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Journal Article

Consolidation and mechanical behaviour of nanophase iron alloy powders prepared by mechanical milling

01 Jan 2000-Powder Metallurgy (Maney)-Vol. 43, Iss: 4, pp 306-310
TL;DR: In this paper, the authors present a brief overview of the recent developments in preparing and characterising bulk nanocrystalline metallic alloys from mechanically milled powders, focusing on the work on iron alloys conducted in the author's laboratory.
Abstract: This special feature presents a brief overview of the recent developments in preparing and characterising bulk nanocrystalline metallic alloys from mechanically milled powders, focusing on the work on iron alloys conducted in the author's laboratory. The strategies and procedures used for consolidating the powders into full density compacts while maintaining the grain sizes in the nanophase regime (< 100 nm) are summarised. The unusual mechanical properties observed of the fully dense nanophase alloys, as well as their potential applications, are discussed in comparison with those of conventional coarse grained counterparts.
Citations
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Journal ArticleDOI
Evan Ma1
01 Apr 2006-JOM
TL;DR: In this article, the authors present a review of recent progress in tailoring the nanostructure to achieve coexisting high strength and high ductility at room temperature, focusing on a summary of the strategies currently being pursued as well as the outstanding issues that await future research.
Abstract: Nanostructured metals and alloys are under intensive research worldwide and being developed into bulk forms for application. While these new materials offer record-high strength, their ductility is often inadequat. This article reviews recent progress in tailoring the nanostructure to achieve coexisting high strength and high ductility at room temperature. The focus is on a summary of the strategies currently being pursued as well as the outstanding issues that await future research.

384 citations

Journal ArticleDOI
TL;DR: In this paper, large scale molecular dynamics simulations are used to simulate the plastic deformation of a nanocrystalline model Ni sample with an average grain size of 5 nm containing 125 grains at 800 K up to 4.0% plastic strain.
Abstract: Large scale molecular dynamics (MD) simulations are used to simulate the plastic deformation of a nanocrystalline model Ni sample with an average grain size of 5 nm containing 125 grains at 800 K up to 4.0% plastic strain. For the first time in MD simulation, emerging shear planes involving several grain boundaries have been observed indicating cooperative plastic deformation activity between grains. It is found that three mechanisms have been involved in the development of such shear planes: grain-boundary migration, continuity of shear plane via intragranular slip, and rotation and coalescence of grains.

151 citations

Journal ArticleDOI
TL;DR: In this article, the relationship between the structure and properties of a cryomilled Al-7.5 pct Mg alloy was investigated and the tensile behavior was characterized by high strength, high ductility, and low-strain-hardening.
Abstract: In the present study, the relationships between the structure and properties of a cryomilled Al-7.5 pct Mg alloy were investigated. The microstructure of the cryomilled Al-7.5 pct Mg alloy consisted of equiaxed grains with an approximate size of 300 nm. Thermal treatment had only a minor effect on microstructure, as evidenced by X-ray diffraction (XRD) and transmission electron microscopy (TEM) results. The tensile behavior was characterized by high strength, high ductility, and low-strain-hardening. The tensile deformation was relatively uniform, with limited necking deformation, and fracture surfaces were characterized by microdimples. The variation of strain rates from 4 · 10−4 to 4 · 10−2 s−1 had an insignificant effect on tensile behavior. Comparison of compressive and tensile behavior revealed similar moduli and yield strengths, although the postyield behavior was markedly asymmetric. The present results indicate that grain-size effects, solid-solution strengthening, Orowan strengthening, and dislocation strengthening contribute significantly to the properties of a cryomilled Al-7.5 pct Mg alloy.

132 citations

Journal ArticleDOI
TL;DR: In this paper, the evolution of dislocation structure in pure Fe during equal channel-angular pressing (ECAP) is investigated, and the effect of the formation of this dislocated structure on deformation and fracture behavior is examined.
Abstract: The evolution of dislocation structure in pure Fe during equal-channel-angular pressing (ECAP) is investigated. Also, the effect of the formation of this dislocation structure on deformation and fracture behavior is examined. The results show that intensive dislocation cell blocks are present after one pass and even more after subsequent pressings. The low-energy dislocation structures (LEDS) may have changed into the high-energy dislocation structures (HEDS) in the final several pressings. The high-density array of dislocations plays a significant role in strengthening. The HEDS may cause the materials to lose work-hardening ability and show a cleavage morphology of the fracture surface. A proper subsequent annealing treatment will lead to the evolution of HEDS to LEDS while maintaining little grain growth. This change in the nature of dislocation structures allows ultrafine-grained materials to achieve an excellent combination of high strength and high ductility.

51 citations

Journal ArticleDOI
TL;DR: In this article, a straight inclined grain boundary intercepting a horizontal free surface is studied, and it is shown that the grain boundary is never pinned and the coupled motion can be separated into two time regimes.

28 citations