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ZnMg coatings can be considered as a potential candidate to protect steel car bodies from corrosion and degradation. However, single layer ZnMg coated steels suffer from the poor adhesion due to the presence of brittle Zn-Mg intermetallic phases in the coating. The insertion of a more ductile Zn layer as an intermediate layer between the steel substrate and the ZnMg layer turns up to improve the adhesion performance, considerably. In the present study, the effect of annealing treatments on the microstructure and adhesion strength of a ZnMg-Zn bi-layered coating have been investigated. The results indicate that the thickness of the Zn interlayer reduces with increasing the annealing time at a certain temperature. This can be related to the diffusion of Zn atoms from the interlayer towards the top ZnMg layer. The diffusion of elements across the interface promotes phase transformations in the ZnMg top layer. Such transformations can be controlled to enhance the adhesion performance. However, prolonged annealing can lead to the complete dissolution of the Zn interlayer and the formation of undesirable Fe-Zn intermetallic compounds, resulting in the adhesion drop. The diffusion phenomenon in ZnMg-Zn system has also been simulated to follow the mechanisms of phase transformations.

For many years zinc coatings have been regarded as one of the most effective corrosion protective coatings for steel. Recently, it has been shown that the addition of even small amounts of magnesium to the zinc coating can noticeably increase its corrosion protection performance. However, poor adhesion of ZnMg coatings to advanced high-strength steels is observed. The addition of a more ductile Zn interlayer between the steel substrate and ZnMg coating is a solution to improve the adhesion. In the present study, a series of ZnMg-Zn bi-layered coatings with different Mg concentrations (up to 14.1 wt.% Mg) and also different thicknesses of the Zn and ZnMg layers were prepared by a thermal evaporation process to investigate the adhesion performance/interfacial adhesion strength. The adhesion performance of the coatings was qualified by the BMW crash adhesion test (BMW AA-M223), while the interfacial adhesion strength at the ZnMg/Zn interface was quantified by scratch test. It is found that the interfacial adhesion strength decreases gradually with increasing the Mg content of the top layer. The novel finding is that the interfacial adhesion strength at the ZnMg/Zn interface is independent of the thickness of the Zn interlayer. However, the adhesion performance of a ZnMg-Zn bi-layered coating during bending test is a complex function of different parameters such as the thickness of Zn and ZnMg layers, interfacial adhesion strength and interfacial defects density.

A method for producing a porous metallic structure comprising a metal element from a metal salt comprising a cation part and an anion part, comprising the steps of: providing a volume of metal salt; exposing the volume of metal salt in an atmosphere comprising a reduction gas at a temperature below a melting temperature of the metal element, leading to converting the volume of metal salt into the porous metallic structure by removing the anion part using the reduction gas; wherein the porous metallic structure has a pore size between 1 nanometer and 50 micrometer, and a ligament size between 1 nanometer and 50 micrometer; wherein the ligament size is controlled by the temperature during the exposing.

Zinc coatings have been used for centuries to protect steel substrates from corrosion and degradation. Recently, it has been reported that the addition of alloying elements such as Mg can improve the corrosion resistance of zinc coatings to a great extent. Although the addition of Mg is beneficial for corrosion resistance, it reduces the adhesion of the coatings to steel substrates. Different strategies can be utilized to improve the adhesion of ZnMg coating to steels such as the insertion of a ductile metallic interlayer and/or modification of the chemical composition. Annealing treatment can also be considered as a potential solution to improve the adhesion strength through the diffusion of elements across the interface. In the present study, the effect of annealing treatment on the adhesion strength and the corrosion resistance of physical vapor deposited ZnMg-Zn coating has been investigated. The results indicate that the annealing treatment is able to modify the nanocrystalline microstructure of the as-deposited coating and enhance the adhesion strength and corrosion properties, simultaneously.

For many years zinc coatings have been regarded as one of the most effective corrosion protective coatings for steel. Recently, it has been shown that the addition of even small amounts of magnesium to the zinc coating can noticeably increase its corrosion protection performance. However, poor adhesion of ZnMg coatings to advanced high-strength steels is observed. The addition of a more ductile Zn interlayer between the steel substrate and ZnMg coating is a solution to improve the adhesion. In the present study, a series of ZnMg-Zn bi-layered coatings with different Mg concentrations (up to 14.1 wt.% Mg) and also different thicknesses of the Zn and ZnMg layers were prepared by a thermal evaporation process to investigate the adhesion performance/interfacial adhesion strength. The adhesion performance of the coatings was qualified by the BMW crash adhesion test (BMW AA-M223), while the interfacial adhesion strength at the ZnMg/Zn interface was quantified by scratch test. It is found that the interfacial adhesion strength decreases gradually with increasing the Mg content of the top layer. The novel finding is that the interfacial adhesion strength at the ZnMg/Zn interface is independent of the thickness of the Zn interlayer. However, the adhesion performance of a ZnMg-Zn bi-layered coating during bending test is a complex function of different parameters such as the thickness of Zn and ZnMg layers, interfacial adhesion strength and interfacial defects density.

Layered transition metal dichalcogenides (TMD) such as WS2 are materials well-known for their solid lubrication properties in vacuum [1]. However, their lubricating property degrades through oxidation in moisture. In addition the material is limited by its low hardness and low load-bearing capacity particularly in high temperature applications. WS2/a-C nanocomposite coatings, namely WS2 lamellae embedded in amorphous diamond-like carbon (DLC) matrix, are reported having excellent tribological characteristics with both low coefficient of friction (CoF) and low wear rate and also imparting environmental robustness [2-4]. WS2/DLC nanocomposite coatings are produced by magnetron co-sputtering WS2 and graphite targets. Surface chemistry, structure and mechanical properties of these coatings reversibly change with applied load and environment, providing the best wear protection and self-healing capability. The coating microstructure and self-adaptive and self-healing triboactivity are scrutinized by microscopy (SEM, FIB and EF/HR-TEM), spectroscopy (GIXRD, micro-Raman and XPS) and pin-on-disc tribotests (varied in dry air to humid air, room temperature to 500 ℃). Experimental observations show that the CoF falls to 0.02 in dry air and reaches 0.10 in humid environment, and reverses as testing atmosphere cycled from dry to humid air, while the CoF can even remain at 0.02 with temperature rising from 100 to 500 ℃. The excellent tribological properties are attributed to the formation of a thin WS2 film on the top of the wear track of the coating and on the counterpart surface, which yields self-healing mechanism on damage. WS2/a-C coatings exhibit favorable self-adaptation and self-healing over a wide range of humidities and temperatures, and thus potentials for tribo-applications in diverse environmental and loading conditions.

Calcium phosphate (Ca-P) ceramics coated on titanium is extensively used in orthopedic implants. This is attributed to the advantages of titanium offering desirable mechanical properties and to the biocompatibility of Ca-P ceramics. Ca-P compounds have excellent biocompatibility due to their compositional similarity to natural bone mineral and exhibit a surface chemistry that promotes the formation of bone-like hydroxyapatite on its surface. Electrochemical deposition (ECD) is the most frequently used technique to produce Ca-P coatings. The parameters of electrochemical deposition significantly affect the thickness, chemical composition, and morphology of the deposited coating. The morphology of the deposited coatings is a critical issue since it strongly influences the interaction with tissue cells. The present work has studied the influence of deposition time (1, 2, 3, 5, and 30 min) on the thickness and the morphology of the deposited coatings by ion milling system and scanning electron microscopy (SEM), respectively. Tissue compatibility is investigated by assessing the interactions of bone-like SaOs cells with the Ca-P surface coatings; the cells’ behaviour was observed via SEM and fluorescence microscopy using immunostaining after 2 days and 7 days culture. At lower deposition time a smooth coating with minimum roughness deposited. By increasing the deposition time the surface roughness increases as well. Different morphologies with different roughness significantly affected the cellular behaviour. SaOs cells can grow and adhere to the smooth coating very well and displaying high spreading area. While, on the rough coatings cells appeared less viable and many rounded cells were observed.

Resistance spot welding is the most predominant joining method in automotive industries. Typically a car body structure contains 4000~5000 spot welds and the safety of vehicles is to a large extent determined by the property of resistance spot welds that assemble all steel components together. Unfortunately, advanced high strength steels are known to be more susceptible to weld metal failure of resistance spot welds than other conventional mild steels. A resistance spot weld exhibits a complex and non-homogenous microstructure with a very strong gradient of mechanical response and microstructural characteristics from one zone to another. Ultra-fast heating and cooling rate imposed by spot welding process make it nearly impossible to ex-situ simulation of the thermal cycle using thermal-mechanical testing methods such as Gleeble to evaluate the local mechanical properties of different zones. This work focuses on the application of micro-scaled fracture tests to measure the fracture toughness of different welding zones for spot welded dual phase steels. Focused ion beam milling was used to fabricate notched micro-sized cantilevers. Due to large plastic deformation associated with the micro-cantilever bending, linear elastic fracture mechanics was inapplicable. J-integral testing was performed at the microscale to apply elastic-plastic fracture mechanics that require a detailed knowledge of crack extension. Therefore, cyclic loading was applied to determine the crack length and critical J value. It was found that the method is useful for the comparative study of the fracture toughness at different welding zones to the accurate correlation between welding parameters, microstructure and mechanical performance.

This invited presentation reports an experimental approach to deposit flexible diamond-like carbon (DLC) films on rubber seals with plasma assisted chemical vapor deposition and an analytical model to describe the self-segmentation mechanism of the DLC films. By making use of the substantial thermal expansion mismatch between the DLC films and the rubber substrates, a dense network of cracks forms in the DLC films and contributes to flexibility. The size of the micro-segments can be controlled by tuning the temperature variation of the substrate during deposition through varying the substrate bias voltage. The formation mechanism of the crack network and its effect on the flexibility of DLC films coated on rubbers are presented. The influence of the size of DLC film microsegments on the frictional performance is further studied. The effect of viscoelasticity of the rubber substrate on the frictional behavior of the DLC film-coated system is scrutinized by tribo-tests and theoretical analysis. The importance of adhesive and hysteresis contributions to friction is revealed, and an overarching model is presented.

We report a new approach for the synthesis of three-dimensional nanoporous metals as binder-free current collectors for batteries. A versatile template-free method is presented which is based on the thermal treatment of metallic salts. The method involves thermal decomposition, hydrogen reduction of metallic precursors, and clusters nucleation and ligament growth. Topological disordered porous metal structures with controllable distribution of pore size and ligaments size ranging from tens nanometers to micrometers are controlled by varying the heating temperature and duration. The synthesis process has been scrutinized through XRD, SEM and TEM. The formation mechanism of nanoporous metals is qualitatively explained. As an application, the as-prepared nanoporous Ni is used as binder-free current collectors for nickel oxalates anodes. The newly designed electrodes with loading of nickel oxalates deliver excellent reversible capacities, good cycling performances and rate performances as anodes for lithium-ion batteries. It is anticipated that the synthesis method has versatility not only because it is suitable for different types of metallic salt precursors but also for synthesizing various metals and alloys such as Ni-Co alloys.

TiO2 is widely studied for its good photocatalysis activity. In this research, CO2 gas was used as carbon and oxygen source to prepare carbon-doped TiO2 (C-TiO2) films on stainless steel using reactive magnetron sputtering. In order to grasp the relationship between sputtering process, microstructure and mechanical and photocatalysis properties of C-TiO2 thin film, orthogonal experiment design combining related mechanical analysis and photo-degradation experiment was employed to find a set of optimal reactive sputtering parameters, including substrate temperature, sputtering power and CO2 gas flow rate. Nano-indentation and nano-scratch tests were employed to analyze the hardness, modules and adhesion strength of as-deposited C-TiO2 films, respectively. Taking hardness, modules and adhesion between the film and substrate as a reference of integrated mechanical properties, range analysis of as-prepared C:Ti-O films were done to search the optimal combination of sputtering parameters. The photocatalytic activities of as-prepared C-TiO2 films using methyl orange (MO) as colored dye indicator were also evaluated by measuring absorbance and calculating the MO’s decolorization rate under different UV light irradiation time. The result of photocatalysis experiment compared with a blank group proved that at the optimized reactive sputtering condition C-TiO2 films can achieve both good photocatalysis and mechanical property.

Layered transition metal dichalcogenides (TMD) such as WS2 are materials well-known for their solid lubrication properties in vacuum [1]. However, the lubricating property degrades through oxidation in moisture and it is also limited by its low hardness and low load-bearing capacity. The nanocomposite WSxC coating, namely WS2 lamellae embedded in an amorphous diamond-like carbon (DLC) matrix, is reported to have excellent tribological characteristics, with both low coefficient of friction and low wear rate in a wide range of humidities [2]. One important issue possibly impairing magnetron sputtering high-quality TMD layers is that the WSxC coating is usually substoichiometric, with x

Dynamic roughening is a common phenomenon observed in plasma processing of materials, including both film deposition and plasma etching. That is to say, the roughness of a growing/etching interface becomes higher and higher with the processing time or the film thickness/etching depth. In film growth, the competition between interface roughening and smoothening essentially determines the nano-/microstructure and consequently the properties of a deposited film. This lecture presents several new findings on the breakdown of dynamic roughening in thin film growth. With increasing energy flux of concurrent ion impingement during pulsed DC magnetron (reactively) sputtering, a transition from dynamic roughening to dynamic smoothening is observed in the growth behavior of TiC/a-C(:H) nanocomposite films. The nanocomposite films show a negative growth exponent and ultra-smoothness (RMS roughness ~0.2 nm at film thickness of 1.5 µm). Based on high resolution cross-sectional transmission electron microscopy observations, an amorphous front layer ~2 nm thick covers the nanocomposite film during growth and suppresses the influence of nanocrystallites on the roughness evolution of the nanocomposite films, which is a solid experimental proof of the impact-induced downhill flow model [1] and subplantation model [2]. We were able to predict the evolution of surface roughness based on a linear equation of surface growth which contains two diffusivity parameters that control the atomic mobility along the growing outer surface. The model is in good agreement with atomic force microscopy measurements of roughness evolution [3-6]. The result indicates a general solution of microstructure control in the deposition of thin films with (reactively) sputtering.

A graded high-vanadium alloy composite coating was synthesized from premixed powders (V, Cr, Ti, Mo, Nb) on ductile iron (DI) substrate via atmospheric plasma surface alloying process. The resulted cross-section microstructure is divided into three distinct zones: upper alloyed zone (AZ) rich with spherical primary carbides, middle melted zone (MZ) with fine white iron structure and lower heat affected zone (HAZ). Spherical or bulk-like primary carbides with diameter < 1 μm in the AZ are formed via in-situ reactions between alloy powders and graphites in DI. Microstructural characterizations indicate that the carbides are primarily MC-type (M=V, Ti, Nb) carbides combined with mixed hard-phases such as M2C, M7C3, M23C6, and martensite. Disperse distribution of spherical, submicro-sized metal carbides in an austenite /ledeburite matrix render the graded coating hard-yet-tough. The maximum microhardness of the upper alloyed zone is 950 HV0.2, which is 5 times that of the substrate. Significant plastic deformation with no cracking in the micro-indentations points to a high toughness. The graded high-vanadium alloy composite coating exhibits superior tribological performance in comparison to Mn13 steel and PTA-remelted DI.

Two welding schemes of single and double pulse were used for the resistance spot welding of DP1000 dual phase steel. The changes in the mechanical performance and variant pairing of martensite under two different welding conditions were scrutinized. It is demonstrated that, although both welds fail in pull-out failure mode, double pulse welding enhances cross-tension strength and energy absorption capability of the weld compared to single pulse welding process. Double pulse welding effectively changes the microstructure of the fusion zone. While the fusion zone of single pulse welds has a typical microstructure of columnar grains, the initial fusion zone of double pulse welds is subdivided into two zones: the outer recrystallized layer composing of martensitic microstructure formed within the equiaxed prior austenite grains, and the inner part of columnar grains resulted from the rapid solidification process of resistance spot welding. Orientation imaging microscopy results show that the recrystallized layer of double pulse welds exhibits a lower fraction of high angle grain boundaries and coarse structure of Bain groups. The coarse grained heat affected zone of double pulse welds has a higher fraction of high angle grain boundaries and finer structure of prior austenite grains and Bain groups compared to that of the single pulse welds.

Layered transition metal dichalcogenides (TMD) such as WS2 are materials well-known for their solid lubrication properties [1]. However, the lubricating property degrades through oxidation or moisture and it is also limited by its low hardness and low load-bearing capacity. In contrast amorphous diamond-like carbon (DLC) films are reported to have many features that contribute to excellent tribological characteristics, such as high hardness, anti-wear property with both low friction coefficient and low wear rate[2]. The present research aims at depositing WS2/a-C nanocomposite coatings by magnetron co-sputtering method. The effects of carbon content and argon flow rate on the microstructure and mechanical performance were investigated. The WS2/a-C nanocomposite tribocoating was scrutinized by electron microscopy and mechanical testing. Transmission electron microscopy reveals feathery WS2 platelets, randomly distributed in the amorphous carbon matrix. The nanocomposite coating turns out to be more amorphous-like with increasing carbon content. Nanoindentations tests show that the hardness and elastic modulus of the coating increase with increasing carbon addition while decreasing with a higher argon flow from 10 sccm to 25 sccm. Ball-on-disk tribotests (100Cr6 steel ball as a counterpart) show that the coefficient of friction can be as low as 0.017 in a dry environment (5% relative humidity). It reaches 0.15 in a high humidity surrounding and remains stable within 20000 sliding cycles.

Layered transition metal dichalcogenides (TMD) such as WS2 are well-known materials for their solid lubricating properties [1]. However, the lubricating performance degrades through oxidation or moisture and it is also limited by its low load-bearing capacity. In contrast amorphous diamond-like carbon (DLC) films are reported to have several features which contribute to excellent tribological characteristics, such as high hardness, wear resistance with both low friction coefficient and low wear rate[2]. The coating processing parameters such as argon pressure may have a strong influence on the structure and properties of the TMD coating[3]. The present research aims at depositing WS2/a-C nanocomposite coatings on silicon wafers by magnetron co-sputtering method. The effect of argon flow rate on the composition, microstructure and mechanical performance of the nanocomposite coating was investigated. The WS2/a-C nanocomposite tribocoating was scrutinized by various microscopy techniques (AFM, HRSEM, and HRTEM) and mechanical testing. Results indicate that with increasing argon flow from 10 sccm to 25 sccm, the S/W stoichiometric ratio and deposition rate of the coating increase whereas the hardness and elastic modulus decrease. These findings indicate that the coating becomes looser and in fact it turns out becoming more columnar-like, as was also confirmed by the enhanced roughness. Ball-on-disk tribotests show that the coefficient of friction against 100 Cr6 steel ball as counterpart can be as low as 0.017 in a dry environment (5% relative humidity). It reaches around a value of 0.15 in a high humidity surrounding and remains rather stable within 20000 sliding cycles. Transmission electron microscopy reveals feathery WS2 platelets distributed in the amorphous carbon matrix, which account for the ultralow friction.

Graphene quantum dots (GQDs) exhibit unique physical and chemical properties due to their quantum confinements and edge defects. In this paper, a facile, green and fast method was developed for large-scale synthesis of GQDs via an ultrasonicassisted liquid-phase exfoliation technique. GQDs with different sizes and structures were obtained through this exfoliation method with different graphitic carbon precursors, such as nano-graphite, acetylene black and even graphite powder. The luminescent properties of as-synthesized GQDs have been investigated. Different light absorption and photoluminescence (PL) properties were identified relevant to the defect characters, namely high-defects GQDs (HD-GQDs) or low-defects GQDs (LD-GQDs). The variable edges and sizes of GQDs are responsible for the variation of luminescent properties induced by changing the excitation wavelength and the pH values of the GQDs dispersions (Figure1). Attributed to the high water dispersancy, excellent biocompatibility, controllable fluorescent performances, as well as the low toxic properties, the as-synthesized HD-GQDs show high potential as fluorescence nanoprobes for bioimaging.

nc-TiC/a-C:H coatings consist of TiC crystallites embedded in an amorphous hydrogenated carbon matrix. Depending mainly on the chemical composition, the properties of these coatings can be tailored from hard coatings, with hardness of greater than 35 GPa to tribological coatings, with coefficients of friction lower than 0.1. In our research, we employed industrial PVD device of Platit equipped with a central titanium rotating cylindrical cathode. Titanium was sputtered in a mixture of argon and acetylene. At critical acetylene supply, a sudden drop in the cathode voltage was observed. This sudden change in the plasma parameters was mirrored in chemical composition and mechanical properties of the deposited coatings. Close to critical acetylene supply, the highest coating hardness of 35 GPa was obtained. The critical acatylene supply shifts as the target get eroded. In our work, we suggest the fully automatic, robust and reliable procedure to deposit hard nc-TiC/a-C:H coatings using the occurrence of the sudden plasma parameters change at critical acetylene supply to set the optimal deposition conditions. Further, the tribological analysis of the series of the titaniumcarbon coatings with different amount of amorphous carbon was carried out. We discovered, that the coefficient of friction strongly depends on humidity of the environment and we found, that the changes of the CoF during the tribological measurements are caused by the changes of the surface roughness.

We have fabricated micro-/nano-pillars of a Zr-based metallic glass, Zr(50)Ti(16.5)Cu(15)Ni(18.5), with pillar tip diameters ranging from similar to 750 nm to similar to 110 nm. These pillars were mechanically tested quantitatively in-situ in a Transmission Electron Microscope (TEM). Due to a slight tapering of similar to 3, the deformation accommodated with shear bands is driven downwards from the top. However, the real time monitoring of shear bands evolution in-situ in TEM makes it possible to measure the effective load-bearing diameter, i.e., the diameter ahead of the most forefront shear band, which enables the precise measurement of yield strength of these pillars. Consequently, it turns out that the yield strength is essentially size independent and close to the bulk value. Statistical physics description of strength of small size metallic glasses is discussed, and it is concluded that Weibull Statistics is inappropriate in describing strength of metallic glasses at micro and nano length scales.

High Power Pulsed Magnetron Sputtering (HIPIMS or HPPMS) is a magnetron sputtering technique that draws increasing interest due to the ability to form droplet-free films out of highly ionized vapor of the target material. Invented by Kouznetsov in 1999 (US patent US6296742), HIPIMS has gone the long way and is nowadays entering the stage of commercial applications. In this work chromium films were deposited by HIPIMS, as well as, by conventional DC magnetron sputtering on a set of substrates with an inclination angle of 0°, 90° and 180° degrees with respect to the target surface normal. The background gas pressure and the average power to the cathode were varied during depositions. Cross-sectional scanning electron microscopy was used for microstructure characterization of produced films and for the determination of deposition rates. The chromium ion content in the plasma, monitored with optical emission spectroscopy, increases with increasing target peak power. Results reveal also quite dramatic quality difference between films grown on tilted substrates by HIPIMS and by conventional DC sputtering.