TAN Yuxu REN Liping LI Gang Xi'an Jiaotong University
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Xi'an
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China TAN Yuxu Associate Professor
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Institute of Metallic Materials and Strength
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Xi'an Jiaotong University
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Xi'an 710048
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China
金属学报(英文版)
In the strengthened layer of stainless steel after shot peening,there are a great amount of deformation microtwins which may act as structural strengthening factor and prevent the gradual relaxation of surface residual stress during fatigue,so as to keep its rather high level of bending fatigue strength.However,in the strengthened surface layer of low carbon steel, dislocation cell structure is so unstalbe during fatigue that its surface residual stress relaxation cannot be retarded.Therefore,the bending fatigue strength of the low carbon steel can not be improred by shot peening.
关键词:
substructure
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null
Journal of Applied Physics
The dependence of yield strength, uniform elongation, and toughness on grain size in metallic structural materials was discussed. The toughness is defined as the product of yield strength and uniform elongation. The yield strength versus grain size can be well described by the Hall-Petch relation; however, the uniform elongation versus grain size is not well understood yet. A simple model involving the densities of geometrically necessary dislocations and statistically stored dislocations was proposed to estimate the uniform elongation versus grain size. Existing data for low carbon steels and aluminum indicate that, in the grain size less than 1 mu m, the materials usually exhibit high strength and low uniform elongation and, in the grain size greater than 10 mu m, the materials usually exhibit low strength and high elongation; in either case the toughness is low. However, in the grain size of several micrometers, the toughness is the highest. It is suggested that we should pay more attention to develop the metallic materials with grain size of several micrometers for structural applications. (c) 2007 American Institute of Physics.
关键词:
nanocrystalline copper;nanostructured metal;steels;deformation;ductility;law
Applied Physics Letters
We report high strength reliability under tension of a bulk metallic glass (BMG), demonstrated by its high uniformity in strength found over a statistically significant number of specimens, despite the fact that the samples all showed no macroscopic plasticity. Weibull statistical analysis showed that the Weibull modulus of the material is 36.5, which is much higher than the values of more typical brittle materials, further confirming BMGs' high reliability [Appl. Mech. Rev. 5, 449 (1952)]. (c) 2008 American Institute of Physics.
关键词:
plasticity;alloys;temperature;brittleness;estimators;fracture;stress
Physical Review Letters
We find that the failure of bulk metallic glassy (BMG) materials follows three modes, i.e., shear fracture with a fracture plane significantly deviating from 45degrees to the loading direction, normal tensile fracture with a fracture plane perpendicular to the loading direction, or distensile fracture in a break or splitting mode with a fracture plane parallel to the loading direction. The actually occurring type of failure strongly depends on the applied loading mode and the microstructure of the material. Extensive evidence indicates that the Tresca fracture criterion is invalid, and for the first time, three fracture criteria are developed for isotropic materials with high strength, such as advanced BMGs or the newly developed bulk nanostructural materials.
关键词:
amorphous-alloys;enhanced plasticity;zr-ti;flow;deformation;composite;strength;microstructure;ribbons;failure
Applied Physics Letters
The authors report a simple Fe-based Fe(71)Nb(6)B(23) ternary bulk metallic glass with a record high strength of 4.85 GPa as well as an appreciable compressive plastic strain of 1.6%. This finding is associated with the unique attribute of the alloying element Nb, which favors the formation of a networklike structure and holds high Poisson's ratio. A fracture feature with a combination of vein pattern and nanoscale corrugations under compression is clearly characterized in this glass. The fractographic observations correlate well with the observed improvements in plasticity. (c) 2008 American Institute of Physics.
关键词:
mechanical-properties;supercooled liquid;alloy;plasticity
Applied Physics Letters
Composite alloys of (Mg0.65Cu0.075Ni0.075Zn0.05Ag0.05Y0.1)(100-x)Fe-x(x=9 and 13) have been produced through copper mold casting, based on a good bulk metallic glass former. Upon cooling the melt, an alpha-Fe solid solution precipitates uniformly with sizes in the 1-10 mum range while the remaining melt undergoes a glass transition. The in situ composite has a compressive strength as high as similar to1 GPa, a factor of 1.6 higher than the single-phase metallic glass. In contrast to all the previous Mg-based monolithic glasses that always fail in the elastic regime, a plastic strain to failure of the order of 1% was obtained for the Fe-toughened composite. (C) 2003 American Institute of Physics.
关键词:
matrix composites;mechanical-properties;amorphous-alloys;behavior;ag
Intermetallics
Usually, bulk metallic glasses exhibit strength values superior to conventional crystalline alloys, often combined with a large elastic limit and rather low Young's modulus. This combination of properties renders such alloys quite unique when compared to commercial materials. However, the major drawback for engineering applications is their limited room temperature ductility and toughness due to the localized deformation processes linked to shear banding, where high plastic deformation is accumulated in a very narrow region without contributing to macroscopic deformation, work hardening or yielding. In this work we report on a new class of metallic glass in a simple Cu-base alloy. Addition of 5 at.% Al increases the glass-forming ability of binary Cu50Zr50. The resulting Cu47.5Zr47.5Al5 glass exhibits high strength (2265 MPa) together with large room temperature ductility up to 18%. After yielding a strong increase in the flow stress is observed during deformation. The structure of the metallic glass exhibits atomic-scale heterogeneities that enable easy nucleation and continuous multiplication of shear bands. The interaction and intersection of shear bands increases the flow stress of the material with further deformation, leading to a 'work hardening'-like behavior and yields a continuous rotation of the shear angle up to fracture resulting in a high compressive ductility. (c) 2006 Elsevier Ltd. All rights reserved.
关键词:
glasses;metallic;mechanical properties at ambient temperature;work-hardening;microstructure;nanostructure-dendrite composite;mechanical-properties;matrix;composites;enhanced plasticity;thermal-stability;amorphous-alloys;zr-ti;bulk;microstructure;particles
材料科学技术（英文）
The deformation, damage, fracture, plasticity and melting phenomenon induced by shear fracture were investigated and summarized for Zr-, Cu-, Ti- and Mg-based bulk metallic glasses (BMGs) and their composites. The shear fracture angles of these BMG materials often display obvious differences under compression and tension, and follow either the Mohr-Coulomb criterion or the unified tensile fracture criterion. The compressive plasticity of the composites is always higher than the tensile plasticity, leading to a significant inconsistency. The enhanced plasticity of BMG composites containing ductile dendrites compared to monolithic glasses strongly depends on the details of the microstructure of the composites. A deformation and damage mechanism of pseudo-plasticity, related to local cracking, is proposed to explain the inconsistency of plastic deformation under tension and compression. Besides, significant melting on the shear fracture surfaces was observed. It is suggested that melting is a common phenomenon in these materials with high strength and high elastic energy, as it is typical for BMGs and their composites failing under shear fracture. The melting mechanism can be explained by a combined effect of a significant temperature rise in the shear bands and the instantaneous release of the large amount of elastic energy stored in the material.
关键词:
bulk metallic glasses (BMGs);mechanical properties;shear fracture;failure criterion;plastic deformation;melting phenomenon;supercooled liquid region;fatigue-crack-propagation;nanostructure-dendrite composite;soft-magnetic properties;serrated;plastic-flow;ni amorphous-alloys;ti-based composites;in-situ;formation;cu-be alloy;high-strength
