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Many efforts have been made recently to produce ultrafine grained (UFG) structural metallic materials having submicrometer grain sizes, since UFG materials are expected to perform superior mechanical properties, i.e., a high strength, good elongation and, mainly superplastic formability at lower temperatures and higher strain rates. One of the promising ways to produce bulk UFG materials is the severe plastic deformation (SPD).

In this paper, the mechanical behavior of ultrafine‐ and coarse‐grained Al at a record low temperature of 0.52 K is presented. It is demonstrated that grain refinement by equal channel angular pressing leads to increased flow stress and to a change in the strain hardening behavior of Al at this temperature. Special emphasis is placed on the effect of the superconducting transition on the mechanical behavior in the different microstructural conditions. It is shown that the magnitude of the stress jump associated with the transition correlates with the strain hardening behavior which, in turn, is related to the microstructure of the material.

Bulk ultra-fine grained (UFG) commercially pure Ti was prepared by cryogenic milling in liquid argon and subsequent spark plasma sintering (SPS). During cryogenic milling, individual powder particles are repetitively severely deformed by attrition forces. Powder particles were not significantly refined, but due to severe repetitive plastic deformation, ultra-fine grained microstructure emerges within each powder particle. Cryogenic milling can be therefore considered as a specific severe plastic deformation (SPD) method. Compactization of cryomilled powder by SPS technique (also referred to as field assisted sintering technique - FAST) requires significantly lower sintering temperatures and shorter sintering times for successful compaction when compared to any other sintering technique. This is crucial for maintaining the UFG microstructure due to its limited thermal stability. Several specimens were prepared by varying processing parameters, in particular the sintering temperature. The microstructure of powders and compacted samples was observed by scanning electron microscopy (SEM). Increased sintering temperature results in recrystallization and grain growth. A trade-off relationship between the density of compacted material and grain size was identified. Microhardness of the material was found to depend on residual porosity rather than grain size. This contribution presents cryogenic milling and spark plasma sintering as a viable alternative for achieving UFG microstructure in commercially pure Ti.

This paper focuses on the study of the aging kinetics of the b-titanium Ti-15Mo alloy prepared by high pressure torsion. The experimental methods of differential scanning calorimetry and transmission electron microscopy were used for structural investigations. It was established that during aging at 500 and 550 degC, in the ultrafine-grained (UFG) alloy, the precipitating a-particles have mostly equiaxed morphology, in contrast to the needle-like and lens one in the coarse-grained (CG) alloy. There have been identified differences in the aging kinetics of the Ti-15Mo alloy in the UFG state identified by a decrease in microhardness within the first 30 minutes of heating, as opposed to the CG alloy coarsening. The influence of morphological features of the alloy microstructure on the strengthening effect after aging is discussed.