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

The nitrogen absorption by iron, Fe-20Cr-10Ni and SUS329J1 stainless steel YAG laser welding in the atmosphere of Ar-N2 mixture gas was investigated in comparison with those during arc welding using the same materials as in this experiment and equilibrium data. Although the nitrogen contents of YAG laser weld metal increase with the nitrogen partial pressure were as well as those of arc weld metal of arc welding, the nitrogen content during YAG laser welding were quite less than those during arc welding. Blowholes can not be observed in Fe-20Cr-10Ni and SUS329J1 stainless steel and can only be found in iron at lower nitrogen partial pressure during YAG laser welding. A discussion on the difference in nitrogen absorption between YAG Laser and arc welding has suggested that small amount of nitrogen absorption results from less opportunity of nitrogen to touch the surface of molten metal due to the active evaporation of metal which covers the major surface of molten metal during laser welding metal. Additionally, the short-time thermal cycle compared with arc welding may bring insufficient nitrogen absorption in the weld metal during cooling. It can be considered that the nitrogen absorption during YAG laser welding is basically different from that during arc welding.

/pdf/nitrogen-absorption-by-iron-and-stainless-steels-during-yag-4hw7z1r4ja.pdf

Nitrogen Absorption by Iron and Stainless Steels during YAG Laser Welding

Corrosion–erosion test of SS316L grain boundary engineering material (GBEM) in lead bismuth flowing loop

Duplex stainless steels were gas tungsten arc welded without filler material in various Ar–N2 mixed gas atmospheres. Weld metals having different nitrogen contents were annealed at 900–1300 K to examine the single effect of nitrogen on the σ transformation. Nitrogen content of the weld metal did not influence the nose temperature and the time for σ initiation in time–temperature–precipitation diagrams for σ, but did decrease the σ content after annealing for long times. These results were correlated with the nitrogen content and microstructure of the weld metals. The effect of σ on the fracture toughness of the weld metal was evaluated by the small punch (SP) test. A small amount of σ in the weld metal led to a marked decrease in the SP energy.

Effect of nitrogen on σ transformation in duplex stainless steel weld metal

There are many occasions during the fusion welding process where a molten weld metal is isolated from the air by means of a shielding gas. If air is enveloped into the welding atmosphere and the molten weld metal actively reacts with the gas, the absorbed gas may affect various weld zone properties. Hydrogen, nitrogen and oxygen are considered typical examples of such gases. They are all key gaseous elements which affect weld metal properties. The focus of this article is the reaction of nitrogen gas with steel weld metal and a description is provided of nitrogen absorption and desorption by steel weld metal during the arc and laser welding processes.

Nitrogen absorption and desorption by steels during arc and laser welding

(2003). Friction stir welding (FSW) process. Welding International: Vol. 17, No. 11, pp. 852-855.

https://link.springer.com/content/pdf/10.1533/wint.2003.3174.pdf

Hiroyuki Kokawa

Papers

Nitrogen Absorption by Iron and Stainless Steels during YAG Laser Welding

Corrosion–erosion test of SS316L grain boundary engineering material (GBEM) in lead bismuth flowing loop

Effect of nitrogen on σ transformation in duplex stainless steel weld metal

Nitrogen absorption and desorption by steels during arc and laser welding

Friction Stir Welding (FSW) process