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Many features of the well-documented yield strength anomaly in B2-structured Fe–Al alloys have been successfully described or predicted by the vacancy-hardening model [George EP, Baker I. Philos Mag 1998;A77: 737]. Interestingly, the model does not predict any orientation dependence for the yield anomaly. Here, we examine this by measuring the yield stress of three different single-slip-oriented Fe–43Al single crystals as a function of temperature. It was found that the critical resolved shear stress of all the alloys decreased rapidly with temperature from 77 K to ∼300 K, showed a plateau from 300 K to 723 K, increased to a peak at 873 K, and then decreased again with further increase in temperature. While neither the low-temperature strength (

Agricultural soils are the primary anthropogenic source of atmospheric nitrous oxide (N2O), contributing to global warming and depletion of stratospheric ozone. Biochar addition has shown potential to lower soil N2O emission, with the mechanisms remaining unclear. We incubated eucalypt biochar (550 °C) – 0, 1 and 5% (w/w) in Ferralsol at 3 water regimes (12, 39 and 54% WFPS) – in a soil column, following gamma irradiation. After N2O was injected at the base of the soil column, in the 0% biochar control 100% of expected injected N2O was released into headspace, declining to 67% in the 5% amendment. In a 100% biochar column at 6% WFPS, only 16% of the expected N2O was observed. X-ray photoelectron spectroscopy identified changes in surface functional groups suggesting interactions between N2O and the biochar surfaces. We have shown increases in -O-C = N /pyridine pyrrole/NH3, suggesting reactions between N2O and the carbon (C) matrix upon exposure to N2O. With increasing rates of biochar application, higher pH adjusted redox potentials were observed at the lower water contents. Evidence suggests that biochar has taken part in redox reactions reducing N2O to dinitrogen (N2), in addition to adsorption of N2O.

In the present work, we have examined the role of active elements in controlling the extent of splashing of plasma sprayed splats. Splats of Copper (Cu) and Copper alloyed with Al, Zr were deposited by plasma spray or as free-falling droplet. The splat formation and splat-substrate interfaces were characterised using SEM and FIB. It was found that the presence of Zr, either in the splat material or the substrate, enhanced disk splat formation in free falling droplets. Similarly, the presence of aluminium in plasma sprayed Cu- 10%Al increased the portion of favourable disk-shaped splats compared to pure copper. It was also found that the disk-shaped splat proportion of Cu-10%Al at room temperature is nearly identical to that of Cu splat at 300ºC, indicating that the addition of Al in the alloy leads to the improvement of splat formation, correlating with the improvement in the interface bonding with the substrate.

Giant electromechanical response viaferroelastic domain switching is achieved in epitaxial (001) ferroelectric tetragonal (T) PbZr0.3Ti0.7O3/rhombohedral (R) PbZr0.55Ti0.45O3 bilayers, grown on La0.67Sr0.33MnO3 buffered SrTiO3 substrates. X-ray diffraction and transmission electron microscopy show that the domain structure of the T films is tuned as a function of its thickness, from a fully a1/a2-domains (30 nm thick T layer) to a three domain stress-free c/a1/c/a2 polytwin state (100 nm thick T layer). A large switchable polarization is found up to 65 μC cm−2. Quantitative piezoelectric force microscopy reveals enhanced piezoelectric coefficients, with d33 coefficients ranging from 250 to 350 pm V−1, which is up to seven times higher than the nominal PbZrxTi1−xO3 thin film values. These are attributed to the motion of nanoscale ferroelastic domains. Fatigue testing proves that these domains are reversible and repeatable up to 107 cycles. In-situ X-ray synchrotron measurements reveal that the ferroelastic domain switching is promoted by a pulsating strain effect imposed by the R layer. The study reports a fundamental understanding of the origin of giant piezoelectric coefficients in epitaxial ferroelectric bilayers.

The process parameters that are used in biochar manufacture have a signifi cant effect on its physical and structural characteristics. These characteristics, in turn, will affect biochar’s interaction with soil systems. Soils are highly complex, multi-component systems that exhibit their own distinctive physical properties. The addition of biochar to soils can thus lead to unique interactions that infl uence soil physical properties such as porosity, particle size distribution, density and packing. As a result, these combined biochar-soil properties will then impact plant yield through, for example, the availability of water and air in the vicinity of the plant root. (Other interactions, such as chemical or biological interactions, will also occur between biochar particles and soil particles, but these will not be considered in this chapter.)Whilst there have been many studies of the physical properties of biochars in anthropogenically produced soils, the pyrolysis process parameters involved are, unsurprisingly, unknown (Glaser et al, 2000; Schaefer et al,2004; Chia et al, 2012). As such, the focus of this chapter will be on the physical and structural properties of biochars derived from known feedstocks under controlled process parameters, particularly the relationship between feedstock structure, processing conditions and biochar structure.

Biochars are complex heterogeneous materials that consist of mineral phases, amorphous C, graphitic C, and labile organic molecules, many of which can be either electron donors or acceptors when placed in soil. Biochar is a reductant, but its electrical and electrochemical properties are a function of both the temperature of production and the concentration and composition of the various redox active mineral and organic phases present. When biochars are added to soils, they interact with plant roots and root hairs, micro-organisms, soil organic matter, proteins and the nutrient-rich water to form complex organo-mineral-biochar complexes Redox reactions can play an important role in the development of these complexes, and can also result in significant changes in the original C matrix. This paper reviews the redox processes that take place in soil and how they may be affected by the addition of biochar. It reviews the available literature on the redox properties of different biochars. It also reviews how biochar redox properties have been measured and presents new methods and data for determining redox properties of fresh biochars and for biochar/soil systems.

In this study, Ni-chrome alloy particles were thermally sprayed onto a variety of substrate materials using the high-velocity air fuel (HVAF) technique. Although the various substrate materials were sprayed using identical powder material and thermal spray conditions, the type and variation of splat morphologies were strongly dependent on the substrate material. Predominantly solid splats are observed penetrating deeply into softer substrates, such as aluminum, whereas molten splats were observed on harder substrates, which resisted particle penetration. The observed correlation between molten splats and substrate hardness could be due a dependency of deposition efficiencies of solid and molten splats on the substrate material. However, it was found that conversion of particle kinetic energy into plastic deformation and heat, dependent on substrate hardness, can make a significant contribution towards explaining the observed behavior.

The deformation behaviour of diamond-like carbon (DLC) coatings on silicon substrates induced by indentation has been investigated. DLC coatings, deposited by a plasma-assisted chemical vapour deposition technique, were subjected to nanoindentation over a range of maximum loads from 100 mN to 300 mN. The resulting load-displacement plots displayed pop-ins for maximum loads of 200 mN and above, with no distinct pop-out for any of the loads studied. Compressive deformation of the coating, up to a strain of ∼ 9%, was observed. The coating–substrate composite was devoid of cracks at lower loads, but at the maximum load of 300 mN, ring cracks in the coating and a median crack in the substrate were observed. Furthermore, cracking, {111} slip and localized phase transformations were observed in the silicon substrate. The onset of these structural changes was correlated to the mechanical behaviour during indentation.

An amorphous carbon coating, approximately 1.7 μm thick, deposited onto a ductile steel substrate, was indented using a 5-μm radius spherical-tipped diamond indenter to a maximum load of 150 mN. Displacement discontinuities were observed during loading, indicative of crack formation in the system. After indentation, a focused ion beam instrument was used to prepare cross-sections, which revealed the presence of ring, radial, and lateral cracks. A three-dimensional reconstruction of the deformation zone beneath the indent was conducted using a dual ion/electron beam instrument, assisted by a commercial three-dimensional visualization software package. These three-dimensional images enabled a detailed analysis of indentation-induced cracking in this film at submicron resolution. In contrast to traditional understanding and modeling, it was observed that the development of ring cracks was asymmetric for this type of coating/substrate system. Based on this observation, it can be deduced that the strain energy release rate was different for the growth of the spiral ring crack compared with the traditional concentric-ring model. Consequently, the concentric ring-crack fracture model may not be appropriate for the evaluation of the fracture toughness of this type of coating. Hence, three-dimensional images have presented a requirement that the asymmetrical nature of ring and radial cracks should be addressed and carefully considered in the fracture mechanics analysis of this type of hard coating system.

As an extension of a previous investigation on the wear behaviour of Ca α-sialon ceramics of differing microstructures at room temperature, wear testing was conducted at 600 °C in air to explore the effects of microstructure, contact pressure and sliding speed on the wear behaviour. Under all loading conditions from 1 MPa to 1 GPa, a constant high friction coefficient was observed and a severe wear process was dominant, in which the sliding contact induced cracks were observed in different microstructures. Wear particles were generated along the wear track, but no tribofilm was detected. Increasing the sliding speed from 10 to 23 cm/s was found to significantly increase wear rate. However, variations in microstructure had little impact. That is, large elongated-grained α-sialon exhibited only a slightly lower wear rate than fine equiaxed-grained α-sialon.

The rare-earth metal nitrides have been predicted to possess a wide range of electronic structures, ranging from ferromagnetic to half-metallic to semiconducting, which makes these materials attractive for a range of applications. In this study, GdN thin films were grown at room temperature on silicon and glass quartz substrates by thermally evaporating gadolinium metal in nitrogen atmospheres. A detailed microstructural characterisation of these films was carried out using a variety of techniques such as transmission electron microscopy (TEM), Rutherford backscattering spectroscopy (RBS) and energy dispersive X-ray spectrometry. TEM analysis indicated the films are nano-crystalline, with crystallite sizes being affected by the ionisation state of the nitrogen atmosphere used. Sources of the films’ internal stress were discussed with a significant amount of oxygen absorption, identified by RBS, being a probable cause. Electron diffraction and energy dispersive X-ray studies found that GdN was the only phase present with oxygen uniformly distributed throughout the film.

The deformation mechanisms and mechanical properties of both TiN and TiAlN coatings on a V820 nitridable steel substrate have been investigated. Deformation was induced by nanoindentation, and the microstructures of the indented regions were studied using various techniques, including focused ion beam (FIB) and transmission electron microscopy (TEM). Two coatings deposited using a cathodic arc process were investigated: a thicker (1.1 μm) TiAlN–TiN dual-layer coating and a slightly thinner (0.7 μm) TiN coating. Hardness was measured using nanoindentation using a 5-μm-radius spherical indenter. A model developed by Korsunsky et al. was used to obtain the hardness of the coatings, accounting for both the thickness of the coating and the influence of the substrate. Hardnesses of 30 and 24 GPa were obtained for the TiAlN and TiN coatings, respectively. Both coatings exhibited broadly similar mechanisms of deformation. Columnar cracking and shear steps at the coating–substrate interface indicated that coatings deform predominantly by shearing along the columnar grain boundaries; however, significant lateral edge cracking was also observed, especially in the case of the TiAlN coating. The interface between the TiAlN and TiN in the dual-layer coating did not appear to affect the deformation behaviour.

The sliding wear behaviour of calcium α-sialon ceramics having two distinct microstructures, large elongated-grained and fine equiaxed-grained was revealed by observing the evolution of wear rate, wear track and debris as a function of apparent contact pressure and sliding speed, using a ball-on-disc type wear tester. The thresholds for the transition from mild to severe wear in terms of apparent contact pressure and the controlling material removal mechanisms were identified for both microstructures. The large elongated-grained microstructure had a higher wear transition threshold and exhibited a reduced wear rate in the severe wear regime, compared to the fine equiaxed-grained microstructure. This behaviour is attributed to a greater resistance to crack extension arising from the large elongated-grained microstructure. As the apparent contact pressure decreased, mild wear occurred at pressures below the thresholds for each of the microstructures. The material removal for the large elongated-grained microstructure was controlled by transgranular fracture, whereas grain pull-out prevailed in the fine equiaxed-grained microstructure. Consequently, a greater wear rate results for the fine equiaxed-grained microstructure in mild wear regime. An increase in sliding speed caused a slight increase in wear rate for both microstructures, more evidently in the mild wear regime. Models were developed to clarify the effect of microstructure on severe and mild wear of Ca α-sialon. They revealed that grain aspect ratio plays a more important role than grain diameter in the control of wear behaviour.

Deformation and fracture of a columnar-grained, ∼1.3-μm-thick TiN coating on a stainless steel substrate was investigated using a spherical tipped conical indenter of 5-μm nominal tip radius. Structural analysis, performed with the support of focused ion beam (FIB) milling and imaging techniques, revealed that the microstructure of the TiN coating had a strong influence on the deformation behavior of the coating. Intergranular sliding in the coating, as well as plastic flow in the ductile substrate, was found to be the predominant processes during the indentation. Neither plastic deformation, in the form of plastic flow, within the coating nor delamination of the interface was observed. Coating deformation was observed to be controlled by the intergranular shear cracking and thus by the interfacial columbic frictional stress between columnar grains. An indentation-energy based model was developed, which deconvolutes the coating behavior from that of the substrate, allowing quantification of the intergranular sliding stress.

In this study, the subsurface microstructure of alumina wear surfaces and the microstructure of agglomerated debris generated from unlubricated sliding wear at room temperature have been investigated through transmission electron microscopy (TEM). Specimens were thinned through the use of a focused ion beam miller (FIB). TEM studies, including analysis of electron diffraction patterns from the agglomerated region of the specimen, revealed the presence of an aggregate of nano crystalline particles embedded in an amorphous phase, together with some larger alumina particles. These larger alumina particles appear at the base of pits in the alumina surface, whereas the finer material appears at the contact surface. The agglomerated debris was readily distinguished from the alumina substrate, which contained localised dislocation damage and microcracking. It is proposed that the wear process involves the removal of 'large' alumina particles from the surface by a combination of trans- and intergranular microcracking. These particles are then ground into very fine, nanometer-sized particles that react on the surface with moisture in the air to form an amorphous hydroxide film. These are then compacted to form a nanocrystalline structure within an amorphous matrix that may also be viewed as a grain boundary phase.

Ni-chrome alloy particles were thermally sprayed onto aluminum substrates using the high-velocity air fuel technique. The particle substrate interface was investigated with focused ion beam microscopy, cross-sectional scanning electron microscopy, and cross-sectional transmission electron microscopy. No evidence of melting or chemical bonding was found in the samples. Instead, evidence of mechanical bonding was found that had been predicted by a previous theoretical study by Grujicic et al. At locations where the particle and substrate are in intimate contact, the interface exhibited interlocking features. These features are caused by the effects of turbulence due to interfacial instability and mixing at the interface during the coating process, resulting in a strong particle-substrate bond. Conversely, separated interfaces exhibited smooth surfaces, suggesting insignificant bonding between the particle and the substrate. The discovery of these interfacial formations, together with no evidence of chemical bonding across the particle-substrate interface indicate that mechanical interlocking is the dominant bonding mechanism.

An austenitic Fe–25Cr–20Ni (wt.%) alloy was first nitrided in N2–H2 then carburised at 1000°C. The nitridation produced lamellar internal precipitates of Cr2N which grew by discontinuous precipitation at a recrystallised austenite boundary formed at the precipitation front. Subsequent carburisation converted the Cr2N to a mixture of chromium-rich M7C3+CrN, and released nitrogen into the austenite matrix. The submicron CrN precipitates were stabilized by a matrix supersaturated with nitrogen and exhibited a strong orientation relationship with the surrounding austenite. The rejected nitrogen diffused deeper into the alloy to form new, more finely spaced Cr2N lamellae. Carbon diffusion overtook the nitride structure and precipitated finely spaced, lamellar M23C6 by a discontinuous precipitation process. This process is available to the carbides only when a prior boundary is present. This phenomenon, and the ability of nitridation to form a boundary and the inability of carburisation to do so, are in...

An outline of the application of the focused ion beam (FIB) workstation to the characterization of wear-resistant coatings is provided. Specimen preparation difficulties sometimes limit the usefulness of electron microscopy for microstructural characterization of coatings. However, FIB technology overcomes many of these difficulties allowing microstructural characterization to be performed both by cross-sectioning and imaging coatings and by specimen preparation of electron transparent cross-sections for subsequent examination by electron microscopy. In addition, the FIB may be combined with other techniques, such as nanoindentation or wear testing, to obtain further information about the mechanisms governing the performance of the coatings in service.

The deformation and fracture of Ti–Six–N coatings of varying Si content were examined by cross-sectional transmission microscopy. Cross-sections were prepared through both undeformed coatings and coatings which had previously been indented using a 5 μm radius spherically tipped diamond indenter. Samples with low silicon contents (0.8 and 1.5 at.%Si) had a columnar grain structure which deformed by intergranular cracking and shear sliding at the grain boundaries. Samples with higher silicon contents (9.5 and 12.5 at.%Si) consisted of TiN nanocrystals ∼5 nm in size connected by an amorphous Si3N4 phase. These coatings contained a limited amount of intergranular cracking. The nanocrystalline coatings are thought to undergo quasi-plastic deformation behaviour via cracking on a nanometer scale, where the crack size is of the order of the grain size.

Preliminary investigations of a new high-strength alloy of composition Fe30Ni20Mn25Al25 (at.%) are described in this paper. The as-cast alloy consisted of a periodic two-phase microstructure of interconnected, ∼50-nm-wide rods with fully coherent {100} interfaces, strongly suggestive of formation by a B2 to [(B2 + body-centered cubic (bcc)] spinodal decomposition. The (Ni,Al)-rich B2 and (Fe,Mn)-rich bcc phases differed in lattice parameter by

The deformation mechanisms operating during nanoindentation of TiN coatings on steel substrates were investigated using FIB cross-sectioning and imaging, as well as cross-sectional transmission electron microscopy of the indented region. Two coatings were investigated: a relatively thick (3.7 μm) coating deposited using a low voltage electron beam system, and a thinner (0.7 μm) coating deposited using a cathodic arc process. Load displacement data from nanoindentation displayed clear pop-ins as the load increased. Cracks were observed at the boundaries between the columnar grains, and steps were observed at the coating/substrate interface. A comparison of the load displacement data and the microscopic observations indicated that deformation occurs primarily by shear sliding along the columnar grain boundaries.

The solid-state reactions between Al and TiO2 that occur during heating an Al/TiO2 nanocomposite powder produced using high-energy mechanical milling have been studied using thermal analysis, x-ray diffractometry (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM) in combination with compositional microanalysis. It has been found that Al and TiO2 react in the temperature range from 650 to 800 °C, forming Al3Ti, but XRD analysis, SEM examination, and detailed TEM characterization of the powder particles heated to 800 °C show that the expected Al2O3 does not form. However, α–Al2O3 particles form during heating from 800 to 1000 °C. The possible reasons for the time gap between formation of Al3Ti and Al2O3 are discussed.

Two hot-pressed sintered α-sialon samples of differing microstructures, but identical chemical composition, were evaluated first, in terms of indentation hardness and modulus, by depth-sensing indentation (DSI) tests on planes parallel and normal to the hot-pressed surface. The surface and subsurface cracks created under the DSI tests have also been investigated in relation to the effect of microstructure. Subsequently, Vickers indentation tests were conducted to explore the deformation and fracture characteristics in the two samples. The effect of microstructure and grain orientation on the development of different types of cracks, in particular subsurface cracks, was revealed and analyzed. Additionally, it suggested that the focused ion beam (FIB) miller is a preferred tool, in comparison to the conventional cross-sectioning techniques, for examining subsurface crack formation and structural characteristics.

The microstructure and mechanical properties of off-stoichiometric single-crystal Fe2AlMn have been investigated. After casting, the alloy contained two sets of thermal antiphase boundaries, (a/4)⟨111⟩ and (a/2)⟨100⟩, which are attributed to the fact that the compound solidifies into a bcc structure and subsequently orders to a B2 structure and then a L21 structure respectively upon further cooling. Crystals strained under tension at room temperature in air at 1s−1 showed 6% elongation, whereas specimens strained at 1 × 10−5 s−1 showed no elongation, indicating that the compound is sensitive to the testing environment. Fracture occurred on {100} in both cases. Compression tests showed that a yield anomaly was present at intermediate temperatures, with the peak yield strength occurring at about 800 K, which is slightly below the L21–B2 transition temperature of 898 K. The slip systems were found to be ⟨111⟩{110} at room temperature and 800 K. Transmission electron microscopy observations showed fourfold-di...

The microstructure and surface morphology of a TiN hard, wear resistant coating on a V820 nitridable alloy ductile steel substrate following nanoindentation have been characterized using focused ion beam (FIB) milling. A TiN coating, ∼0.6 μm in thickness, was deposited on a ductile steel substrate using a cathodic arc evaporation (CAE) technique. Pop-in events were observed in the load–displacement curves and correlated to the observed microstructural features. Following nanoindentation with a 1 μm radius spherical indenter at loads of 100 mN and 500 mN, circumferential cracks were observed inside the indentation. Observations of nanoindented cross-sections prepared using FIB revealed both columnar cracks in the coating and shear steps at the coating–substrate interface. These structural features were observed at higher resolution using a transmission electron microscope (TEM).

The recrystallization kinetics and final grain size following cold rolling and annealing of an Al alloy (AA2014) and a particulate reinforced AA2014 composite containing 20 vol% alumina particulates of average diameter 15 μm were investigated. For a given level of strain (5–95% reduction), annealing was carried out at temperatures from 350 to 500 °C and heating rates from 2.5×10−3 to 30 °C/s. The alumina particles in the composite act as potential sites for particle stimulated nucleation (PSN) of recrystallization. Compared with the alloy, recrystallization in the composite was accelerated, particularly following low levels of cold-work. This was attributed to extensive PSN at low strains in the composite and from an increased stored energy of the matrix thereby increasing the driving force for recrystallization. For a given set of processing conditions, the recrystallized grain size in the composite was finer than in the alloy. This was most notable for material strained to less than 50% reduction and annealed at low temperatures and low heating rates and was attributable to the same factors influencing the recrystallization kinetics. A model is presented for the composite to predict the recrystallized grain size as a function of strain, with respect to the size distribution and number density of alumina particles. This model predicts the strain dependence of the recrystallized grain size and, in particular, the grain size insensitivity to strain at moderate-to-high levels of cold-work.

Polycrystalline MgB 2 samples with 0, 5, 10, and 20 wt% nano- Y - ZrO 2 (YSZ) powder addition were prepared by short time, as little as several minutes, or long time in-situ reaction process. The phases, microstructures and flux pinning behaviors were characterized using X-ray diffractometry (XRD), Scanning Electron Microscopy (SEM), Transmission Electron Microscope (TEM) and Magnetic Measurements. Results indicated that nano-YSZ particles included in MgB 2 grains. Samples doped with 10wt% YSZ powders showed new record of critical current density Jc as high as 1×106 and 4×106 A/cm 2 in low magnetic fields at 30 and 20K, respectively. However, the Jc drops faster compared to that made by long time sintering samples. It is proposed that the improved Jc in low fields was due to the enhanced density of the sample, which was caused by the YSZ nano-particle inclusion.

Strain-induced ferromagnetism in B2-structured Fe–Al arises mostly from anti-phase boundary (APB) tubes where groups of moment-bearing Fe atoms with at least three like nearest-neighbors are large enough to be magnetically coupled and behave ferromagnetically. Following our previous work on binary Fe–Al, strain-induced ferromagnetism in ternary single crystals of Fe–40 at.%Al–3 at.%Cu and Fe–40 at.%Al–3 at.%Cr was studied. When deformed to similar rolling strains along the same orientation, the saturation magnetization, M S , was found to be greatest for Fe–40 at.%Al, followed by Fe–40 at.%Al–3 at.%Cu, Fe–40 at.%Al–3 at.%Cr and Fe–43 at.%Al. This behavior can be explained by the site preferences of the Cu and Cr atoms on the Fe and Al sublattices, which both change the probability of a Fe atom having like nearest-neighbors in the APB tubes and affect the energy of the anti-phase boundaries. Calculations of M S at 0 K of rolled Fe–40 at.%Al–3 at.%Cu and Fe–40 at.%Al–3 at.%Cr specimens, based on APB tube densities and considerations of the APB tube size and geometry, were found to be in reasonable agreement with experimentally determined values. APB tubes were observed by transmission electron microscopy in Fe–40 at.%Al, Fe–40 at.%Al–3 at.%Cu and Fe–40 at.%Al–3 at.%Cr.

The damage created in silicon transmission electron microscope specimens prepared using a focused ion beam miller is assessed using cross-sections of trenches milled under different beam conditions. Side-wall damage consists of an amorphous layer formed by direct interaction with the energetic gallium ion beam; a small amount of implanted gallium is also detected. By contrast, bottom-wall damage layers are more complex and contain both amorphous films and crystalline regions that are richer in implanted gallium. More complex milling sequences show that redeposition of milled material, enriched in gallium, can occur depending on the geometry of the mill employed. The thickness of the damage layers depends strongly on beam energy, but is independent of beam current. Monte Carlo modelling of the damage formed indicates that recoil silicon atoms contribute significantly to the damaged formed in the specimen.

This paper presents the first observations of antiphase boundary (APB) tubes in the L21-structured intermetallic compound Fe2AlMn after deformation and of a corresponding deformation-induced paramagnetic to ferromagnetic transition. Annealed Fe2AlMn also shows a magnetic transition below approximately 165 K. The saturation magnetization of both annealed and strained Fe2AlMn increases with decreasing temperature.

TiN and TiAlN/TiN PVD coatings deposited onto as-ground surfaces have been characterised via direct cross-sectional imaging and transmission electron microscopy with the aid of a focused ion beam system. Cross-sections showed that the coatings exhibit consistent coverage, even in sheltered areas such as at the base of grooves resulting from prior grinding. A columnar grain structure was observed in all coatings. A number of defects were observed such as seams and voids resulting from coating onto the as-ground surface and macroparticles which were shown to be deposited during the metal ion etching stage. Cross-sections through nanoindents revealed that the coatings deform by through-thickness shear cracking.

Cathodic arc evaporation (CAE) is a widely used technique for generating highly ionised plasma from which hard, wear-resistant PVD coatings can be deposited. A major drawback of this technique is the emission of micrometer-sized droplets of cathode material from the arc spot, which are commonly referred to as ‘macroparticles’. In this study, the effect of cathode poisoning was investigated as a method to reduce the number of macroparticles in PVD coatings. While the study focuses on the reduction of macroparticles in titanium nitride coatings, the outcomes and key findings can be broadly applied to the cathodic arc process, in particular, for the reduction of macroparticles in more advanced CAE coatings. The results support earlier findings that have shown that poisoning of the cathode can reduce the number of macroparticles emitted from the arc spot. The results of glow discharge optical emission spectroscopy (GD-OES) showed that the titanium content of the coatings varied little between the respective coatings despite changes in the deposition pressure from 0.1 to 1.2 Pa. The GD-OES results also showed the presence of oxide contamination at the surface of the coatings, which was significantly reduced with increasing deposition pressure. The coatings were also deposited onto high-speed steel twist drills to compare the metal-cutting performance when dry drilling a workpiece of cast iron. The results of the drill tests showed that tool life increased with a reduction in the number of macroparticles.

The microstructures of a series of TiN and TiAlN wear resistant coatings on steel substrates are characterized using cross-sectional transmission electron microscopy. TiN coatings were deposited using both low-voltage electron beam evaporation and cathodic arc techniques, and a dual-layer TiN–TiAlN coating was prepared using cathodic arc deposition. All of the coatings consisted of columnar grains separated by high-angle grain boundaries. In all specimens, the substrate/coating interface was sharp and no Ti interlayer or modification of the substrate was observed. The TiN/TiAlN dual-layer coating contained a layered interfacial region where both the Ti and TiAl sources were operating concurrently. The TiAlN regions consisted of extremely fine sub-layers ∼2 nm thick, which are thought to result from the threefold planetary rotation of the specimen in the deposition chamber. The columnar grains grew epitaxially through the entire TiN/TiAlN interfacial region. TEM specimens were prepared using the focused ion beam, which allowed large, uniformly thin areas to be prepared with relative ease.

The U/n method is a well-established means of improving flux pinning and critical current performance in cuprate superconductors. The method involves the doping of the superconductor with 235U followed by irradiation with thermal neutrons to promote fission. The resultant columnar damage tracks produced by the energetic fission products pin flux vortices and improve critical current performance in magnetic fields. No such improvement could be observed when the U/n method was applied to MgB2 superconductor. No fission tracks could be observed in TEM, even for samples that were irradiated at the highest fluence. Gamma-ray spectroscopy indicated that fission had occurred in the expected way.

Bulk density and dilatometer measurements were carried out for stoichiometric iron aluminide (FeAl) in order to determine the thermal vacancy concentrations as a function of time and temperature. For temperatures of 600 °C and below the specimen bulk density or length were found to depend on heat treatment history, i.e., they were not unique functions of the temperature. This path dependence suggests a lack of active sources and sinks for thermal vacancies in FeAl at temperatures below ≈600 °C.

The microstructural development during cold rolling and static recovery of an Al alloy (AA 2014) and an AA 2014 particulate-reinforced metal matrix composite (PMMC) was investigated. The composite contained 20 vol.% of 15 μm diameter Al 2 O 3 particulates. Both materials were rolled at room temperature and subsequently annealed to determine the effect of the reinforcement on static recovery. The addition of the ceramic reinforcement affected the matrix deformation microstructure by refining the cellular substructure near Al 2 O 3 particles and generating shear bands and complex deformation zones in the vicinity of particle clusters. Following deformation, room temperature storage was sufficient to decrease the hardness of the composite, and annealing at 200 °C resulted in a more rapid rate of recovery compared with the alloy. This enhanced recovery was attributable to a larger driving force brought about by the finer cell size near the particles, but internal stress relaxation and interfacial diffusion may also be important factors, particularly at ambient temperature. The Al 2 O 3 particles, particularly those in clusters, enhanced considerably the rate of subgrain growth of the matrix. Based on models of various stages of recovery, the enhanced rate of softening in the composite is not likely to be associated with a particular mechanism but involves a number of separate, but overlapping mechanisms.

Focused ion beam (FIB) milling and imaging are powerful techniques for evaluation of surface contact-induced crack structures and the effect of microstructure on crack growth in ceramics. Two distinct α-sialon microstructures made from the same composition were tested under indentation, scratching and grinding conditions. Following each test, the FIB was used to analyze fracture events in both the surface and subsurface, and reveal the factors that control material removal during surface contact.

SiC doped MgB/sub 2/ polycrystalline samples were fabricated by in-situ reaction using different grain sizes (20 nm, 100 nm, and 37 /spl mu/m) of SiC and different doping levels (0, 8, 10, 12, 15 wt%). Phases, microstructures, superconductivity, critical current density and flux pinning have been systematically investigated using XRD, SEM, TEM, and magnetic measurements. Results show that grain sizes of the starting precursors of SiC have a strong effect on the critical current density and its field dependence. The smaller the SiC grains are, the better the J/sub c/ field performance is. Significant enhancement of J/sub c/ and the irreversibility field H/sub irr/ were revealed for all the SiC doped MgB/sub 2/ with additions up to 15 wt%. A J/sub c/ as high as 20,000 A/cm/sup 2/ in 8 Tesla at 5 K was achieved for the sample doped with 10 wt% SiC with a grain size of 20 nm. Results indicate that the nano-inclusions and substitution inside MgB/sub 2/ are responsible for the enhancement of flux pinning.

A sputter-coated gold film, of variable thickness, was used to protect the near surface region structure of an AlAs–InAs superlattice from damage during transmission electron microscope (TEM) specimen preparation using a focused ion beam (FIB) miller. This coating was applied before the deposition of any platinum protective film in the FIB. The extent of any damage in this specimen was investigated by TEM. Where the gold film was either locally absent or of low thickness (

Scratch tests were conducted using a standard pyramid indenter against α-SiAlON ceramics with different microstructures: (i) fine equiaxed grains and (ii) large elongated grains. The formation and propagation of cracks were investigated via focused ion-beam milling, with an emphasis on the effect of microstructure on material removal. The fine equiaxed microstructure exhibited high resistance to material removal at low loads, because of its high hardness and homogeneous structure. As the load increased, radial and lateral cracks developed, resulting in large-scale chipping. In contrast, the large elongated microstructure showed a propensity to form microcracks and microabrasion, which is characteristic of partial grain removal, at low loads. With increasing loads, however, the large elongated grains suppressed the propagation of radial and lateral cracks, and, consequently, no large-scale chipping occurred. Implications for material design in abrasive-wear conditions have been discussed.

Model Fe–25 w/o (weight percent) Cr and Fe–25 Cr–Ni alloys containing 2.5, 5, 10 and 25w/o nickel were exposed to a CO–26H2–6H2O (vol. pct) mixture at 680°C under thermal cycling conditions. The supersaturated carbon activity was calculated to be 2.9 (referred to graphite) and M3C was predicted to form on Fe–25Cr and Fe–25 Cr–2.5 Ni, but not on higher nickel content alloys. Metal dusting occurred on all alloys, accompanied by internal carburisation. Transmission electron microscopy of the dusting deposit showed that much of the carbon consisted of hollow graphite nanotubes. Small, metal-rich particles were found at the carbon filament tips. These were identified as single crystal Fe3C in the case of Fe–25 Cr, and M3C, containing low levels of nickel, in the case of Fe–25 Cr–2.5 Ni and Fe–25 Cr–5 Ni. In contrast, the particles found at the filament tips on the higher nickel, two phase, alloys were both M3C and austenitic Fe–Ni. Strong orientation relationships were determined between the graphite a...

Operating conditions in a current design for a planar geometry oxide fuel cell plant are briefly reviewed and the danger of encountering “metal dusting” conditions identified. Laboratory tests were designed to produce accelerated metal dusting by exposing heat resisting alloys to a CO–26 H2–6 H2O (vol. pct) gas mixture at 680°C under thermal cycling conditions. The hot gas composition corresponded to ac = 2.9 and an oxygen potential high enough to oxidise chromium and aluminium, but not iron or nickel. The alloys tested included ferritic and austenitic chromia formers and two ferritic alumina formers, all with electropolished surfaces. Thermal cycling of the chromia formers led to oxide scale damage followed by internal carburisation, metal dusting and coking. This failure occurred very rapidly on most austenitic materials (Alloy 800, Inconel 601, 690, 693, Alloy 602CA), but did not commence until after approximately 50 one-hour cycles for the ferritic steel Fe–27Cr–0.001Y (wt %). The alloy with t...

It is well established that single crystals of B2-structured Fe-Al change from paramagnetic to ferromagnetic upon plastic deformation. This strain-induced ferromagnetism arises mostly from Fe atoms which have three or more like nearest neighbours (NNs) in antiphase-boundary (APB) tubes. Such Fe atoms carry magnetic moments according to their local environment. In this study, the saturation magnetizations, M S , of cold-rolled Fe-34 at.% Al, Fe-40 at.% Al and Fe-43 at.% Al single crystals were measured in a vibrating-sample magnetometer from 77 K to room temperature and transmission electron microscopy was used to confirm the presence of APB tubes. After magnetic measurements, rolled single crystals were heated in a differential scanning calorimeter at 20 K min m1 to 973 K and the enthalpy associated with the removal of the APB tubes measured. From the enthalpy measurement, the APB tube density and the number of Fe NNs were estimated. Hence, the M S values at 0 K were calculated. These were in good agreeme...

The recrystallized grain size following cold rolling and annealing of an Al alloy (AA2014) and a particulate reinforced AA2014 composite was investigated. The composite contained 20 vol% alumina particulates of average diameter 15 μm. The recrystallized grain size in the composite was finer than in the alloy, for a given set of conditions; this was most notable for material strained less than 50% cold-work. This behaviour was attributable to a higher nucleation efficiency in the matrix adjacent to coarse alumina particles in the composite. A model was presented for the composite to predict the recrystallized grain size as a function of strain, with respect to the size distribution and number density of alumina particles. This model predicted the strain dependence of the recrystallized grain size and, in particular, the grain size insensitivity to strain at moderate-to-high levels of cold-work.

In this work contact pressure and sliding distance-induced changes in wear rate and mechanism, and friction behaviour of alumina are investigated by consideration of sub-surface damage. Sub-surface cracking and the formation of tribochemical reaction products are observed through the use of a novel sectioning technique; focused ion-beam milling. Initially wear rate experiments with three different grain sizes and different contact loads were undertaken. These were followed by extensive sub-surface microscopic investigations. Wear experiments, undertaken on a pin-on-disc tribometer over a range of contact pressures, revealed that wear mechanisms changed as contact pressure decreased. Both wear rate and friction were monitored. Debris and surface layers which formed were characterised using X-ray photoelectron spectroscopy (XPS). This identified an oxide/hydroxide layer which formed during wear and which was found to significantly affect friction. The nature of this layer varied significantly with contact pressure and sliding distance. It was found that mild wear of alumina in air involves the continual formation and removal of a surface layer at differing rates.

The purpose of this paper is to describe the microstructure, mechanical properties and wear behavior of NiAl-based alloys both with and without a ductile b.c.c. phase. The materials studied had equiatomic amounts of Ni and Al, with four different additions of iron – 10, 20, 30 and 44 at.%. The microstructures were examined using both optical microscopy and transmission electron microscopy. The alloys containing 10 and 20% iron were single phase with an ordered b.c.c. (or B2 structure), whilst those containing 30 and 44% Fe were two-phase with a B2 matrix containing fine b.c.c. precipitates. The addition of iron did not improve the room temperature tensile ductility significantly, although some increase in both the compressive yield strength and the hardness was noted as the iron content increased. Wear tests, which were conducted in an argon atmosphere to minimize environmental effects, showed a higher wear rate for the two-phase alloys despite their slightly higher hardnesses, presumably due to shear of the ductile phases present in these alloys.

Metal dusting is the disintegration of alloys into carbon and metal particles during high-temperature exposure to carbon-bearing gases. Model Fe–Cr and Fe–Ni–Cr alloys were studied to test the hypothesis that M3C formation is necessary for metal dusting to occur. The alloys were exposed to a 68% CO–26% H2–6% H2O gas mixture at 680°C (ac=2.9) under thermal cycling conditions. Equilibrium calculations predicted the formation of M3C at the surface of Fe–25Cr, but not Fe–60Cr. All compositions were expressed in w/o, weight percent. Alloys of Fe–25Cr with 2.5, 5, 10, and 25 w/o nickel additions were also exposed to the same conditions to study the role of nickel in destabilizing the precipitation of M3C and, hence, altering the resistance to metal dusting. Metal dusting was observed on all the alloys except Fe–60Cr. For Fe–25Cr, Fe–25Cr–2.5Ni, and Fe–25Cr–5Ni, the carbonization and dusting process was localized, and its incidence decreased in Fe–25Cr–2.5Ni, consistent with the increased destabilization of M3C precipitation. However, Fe–25Cr–10Ni and Fe–25Cr–25Ni both underwent extensive dusting in the absence of protective Cr2O3 formation. The carbon deposits formed consisted of carbon filaments, which contained particles at their tips. These were shown by electron diffraction to be exclusively Fe3C in Fe–25Cr, Fe–25Cr–2.5Ni, and Fe–25Cr–5Ni, and a mixture of austenite and (Fe,Ni)3C in Fe–25Cr–10Ni and Fe–25Cr–25Ni.