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The possibilities of controlling the structure and properties of a Cu-Al-Ni shape memory alloy due to the use of different schemes of the thermomechanical treatment, including forging, homogenizing in the austenitic state and subsequent quenching, and high-pressure torsion have been found. For the first time, an ultrafine-grain structure has been produced in this alloy via severe plastic deformation using high-pressure torsion. It has been detected that high-pressure torsion using ten revolutions of the anvils leads to the formation of a nanocrystalline structure with a grain size of less than 100 nm. The subsequent short-term heating of the alloy to 800°С (10 s) in the temperature region of the existence of the homogeneous β phase made it possible to form an ultrafine-grain structure with predominant sizes of recrystallized grains of 1 and 8 μm. The quenching after heating prevented the decomposition of the solid solution. The refinement of the grain structure changed the deformation behavior of the alloy, having provided the possibility of the significant plastic deformation upon mechanical tensile tests. The coarse-grained hot-forged quenched alloy was brittle, and fracture occurred along the boundaries of former austenite grains and martensite packets. The highstrength ultrafine-grained alloy also experienced mainly the intercrystalline fracture along the high-angle boundaries of elements of the structure, the grain size of which was less by two orders than that in the initial alloy. This determined an increase in its relative elongation upon mechanical tests. [ABSTRACT FROM AUTHOR]

The aim of this paper is to consider the features of structure evolution during severe plastic deformation (SPD) of steels and its influence on mechanical properties. The investigation have been carried out mainly on low carbon steels as well as on austenitic stainless steels after SPD by torsion under high pressure (HPT) and equal channel angular (ECA) pressing. Structure formation dependencies on temperature deformation conditions, strain degree, chemical composition, initial state and pressure are considered. The role of phase transformations for additional grain refinement, namely, martensitic transformation, precipitation of carbide particles during SPD and heating is underlined.

Abstract: It is shown that cold equal-channel angular pressing (ECAP) of corrosion resistant austenitic 0.07%C–17.3%Cr–9.2%Ni–0.7%Ti steel leads to formation of submicrocrystalline structure: generally oriented subgrains and cells with separated grains (100–250nm in size). The steel samples 20mm in diameter and 80mm in length were subjected to ECAP at room temperature for four passes. The angle between the channels was 120°. ECAP promotes the martensitic transformation which becomes more active only after four passes, leading to the formation of 45% martensite. During heating, the fraction of high-angle boundaries and the volume of austenite are increased, and the microstructure becomes more equiaxed. Submicrocrystalline structure with grain size 150–250nm and 80% of austenite was obtained upon heating to 550°C. Such structure exhibits a substantial strain hardening (yield strength 1090MPa relative to the initial with 320MPa) and an elongation of 12%. [Copyright &y& Elsevier]