Igor V. Alexandrov

Bio: Igor V. Alexandrov is an academic researcher from Ufa State Aviation Technical University. The author has contributed to research in topics: Severe plastic deformation & Microstructure. The author has an hindex of 28, co-authored 148 publications receiving 9442 citations.

Paradox of strength and ductility in metals processed by severe plastic deformation

Abstract: It is well known that plastic deformation induced by conventional forming methodssuch as rolling, drawing or extrusion can significantly increase the strength of metalsHowever, this increase is usually accompanied by a loss of ductility. For example, Fig.1 shows that with increasing plastic deformation, the yield strength of Cu and Almonotonically increases while their elongation to failure (ductility) decreases. Thesame trend is also true for other metals and alloys. Here we report an extraordinarycombination of high strength and high ductility produced in metals subject to severeplastic deformation (SPD). We believe that this unusual mechanical behavior is causedby the unique nanostructures generated by SPD processing. The combination ofultrafine grain size and high-density dislocations appears to enable deformation by newmechanisms. This work demonstrates the possibility of tailoring the microstructures ofmetals and alloys by SPD to obtain both high strength and high ductility. Materialswith such desirable mechanical properties are very attractive for advanced structuralapplications.

Influence of ECAP routes on the microstructure and properties of pure Ti

Abstract: Equal channel angular pressing (ECAP) is an innovative technique that can produce bulk ultrafine-grained (UFG) materials in product forms large enough for structural applications. It is well known that ECAP route, defined by the sequence of orientations of the billets relative to the die during the iterative ECAP passes, significantly affects the microstructural development of the work piece. Studies reported in the literature have so far focused on fcc metals such as Al and Cu. In this work, we have studied the influence of ECAP routes on the microstructures and properties of hcp commercially-pure Ti. Three ECAP routes, conventionally defined as BA, BC and C, were used to process the Ti billets. Surface quality, microstructures, microhardness, tensile properties, anisotropy, and thermal stability were studied. The route BC is shown to be the best route for processing hcp Ti.

Grain refinement and properties of pure Ti processed by warm ECAP and cold rolling

Abstract: This work explored a two-step severe plastic deformation process to produce ultrafine-grained (UFG) Ti with significantly enhanced strength. Warm equal channel angular pressing (ECAP) was first used to refine the grain size of Ti billets to about 350 nm. The Ti billets were further processed by repetitive cold rolling (CR). This two-step process produced UFG Ti with strengths higher than those of common titanium alloys such as Ti–6Al–4V. This paper reports the microstructures, tensile properties, and thermal stability of these Ti billets processed by a combination of warm ECAP and CR.

Microstructural evolution, microhardness and thermal stability of HPT-processed Cu

Abstract: Coarse-grained copper was subject to high-pressure torsion (HPT) and thermal treatment to study the effects of increasing amounts of deformation and subsequent annealing on the evolution of microstructure and microhardness. Cellular subgrains with low-angle grain boundaries were first formed at low strain. Some of the low-angle subgrain boundaries transformed to high-angle grain boundaries at higher strains, refining the average grain size from 200 μm to 150 nm. X-ray diffraction patterns showed the formation of crystallographic texture. Microhardness increased monotonically with increasing torsional strain. High internal stress and nonequilibrium grain boundaries were observed in unannealed samples. Annealing as-deformed samples at temperatures as low as 50°C decreased the microhardness, indicating a very low thermal stability of the deformation induced microstructures. Differential scanning calorimetry (DSC) revealed an exothermal peak between 180 and 280°C, caused by recrystallization. Annealing twins were also formed during recrystallization.

High tensile ductility in a nanostructured metal.

Abstract: Nanocrystalline metals--with grain sizes of less than 100 nm--have strengths exceeding those of coarse-grained and even alloyed metals, and are thus expected to have many applications. For example, pure nanocrystalline Cu (refs 1-7) has a yield strength in excess of 400 MPa, which is six times higher than that of coarse-grained Cu. But nanocrystalline materials often exhibit low tensile ductility at room temperature, which limits their practical utility. The elongation to failure is typically less than a few per cent; the regime of uniform deformation is even smaller. Here we describe a thermomechanical treatment of Cu that results in a bimodal grain size distribution, with micrometre-sized grains embedded inside a matrix of nanocrystalline and ultrafine (<300 nm) grains. The matrix grains impart high strength, as expected from an extrapolation of the Hall-Petch relationship. Meanwhile, the inhomogeneous microstructure induces strain hardening mechanisms that stabilize the tensile deformation, leading to a high tensile ductility--65% elongation to failure, and 30% uniform elongation. We expect that these results will have implications in the development of tough nanostructured metals for forming operations and high-performance structural applications including microelectromechanical and biomedical systems.