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.

/pdf/friction-stir-welding-and-processing-3hu3ejo7ub.pdf

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

https://www.jstage.jst.go.jp/article/tetsutohagane1955/92/5/92_5_295/_pdf

A New Approach for Interpretation of Strengthening Mechanism of Martensitic Steel through Characterization of Local Deformation Behavior

軸比は鉄鋼の材料特性に大きな影響を及ぼす重要な因 子である。例えば鉄系形状記憶合金においてはマルテンサ イトの軸比が大きいほど形状記憶特性は向上する。軸比が 大きいほど形状記憶合金に適した thin plate型のマルテン サイトが生成するようになり,オーステナイト/マルテン サイト界面の易動度が増加するためである。Ohtsuka and Kajiwaraは,FeNiCoAl合金の形状記憶特性を向上させる ことを目的として炭素を添加し,適当な時効熱処理を行う と生成するマルテンサイトの軸比は増大し,形状記憶特性 も向上することを報告した。また,軸比は磁気特性とも密 接に関係することがMitsuokaらにより指摘された 。彼ら はいくつかのFe-C,Fe-NおよびFe-Ni-C合金を作成して磁 気モーメントを測定し,炭素添加により鉄の磁気モーメン トは増加すること,その原因は体積膨張と軸比増大の両方 の効果であることを報告した。炭素添加は鉄の磁気モーメ ント増加のためのよく知られた方法の一つであるが,Fe-C 合金の磁気モーメントの測定データはまだ少なく,磁気 モーメント増加のメカニズムについてもまだ不明な点があ BCC-Feの軸比と磁気モーメントに及ぼす 炭素の影響の第一原理計算

First-Principles Calculation of the Effects of Carbon on Tetragonality and Magnetic Moment of BCC-Fe

The shape memory behavior of an Fe-33%Mn-6%Si alloy pre-strained at 573K (above Af) by various amounts up to 7% was examined. The shape memory effect was improved by pre-straining. However, it was hardly dependent on the amount of pre-strain and a small pre-strain of 1% was enough to improve the shape memory effect. The results were discussed from the viewpoint of the change in the strength of matrix and the flow stress in a shape change by applying the pre-strain. The importance of crystallographic reversibility in fee ↔ hcp martensitic transformations for the shape memory effect was also pointed out from the surface relief observation.

Kaneaki Tsuzaki

Papers

A New Approach for Interpretation of Strengthening Mechanism of Martensitic Steel through Characterization of Local Deformation Behavior

First-Principles Calculation of the Effects of Carbon on Tetragonality and Magnetic Moment of BCC-Fe

Role of pre-straining of austenite in the improvement of shape memory effect in an Fe-33Mn-6Si alloy*

Hydrogen embrittlement of high strength steels and environmental hydrogen entry

Hydrogen embrittlement in Al-added twinning-induced plasticity steels evaluated by tensile tests during hydrogen charging