羟氨苄青霉素引起大疱性类天疱疮样疹

Alloying has long been used to confer desirable properties to materials. Typically, it involves the addition of relatively small amounts of secondary elements to a primary element. For the past decade and a half, however, a new alloying strategy that involves the combination of multiple principal elements in high concentrations to create new materials called high-entropy alloys has been in vogue. The multi-dimensional compositional space that can be tackled with this approach is practically limitless, and only tiny regions have been investigated so far. Nevertheless, a few high-entropy alloys have already been shown to possess exceptional properties, exceeding those of conventional alloys, and other outstanding high-entropy alloys are likely to be discovered in the future. Here, we review recent progress in understanding the salient features of high-entropy alloys. Model alloys whose behaviour has been carefully investigated are highlighted and their fundamental properties and underlying elementary mechanisms discussed. We also address the vast compositional space that remains to be explored and outline fruitful ways to identify regions within this space where high-entropy alloys with potentially interesting properties may be lurking. High-entropy alloys have greatly expanded the compositional space for alloy design. In this Review, the authors discuss model high-entropy alloys with interesting properties, the physical mechanisms responsible for their behaviour and fruitful ways to probe and discover new materials in the vast compositional space that remains to be explored.

High-entropy alloys

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

Friction stir processing (FSP), developed based on the basic principles of friction stir welding (FSW), a solid-state joining process originally developed for aluminum alloys, is an emerging metalworking technique that can provide localized modification and control of microstructures in near-surface layers of processed metallic components. The FSP causes intense plastic deformation, material mixing, and thermal exposure, resulting in significant microstructural refinement, densification, and homogeneity of the processed zone. The FSP technique has been successfully used for producing the fine-grained structure and surface composite, modifying the microstructure of materials, and synthesizing the composite and intermetallic compound in situ. In this review article, the current state of the understanding and development of FSP is addressed.

Friction stir processing technology: A review

Friction stir welding (FSW) is a widely used solid state joining process for soft materials such as aluminium alloys because it avoids many of the common problems of fusion welding. Commercial feasibility of the FSW process for harder alloys such as steels and titanium alloys awaits the development of cost effective and durable tools which lead to structurally sound welds consistently. Material selection and design profoundly affect the performance of tools, weld quality and cost. Here we review and critically examine several important aspects of FSW tools such as tool material selection, geometry and load bearing ability, mechanisms of tool degradation and process economics.

Review: friction stir welding tools

Effects of friction stir processing on mechanical properties of the cast aluminum alloys A319 and A356

Advances in processing of Ni3Al-based intermetallics and applications

High strength metal alloys are described. At least one composition of a metal alloy includes chromium, nickel, copper, manganese, silicon, niobium, tungsten and iron. A heater system may include a canister at least partially made from material containing at least one of the metal alloys. A system for heating a subterranean formation may include a tublar that is at least partially made from a material containing at least one of the metal alloys.

High strength alloys

This work details some aspects of the microstructure–properties–processing relations in spot friction welded (also known as friction stir spot welded) 6111 Al sheets, joined in a lap configuration. We have shown that the tool pin penetration depth has a strong effect on the failure mode of the joined samples and a lesser effect on the joint shear strength. With increasing tool pin penetration depth, and consequently with increasing depth of the tool shoulder pressing into the top sample, the failure mode in a lap-shear test changes from brittle and concentrated near the pin hole, to ductile and away from the weld towards the base metal. The sheet interface under the tool shoulder consists four regions; a region where there is no contact at all between the two surfaces, a region where only a mechanical bond (“kissing bond”) exists, a region where there is partial metallurgical bond, and a region with full metallurgical bonding. There is evidence that during welding the Fe–Si–Mn–Cu inclusions present in the as-received material are swept towards the joint interface, thus degrading the joint quality. The aluminum in the partially metallurgically bonded region, in the fully metallurgically bonded region and under the tool pin is fully recrystallized. In these regions, the presence of low angle grain boundaries indicates that additional deformation has occurred after recrystallized grains were formed. It is thus likely that recrystallization has occurred dynamically during the welding process. The material under the shoulder (a portion of the non-contacting region, the “kissing bond”, the partial metallurgical and the full metallurgical regions) has a significantly larger grain size than under the pin, as well as a different texture.

Structure–properties relations in spot friction welded (also known as friction stir spot welded) 6111 aluminum

A new family of alumina-forming austenitic stainless steels is under development at Oak Ridge National Laboratory for structural use in aggressive oxidizing environments at 600–900°C. Data obtained to date indicate the potential to achieve superior oxidation resistance compared to conventional Cr2O3-forming iron-and nickel-based heat-resistant alloys, with creep strength comparable to state-of-the-art advanced austenitic stainless steels. A preliminary assessment also indicated that the newly developed alloys are amenable to welding. Details of the alloy design approach and composition-microstructure-property relationships are presented.

Michael L. Santella

Papers

Effects of friction stir processing on mechanical properties of the cast aluminum alloys A319 and A356

Advances in processing of Ni3Al-based intermetallics and applications

High strength alloys

Structure–properties relations in spot friction welded (also known as friction stir spot welded) 6111 aluminum

The development of alumina-forming austenitic stainless steels for high-temperature structural use