Search

A novel active screen (AS) plasma process is developed for the in situ growth of one-dimensional Ag wires and the deposition of reinforced composite coating thereof. Silver wires embedded in the matrix were deposited with Ag nanoparticles, stainless steel nanoparticles and carbon during the AS plasma sputtering process in the ambient of methane and hydrogen. This provided a relatively low-temperature processing route for one-step synthesis of abrasion resistant coating on metallic substrate. Microstructure evolution during sliding with ductile materials proven the ultra-low friction deriving from the molecular ordering of carbon and the high-strength structural holding by the Ag wires.

The nano-scale studies in the literature have revealed the excellent anti-friction properties of graphene and its great potential as a nano solid lubricant. However, for macro-scale applications the integrity and durability are main problems for most graphene-based surface coatings. One way to mediate the durability issue while exploiting the tribology of graphene is graphene-based composites. In this work, nickel-graphene oxide (GO) composite coatings were fabricated on steel by electro-brush plating. The effects of GO on the tribological properties were investigated. The results show that the composite coatings possess much lower friction than GO-free nickel coating (up to 47% less against a bearing steel ball, and 30% less against an alumina ball). As the GO load increases from 0 to 4 mg/ml, the wear rate of the resulting composite can be reduced significantly by approximately 90%. Detailed post-test studies of the wear tracks and the counterpart were conducted using SEM, EDS, Raman and FIB/SEM. The improved tribological properties can be attributed to the strengthening effect, the retention of oxide tribo-films and the formation of GO rolls during sliding. The tribological behaviour of the Ni-GO nano-composite coating and a Ni-graphite composite coating was compared, and their different wear mechanisms have been discussed.

Low-cost beta (LCB) alloy (Ti-6.8Mo-4.5Fe-1.5Al) is developed specifically for non-aerospace (e.g. automotive and motor sports) applications. However, as for all other titanium alloys, LCB alloy is characterised by a high and unstable coefficient of friction and a strong scuffing tendency. Hence, a new surface engineering process based on optimal integration of bulk heat treatment with surface ceramic conversion has been developed, and this paper reports the tribological performance of surface engineered LBC titanium alloy. TEM analysis carried out on the microstructure of the ceramic conversion layer. Reciprocating pin-on-disc sliding wear tests were conducted against both WC and hardened steel balls under unlubricated and oil lubricated conditions. Post-examination of the wear tracks, counterparts and wear debris was carried out to investigate the wear mechanisms involved. The experimental results show that the wear resistance of the LCB alloy can be improved by 4–16 times by the novel combined bulk/surface treatment; the coefficient of friction is reduced from 0.8 to 1.0 for the untreated material to 0.2–0.4 for the treated samples. The wear mechanisms evolve from severe adhesive wear for the untreated material to mild abrasive wear for the treated material when sliding against a WC-Co ball in air. However, severe wear to the steel counterpart occurred and hence large frictional forces formed, which led to delamination wear of treated surfaces. It is also interesting to find that oil lubrication cannot reduce but rather increases the wear of treated surfaces especially when sliding against a hardened steel ball mainly due to oil pressure induced delamination wear.

Possibility of improving the resistance of AISI H13 steel to molten aluminum corrosion by liquid nitrocarburizing (LNC) was explored. The effects of the LNC parameters in terms of temperatures (703/723/743 K) and soaking time (4/8/12 h) on phase transformation, microstructure, and resistance to molten aluminum were fully studied. The surface phase compositions and the cross-sectional phase distribution of the LNC treated specimens were studied by implementable X-ray diffraction analysis. Microstructure, element distribution, microhardness, and the kinetics of the nitrocarburized case formation were fully researched. Immersion test of corrosion resistance to molten aluminum was carried out at 1023 K for 30min. It is observed that an oxide layer can be produced on the top of the nitrocarburized case during LNC treatment, which cannot be regularly produced by other nitriding methods. The nitrocarburized case consists of a compound layer, a diffusion layer, and a transition layer. The growth of the nitrocarburized case is proportional to the squared treatment time and follows the Arrhenius law for the treatment temperature. The activation energy is estimated to be 195.4 kJ mol−1. While the nitrocarburized case provided limited resistance to molten aluminum, the oxide layer formed on the top of the nitrocarburized case conferred significantly improved molten aluminum corrosion resistance, especially a duplex oxide layer produced at 743 K.

One-dimensional nanocomposite coatings are a new generation of coatings, which have promising applications in versatile fields. In this study, the novel carbon nanotubes (CNTs) reinforced nanocomposite coatings were explored through two-step strategy using both physical vapour deposition (PVD) approach and chemical vapour deposition (CVD) approach. Vertically aligned CNT films were deposited by plasma enhanced CVD at 450 °C, while density of the VACNT films was modified by using Ag impregnated composite catalyst films. Subsequently, Pt-CNT, Ag-CNT and DLC-CNT nanocomposite coatings were explored to find a feasible way to achieve the well-designed composite structure. Morphologies and microstructures of these nanostructures were characterized by scanning electron microscopy, atomic force microscopy, transmission electron microscopy and Raman spectroscopy, while four-probe tester was applied to evaluate the electrical conductivity of the nanocomposite coatings. The results indicated that well-composited DLC-CNT nanocomposite coating can be achieved which exhibited better electrical conductivity compare to that of the pristine DLC coating.

A union of surface with rough micro/nano structures and low surface free energy is critical for the preparation of superhydrophobic surfaces. In this study, a rapid one-step pulse electrodepositing method was used to prepare superhydrophobic surfaces on Cu substrates. The electrolyte was prepared with ethanol, myristic acid (CH3(CH2)12COOH) and lanthanum chloride (LaCl3·6H2O). The surface morphology, chemical composition and superhydrophobic property were characterized by SEM, XRD, FTIR, EDX, optical contact angle instrument and high-speed camera. It turned out that the deposited surfaces have micro/nano hierarchical structures mainly being composed of lanthanum myristate. It is found that the optimal water contact angle is approximately 160.3° with a sliding angle of around 5°. The effects of pulse frequency on the surface morphology and wettability were specifically studied and discussed under an equivalent electrolytic time of 10 min. In this way, it can effectively save time and be simply applied to other materials with good conductivity and has a promising wide range application.

Push-out is one of the available techniques to assess the bond strength between the reinforcing fibres and the matrix in composite materials. The test is conducted on thin sections of composite, and a small indenter is used to apply increasing load on single fibres while measuring the displacement, until the debonding occurs. This study used push-out tests to assess the debonding mechanism of carbon fibres in an epoxy matrix. The tests were conducted at multiple loading rates (0.1 mN/s, 1 mN/s and 10 mN/s) and temperatures (24 °C and 125 °C). The results were analysed and contrasted with scanning electron microscopy and atomic force microscopy observations. The data showed evidence of push-out events and provided new insights into the contribution of the viscoelastic behaviour of the fibre/matrix interface and/or the matrix. This finding could pave new pathways for improving the bond strength between the carbon fibres and the matrix in composite materials.

To alleviate spallation and effectively hardened the spheroidal graphite cast iron, a diffusion-prevalent hardened case was produced on the spheroidal graphite iron surface by a new two-stage bright nitriding process. The unique feature of this process in treating the sharp edges with high strength and controllable layer thickness has been emphasised. An exceptionally deep diffusion layer of 300 μm was produced during bright nitriding, and the formation and thickness of the compound layer were easily controlled in this continuous short nitriding process. The produced hardened case after the first nitriding stage was mainly composed by polyphase of α/Fe4N, in comparison to the conventional Fe2N3/Fe4N of compound layer, formed along the new pearlite laminae, resulting in significantly improved surface hardness and corrosion resistance.

A novel anti-adhesive NC/WC:C surface processing is presented enabling green machining of ductile materials at elevated temperatures. The duplex coatings are produced by the active screen plasma nitrocarburising followed by physical vapour WC:C deposition. Microstructure analysis showed that duplex NC/WC:C system is composed by a nanolayered low adhesive WC:C coating and an extra load-bearing NC hardened case, obtaining favourable frictional properties at elevated temperatures. The coefficient of friction of duplex coating NC/WC:C was significantly lower compared to sole WC:C coating or untreated surfaces, and as demonstrated, depending on the testing temperature non-linearly, including an ultra-low adhesion at 350 °C. Furthermore, the quantified adhesion rate is clearly correlated with the nanomechanical properties especially the elastic parameters.

A molybdenum alloy (TZM: 0.50 wt% titanium, 0.08 wt% zirconium and 0.02 wt% carbon with balanced molybdenum) was used to investigate its response to plasma nitriding in terms of layer formation and hardening at temperatures between 500 and 760 °C using various times. A thin hard nitride case plus a shallow diffusion zone was formed after plasma nitriding. The thickness of nitride layer increased with the treatment temperature and time. The nitrided surface of molybdenum alloy had a low coefficient of friction against the Al2O3 counterpart ball at ambient atmosphere and elevated temperatures, and the wear resistance of the surface was greatly improved. Molybdenum had a tendency to react with nitrogen to form a mixed nitride phases at the tested temperature range, and the TZM alloy had an activation energy of 330 kJ/mol.

Active screen plasma nitriding (ASPN), a novel surface modification process, has been widely applied to improve various surface properties of austenitic stainless steels, such as wear resistance, electrical conductivity and corrosion resistance. All the improvement of surface properties attributes to the formation of a unique phase under low nitriding temperature, called S-phase. A “sputter – deposit – decompose –diffusion model” has been established to explain the formation of S-phase, however, the mechanism of nitrogen mass transfer to the substrate during ASPN still remains controversial. By comprehensively comparing the surface responds of three different surfaces (bare 316L stainless steel surface, Au-coated 316L stainless steel surface and Si wafer surface) during ASPN treatments, this paper provides the direct evidence and clarifies the mechanism of nitrogen mass transfer between the deposition layer and the substrate during ASPN treatment.

Adhesion between blank and die is the main reason for seizure and short tooling life during metal forming processes at elevated temperatures. This study applied novel complex-structured composite coatings, NC/NiBN and NC/WC:C, to the hot forming die flange and radius to reduce the use of lubricant. The high-temperature adhesion resistance and hot forming properties of the hybrid coated dies were tested and correlated with the microstructure and mechanical properties of the contacted blank/tool surfaces. The results show that the coated dies experienced little adhesion at elevated temperatures, consequently, ultra-low coefficients of friction of 0.11 against steel and 0.10 against Al at 350 °C were obtained. The minimum weight of lubricant per unit area required for a successful deep drawing of AA6082 was quantified by hot forming tests at various temperatures, and it was reduced by 83% at 400 °C. Complete lubricant-free deep drawing was achieved with limited blankholding force and forming temperature. Based on this experimental data and theoretical analysis of two disparate stress states, a model comparing the frictional state of material surfaces using the geometric features on formed parts is proposed.

The extraordinary mechanical and anti-corrosion properties of graphene call for facile fabrication of graphene-based coatings with high uniformity and in large area. This research was aimed at exploring the use of an electro-brush plating technique for the production of graphene-metal nano-composite coatings. Graphene oxide (GO) was introduced into the nickel plating solution at varied concentrations and composite coatings were fabricated on stainless steel surfaces by brush plating under the same conditions. The morphology and microstructure of the obtained Ni-GO composite coatings were fully characterised and compared with neat Ni coating. The results confirm that GO sheets have been incorporated into the nickel matrix homogeneously, leading to a considerably reduced average crystallite size. Nanoindentation measurements demonstrated that GO can not only improve the hardness and reduce the plasticity of the composite matrix, but also enhance the thermal stability of the composite coating effectively. It has also been revealed by polarisation and electrochemical impedance spectroscopy (EIS) analysis that GO can increase the corrosion resistance of the composite coating owing to its barrier effect. However, it was also noticed that excessive GO content resulted in a degradation of both mechanical and corrosion properties, likely due to a more defective microstructure.

It is well-known that biologically active Ag/Cu ions are strong bactericides and silver or copper nanoparticles have been used in polymer-based antibacterial coatings. However, their poor durability has limited their use in tribological applications. This problem has been largely addressed recently by developing novel plasma co-alloying of austenitic stainless steel surfaces with both nitrogen and Ag/Cu to form wear resistant antibacterial S-phase. However, this technology is only applicable to austenitic stainless steel as the S-phase cannot be formed to other materials. In this study, S-phase based anti-bacterial coatings have been, for the first time, developed using magnetron sputtering through co-deposition of austenitic stainless steel with Ag/Cu to form hard S-phase doped with Ag, Cu or both in monolayer and multilayer structures. These coatings were fully characterised using multiple techniques such as SEM, TEM, XRD, GDOES and anti-bacterial tests. It has been found that it is possible to produce dense Ag and Cu doped S-phase layer with significant anti-bacterial efficacy. This was achieved while preserving the advantageous properties of the S-phase microstructure. As opposed to the popular diffusion based S-phase production such as plasma nitriding, this technology can also be applied on all kinds of surfaces, including low-cost steel surfaces, polymers and ceramics.

In this study, hydrostatic compressive stresses are applied on the prior-carburized samples of 316 ASS to discover the relationship between interstitial diffusion process and the applied stresses. Carbon diffusion profiles are compared and concentration dependent diffusion coefficients are discussed to further advance scientific understanding of diffusion process in supersaturated S-phase. The experimental results demonstrate that the applied compressive stress can retard the fast diffusion process comparing to the unstressed one. Based on theoretical modelling, the effect of the applied hydrostatic compressive stresses on the diffusion of carbon in carbon supersaturated 316 austenitic stainless steel is discussed.

Antibacterial textures provide an attractive solution to the problem of cross contamination of foods and healthcare-acquired infections that regularly affect the food and medical industries. However, the functional properties associated with such textures typically arise due to fragile nanoscale features, and unfortunately, there is almost no information available on the longevity of those features or the properties that they bring. Therefore, this study has examined the antibacterial durability of state-of-the-art triangular LIPSS produced using femtosecond pulsed laser texturing on untreated and S phase hardened AISI 316L austenitic stainless steel surfaces. Prior to wearing, the triangular LIPSS were found to have strong antibacterial properties against S. aureus (>90% reduction) and E. coli (>75% reduction). Following large area wearing, the untreated and textured surfaces became dramatically more susceptible (>50% increase) to bacterial colonisation, while almost no change was found on S phase hardened samples (

In this work, the development of a duplex nitriding (DN) surface treatment combining High Temperature Gas Nitriding (HTGN) and Low Temperature Plasma Nitriding (LTPN) is reported. The microstructure and hardness variation of the duplex treated steel is compared with the properties obtained during single HTGN and single LTPN of UNS S31803 stainless steel. Single LTPN of UNS S31803 was carried out in an Active Screen Plasma Nitriding reactor, at 400 °C for 20 h, in a 75% N2 + 25% H2 atmosphere. Single HTGN of UNS S31803 was carried out at 1200 °C, under a 0.1 MPa high purity N2 gas atmosphere, during 8 h. The developed duplex nitriding (DN) surface treatment consists of a combination of both, HTGN and LTPN treatments, carried out in the same conditions described above. The microstructure of the as received material was composed by ferrite and austenitic stringers, aligned in the rolling direction. The results showed that LTPN of the UNS S31803 duplex stainless steel promotes the formation of a duplex modulated structure composed by 2.5 μm thick, 1510 ± 52 HV hard, expanded ferrite (αN) regions, and 3.0 μm thick, 1360 ± 81 HV hard, expanded austenite (γN) regions on ferrite and austenite grains, respectively. Intense coherent e-Fe3N nitride precipitation inside expanded ferrite was observed. e-Fe3N nitrides precipitated with an orientation relationship [111] αN//[120] e-Fe3N, leading to increased microhardness of the expanded ferrite regions. After the first step of the duplex nitriding treatment (HTGN) a 550 μm thick, 330 HV hard, nitrogen rich, fully austenitic layer formed at the surface of the specimens, by transformation of ferrite stringers into austenite. The second nitriding step (LTPN) led to the formation of a homogeneous expanded austenite layer, 1227 ± 78 HV on top of the thick fully austenitic layer, formed during the first step. The duplex treatment resulted in a more homogeneous, precipitate-free, microstructure and a better transition between the mechanical properties of the hardened outermost layer and the softer substrate.

In this study, an in-situ low temperature method to cost-effectively grow vertically aligned carbon nanotube (VACNT) films has been developed by combining advanced active screen plasma (ASP) technique with plasma enhanced chemical vapour deposition (PECVD). A novel active screen consisting of 316 stainless steel cylinder with double top lids was designed for the in-situ low-cost high-efficient preparation of catalyst films within a PECVD device, and VACNT films were grown from the catalyst films subsequently at low temperatures (≤ 500 °C). The deposited catalyst films and the VACNT films were characterised by SEM, AFM, XRD, Raman and TEM/EDS. The results show that the catalyst films consist of stainless steel nanoparticles with sizes around 50 nm. The growth of the CNTs is related to the PECVD temperature and the density of the CNTs is determined by the status of the catalyst films. The CNTs are multiwalled with nanoparticles at their tips. The mechanisms behind the in-situ low temperature synthesis are discussed based on the plasma physics, growth parameters and physical status of the catalyst films.

Due to its resistant to thermal shock and strength at elevated temperature, Titanium-Zirconium-Molybdenum (TZM) alloy is used for hot-work tooling up to 1500 °C. The friction and wear behaviour of the TZM alloy reciprocating against Al 2 O 3 and Si 3 N 4 in different conditions were investigated. It has an adhesion and/or oxidation character with a high coefficient of friction when dry sliding against an alumina ceramic ball. It is characterised with reduced wear in an abrasion mode when reciprocally sliding against a Si 3 N 4 ceramic ball. In addition, the friction and wear between TZM and an Al 2 O 3 ball under unidirectional sliding conditions can be reduced when lubricating molybdenum oxides was formed at higher temperature i.e. 600 °C. Finally, the friction and wear mechanisms involved are discussed.

A nitrided case composed of expanded martensite and small quantities of hexagonal e-Fe 24 N 10 iron nitrides was formed in a martensitic stainless steel by means of active screen plasma nitriding process. Nanoindentation tests were carried out in order to assess the mechanical properties and to obtain an energy dissipation coefficient defined as the ratio of plastic to total deformation energy. Friction coefficient, mechanical failure mode and critical load for damaging the nitrided case were determined using linear scratch tests performed at both linearly-increased normal force and constant normal force according to ASTM C1624 standard. The scratch test results showed that the groove features and the friction coefficient could be well correlated to the energy dissipation coefficient. The expanded martensite strongly decreased the friction coefficient in comparison to the non-nitrided martensitic stainless steel. The critical load was 14 N and tensile cracking was the mechanical failure mode of the nitrided case.

In-situ high temperature nanoscratching of Si(110) wafer under reduced oxygen condition was carried out for the first time using a Berkovich tip with a ramp load at low and high scratching speeds. Ex-situ Raman spectroscopy and AFM analysis were performed to characterize high pressure phase transformation, nanoscratch topography and nanoscratch hardness. No remnants of high pressure silicon phases were observed along all the nanoscratch residual tracks in high temperature nanoscratching, whereas in room temperature nanoscratching, phase transformation showed a significant dependence on the applied load and scratching speed i.e. the deformed volume inside the nanoscratch made at room temperature was comprised of Si-I, Si-XII and Si-III above different threshold loads at low and high scratching speeds. Further analysis through AFM measurements demonstrated that the scratch hardness and residual scratch morphologies i.e. scratch depth, scratch width and total pile-up heights are greatly affected by the wafer temperature and scratching speed.

316 stainless steel has been regarded as one of the promising candidates to replace graphite for bipolar plate application. However, the relatively high electrical resistance caused by the formation of passive oxide film and the insufficient corrosion resistance in long-term operation are two main concerns of 316 stainless steel bipolar plates. Low temperature active screen plasma alloying technology shows the ability to reduce electrical resistance and enhance corrosion resistance of 316 stainless steel bipolar plates to some extent, but still can not satisfy the Department of Energy (DOE) requirements. In this paper, active screen plasma co-alloying treatments with nitrogen and platinum are conducted to modify the surface of 316 stainless steel. The surface morphology, phase constitute, chemical composition and layer structure of treated 316 stainless steel are fully studied. A dense, columnar structured and single phase Pt3Fe deposition layer is produced on the surface of 316 stainless steel after treatments. Thanks to the excellent electrical conductivity and corrosion resistance of Pt3Fe, the surface electrical conductivity and corrosion resistance are greatly enhanced and satisfies the DOE requirements, contributing to the significant improvement of single cell performances.

In the present work, low temperature active screen plasma nitriding of a 17–4 PH precipitation-hardening stainless steel was investigated. The active screen technique has been used to avoid undesirable plasma concentration, edge effects and arching during D/C plasma nitriding. Solution treated (S) and Solution treated and aged (S + A) 17–4 PH stainless steel samples were Active Screen Plasma Nitrided (ASPN) for 20 h at low temperature (400 °C), in order to avoid undesirable precipitation of chromium nitrides. Formation of these nitrides impairs corrosion resistance of the stainless steel because they act as Cr sinks, reducing the overall amount of Cr available in the matrix. The main objective of this work was to characterize the effect of the starting conditions on the microstructure of the nitrided layers. Besides, the chemical gradients and hardness evolution during low-temperature, long term active screen plasma nitriding were also studied. A homogeneous nitrided layer was obtained along the entire surface after the nitriding process. Hardness measurements along the nitrided surface showed virtually constant hardness values, indicating that ASPN was effective to avoid edge effects. Moreover, the nitrided layer could not be etched by Villela reagent, suggesting that the corrosion resistance was not impaired. Nitrogen supersaturation after plasma nitriding was indicated for both starting conditions (S) and (S + A) by X-ray diffraction patterns, as the expanded martensite peaks were broadened and shifted to lower 2θ angles compared to the martensite peaks of the substrate. The nitrided layer of the (S + A) specimen was thicker (9.2 μm) than the nitrided layer of the (S) specimen (5.7 μm). Also, the maximum nitrogen content (measured by WDX) of the (S + A) specimen (3.7%) was greater than the maximum nitrogen content measured on the simply solution treated (S) specimen (1.9%). The difference in nitrogen pick-up was related to greater hardness values for the (S + A) specimens (max. Hardness 1130 HV0.01) in comparison with the (S) condition (max. hardness 950 HV0.01). The latter results were discussed in terms of the effect of Cu in the activity of Fe-N solid solutions. Thermo-Calc® simulations showed that when copper is in solid solution, it increases the nitrogen activity in iron-nitrogen alloys, decreasing the maximum nitrogen solubility in the steel. On the other hand, when copper is precipitated as nanoparticles in the matrix — as in the (S + A) condition — nitrogen activity decreases, implying a greater solubility of nitrogen. The substrate hardness after aging was not changed by the 400 °C/20 h nitriding treatment, indicating that the surface treatment can be carried out without affecting the bulk properties.

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 (γN) 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-eN) were seen in the γN-AG17 layer, that could be correlated to comparatively higher surface hardness and better wear resistance. Several slip/shear bands were also seen in the γN-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 γN-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 γN after nitriding at low-to-intermediate temperatures.

Airway respiratory epithelium forms a physical barrier through intercellular tight junctions, which prevents debris from passing through to the internal environment while ciliated epithelial cells expel particulate-trapping mucus up the airway. Polymeric solutions to loss of airway structure and integrity have been unable to fully restore functional epithelium. We hypothesized that plasma treatment of polymers would permit adsorption of α-helical peptides and that this would promote functional differentiation of airway epithelial cells. Five candidate plasma compositions are compared; Air, N2, H2, H2:N2 and Air:N2. X-ray photoelectron spectroscopy shows changes in at% N and C 1s peaks after plasma treatment while electron microscopy indicates successful adsorption of hydrogelating self-assembling fibres (hSAF) on all samples. Subsequently, adsorbed hSAFs support human nasal epithelial cell attachment and proliferation and induce differentiation at an air-liquid interface. Transepithelial measurements show that the cells form tight junctions and produce cilia beating at the normal expected frequency of 10-11 Hz after 28 days in culture. The synthetic peptide system described in this study offers potential superiority as an epithelial regeneration substrate over present “gold-standard” materials, such as collagen, as they are controllable and can be chemically functionalised to support a variety of in vivo environments. Using the hSAF peptides described here in combination with plasma-treated polymeric surfaces could offer a way of improving the functionality and integration of implantable polymers for aerodigestive tract reconstruction and regeneration.

A novel approach to produce a hard ceramic hard layer on the surface of Ti6Al4V alloy in a more efficient way was developed in this research. A thin layer of gold was pre-deposited on a Ti6Al4V alloy before ceramic conversion treatment (CCT), and the gold particles accelerated the thermal oxidation of Ti6Al4V alloy especially in the beginning period and produced a smoother and harder surface. Surface morphologies, microstructure and elemental compositions of the samples before and after treatment were characterised by SEM, EDX, and XRD. The role of the gold in the rapid oxidation and a potential mechanism have been elucidated. The mechanical properties of the surfaces were assessed by microhardness, scratch and reciprocating friction and wear tests. Fine dispersed gold nanoparticles and clusters in the oxide layer of the pre-deposited Ti6Al4V samples were found, and they had much better tribological properties in terms of reduced coefficient of friction and wear volume than those samples treated by conventional long duration thermal oxidation treatments without a pre-deposited gold layer. The anti-bacterial properties were improved significantly.

Catalyst layers play an important role in direct methanol fuel cells (DMFCs), providing the reaction sites and catalysing the electrochemical reactions. For gas diffusion electrodes with Pt nanowires in-situ grown on gas diffusion layers (GDLs), the hydrophobic property of the GDL surface negatively affects the growth of the Pt nanowire catalysts, leading to the unsatisfied catalysis performance. In this work, the influence of active screen plasma (ASP) treatment temperature and duration on the growth of Pt nanowire catalyst layer was systemically studied. Single cell performance test with in-situ electrochemical surface area (ECSA) measurement were conducted to evaluate the catalysis performance of the Pt nanowire catalyst layer grown on the ASP treated carbon paper; scanning electron microscopy (SEM) was used to observe the surface morphology of the catalyst layer formed. Results revealed that the ASP treatment conducted at 120 °C for 10 min can effectively promote the growth of Pt nanowires on carbon paper gas diffusion layer, which exhibited the best catalysis performance.

A transparent graphene oxide layer on a non-conductive poly(ethylene terephthalate) film was treated by a new active screen plasma technology at temperatures ranging from 100 °C to 200 °C in pure hydrogen and in a gas mixture of hydrogen and nitrogen. To study the thermal reducing effects of the active screen plasma, parallel thermal annealing treatments were also carried out at the same temperatures. UV–visible absorption spectra, X-ray diffraction, Raman spectroscopy, X-ray photoelectron spectroscopy (XPS) and electrical properties confirmed that the graphene oxide can be effectively reduced by the active screen plasma treatments. Detailed XPS quantitative analyses have revealed that the carboxylic groups are not stable, and their amount can be decreased effectively by the active screen plasma treatments. Only about one third of the carbonyl type C O can be reduced at the same time. In addition to the reduction, simultaneous multi-element doping of GO with nitrogen from the gas supply and with Fe, Cr and Mo from the stainless steel active screen was also detected by XPS.

In this study, we performed three surface modifications for AISI H13 steel to study their protective effects in 1023 K molten aluminum. Results showed that air oxidation can produce a thin film of Fe2O3 and little FeO, and the liquid-nitriding formed a surface of iron nitrides and oxides (Fe2O3 + Fe3O4). While liquid-nitriding with post-oxidation can form a surface of Fe3O4 and little Fe2O3 by oxidizing the nitrides into Fe3O4 on the liquid-nitriding samples. The Fe3O4 has low wettability and good chemical stability against molten aluminum, thus the corrosion behaviors of molten aluminum to the samples change from dissolution to oxidation.

The aim of this study has been to investigate the rolling contact behaviour of plasma nitrided and duplex treated (plasma nitrided and diamond-like carbon (DLC)) EN40B steel under overloading and intermittent lubricating conditions using the acoustic emission technique (AE). The signal amplitude and energy were monitored and related to cracking and delamination events observed from scanning electron micrographs. AE technique was found to be capable of detecting cracking and delamination on both surface treatments, proving to be a useful tool for monitoring rotating machinery condition effectively.

The enhanced performance of carbon nanotubes (CNTs) over carbon black as a catalyst support and the outstanding catalytic activities of one-dimensional (1D) Pt nanostructures endow them big potential for applications in fuel cells. However, the research has been mainly focused on the materials, and a combination of both 1D Pt nanostructures and CNTs to fabricate practical high power performance fuel cell electrodes still remains a challenge. In this work, we demonstrate catalyst electrodes from Pt nanorods grown on aligned nitrogen doped CNTs for proton exchange membrane fuel cell (PEMFC) applications. Short Pt nanorods are grown on CNTs deposited directly on 16 cm2 carbon paper gas diffusion layers (GDLs) via plasma enhanced chemical vapour deposition (PECVD) and nitrided using active screen plasma (ASP) treatment, which are directly employed as cathodes for H2/air PEMFCs. The thin open catalyst layer effectively enhances mass transfer performance and, with a less than half of the Pt loading, 1.23 fold power density is achieved as compared with that from commercial Pt/C catalysts. A better durability is also confirmed which can be attributed to the good structure stability of nanorods and the enhancement effects from the N-CNT support.

Quenched and tempered AISI 410 martensitic stainless steel specimens were active screen plasma nitrided in a mixture of 75% of nitrogen and 25% of hydrogen during 20 h at 400 °C. The microstructure of the nitrided case was characterized by optical microscopy, scanning electron microscopy and microhardness measurements. The phases were identified by X-ray diffraction and the nitrogen content as a function of depth was measured using wavelength dispersive X-ray spectrometer coupled to SEM. Nanoindentation tests were carried out in order to assess hardness ( H ), Young modulus ( E ), H / E and H 3 / E 2 ratios and the elastic recovery ( W e ) of the nitrided layer. Cavitation erosion tests were carried out according to ASTM G32 standard during 20 h, with periodical interruptions for registering the mass losses. Additional cavitation erosion tests were performed to identify the wear mechanisms in both specimens, through assessment of the evolution of the damage on the surface, in a scanning electron microscope. A ~28 µm thick, 1275 HV hard nitrided case formed at the surface of the martensitic stainless steel, composed of nitrogen supersaturated expanded martensite and hexagonal e-Fe 24 N 10 iron nitrides. The expanded martensite decreased 27 times the mass loss shown by the non-nitrided stainless steel and the erosion rate decreased from 2.56 mg/h to 0.085 mg/h. The increase in cavitation erosion resistance can be mainly attributed to the increase in hardness and to the elastic response of the expanded martensite. The non-nitrided specimen changed from initially ductile to brittle behavior, exhibiting two different modes of material detachment. The first mode was characterized by a great degree of plastic deformation, fatigue and ductile fracture. The second failure mode could be associated to brittle fracture by cleavage mechanisms. In contrast, the wear mechanism observed in the nitrided specimen was brittle fracture without evident plastic deformation.

The thermo-mechanical stability and oxidation behavior of S-phase are critical issues for some industrial applications at elevated temperatures owing to its metastable nature. In this study, the stability and oxidation behavior of carbon S-phase generated by plasma carburizing on AISI316 under both thermal and mechanical conditions was investigated for the first time. The experimental results demonstrate that when tested at a fixed temperature the thickness of the carbon S-phase layer increased with the stress applied to the tensile specimens during the thermo-mechanical stability tests. This indicates that tensile stress promotes the diffusion of carbon in the carbon-S-phase. The oxidation resistance of the carbon S-phase at 500 °C is inferior to untreated AISI 316, which further deteriorated under tensile stress. The lattice expansion and high density of crystal defects in the S-phase and the applied tensile stress would facilitate the diffusion of oxygen and iron, thus promoting oxidation.

Developing a fast-ageing treatment can significantly reduce the current processing time (180 °C × 9 h) of high strength AA6082 automotive components. In this study, a fast ageing treatment in supersaturated solid solution state was developed, such that the mechanical properties can be rapidly achieved after the paint bake (PB) treatment through introducing a pre-ageing (PA) treatment. The determined fast ageing method considered effects of temperature & time, heating rate and subsequent PB on the ageing response. Tensile tests and TEM observations of typical conditions were undertaken to examine evolved strength and precipitate distribution. Results showed that 210 °C was the optimum pre-ageing temperature as uniformly sized and distributed small precipitates were obtained. The final strength of about 280 MPa, that is 95% of the nominal strength for T6 temper, can be obtained within 15 min soaking for fast heating, and nearly this value for slow heating. More prolific nucleation occurred during slow heating, resulting in more finely distributed precipitates and a higher strengthening. It was observed that PB further increased the strength of over-aged alloy pre-aged at a high temperature of 240 °C. The subsequent PB enabled further nucleation of small clusters and growth of the pre-ageing-induced precipitates which were smaller than 20 nm. This resulted in an improvement in the material strength potentially to satisfy the safety requirements in automotive industry.

Hot form Quench (HFQ®) represents a leading-edge hot sheet stamping technology for manufacturing complex-shaped high strength aluminium alloy panel components. Transfer of sheet blank from the furnace to the press is the first crucial step in the process. This paper reports work in which the effects of the blank transfer on the deformation of material during pressing and on the final properties after ageing through thermal-mechanical testing and microstructural observations. Two aluminium alloys are investigated, 6082 and 7075. Hardness, quasi-static uniaxial tensile measurements and TEM microstructure observations provide evidence that post-treatment properties and the underlying microstructure are strongly influenced by the blank transfer step. Severe deterioration in the post-treatment strength was observed for blank transfer temperature, ranging from 250 °C to 400 °C. The temperature-time-property (TTP) diagrams showed that 350 °C was the most sensitive temperature that reduced the post-treatment strength by 45% within 10 s holding. As evidenced by TEM, typical coarse η and S precipitates at high temperatures were identified, which resulted in different post-treatment properties and hot deformation behavior. Finally, the results from HFQ® technology processed aluminium alloys 7075 and 6082 were compared with conventional TTP diagrams, enabling comparison with conventional scientific understanding of quenching effects.

Both modelling analyses and experimental work have recently confirmed that the failure of thin coatings on steel, especially under high loads for some demanding applications, is related to the lack of mechanical support from the substrate, which means that the exceptional hardness, toughness and wear resistance of state of the art PVD coatings cannot be fully exploited. To this end, two types of new duplex surface systems have been developed from this research: i) PVD (specifically Closed Field UnBalanced Magnetron Sputter Ion Plating, CFUBMSIP) CrAlN multilayer coating deposited on ex-situ, 20-h active-screen plasma nitrided (ASPN) steel samples, and ii) in-situ 3-h, high power medium frequency pulsed plasma nitriding (HPMFPPN) treatment, followed by a similar CrAlN coating, but performed in a serial, single batch process in an otherwise conventional CFUBMSIP equipment. The microstructures of these two duplex surface engineered systems were characterised using XRD and SEM, while their hardness, adhesion, load bearing capacity and tribological properties were compared by micro-hardness tests, scratch adhesion tests and pin-on-disc sliding wear measurements. Post-test examinations were conducted and the results confirmed that a hard coating on a nitrided substrate can fully exploit the advantages of both the nitrided sub-surfaces for increased load bearing capacity and of the PVD coating for increased hardness, high temperature stability and extreme wear resistance. Finally, the advantages and disadvantages of these two new duplex surface systems were compared and their potential applications were discussed.

Active screen plasma nitriding (ASPN) is a well-established technique used for the surface modification of materials, the result of which is often a product with enhanced functional performance. Here we report the modification of the chemical and mechanical properties of ultra-high molecular weight poly(ethylene) (UHMWPE) using 80:20 (v/v) N2/H2 ASPN, followed by growth of 3T3 fibroblasts on the treated and untreated polymer surfaces. ASPN-treated UHMWPE showed extensive fibroblast attachment within 3 h of seeding, whereas fibroblasts did not successfully attach to untreated UHMWPE. Fibroblast coated surfaces were maintained for up to 28 days, monitoring their metabolic activity and morphology throughout. The chemical properties of the ASPN-treated UHMWPE surface were studied using X-ray photoelectron spectroscopy, revealing the presence of C N, C N, and C N chemical bonds. The elastic modulus, surface topography, and adhesion properties of the ASPN-treated UHMWPE surface were studied over 28 days during sample storage under ambient conditions and during immersion in two commonly used cell culture media.

S-phase, or expanded austenite, is a corrosion resistant diffused hardened layer which can be created in austenitic stainless steels and cobalt–chromium(Co-Cr) alloys. It is a precipitate-free metastable supersaturated solid solution of nitrogen or carbon or both. S-phase layers formed on biomedical grade austenitic stainless steels have demonstrated significantly enhanced in-vitro wear and corrosion properties. To date, all these tribo-corrosion studies on S-phase treated alloys were conducted using an alumina or tungsten carbide ball as the counterface material. Testing S-phase against S-phase is both scientifically interesting and technologically important in view of their potential applications for the articulating surfaces of metal-on-metal joint prostheses. In this work, biomedical grade 316LVM and High-N stainless steel discs together with AISI 316 balls were low temperature plasma surface alloyed with: nitrogen (nitriding); carbon (carburising); and both carbon and nitrogen (carbonitriding). The S-phase layers created by these treatments were in-vitro corrosion–wear tested in Ringer’s solution using an S-phase engineered ball reciprocating against an S-phase engineered disc. In addition, self-mated tribopairs of untreated stainless steel and Co–Cr alloy were used as benchmarks. The results demonstrate that the self-mated S-phase tribopairs can produce a marked decrease in material loss when compared to self-mated untreated stainless steel tribopairs. This is partially because of significantly increased surface hardness and thus an enhanced mechanical support for the surface oxide film. The combined wear loss of the S-phase stainless steel tribopairs was close to that of the benchmark Co–Cr tribopair. It can be concluded from this work that S-phase surface engineering can effectively combat scuffing or seizure of biomedical austenitic stainless steels when self mated. Therefore S-phase hardened austenitic stainless steels could compete against more expensive alloys such as Co–Cr alloys in metal-on-metal wear applications in the biomedical industry., peer-reviewed

Nanomechanical testing (nano-impact and nanoindentation mapping) has been carried out on the top surfaces of as-received and aged 8 wt.% yttria stabilised zirconia (YSZ) thermal barrier coatings (TBCs) produced by electron-beam physical vapour deposition (EB-PVD). The correlation between the nanomechanical test results and the previously reported erosion resistance of the TBCs has been investigated. The experimental results revealed that aged TBCs on zirconia for 24 h at 1500 °C or on alumina for 100 h at 1100 °C resulted in large increases in their hardness ( H ), modulus ( E ), H/E and H 3 /E 2 ratios but their erosion resistance was reduced. Nano-impact tests showed a dramatic decrease in impact resistance following the ageing of these TBCs, which is consistent with the erosion results. The strong correlation between the nano-impact and erosion resistances has confirmed the premise that rapid laboratory impact tests must produce deformation with similar contact footprint to that produced in the erosion tests.

In order to improve the surface properties of polyurethane (PU), samples of polyurethane have been surface modified using a newly developed active screen plasma modification (ASPM) technique. The change in the surface topography was investigated by profilometry, atomic force microscopy (AFM) and scanning electron microscopy (SEM); the chemical composition and bonding structure of the plasma modified PU surface were characterized by X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared spectroscopy (FTIR); and the wettability of the modified surface was studied by contact angle and surface energy was calculated. The results show that the ASPM technique not only can effectively alter the surface topography of polyurethane from a closed cell structure to porous open structure but also result in transformation of ester groups into new O H groups in the top surface layer. The changes of surface topography, structure and chemical composition by plasma treatment have also effectively modified the wettability of the polyurethane surface.

Low temperature plasma carburising (LTPC) has been increasingly accepted as a hardening process for austenitic stainless steels because it produces a good combination of tribological and corrosion properties. The hardening mechanism is based on the supersaturation of the austenitic structure with carbon, which greatly hardens the material, significantly expands the fcc unit cell, produces high levels of compressive residual stresses and, ultimately, leads to the occurrence of deformation bands and rotation of the crystal lattice. The microstructural changes introduced during plasma carburising have a significant impact on the mechanical, tribological and corrosion performance and, for this reason, the microstructure of expanded austenite or S-phase has been extensively studied. However, modern surface characterisation techniques could provide new insights into the formation mechanism of S-phase layers. In this work, backscattered electron diffraction and atomic force microscopy were used to characterise the surface layers of expanded austenite produced by LTPC in an active screen furnace. Based on the experimental results, the plastic deformation, its dependence on crystallographic orientation, the evolution of grain boundaries, and their effects on mechanical, tribological and corrosion properties are discussed.

Low-temperature plasma carburizing of austenitic stainless steel can produce a carbon-supersaturated austenite layer, the “S-phase”, on the surface, which has high hardness, excellent wear and fatigue properties, and good corrosion resistance. Although the S-phase was discovered some years ago, the basic understanding of S-phase formation remains incomplete. In this paper, the effect of tensile stresses (0–80 MPa) on the formation and stability of S-phase during carburizing of 316L stainless steel foils at 400, 425 and 450 °C for 10 h has been investigated for the first time. The microstructures were characterized by X-ray diffraction, scanning electron microscopy and transmission electron microscopy and the mechanical properties were evaluated by microhardness and tensile tests. The results showed that the in situ applied tensile stress effectively thickened S-phase layers. The calculated activation energy for carbon diffusion in 316L was reduced from 142.76 to 133.91 kJ mol −1 when a tensile stress of 40 MPa was applied. However, chromium carbides were formed in the outmost surface when the tensile stress exceeded 40 MPa. The results are discussed and explained through appropriate thermodynamic calculations.

W-containing carbon coatings were deposited on plain carbon steel and titanium substrates by Combined Magnetron Sputtering and Ion Implantation (CMSII) technique. A target made of fine grain graphite with cylindrical tungsten pins mounted in the area of maximum sputtering rate was used. High voltage pulses (− 30 kV, 20 μs, and 25 Hz) were superposed over the DC bias. By adjusting the processing parameters nanocomposite nc-WC1 − x/a-C coatings with a W content from 20 to 45 at.%, with a hardness of 12–22 GPa and a friction coefficient in the range of 0.12–0.22 were produced. These coatings have a thickness of 10–13 μm, good wear resistance and a good thermal stability up to 673 K.

Antibacterial surface modification of biomedical materials has evolved as a potentially effective method for preventing bacterial proliferation on the surfaces of devices. However, thin antibacterial coatings or modified layers can be easily worn down when interacting with other surfaces in relative motion, thus leading to a low durability of the antibacterial surface. To this end, novel biomaterial surfaces with antibacterial Ag agents and a wear-resistant S-phase have been generated on stainless steel by duplex plasma silvering–nitriding techniques for application to load-bearing medical devices. The chemical composition, microstructure, surface topography, roughness and wettability of SS surfaces were characterised using glow discharge optical emission spectroscopy, energy-dispersive spectroscopy/wavelength dispersive spectrometry (WDS), X-ray diffraction, atomic force microscopy and a contact angle goniometer. Optimal surface design for high antimicrobial activity and prolonged durability has been achieved, as evidenced by rapid bacterial killing rates (within 6 h), an ultra hard matrix (875 ± 25 Hv), high load-bearing capacity (critical load 37 N) and excellent wear resistance (wear rate 4.9 × 10 −6 mm 3 m −1 ). Ag embedded in the hard substrate of fcc compounds M 4 N (M = Fe, Cr, Ag, etc.) and the expanded fcc nitrogen S-phase shows deep infiltration of 6 ± 1 μm, and provides bactericidal activity against both Gram-negative Escherichia coli NCTC 10418 and Gram-positive Staphylococcus epidermidis NCTC 11047 of over 97% and 90%, respectively, within 6 h. The presence of silver in the surface before and after scratching under a progressive load applied up to 60 N using a diamond stylus was confirmed by WDS.

Plasma electrolytic oxidation (PEO) is a specialised but well-developed process which has found applications in aerospace, oil/gas, textile, chemical, electrical and biomedical sectors. A novel range of coatings having technologically attractive physical and chemical properties (e.g. wear- and corrosion-resistance) can be produced by suitable control of the electrolyte as well as electrical parameters of the PEO process. Oxide ceramic films, 3 to 40 μm thick, were produced on 6082 aluminium alloy by DC PEO using 5 to 20 A/dm 2 current density in KOH electrolyte with varied concentration (0.5 to 2.0 g/l). Phase analysis (composition and crystallite size) was carried out using X-ray diffraction and TEM techniques. Residual stresses associated with the crystalline coating phase (α-Al 2 O 3 ) were evaluated using the X-ray diffraction Sin 2 ψ method. Nanoindentation studies were conducted to evaluate the hardness and elastic modulus. SEM, SPM and TEM techniques were utilised to study surface as well as cross-sectional morphology and nano features of the PEO coatings. Correlations between internal stress and coating thickness, surface morphology and phase composition are discussed. It was found that, depending on the current density and electrolyte concentration used, internal direct and shear stresses in DC PEO alumina coatings ranged from − 302 ± 19 MPa to − 714 ± 22 MPa and − 25 ± 12 MPa to − 345 ± 27 MPa, respectively. Regimes of PEO treatment favourable for the production of thicker coatings with minimal stress level, dense morphology and relatively high content of α-Al 2 O 3 phase are identified.