Hongwang Yang - Academia.edu (original) (raw)

Papers by Hongwang Yang

Materials, Nov 30, 2022

This article is an open access article distributed under the terms and conditions of the Creative... more This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY

Al-based amorphous alloy is one of the most important research fields among amorphous alloys,show... more Al-based amorphous alloy is one of the most important research fields among amorphous alloys,showing excellent mechanical properties,high strength,high toughness,wear resistance and corrosion resistance etc.The history,development and mechanical properties of Al-based amorphous alloy have been reviewed in this paper.Also,the application fields,main problems and developing direction of Al-based amorphous alloy have been discussed.

Journal of Physics: Condensed Matter, 2007

ABSTRACT Al-based metallic glasses with relatively high glass-forming ability have been studied u... more ABSTRACT Al-based metallic glasses with relatively high glass-forming ability have been studied using fluctuation electron microscopy (FEM). These glasses exhibited well-defined glass transition and remained fully amorphous throughout the FEM experiments. Peaks were observed in the normalized intensity variance curves, evolving with sample composition and thermal history, while diffraction patterns remained identical. Specifically, minor alloying of Co into the Al85Ni5Y10 glass improved its medium-range homogeneity. This is in accord with, and partly explains, the increase in the glass-forming ability. After annealing of Al85Ni5Y8Co2 below its glass transition temperature, FEM suggests structural homogenization or intensified medium-range fluctuations, depending on the annealing temperature. Such dissolution versus growth of quenched-in heterogeneity accompanying structural relaxation was not detectable using other techniques.

Journal of Materials Research, 2006

ABSTRACT Melt-spun and annealed Al85Ni5Y8Co2 metallic glass, with a large supercooled liquid regi... more ABSTRACT Melt-spun and annealed Al85Ni5Y8Co2 metallic glass, with a large supercooled liquid region, were investigated by means of differential scanning calorimetry (DSC), transmission electron microscopy (TEM), and small-angle x-ray scattering (SAXS). TEM studies revealed that the as-quenched ribbons were fully amorphous. Further, the SAXS measurements showed that no evidence for compositional inhomogeneities associated with amorphous phase separation was found in the as-quenched state and the early stage annealing prior to devitrification. The primary crystallization of this glass was characterized, intriguingly, which appeared to be proceeded with an initial thermal relaxation, then α-Al nanocrystal nucleation with a limited number, finally a high density of nanocrystals nucleation and growth.

Journal of Alloys and Compounds, 2009

Al 85 Ni 5 Y 8 Co 2 glassy ribbon was prepared by melt spinning. Two endothermic steps were obser... more Al 85 Ni 5 Y 8 Co 2 glassy ribbon was prepared by melt spinning. Two endothermic steps were observed on the differential scanning calorimetry (DSC) curve of the sample annealed at 215 • C for 30 min. Temperature modulated differential scanning calorimetry (TMDSC) data reveals that the "two endothermic steps" are related to overlapping of one single reversible endothermic process (glass transition) with a small exothermic peak, rather than two distinct glass transitions as a consequence of amorphous phase separation.

The influence of the refilled gas pressure on the glass forming behaviour of one of the best tern... more The influence of the refilled gas pressure on the glass forming behaviour of one of the best ternary glass forming alloys Zr50Cu40Al10 was studied for the melt spinning process. The amorphicity of as-quenched ribbons was characterized by X-ray diffraction (XRD) and differential scanning calorimetry (DSC). The refilled chamber atmospheric pressure is crucial to the cooling rate of melt spinning. At high vacuum, at pressure less than 0.0001 atm, fully crystalline fragments are obtained. Monolithic amorphous ribbons were only obtained at a gas pressure of 0.1 atm or higher. The extended contact length between thecribbons and the copper wheel contributes to the high cooling rate of melt spinning. Higher chamber gas pressure leads to more turbulence of liquid metal beneath the nozzle; therefore, lower pressure is preferable at practical melt spinning processes once glass forming conditions are fulfilled.

Vacuum, 2021

Abstract Al2O3 ceramics were successfully brazed under high vacuum conditions using the active Ni... more Abstract Al2O3 ceramics were successfully brazed under high vacuum conditions using the active Ni50Ti50 master alloy at 1320 °C with different holding time. The interfacial microstructure of the joint was characterized using SEM, EDS and TEM. The effects of holding time on the microstructure evolution and mechanical properties of the joints were investigated. The results revealed that the typical structure of the Al2O3/Ni–Ti joint brazed at 1320 °C for 45 min was Al2O3/AlNi2Ti + Ni2Ti4O/Ni2Ti4O/TiNi. Ni2Ti4O was continuously distributed as a layer adjacent to the Al2O3 substrate, whereas columnar AlNi2Ti phase existed in the Ni2Ti4O layer near the Al2O3 side. With the prolongation of holding time, the thickness of Ni2Ti4O layer increased obviously, and AlNi2Ti became longer and coarser. The maximum shear strength of 109 MPa was obtained when the joint was brazed at 1320 °C for 45 min. The hardness, Young's modulus and elastic recovery of the phases across the joints became a gradient property. The interfacial reaction layer with appropriate thickness was found beneficial for enhancing the Al2O3/Ni–Ti/Al2O3 joint strength.

Journal of Materials Science & Technology, 2015

A new Al-based composite consisting of submicron-sized a-Al matrix embedded with precipitated int... more A new Al-based composite consisting of submicron-sized a-Al matrix embedded with precipitated intermetallic phases was developed by controlling the devitrification process of an AleNieYeCoeLa amorphous alloy. Such a homogeneous composite structure presented an ultrahigh strength of about 1.34 GPa and a large compressive plastic strain up to 22%. The unique mechanical properties during compression are mainly attributed to the dislocation slip deformation of ductile a-Al matrix and the shear-induced refinement of strengthening intermetallic phases.

Materials Science and Engineering: A, 2019

The shear transformation zone (STZ) and ductility of Zr-based bulk metallic glass with varying hy... more The shear transformation zone (STZ) and ductility of Zr-based bulk metallic glass with varying hydrogen content were analyzed using serrated flow in nanoindentation, with each serration representing the formation and expansion of one or more shear bands. An exponential model was employed to extract the serrations and obtain a certain range of shear stress, and STZ size was estimated via thorough statistical data analysis. The experimental results demonstrated a striking decrease in the serration number and width of the load-displacement curve after hydrogenation, which is similar to the effects of the nanoindentation loading rate. The calculated STZ volume and atomic number were in good agreement with those reported in the literature. The STZ volume, size, activation energy, and activation volume also increased with the increased hydrogen content, leading to shear band formation and proliferation as well as increased shear band density, plastic zone, and plasticity. At the microscopic level, the hydrogen addition accelerated free volume formation and enhanced flow ability between the atoms, as characterized by the improvement of plasticity. At the macroscopic level, hydrogen addition promoted shear band nucleation and multiplication and increased shear band density, plastic zones, and plasticity. The metallic glass plasticity was greatly improved after hydrogenation as assessed via compression tests at room temperature, confirming the rationale of the experimental results.

Scripta Materialia, 2006

ABSTRACT An asymptotically decreasing signal is observed in the initial part of the isothermal DS... more ABSTRACT An asymptotically decreasing signal is observed in the initial part of the isothermal DSC curves at 275, 285 and 290 °C of an Al85Ni5Y6Co2Fe2 metallic glass with a supercooled liquid region. We demonstrate that the monotonically decaying signal originates from the structural relaxation of the quenched glass, rather than from the growth of the quenched-in nuclei. At 285 and 290 °C, an exothermic peak overlaps with the structural relaxation, corresponding to the precipitation of nanometer-sized Al crystals.

High Pressure Research, 2017

In situ high-energy X-ray diffraction of Nd 60 Fe 30 Al 10 and Ce 70 Al 10 Cu 20 metallic glasses... more In situ high-energy X-ray diffraction of Nd 60 Fe 30 Al 10 and Ce 70 Al 10 Cu 20 metallic glasses is carried out under high pressure. During compression, Ce 70 Al 10 Cu 20 and Nd 60 Fe 30 Al 10 exhibit a polyamorphic transition from low-density state below 2.0 and 10.0 GPa, to high-density state above 8.4 and 21.1 GPa, respectively. The intermediate hysteresis regions are the mixture of both phases. Electrical resistance measurements under high pressure show that Ce 70 Al 10 Cu 20 display a discontinuous change in pressure dependence curve of resistivity at around 1.7 GPa. The addition of Fe atom gives a significant standoff of phase transition pressure in Nd 60 Fe 30 Al 10. The results in this work suggest that the solute element and microstructure of lanthanide solvent aggregates have implications on the polyamorphic transition in metallic glasses.

Journal of Alloys and Compounds, 2017

We utilized the pair distribution function method to characterize the pressure-induced polyamorph... more We utilized the pair distribution function method to characterize the pressure-induced polyamorphic transition in Ce 60 Al 20 Cu 20 and Ce 55 Al 45 metallic glass at room temperature. Using synchrotron high-energy x-ray diffraction we collected scattering information from a large Q-space coverage, which in turn gave a high resolution g(r) that provided accurate local structure information. We observed a sudden change in compressibility and the nearest neighbor distance at 3.50-6.32 GPa for Ce 60 Al 20 Cu 20 and 2.20-6.89 GPa for Ce 55 Al 45. The origin of the volume collapse seemed to be pressure-induced qualitative changes in bond shortening that corresponded to different coordination spheres. The polyamorphic transitions in these two systems from low-density glass (LDG) to high-density glass (HDG) are associated with local atomic rearrangements.

The morphology of chromium in chilled Cu-Cr alloys with 0.14%-2.0% Cr has been studied. The resul... more The morphology of chromium in chilled Cu-Cr alloys with 0.14%-2.0% Cr has been studied. The results showed that eutectic Cr phase takes a fibrous shape, and pre-eutectic Cr is dendritic in the studied chilled Cu-Cr alloy. During solute treatment of the eutectic and super-eutectic Cu-Cr alloys, only part of chromium particles dissolved in copper phase,some fiber and dendritic chromium still remained. Forging before solute treatment can reduce the size of primary Cr particles, which benefits the aging structure.

ABSTRACT Cu-Cr alloys containing Cr from 0.14% to 2.0% in mass were prepared as foils for TEM obs... more ABSTRACT Cu-Cr alloys containing Cr from 0.14% to 2.0% in mass were prepared as foils for TEM observation before and after being extruded. The results show that before extrusion, the spheroid or short bar chromium disperse in copper matrix of the Cu-Cr alloy, and the relationship between Cu and Cr follows the Nishiyama-Wasserman (NW) relationship, i.e. [110](Cu)//[001](Cr). After the Cu-Cr alloy was extruded at 860degreesC, dark field image along (224)(Cu) clearly shows that there are precipitated chromium particles in copper matrix. However, the SADP comprises only (112)(Cu) zone.

ABSTRACT Transmission electron microscopy (TEM) is usually used to identify the amorphicity. Howe... more ABSTRACT Transmission electron microscopy (TEM) is usually used to identify the amorphicity. However, some artifacts may be introduced due to improper TEM foil preparation. In this paper, three Al-rich metallic glasses with and without a glass transition were selected for characterizing the effect of the electropolishing condition on the as-quenched structure during TEM specimen preparation. It is shown that the occurrence of the modulated bright-dark structure under TEM observation is closely sensitive to the electropolishing condition, which suggests us being careful about the possible artifacts induced by specimen preparation when examining amorphous alloys under TEM.

The effect of Fe additions on glass formation and stability of an amorphous Al 85 Ni 5 Y 8 Co 2 a... more The effect of Fe additions on glass formation and stability of an amorphous Al 85 Ni 5 Y 8 Co 2 alloy with a large supercooled liquid region has been studied using differential scanning calorimetry (DSC), X-ray diffraction (XRD), and transmission electron microscopy (TEM) techniques. It was found that the Fe content significantly affects the primary crystallization kinetics of this alloy, but little on its glass-forming ability (GFA). Interestingly, an Al 85 Ni 5 Y 6 Fe 2 Co 2 glassy alloy, with a wide supercooled liquid region of 24 K and a superior stability against primary crystallization up to 570 K, was synthesized. Its devitrification kinetics appears to be proceeded by two-stage primary reaction over the temperature range of 570-645 K through a continuous process of the nucleation and growth of Al nanocrystals, followed by the concurrence of Al 3 (Ni, Fe), Al 9 Co 2 and Al 3 Y intermetallics. The formation of such a more stable glass due to partial replacement of Y by Fe in Al 85 Ni 5 Y 8 Co 2 is proposed to be associated with the amorphous structure and the solute concentration distribution feature.

Scripta Materialia, 2006

ABSTRACT After carefully ruling out the known sample preparation artifacts, high-angle annular de... more ABSTRACT After carefully ruling out the known sample preparation artifacts, high-angle annular detector dark-field scanning transmission electron microscopy, nanobeam composition analysis and energy-filtered imaging suggest that phase separation occurs upon heating in the Al85Ni5Y6Fe2Co2 amorphous ribbon prior to the onset of primary crystallization, but not in its as-prepared state. The length scale of the phase separation appears to correlate with the dimensions of the nanocrystals formed upon crystallization.

Scripta Materialia, 2012

ABSTRACT Tensile tests were carried out on amorphous Al88Ni4Y8 ribbons at room and high temperatu... more ABSTRACT Tensile tests were carried out on amorphous Al88Ni4Y8 ribbons at room and high temperatures. The fracture strength at room temperature was 889 MPa, with an elastic strain of ∼1.35%. At 200 °C the tensile strength was 816 MPa, with a total strain of 16.8%. Modulated differential scanning calorimeter results revealed the existence of a “hidden” glass transition, which resulted in viscous flow and large plastic deformation. Dynamic crystallization during tensile tests accounted for the observed strain hardening behavior.

Scripta Materialia, 2009

Aluminum-based amorphous metals are interesting lightweight alloys with superior mechanical and c... more Aluminum-based amorphous metals are interesting lightweight alloys with superior mechanical and corrosion properties, but have never been achieved in bulk form. Here we report the first success of obtaining Al-rich (86 at.% Al) bulk metallic glasses (BMGs), based on an alloy composition designed from the preferable internal glass structure. The Al BMGs discovered exhibit ultrahigh specific strength, as well as obvious plasticity.

Materials, Nov 30, 2022

This article is an open access article distributed under the terms and conditions of the Creative... more This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY

Al-based amorphous alloy is one of the most important research fields among amorphous alloys,show... more Al-based amorphous alloy is one of the most important research fields among amorphous alloys,showing excellent mechanical properties,high strength,high toughness,wear resistance and corrosion resistance etc.The history,development and mechanical properties of Al-based amorphous alloy have been reviewed in this paper.Also,the application fields,main problems and developing direction of Al-based amorphous alloy have been discussed.

Journal of Physics: Condensed Matter, 2007

ABSTRACT Al-based metallic glasses with relatively high glass-forming ability have been studied u... more ABSTRACT Al-based metallic glasses with relatively high glass-forming ability have been studied using fluctuation electron microscopy (FEM). These glasses exhibited well-defined glass transition and remained fully amorphous throughout the FEM experiments. Peaks were observed in the normalized intensity variance curves, evolving with sample composition and thermal history, while diffraction patterns remained identical. Specifically, minor alloying of Co into the Al85Ni5Y10 glass improved its medium-range homogeneity. This is in accord with, and partly explains, the increase in the glass-forming ability. After annealing of Al85Ni5Y8Co2 below its glass transition temperature, FEM suggests structural homogenization or intensified medium-range fluctuations, depending on the annealing temperature. Such dissolution versus growth of quenched-in heterogeneity accompanying structural relaxation was not detectable using other techniques.

Journal of Materials Research, 2006

ABSTRACT Melt-spun and annealed Al85Ni5Y8Co2 metallic glass, with a large supercooled liquid regi... more ABSTRACT Melt-spun and annealed Al85Ni5Y8Co2 metallic glass, with a large supercooled liquid region, were investigated by means of differential scanning calorimetry (DSC), transmission electron microscopy (TEM), and small-angle x-ray scattering (SAXS). TEM studies revealed that the as-quenched ribbons were fully amorphous. Further, the SAXS measurements showed that no evidence for compositional inhomogeneities associated with amorphous phase separation was found in the as-quenched state and the early stage annealing prior to devitrification. The primary crystallization of this glass was characterized, intriguingly, which appeared to be proceeded with an initial thermal relaxation, then α-Al nanocrystal nucleation with a limited number, finally a high density of nanocrystals nucleation and growth.

Journal of Alloys and Compounds, 2009

Al 85 Ni 5 Y 8 Co 2 glassy ribbon was prepared by melt spinning. Two endothermic steps were obser... more Al 85 Ni 5 Y 8 Co 2 glassy ribbon was prepared by melt spinning. Two endothermic steps were observed on the differential scanning calorimetry (DSC) curve of the sample annealed at 215 • C for 30 min. Temperature modulated differential scanning calorimetry (TMDSC) data reveals that the "two endothermic steps" are related to overlapping of one single reversible endothermic process (glass transition) with a small exothermic peak, rather than two distinct glass transitions as a consequence of amorphous phase separation.

The influence of the refilled gas pressure on the glass forming behaviour of one of the best tern... more The influence of the refilled gas pressure on the glass forming behaviour of one of the best ternary glass forming alloys Zr50Cu40Al10 was studied for the melt spinning process. The amorphicity of as-quenched ribbons was characterized by X-ray diffraction (XRD) and differential scanning calorimetry (DSC). The refilled chamber atmospheric pressure is crucial to the cooling rate of melt spinning. At high vacuum, at pressure less than 0.0001 atm, fully crystalline fragments are obtained. Monolithic amorphous ribbons were only obtained at a gas pressure of 0.1 atm or higher. The extended contact length between thecribbons and the copper wheel contributes to the high cooling rate of melt spinning. Higher chamber gas pressure leads to more turbulence of liquid metal beneath the nozzle; therefore, lower pressure is preferable at practical melt spinning processes once glass forming conditions are fulfilled.

Vacuum, 2021

Abstract Al2O3 ceramics were successfully brazed under high vacuum conditions using the active Ni... more Abstract Al2O3 ceramics were successfully brazed under high vacuum conditions using the active Ni50Ti50 master alloy at 1320 °C with different holding time. The interfacial microstructure of the joint was characterized using SEM, EDS and TEM. The effects of holding time on the microstructure evolution and mechanical properties of the joints were investigated. The results revealed that the typical structure of the Al2O3/Ni–Ti joint brazed at 1320 °C for 45 min was Al2O3/AlNi2Ti + Ni2Ti4O/Ni2Ti4O/TiNi. Ni2Ti4O was continuously distributed as a layer adjacent to the Al2O3 substrate, whereas columnar AlNi2Ti phase existed in the Ni2Ti4O layer near the Al2O3 side. With the prolongation of holding time, the thickness of Ni2Ti4O layer increased obviously, and AlNi2Ti became longer and coarser. The maximum shear strength of 109 MPa was obtained when the joint was brazed at 1320 °C for 45 min. The hardness, Young's modulus and elastic recovery of the phases across the joints became a gradient property. The interfacial reaction layer with appropriate thickness was found beneficial for enhancing the Al2O3/Ni–Ti/Al2O3 joint strength.

Journal of Materials Science & Technology, 2015

A new Al-based composite consisting of submicron-sized a-Al matrix embedded with precipitated int... more A new Al-based composite consisting of submicron-sized a-Al matrix embedded with precipitated intermetallic phases was developed by controlling the devitrification process of an AleNieYeCoeLa amorphous alloy. Such a homogeneous composite structure presented an ultrahigh strength of about 1.34 GPa and a large compressive plastic strain up to 22%. The unique mechanical properties during compression are mainly attributed to the dislocation slip deformation of ductile a-Al matrix and the shear-induced refinement of strengthening intermetallic phases.

Materials Science and Engineering: A, 2019

The shear transformation zone (STZ) and ductility of Zr-based bulk metallic glass with varying hy... more The shear transformation zone (STZ) and ductility of Zr-based bulk metallic glass with varying hydrogen content were analyzed using serrated flow in nanoindentation, with each serration representing the formation and expansion of one or more shear bands. An exponential model was employed to extract the serrations and obtain a certain range of shear stress, and STZ size was estimated via thorough statistical data analysis. The experimental results demonstrated a striking decrease in the serration number and width of the load-displacement curve after hydrogenation, which is similar to the effects of the nanoindentation loading rate. The calculated STZ volume and atomic number were in good agreement with those reported in the literature. The STZ volume, size, activation energy, and activation volume also increased with the increased hydrogen content, leading to shear band formation and proliferation as well as increased shear band density, plastic zone, and plasticity. At the microscopic level, the hydrogen addition accelerated free volume formation and enhanced flow ability between the atoms, as characterized by the improvement of plasticity. At the macroscopic level, hydrogen addition promoted shear band nucleation and multiplication and increased shear band density, plastic zones, and plasticity. The metallic glass plasticity was greatly improved after hydrogenation as assessed via compression tests at room temperature, confirming the rationale of the experimental results.

Scripta Materialia, 2006

ABSTRACT An asymptotically decreasing signal is observed in the initial part of the isothermal DS... more ABSTRACT An asymptotically decreasing signal is observed in the initial part of the isothermal DSC curves at 275, 285 and 290 °C of an Al85Ni5Y6Co2Fe2 metallic glass with a supercooled liquid region. We demonstrate that the monotonically decaying signal originates from the structural relaxation of the quenched glass, rather than from the growth of the quenched-in nuclei. At 285 and 290 °C, an exothermic peak overlaps with the structural relaxation, corresponding to the precipitation of nanometer-sized Al crystals.

High Pressure Research, 2017

In situ high-energy X-ray diffraction of Nd 60 Fe 30 Al 10 and Ce 70 Al 10 Cu 20 metallic glasses... more In situ high-energy X-ray diffraction of Nd 60 Fe 30 Al 10 and Ce 70 Al 10 Cu 20 metallic glasses is carried out under high pressure. During compression, Ce 70 Al 10 Cu 20 and Nd 60 Fe 30 Al 10 exhibit a polyamorphic transition from low-density state below 2.0 and 10.0 GPa, to high-density state above 8.4 and 21.1 GPa, respectively. The intermediate hysteresis regions are the mixture of both phases. Electrical resistance measurements under high pressure show that Ce 70 Al 10 Cu 20 display a discontinuous change in pressure dependence curve of resistivity at around 1.7 GPa. The addition of Fe atom gives a significant standoff of phase transition pressure in Nd 60 Fe 30 Al 10. The results in this work suggest that the solute element and microstructure of lanthanide solvent aggregates have implications on the polyamorphic transition in metallic glasses.

Journal of Alloys and Compounds, 2017

We utilized the pair distribution function method to characterize the pressure-induced polyamorph... more We utilized the pair distribution function method to characterize the pressure-induced polyamorphic transition in Ce 60 Al 20 Cu 20 and Ce 55 Al 45 metallic glass at room temperature. Using synchrotron high-energy x-ray diffraction we collected scattering information from a large Q-space coverage, which in turn gave a high resolution g(r) that provided accurate local structure information. We observed a sudden change in compressibility and the nearest neighbor distance at 3.50-6.32 GPa for Ce 60 Al 20 Cu 20 and 2.20-6.89 GPa for Ce 55 Al 45. The origin of the volume collapse seemed to be pressure-induced qualitative changes in bond shortening that corresponded to different coordination spheres. The polyamorphic transitions in these two systems from low-density glass (LDG) to high-density glass (HDG) are associated with local atomic rearrangements.

The morphology of chromium in chilled Cu-Cr alloys with 0.14%-2.0% Cr has been studied. The resul... more The morphology of chromium in chilled Cu-Cr alloys with 0.14%-2.0% Cr has been studied. The results showed that eutectic Cr phase takes a fibrous shape, and pre-eutectic Cr is dendritic in the studied chilled Cu-Cr alloy. During solute treatment of the eutectic and super-eutectic Cu-Cr alloys, only part of chromium particles dissolved in copper phase,some fiber and dendritic chromium still remained. Forging before solute treatment can reduce the size of primary Cr particles, which benefits the aging structure.

ABSTRACT Cu-Cr alloys containing Cr from 0.14% to 2.0% in mass were prepared as foils for TEM obs... more ABSTRACT Cu-Cr alloys containing Cr from 0.14% to 2.0% in mass were prepared as foils for TEM observation before and after being extruded. The results show that before extrusion, the spheroid or short bar chromium disperse in copper matrix of the Cu-Cr alloy, and the relationship between Cu and Cr follows the Nishiyama-Wasserman (NW) relationship, i.e. [110](Cu)//[001](Cr). After the Cu-Cr alloy was extruded at 860degreesC, dark field image along (224)(Cu) clearly shows that there are precipitated chromium particles in copper matrix. However, the SADP comprises only (112)(Cu) zone.

ABSTRACT Transmission electron microscopy (TEM) is usually used to identify the amorphicity. Howe... more ABSTRACT Transmission electron microscopy (TEM) is usually used to identify the amorphicity. However, some artifacts may be introduced due to improper TEM foil preparation. In this paper, three Al-rich metallic glasses with and without a glass transition were selected for characterizing the effect of the electropolishing condition on the as-quenched structure during TEM specimen preparation. It is shown that the occurrence of the modulated bright-dark structure under TEM observation is closely sensitive to the electropolishing condition, which suggests us being careful about the possible artifacts induced by specimen preparation when examining amorphous alloys under TEM.

The effect of Fe additions on glass formation and stability of an amorphous Al 85 Ni 5 Y 8 Co 2 a... more The effect of Fe additions on glass formation and stability of an amorphous Al 85 Ni 5 Y 8 Co 2 alloy with a large supercooled liquid region has been studied using differential scanning calorimetry (DSC), X-ray diffraction (XRD), and transmission electron microscopy (TEM) techniques. It was found that the Fe content significantly affects the primary crystallization kinetics of this alloy, but little on its glass-forming ability (GFA). Interestingly, an Al 85 Ni 5 Y 6 Fe 2 Co 2 glassy alloy, with a wide supercooled liquid region of 24 K and a superior stability against primary crystallization up to 570 K, was synthesized. Its devitrification kinetics appears to be proceeded by two-stage primary reaction over the temperature range of 570-645 K through a continuous process of the nucleation and growth of Al nanocrystals, followed by the concurrence of Al 3 (Ni, Fe), Al 9 Co 2 and Al 3 Y intermetallics. The formation of such a more stable glass due to partial replacement of Y by Fe in Al 85 Ni 5 Y 8 Co 2 is proposed to be associated with the amorphous structure and the solute concentration distribution feature.

Scripta Materialia, 2006

ABSTRACT After carefully ruling out the known sample preparation artifacts, high-angle annular de... more ABSTRACT After carefully ruling out the known sample preparation artifacts, high-angle annular detector dark-field scanning transmission electron microscopy, nanobeam composition analysis and energy-filtered imaging suggest that phase separation occurs upon heating in the Al85Ni5Y6Fe2Co2 amorphous ribbon prior to the onset of primary crystallization, but not in its as-prepared state. The length scale of the phase separation appears to correlate with the dimensions of the nanocrystals formed upon crystallization.

Scripta Materialia, 2012

ABSTRACT Tensile tests were carried out on amorphous Al88Ni4Y8 ribbons at room and high temperatu... more ABSTRACT Tensile tests were carried out on amorphous Al88Ni4Y8 ribbons at room and high temperatures. The fracture strength at room temperature was 889 MPa, with an elastic strain of ∼1.35%. At 200 °C the tensile strength was 816 MPa, with a total strain of 16.8%. Modulated differential scanning calorimeter results revealed the existence of a “hidden” glass transition, which resulted in viscous flow and large plastic deformation. Dynamic crystallization during tensile tests accounted for the observed strain hardening behavior.

Scripta Materialia, 2009

Aluminum-based amorphous metals are interesting lightweight alloys with superior mechanical and c... more Aluminum-based amorphous metals are interesting lightweight alloys with superior mechanical and corrosion properties, but have never been achieved in bulk form. Here we report the first success of obtaining Al-rich (86 at.% Al) bulk metallic glasses (BMGs), based on an alloy composition designed from the preferable internal glass structure. The Al BMGs discovered exhibit ultrahigh specific strength, as well as obvious plasticity.