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

비만아 부모의 돌봄 경험: q 방법론

High-entropy alloys (HEAs) are alloys with five or more principal elements. Due to the distinct design concept, these alloys often exhibit unusual properties. Thus, there has been significant interest in these materials, leading to an emerging yet exciting new field. This paper briefly reviews some critical aspects of HEAs, including core effects, phases and crystal structures, mechanical properties, high-temperature properties, structural stabilities, and corrosion behaviors. Current challenges and important future directions are also pointed out.

https://www.tandfonline.com/doi/pdf/10.1080/21663831.2014.912690

High-Entropy Alloys: A Critical Review

This article presents an overview of the developments in stainless steels made since the 1990s. Some of the new applications that involve the use of stainless steel are also introduced. A brief introduction to the various classes of stainless steels, their precipitate phases and the status quo of their production around the globe is given first. The advances in a variety of subject areas that have been made recently will then be presented. These recent advances include (1) new findings on the various precipitate phases (the new J phase, new orientation relationships, new phase diagram for the Fe–Cr system, etc.); (2) new suggestions for the prevention/mitigation of the different problems and new methods for their detection/measurement and (3) new techniques for surface/bulk property enhancement (such as laser shot peening, grain boundary engineering and grain refinement). Recent developments in topics like phase prediction, stacking fault energy, superplasticity, metadynamic recrystallisation and the calculation of mechanical properties are introduced, too. In the end of this article, several new applications that involve the use of stainless steels are presented. Some of these are the use of austenitic stainless steels for signature authentication (magnetic recording), the utilisation of the cryogenic magnetic transition of the sigma phase for hot spot detection (the Sigmaplugs), the new Pt-enhanced radiopaque stainless steel (PERSS) coronary stents and stainless steel stents that may be used for magnetic drug targeting. Besides recent developments in conventional stainless steels, those in the high-nitrogen, low-Ni (or Ni-free) varieties are also introduced. These recent developments include new methods for attaining very high nitrogen contents, new guidelines for alloy design, the merits/demerits associated with high nitrogen contents, etc.

Recent developments in stainless steels

The 𝜎 phase which exists in various series of stainless steels is a significant subject in steels science and engineering. The precipitation of the 𝜎 phase is also a widely discussed aspect of the science and technology of stainless steels. The microstructural variation, precipitation mechanism, prediction method, and effects of properties of 𝜎 phase are also of importance in academic discussions. In the first section, a brief introduction to the development and the precipitation characteristics (including morphologies and precipitation sites) of 𝜎 phase in stainless steels is presented. In the second section, the properties effect, prediction method, processing effect, elemental addition, retardation method and Thermo-Calc simulation of the 𝜎 phase in stainless steels are highlighted.

/pdf/overview-of-intermetallic-sigma-phase-precipitation-in-1d817vlxbh.pdf

Overview of Intermetallic Sigma () Phase Precipitation in Stainless Steels

A series of high chromium Fe–Cr–C hardfacing alloys were produced by gas tungsten arc welding (GTAW). Chromium and graphite alloy fillers were used to deposit coatings on ASTM A36 steel substrates. These coatings were especially designed to vary the size and proportion of the (Cr,Fe)23C6 carbides that are present in the microstructure at room temperature. Depending on the three different graphite additions of those alloy fillers, hypoeutectic, eutectic and hypereutectic microstructures were obtained on coated surfaces. No crack formation was found on the coatings. According to the X-ray diffraction analysis and microstructure characteristics, the hypereutectic composites consist of three phases, i.e. Cr–Fe solid solution (α), (Cr,Fe)23C6 and trace amounts of (Cr,Fe)7C3. Massive (Cr,Fe)23C6 contain (Cr,Fe)7C3 in the center, and cause its high hardness value up to HRC 70. And the massive (Cr,Fe)23C6 are surrounded by a eutectic structure to restrain cracks from appearing. All the microstructure constituents were rationalized in terms of a ternary diagram.

Microstructure change caused by (Cr,Fe)23C6 carbides in high chromium Fe–Cr–C hardfacing alloys

The evolution of microstructures and mechanical properties during accumulative roll bonding of Al/Mg composite

TiAlN coatings have been known to be superior to other coatings such as TiN and TiCN in protecting tools which may be damaged by high thermal load (high cutting speed). Unfortunately, these coatings normally suffer greater damage than TiN and TiCN in more mechanically influenced processes such as interrupted cutting or slow speed cutting. The present study aims at developing multi-layered TiN/TiAlN coatings which may offer a good compromise between the properties of TiN and TiAlN. Three approaches including shutter control, power supply control, and rotational stage control were used to deposit multi-layered TiN/TiAlN coatings using unbalanced magnetrons. These coatings were then characterized using SEM, GDOS, nano-indention system, and tribometer. It was found that, in general, these multi-layered TiN/TiAlN coatings had lower wear rate than single-layered TiAlN within the tested sliding speeds. At certain sliding speeds, these coatings also had lower wear rate than TiN. In some tests, a thin layer (0.1 μm) of TiCN was coated on multi-layered coatings in an attempt to reduce frictional damage particularly during run-in stage. The result shows that the wear resistance of the TiCN–(TiN/TiAlN) coating was significantly improved especially at low sliding speed.

Weite Wu

Papers

Overview of Intermetallic Sigma () Phase Precipitation in Stainless Steels

Microstructure change caused by (Cr,Fe)23C6 carbides in high chromium Fe–Cr–C hardfacing alloys

The evolution of microstructures and mechanical properties during accumulative roll bonding of Al/Mg composite

Deposition and characterization of TiAlN and multi-layered TiN/TiAlN coatings using unbalanced magnetron sputtering

Microstructural and abrasive characteristics of high carbon Fe-Cr-C hardfacing alloy