Papers by Veronika Polyakova
Advanced Engineering Materials, Dec 3, 2019
is a Higher Degree Doctorate (Material Science) who has been the lead researcher at the Institute... more is a Higher Degree Doctorate (Material Science) who has been the lead researcher at the Institute of Physics of Advanced Materials at the Ufa State Aviation University in Russia since 2002. From 1981 to 2001, she was the head of the nonferrous alloys department at the ISC Ufa Enginebuilding Production Association (Russia): She has over 130 papers in refereed journals and 8 patents. Her h-index value is 18 in Web of Science. nano-/ ultrafine-grained titanium materials processed by severe plastic deformation; microstructure and properties of ultrafine-grained titanium and its alloys; innovative potential of ultrafine-grained titanium alloys for use in medicine and engineering. This article presents an overview of our recent research on the relationship between the ultrafine-grained structure of titanium and its alloys and the physical and mechanical properties of the materials, as well as the formation of advanced functional and service properties, including fatigue strength, creep behaviour, and impact and fracture toughness. We show that due to the record properties achieved in ultrafine-grained (UFG) titanium and its alloys, these materials have an innovative potential for successful application in medicine and engineering industries. Some of these works were carried out in cooperation with the team of Prof. Terence G. Langdon. Professor Langdon made a significant contribution to the development of modern materials science in the field of nanostructured metallic materials.
Journal of Alloys and Compounds, Sep 1, 2015
ABSTRACT Ti–6Al–7Nb containing harmless for tissues niobium can be a good choice replacing Ti–6Al... more ABSTRACT Ti–6Al–7Nb containing harmless for tissues niobium can be a good choice replacing Ti–6Al–4V for ortho-pedic implants application. Formation of ultrafine-grained (UFG) structure in metals and alloys by severe plastic deformation (SPD) techniques allows for achieving unique mechanical properties. Using equal channel angular pressing (ECAP) UFG structure in Ti–6Al–7Nb alloy with an average size of grains/sub-grains of 200 nm was obtained. This UFG Ti–6Al–7Nb alloy has high mechanical (ultimate tensile strength 1470 MPa) and fatigue properties, suitable for practical application. Additionally, surface modifications of titanium alloys aim induce specific responses on osteoblastic cells after implantation. Chemical surface treatments are simple methods to obtain a bioactive for apatite precipitation surface. Phosphoric acid etching combined or not with alkaline treatment presented bioac-tivity after seven days soaked in simulated body fluid (SBF) solution.
This paper deals with the cyclic deformation behavior of the ultrafine-grained (UFG) Ti-6Al-7Nb a... more This paper deals with the cyclic deformation behavior of the ultrafine-grained (UFG) Ti-6Al-7Nb alloy with extra low content of impurities (ELI) produced by severe plastic deformation (SPD). The SPD processing comprised equal channel angular pressing (ECAP) and subsequent thermomechanical treatment and was aimed at improvement of mechanical properties of the alloy. Formation of a UFG structure with the average a phase grain size of 250 h 50 nm led to enhancement of fatigue endurance limit by 40% as compared to the coarse-grained state. The presented microstructural investigations demonstrated that the UFG microstructure significantly influences the crack paths and is very stable in the course of cyclic deformation. A high potential for prospective use of the UFG alloy in biomedical and engineering applications was discussed.
Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, Jun 1, 2017
This paper reports on a study of the relationship between microstructure, mechanical behavior and... more This paper reports on a study of the relationship between microstructure, mechanical behavior and impact toughness of the UFG Grade 5 Ti alloy. The mechanical behavior and impact toughness of the Grade 5 Ti alloy in a coarse-grained state, and in an ultrafine-grained (UFG) state produced by equal-channel angular pressing (ECAP) with subsequent deformationand-thermal treatments via extrusion and warm upsetting in isothermal conditions, were studied extensively. It is shown that a strong refinement of α-grains (less than 250 nm) in the alloy by ECAP and extrusion leads to high strength but with low values of the uniform elongation and lower impact toughness. It is demonstrated that, in order to increase the impact toughness of UFG Ti alloys, it is possible to use approaches realizing ductility enhancement associated with an increase of the strain hardening capacity. An enhancement in the impact toughness of the UFG alloy through an increase in the uniform tensile elongation of the sample is achieved by the preservation of the ultrafine size of α-grains (about 800 nm) with predominantly high-angle boundaries and a decrease in the dislocation density due to recovery and dynamic recrystallization during warm upsetting.
Materials
At present, researchers pay great attention to the development of metastable β-titanium alloys. A... more At present, researchers pay great attention to the development of metastable β-titanium alloys. A task of current importance is the enhancement of their strength and fatigue properties. An efficient method for increasing the strength of such alloys could be severe plastic deformation. The object of this study was a medical metastable β-titanium alloy Ti-15Mo (ASTM F2066). The alloy in the (α + β) state was for the first time deformed by combined processing, including equal channel angular pressing-conform and drawing. Such processing enabled the production of long-length rods with a length of 1500 mm. The aim of the work was to study the effect of the combined processing on the alloy’s microstructure and mechanical properties. An ultrafine-grained structure with an average size of structural elements less than 100 nm was obtained. At the same time, high strength and ductility (σuts = 1590 MPa, δ = 10%) were achieved, which led to a record increase in the endurance limit (σ−1 = 710 M...
Metals, 2021
Ti15Mo alloy was subjected to two techniques of intensive plastic deformation, namely high pressu... more Ti15Mo alloy was subjected to two techniques of intensive plastic deformation, namely high pressure torsion and rotary swaging at room temperature. The imposed strain resulted in the formation of an ultrafine-grained structure in both deformed conditions. Detailed inspection of the microstructure revealed the presence of grains with a size of around 100 nm in both conditions. The microstructure after rotary swaging also contained elongated grains with a length up to 1 µm. Isothermal ageing at 400 °C and 500 °C up to 16 h was applied to both conditions to investigate the kinetics of precipitation of the α phase and the recovery of lattice defects. Positron annihilation spectroscopy indicated that the recovery of lattice defects in the β matrix had already occurred at 400 °C and, in terms of positron trapping, was partly compensated by the precipitation of incoherent α particles. At 500 °C the recovery was fully offset by the formation of incoherent α/β interfaces. Contrary to common ...
Metals, 2019
Ti15Mo metastable beta Ti alloy was solution treated and subsequently deformed by high-pressure t... more Ti15Mo metastable beta Ti alloy was solution treated and subsequently deformed by high-pressure torsion (HPT). HPT-deformed and benchmark non-deformed solution-treated materials were annealed at 400 °C and 500 °C in order to investigate the effect of UFG microstructure on the α-phase precipitation. Phase evolution was examined using laboratory X-ray diffraction (XRD) and by high-energy synchrotron X-ray diffraction (HEXRD), which provided more accurate measurements. Microstructure was observed by scanning electron microscopy (SEM) and microhardness was measured for all conditions. HPT deformation was found to significantly enhance the α phase precipitation due the introduction of lattice defects such as dislocations or grain boundaries, which act as preferential nucleation sites. Moreover, in HPT-deformed material, α precipitates are small and equiaxed, contrary to the α lamellae in the non-deformed material. ω phase formation is suppressed due to massive α precipitation and consequ...
Advanced Engineering Materials, 2019
Herein, an overview of the recent research on the relationship between the ultrafine‐grained (UFG... more Herein, an overview of the recent research on the relationship between the ultrafine‐grained (UFG) structure of titanium and its alloys and the physical and mechanical properties of the materials, as well as the formation of advanced functional and service properties, including fatigue strength, creep behavior, and impact and fracture toughness is presented. It is shown that due to the record properties achieved in UFG titanium and its alloys, these materials have an innovative potential for successful application in medicine and engineering industries. Some of these works are carried out in cooperation with the team of Prof. Terence G. Langdon. Professor Langdon made a significant contribution to the development of modern materials science in the field of nanostructured metallic materials.
Journal of Alloys and Compounds, 2019
Biomedical Ti-6Al-7Nb alloy was prepared by a dedicated thermal treatment followed by equal-chann... more Biomedical Ti-6Al-7Nb alloy was prepared by a dedicated thermal treatment followed by equal-channel angular pressing (ECAP) and extrusion. Ultra-fine grained duplex microstructure consisting of deformed primary α-grains and fragmented α + β region was achieved. Microstructural changes during heating with the rate of 5°C/min were studied by in-situ electrical resistance. Microstructure after deformation and also after subsequent heating was thoroughly characterized by scanning electron microscopy, X-ray diffraction, and positron annihilation spectroscopy (PAS). X-ray diffraction and positron annihilation spectroscopy proved a very high dislocation density and the presence of high concentration of vacancy clusters in deformed material. The ultra-fine grained microstructure of Ti-6Al-7Nb alloy is stable up to 440°C, while upon heating to 550°C and to 660°C, the dislocation density decreases and vacancy clusters disappear. Enhanced microhardness can be achieved by ECAP followed by aging at 500°C. Upon heating to 660°C, the microhardness decreases due to ongoing recovery and recrystallization. Coincidence Doppler broadening (CDB), a special method of PAS, Highlights • Recovery and recrystallization processes of the UFG Ti-6Al-7Nb alloy were studied. • The thermally activated processes were proved by several experimental methods. • Coincidence Doppler broadening proved substitutional solid solution strengthening by Al. • Enhanced microhardness can be achieved by ECAP followed by annealing treatment.
Materials Science and Engineering: A, 2018
The influence of ultra fine grained (UFG) and coarse grained (CG) microstructure of the titanium ... more The influence of ultra fine grained (UFG) and coarse grained (CG) microstructure of the titanium alloy Ti-6Al-4V on the strength of a diffusion bonded (DB) joint was studied using a laboratory DB fixture and a new shear test rig. The DB process was carried out at 725 °C and 825 °C during 2 and 4 h in a vacuum furnace. Coarsening of grain structure resulting from different DB cycles was quantified. The chain pores were observed at 725 °C for both microstructure conditions bonded during 2 h. The increase of bonding time up to 4 h leads to subsequent elimination of the pores. The UFG samples bonded at 725 °C showed a higher level of the shear strength than CG samples for both bonding times. The CG material demonstrated the highest shear strength after 4 h of DB bonding at 825 °C. The increase of the creep deformation of UFG samples when compared to the CG condition was observed as a result of DB at of 725 °C during 4 h.
IOP Conference Series: Materials Science and Engineering, 2017
Processing of metastable titanium alloys by severe plastic deformation provides an opportunity to... more Processing of metastable titanium alloys by severe plastic deformation provides an opportunity to achieve exceptional grain refinement, to enhance the strength and to affect phase transformations occurring during thermal treatment. The main aim of this study is to investigate the microstructure of ultra-fine grained (UFG) material and effect of microstructural changes on phase transformations in metastable β-Ti alloy Ti-15Mo. Metastable β-Ti alloys are currently the most studied Ti-based materials with prospective use in medicine. Ti-15Mo alloy after solution treatment contains metastable β-phase. Metastable ωphase and stable α-phase particles are formed upon annealing,. Solution treated Ti-15Mo alloy was deformed by high pressure torsion (HPT) at room temperature. Severely deformed structure after HPT with grain size of ~200 nm was studied by transmission electron microscopy. In-situ electrical resistance measurements showed significant changes in undergoing phase transformations when compared to coarse-grained (CG) material. Scanning electron microscopy revealed heterogeneous precipitation of α-particles at grain boundaries (GB). Due to the high density of GBs in UFG structure, these precipitates are very fine and equiaxed. The study demonstrates that SPD is capable of enhancing mechanical properties due to grain refinement and via affecting precipitation processes in metastable β-Ti alloys.
Materials Letters, 2017
A near-α Ti-6Al-7Nb alloy was processed by equal-channel angular pressing (ECAP) and the features... more A near-α Ti-6Al-7Nb alloy was processed by equal-channel angular pressing (ECAP) and the features of microstructural transformation were studied using EBSD analysis and transmission electron microscopy. The results show a non-monotonic variation in the density of low-angle and high-angle boundaries of the α-phase grains with increasing strain during ECAP. The relationship between the misorientations of the grain boundaries and the mechanical properties of the alloy were examined.
Materials Science and Engineering: A, 2017
This paper reports on a study of the relationship between microstructure, mechanical behavior and... more This paper reports on a study of the relationship between microstructure, mechanical behavior and impact toughness of the UFG Grade 5 Ti alloy. The mechanical behavior and impact toughness of the Grade 5 Ti alloy in a coarse-grained state, and in an ultrafine-grained (UFG) state produced by equal-channel angular pressing (ECAP) with subsequent deformationand-thermal treatments via extrusion and warm upsetting in isothermal conditions, were studied extensively. It is shown that a strong refinement of α-grains (less than 250 nm) in the alloy by ECAP and extrusion leads to high strength but with low values of the uniform elongation and lower impact toughness. It is demonstrated that, in order to increase the impact toughness of UFG Ti alloys, it is possible to use approaches realizing ductility enhancement associated with an increase of the strain hardening capacity. An enhancement in the impact toughness of the UFG alloy through an increase in the uniform tensile elongation of the sample is achieved by the preservation of the ultrafine size of α-grains (about 800 nm) with predominantly high-angle 2 boundaries and a decrease in the dislocation density due to recovery and dynamic recrystallization during warm upsetting.
European Microscopy Congress 2016: Proceedings, 2016
Materials Science and Engineering: A, 2016
Ultrafine-grained (UFG) commercial purity Ti and Ti-6Al-7Nb alloy produced by equal channel angul... more Ultrafine-grained (UFG) commercial purity Ti and Ti-6Al-7Nb alloy produced by equal channel angular pressing (ECAP) were investigated in this study. In-situ electrical resistance measurements conducted on ultra-fine grained and coarse grained material during linear heating revealed different behaviors of UFG material. Electrical resistance measurements were capable to detect recovery and recrystallization processes in UFG material. Thermal stability of UFG structure was further investigated by microhardness measurements and scanning electron microscopy.
This paper presents the microstructure investigation results of linear friction welded joints of ... more This paper presents the microstructure investigation results of linear friction welded joints of Ti-6Al-4V samples with coarse-grained (CG) and ultrafine grained (UFG) structure. The features of phase and structural transformations in the weld and the thermo-mechanically affected areas, as well as the microhardness distribution across the width of the welded joint were demonstrated.
Materials Science Forum, 2010
This work is devoted to enhancement of strength and ductility of the Ti-6Al-7Nb ELI alloy, which ... more This work is devoted to enhancement of strength and ductility of the Ti-6Al-7Nb ELI alloy, which is less harmful from medical point of view for human body in comparison to Ti-6Al-4V. It has been demonstrated that formation of an ultrafine-grained structure in the alloy with the help of equal-channel angular pressing in combination with heat and deformation treatments allows reaching high strength (UTS = 1400 MPa) and sufficient ductility (elongation 10 %).
IOP Conference Series: Materials Science and Engineering, 2014
Ultrafine-grained (UFG) Ti alloys have potential applications in osteosynthesis and orthopedics d... more Ultrafine-grained (UFG) Ti alloys have potential applications in osteosynthesis and orthopedics due to high bio-compatibility and increased weight-tostrength ratio. In current study, Ti6Al7Nb ELI alloy is processed through equal channel angular pressing-conform (ECAP-Conform) and subsequent thermomechanical processing to generate a UFG microstructure. The fatigue properties of UFG alloys are compared to coarse grained (CG) alloys. Our study demonstrates that the UFG alloys with an average grain size of ~180 nm showed 35% enhancement of fatigue endurance limit as compared to coarse-grained alloys. On the fracture surfaces of the UFG and CG samples fatigue striations and dimpled relief were observed. However, the fracture surface of the UFG sample looks smoother; fewer amounts of secondary micro-cracks and more ductile rupture were also observed, which testifies to the good crack resistance in the UFG alloy after high-cyclic fatigue tests.
Materials Research-Ibero-American Journal of Materials, 2012
The ASTM F1295/Ti-6Al-7Nb alloy present mechanical properties and biocompatibility very attractiv... more The ASTM F1295/Ti-6Al-7Nb alloy present mechanical properties and biocompatibility very attractive for application in medical and dental implants. In this context, processing of these Ti-based alloys by severe plastic deformation (SPD) has been extensively reported recently. However, the mechanical properties of equal channel angular pressed (ECAP) ASTM F1295 alloy are still a matter of research. In the present study, Ti-6Al-7Nb samples were processed by ECAP following thermomechanical processing which effects on the microstructure of Ti-6Al-7Nb alloy were investigated by X-ray diffraction (XRD) and transmission electron microscopy (TEM). The analyses have shown that the microstructure was composed by ultrafine grains (UFG) with sizes ranging from 200 to 400 nm. Ring-type selected area electron diffraction patterns (SAEDP) suggested the coexistence of low-and high-angle grain boundaries. Some regions of the samples have presented evidences of the presence of grains with unfavorable orientation to the plastic deformation. These grains can act as rigid bodies and concentrate the deformation in its surrounding areas, as an "open-die grain" mechanism. Such deformation mechanism could be attributed to the differences in the plastic behavior between the alpha and beta titanium phases.
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Papers by Veronika Polyakova