- Email: [email protected]
steel hybrid material during severe plastic deformation
Materials Letters 173 (2016) 123–126
Contents lists available at ScienceDirect
Materials Letters journal homepage: www.elsevier.com/locate/matlet
Evolution of the structure and strength of steel/vanadium alloy/steel hybrid material during severe plastic deformation S.O. Rogachev a, R.V. Sundeev b,c,n, V.M. Khatkevich a a
National Science and Technology University “MISIS”, Leninskiy prospect 4, 119049 Moscow, Russia I.P. Bardin Science Institute for Ferrous Metallurgy, 105005, Radio st. 23/9, Moscow, Russia c Moscow Technological University, “MIREA”, Vernadskogo Аv. 78, 119454 Moscow, Russia b
art ic l e i nf o
a b s t r a c t
Article history: Received 15 February 2016 Accepted 8 March 2016 Available online 9 March 2016
In the present study, severe plastic deformation (SPD) has been used to joint dissimilar materials and form a multilayer hybrid material with nano- and submicrocrystalline structure. The evolution of the structure and strength of steel/vanadium alloy/steel hybrid material during SPD by high-pressure torsion (HPT) has been studied. The HPT of three-layer metal block with from ¼ to 5 revolutions leads to the formation of firm joint of all layers. Deformation twists at steel/vanadium alloy boundaries are observed in the hybrid material subjected to HPT with the number of revolutions N ¼1. After HPT with N ¼5, the fragmentation of all vanadium alloy layer into thinner layers, which are rounded, vortex-like in shape, is observed. In this case, the microhradness of steel layers (measured at the sample midradius) increases by 3.2–3.5 times; the hardness of vanadium alloy layer increases by 2.0 times. & 2016 Elsevier B.V. All rights reserved.
Keywords: Severe plastic deformation High pressure torsion Nanostructure Metal hybrid materials Vanadium alloys Ferritic corrosion-resistant steel
1. Introduction At present, the development of materials science is related to designing materials that exhibit a combination of higher properties and wider functionality. This is due to the fact that modern high-technology products and processes make high demands for the materials. Significant scientific interest of investigators to structural bulk ultrafine-grained nano- and submicrocrystalline materials is caused by specific combination of their mechanical, physical, and functional properties, which differ from those of coarse-grained analogs [1–5]. Recent years are characterized by substantial progress in designing new SPD techniques and improvement of existing methods for the preparation of ultrafine-grained materials; technological conditions of SPD were elaborated, fundamental regularities of the formation of nanocrystalline structure in metallic materials were found, and factors determining the combination of properties of such materials were studied. The range of metallic materials, in which the nano- and submicrocrystalline structure was realized, becomes wider [1,6–9]. A hybrid material is a combination of two or several materials, which is characterized by given geometry, sizes, and arrangement of the materials [10,11]. This allows one to reach the required combination of various properties for concrete engineering
functionality. Fiber composites, lattices, sandwich structures, and almost all natural biological materials can be considered as examples of hybrid materials. The designing of hybrid materials allows one to reach the combination of high properties and to increase their functionality [10]. Thus, hybrid materials, the combination of properties of which differ from that of individual components, can be realized by very wide range of ways and can be applied in cardinally different areas. The use of SPD to form a hybrid multilayer material by joining dissimilar materials, which is accompanied by grain structure refining, is of special interest. For example, a nano-structured aluminum/copper hybrid with a helical architecture has been prepared by SPD. However, in this case, the material was single-layer and composed from aluminum and copper fragments [12]. Studies related to the problem are scanty. Three-layer steel/vanadium alloy/steel composite material is considered as a structural material for the operation under super heavy service conditions (corrosive media, mechanical stresses, radiation, etc.) [13,14]. The present work is aimed at the systematic study of the evolution of structure and strength of hybrid steel/vanadium alloy/ steel material under different HPT conditions.
2. Materials and research methods n
Corresponding author at: I.P. Bardin Science Institute for Ferrous Metallurgy, 105005, Radio st. 23/9, Moscow, Russia. E-mail address: [email protected] (R.V. Sundeev). http://dx.doi.org/10.1016/j.matlet.2016.03.044 0167-577X/& 2016 Elsevier B.V. All rights reserved.
of
The initial flat samples 8 mm in diameter were cut from sheets 0.08C 18Cr–0.5Ti steel and V–10Ti–5Cr alloy in the
124
S.O. Rogachev et al. / Materials Letters 173 (2016) 123–126
the top to the bottom surface of the sample. Microhardness measurements with load 0.5 N and holding time 10 s using Micromet 5101. Electron microscopic studies of the structure of each layer of the hybrid material were performed using a transmission electron microscopes JEM-2100 and JEM 200CX (JEOL). To prepare foils of disk-shaped HPT-samples, one of its layers was thinned to a thickness of 100 mm by mechanical grinding. After that, disks 3 mm in diameter were cut by ultrasonic cutting and subjected to jet electropolishing at 20 °C using a Struers Lectropol-5 system, a voltage of 20–30 V, and an A2 electrolyte containing perchloric acid, ethanol, 2-butoxyethanol, and distilled water. The final polishing was performed using an ion gun. Analysis of the structure and the distribution of chemical elements (the concentration maps and profiles) in cross sections of hybrid material were performed using scanning electron microscope JSM-6610LV (JEOL) with electron microprobe analyzer and back-scattered electron mode. Fig. 1. Schematic diagram of three-layer metal block for HPT.
recrystallized state. The average grain size was (25 74) μm for the steel and (16 76) μm for the alloy. The three-layer block was collected before HPT: bottom steel layer with 0.3 mm thick (near the “hole”), the central layer of the vanadium alloy 0.2 mm thick and top steel layer 0.5 mm thick (in accordance with Fig. 1). HPT of three-layer block was performed in the “hole” with depth of 0.5 mm, at room temperatures, with the quasi-hydrostatic pressure 6 GPa and the 5 number of turns. The quasi-hydrostatic compression of three-layer block was also performed without torsion (N ¼0). The Vickers microhardness in cross section of the samples was measured for analysis of homogeneous of the deformation of the samples after HPT. Measurement of the microhardness was performed with step of 0.5 mm in the direction from edge to the center of the sample and with step of 50 mm in the direction from
3. Results and discussion Fig. 2 shows SEM micrographs of cross-section of the hybrid material produced by HPT. Bright and dark areas correspond to the 0.08C 18Cr–0.5Ti steel and V-10Ti-5Cr alloy, respectively. It is seen that, when the three-layer metal block is subjected to HPT with numbers of revolution of from ¼ to 5, the formation of firm joint without pores and exfoliation. Already after HPT with N ¼1, deformation twists form at steel/vanadium alloy boundaries (see Fig. 2b). After HPT with N¼ 5, the fragmentation of all vanadium alloy into thinner layers takes place; the layers are rounded, twisted in shape. As the distance from the sample center increases, their number increases and thickness decreases (see Fig. 2c). This fact can be related to peculiarities of shear strain during HPT, its
Fig. 2. Micrographs of the cross-section of three-layer hybrid after HPT at 20 °C with different number of revolutions N: (a) ¼; (b) 1; and (c) 5.
S.O. Rogachev et al. / Materials Letters 173 (2016) 123–126
nonuniformity over the sample area, and different deformation abilities of steel and vanadium alloy as well (the strain hardening exponent is 0.17 and 0.13 for steel and vanadium alloy, respectively). The thickness of individual layers does not exceed 100 nm. Thus, we can state that the increase in the degree of deformation during HPT leads to mixing steel and vanadium alloy layers to form multilayer hybrid material. Element concentration distribution profiles, which were taken directly at the vanadium alloy/steel boundary of the hybrid using electron microprobe analysis, show the existence of mutual diffusion between the steel and vanadium alloy, which results in the formation of transition area characterized by variable chemical composition. After HPT with numbers of revolutions of from ¼ to 5, the depth of diffusion of vanadium into the steel is almost the same and equal to 3 mm. TEM studies of the microstructure were performed for hybrid after HPT with N ¼5 since, in this case, it has the most developed structure. The analysis was performed for the area corresponding to the midradius of sample. The TEM studies of the microstructure of steel layers of hybrid have shown that HPT with N ¼5 leads to the formation of mainly equiaxed nanostructure with an average size of structural elements of 90 nm (Fig. 3a). There are a mix of nano- and submicrocrystalline structures of the steel and vanadium alloy (Fig. 3b) in the central area of the hybrid material after HPT. In the electron diffraction image (that was obtained from this area) twin wheels were found, due to the superposition of reflections from the steel and vanadium alloy (Fig. 3c). Areas of the steel and vanadium alloys, respectively, were well distinguished in a dark field of TEM photographs when shooting in the corresponding reflexes (Fig. 3d). The use only the quasi-hydrostatic pressure without torsion
125
shear strain (N ¼ 0) does not provide adhesion layers. However, the layer thickness decreases. The relative thickness reduction of the steel layers was 22%, and vanadium alloy layer was 16%. Microhardness of steel layer increased from 180 to 255-280 HV (1.4-1.5 times) and vanadium alloy layer from 230 to 275-300 HV (1.2-1.3 times) because of increasing the density of dislocations in the compressive deformation. The increase in the degree of deformation during HPT (as the number of revolutions increases from ¼ to 5 revolutions) leads to an increase in the microhardness of steel and vanadium alloy layers; in this case, the strengthening of steel layers is more rapid than that of vanadium alloy. After HPT with N¼ 5, the microhardness of steel layers (measured at the midradius) increases to 570-630 HV (i.e. by 3.2-3.5 times); the microhardness of vanadium alloy increases to 440-520 HV (i.e., by 2.0 times). The fact that the increase in the number of revolutions during HPT to N ¼5 assures the more uniform distribution of microhardness over the hybrid thickness indicates that the formation of disperse mixture of vanadium alloy with steel leads to the additional strengthening. The deformation of three-layer metal block during HPT is likely to occur in two stages: (1) at the first stage (N ¼0.25–1), the macroplastic and shear deformation of top and bottom steel layers takes place, which leads to their substantial strengthening. At this stage, the macroplastic deformation of vanadium alloy also takes place; however, the torsional strain is not high and, therefore, the strengthening of vanadium alloy also is not high. (2) at the second stage (N ¼1–5), the strengthening of vanadium alloy takes place, which results from the shear deformation by
Fig. 3. Microstructure of hybrid after HPT at 20 °C: (a, b) steel layer and (c, d) central layer.
126
S.O. Rogachev et al. / Materials Letters 173 (2016) 123–126
torsion; in this case, the shear deformation also leads to the formation of deformation twists at the steel/vanadium alloy interface.
4. Conclusions The HPT of three-layer steel/vanadium alloy/steel block with a number of evolutions of from ¼ to 5 leads to the formation of the hybrid material with firm joint of the layers. Nano- and submicrocrystalline structure is formed in the layers of the hybrid material. Deformation twists at the steel/vanadium alloy boundaries are observed after HPT with the number of revolutions N ¼1. The increase in the degree of deformation during HPT leads to an increase in the microhardness of steel and vanadium alloy layers. After HPT with N ¼5, the fragmentation of all vanadium alloy into thinner layers, which are rounded, vortex-like in shape, takes place. In this case, the microhardness of steel layers (measured at the midradius) increases by 3.2–3.5 times; the microhardness of vanadium alloy increases by 2 times.
Acknowledgement The authors gratefully acknowledge the financial support of the Ministry of Education and Science of the Russian Federation in the framework of Increasing Competitiveness Program of MISiS.
References [1] R.Z. Valiev, A.P. Zhilyaev, T.G. Langdon, Nanostructured Materials: Fundamentals
and Applications, John Wiley Sons, Inc., Hoboken, New Jersey, USA 2014, p. 456. [2] K. Edalati, T. Fujioka, Z. Horita, Evolution of mechanical properties and microstructures with equivalent strain in pure Fe processed by high pressure torsion, Mater. Trans. 50 (2009) 44–50. [3] S.A. Nikulin, S.O. Rogachev, A.B. Rozhnov, M.V. Gorshenkov, V.I. Kopylov, S. V. Dobatkin, Resistance of alloy Zr–2.5% Nb with ultrafine-grain structure to stress corrosion cracking, Met. Sci. Heat. Treat. 54 (2012) 407–413. [4] O.N. Senkov, F.H. Froes, V.V. Stolyarov, R.Z. Valiev, J. Liu, Microstructure of aluminum-iron alloys subjected to severe plastic deformation, Scr. Mater. 38 (1998) 1511–1516. [5] C. Xu, S.V. Dobatkin, Z. Horita, T.G. Langdon, Superplastic flow in a nanostructured aluminum alloy produced using high-pressure torsion, Mater. Sci. Eng. A. 500 (2009) 170–175. [6] A.A. Mazilkin, B.B. Straumal, S.G. Protasova, S.V. Dobatkin, B. Baretzky, Structure, phase composition and microhardness of carbon steels after high-pressure torsion, J. Mater. Sci. 43 (2008) 3800–3805. [7] M.T. Pérez-Prado, A.A. Gimazov, O.A. Ruano, M.E. Kassner, A.P. Zhilyaev, Bulk nanocrystalline ω-Zr by high-pressure torsion, Scr. Mater. 58 (2008) 219–222. [8] V.F. Terent’ev, S.V. Dobatkin, S.A. Nikulin, V.I. Kopylov, D.V. Prosvirnin, S. O. Rogachev, I. Bannykh, Fatigue strength of submicrocrystalline Ti and Zr-2.5% Nb alloy after equal channel angular pressing, Kov. Mater. 49 (2011) 65–73. [9] G. Purcek, H. Yanar, M. Demirtas, Y. Alemdag, D.V. Shangina, S.V. Dobatkin, Optimization of strength, ductility and electrical conductivity of Cu–Cr–Zr alloy by combining multi-route ECAP and aging, Mater. Sci. Eng.: A 649 (2016) 114–122. [10] M.F. Ashby, Y.J.M. Brechet, Designing hybrid materials, Acta Mater. 51 (2003) 5801–5821. [11] R.V. Sundeev, A.M. Glezer, A.V. Shalimova, Structural and phase transitions in the amorphous and nanocrystalline Ti50Ni25Cu25 alloys upon high-pressure torsion, Mater. Lett. 133 (2014) 32–34. [12] O. Bouaziz, H.S. Kim, Y. Estrin, Architecturing of metal-based composites with concurrent nanostructuring: a new paradigm of materials design, Adv. Eng. Mater. 15 (2013) 336–340. [13] S.N. Votinov, V.P. Kolotushkin, S.A. Nikulin, V.Y. Turilina, Making vanadiumbased radiation-resistant alloys for fast-neutron reactor pin sheaths, Met. Sci. Heat Treat. 51 (2009) 238–244. [14] S.A. Nikulin, A.B. Rozhnov, T.A. Nechaikina, S.O. Rogachev, S.Yu Zavodchikov, V. M. Khatkevich, Structure and mechanical properties of the three-layer material based on a vanadium alloy and corrosion-resistant steel, Russ. Metall. (Met.) 2014 (2014) 793–799.
Contents lists available at ScienceDirect
Materials Letters journal homepage: www.elsevier.com/locate/matlet
Evolution of the structure and strength of steel/vanadium alloy/steel hybrid material during severe plastic deformation S.O. Rogachev a, R.V. Sundeev b,c,n, V.M. Khatkevich a a
National Science and Technology University “MISIS”, Leninskiy prospect 4, 119049 Moscow, Russia I.P. Bardin Science Institute for Ferrous Metallurgy, 105005, Radio st. 23/9, Moscow, Russia c Moscow Technological University, “MIREA”, Vernadskogo Аv. 78, 119454 Moscow, Russia b
art ic l e i nf o
a b s t r a c t
Article history: Received 15 February 2016 Accepted 8 March 2016 Available online 9 March 2016
In the present study, severe plastic deformation (SPD) has been used to joint dissimilar materials and form a multilayer hybrid material with nano- and submicrocrystalline structure. The evolution of the structure and strength of steel/vanadium alloy/steel hybrid material during SPD by high-pressure torsion (HPT) has been studied. The HPT of three-layer metal block with from ¼ to 5 revolutions leads to the formation of firm joint of all layers. Deformation twists at steel/vanadium alloy boundaries are observed in the hybrid material subjected to HPT with the number of revolutions N ¼1. After HPT with N ¼5, the fragmentation of all vanadium alloy layer into thinner layers, which are rounded, vortex-like in shape, is observed. In this case, the microhradness of steel layers (measured at the sample midradius) increases by 3.2–3.5 times; the hardness of vanadium alloy layer increases by 2.0 times. & 2016 Elsevier B.V. All rights reserved.
Keywords: Severe plastic deformation High pressure torsion Nanostructure Metal hybrid materials Vanadium alloys Ferritic corrosion-resistant steel
1. Introduction At present, the development of materials science is related to designing materials that exhibit a combination of higher properties and wider functionality. This is due to the fact that modern high-technology products and processes make high demands for the materials. Significant scientific interest of investigators to structural bulk ultrafine-grained nano- and submicrocrystalline materials is caused by specific combination of their mechanical, physical, and functional properties, which differ from those of coarse-grained analogs [1–5]. Recent years are characterized by substantial progress in designing new SPD techniques and improvement of existing methods for the preparation of ultrafine-grained materials; technological conditions of SPD were elaborated, fundamental regularities of the formation of nanocrystalline structure in metallic materials were found, and factors determining the combination of properties of such materials were studied. The range of metallic materials, in which the nano- and submicrocrystalline structure was realized, becomes wider [1,6–9]. A hybrid material is a combination of two or several materials, which is characterized by given geometry, sizes, and arrangement of the materials [10,11]. This allows one to reach the required combination of various properties for concrete engineering
functionality. Fiber composites, lattices, sandwich structures, and almost all natural biological materials can be considered as examples of hybrid materials. The designing of hybrid materials allows one to reach the combination of high properties and to increase their functionality [10]. Thus, hybrid materials, the combination of properties of which differ from that of individual components, can be realized by very wide range of ways and can be applied in cardinally different areas. The use of SPD to form a hybrid multilayer material by joining dissimilar materials, which is accompanied by grain structure refining, is of special interest. For example, a nano-structured aluminum/copper hybrid with a helical architecture has been prepared by SPD. However, in this case, the material was single-layer and composed from aluminum and copper fragments [12]. Studies related to the problem are scanty. Three-layer steel/vanadium alloy/steel composite material is considered as a structural material for the operation under super heavy service conditions (corrosive media, mechanical stresses, radiation, etc.) [13,14]. The present work is aimed at the systematic study of the evolution of structure and strength of hybrid steel/vanadium alloy/ steel material under different HPT conditions.
2. Materials and research methods n
Corresponding author at: I.P. Bardin Science Institute for Ferrous Metallurgy, 105005, Radio st. 23/9, Moscow, Russia. E-mail address: [email protected] (R.V. Sundeev). http://dx.doi.org/10.1016/j.matlet.2016.03.044 0167-577X/& 2016 Elsevier B.V. All rights reserved.
of
The initial flat samples 8 mm in diameter were cut from sheets 0.08C 18Cr–0.5Ti steel and V–10Ti–5Cr alloy in the
124
S.O. Rogachev et al. / Materials Letters 173 (2016) 123–126
the top to the bottom surface of the sample. Microhardness measurements with load 0.5 N and holding time 10 s using Micromet 5101. Electron microscopic studies of the structure of each layer of the hybrid material were performed using a transmission electron microscopes JEM-2100 and JEM 200CX (JEOL). To prepare foils of disk-shaped HPT-samples, one of its layers was thinned to a thickness of 100 mm by mechanical grinding. After that, disks 3 mm in diameter were cut by ultrasonic cutting and subjected to jet electropolishing at 20 °C using a Struers Lectropol-5 system, a voltage of 20–30 V, and an A2 electrolyte containing perchloric acid, ethanol, 2-butoxyethanol, and distilled water. The final polishing was performed using an ion gun. Analysis of the structure and the distribution of chemical elements (the concentration maps and profiles) in cross sections of hybrid material were performed using scanning electron microscope JSM-6610LV (JEOL) with electron microprobe analyzer and back-scattered electron mode. Fig. 1. Schematic diagram of three-layer metal block for HPT.
recrystallized state. The average grain size was (25 74) μm for the steel and (16 76) μm for the alloy. The three-layer block was collected before HPT: bottom steel layer with 0.3 mm thick (near the “hole”), the central layer of the vanadium alloy 0.2 mm thick and top steel layer 0.5 mm thick (in accordance with Fig. 1). HPT of three-layer block was performed in the “hole” with depth of 0.5 mm, at room temperatures, with the quasi-hydrostatic pressure 6 GPa and the 5 number of turns. The quasi-hydrostatic compression of three-layer block was also performed without torsion (N ¼0). The Vickers microhardness in cross section of the samples was measured for analysis of homogeneous of the deformation of the samples after HPT. Measurement of the microhardness was performed with step of 0.5 mm in the direction from edge to the center of the sample and with step of 50 mm in the direction from
3. Results and discussion Fig. 2 shows SEM micrographs of cross-section of the hybrid material produced by HPT. Bright and dark areas correspond to the 0.08C 18Cr–0.5Ti steel and V-10Ti-5Cr alloy, respectively. It is seen that, when the three-layer metal block is subjected to HPT with numbers of revolution of from ¼ to 5, the formation of firm joint without pores and exfoliation. Already after HPT with N ¼1, deformation twists form at steel/vanadium alloy boundaries (see Fig. 2b). After HPT with N¼ 5, the fragmentation of all vanadium alloy into thinner layers takes place; the layers are rounded, twisted in shape. As the distance from the sample center increases, their number increases and thickness decreases (see Fig. 2c). This fact can be related to peculiarities of shear strain during HPT, its
Fig. 2. Micrographs of the cross-section of three-layer hybrid after HPT at 20 °C with different number of revolutions N: (a) ¼; (b) 1; and (c) 5.
S.O. Rogachev et al. / Materials Letters 173 (2016) 123–126
nonuniformity over the sample area, and different deformation abilities of steel and vanadium alloy as well (the strain hardening exponent is 0.17 and 0.13 for steel and vanadium alloy, respectively). The thickness of individual layers does not exceed 100 nm. Thus, we can state that the increase in the degree of deformation during HPT leads to mixing steel and vanadium alloy layers to form multilayer hybrid material. Element concentration distribution profiles, which were taken directly at the vanadium alloy/steel boundary of the hybrid using electron microprobe analysis, show the existence of mutual diffusion between the steel and vanadium alloy, which results in the formation of transition area characterized by variable chemical composition. After HPT with numbers of revolutions of from ¼ to 5, the depth of diffusion of vanadium into the steel is almost the same and equal to 3 mm. TEM studies of the microstructure were performed for hybrid after HPT with N ¼5 since, in this case, it has the most developed structure. The analysis was performed for the area corresponding to the midradius of sample. The TEM studies of the microstructure of steel layers of hybrid have shown that HPT with N ¼5 leads to the formation of mainly equiaxed nanostructure with an average size of structural elements of 90 nm (Fig. 3a). There are a mix of nano- and submicrocrystalline structures of the steel and vanadium alloy (Fig. 3b) in the central area of the hybrid material after HPT. In the electron diffraction image (that was obtained from this area) twin wheels were found, due to the superposition of reflections from the steel and vanadium alloy (Fig. 3c). Areas of the steel and vanadium alloys, respectively, were well distinguished in a dark field of TEM photographs when shooting in the corresponding reflexes (Fig. 3d). The use only the quasi-hydrostatic pressure without torsion
125
shear strain (N ¼ 0) does not provide adhesion layers. However, the layer thickness decreases. The relative thickness reduction of the steel layers was 22%, and vanadium alloy layer was 16%. Microhardness of steel layer increased from 180 to 255-280 HV (1.4-1.5 times) and vanadium alloy layer from 230 to 275-300 HV (1.2-1.3 times) because of increasing the density of dislocations in the compressive deformation. The increase in the degree of deformation during HPT (as the number of revolutions increases from ¼ to 5 revolutions) leads to an increase in the microhardness of steel and vanadium alloy layers; in this case, the strengthening of steel layers is more rapid than that of vanadium alloy. After HPT with N¼ 5, the microhardness of steel layers (measured at the midradius) increases to 570-630 HV (i.e. by 3.2-3.5 times); the microhardness of vanadium alloy increases to 440-520 HV (i.e., by 2.0 times). The fact that the increase in the number of revolutions during HPT to N ¼5 assures the more uniform distribution of microhardness over the hybrid thickness indicates that the formation of disperse mixture of vanadium alloy with steel leads to the additional strengthening. The deformation of three-layer metal block during HPT is likely to occur in two stages: (1) at the first stage (N ¼0.25–1), the macroplastic and shear deformation of top and bottom steel layers takes place, which leads to their substantial strengthening. At this stage, the macroplastic deformation of vanadium alloy also takes place; however, the torsional strain is not high and, therefore, the strengthening of vanadium alloy also is not high. (2) at the second stage (N ¼1–5), the strengthening of vanadium alloy takes place, which results from the shear deformation by
Fig. 3. Microstructure of hybrid after HPT at 20 °C: (a, b) steel layer and (c, d) central layer.
126
S.O. Rogachev et al. / Materials Letters 173 (2016) 123–126
torsion; in this case, the shear deformation also leads to the formation of deformation twists at the steel/vanadium alloy interface.
4. Conclusions The HPT of three-layer steel/vanadium alloy/steel block with a number of evolutions of from ¼ to 5 leads to the formation of the hybrid material with firm joint of the layers. Nano- and submicrocrystalline structure is formed in the layers of the hybrid material. Deformation twists at the steel/vanadium alloy boundaries are observed after HPT with the number of revolutions N ¼1. The increase in the degree of deformation during HPT leads to an increase in the microhardness of steel and vanadium alloy layers. After HPT with N ¼5, the fragmentation of all vanadium alloy into thinner layers, which are rounded, vortex-like in shape, takes place. In this case, the microhardness of steel layers (measured at the midradius) increases by 3.2–3.5 times; the microhardness of vanadium alloy increases by 2 times.
Acknowledgement The authors gratefully acknowledge the financial support of the Ministry of Education and Science of the Russian Federation in the framework of Increasing Competitiveness Program of MISiS.
References [1] R.Z. Valiev, A.P. Zhilyaev, T.G. Langdon, Nanostructured Materials: Fundamentals
and Applications, John Wiley Sons, Inc., Hoboken, New Jersey, USA 2014, p. 456. [2] K. Edalati, T. Fujioka, Z. Horita, Evolution of mechanical properties and microstructures with equivalent strain in pure Fe processed by high pressure torsion, Mater. Trans. 50 (2009) 44–50. [3] S.A. Nikulin, S.O. Rogachev, A.B. Rozhnov, M.V. Gorshenkov, V.I. Kopylov, S. V. Dobatkin, Resistance of alloy Zr–2.5% Nb with ultrafine-grain structure to stress corrosion cracking, Met. Sci. Heat. Treat. 54 (2012) 407–413. [4] O.N. Senkov, F.H. Froes, V.V. Stolyarov, R.Z. Valiev, J. Liu, Microstructure of aluminum-iron alloys subjected to severe plastic deformation, Scr. Mater. 38 (1998) 1511–1516. [5] C. Xu, S.V. Dobatkin, Z. Horita, T.G. Langdon, Superplastic flow in a nanostructured aluminum alloy produced using high-pressure torsion, Mater. Sci. Eng. A. 500 (2009) 170–175. [6] A.A. Mazilkin, B.B. Straumal, S.G. Protasova, S.V. Dobatkin, B. Baretzky, Structure, phase composition and microhardness of carbon steels after high-pressure torsion, J. Mater. Sci. 43 (2008) 3800–3805. [7] M.T. Pérez-Prado, A.A. Gimazov, O.A. Ruano, M.E. Kassner, A.P. Zhilyaev, Bulk nanocrystalline ω-Zr by high-pressure torsion, Scr. Mater. 58 (2008) 219–222. [8] V.F. Terent’ev, S.V. Dobatkin, S.A. Nikulin, V.I. Kopylov, D.V. Prosvirnin, S. O. Rogachev, I. Bannykh, Fatigue strength of submicrocrystalline Ti and Zr-2.5% Nb alloy after equal channel angular pressing, Kov. Mater. 49 (2011) 65–73. [9] G. Purcek, H. Yanar, M. Demirtas, Y. Alemdag, D.V. Shangina, S.V. Dobatkin, Optimization of strength, ductility and electrical conductivity of Cu–Cr–Zr alloy by combining multi-route ECAP and aging, Mater. Sci. Eng.: A 649 (2016) 114–122. [10] M.F. Ashby, Y.J.M. Brechet, Designing hybrid materials, Acta Mater. 51 (2003) 5801–5821. [11] R.V. Sundeev, A.M. Glezer, A.V. Shalimova, Structural and phase transitions in the amorphous and nanocrystalline Ti50Ni25Cu25 alloys upon high-pressure torsion, Mater. Lett. 133 (2014) 32–34. [12] O. Bouaziz, H.S. Kim, Y. Estrin, Architecturing of metal-based composites with concurrent nanostructuring: a new paradigm of materials design, Adv. Eng. Mater. 15 (2013) 336–340. [13] S.N. Votinov, V.P. Kolotushkin, S.A. Nikulin, V.Y. Turilina, Making vanadiumbased radiation-resistant alloys for fast-neutron reactor pin sheaths, Met. Sci. Heat Treat. 51 (2009) 238–244. [14] S.A. Nikulin, A.B. Rozhnov, T.A. Nechaikina, S.O. Rogachev, S.Yu Zavodchikov, V. M. Khatkevich, Structure and mechanical properties of the three-layer material based on a vanadium alloy and corrosion-resistant steel, Russ. Metall. (Met.) 2014 (2014) 793–799.