Ross Marceau | Deakin University (original) (raw)
Papers by Ross Marceau
Advanced Functional Materials, 2018
Journal of Materials Science, 2018
Molybdenum (Mo) is known to have a complex effect on phase transformations and precipitation in s... 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.
Journal of Materials Chemistry A, 2019
A common strategy to enhance the fibre-to-matrix adhesion of carbon fibres is to increase the sur... more 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...
Materials Science and Engineering: A, 2018
Abstract The isothermal evolution of nanometre-sized precipitates formed in a Ti-Mo microalloyed ... 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.
Science, 2019
High-strength aluminum alloys are important for lightweighting vehicles and are extensively used ... 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.
Materials Science and Engineering: A, 2018
Abstract Medium to high strength heat-treatable aluminum alloys of the 6000 series (Al-Mg-Si) hav... 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.
Acta Materialia, 2018
Abstract For several decades, the formation of carbon(C)-rich domains upon room temperature aging... 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.
Acta Materialia, 2015
ABSTRACT The decomposition sequence of the supersaturated solid solution leading to the formation... 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.
Materials Science and Technology, 2016
The present paper reviews recent progress in atomic-scale characterisation of composition and nan... 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.
Acta Materialia, 2017
Abstract Ultra-high strength steels are interesting materials for light-weighting applications in... 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.
Materials & Design, 2016
Abstract Microalloying trace elements into aluminium alloys have been shown to improve mechanical... 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.
Materials Science and Technology, 2016
Acta Materialia, 2015
ABSTRACT The deformation behaviour of two single phase binary alloys, Mg–5Y and Mg–10Y, have been... 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.
Ultramicroscopy, Oct 13, 2017
We present a novel approach for analysis of low-conductivity and insulating materials with conven... 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 ...
Corrosion Science, 2017
High-strength aluminium alloys such as AA2024-T3 are often developed by the introduction of plast... 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.
Advanced Functional Materials, 2018
Journal of Materials Science, 2018
Molybdenum (Mo) is known to have a complex effect on phase transformations and precipitation in s... 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.
Journal of Materials Chemistry A, 2019
A common strategy to enhance the fibre-to-matrix adhesion of carbon fibres is to increase the sur... more 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...
Materials Science and Engineering: A, 2018
Abstract The isothermal evolution of nanometre-sized precipitates formed in a Ti-Mo microalloyed ... 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.
Science, 2019
High-strength aluminum alloys are important for lightweighting vehicles and are extensively used ... 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.
Materials Science and Engineering: A, 2018
Abstract Medium to high strength heat-treatable aluminum alloys of the 6000 series (Al-Mg-Si) hav... 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.
Acta Materialia, 2018
Abstract For several decades, the formation of carbon(C)-rich domains upon room temperature aging... 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.
Acta Materialia, 2015
ABSTRACT The decomposition sequence of the supersaturated solid solution leading to the formation... 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.
Materials Science and Technology, 2016
The present paper reviews recent progress in atomic-scale characterisation of composition and nan... 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.
Acta Materialia, 2017
Abstract Ultra-high strength steels are interesting materials for light-weighting applications in... 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.
Materials & Design, 2016
Abstract Microalloying trace elements into aluminium alloys have been shown to improve mechanical... 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.
Materials Science and Technology, 2016
Acta Materialia, 2015
ABSTRACT The deformation behaviour of two single phase binary alloys, Mg–5Y and Mg–10Y, have been... 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.
Ultramicroscopy, Oct 13, 2017
We present a novel approach for analysis of low-conductivity and insulating materials with conven... 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 ...
Corrosion Science, 2017
High-strength aluminium alloys such as AA2024-T3 are often developed by the introduction of plast... 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.