Perspectives on Titanium Science and Technology

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

A review of dynamic recrystallization phenomena in metallic materials

Magnesium and its alloys do not in general undergo the same extended range of plasticity as their competitor structural metals. The present work is part I of a study that examines some of the roles deformation twinning might play in the phenomenon. A series of tensile test results are reported for the common wrought alloy AZ31. These data are employed in conjunction with a simple constitutive model to argue that View the MathML source twinning (which gives extension along the c-axis) can increase the uniform elongation in tensile tests. This effect appears to be similar to that seen in Ti, Zr and Cu–Si and in the so called TWIP phenomenon in steel.

Twinning and the ductility of magnesium alloys Part I: “Tension” twins

X-ray computer tomography (CT) is fast becoming an accepted tool within the materials science community for the acquisition of 3D images. Here the authors review the current state of the art as CT transforms from a qualitative diagnostic tool to a quantitative one. Our review considers first the image acquisition process, including the use of iterative reconstruction strategies suited to specific segmentation tasks and emerging methods that provide more insight (e.g. fast and high resolution imaging, crystallite (grain) imaging) than conventional attenuation based tomography. Methods and shortcomings of CT are examined for the quantification of 3D volumetric data to extract key topological parameters such as phase fractions, phase contiguity, and damage levels as well as density variations. As a non-destructive technique, CT is an ideal means of following structural development over time via time lapse sequences of 3D images (sometimes called 3D movies or 4D imaging). This includes information nee...

https://www.tandfonline.com/doi/pdf/10.1179/1743280413Y.0000000023

Quantitative X-ray tomography

Microstructural changes during high-temperature extrusion and torsion of an AZ91 alloy (Mg–9Al–1Zn, wt.%) were investigated. In the experimental domain studied, dynamic recrystallisation (DRX) occurs and the effect of temperature and strain rate on the resulting recrystallised grain size was investigated. Complete recrystallisation in torsion is associated with the development of a stress plateau after softening from the peak stress, which is systematically observed in the first steps of straining. The resulting grain size can be related to the value of the peak stress. It appears that the precipitation of the Mg 17 Al 12 phase does not affect significantly the torsion behaviour of the alloy in the experimental domain investigated here. This study supports the idea that very fine-scale microstructures (i.e. with a mean grain size smaller than 5 μm) can be easily produced by DRX during high-temperature extrusion of the AZ91 alloy.

Grain refinement in AZ91 magnesium alloy during thermomechanical processing

Dynamic recrystallization mechanisms of an Fe–8% Al low density steel under hot rolling conditions

A simple Eulerian thermomechanical modeling of friction stir welding

Torsion and compression tests were used to simulate simple deformation paths within the upper α-range of β-treated Zircaloy-4 (i.e. 500−750 °C). The mechanical behaviour exhibits two different domains: at low temperatures and large strain rates strain hardening takes place before flow softening, whereas this first stage disappears at lower flow stress levels. Deformation microstructures were investigated using the electron backscattering diffraction (EBSD) technique. Continuous dynamic recrystallization (CDRX), based on the increasing misorientation of subgrain boundaries and their progressive transformation into large angle boundaries, mainly occurs during straining. Geometric dynamic recrystallization (GDRX), that involves the transformation of the initial high angle boundaries, also contributes to the “fragmentation” of the initial lamellar microstructure. This mechanism is favoured by higher temperatures and lower strain rates.

F. Montheillet

Papers

Grain refinement in AZ91 magnesium alloy during thermomechanical processing

Dynamic recrystallization mechanisms of an Fe–8% Al low density steel under hot rolling conditions

A simple Eulerian thermomechanical modeling of friction stir welding

Microstructure transformation during warm working of β-treated lamellar Zircaloy-4 within the upper α-range

Three-dimensional microtomographic study of Widmanstätten microstructures in an alpha/beta titanium alloy