Electric resistivity measurements and X-ray diffraction analysis were performed to study the isothermal phase transformation in amorphous Au-Si ribbons with eutectic composition pre- pared using melt-spinning techniqu...Electric resistivity measurements and X-ray diffraction analysis were performed to study the isothermal phase transformation in amorphous Au-Si ribbons with eutectic composition pre- pared using melt-spinning technique.A series of phase transformations take place spontaneously at room temperature and accelerate at elevated temperatures.Four stages of the transformation from amorphous state to the equilibrium state can be distinguished.Dis- cussion on the structural character of the metastable phases indicates that Hume-Rothery electron compounds and size factor compounds could form during isothermal aging.展开更多
Starting from elemental powders, complete MoSi2 powder forms abruptly between 3.5and 4 h during mechanical alloying (MA) of the Mo-66 at.% Si powders. Continuous milling of this MoSi2 Phase leads to a nanocrystalline ...Starting from elemental powders, complete MoSi2 powder forms abruptly between 3.5and 4 h during mechanical alloying (MA) of the Mo-66 at.% Si powders. Continuous milling of this MoSi2 Phase leads to a nanocrystalline powder and amorphizationtransformation takes place after 100 h milling. Howeven MA of the Mo-37.5 at.%Si powders does not result in the formation of the Mo5Si3 crystalline phase, but the formation of a Mo(Si) supersaturated solid solution (SSS) and a completely amorphots phase after 5 h and 70 h milling, respectively. The free energy of the Mo-Sisystem has been calculated and it has been found that there is no driving force for the amorphization reaction under normal conditions. The amorphization by MA of the Mo-Si system is attributed to a solid-state amorphization reaction in which defects and a very fine grain size induced during milling process may raise the free energy of the crystalline intermetallic phase (for MoSi2) or the Mo(Si) supersaturated solid solution (for Mo5Si3) above that of the amorphous phase.展开更多
Rapidly solidified ribbons of Al90Nd7Ni3 metallic glasses were prepare d by using melt spinning. Crystallization process of the totally amorphous ribbo ns was investigated by differential scanning calorimetry and X-ra...Rapidly solidified ribbons of Al90Nd7Ni3 metallic glasses were prepare d by using melt spinning. Crystallization process of the totally amorphous ribbo ns was investigated by differential scanning calorimetry and X-ray diffraction analysis,under continuous heating regime. The results show that,under continuo us heating regime,the metallic glass devitrifies via two main stages: primary c rystallization,resulting in two-phase mixture of α（Al） plus residual amor phous phase,and secondary crystallization,corresponding to some inter-metalli c phases appearing,successively including Al11Nd3,Al3Ni,and some un known phases,in the Al amorphous/crystal matrix. Four peaks appear on the conti nuous heating DSC curves. Their peak temperatures are respectively 470.8,（570. 8,） （585.6,） and 731.6 K at infinitesimal heating rate,and their activation energies of the respective phase transformation are 183.0,294.7,232.5 and 269.1 kJ/mol. The values of Avrami exponent of the four reactions decrease with increasing relative transformation degree. At the earlier stage of phase trans formation,the values of n are larger than 4,and at the later stage the val ues of n become close to some value from 0.5 to 2.0.展开更多
The present work aims to compare the amorphous phase forming ability of ternary and quaternary Al based alloys （Al86Ni8Y6, Al86GNi6Y6Co2, Al86NigLa6 and Al86Ni8Y45La15） synthesized via mechanical alloying by varying...The present work aims to compare the amorphous phase forming ability of ternary and quaternary Al based alloys （Al86Ni8Y6, Al86GNi6Y6Co2, Al86NigLa6 and Al86Ni8Y45La15） synthesized via mechanical alloying by varying the composition, i.e. fully or partially replacing rare earth （RE） and transition metal （TM） elements based on similar atomic radii and coordination number. X-ray diffraction and high resolution transmission electron microscopy study revealed that the amorphization process occurred through formation of various intermetallic phases and nanocrystalline FCC Al. Fully amorphous phase was obtained for the alloys not containing lanthanum, whereas the other alloys containing La showed partial amorphization with reappearance of intermetallic phases attributed to mechanical crystallization. Differential scanning calorimetry study confirmed better thermal stability with wider transformation temperature for the alloys without La.展开更多
The addition of a small amount of oxygen improves the mechanical properties,especially plasticity,of Ti_(45.7)Zr_(33)Ni_(3)Cu_(5.8)Be_(12.5) amorphous alloy composites(AACs)at room temperature(298 K).Compared to the p...The addition of a small amount of oxygen improves the mechanical properties,especially plasticity,of Ti_(45.7)Zr_(33)Ni_(3)Cu_(5.8)Be_(12.5) amorphous alloy composites(AACs)at room temperature(298 K).Compared to the plasticity of AACs without added O(5%),the plasticity of the composites with 0.73 at.%O(nominal composition)was much higher(11%).Even at O content higher than 0.73 at.%,the AACs exhibited good plasticity.The highest plasticity of∼12.3%was observed with 2.87 at.%O.Two distinct mechanisms are proposed to explain the enhanced plasticity of the AACs.At low O content,although deformation-induced phase transformation was suppressed,a substantial amount of α" martensite was formed.The microstructural features of α" martensite,such as thinner laths and homogeneous distribution,induced the formation of multiple shear bands in the amorphous matrix.At high O content,deformation-induced phase transformation was seriously suppressed.A dispersed nanoωphase was formed during rapid solidification in AACs with O content higher than 1.45 at.%.This resulted in a weakening in the anisotropy ofβdendrites and led to their homogenous deformation.Furthermore,multiple shear bands were formed in the amorphous matrix.Apart from plasticity,the strength of the AACs also increased with an increase in the O content.This phenomenon was explained in terms of three mechanisms,viz.the solid-solution-strengthening effect of O,fine-grain strengthening of β dendrites,and secondary phase strengthening by the nano ω phase.展开更多
文摘Electric resistivity measurements and X-ray diffraction analysis were performed to study the isothermal phase transformation in amorphous Au-Si ribbons with eutectic composition pre- pared using melt-spinning technique.A series of phase transformations take place spontaneously at room temperature and accelerate at elevated temperatures.Four stages of the transformation from amorphous state to the equilibrium state can be distinguished.Dis- cussion on the structural character of the metastable phases indicates that Hume-Rothery electron compounds and size factor compounds could form during isothermal aging.
文摘Starting from elemental powders, complete MoSi2 powder forms abruptly between 3.5and 4 h during mechanical alloying (MA) of the Mo-66 at.% Si powders. Continuous milling of this MoSi2 Phase leads to a nanocrystalline powder and amorphizationtransformation takes place after 100 h milling. Howeven MA of the Mo-37.5 at.%Si powders does not result in the formation of the Mo5Si3 crystalline phase, but the formation of a Mo(Si) supersaturated solid solution (SSS) and a completely amorphots phase after 5 h and 70 h milling, respectively. The free energy of the Mo-Sisystem has been calculated and it has been found that there is no driving force for the amorphization reaction under normal conditions. The amorphization by MA of the Mo-Si system is attributed to a solid-state amorphization reaction in which defects and a very fine grain size induced during milling process may raise the free energy of the crystalline intermetallic phase (for MoSi2) or the Mo(Si) supersaturated solid solution (for Mo5Si3) above that of the amorphous phase.
文摘Rapidly solidified ribbons of Al90Nd7Ni3 metallic glasses were prepare d by using melt spinning. Crystallization process of the totally amorphous ribbo ns was investigated by differential scanning calorimetry and X-ray diffraction analysis,under continuous heating regime. The results show that,under continuo us heating regime,the metallic glass devitrifies via two main stages: primary c rystallization,resulting in two-phase mixture of α（Al） plus residual amor phous phase,and secondary crystallization,corresponding to some inter-metalli c phases appearing,successively including Al11Nd3,Al3Ni,and some un known phases,in the Al amorphous/crystal matrix. Four peaks appear on the conti nuous heating DSC curves. Their peak temperatures are respectively 470.8,（570. 8,） （585.6,） and 731.6 K at infinitesimal heating rate,and their activation energies of the respective phase transformation are 183.0,294.7,232.5 and 269.1 kJ/mol. The values of Avrami exponent of the four reactions decrease with increasing relative transformation degree. At the earlier stage of phase trans formation,the values of n are larger than 4,and at the later stage the val ues of n become close to some value from 0.5 to 2.0.
基金financial support obtained from the Science and Engineering Research Board,Department of Science & Technology,Government of India(SB/S3/ME/0044/2013)Sponsored Research and Industrial Consultancy,Indian Institute of Technology Kharagpur,India(GAF)
文摘The present work aims to compare the amorphous phase forming ability of ternary and quaternary Al based alloys （Al86Ni8Y6, Al86GNi6Y6Co2, Al86NigLa6 and Al86Ni8Y45La15） synthesized via mechanical alloying by varying the composition, i.e. fully or partially replacing rare earth （RE） and transition metal （TM） elements based on similar atomic radii and coordination number. X-ray diffraction and high resolution transmission electron microscopy study revealed that the amorphization process occurred through formation of various intermetallic phases and nanocrystalline FCC Al. Fully amorphous phase was obtained for the alloys not containing lanthanum, whereas the other alloys containing La showed partial amorphization with reappearance of intermetallic phases attributed to mechanical crystallization. Differential scanning calorimetry study confirmed better thermal stability with wider transformation temperature for the alloys without La.
基金This work was financially supported by the National Natural Science Foundation of China(Nos.51771049 and 51790484)。
文摘The addition of a small amount of oxygen improves the mechanical properties,especially plasticity,of Ti_(45.7)Zr_(33)Ni_(3)Cu_(5.8)Be_(12.5) amorphous alloy composites(AACs)at room temperature(298 K).Compared to the plasticity of AACs without added O(5%),the plasticity of the composites with 0.73 at.%O(nominal composition)was much higher(11%).Even at O content higher than 0.73 at.%,the AACs exhibited good plasticity.The highest plasticity of∼12.3%was observed with 2.87 at.%O.Two distinct mechanisms are proposed to explain the enhanced plasticity of the AACs.At low O content,although deformation-induced phase transformation was suppressed,a substantial amount of α" martensite was formed.The microstructural features of α" martensite,such as thinner laths and homogeneous distribution,induced the formation of multiple shear bands in the amorphous matrix.At high O content,deformation-induced phase transformation was seriously suppressed.A dispersed nanoωphase was formed during rapid solidification in AACs with O content higher than 1.45 at.%.This resulted in a weakening in the anisotropy ofβdendrites and led to their homogenous deformation.Furthermore,multiple shear bands were formed in the amorphous matrix.Apart from plasticity,the strength of the AACs also increased with an increase in the O content.This phenomenon was explained in terms of three mechanisms,viz.the solid-solution-strengthening effect of O,fine-grain strengthening of β dendrites,and secondary phase strengthening by the nano ω phase.
