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

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

[Lu, K.; Lu, L.] Chinese Acad Sci, Inst Met Res, Shenyang Natl Lab Mat Sci, Shenyang 110016, Peoples R China. [Lu, L.; Suresh, S.] MIT, Sch Engn, Cambridge, MA 02139 USA.;Lu, K (reprint author), Chinese Acad Sci, Inst Met Res, Shenyang Natl Lab Mat Sci, Shenyang 110016, Peoples R China;lu@imr.ac.cn ssuresh@mit.edu

/pdf/strengthening-materials-by-engineering-coherent-internal-4fkjmv3btq.pdf

Strengthening Materials by Engineering Coherent Internal Boundaries at the Nanoscale

Recent advances in friction-stir welding : Process, weldment structure and properties

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

Microstructural Characterizations Following Friction Stir Welding of Dissimilar Alloys of Low- and High-Carbon Steels

Control of grain boundary microstructure for grain boundary engineering (GBE) is effective to prevent intergranular corrosion by disconnection of corrosive random boundary network resulting from the introduction of coincidence site lattice boundaries during the frequent formation of annealing twins in bulk austenitic stainless steels. Since the practical use of austenitic stainless steels often includes straining and heating processes, such as forming, annealing and welding, the processes after the GBE treatment could degrade the optimised grain boundary microstructure and the high corrosion resistance of grain boundary engineered (GBEed) austenitic stainless steels. Therefore the present study examined the effects of post-GBE strain-sensitisation on grain boundary microstructure and corrosion resistance of a GBEed 304 austenitic stainless steel produced by a single-step thermomechanical processing for GBE. The results showed that the grain boundary microstructure was changed apparently and the corrosion ...

Effect of post-GBE strain-sensitisation on corrosion resistance of grain boundary engineered 304 austenitic stainless steel

Anisotropy of structural response of single crystal austenitic stainless steel to friction stir welding

Mechanical properties of friction stir welded 11Cr-ferritic/martensitic steel

The present study applied friction spot joining (FSJ), which was recently developed as a lap joining technique of Al alloys, to two sheets of Al alloy 6061, 1 mm in thickness, and then examined the microstructural feature in the weld. The weld had the nugget-shaped stir zone around the exit hole of the probe, and the stir zone exhibited the equiaxed grain structure having finer grain size than that of the base material. The crystallographic texture analysis using electron backscattered diffraction method suggested that the material movement occurred along the rotating direction of the welding tool in the wide region including the stir zone. In the periphery of the nugget-shaped stir zone, which was characterized as the region having the finer grain size than that of the stir zone interior, any inclusions and precipitates were not found in the SEM scale. The weld was softened around the weld centre. The softening could be explained by dissolution and/or growth of the strengthening precipitates due to therm...

https://www.jstage.jst.go.jp/article/qjjws/25/4/25_4_553/_pdf

Hiroyuki Kokawa

Papers

Microstructural Characterizations Following Friction Stir Welding of Dissimilar Alloys of Low- and High-Carbon Steels

Effect of post-GBE strain-sensitisation on corrosion resistance of grain boundary engineered 304 austenitic stainless steel

Anisotropy of structural response of single crystal austenitic stainless steel to friction stir welding

Mechanical properties of friction stir welded 11Cr-ferritic/martensitic steel

Microstructural analysis of the stir zone of Al alloy produced by friction stir spot welding