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

Friction stir welding (FSW) is a relatively new solid-state joining process. This joining technique is energy efficient, environment friendly, and versatile. In particular, it can be used to join high-strength aerospace aluminum alloys and other metallic alloys that are hard to weld by conventional fusion welding. FSW is considered to be the most significant development in metal joining in a decade. Recently, friction stir processing (FSP) was developed for microstructural modification of metallic materials. In this review article, the current state of understanding and development of the FSW and FSP are addressed. Particular emphasis has been given to: (a) mechanisms responsible for the formation of welds and microstructural refinement, and (b) effects of FSW/FSP parameters on resultant microstructure and final mechanical properties. While the bulk of the information is related to aluminum alloys, important results are now available for other metals and alloys. At this stage, the technology diffusion has significantly outpaced the fundamental understanding of microstructural evolution and microstructure–property relationships.

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Friction Stir Welding and Processing

Metals have been mankind's most essential materials for thousands of years; however, their use is affected by ecological and economical concerns Alloys with higher strength and ductility could alleviate some of these concerns by reducing weight and improving energy efficiency However, most metallurgical mechanisms for increasing strength lead to ductility loss, an effect referred to as the strength-ductility trade-off Here we present a metastability-engineering strategy in which we design nanostructured, bulk high-entropy alloys with multiple compositionally equivalent high-entropy phases High-entropy alloys were originally proposed to benefit from phase stabilization through entropy maximization Yet here, motivated by recent work that relaxes the strict restrictions on high-entropy alloy compositions by demonstrating the weakness of this connection, the concept is overturned We decrease phase stability to achieve two key benefits: interface hardening due to a dual-phase microstructure (resulting from reduced thermal stability of the high-temperature phase); and transformation-induced hardening (resulting from the reduced mechanical stability of the room-temperature phase) This combines the best of two worlds: extensive hardening due to the decreased phase stability known from advanced steels and massive solid-solution strengthening of high-entropy alloys In our transformation-induced plasticity-assisted, dual-phase high-entropy alloy (TRIP-DP-HEA), these two contributions lead respectively to enhanced trans-grain and inter-grain slip resistance, and hence, increased strength Moreover, the increased strain hardening capacity that is enabled by dislocation hardening of the stable phase and transformation-induced hardening of the metastable phase produces increased ductility This combined increase in strength and ductility distinguishes the TRIP-DP-HEA alloy from other recently developed structural materials This metastability-engineering strategy should thus usefully guide design in the near-infinite compositional space of high-entropy alloys

Metastable high-entropy dual-phase alloys overcome the strength–ductility trade-off

Dynamic and post-dynamic recrystallization under hot, cold and severe plastic deformation conditions

Fabrication of Ultra High Strength Bol t and Its Mechanical Properties

When a polycrystalline material is deformed, each grain must satisfy the continuity of stress and strain at grain boundaries during deformation. It is called constraint'' by grain boundaries. It has been thought that the constraint affects the deformation behavior of grains, such as crystal rotation and deformed microstructure. However, the details of the effect, particularly the initial orientation dependence, have not been clarified sufficiently. It is well known that in the (001)[100] single crystals in Fe-Si alloys or in iron the matrix bands'' are formed by rolling. The matrix bands are composed of the banded regions which are rotated toward (001) orientation either clockwise or counterclockwise. However, the matrix bands in (001)[100] crystals have not been reported in polycrystalline materials. Although there have been many investigations on the matrix bands in the (001)[100] single crystals, no information as to how the constraint affects the rolled microstructure of the crystals is available. The purpose of the present study is to clarify the effect of the constraint on the rolled microstructure of the (001)[100] oriented single crystal in an Fe-19%Cr ferritic alloy.

Effect of constraint on the rolled microstructure of (001)[100] oriented single crystals in an Fe-19%Cr ferritic alloy

Crystallography of grain boundary (GB) bcc-precipitates formed in a lightly pre-deformed fcc-matrix phase was examined in a Ni-43Cr alloy by EBSD with emphasis on a misorientation from the Kurdjumov-Sachs orientation relationship. The misorientation of GB bcc-precipitates became somewhat larger when the matrix phase was lightly pre-deformed. The GB bcc-precipitates were preferentially formed at the intersection of geometrically necessary dislocation boundaries (GNB) with grain boundaries. In contrast, the pre-deformation did not influence the misorientation of intragranular bcc-precipitates. The preferential precipitation and the increased misorientation at the GNB-GB intersection were discussed.

Light Pre-deformation induced misorientation of grain boundary bcc-precipitates from the Kurdjumov-Sacks relationship in a Ni−Cr alloy

A fine ferrite-based steel is disclosed, wherein at least 60% of the ferrite grain boundary is a large angle grain boundary of at least 15°, and the mean ferrite grain size is not more than 2.5 μm. The fine ferrite-based steel of the invention has a high strength and a long fatigue life.

Fine ferrite-based structure steel production method

Reply to comments on the paper “In situ observations of silver-decoration evolution under hydrogen permeation: Effects of grain boundary misorientation on hydrogen flux in pure iron” by Gavriljuk and Teus

Kaneaki Tsuzaki

Papers

Fabrication of Ultra High Strength Bol t and Its Mechanical Properties

Effect of constraint on the rolled microstructure of (001)[100] oriented single crystals in an Fe-19%Cr ferritic alloy

Light Pre-deformation induced misorientation of grain boundary bcc-precipitates from the Kurdjumov-Sacks relationship in a Ni−Cr alloy

Fine ferrite-based structure steel production method

Reply to comments on the paper “In situ observations of silver-decoration evolution under hydrogen permeation: Effects of grain boundary misorientation on hydrogen flux in pure iron” by Gavriljuk and Teus