- Geelong, Victoria, Australia
Ross Marceau
Deakin University, Institute for Frontier Materials, Department Member
- Thermodynamics, Mechanical Behavior Of Materials, Microstructure, Atom probe tomography, Atom Probe, Atom probe field ion microscopy, and 7 moreModeling and Simulation, Scanning Electron Microscopy, Steel, Nanosteel, Structured Steel, Pearlite, and Cementite(Modeling and Simulation, Scanning Electron Microscopy, Steel, Nanosteel, Structured Steel, Pearlite, and Cementite)edit
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Molybdenum (Mo) is known to have a complex effect on phase transformations and precipitation in steels manufactured by conventional casting. The present work aims to examine the effect of Mo on phase transformations in Nb-containing... more
Molybdenum (Mo) is known to have a complex effect on phase transformations and precipitation in steels manufactured by conventional casting. The present work aims to examine the effect of Mo on phase transformations in Nb-containing steels produced by strip casting. Advanced experimental techniques have been utilised to simulate the strip casting process, and the microstructural features of the rapid solidification are retained for further study. Two cooling conditions from the austenite phase field were examined, isothermal holding and continuous cooling. It was found that at high cooling rates, the addition of Mo delayed the nucleation of bainite and lowered the bainite start temperature, but did not alter the bainite growth rate. The addition of Mo was also found to result in a slower transformation rate of polygonal ferrite under both isothermal and continuous cooling conditions. Thermodynamic simulations indicated that Mo did not affect the growth velocity of the polygonal ferrite, and quantitative metallography showed the nucleation density was significantly reduced by Mo addition. For the slowest continuous cooling rate, the addition of Mo completely inhibited pearlite formation, with bainitic ferrite forming instead. This has been suggested to be the result of the suppression of pearlite nucleation, rather than inhibition of growth.
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A common strategy to enhance the fibre-to-matrix adhesion of carbon fibres is to increase the surface polarity using extensive and harsh oxidation techniques. In this work, we use a novel...
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Abstract The isothermal evolution of nanometre-sized precipitates formed in a Ti-Mo microalloyed steel through interphase precipitation has been investigated using atom probe tomography and small-angle neutron scattering. The coiling time... more
Abstract The isothermal evolution of nanometre-sized precipitates formed in a Ti-Mo microalloyed steel through interphase precipitation has been investigated using atom probe tomography and small-angle neutron scattering. The coiling time and applied strain have been varied to observe the precipitate evolution at a constant coiling temperature of 650 °C, where various evolution parameters such as particle radius, number density, volume fraction and chemical composition have been evaluated and compared. The possibility of early stage solute clustering and its effect on precipitate formation have also been investigated. Clustering of Ti, Mo and C atoms as Ti-C and Mo-C has been observed at the shortest coiling time of 5 min. These clusters are assumed to be precursors to the carbide precipitates observed in the system, which exhibit a metastable composition, containing a carbon fraction (C/Ti+Mo ratio) in the range of 0.2–1. In particles having a Guinier radius > 3 nm, however, the average chemical composition approached the stable MC carbide stoichiometry with Ti/Mo ratio ~2.5 and C/(Ti+Mo) ratio ~0.55. This study reveals that the precipitate coarsening kinetics are very slow, with average particle diameter 10 h) in both the undeformed and deformed conditions. This is believed to be due to the reduction in equilibrium Ti content in the matrix as a result of partial replacement of Ti by Mo (Ti/Mo ratio > 2) in the precipitate lattice, in the presence of excess C in the system.
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High-strength aluminum alloys are important for lightweighting vehicles and are extensively used in aircraft and, increasingly, in automobiles. The highest-strength aluminum alloys require a series of high-temperature “bakes” (120° to... more
High-strength aluminum alloys are important for lightweighting vehicles and are extensively used in aircraft and, increasingly, in automobiles. The highest-strength aluminum alloys require a series of high-temperature “bakes” (120° to 200°C) to form a high number density of nanoparticles by solid-state precipitation. We found that a controlled, room-temperature cyclic deformation is sufficient to continuously inject vacancies into the material and to mediate the dynamic precipitation of a very fine (1- to 2-nanometer) distribution of solute clusters. This results in better material strength and elongation properties relative to traditional thermal treatments, despite a much shorter processing time. The microstructures formed are much more uniform than those characteristic of traditional thermal treatments and do not exhibit precipitate-free zones. These alloys are therefore likely to be more resistant to damage.
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Abstract Medium to high strength heat-treatable aluminum alloys of the 6000 series (Al-Mg-Si) have long been used for structural engineering applications. Their use in the automotive industry is growing rapidly, however the detrimental... more
Abstract Medium to high strength heat-treatable aluminum alloys of the 6000 series (Al-Mg-Si) have long been used for structural engineering applications. Their use in the automotive industry is growing rapidly, however the detrimental effects of room temperature storage (natural aging) on hardenability (artificial aging) hinders widespread applicability. Although numerous explanations have been proposed, there is no unified description of the mechanisms behind the negative effect. The current work builds on previous studies that identified a compositional (Mg:Si) dependence of the negative effect on hardening behavior, and finds a corresponding difference in the effect of room temperature clusters at artificial aging temperatures. Model alloys with different Mg:Si ratios were subjected to various thermal treatments including natural and artificial aging, and analyzed using atom probe tomography. This work represents the only atom probe tomography evidence to date showing increased thermal stability of naturally aged solute clusters in Mg-rich 6000 series alloys relative to Si-rich counterparts.
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Abstract For several decades, the formation of carbon(C)-rich domains upon room temperature aging of supersaturated martensite has been a matter of debate. C-rich tweed-like patterns are observed to form after short aging times at room... more
Abstract For several decades, the formation of carbon(C)-rich domains upon room temperature aging of supersaturated martensite has been a matter of debate. C-rich tweed-like patterns are observed to form after short aging times at room temperature and coarsen upon further aging. Here, we present a systematic atomic-scale investigation of carbide formation in Fe-15Ni-1C (wt.%) martensite after two to three years of isothermal room temperature aging by a combination of atom probe tomography and transmission electron microscopy. Owing to the sub-zero martensite start temperature of −25 °C, a fully austenitic microstructure is maintained at room temperature and the martensitic phase transformation is initiated during quenching in liquid nitrogen. In this way, any diffusion and redistribution of C in martensite is suppressed until heating up the specimen and holding it at room temperature. The microstructural changes that accompany the rearrangement of C atoms have been systematically investigated under controlled isothermal conditions. Our results show that after prolonged room temperature aging nanometer-sized, plate-shaped η-Fe2C carbides form with a macroscopic martensite habit plane close to {521}. The orientation relationship between the η-Fe2C carbides and the parent martensite grain (α′) follows [001]α’//[001]η, ( 1 ¯ 10 ) α’//(020)η. The observation of η-Fe2C–carbide formation at room temperature is particularly interesting, as transition carbides have so far only been reported to form above 100 °C. After three years of room temperature aging a depletion of Fe is observed in the η carbide while Ni remains distributed homogenously. This implies that the substitutional element Fe can diffuse several nanometers in martensite at room temperature within three years.
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ABSTRACT The decomposition sequence of the supersaturated solid solution leading to the formation of the equilibrium S (Al2CuMg) phase in Al-Cu-Mg alloys has long been the subject of ambiguity and debate. Recent high-resolution... more
ABSTRACT The decomposition sequence of the supersaturated solid solution leading to the formation of the equilibrium S (Al2CuMg) phase in Al-Cu-Mg alloys has long been the subject of ambiguity and debate. Recent high-resolution synchrotron powder diffraction experiments have shown that the decomposition sequence does involve a metastable variant of the S phase (denoted S1), which has lattice parameters that are distinctly different to those of the equilibrium S phase (denoted S2). In this paper, the difference between these two phases is resolved using high-resolution synchrotron and neutron powder diffraction and atom probe tomography, and the transformation from S1 to S2 is characterised in detail by in situ synchrotron powder diffraction. The results of these experiments confirm that there are no significant differences between the crystal structures of S1 and S2, however, the powder diffraction and atom probe measurements both indicate that the S1 phase forms with a slight deficiency in Cu. The in situ isothermal aging experiments show that S1 forms rapidly, reaching its maximum concentration in only a few minutes at high temperatures, while complete conversion to the S2 phase can take thousands of hours at low temperature. The kinetics of S phase precipitation have been quantitatively analysed for the first time and it is shown that S1 phase forms with an average activation energy of 75 kJ/mol, which is much lower than the activation energy for Cu and Mg diffusion in an Al matrix (136 kJ/mol and 131 kJ/mol, respectively). The mechanism of the replacement of S1 with the equilibrium S2 phase is discussed.
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The present paper reviews recent progress in atomic-scale characterisation of composition and nanostructure of light alloy materials using the technique of atom probe tomography. In particular, the present review will highlight... more
The present paper reviews recent progress in atomic-scale characterisation of composition and nanostructure of light alloy materials using the technique of atom probe tomography. In particular, the present review will highlight atom-by-atom analysis of solid solution architecture, including solute clustering and short-range order, with reference to current limitations of spatial resolution and detector efficiency of atom probe tomography and methods to address these limitations. This leads to discussion of prediction of mechanical properties by simulation and modelling of the strengthening effect exerted by solute clusters and the role of experimental atom probe data to assist in this process. The unique contribution of atom probe tomography to the study of corrosion and hydrogen embrittlement of light alloys will also be discussed as well as a brief insight into its potential application for the investigation of solute strengthening of twinning in Mg alloys.
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Abstract Ultra-high strength steels are interesting materials for light-weighting applications in the transportation industries. A key requirement of these applications is weldability and consequently a low carbon content is desirable.... more
Abstract Ultra-high strength steels are interesting materials for light-weighting applications in the transportation industries. A key requirement of these applications is weldability and consequently a low carbon content is desirable. Maraging steels are examples of ultra-high strength, low carbon steels but their disadvantage is their high cost due to the large Ni and/or Co additions required. This contribution is focussed on the development of steels with maraging-like strengths but with low solute contents (less than 10%). A series of alloy compositions were designed to exploit precipitation of the G phase in a ferritic matrix at temperatures of 450–600 °C in order to obtain yield strengths in excess of 2 GPa. The mechanical response of the materials was measured using tension and compression testing and the precipitate evolution has been characterized using atom probe tomography (APT) and in-situ small angle X-ray scattering (SAXS) at a synchrotron beamline. Precipitate number densities of 1025 m−3 are obtained, which are amongst the highest number densities so far observed in engineering alloys. The intrinsic strength of the G phase is shown to be proportional to its size, and deviations in the chemistry of the precipitates do not significantly affect their strengthening behaviour. An important outcome is that the common temper embrittlement issues known to occur during aging of martensite in the 450–600 °C range were mitigated in one alloy by starting with a cold-rolled and partially fragmented lath martensite instead of a freshly quenched martensite.
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Abstract Microalloying trace elements into aluminium alloys have been shown to improve mechanical properties by altering the precipitation process. Here, trace amounts of Sn and (Sn + Ag) have been added to Al-1.1Cu-1.7Mg (at.%) and the... more
Abstract Microalloying trace elements into aluminium alloys have been shown to improve mechanical properties by altering the precipitation process. Here, trace amounts of Sn and (Sn + Ag) have been added to Al-1.1Cu-1.7Mg (at.%) and the effects have been investigated by a combination of hardness testing and transmission electron microscopy (TEM). Hardness testing shows that the addition of Sn increases the hardness throughout the ageing process, and in combination with Ag, further increases the hardness and shortens the time to reach the peak hardness. The increase in hardness via Sn microalloying is attributed to the homogeneous distribution of S phase (Al 2 CuMg) precipitates. In the alloy microalloyed with both Sn and Ag, the microstructure is dominated by homogeneously distributed Ω phase (Al 2 Cu) precipitates in the peak strengthened condition. Given that neither spherical β-Sn precipitates, nor any other obvious nucleation sites for the Ω phase precipitates were observed using TEM, the mechanism for development of such homogeneous precipitation remains to be determined.
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ABSTRACT The deformation behaviour of two single phase binary alloys, Mg–5Y and Mg–10Y, have been examined. In compression, two twin types were observed, the common {101-2} twin as well as the less common {112-1} extension twin. It is... more
ABSTRACT The deformation behaviour of two single phase binary alloys, Mg–5Y and Mg–10Y, have been examined. In compression, two twin types were observed, the common {101-2} twin as well as the less common {112-1} extension twin. It is shown that the {112-1} twin is much less sensitive to solute concentration than the {101-2} twin, and it is suggested that the simple atomic shuffle of the {112-1} twin reduces the solute strengthening imparted by Y additions. The common {101-2} twin showed significant hardening as a result of alloying with Y. An analysis of solute behaviour has indicated that of the four chemical parameters investigated, i.e. atomic size, shear modulus, electronegativity and solute distribution, it appears to be the larger atomic radius of Y compared to Mg that increases the stress required to activate the {101-2} twin. It is suggested that the large atomic radius inhibits the atomic shuffling process which accompanies the twinning shear in this twin type.
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We present a novel approach for analysis of low-conductivity and insulating materials with conventional pulsed-voltage atom probe tomography (APT), by incorporating an ultrathin metallic coating on focused ion beam prepared needle-shaped... more
We present a novel approach for analysis of low-conductivity and insulating materials with conventional pulsed-voltage atom probe tomography (APT), by incorporating an ultrathin metallic coating on focused ion beam prepared needle-shaped specimens. Finite element electrostatic simulations of coated atom probe specimens were performed, which suggest remarkable improvement in uniform voltage distribution and subsequent field evaporation of the insulated samples with a metallic coating of approximately 10nm thickness. Using design of experiment technique, an experimental investigation was performed to study physical vapor deposition coating of needle specimens with end tip radii less than 100nm. The final geometries of the coated APT specimens were characterized with high-resolution scanning electron microscopy and transmission electron microscopy, and an empirical model was proposed to determine the optimal coating thickness for a given specimen size. The optimal coating strategy was ...
Research Interests: Materials Science, Computational Biology, Transmission/Scanning Electron Microscopy, Transmission Electron Microscopy, Scanning Transmission Electron Microscopy, and 9 moreMedicine, Tomography, Gold, Bacteria, Empirical Research, Ultramicroscopy, Optical physics, Nanospheres, and Electric Conductivity
High-strength aluminium alloys such as AA2024-T3 are often developed by the introduction of plastic deformation to a precipitate containing microstructure. These alloys contain complex, near-surface nanostructures whose effects on... more
High-strength aluminium alloys such as AA2024-T3 are often developed by the introduction of plastic deformation to a precipitate containing microstructure. These alloys contain complex, near-surface nanostructures whose effects on localised corrosion processes have not been well understood due primarily to the difficulty of characterising these heterogeneous compositions and structures. In this work, we observed entangled oxide networks co-located with dislocation structures piled up at corroded intermetallic particles of an AA2024-T3 alloy. It was revealed that dislocation arrays act as pathways for corrosive species and promote structural degradation at interfacial regions, providing a new insight into corrosion initiation at the nano-scale.
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Emergence of multi-drug resistant Gram-negative bacteria has caused a global health crisis and polymyxins are increasingly used as the last-line class of antibiotics. The chemical composition at the cell surface plays a key role in... more
Emergence of multi-drug resistant Gram-negative bacteria has caused a global health crisis and polymyxins are increasingly used as the last-line class of antibiotics. The chemical composition at the cell surface plays a key role in polymyxin resistance. Unlike imaging the cellular ultrastructure with well-developed electron microscopy, acquisition of a high-resolution chemical map of the bacterial surface still remains a technological challenge. In this study, we developed an atom probe tomography (APT) analysis approach to acquire mass spectra in the pulsed-voltage mode and reconstructed the 3D chemical distribution of atoms and molecules in the subcellular domain at the near-atomic scale. Using focused ion beam (FIB) milling together with micromanipulation, site-specific samples were retrieved from a single cell of Acinetobacter baumannii prepared as needle-shaped tips with end radii less than 60 nm, followed by a nano-scale coating of silver in the order of 10 nm. The significant...
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ABSTRACT Short-range-order (SRO) has been quantitatively evaluated in an Fe-18Al (at%) alloy using atom probe tomography (APT) data and by calculation of the generalised multicomponent short-range order (GM-SRO) parameters, which have... more
ABSTRACT Short-range-order (SRO) has been quantitatively evaluated in an Fe-18Al (at%) alloy using atom probe tomography (APT) data and by calculation of the generalised multicomponent short-range order (GM-SRO) parameters, which have been determined by shell-based analysis of the three-dimensional atomic positions. The accuracy of this method with respect to limited detector efficiency and spatial resolution is tested against simulated D03 ordered data. Whilst there is minimal adverse effect from limited atom probe instrument detector efficiency, the combination of this with imperfect spatial resolution has the effect of making the data appear more randomised. The value of lattice rectification of the experimental APT data prior to GM-SRO analysis is demonstrated through improved information sensitivity. Copyright © 2015 Elsevier B.V. All rights reserved.
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We have investigated the strain-hardening mechanisms across the relevant scales in a Fe-22Mn-0.6C (wt.%) twinning induced plasticity steel by multi-scale microstructure characterization. The approach makes use of electron microscopy... more
We have investigated the strain-hardening mechanisms across the relevant scales in a Fe-22Mn-0.6C (wt.%) twinning induced plasticity steel by multi-scale microstructure characterization. The approach makes use of electron microscopy techniques such as electron channeling contrast imaging (ECCI) to characterize microstructure features at the micro/nanoscale, and atomic-scale investigations of partitioning behavior across interfaces and solid solution/clustering effects by atom probe tomography (APT). The contribution of most relevant microstructure features to strain hardening is analyzed.
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Atom probe tomography (APT) has been used to investigate the surface and sub-surface microstructures of aluminum alloy 2024 (AA2024) in the T3 condition (solution heat treated, cold worked, and naturally aged to a substantially stable... more
Atom probe tomography (APT) has been used to investigate the surface and sub-surface microstructures of aluminum alloy 2024 (AA2024) in the T3 condition (solution heat treated, cold worked, and naturally aged to a substantially stable condition). This study revealed surface Cu enrichment on the alloy matrix, local chemical structure around a dispersoid Al20Mn3Cu2 particle including a Cu-rich particle and S-phase particle on its external surface. Moreover, there was a significant level of hydrogen within the dispersoid, indicating that it is a hydrogen sink. These observations of the nanoscale structure around the dispersoid particle have considerable implications for understanding both corrosion and hydrogen embrittlement in high-strength aluminum alloys.
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A high-Mn TWIP steel having composition Fe-22Mn-0.6C (wt%) is considered in this study, where the need for accurate and quantitative analysis of clustering and short-range ordering by atom probe analysis requires a better understanding of... more
A high-Mn TWIP steel having composition Fe-22Mn-0.6C (wt%) is considered in this study, where the need for accurate and quantitative analysis of clustering and short-range ordering by atom probe analysis requires a better understanding of the detection of carbon in this system. Experimental measurements reveal that a high percentage of carbon atoms are detected as molecular ion species and on multiple hit events, which is discussed with respect to issues such as optimal experimental parameters, correlated field evaporation and directional walk/migration of carbon atoms at the surface of the specimen tip during analysis. These phenomena impact the compositional and spatial accuracy of the atom probe measurement and thus require careful consideration for further cluster-finding analysis.
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A multi-scale investigation of twin bundles in Fe–22Mn–0.6C (wt%) twinning-induced plasticity steel after tensile deformation has been carried out by truly correlative means; using electron channelling contrast imaging combined with... more
A multi-scale investigation of twin bundles in Fe–22Mn–0.6C (wt%) twinning-induced plasticity steel after tensile deformation has been carried out by truly correlative means; using electron channelling contrast imaging combined with electron backscatter diffraction, high-resolution secondary ion mass spectrometry, scanning transmission electron microscopy, and atom probe tomography on the exact same region of interest in the sample. It was revealed that there was no significant segregation of Mn or C to the twin boundary interfaces.
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Atom probe tomography (APT) represents a significant step toward atomic resolution microscopy, analytically imaging individual atoms with highly accurate, though imperfect, chemical identity and three-dimensional (3D) positional... more
Atom probe tomography (APT) represents a significant step toward atomic resolution microscopy, analytically imaging individual atoms with highly accurate, though imperfect, chemical identity and three-dimensional (3D) positional information. Here, a technique to retrieve crystallographic information from raw APT data and restore the lattice-specific atomic configuration of the original specimen is presented. This lattice rectification technique has been applied to a pure metal, W, and then to the analysis of a multicomponent Al alloy. Significantly, the atoms are located to their true lattice sites not by an averaging, but by triangulation of each particular atom detected in the 3D atom-by-atom reconstruction. Lattice rectification of raw APT reconstruction provides unprecedented detail as to the fundamental solute hierarchy of the solid solution. Atomic clustering has been recognized as important in affecting alloy behavior, such as for the Al-1.1Cu-1.7Mg (at. %) investigated here,...
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ABSTRACT A diffusion couple approach is demonstrated for the combinatorial study of the compositional dependence of the rapid hardening phenomena in Al–Cu–Mg alloys. A series of Al–Cu/Al–Cu–Mg and Al–Mg/Al–Cu–Mg diffusion couples have... more
ABSTRACT A diffusion couple approach is demonstrated for the combinatorial study of the compositional dependence of the rapid hardening phenomena in Al–Cu–Mg alloys. A series of Al–Cu/Al–Cu–Mg and Al–Mg/Al–Cu–Mg diffusion couples have been successfully fabricated to contain a gradient in Mg or Cu concentration, respectively. The effects of both total solute content and Cu:Mg ratio of the rapid hardening phenomena are considered. The rapid hardening response has been monitored by measuring the hardness profile across the diffusion gradients before and after artificial ageing. The composition profiles were quantitatively verified by electron probe microanalysis (EPMA) and the microstructure of the ternary end members has been characterised using atom probe tomography (APT). It is demonstrated that a critical Cu content exists, above which the rapid hardening phenomena diminishes. A change in the chemistry of the Cu–Mg clusters that form, and which are thought to determine the rapid hardening increment, also occurs with changes in the bulk alloy chemistry. The results suggest that Cu–Mg clusters rich in Mg have greater strengthening potency and this is consistent with recent suggestions by Marceau et al. The need for the development of combinatorial approaches to characterisation (microstructural and mechanical) for the full utilisation of such approaches in physical metallurgy is emphasised.
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This chapter reviews new research techniques and recent progress in the development and understanding of aluminium alloys by the application of advanced characterization for composition and structure determination. In particular, this... more
This chapter reviews new research techniques and recent progress in the development and understanding of aluminium alloys by the application of advanced characterization for composition and structure determination. In particular, this chapter will focus on high-resolution transmission electron microscopy, atom probe tomography, and small-angle X-ray scattering, which all allow atomic-scale characterization. Furthermore, the complementary use of these techniques as well as correlation with other microscopy and microanalysis techniques, provide opportunities to overcome the inherent limitations of the individual methods and to capitalize on their unique advantages. This multitechnique approach will also be discussed in the context of both combinatorial studies and direct correlation with atomic-scale, first-principles modelling, namely density functional theory simulations, in the process of aluminium alloy development by investigating structure–property relationships.
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Two low-C steels microalloyed with niobium (Nb) were fabricated by simulated strip casting, one with molybdenum (Mo) and the other without Mo. Both steels were heat treated to simulate coiling at 900 °C to investigate the effect of Mo on... more
Two low-C steels microalloyed with niobium (Nb) were fabricated by simulated strip casting, one with molybdenum (Mo) and the other without Mo. Both steels were heat treated to simulate coiling at 900 °C to investigate the effect of Mo on the precipitation behaviour in austenite in low-C strip-cast Nb steels. The mechanical properties results show that during the isothermal holding at 900 °C the hardness of both steels increases and reaches a peak after 3000 s and then decreased after 10,000 s. Additionally, the hardness of the Mo-containing steel is higher than that of the Mo-free steel in all heat-treated conditions. Thermo-Calc predictions suggest that MC-type carbides exist in equilibrium at 900 °C, which are confirmed by transmission electron microscopy (TEM). TEM examination shows that precipitates are formed after 1000 s of isothermal holding in both steels and the size of the particles is refined by the addition of Mo. Energy dispersive spectroscopy (EDS) and electron energy ...
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As-cast low-carbon low-niobium steels fabricated by direct strip casting (DSC) were treated by simulated coiling in the lab. Coiling temperatures were carefully selected: (1) 900 ̊C (in the austenite); (2) 700 ̊C (during the... more
As-cast low-carbon low-niobium steels fabricated by direct strip casting (DSC) were treated by simulated coiling in the lab. Coiling temperatures were carefully selected: (1) 900 ̊C (in the austenite); (2) 700 ̊C (during the austenite-to-ferrite transformation); (3) 650 ̊C (in the ferrite). Optical microscopy and transmission electron microscopy were used to examine the microstructure constituents and the precipitates. Mechanical properties were evaluated by Vickers macrohardness measurements. The results show that coiling treatment has a strong influence on the final microstructure and mechanical properties, thus highlighting the necessity to carefully design the coiling treatment. In addition, the differences in hardness for the three coiling temperatures derive from a complex combination of different strengthening mechanisms.
ABSTRACT Recent development of characterisation techniques and computer simulation has extended our ability to access atomic scale information regarding materials microstructure evolution. New results from such techniques have... more
ABSTRACT Recent development of characterisation techniques and computer simulation has extended our ability to access atomic scale information regarding materials microstructure evolution. New results from such techniques have significantly progressed our knowledge about solute behaviour during the earliest stages of decomposition of the solid solution. This chapter updates current understanding about solute clustering and discusses the effect of solute clustering and micro-alloying on precipitate microstructure evolution in aluminium alloys. In addition, a brief review is given on the effect of severe plastic deformation on precipitate evolution in Al alloys.
An Al-0.2Sc and Al-2.2-Mg-0.1Sc alloy (wt.%) were deformed by ECAP in the solution treated condition then aged for 3h at 350 °C to produce a submicron microstructure containing nanosized Al3Sc particles. The alloys were then deformed in... more
An Al-0.2Sc and Al-2.2-Mg-0.1Sc alloy (wt.%) were deformed by ECAP in the solution treated condition then aged for 3h at 350 °C to produce a submicron microstructure containing nanosized Al3Sc particles. The alloys were then deformed in tension over a range of strain rates and temperatures. The addition of Mg to the binary alloy resulted in a higher ductility during testing at a given set of conditions. Despite the lower concentration of Sc in the ternary alloy, both the fine Al3Sc particles and Mg in solution stabilises the initial fine grain size by impeding dynamic grain growth thereby resulting in higher ductility.
The heat-transfer characteristics of a rapid hardening Al-1.1Cu-1.7Mg at.pct alloy during the early stages of age hardening have been tested, both by experiment and finite element modeling, for a typical laboratory-scale sample, and... more
The heat-transfer characteristics of a rapid hardening Al-1.1Cu-1.7Mg at.pct alloy during the early stages of age hardening have been tested, both by experiment and finite element modeling, for a typical laboratory-scale sample, and subsequently a maximum diffusion distance by random walk has been calculated for the solute atom species. It is found that due to small diffusion distances compared to the average dislocation loop interspacing, the dislocation-locking hardness mechanism is not likely, and rather, the cluster hardening model is more accurate.
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ABSTRACT We study an Fe–18Al (at.%) alloy after various thermal treatments at different times (24–336 h) and temperatures (250–1100 °C) to determine the nature of the so-called ‘komplex’ phase state (or “K-state”), which is common to... more
ABSTRACT We study an Fe–18Al (at.%) alloy after various thermal treatments at different times (24–336 h) and temperatures (250–1100 °C) to determine the nature of the so-called ‘komplex’ phase state (or “K-state”), which is common to other alloy systems having compositions at the boundaries of known order-disorder transitions and is characterised by heterogeneous short-range-ordering (SRO). This has been done by direct observation using atom probe tomography (APT), which reveals that nano-sized, ordered regions/particles do not exist. Also, by employing shell-based analysis of the three-dimensional atomic positions, we have determined chemically sensitive, generalised multicomponent short-range order (GM-SRO) parameters, which are compared with published pairwise SRO parameters derived from bulk, volume-averaged measurement techniques (e.g. X-ray and neutron scattering, Mössbauer spectroscopy) and combined ab-initio and Monte Carlo simulations. This analysis procedure has general relevance for other alloy systems where quantitative chemical-structure evaluation of local atomic environments is required to understand ordering and partial ordering phenomena that affect physical and mechanical properties.
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For several decades, the formation of carbon(C)-rich domains upon room temperature aging of super-saturated martensite has been a matter of debate. C-rich tweed-like patterns are observed to form after short aging times at room... more
For several decades, the formation of carbon(C)-rich domains upon room temperature aging of super-saturated martensite has been a matter of debate. C-rich tweed-like patterns are observed to form after short aging times at room temperature and coarsen upon further aging. Here, we present a systematic atomic-scale investigation of carbide formation in Fe-15Ni-1C (wt.%) martensite after two to three years of isothermal room temperature aging by a combination of atom probe tomography and transmission electron microscopy. Owing to the sub-zero martensite start temperature of À25 C, a fully austenitic microstructure is maintained at room temperature and the martensitic phase transformation is initiated during quenching in liquid nitrogen. In this way, any diffusion and redistribution of C in martensite is suppressed until heating up the specimen and holding it at room temperature. The microstructural changes that accompany the rearrangement of C atoms have been systematically investigated under controlled isothermal conditions. Our results show that after prolonged room temperature aging nanometer-sized, plate-shaped h-Fe 2 C carbides form with a macroscopic martensite habit plane close to {521}. The orientation relationship between the h-Fe 2 C carbides and the parent martensite grain (a 0) follows [001] a' //[001] h , ð110Þ a' //(020) h. The observation of h-Fe 2 Cecarbide formation at room temperature is particularly interesting, as transition carbides have so far only been reported to form above 100 C. After three years of room temperature aging a depletion of Fe is observed in the h carbide while Ni remains distributed homogenously. This implies that the substitutional element Fe can diffuse several nanometers in martensite at room temperature within three years.