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Powders of two-phase B2/L21 Fe30Ni20Mn20Al30 (in at.%) were mechanically milled, and both as-milled powders and powders annealed at 823 K were examined using a combination of X-ray diffractometry, scanning electron microscopy and transmission electron microscopy. The as-milled powder consisted of B2 (ordered b.c.c.) phases, whereas after a short anneal at 823 K β-Mn-structured precipitates were present and recrystallized B2 grains were observed in a L21 matrix. The longer the milling time, the finer the resulting powder size and the shorter the annealing time before precipitation occurred. The latter behavior is believed to be associated with nucleation occurring on dislocations formed during milling.

In the present study, the tribological behavior of a Zr52.5Cu17.9Ni14.6Ti5Al10 bulk metallic glass (BMG) was investigated using pin-on-disk sliding measurements under an argon atmosphere, rubbing against a type 303 stainless steel counterface. The tested pins and disk were examined using X-ray diffractometry, optical microscopy, profilometry, scanning electron microscopy and transmission electron microscopy. The results showed that the wear of the BMG pins was substantially larger compared with previous tests performed against a zirconia counterface. Strain softening was found in the near-surface region of the glassy pin due to the highly localized shearing. Frictional heating contributed to the occurrence of viscous flow and material transfer on the worn surface of the wear pin and the disk, respectively. Thus, the pin exhibited a severe adhesive-dominated sliding wear.

In this study, novel MoSi2-based nanocomposite coatings were deposited on Ti-6Al-4V substrates byna two-step process involving firstly, deposition of MoSi2-based coatings, using a double cathode glow discharge process and, secondly, plasma nitridation of the as-deposited coatings. The aim of this latter step is to introduce nitrogen into the coating and promote the formation of amorphous silicon nitride. The resulting coatings were characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscope (XPS), transmission electron microscopy (TEM) and scanning electron microscopy (SEM). It was found that the nanocomposite coatings were composed of nanocrystallite Mo5Si3 and MoSi2 grains embedded in an amorphous Si3N4 matrix. The mechanical properties and damage resistance of the coatings were evaluated by both Vickers indentation and nanoindentation techniques. Dry sliding wear tests were performed using a ball-on-disc type tribometer, in which the coated samples were tested against a ZrO2 ceramic ball at normal loads of 2.8 and 4.3 N under ambient conditions. Compared with the monolithic MoSi2 nanocrystalline coating, the specific wear rates of thennnanocomposite coatings decreased by an order of magnitude. The specific wear rate was further improved by about 20% through the addition of Al, which was attributed to an optimum combination of mechanical properties.

In this study biochar mixtures comprising a Jarrah-based biochar, chicken litter (CL), clay and other minerals were thermally treated, via torrefaction, at moderate temperatures (180 and 220 °C). The objectives of this treatment were to reduce N losses from CL during processing and to determine the effect of both the type of added clay and the torrefaction temperature on the structural and chemical properties of the final product, termed as an enhanced biochar (EB). Detailed characterisation indicated that the EBs contained high concentrations of plant available nutrients. Both the nutrient content and plant availability were affected by torrefaction temperature. The higher temperature (220 °C) promoted the greater decomposition of organic matter in the CL and dissociated labile carbon from the Jarrah-based biochar, which produced a higher concentration of dissolved organic carbon (DOC). This DOC may assist to solubilise mineral P, and may also react with both clay and minerals to block active sites for P adsorption. This subsequently resulted in higher concentrations of plant available P. Nitrogen loss was minimised, with up to 73% of the initial total N contained in the feedstock remaining in the final EB. However, N availability was affected by both torrefaction temperature and the nature of the clay minerals added.

Nanocomposite coatings were synthesized, and subsequently annealed, in an attempt to understand the influence of residual stress upon their resistance to corrosion under acidic attack. Pitting corrosion, originating from microscopic coating defects, was commonly identified in the coatings subject to annealing. Finite element analysis was used to map the residual stress distribution adjacent to these defects and quantify resulting geometrical changes. The results show that with the presence of compressive residual stress in the coatings, corrosion-initiated cracking along weak interfaces was suppressed, and structural integrity maintained. Moreover, compressive residual stress helped constrict pre-existing structural defects in columnar-structured coatings and, in doing so, block the pathway of corrosive agents and limit corrosion damage to the coating–substrate interface and the substrate. The closure aspect ratio of the coating defects, defined as a new key indicator to the corrosion resistance, was numerically evaluated and quantitatively discussed for TiN coatings. Coating corrosion resistance may be improved by optimizing the residual stress in conjunction with coating thickness and the geometry of common defects.

This paper reports on the effects of adding Ni nanoparticles to a Sn–3.8Ag–0.7Cu solder. The nanocomposite was prepared by manual blending of SAC solder paste with various percentages of Ni particles. Results showed that the addition of Ni nanoparticles did not bring any significant change in the onset melting temperature of the solder. An increase in the weight percentage of nanoparticles in the solder caused an increase of the wetting angle and a decrease of spreading rate. Moreover, the addition of Ni nanoparticles changed the interfacial intermetallic compound morphology from a scalloped structure into a planar type structure, enhanced the growth of (Cu,Ni)6Sn5 and suppressed that of Cu3Sn. The concentration of Ni in (Cu,Ni)6Sn5 was higher at the solder side compared with the substrate side. No nickel was detected in the Cu3Sn phase. Ni nanoparticle additions caused an increase in the interdiffusion coefficient in (Cu,Ni)6Sn5, but a reduction in Cu3Sn. All these effects found in the Ni nanoparticle doped solder are similar to the case when Ni is added as an alloying element. Hence, it is suggested that Ni nanoparticles dissolve into the molten solder and influence the intermetallic compound formation through conventional alloying effects.

A novel TiC–Ti5Si3 nanocomposite film was successfully engineered onto a Ti–6Al–4V substrate using a double glow discharge plasma technique. This type of film exhibits a self-toughened, hierarchical structure, consisting of cauliflower-like Ti5Si3 grains together with TiC nanoparticles distributed at the boundaries. The electrochemical behavior and electronic properties of the passive layers formed on the TiC–Ti5Si3 nanocomposite film were compared to a monolithic Ti5Si3 film and uncoated Ti–6Al–4V in a 3.5 wt% NaCl solution by various electrochemical analytical techniques, including low frequency impedance, potentiodynamic polarization, electrochemical impedance spectroscopy (EIS), potentiostatic polarization and Mott–Schottky analysis. The results showed that the corrosion resistance of the TiC–Ti5Si3 nanocomposite film was comparable to that of the monolithic Ti5Si3 film, but was significantly higher than that of uncoated Ti–6Al–4V. The TiC–Ti5Si3 nanocomposite film is thus an attractive candidate for surface protection of components against mechanical and chemical attacks.

Functionally graded, multilayer coatings consisting of alternating TiN/TiSiN layers were synthesized in an attempt to overcome the innate brittleness of TiSiN nanocomposite coatings, whilst maintaining high hardness. These coatings exhibited key structural characteristics that are known to render many naturally occurring materials extremely hard and robust. Transmission electron microscopy revealed that shear sliding of columnar TiN grains played a vital role in controlling the inelastic deformation of these coatings, conferring a greater resistance to contact damage. Moreover, nanoindentation experiments showed that the multilayer coatings exhibited high hardness, attributed to the strong shear resistance offered by the hard TiSiN layers. A dependence of coating hardness upon indentation penetration depth (ht) was found to be proportional to 1/√ht, according to a mechanistically based model, from which the shear stress was determined. The energy dissipation during indentation was also quantified to show the critical role of the shear stress, regulated by the thickness of TiSiN layers, in resisting contact damage in the coatings. Finite-element models were constructed and the presence of transgranular cracks in the monolithic TiSiN coating was clarified based upon experimental observations. Furthermore, the simulations revealed that the transition of the dominant deformation mechanism from brittle transgranular cracking to intergranular shear sliding was controlled by the microstructural characteristics of the coatings. Enabled by the shear sliding, as well as periodic changes in elastic modulus, such a functionally graded multilayer structure was effective in lowering the magnitude and extent of stress concentrations, thereby extending the damage tolerance accessible to a ceramic coating.

Two types of as-cast microstructures have been observed in a series of near-equiatomic FeNiMnAl alloys: 1) an ultrafine microstructure in Fe30Ni20Mn20Al30 [1] and Fe25Ni25Mn20Al30, which consists of (Fe, Mn)-rich B2-ordered (ordered b.c.c.) and (Ni, Al)-rich L21-ordered (Heusler) phases aligned along ; and 2) a fine two-phase microstructure in Fe30Ni20Mn30Al20 and Fe25Ni25Mn30Al20, which consists of alternating (Fe, Mn)-rich f.c.c. and (Ni, Al)-rich B2-ordered platelets with an orientation relationship close to f.c.c (002) // B2 (002); f.c.c. [011] // B2 [001] [2]. The phases in Fe25Ni25Mn20Al30 coarsened upon annealing with no significant change in the chemical partitioning. The hardness behavior was studied as a function of the annealing time at 823 K. AnL21-to-B2 transition, which occurred at 573-623K, was observed using in-situ heating in a TEM. After annealing at 973 K for 100 h, needle-shaped clusters of (Fe, Mn)-rich precipitates were observed along the grain boundaries and in the matrix. The temperature dependence of the yield strength of as-cast Fe25Ni25Mn20Al30 was also studied.

The influence of substitutional alloying elements (Al, Nb and W) on the mechanical properties of MoSi2 with both C11b and C40 structures was explored by first principles calculations. Using the shear modulus/bulk modulus ratio (G/B), Poisson’s ratio and Peierls stress, the change in the mechanical properties of the C40 and C11b structured MoSi2 due to the addition of the solute atom has been investigated. The results showed that the ductility of C11b MoSi2 was increased by alloying with the elements (Al and Nb) that form a C40 structured disilicide but decreased by alloying with the elements (W) that form a C11b structured disilicide. In contrast, the effect of alloying elements on the ductility of C40 MoSi2 showed a reverse trend to that of C11b MoSi2.

Recent interest in biochar characterisation has been driven by its effectiveness as a soil additive, where it can act as a carbon sink, a detoxification agent, and as a means to improve crop yields, especially when prepared as a char–mineral composite. Optimising biochar performance, raw material selection and manufacturing conditions, demands an understanding of structure and chemistry in these complex materials that typically comprise numerous minerals and organic phases. This study presents techniques to successfully image these challenging materials using Fourier transform infrared (FTIR) spectroscopy and Raman spectroscopy. The FTIR and Raman results are presented with results from scanning electron microscopy with energy dispersive X-ray spectroscopy (SEM–EDX), and X-ray photoelectron spectroscopy (XPS). We demonstrate that millimetre-scale organic phases are present in Acacia saligna biochar particles. Mineral enrichment of this biochar with bentonite-iron oxide generates new chemical phases, most likely through acid catalysed dehydration.

One of the toughest challenges that hinders the application of ceramic coatings is their poor damage tolerance. Addressing this problem requires the development of novel micro- or nanostructures that would impart to these coatings both high hardness and high toughness. In this paper, CrAlN coatings, with varying Al contents up to 30 at.%, were engineered onto steel substrates using the magnetron sputtering technique. Whilst the addition of Al does not significantly alter the columnar microstructure, it does change the preferred grain orientation and increase the compressive residual stress. Moreover, the hardness, elastic strain to failure (H/E) and plastic deformation resistance (H 3/E 2) of the resultant CrAlN coating with the highest Al content were found to increase ∼47, ∼29 and ∼140%, respectively, as compared to CrN. Evidence collected from transmission electron microscopy and X-ray photoelectron spectroscopy experiments shows that AlN, existing in an amorphous state at the columnar CrN grain boundaries, has a crucial role in providing the unusual combination of high hardness and exceptional damage resistance. The results provide a new pathway to developing durable ceramic coatings suitable for applications involving severe loading conditions.

A hierarchically structured α-Al2O3/Al3Ti composite was fabricated by an in situ process called exothermic dispersive synthesis from a powder blend of Al and TiO2. The microstructure of the composite was investigated by X-ray diffraction, scanning electron microscopy, and X-ray energy dispersive spectroscopy. Three transitional phases, specifically TiO, Ti2O3, and γ-Al2O3, were found to form during the reactive process. Using differential scanning calorimetry, it was found that the reaction between the Al and TiO2 occurred through three intermediate steps and their corresponding activation energies were 390, 205, and 197 kJ/mol, respectively. Moreover, the reaction rate of the third step was found to be much higher than that of the second step, and the time taken by each reaction step decreased with the increase of the heating rate. The findings are critical to understanding the microstructural development in the synthesis of strong and tough Al2O3/Al3Ti composites.

Ceramic coatings of distinct microstructures, namely TiSiN and CrN, were deposited on tool steels. The corrosion resistance of the coated steels was measured. Following nanoindentation, immersion tests were conducted in 70% HNO3 solution for 96 h. Deformed CrN, where deformation occurred through shear sliding of columnar grains, was insensitive to corrosion attack. In contrast, open cracks formed in the indented TiSiN coating, serving as pathway for reactive agents to penetrate through the coatings. Finite element analysis was applied to evaluate the damage tolerance of the coatings and its impact on the corrosion resistance of the coated steels.

Nanocrystalline C40-structured (Mo1 − xCrx)Si2 films were engineered onto Ti 6Al 4V substrates by a double glow discharge plasma technique. The electrochemical behavior of the newly developed films in a 3.5 wt.% NaCl solution was characterized by electrochemical techniques including open circuit potential, potentiodynamic polarization, and electrochemical impedance spectroscopy. To gain a deeper understanding of the role of Cr alloying in corrosion resistance, both cohesive energy and Mulliken population of the interatomic bonds in C40 (Mo1 − xCrx)Si2 were calculated based on the first-principles density-functional theory.

A nanocomposite of CoO and a mesoporous carbon (CMK-3) has been studied as a cathode catalyst for lithium-oxygen batteries in alkyl carbonate electrolytes. The morphology and structure of the as-prepared nanocomposite were characterized by field emission scanning electron microscopy, transmission electron microscopy and high resolution transmission electron microscopy. The electrochemical properties of the mesoporous CoO/CMK-3 nanocomposite as a cathode catalyst in lithium-oxygen batteries were studied using galvanostatic charge-discharge methods. The reaction products on the cathode were analyzed by Fourier transform infrared spectroscopy. The CoO/CMK-3 nanocomposite exhibited better capacity retention than bare mesoporous CMK-3 carbon, Super-P carbon or CoO/Super-P nanocomposite. The synergistic effects arising from the combination of CoO nanoparticles and the mesoporous carbon nanoarchitecture may be responsible for the optimum catalytic performance in lithium-oxygen batteries. © 2012 Tsinghua University Press and Springer-Verlag Berlin Heidelberg.

The high hardness of bulk metallic glasses (BMGs) makes them promising candidates for high wear applications. This paper focuses on the effects of oxygen on the tribological behavior of a zirconium-based BMG using pin-on-disk wear tests in three different environments, i.e. air, oxygen and argon. It was found that the wear rate of the BMG specimens increased dramatically with increasing oxygen content in the testing environment, i.e. in the order argon, air, oxygen. The pins and disk were examined using X-ray diffractometry, scanning electron microscopy and transmission electron microscopy. A number of cracks and pits were present on the worn surface of the pin tested in oxygen-containing environments, whilst a relatively smooth worn surface and a mixed layer with a thickness of about 2–10 μm were observed in the specimens tested in argon. For the tests in oxygen, abrasive particles induced by oxidation protruded and peeled off from the glassy matrix, resulting in a combination of two-body and three-body abrasion. In an oxygen-free environment, plastic flow took place, presumably accompanied by work-softening, due to frictional heating and local stress concentrations. This led to the formation of the mixed layer on the pin and a material-transfer film on the disk.

A nanostructured MoSi 2 coating with the average grain size of 5 nm and a strong (111) preferred orientation, was synthesized potentially for jet engine hot-zone components against volcanic ash damage. The high hardness of the resulting coating was predicted using first-principles calculations and found to agree well with the experimental data determined by nanoindentation. We also found that the softening and subsequent breaking of the Mo―Si bonds were responsible for the failure of this nanostructured coating under tensile loading.

The objective of this work was to determine the contribution of dissolved organic carbon (DOC) from a biochar mineral complex (BMC), so as to better understand the interactions between DOC, biochar, clay, and minerals during thermal treatment, and the effects of BMC on amended soils. The BMC was prepared by heating a mixture of a H3PO4-treated saligna biochar from Acacia saligna, clays, other minerals, and chicken manure. The BMC was applied to a sandy loam soil in Western Australia, where wheat was grown. Liquid chromatography-organic carbon detection (LC-OCD) tests were carried out on water extracts from the untreated biochar, the BMC, the BMC-amended soil, and on a control soil to measure the DOC concentration. LC-OCD tests provide a fingerprint of the DOC, which allows the fractions of DOC to be determined. Thermal processing enhanced the reaction of the A. saligna biochar with manure, clays and minerals, and affected the distribution of the DOC fractions. Notably, the process leads to immobilization of hydrophobic DOC and to an increase in the concentration of low-molecular-weight neutrals in the BMC. The application of the BMC to soil increases the DOC in the amended soil, especially the biopolymer fraction. O objetivo deste trabalho foi determinar a contribuição do carbono orgânico dissolvido (COD), de um complexo mineral de "biochar" (BMC), para uma melhor compreensão das interações entre COD, "biochar", argila e minerais durante o tratamento térmico, e dos efeitos do BMC sobre solos tratados. O BMC foi preparado por meio do aquecimento de uma mistura de "biochar" produzido a partir de Acacia saligna, tratado com H3PO4, argilas, outros minerais e esterco de galinha. O BMC foi aplicado a um Argissolo Vermelho-Amarelo distrófico arênico na Austrália Ocidental, onde cultivou-se trigo. Testes de cromatografia líquida com detecção de carbono orgânico (LC-OCD) foram realizados em extratos aquosos do biocarvão não tratado, do BMC, do solo tratado com BMC, e de um solo testemunha, para medir a concentração de COD. Os testes de LC-OCD fornecem uma identificação do COD, o que permite que as frações de COD sejam determinadas. O processamento térmico aumentou a reação do "biochar" produzido a partir de A. saligna com o esterco, argilas e minerais, e afetou a distribuição das frações de COD. Notavelmente, o processo leva à imobilização do COD hidrofóbico e a um aumento na concentração de substâncias neutras com baixo peso molecular no BMC. A aplicação do BMC ao solo aumenta o COD no solo tratado, principalmente a fração de biopolímero.

A nanocomposite NiSi 2 /Ti 5 Si 3 bilayer film was engineered onto Ti–6Al–4V alloy by double cathode glow discharge. The outer layer of the resulting film comprised of NiSi 2 , having dense and fine-grained (35 nm in size) columnar structure with a fraction of nanoscale twin bundles, and the inner layer consisted of equiaxed Ti 5 Si 3 with a grain size of 50 nm. Nanoindentation was carried out on polished cross-sections to measure the elastic modulus and hardness of each layer of the as-deposited film. Scratch tests were undertaken to evaluate the resistance of the as-deposited film to both abrasive and adhesive damage. The dry sliding wear experiments were conducted against ZrO 2 ceramic balls under the applied load ranging from 3.3 N to 4.8 N at room temperature and 500 °C using a ball-on-disc tribometer. Compared with the Ti–6Al–4V alloy, the specific wear rates of the alloy coated with the bilayer film decreased by one order of magnitude at room temperature and were further reduced by one order of magnitude at 500 °C. The electrochemical behavior of the coated alloy was characterized by potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) in 5 wt.% HCl solution. The results revealed that nanocomposite NiSi 2 /Ti 5 Si 3 bilayer film exhibited a higher corrosion resistance than the Ti–6Al–4V alloy.

Biochar, as a soil amendment, can increase concentrations of soil organic matter, especially water-extractable organic carbon (WEOC). This can affect the adsorption-desorption equilibrium between the dissolved solid phases in soil organic matter. Dissolved organic carbon (DOC) represents a small proportion of soil organic matter, but is of significant importance in the soil ecosystem due to its mobility and reactivity. Here, water extracts obtained from twelve non-herbaceous biochars (before, and after, chemical treatment with either H(3)PO(4) or KOH), were tested by Liquid Chromatography - Organic Carbon Detection (LC-OCD) to identify the effects of both pyrolysis conditions and chemical treatments on WEOC content. LC-OCD has the capacity to provide a fingerprint of WEOC, which allows analysis of the various fractions present. WEOC content was affected by both the pyrolysis temperature and the feedstock used. High mineral ash contents deriving from the feedstock can prompt thermochemical reactions of lignocelluloses to produce a relatively high WEOC content, which includes low molecular weight neutrals and humic acids as dominant components. A significant change in WEOC occurred during pyrolysis due to secondary reactions which resulted in a much lower WEOC in the high temperature biochars where fractions of low molecular weight acids and neutrals are dominant. Chemical treatments with H(3)PO(4) or KOH increased WEOC concentration, possibly by promoting hydrolysis reactions on biochar surfaces. These observations assist in assessing the contribution of biochar additions to the soil ecosystem and demonstrate the utility of LC-OCD in providing an understanding of how biochar additions to soil can alter DOC.

The wear of both as-cast and annealed nanostructured Fe30Ni20Mn20Al30, which consists of fine alternating B2 (ordered b.c.c.) and L21 (further ordering B2) phases, was studied using pin-on-disk tribotests in three different test environments, oxygen, air and argon. The counterface in all tests was yttria-stabilized zirconia. It was found that the annealed alloy showed better wear resistance than the as-cast material, probably because the annealed Fe30Ni20Mn20Al30 has both a higher hardness and better ductility. The wear was reduced dramatically by the removal of the oxygen from the test environment. The zirconia counterface showed similar wear behavior in all environments. The tips of the wear pins were examined using a combination of X-ray diffractometry, scanning electron microscopy and transmission electron microscopy, the latter using specimens produced by focused ion beam milling. A considerable number of cracks and pits were present on the worn surface of pins tested in oxygen-containing environments, while a relatively smooth mixed layer and plastic flow were evident on the worn surface of pins tested in argon. Both two-body and three-body abrasive wear, as well as deformation and delamination, contributed to the wear.

Aims In this study, a chicken manure biochar (CM biochar) and a paper sludge biochar (PS biochar), prepared under similar treatment conditions, were amended into ferrosol as part of an agronomic field trial. The aim of this study is to investigate interactions between these biochars and the soil after a 3 month trial. Methods Soil samples following field trials were taken and biochar was separated from the soil, and studied for both surface oxidation and the degree of interaction with surrounding soil by X-ray photoelectron spectroscopy (XPS), SEM and TEM equipped with EDS for elemental analysis. Results Following incubation in field soil, both biochars showed that soil mineral incorporation on to their surfaces occurred within the first year, although the attachment was localized at specific sites on the surface. A relatively high concentration of Al was found at the interface between the biochar and mineral phases in both aged biochars, indicating a binding role of Al. For the CM biochar, a soil-iron redox reaction may be associated with the formation of biocharmineral complexes due to the relatively higher labile carbon content and higher pH value of this biochar. Conclusions Soilmineralattachmentmayoccurdirectly on to the biochar surface because of the formation of carboxylic and phenolic functional groups on the aged CM biochar surface by an oxidation reaction. For the PS biochar, adsorption of organic matter from the soil facilitated interactions between the biochar and mineral phases in the soil. Calcium is believed to be important in this process.

The wear of as-cast eutectic Fe30Ni20Mn35Al15, which consists of lamellar f.c.c. and B2 phases, was studied using pin-on-disk tribotests in four different environments: air, dry oxygen, dry argon, and a 4% hydrogen/nitrogen mixture. The counterface in all the tests was yttria-stabilized zirconia. Wear debris and wear tracks were examined in detail to investigate the surface effects during dry sliding and these were correlated with the wear properties. It was found that the wear rate was about 40% lower in tests performed under argon, compared to tests conducted in either air or oxygen. However, the wear rate was about 1000% higher when the tests were conducted in a hydrogen-containing environment. The near-surface regions of the pins were examined using transmission electron microscopy of cross-sectional specimens produced by focused ion beam milling. For tests in oxygen-containing environments, abrasive particles were produced by oxidation. These, protruded and peeled off from the matrix and mixed with the debris from the counterface, producing a combination of a two-body and three-body abrasive wear-controlled processes. In contrast, for tests under argon, plastic flow mechanisms dominated. The dramatic increase of wear in 4% hydrogen/nitrogen was due to hydrogen embrittlement, which meant that little plastic flow occurred, a feature consistent with the results of prior tensile tests.

Nanoindentation-induced phase transformations in both crystalline silicon (c-Si) (100) and ion-implanted amorphous silicon have been studied at temperatures up to 200 °C. The region under the indenter undergoes rapid volume expansion at temperatures above 125 °C during unloading, which is indicated by “bowing” behavior in the load-displacement curve. Polycrystalline Si-I is the predominant end phase for indentation in crystalline silicon whereas high-pressure Si-III/Si-XII phases are the result of indentation in amorphous silicon. We suggest that the Si-II phase is unstable in ac-Si matrix at elevated temperatures and can directly transform to Si-I during the early stages of unloading.

Biochar technology has been proposed as a geoengineering solution that has potential to actively reduce the atmospheric concentrations of greenhouse gases and enhance the sustainability of agriculture. The magnitude of the technologies’ net benefit must be considered in relation to the associated risks. Hazards posed by biochar technology need to be managed to a level that the resulting risks are deemed acceptable by society; identification of hazards is an essential first step. Effectively implemented risk management and sustainability guidelines, driven by informed policy directives, will result in biochar technology being an important tool for environmental and atmospheric greenhouse gas management.

A direct link between the microstructure and mechanical properties of CrSiN coatings with varying Si contents was established by examining their microstructural evolution and deformation behaviour, enabled by cross-sectional transmission electron microscopy. A transformation from a columnar-grained structure, in the binary compound, to a nanocomposite structure, consisting of CrN nanocrystallites embedded in an amorphous matrix, was observed in the coating having a Si content of 28.5 at.%. The columnarstructured coatings were observed to deform by grain boundary shear sliding, whilst cracks occurred in nanocomposite coatings. Moreover, the coating having a Si content of 14.3 at.% exhibited the highest hardness as a result of grain boundary strengthening facilitated by Si3N4 segregation, together with solid solution strengthening of Si in CrN, the Hall–Petch effect for the finer CrN grains and a high compressive residual stress. A further increase of Si content to 28.5 at.% led to a reduction in hardness due to the high volume fraction of the amorphous phase, together with the presence of cracks in the as-deposited coating. The findings provide deeper insight into the origin of the mechanical behaviour of CrSiN coatings.

The pin-on-disc wear behavior of nanostructured two-phase Fe30Ni20Mn20Al30 and eutectic lamellar-structured Fe30Ni20Mn35Al15 is compared emphasizing the influence of the microstructure and mechanical properties of alloys as well as the effect of test environment. Although the wear of both alloys was greater in oxygen-containing environments, eutectic Fe30Ni20Mn35Al15 is less sensitive to oxygen than nanostructured Fe30Ni20Mn20Al30. Abrasive wear dominated during the wear in all cases, while plastic deformation also occurred during the wear of eutectic Fe30Ni20Mn35Al15. A tribolayer of zirconia, which was embedded in the surface of the wear pin, was characterized using a scanning transmission electron microscope equipped with an energy dispersive spectrometer.

Novel nanocrystalline Mo(Si1−xAlx)2 films, with differing Al contents were synthesized by double cathode glow discharge. The films exhibited a compact columnar microstructure having a pronounced (111) preferred orientation. The corrosion behaviour of these films were characterized by using various electrochemical techniques including open circuit potential (OCP), potentiodynamic polarization, and electrochemical impedance spectroscopy (EIS) in 3.5 wt% NaCl solution. The corrosion resistance of the films increased with increasing Al content in the as-synthesized films. The composition and chemical state of the passive layers formed on the films were investigated by X-ray photoelectron spectroscopy (XPS). It was demonstrated that the passive layer formed on the binary MoSi2 film was highly enriched in SiO2 with minor amounts of MoO42−, MoO2 and SiOx. With the increase of Al content in the films, Al2O3 was generated and incorporated into the passive layers, enhancing the corrosion resistance of the films by inhibiting the dissolution of Mo. Built upon the experimental results, the first-principles density-functional theory was applied to calculate the inter-atomic bonding strength in Mo(Si1−xAlx)2 and elucidate the role of Al in controlling the corrosion resistance of the films. The new findings lay a solid basis for the development and application of MoSi2 based corrosion-resistant films.

Polyhedral magnetite nanocrystals with multiple facets were synthesised by a low temperature hydrothermal method. Atomistic simulation and calculations on surface attachment energy successfully predicted the polyhedral structure of magnetite nanocrystals with multiple facets. X-ray diffraction, field emission scanning electron microscopy, and high resolution transmission microscopy confirmed the crystal structure of magnetite, which is consistent with the theoretical modelling. The magnetic property measurements show the superspin glass state of the polyhedral nanocrystals, which could originate from the nanometer size of individual single crystals. When applied as an anode material in lithium ion cells, magnetite nanocrystals demonstrated an outstanding electrochemical performance with a high lithium storage capacity, a satisfactory cyclability, and an excellent high rate capacity. Crystal class: Polyhedral magnetite nanocrystals were prepared by a low temperature hydrothermal method, in which multiple facets can be theoretically predicated (see figure). The as-prepared magnetite nanocrystals show a magnetic property of superspin glass state, and demonstrated an outstanding electrochemical performance for lithium storage in lithium ion cells. Copyright © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Lamellar bands are the primary structural features in accumulative roll bonding (ARB) of sheet metals. The structural refinement in ARB sheets occur by forming a dense distribution of lamellar band boundaries. The lamellar band boundaries initiate as low angle interfaces, parallel to the existing lamellar band boundaries, irrespective of the crystallographic orientations of the parent lamellar bands. From an extensive investigation it was found that the transverse directions across the lamellar band boundaries are rotated by an angle equal to their misorientations. Such a phenomenon is not sustained when the boundaries turn to high angle.

Nanocomposite Cr–Si–N films were prepared on to Ti–6Al–4V substrates by a novel duplex surface treatment technique. Coatings consisting of a Cr3Si surface layer were deposited using a double cathode glow plasma and subsequent surface plasma nitriding. The surface topography, chemical composition, and microstructure of these treated alloys were analyzed by a variety of surface characterization techniques. The resulting Cr–Si–N films consisted of nanocrystallite CrN grains embedded in amorphous SiNx phase. Nanoindentation tests showed that with increasing nitrogen partial pressure the hardness of the Cr–Si–N films increased and the elastic modulus decreased. Wear experiments showed that the Cr–Si–N films produced at a nitrogen partial pressure of 4.5Pa and 800 °C possessed the lowest wear rate and friction coefficient. Moreover, electrochemical measurements in 5 wt% HCl solution indicated that the Cr–Si–N films acted as an effective barrier against acid attack on the alloys.

Nanocomposite TiSiN coatings were deposited on tool steels. Detailed mechanisms that govern the corrosion of these coated steels were revealed, following immersion tests in a 70% nitric acid solution. Pitting originated preferentially from coating defect sites and expanded with increasing immersion time. Both Young’s modulus and hardness measured by nanoindentation decreased as the corrosion damage intensified. A thin oxide layer formed from the thermal annealing of the as-deposited samples at 900 °C was found to be effective against corrosive attack. In addition, compressive residual stress was noted to suppress the propagation of corrosion-induced cracks. The role of residual stress in controlling the corrosion resistance of these ceramic-coated steels is clarified by finite element analysis.

A microstructural analysis of two FeNiMnAl alloys, Fe{sub 30}Ni{sub 20}Mn{sub 30}Al{sub 20} and Fe{sub 25}Ni{sub 25}Mn{sub 30}Al{sub 20}, was performed by a combination of atom probe tomography and transmission electron microscopy techniques. Although the microstructures of both alloys, which consist of alternating platelets aligned along of the B2-ordered phase, are similar to B2/b.c.c. two-phase alloys previously observed in the FeNiMnAl system, the two phases present in the current alloys are B2-ordered and f.c.c., with the latter phase being heavily twinned. Very fine ({approx} 5 nm) precipitates, whose chemistry was similar to that of the f.c.c. (Fe, Mn)-rich phase, were found within the B2 (Ni, Al)-rich phase in both alloys. - Highlights: {yields} The microstructures of the novel alloys Fe{sub 30}Ni{sub 20}Mn{sub 30}Al{sub 20} and Fe{sub 25}Ni{sub 25}Mn{sub 30}Al{sub 20} were characterized. {yields} Atom probe tomography and transmission electron microscopy were used in the study. {yields} A -aligned B2-ordered phase and heavily-twinned f.c.c. phase were present. {yields} Very fine (Fe, Mn)-rich precipitates were found within the B2 (Ni, Al)-rich phase.

Summary Black carbon (BC) is one of the most stable forms of soil organic matter. Its surface functional groups and structure havebeenwellcharacterizedbyarangeofanalyticalmethods. However,littleisknownaboutthemechanismsofinteractions betweentheBCparticlesandthesurroundingmineralmatter. In this paper a range of microscopy techniques, such as transmission electron microscopy and scanning transmission electron microscopy, were used to investigate the possible reactions of BC particles within microaggregates (

A novel hierarchical structured coating was prepared on a pure titanium substrate by a double cathode glow discharge technique. This coating consisted of a 1 μm thick C40-structured MoSi2 outer layer with an average grain size of 5 nm and an underlying MoSi2/Mo5Si3 layer having a gradient, bimodal microstructure, in which C40-structured MoSi2, with an average grain size of 5 nm, is embedded within an intergranular region of D8m-structured Mo5Si3, with an average grain size of 40 nm. The ratio of Mo5Si3 to MoSi2 increased gradually away from the outer surface. Compared with a monolithic MoSi2 coating, the hierarchical structured coating exhibited a marked increase in toughness, while maintaining its hardness.

The interaction between diamond and a 30 kV Ga+ focused ion beam, has been studied. Electron backscattered diffraction identified the critical dose for amorphisation of the diamond surface at 2 × 1014 Ga+/cm2. Scanning transmission electron microscopy identified a 35 nm amorphous carbon layer which, at higher doses, can swell up to 31% its original volume and accommodate a significant quantity of gallium. Electron energy loss and energy dispersive X-ray spectroscopy further characterised this layer and identified both excess hydrogen and oxygen contained within a stable amorphous carbon structure.

In the present work, five kinds of nanocrystalline (MoxCr1−x)5Si3(x = 1, 0.78, 0.75, 0.64, 0.57) films with average grain size 8 nm have successfully been prepared on Ti6Al4V alloy by a double cathode glow discharge technique in order to improve its poor tribological properties. The influence of the Cr additions on the mechanical and tribological properties of nanocrystalline (MoxCr1−x)5Si3 films have been studied. The microstructure of the films was characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and high-resolution transmission electron microscopy (HRTEM). Nanoindentation was used to measure hardness (H) and elastic modulus (E) of the as-deposited films, and the adhesion strength between the as-deposited films and substrate was evaluated by scratch test. The dry sliding wear properties of the as-deposited films were investigated using against different counterbodies (ZrO2 ceramic balls and GCr15 rolling bearing steel) in ball-on-disk system at room temperature. The results indicated that alloying additions of Cr affected considerably the wear performance of nanocrystalline (MoxCr1−x)5Si3 films. The friction coefficients and specific wear rates of nanocrystalline (MoxCr1−x)5Si3 films were significantly reduced by the increasing Cr substitution, and its specific wear rates have been shown to be two orders of magnitude lower than for Ti6Al4V alloy. The dominant wear mechanism of the nanocrystalline (MoxCr1−x)5Si3 films experiences a transition from delamination to tribo-oxidation wear, along with the increasing amount of Cr additions.

The nature of newly forming lamellar band boundaries was investigated in accumulative roll bonded aluminum. These boundaries initiate as low angle interfaces parallel to the existing lamellar band boundaries irrespective of the crystallographic orientation of the parent lamellar band. The transverse directions of the divided segments were found to rotate at an angle equal to the degree of misorientation between segments. Such a phenomenon is not sustained when the boundaries become high angle.

Thermal annealing has often been used to reduce residual stress and improve mechanical properties and performance of hard coatings. In this work, nanocomposite TiSiN coatings were engineered onto steel substrates by reactive unbalanced magnetron sputtering. Following deposition, thermal annealing was performed at temperatures up to 900 °C. A marked decrease in residual stress was observed in the coatings with the increase of thermal annealing temperature. To ascertain the role of residual stress in the response of the coatings to contact damage, nanoindentation was used to probe the damage resistance of the coatings and Rockwell-C test used to evaluate their adhesion strength, as a function of thermal annealing temperature. A combination of high damage resistance and good adhesion strength was observed for the coating annealed at an intermediate temperature of 600 °C.

Iron oxide nanoparticles, nanowires, and nanobelts were prepared from a 50 vol % ethanol solution of 28 mM iron(III) chloride and 0.3 mM polyethylene glycol (20 kDa) by hydrothermal treatment at 120 °C, using hydrazine monohydrate (N2H4) as a reducing agent. Factors governing phase and morphology of the iron oxide nanoparticles were studied. The amount of hydrazine added affected the hydrolysis of iron(III); therefore, the type of iron oxyhydroxide formed; this in turn controlled whether akaganeite, goethite, hematite, or magnetite was obtained after the hydrothermal treatment step. For conditions that favored the formation of magnetite, the addition rate of hydrazine was shown to affect the reduction of iron(III) to iron(II) and, hence, the relative amount of magnetite and goethite in the final product. Increasing the pH of the precursor solution to 14 resulted in the formation of magnetite nanobelts. Phase analysis of the intermediate products showed that the magnetite nanobelts were formed from the dis...

It is a common practice to study crack patterns in brittle solids for strength analysis. Observations based on cracks visible on surfaces or randomly chosen cross-sectional planes may be ambiguous and lead to an inaccurate interpretation of deformation behavior. In this study, three-dimensional reconstruction obtained using a focused ion beam–scanning electron microscopic tomography technique was applied, for the first time, to observe the site-specific deformation created by a scratching load on a TiSiN/TiN multilayer hard coating. This technique was demonstrated to be a powerful tool in providing detailed morphology of cracks that formed in coatings with complex structures, which would be difficult to obtain by conventional experimental methods. The cracks observed in the TiSiN/TiN multilayer coating are similar in morphology to cone cracks, which are commonly observed in homogeneous brittle solids; however, they are slightly different in this work due to the presence of sublayers in the coating with differing moduli. By locating the first crack visible on the scratched surface, in conjunction with scratch data obtained from the nanoindenter, the critical tensile stress for the formation of the cracks observed in this TiSiN/TiN multilayer coating was estimated to be ∼2.6 GPa.

Nanostructured TiSiN coatings were deposited onto a tool steel substrate. The coated samples were then annealed under vacuum at temperatures ranging from 400° to 900°C. Both mechanical properties and residual stresses in the coatings were determined using nanoindentation methods, assisted by finite element analysis. Intrinsic residual stress was found to be dominant in the as-deposited coatings, but decreased with the increased annealing temperature. In contrast, thermal annealing has little impact on either the Young's modulus or hardness of the coatings at temperatures up to 800°C. Grazing incidence X-ray diffraction analysis indicated that stress relaxation occurred in nanocrystalline TiN grains during thermal annealing. Direct subsurface observation, enabled by focused ion beam microscopy, revealed that microstructural characteristics, responsible for both the Young's modulus and hardness of the coatings remained unaffected during thermal annealing. The degradation of mechanical properties for the coatings annealed at 900°C resulted primarily from the formation of a thin, soft titanium oxide layer at the outer surface.

Soils developed on the sites of Australian Aboriginal oven mounds along the Murray River in SE Australia, classified as Cumulic Anthroposols under the Australian Soil Classification, are shown to have traits similar to the Terra Preta de Indio of the Amazon basin. Seven such sites were characterised and compared with adjacent soils. The Cumulic Anthroposols contained significantly (p

Stress concentrations undermine the load-bearing ability of superhard TiSiN coatings. Experimental studies have shown that multilayer coatings that contain TiSiN layers alternating with ceramic layers with dissimilar mechanical properties suppress contact damage during nanoindentation. In this work, nanoindentation-induced deformation in TiSiN-based multilayer coatings was simulated by means of finite element modelling (FEM). Stress distributions under moderate indentation loading in the structure were quantified with particular emphasis on the relationship between stress concentrations and crack initiation. The results showed that the structural layering can be used to modify the stress distribution, and lower the overall stress level within the coating. In the case of radial tensile stresses at the coating/substrate interface, a reduction ∼50% has been achieved through layering. The resistance to shear damage can also be improved by optimising the multilayer structure.

Wear resistance has been found to improve for Al–Si alloyswith increasing silicon content up to the eutectic compo-sition (12.6 at.% Si), after which it deteriorates [1–3].Wear in Al–Si alloys has been characterized into mild andsevere wear regimes. Mild wear occurs under conditions oflow normal loads, and an oxide layer that forms on thewear surface usually slows down the wear process. Severewear occurs under high normal loads and is often charac-terized by inclusions of the worn counterface, along withoxides, in the mechanically mixed surface tribolayers [4,5]. The results of Razavizadeh and Eyre [6] suggest thatthere is generally insufficient frictional heating on the wearsurface for general oxide formation. Instead, a mechanismof oxidation of asperities followed by fracture and com-paction of these oxidized asperities into the valleys on themetal wear surface has been suggested [7, 8]. During mildwear of Al–Si alloys, a smooth surface is generallyobserved with interspaced wear scar areas [1]. The pres-ence of material from the worn counterface embedded inthe wear pin has been observed on both smooth and scarredareas [7, 9, 10].Lower wear rates may be observed when harder coun-terfaces, such as diamond-like carbon (DLC) or yttria-stabilized zirconia, are used instead of the hardened steelsurfaces traditionally employed in wear tests, particularly ifthe hard counterface has a smooth surface [11]. Also, argontest environments have shown reduced wear rates ascompared to tests performed in air, with the wear ratesunder argon being as much as ten times lower in somecases [11, 12]. The increase in wear rates in atmosphereswith higher oxygen content has been attributed to thepresence of abrasive wear debris on the surface [12].In a recent paper [12], we studied the wear of as-casteutectic Al–Si against a yttria-stabilized zirconia counter-face using pin-on-disk tribotests in two different environ-ments, air and dry argon. The wear rate of the pins tested inair was more than twice that of those tested under argon.Similarly, the zirconia counterface showed much morewear for tests conducted in air. There was substantialsubsurface cracking in the pins during wear testing in air,but none was observed in pins tested under argon. Scanningtransmission electron microscope (STEM) examination ofthe near-surface region of the pins that had been worn in airshowed mechanically mixed regions with considerableamounts of both aluminum oxide and zirconium oxide—the aluminum oxide particles had evidently acted as abra-sive particles to remove material from the zirconia coun-terface. In contrast, the pins tested in argon showed littlezirconium oxide in the near-surface regions.In that study [12], it was unclear whether the moisturepresent in air made a significant contribution to the wearrate. Thus, the objective of the present study was to clarifythe influence of moisture in the wear environment and itseffects on the proposed wear mechanism of crack forma-tion and debris accumulation on wear surfaces. To that end,pin-on-disc wear tests were performed in a flowing dryoxygen environment using the same materials and condi-tions as in our previous study, and the resulting wear sur-faces were characterized in the same fashion [12]. Theresults, described below, are compared with those fromprevious tests conducted in air and in dry argon. It ispossible that the size of the Si particles may affect the wear

Iron and Fe–Si alloys (1, 2, 3 and 5 wt.% Si) were reacted at 680 °C with a gas mixture of 68% CO, 26% H 2 and 6% H 2 O ( a C = 2.9, p O 2 = 2 × 10 −23 atm). Alloy reaction products consisted of internally precipitated SiO 2 , an external scale of Fe 3 C + SiO 2 and surface coke deposits containing cementite and silica particles. Coking and metal dusting rates both increased with alloy silicon level. This is proposed to be related to an increase in graphite nucleation sites at Fe 3 C/SiO 2 phase boundaries, and the volume expansion accompanying graphite precipitation.

A CrCoNi medium entropy alloy thin film is fabricated using magnetron sputtering. It exhibits a unique hierarchical nanostructure, featuring (1) a high density of planar defects (mostly stacking faults plus a small number of twin boundaries), (2) a dual-phase configuration (a mix of face-centred-cubic and hexagonal-close-packed), and (3) vertically aligned, textured nanocolumns, each with a width of ∼100 nm. The hierarchical nanostructure in this study is original, especially for its dual phase combination, since the bulk CrCoNi medium entropy alloy generally presents a single phase face-centred-cubic structure. The CrCoNi film shows a hardness quadruple that of its face-centred-cubic structured counterpart. The formation and its role of the hierarchical nanostructure in producing such mechanical strength are discussed.

Three different functionally graded amorphous carbon (a-C) thin films were deposited on to aluminium substrates using a closed-field unbalanced magnetron sputtering ion plating method. The closed-field configuration prohibits the loss of secondary electrons and consequently enhances the plasma density significantly. The functional gradient of the a-C films was achieved by varying the bias voltage linearly during deposition. Three graded a-C systems possessing different variations in Young's modulus were deposited with the highest Young's modulus at the (i) top surface, (ii) interface or (iii) middle of the film. Of the three systems investigated, the one with the highest Young's modulus at the middle of the film thickness was found to exhibit significantly lower levels of cracking at higher indentation depths. Finite element models that included an embedded ring crack controlled by cohesive zone elements were developed to clarify the effect of ring cracks on the deformation of the films. This study provides guidance for the design of functionally graded coatings against contact damage.