Terence G. Langdon

The static recrystallization and grain growth of a hybrid AZ31/Mg-0.6Gd (wt.%) material fabricated by high-pressure torsion (HPT) through 20 turns were explored after isochronal annealing at 150, 250, 350 and 450 °C for 1 h using electron backscatter diffraction, transmission electron microscopy and Vickers microhardness measurements. The results reveal heterogeneity in the grain size distributions of the AZ31 and Mg-0.6Gd regions after annealing at the lower temperatures of 150 and 250 °C leading to a clear AZ31/Mg-0.6Gd interfacial border. At the higher temperatures of 350 and 450 °C the AZ31/Mg-0.6Gd interfaces were not well-defined owing to the occurrence of grain growth. It is shown that grain growth is restricted in the AZ31 and Mg-0.6Gd regions due to the presence of stable nano-size Al8Mn5 particles and the precipitation of Mg17Al12 and Mg12Zn at 250 °C and of Mg5Gd and Mg12Gd phases at …

The formation of ultrafine grains with nanostructural features in metallic materials by SPD processing can provide superior mechanical and, simultaneously, functional properties of metals and alloys, for example, high strength and electrical conductivity in Cu and Al alloys, enhanced fatigue endurance and high corrosion and erosion resistance in Ti alloys and many other so-called multifunctional properties. This chapter demonstrates that the level of the above properties is determined by small grain size, nonequilibrium grain boundaries with high density of grain boundary dislocations, nanoscale grain boundary segregations and precipitations, etc. Changes in the physical properties of UFG materials are associated with the comparability of grain sizes and characteristics, including the free path length of electrons and the size of magnetic domains.In particular, nanocrystalline magnetic hard materials are …

Advanced structural materials are expected to display significantly improved mechanical properties and this may be achieved, at least in part, by refining the grain size to the submicrometer or the nanocrystalline range. This report provides a detailed summary of the role of grain size in the mechanical properties of metals. The effect of grain size on the high temperature behavior and the development of superplasticity is illustrated using deformation mechanism maps and the development of exceptional strength through grain refinement hardening at low temperatures is also discussed. It is shown that the deformation mechanism of grain boundary sliding, as developed theoretically, can be used to effectively predict both the high and low temperature behavior of metals having different grain sizes. This analysis explains the increase in strain rate sensitivity in ultrafine-grained metals with low and moderate melting …

Zinc alloys have emerged as promising candidates for biodegradable materials due to their remarkable biocompatibility and favorable mechanical characteristics. The incorporation of alloying elements plays an essential role in advancing the tensile strength of Zn alloys. Nevertheless, achieving uniform dispersion of these elements poses challenges due to chemical segregation during solidification. In this study, rapid solidification followed by high-pressure torsion was successfully employed to fabricate Zn–Li–Mn–Mg–Cu alloys characterized by ultrafine-grained microstructures with evenly distributed nanometric intermetallic phases. A comprehensive examination, including phase composition, microstructural evolution, tensile properties and deformation mechanisms, was conducted. The impact of varying annealing temperatures on microstructural stability was systematically examined. The combined …

Aluminium matrix nanocomposites reinforced with carbon nanotubes were fabricated in a new way by direct synthesis using high-pressure torsion (HPT). Aluminium of 99.99 % and 99.5 % purities were used as matrix materials with carbon nanotubes in amounts of 0.5 and 1 wt% as reinforcement. The HPT processing led to extensive grain size refinement which was significantly higher than for pure metals and to a relatively uniform distribution of the fillers. The grain size of the matrix was smaller for Al99.5 compared to Al99.99 while the particle spatial distribution was more homogenous for the Al99.99 matrix. This was attributed to a lower hardness and higher plasticity of Al 99.99 alloy. The addition of carbon nanotubes also improved the thermal stability of the ultrafine-grained structure, especially if homogenously distributed as for the Al99.99 matrix nanocomposites.

UFG metals and alloys attract the materials science community owing to their superior mechanical properties. This chapter considers achieving enhanced mechanical properties in the UFG materials processed by SPD techniques. Special emphasis is laid on the examples and origins of the phenomenon of superstrength as well as the description of the hardening mechanisms in the materials. The chapter views the manifestation of the SPD paradox caused by the formation of equiaxial UFG structure and control of grain boundary type and segregations. The SPD paradox is evident in the simultaneous growth of strength and ductility. Mechanisms for enhancing the ductility of UFG materials are considered. The chapter also focuses on the importance of grain refinement in increasing fatigue strength and endurance, creep resistance of materials, the manifestation of the superplasticity effect at lower temperatures, and …

The Geometrically Necessary Dislocation (GND) density was estimated from Electron Backscatter Diffraction (EBSD) data for an AZ31/Mg-0.6Gd (wt.%) hybrid material fabricated by high-pressure torsion (HPT) at room temperature through an equivalent strain range of ϵeq = 0.3–144 using Kernel Average Misorientation (KAM) and the Nye tensor approaches. The results show that generally the GND densities are significant at the beginning of the deformation (ϵeq = 0.3) and decrease in both alloys when ϵeq increases. The Mg-0.6Gd alloy exhibits a lower GND density due to rapid dynamic recrystallization. These results were compared to the GND densities measured in AZ31 and Mg-0.6Gd mono-materials processed separately by HPT under the same experimental conditions. In these mono-materials the GND densities increase with increasing equivalent strain up to 7 and then decrease with further straining …

The authors regret but we accidentally left out one person who should have been included in this article: Aleksandra Bartkowska from European Organization for Nuclear Research (CERN), 1211 Geneva, Switzerland,[email protected]. If it is possible could you include her to this article with the following order: