Mechanical properties of nanocrystalline materials

Principles of equal-channel angular pressing as a processing tool for grain refinement

The current understanding of the fundamentals of recrystallization is summarized. This includes understanding the as-deformed state. Several aspects of recrystallization are described: nucleation and growth, the development of misorientation during deformation, continuous, dynamic, and geometric dynamic recrystallization, particle effects, and texture. This article is authored by the leading experts in these areas. The subjects are discussed individually and recommendations for further study are listed in the final section.

/pdf/current-issues-in-recrystallization-a-review-12181rj4pn.pdf

Current issues in recrystallization: a review

Dynamic and post-dynamic recrystallization under hot, cold and severe plastic deformation conditions

A review of dynamic recrystallization phenomena in metallic materials

Transition from strengthening to softening by grain boundaries in ultrafine-grained Cu

A recent OIM study of the substructure in hot compressed Al has observed an increase in the fraction of boundaries both of 15–20° and above 20° as strain rises from 0.9 to 1.5. This was interpreted as evidence of continuous dynamic recrystallization being the mechanism for the steady state deformation. However, when the original grain boundaries and transition boundaries between deformation bands are discounted, the fraction of 15–20° boundaries is reduced to less than 20% and would be much lower if subboundaries less than 0.5° visible in TEM were taken into account. The present authors argue that dynamic recovery maintains the subgrains of constant size, low misorientation and equiaxed to produce a steady state and can permit a limited number of discrete segments with higher misorientation notably as temperature falls. Moreover, continuous dynamic recrystallization is not appropriate terminology because it is far from reaching the completion observed in other instances of continuous recrystallization.

Dynamic recovery: sufficient mechanism in the hot deformation of Al (<99.99)

Geometric dynamic recrystallization (GDRX) is a process in which a refined and nearly equiaxed grain structure is formed, because grain boundaries which have become serrated during formation of subgrains in the course of hot deformation recombine as serrations pinch off or as the grains thin down. GDRX was first found in aluminium and more recently in AlMg solid solution. In the present work the question was addressed whether GDRX occurs also in an industrial Al alloy (5083) containing particles. Specimens were deformed in torsion from 473 to 773 K at equivalent (surface) strain rates between 10−3 and 4 s−1 to strains up to 3.6. Under these conditions the egg tray model predicts that GDRX will occur. This is indeed found from observations of the grain structure with light and electron microscopy. The results indicate that GDRX occurs not only by recombination of opposite boundaries of the thinned grain but also by pinching off of serrations. The size of the GDRX grains is about two to three times the subgrain size. The close similarity to Al5Mg means that the particles in the alloy do not prevent the small-scale grain boundary migration which is necessary to form the serrations. Static recrystallization after hot deformation destroys the DRX structure, if the specimen is not cooled fast enough.

Geometric dynamic recrystallization in hot torsion of Al5Mg0.6Mn (AA5083)

Temperature dependence of the strength of fine- and ultrafine-grained materials

A simple dislocation model of deformation resistance of ultrafine-grained materials explaining Hall-Petch strengthening and enhanced strain rate sensitivity

Wolfgang Blum

Papers

Transition from strengthening to softening by grain boundaries in ultrafine-grained Cu

Dynamic recovery: sufficient mechanism in the hot deformation of Al (<99.99)

Geometric dynamic recrystallization in hot torsion of Al5Mg0.6Mn (AA5083)

Temperature dependence of the strength of fine- and ultrafine-grained materials

A simple dislocation model of deformation resistance of ultrafine-grained materials explaining Hall-Petch strengthening and enhanced strain rate sensitivity