a high surface area activated carbon to engineer its affinity towards organic contaminants. A nanoporous activated carbon cloth with a surface area of ∼1220 m 2 g -1 and a pore volume of ∼0.42 cm 3 g -1 was produced by chemical impregnation, carbonisation and high-temperature CO 2 activation of a commercially available viscose rayon cloth. The subsequent modification with a silane polymer resulted in a nanoscale self-assembled monolayer that made it selective towards organic solvents (contact angle <10°) and repellant towards water (contact angle >145°). The adsorbent showed more than 95% efficiency in the separation of various types of oil/water mixtures under neutral, basic and acidic conditions. Benefiting from inherent nanoscale features, a robust hierarchical structure and a thermally stable monolayer (∼300 °C), this nanoporous adsorbent maintained high efficiency for more than 20 cycles and separated surfactant stabilised emulsion with >92% oil removal efficiency. The adsorbent was studied extensively with a series of advanced characterisation techniques to establish the formation mechanism and performance in emulsion separation. Findings from this work provide crucial insights towards large-scale implementation of surface engineered activated carbon-based materials for a wide range of industrial separation applications.

Oil/water mixtures are a potentially major source of environmental pollution if efficient separation technology is not employed during processing. A large volume of oil/water mixtures is produced via many manufacturing operations in food, petrochemical, mining, and metal industries and can be exposed to water sources on a regular basis. To date, several techniques are used in practice to deal with industrial oil/water mixtures and oil spills such as in situ burning of oil, bioremediation, and solidifiers, which change the physical shape of oil as a result of chemical interaction. Physical separation of oil/water mixtures is in industrial practice; however, the existing technologies to do so often require either dissipation of large amounts of energy (such as in cyclones and hydrocyclones) or large residence times or inventories of fluids (such as in decanters). Recently, materials with selective wettability have gained attention for application in separation of oil/water mixtures and surfactant stabilized emulsions. For example, a superhydrophobic material is selectively wettable toward oil while having a poor affinity for the aqueous phase; therefore, a superhydrophobic porous material can easily adsorb the oil while completely rejecting the water from an oil/water mixture, thus physically separating the two components. The ease of separation, low cost, and low-energy requirements are some of the other advantages offered by these materials over existing practices of oil/water separation. The present review aims to focus on the surface engineering aspects to achieve selectively wettability in materials and its their relationship with the separation of oil/water mixtures with particular focus on emulsions, on factors contributing to their stability, and on how wettability can be helpful in their separation. Finally, the challenges in application of superwettable materials will be highlighted, and potential solutions to improve the application of these materials will be put forward., (Copyright © 2020 Zulfiqar, Thomas, Matthews and Lewis.)

Plasma electrolytic oxidation (PEO) is an advanced coating process based on high-voltage anodizing. Notwithstanding the anodic nature of the PEO process, it is known that negative polarization leads to synergetic effects in oxide formation efficiency and characteristics of resulting coatings. In this work, we used dynamic anodic voltammograms derived from polarization signal, combining working and diagnostic segments to evaluate in real time the effects of negative polarization on the formation of PEO on the coating on Al in the bipolar regime with a frequency of 50 Hz and a negative-to-positive charge ratio of 1.3. It was found that the hysteresis between ascending and descending branches of the voltammogram can be both caused by prior cathodic polarization and spontaneously generated under unpolarized conditions. This indicated the existence of a quasi-equilibrium in the chemical state of the coating material, which could be perturbed by the external bipolar polarization. The characteristic relaxation time for this system was found to be 40-370 ms. The quasi-equilibrium was attributed to a reversible hydration/dehydration reaction taking place in the active zone of anodic alumina layer (degree of hydration: 10-40%). Coating response analysis via kinetic hydration model allowed both explanations to be provided to a number of previous experimental observations and practical recommendations to be made for the design of efficient electrical regimes for intelligent PEO processes. The latter includes recommendations on avoiding long pauses during negative to positive switching., Competing Interests: The authors declare no competing financial interest., (© 2020 American Chemical Society.)

Providing materials with smart functionalities such as self-healing properties is primarily a domain for organic materials, although their applicability is restricted to mild environments and loads because of poor thermal and mechanical properties. This work seeks to achieve the active functionalities obtained in organic materials but in ceramics, which are much more heat resistant and robust. Ceramic coatings were produced by plasma electrolytic oxidation (PEO), which is an environmentally friendly technique that offers an alternative to potentially carcinogenic treatments used widely in the automotive and aircraft industries to protect light alloys against corrosion. The active functionalization was achieved by incorporating corrosion inhibitors encapsulated into halloysite nanotubes (HNTs) into the PEO coatings. This allowed controlled release of active agents when detecting environmental pH changes associated with the corrosion initiation of the metal substrate. Three corrosion inhibitors-vanadate, molybdate salts, and 8-hydroxyquinoline (8-HQ)-were assessed within the PEO-HNT system and demonstrated considerable improvements in the corrosion resistance by decreasing the kinetics of both anodic and cathodic reactions. For immersion times up to 72 h, vanadate offered a consistently higher corrosion resistance, which was followed by molybdate, whereas the positive effect of 8-HQ was time-limited. The improvement in corrosion resistance was associated with the combined enhancement of the barrier and active protection properties of ceramic coatings. All coatings containing corrosion inhibitors were capable of providing self-healing to small scratches, whereas only vanadate could partially restore a more severe damage.

This study examined the tribological performance of three gear oils (Oils A, B and C), in relation to surface and microstructural changes. Oil A contains molybdenum dithiophosphate friction modifier, Oil B contains amine molybdate combined with zinc dialkyl dithiophosphate antiwear additive, while Oil C contains phosphonate and a commercial gear oil package. Following sliding tests of a hardened AISI 52100 steel ball on a spheroidized AISI 52100 steel disc, the worn surfaces were chemically studied using Raman and energy-dispersive X-ray spectroscopy. The tribological performance for each oil was different, likewise the nature of the tribofilm formed. After a 5 min sliding test, the hardness-depth profile of the worn surfaces was measured; also the cross-sectional microstructure was examined using scanning electron microscopy combined with focused ion beam preparation and transmission electron backscattered diffraction (t-EBSD) techniques. With Oil A, there was a relatively small increase in surface hardness (33% greater than that of the unworn surface), whereas with Oils B and C, the average hardness near the surface was 100% greater than that of the unworn surface. The cross-sectional microstructure using Oil A also differed from Oils B and C, which were quite similar. The result shows that with Oil A refinement of the ferrite grains spreads deeper into the material (> 10 µm), whilst with Oils B and C it was largely limited to 2-3 µm below the surface. It is concluded that the lubricant formulations and their associated tribofilms influenced the extent of deformation in the subsurface layers and consequently influenced the wear performance.

Hydroxyapatite-magnesia coatings were formed on cp-magnesium by plasma electrolytic oxidation (PEO) followed by cathodic electrodeposition (CED). The static tensile and cyclic fatigue performance of the coated samples were investigated. The cracking behaviour of the coatings during the tensile tests was studied by fracture analysis. The effects of the surface treatment on the fatigue performance of the magnesium substrate were addressed. Tensile strength of cp-Mg was not significantly affected, whereas the fatigue performance was improved by the PEO+CED coatings in the low-cycle region, possibly due to compressive residual stress induced to the metal substrate by the surface treatment. However, reduced fatigue strength was observed in the high-cycle region, which might be attributed to the defects at the coating/substrate interface produced during the surface modification. The in vitro corrosion reduced the fatigue strength in both the low- and high-cycle regions. Finally, the applicability of surface engineered magnesium for biomedical applications was demonstrated from the mechanical standpoint., (Copyright © 2014 Elsevier B.V. All rights reserved.)