Proceedings of the Institution of Mechanical Engineers, Part L: Journal of Materials: Design and Applications
Al–Si alloys, with excellent properties such as low weight, low thermal expansion coefficient, an... more Al–Si alloys, with excellent properties such as low weight, low thermal expansion coefficient, and high wear-resistance, are ideal materials for the automobile and aerospace industries. However, their applications have been hampered by the coarsening of the primary-Si particles in Al–Si alloys. In this study, the rolling-and-T6-treatments effect on A6061/Al2O3 metal-matrix composites is investigated. The A6061/Al2O3 metal-matrix composites with different amounts of reinforcing Al2O3 particles are examined in the aspects of wear resistance and hardness. Upon the T6 treatment, the hardness is enhanced in all cases and is summarized. The results suggest that the increase of Al2O3 particles reduce the wear rate. The possible reinforce mechanisms and the environmental temperature effects are discussed. This improvement in wear resistance is due to the particle size refinement of silicon at a high percentage-roll-reduction.
Fatigue & Fracture of Engineering Materials & Structures
In-situ neutron-diffraction and temperature measurements were simultaneously applied to investiga... more In-situ neutron-diffraction and temperature measurements were simultaneously applied to investigate low-cycle-fatigue behaviour of a nano-precipitate strengthened nickel-based superalloy. Two transitions in the temperature-evolution are observed subjected to cyclic loading. Two models are compared with the measured temperature evolution. One is based on bulk stress, and the other is based on lattice-strain evolution. The calculated thermoelastic responses in both models qualitatively agree with the measured bulk-temperature evolution for the first transition. The in-situ neutron-diffraction results reveal that the first transition is associated with the cyclic hardening/softening dislocation-structural transformation. However, the second transition, which is observed at larger number of fatigue cycles during the steady cycles, does not correlate with the dislocation evolution. A phenomenological model is applied to describe the second temperature-transition stages. The energy dissipation evolutions in the second fatigue stage indicate the initiation and the growth activities of fatigue microcrack. The data reported here may be useful for cohesive zone model.
Abstract Insights into the phase transformation kinetics and lattice dynamics associated with the... more Abstract Insights into the phase transformation kinetics and lattice dynamics associated with the newly discovered confined martensitic transformation are of great significance to the in-depth understanding of the phase transformation behavior responsible for the rich new physical phenomena in shape memory alloys and could shed light on the design of novel multifunctional properties through tuning the confined martensitic transformation. Here, we employ in-situ elastic and inelastic neutron scattering techniques to reveal the characteristics of transformation kinetics and lattice dynamics in two Ni 55-x Co x Fe 18 Ga 27 magnetic shape memory alloys with x = 5.5 and 6.5. With a remarkable difference in transformation temperature, these two alloys show similar vibrational properties. Phonon softening of the TA 2 [ξξ0] phonon branch, manifested as a dip at ξ ∼ 0.33 on the phonon dispersion curves, was disclosed by inelastic neutron scattering experiments; but this phonon softening is much less pronounced than that observed in stoichiometric Ni 2 MnGa or near-stoichiometric Ni–Fe–Ga Heusler alloys. The dispersion curves for the TA 2 [ξξ0] phonon branch are only weakly dependent on temperature. The less pronounced phonon softening and very weak temperature dependence of the phonon dispersion curves could be attributed to the martensitic transformation which is confined by local inhomogeneities. This confined martensitic transformation shows a sluggish nature and occurs in a broad temperature range. The sluggish transformation was evidenced by the existence of residual austenite at low temperatures far below the martensitic transformation start temperature.
Fatigue crack growth experiments were carried out on a 304 L stainless steel compact-tension(CT) ... more Fatigue crack growth experiments were carried out on a 304 L stainless steel compact-tension(CT) specimen under load control mode. Neutron diffraction was employed to quantitatively measure the residual strains/stresses and the evolution of stress fields in the vicinity of a propagating fatigue-crack tip. Three principal stress components (i.e. crack growth, crack opening, and through-thickness direction stresses) were examined in-situ under loading as a function of distance from the crack tip along the crack-propagation path. The stress/strain fields, measured both at the mid-thickness and near the surface of the CT specimen, were compared. The results show that much higher compressive residual stress fields developed in front of the crack tip near the surface than developed at the mid-thickness area. The change of the stresses ahead of the crack tip under loading is more significant at the mid-thickness area than it is near the surface.
In situ synchrotron X-ray diffraction is used to investigate a three-way piezo-phototronic soft m... more In situ synchrotron X-ray diffraction is used to investigate a three-way piezo-phototronic soft material. This new system is composed of a semi-crystalline poly(vinylidene fluoride-co-trifluoro-ethylene) piezoelectric polymer and titanium oxide nanoparticles. Under light illumination, photon-induced piezoelectric responses are nearly two times higher at both the lattice-structure and macroscopic level than under conditions without light illumination. A mechanistic model is proposed.
ABSTRACT An equiatomic, face-centered-cubic, CoCrFeMnNi high-entropy alloy was tensile tested at ... more ABSTRACT An equiatomic, face-centered-cubic, CoCrFeMnNi high-entropy alloy was tensile tested at 800 K and 1,000 K with a nominal strain rate of 6.7 Â 10 À6 s À1. In addition to the macroscopic (bulk) behavior, mesoscopic (lattice) phenomena during the pseudo-creep deformation were investigated simultaneously using in-situ neutron diffraction. The evolutions of lattice strains, peak widths, and intensities of several hkl reflections suggest that the dominant deformation mode is the dislocation glide at 800 K and diffusion-controlled dislocation creep at 1,000 K.
Langmuir : the ACS journal of surfaces and colloids, Jan 30, 2014
The structures of C- and N-terminally monoPEGylated human parathyroid hormone fragment hPTH(1-34)... more The structures of C- and N-terminally monoPEGylated human parathyroid hormone fragment hPTH(1-34) as well as their unmodified counterparts, poly(ethylene glycol) (PEG) and hPTH(1-34), have been studied by small-angle neutron scattering (SANS). The scattering results show that free hPTH(1-34) in 100 mM phosphate buffer (pH 7.4) aggregates into clusters. After conjugation with PEG, the PEG-peptide conjugates self-assemble into a supramolecular core-shell structure with a cylindrical shape. The PEG chains form a shell around the hPTH(1-34) core to shield hPTH(1-34) from the solvent. The detailed structural information on the self-assembled structures is extracted from SANS using a model of the cylindrical core with a shell of Gaussian chains attached to the core surface. On the basis of the data, because of the charge-dipole interactions between the conjugated PEG chain and the peptide, the conjugated PEG chain forms a more collapsed conformation compared to free PEG. Moreover, the siz...
An analysis of residual stress, one of the contributory factors to the crack tip driving force, i... more An analysis of residual stress, one of the contributory factors to the crack tip driving force, is extremely important to probe the fatigue crack growth mechanism and to further develop the life prediction methodology. Since fatigue crack growth is governed by crack-tip plasticity and crack closure in the wake of the crack tip, the investigation of residual stain/stress field in both behind and in front of the crack tip is crucial. In the current work, a 304L stainless steel compact-tension specimen is pre-cracked under constant-amplitude cyclic loading. Neutron diffraction is employed to directly measure the three orthogonal residual strain fields with 1-mm spatial resolution as a function of distance from the crack tip. The mapping results show that the three orthogonal residual-strain distributions around the crack tip depend on the stress multiaxiality, not following a single Poisson relationship to each axis.
Carbon-carbon composites are deemed as candidate materials for application in very high temperatu... more Carbon-carbon composites are deemed as candidate materials for application in very high temperature reactors. In a very high temperature reactor, carbon-carbon composite materials would experience severe environmental impacts from high temperatures. As a result, we applied non-destructive ex-situ diffraction experiments to investigate the microstructure changes of the carbon-carbon composite materials experiencing different temperatures. In this study, the samples were prepared in a format of a three-dimensional pitch-based carbon-carbon composite. The samples were heated to 500 (°C), 700 (°C), and 900 (°C) for 2 minutes, respectively. In order to understand the temperature effect on carbon-carbon composite, we facilitated the high penetration of the synchrotron X-ray diffraction at National Synchrotron Radiation Research Center to examine the evolution of microstructures subjected to heat treatment. The results show that the lattice parameters of a-axis and c-axis evolve upon heati...
An experimental investigation, combining synchrotron X-ray powder diffraction, small-angle neutro... more An experimental investigation, combining synchrotron X-ray powder diffraction, small-angle neutron scattering and transmission electron microscopy, has been undertaken to study the microstructure of nanoprecipitates in a nickel-based superalloy. Upon increasing the ageing time during a heat-treatment process, the average size of the precipitates first decreases before changing to a monotonically growth stage. Possible reasons for this observed structural evolution, which is predicted thermodynamically, are suggested.
Proceedings of the Institution of Mechanical Engineers, Part L: Journal of Materials: Design and Applications
Al–Si alloys, with excellent properties such as low weight, low thermal expansion coefficient, an... more Al–Si alloys, with excellent properties such as low weight, low thermal expansion coefficient, and high wear-resistance, are ideal materials for the automobile and aerospace industries. However, their applications have been hampered by the coarsening of the primary-Si particles in Al–Si alloys. In this study, the rolling-and-T6-treatments effect on A6061/Al2O3 metal-matrix composites is investigated. The A6061/Al2O3 metal-matrix composites with different amounts of reinforcing Al2O3 particles are examined in the aspects of wear resistance and hardness. Upon the T6 treatment, the hardness is enhanced in all cases and is summarized. The results suggest that the increase of Al2O3 particles reduce the wear rate. The possible reinforce mechanisms and the environmental temperature effects are discussed. This improvement in wear resistance is due to the particle size refinement of silicon at a high percentage-roll-reduction.
Fatigue & Fracture of Engineering Materials & Structures
In-situ neutron-diffraction and temperature measurements were simultaneously applied to investiga... more In-situ neutron-diffraction and temperature measurements were simultaneously applied to investigate low-cycle-fatigue behaviour of a nano-precipitate strengthened nickel-based superalloy. Two transitions in the temperature-evolution are observed subjected to cyclic loading. Two models are compared with the measured temperature evolution. One is based on bulk stress, and the other is based on lattice-strain evolution. The calculated thermoelastic responses in both models qualitatively agree with the measured bulk-temperature evolution for the first transition. The in-situ neutron-diffraction results reveal that the first transition is associated with the cyclic hardening/softening dislocation-structural transformation. However, the second transition, which is observed at larger number of fatigue cycles during the steady cycles, does not correlate with the dislocation evolution. A phenomenological model is applied to describe the second temperature-transition stages. The energy dissipation evolutions in the second fatigue stage indicate the initiation and the growth activities of fatigue microcrack. The data reported here may be useful for cohesive zone model.
Abstract Insights into the phase transformation kinetics and lattice dynamics associated with the... more Abstract Insights into the phase transformation kinetics and lattice dynamics associated with the newly discovered confined martensitic transformation are of great significance to the in-depth understanding of the phase transformation behavior responsible for the rich new physical phenomena in shape memory alloys and could shed light on the design of novel multifunctional properties through tuning the confined martensitic transformation. Here, we employ in-situ elastic and inelastic neutron scattering techniques to reveal the characteristics of transformation kinetics and lattice dynamics in two Ni 55-x Co x Fe 18 Ga 27 magnetic shape memory alloys with x = 5.5 and 6.5. With a remarkable difference in transformation temperature, these two alloys show similar vibrational properties. Phonon softening of the TA 2 [ξξ0] phonon branch, manifested as a dip at ξ ∼ 0.33 on the phonon dispersion curves, was disclosed by inelastic neutron scattering experiments; but this phonon softening is much less pronounced than that observed in stoichiometric Ni 2 MnGa or near-stoichiometric Ni–Fe–Ga Heusler alloys. The dispersion curves for the TA 2 [ξξ0] phonon branch are only weakly dependent on temperature. The less pronounced phonon softening and very weak temperature dependence of the phonon dispersion curves could be attributed to the martensitic transformation which is confined by local inhomogeneities. This confined martensitic transformation shows a sluggish nature and occurs in a broad temperature range. The sluggish transformation was evidenced by the existence of residual austenite at low temperatures far below the martensitic transformation start temperature.
Fatigue crack growth experiments were carried out on a 304 L stainless steel compact-tension(CT) ... more Fatigue crack growth experiments were carried out on a 304 L stainless steel compact-tension(CT) specimen under load control mode. Neutron diffraction was employed to quantitatively measure the residual strains/stresses and the evolution of stress fields in the vicinity of a propagating fatigue-crack tip. Three principal stress components (i.e. crack growth, crack opening, and through-thickness direction stresses) were examined in-situ under loading as a function of distance from the crack tip along the crack-propagation path. The stress/strain fields, measured both at the mid-thickness and near the surface of the CT specimen, were compared. The results show that much higher compressive residual stress fields developed in front of the crack tip near the surface than developed at the mid-thickness area. The change of the stresses ahead of the crack tip under loading is more significant at the mid-thickness area than it is near the surface.
In situ synchrotron X-ray diffraction is used to investigate a three-way piezo-phototronic soft m... more In situ synchrotron X-ray diffraction is used to investigate a three-way piezo-phototronic soft material. This new system is composed of a semi-crystalline poly(vinylidene fluoride-co-trifluoro-ethylene) piezoelectric polymer and titanium oxide nanoparticles. Under light illumination, photon-induced piezoelectric responses are nearly two times higher at both the lattice-structure and macroscopic level than under conditions without light illumination. A mechanistic model is proposed.
ABSTRACT An equiatomic, face-centered-cubic, CoCrFeMnNi high-entropy alloy was tensile tested at ... more ABSTRACT An equiatomic, face-centered-cubic, CoCrFeMnNi high-entropy alloy was tensile tested at 800 K and 1,000 K with a nominal strain rate of 6.7 Â 10 À6 s À1. In addition to the macroscopic (bulk) behavior, mesoscopic (lattice) phenomena during the pseudo-creep deformation were investigated simultaneously using in-situ neutron diffraction. The evolutions of lattice strains, peak widths, and intensities of several hkl reflections suggest that the dominant deformation mode is the dislocation glide at 800 K and diffusion-controlled dislocation creep at 1,000 K.
Langmuir : the ACS journal of surfaces and colloids, Jan 30, 2014
The structures of C- and N-terminally monoPEGylated human parathyroid hormone fragment hPTH(1-34)... more The structures of C- and N-terminally monoPEGylated human parathyroid hormone fragment hPTH(1-34) as well as their unmodified counterparts, poly(ethylene glycol) (PEG) and hPTH(1-34), have been studied by small-angle neutron scattering (SANS). The scattering results show that free hPTH(1-34) in 100 mM phosphate buffer (pH 7.4) aggregates into clusters. After conjugation with PEG, the PEG-peptide conjugates self-assemble into a supramolecular core-shell structure with a cylindrical shape. The PEG chains form a shell around the hPTH(1-34) core to shield hPTH(1-34) from the solvent. The detailed structural information on the self-assembled structures is extracted from SANS using a model of the cylindrical core with a shell of Gaussian chains attached to the core surface. On the basis of the data, because of the charge-dipole interactions between the conjugated PEG chain and the peptide, the conjugated PEG chain forms a more collapsed conformation compared to free PEG. Moreover, the siz...
An analysis of residual stress, one of the contributory factors to the crack tip driving force, i... more An analysis of residual stress, one of the contributory factors to the crack tip driving force, is extremely important to probe the fatigue crack growth mechanism and to further develop the life prediction methodology. Since fatigue crack growth is governed by crack-tip plasticity and crack closure in the wake of the crack tip, the investigation of residual stain/stress field in both behind and in front of the crack tip is crucial. In the current work, a 304L stainless steel compact-tension specimen is pre-cracked under constant-amplitude cyclic loading. Neutron diffraction is employed to directly measure the three orthogonal residual strain fields with 1-mm spatial resolution as a function of distance from the crack tip. The mapping results show that the three orthogonal residual-strain distributions around the crack tip depend on the stress multiaxiality, not following a single Poisson relationship to each axis.
Carbon-carbon composites are deemed as candidate materials for application in very high temperatu... more Carbon-carbon composites are deemed as candidate materials for application in very high temperature reactors. In a very high temperature reactor, carbon-carbon composite materials would experience severe environmental impacts from high temperatures. As a result, we applied non-destructive ex-situ diffraction experiments to investigate the microstructure changes of the carbon-carbon composite materials experiencing different temperatures. In this study, the samples were prepared in a format of a three-dimensional pitch-based carbon-carbon composite. The samples were heated to 500 (°C), 700 (°C), and 900 (°C) for 2 minutes, respectively. In order to understand the temperature effect on carbon-carbon composite, we facilitated the high penetration of the synchrotron X-ray diffraction at National Synchrotron Radiation Research Center to examine the evolution of microstructures subjected to heat treatment. The results show that the lattice parameters of a-axis and c-axis evolve upon heati...
An experimental investigation, combining synchrotron X-ray powder diffraction, small-angle neutro... more An experimental investigation, combining synchrotron X-ray powder diffraction, small-angle neutron scattering and transmission electron microscopy, has been undertaken to study the microstructure of nanoprecipitates in a nickel-based superalloy. Upon increasing the ageing time during a heat-treatment process, the average size of the precipitates first decreases before changing to a monotonically growth stage. Possible reasons for this observed structural evolution, which is predicted thermodynamically, are suggested.
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