There is, I think, something ethereal about i —the square root of minus one. I remember first hearing about it at school. It seemed an odd beast at that time—an intruder hovering on the edge of reality.

Usually familiarity dulls this sense of the bizarre, but in the case of i it was the reverse: over the years the sense of its surreal nature intensified. It seemed that it was impossible to write mathematics that described the real world in …

I and i

다중혈관 관상동맥 환자에서 y-문합을 이용하여 양쪽 내흉동맥만을 사용한 우회술의 조기 성적

[신간의 별자리x] 우리/미술, 그리고 ‘슬픔의 박물관’

Strengthening and toughening mechanisms in Mg–Zn–Y alloy with a long period stacking ordered structure

Bulk nanostructured (ns)/ultrafine-grained (UFG) metallic materials possess very high strength, making them attractive for high strength, lightweight and energy efficient applications. The most effective approach to produce bulk ns/UFG metallic materials is severe plastic deformation (SPD). In the last 30 years, significant research efforts have been made to explore SPD processing of materials, SPD-induced microstructural evolutions, and the resulting mechanical properties. There have been a few comprehensive reviews focusing mainly on SPD processing and the mechanical properties of the resulting materials. Yet no such a review on SPD-induced microstructural evolutions is available. This paper aims to provide a comprehensive review on important microstructural evolutions and major microstructural features induced by SPD processing in single-phase metallic materials with face-centered cubic structures, body-centered cubic structures, and hexagonal close-packed structures, as well as in multi-phase alloys. The corresponding deformation mechanisms and structural evolutions during SPD processing are discussed, including dislocation slip, deformation twinning, phase transformation, grain refinement, grain growth, and the evolution of dislocation density. A brief review on the mechanical properties of SPD-processed materials is also provided to correlate the structure with mechanical properties of SPD-processed materials, which is important for guiding structural design for optimum mechanical properties of materials.

Structural evolutions of metallic materials processed by severe plastic deformation

The effects of rare earth erbium (Er) on microstructures and fatigue fracture behavior of an Al–Cu–Mg–Ag alloy were investigated. Microstructural examinations first revealed that the precipitation kinetics of Ω phase was distinctly retarded by promoting the formation of θ′ phase with the Er addition during the initial aging. The fatigue crack propagation resistance of Er-containing microstructure was significantly enhanced arising from the presence of the crystallographic secondary cracks, which was directly relative to the large grain size. Results also suggested that the dendritic substructure of as-cast Al–Cu–Mg–Ag alloy was refined remarkably by Er addition.

Microstructures and fatigue fracture behavior of an Al–Cu–Mg–Ag alloy with addition of rare earth Er

The deformable θ′ particle in Al–Cu binary alloy was found to dissolve more rapidly than the indeformable θ particle due to an additional increasing strain energy accumulated in the deformed θ′ plate as well as an increasing interface energy led by the formation of sub-boundary in the θ′ plate and fragmentation of the particle during equal channel angular pressing (ECAP). The critical radius and the free energy barrier for the strain-induced dissolution of both θ′ and θ particles were calculated.

On strain-induced dissolution of θ′ and θ particles in Al–Cu binary alloy during equal channel angular pressing

The fatigue behavior of three different AA2524 alloy sheets respectively with dominant Goss+Cube-grains, Cube-grains and Cube+Brass-grains was characterized in present work. Results showed Goss+Cube-grain sheet possessed a much lower fatigue crack propagation (FCP) rate than Cube-grain sheet and Cube+Brass sheet. The Cube+Brass sheet had the greatest fatigue crack propagation rate among the three kinds of commercial sheet in spite of the grain size smaller than Cube-grain sheet. EBSD detection results indicated Goss-grains had a twist component boundary or great tilt angle component boundary with the neighboring grains, thereby retarding fatigue crack propagation in fatigue Stage II more effectively. Apparently, the high intense Goss-grains were responsible for the enhanced fatigue crack propagation resistance of AA2524 alloy.

Song Bai

Papers

Microstructures and fatigue fracture behavior of an Al–Cu–Mg–Ag alloy with addition of rare earth Er

On strain-induced dissolution of θ′ and θ particles in Al–Cu binary alloy during equal channel angular pressing

Mechanisms for Goss-grains induced crack deflection and enhanced fatigue crack propagation resistance in fatigue stage II of an AA2524 alloy

Enhanced fatigue crack propagation resistance in a superhigh strength Al–Zn–Mg–Cu alloy by modifying RRA treatment

Effects of natural aging on the formation and strengthening effect of G.P. zones in a retrogression and re-aged Al–Zn–Mg–Cu alloy