The new severe plastic deformation technique known as high-pressure tube twisting (HPTT) is a con... more The new severe plastic deformation technique known as high-pressure tube twisting (HPTT) is a continuous process to obtain grain refinement in bulk metallic materials of tubular geometry. HPTT was applied to commercially pure aluminum up to a shear strain of 24. The mechanical properties were enhanced markedly and were characterized by compression and ring-hoop tensile tests. It was shown that the axial force during HPTT does not contribute to the plastic flow of the material; it is only controlled by the shear component of the applied stress. The microstructure and the crystallographic texture were examined in detail by electron backscatter diffraction, transmission electron microscopy, and X-ray diffraction, and these showed the existence of a gradient within the cross-section of the tube. The next-neighbor grain misorientation distribution showed a bimodal nature, of which the small-angle peak was attributed to the "internal" new grains originating from the interior of the initial grains and the second one from the new grains situated at the grain boundaries of the initial grains. The measured textures were typical shear textures with specific tilts in the sense of the shear direction at large strains, which can be attributed to the effect of strain rate sensitivity of slip. The main component of the textures was the C component, which continuously strengthened with the shear. The results obtained suggest that HPTT is an efficient processing way to transform the microstructure of Al tubes into ultra-fine-grained structures in one single operation.
In this communication we report on the results of an investigation of steady state mechanical res... more In this communication we report on the results of an investigation of steady state mechanical response of Alloy 800H to cyclic tension-compression. The investigation covered the temperature range of 973 K to 1228 K, which included the temperatures of interest for most current and potential applications of the alloy [ 1 ]. Phenomenological relations between the pertinent mechanical quantities were established. The observed regularities of cyclic deformation, condensed in a simple mathematical expression given below, may provide a convenient tool for users of the alloythe more so as the literature data on cyclic deformation behaviour of the alloy available so far are scarce [2-5]. The tension-compression results are complemented with those on steady state deformation in monotonic tensile tests. The Material The compositon of the batch of Alloy 800H studied is as follows (in wt.%): 32.7 Ni, 21.1 Cr, 0.39 Si, 0.95 Mn, 0.38 Ti, 0.42 Al, 0.006 S, 0.34 Cu, Fe balance. The carbon content (0.08 wt.%) is bound in Ti and Cr carbides [6,7]. The material was supplied by Wiggin Alloys in solution annealed condition as hot rolled bars. The average grain size was 8O Inn. Testing Details Cyclic tension-compression tests were carried out in a screw-driven 1484 Zwick testing machine under strain control. Cylindrical specimens with gauge length of 7 mm and diameter of 5 mm were used. Specimen length measurements were performed using LVDTs. A numerical data acquisition system was used for recording the measurements and for strain control. The plastic strain amplitude ea and the magnitude of the cross-head velocity were kept constant in each test, i.e. the sign of the crosshead velocity was reversed each time the plastic strain reached the value of +e a. The plastic strain amplitude e~ and the total strain rate ~ were varied between 8.10-4 and 8-10-3 and between 5.10-4 and 7.10-3 s-l, respectively. The tests were conducted at 973 K, 1073 K, 1123 K, 1173 K and 1228 K which corresponds to the homologous temperatures between about 0.59 and 0.74. At the same temperatures complementary monotonic tensile tests were conducted in the same testing machine. Typically, four strain rates were used at each temperature. Results Cyclic Deformation Cyclic variation of stress with plastic strain under tension-compression is represented by hysteresis loops exemplified by Fig. 1. The shape of the hysteresis loops evolves with the cycle number N but saturates very quickly to a steady state hysteresis loop.
Severe plastic deformation processes involve large grain rotations due to the action of different... more Severe plastic deformation processes involve large grain rotations due to the action of different modes of plastic deformation and other microstructural changes which lead to characteristic texture formation. The present review deals with the evolution of texture during the most important severe plastic deformation processes, namely Equal Channel Angular Pressing (ECAP), High Pressure Torsion (HPT), Friction Stir Processing (FSP), Accumulative Roll Bonding (ARB) and Multi-Axial Forging (MAF). First three of the processes are shear based, while the latter two are plane-strain based. The textures formed during ECAP are visually different from simple shear textures due to (i) the inclination of the shear plane, (ii) additional contribution of non-shear based deformation. The relative intensities of texture components are function of deformation micro-mechanisms, amount of straining and configuration of the strain path. The texture evolved during HPT is very similar to simple shear texture, with additional consequences of microstructural changes that occur due to very large deformations. The textures formed in FSP process also resemble shear textures. On the other hand, texture evolution during ARB and MAF can be described using plane strain deformation. The present review deals with texture evolution during severe plastic deformation as a function of nature of processes and type of materials.
It is proposed to use a miniaturized version of equal channel angular pressing (ECAP) as a means ... more It is proposed to use a miniaturized version of equal channel angular pressing (ECAP) as a means of producing micro electro-mechanical systems (MEMS) parts. The benefits of such a processing technique are the possibility to reach the desired grain refinement down to the micron scale and to enhance the strength of the material at the same time. The viability of
Abstract High-manganese FeMnC and FeMnAlC austenitic twinning-induced plasticity (TWIP) steel exh... more Abstract High-manganese FeMnC and FeMnAlC austenitic twinning-induced plasticity (TWIP) steel exhibits excellent strain-hardening properties due to the gradual reduction of the mean free path for dislocations glide resulting from deformation twinning. Serrated ...
The work focuses on experimental examination of the fatigue behavior of magnesium alloy AZ31 prod... more The work focuses on experimental examination of the fatigue behavior of magnesium alloy AZ31 produced by three different procedures: squeeze casting (SC), hot rolling (HR), and equal-channel angular pressing (ECAP). The microstructures produced were studied by light and transmission electron microscopy (TEM). Squeeze-cast AZ31 had low porosity and coarse grains, while hot-rolled material showed microstructure with grain size of 3
The purpose of this work is to model the mechanical behavior of nanocrystalline materials. Based ... more The purpose of this work is to model the mechanical behavior of nanocrystalline materials. Based on previous rigid viscoplastic models proposed by Kim et al. (Acta Mater, 48: 493, 2000) and Kim and Estrin (Acta Mater, 53: 765, 2005), the nanocrystalline material is described as a two phase composite material. Using the Taylor–Lin homogenisation scheme in order to account for elasticity, the yield stress of nanocrystalline materials can be evaluated. The transition from a Hall–Petch relation to an inverse Hall–Petch relation is defined and is related to a change in plastic deformation mode in the crystallite phase from a dislocation glide driven mechanism to a diffusion-controlled process.
Given the increasing number of antibiotic-resistant bacteria and the need to synthesize new antim... more Given the increasing number of antibiotic-resistant bacteria and the need to synthesize new antimicrobials, silver has attracted interest in the scientific community because of its recognized antimicrobial activity. This study aimed to evaluate the antimicrobial effects of silver nanoparticles (NP) obtained by a new method and tested at concentrations of 6 μg/ml and 60 μg/ml against the species Staphylococcus aureus, Listeria innocua, Salmonella Choleraesuis, Pseudomonas aeruginosa, Escherichia coli, and Bacillus cereus. The ability of these nanoparticles to remove or kill vegetative cells adhered to stainless steel surfaces was also evaluated. We observed that the NP obtained with the new method, concentrated silver nanoparticles (CNP), and silver nanoparticles with added sodium chloride (NPNaCl) had high antimicrobial activities (P < 0.05). We also verified that the most effective condition for the removal of P. aeruginosa cells on stainless steel coupons (10 by 10 mm) was imme...
Dislocation patterning driven by interactions of dislocations with deformation-induced point defe... more Dislocation patterning driven by interactions of dislocations with deformation-induced point defects is considered. The effect of concurrent irradiation-induced production of point defects is also included. The uniform time-dependent solution of the set of equations describing the evolution of the system is "probed" by small periodic perturbations. A linear stability condition obtained in this way as well as the preferred wavelength of the emerging pattern depend on the values of the parameters reflecting biases in the production and annihilation of vacancies and interstitial atoms. It is proposed that by studying the effect of different types of radiation and different irradiation intensities on the occurrence and the wavelength of the dislocation pattern information about the deformationinduced point defect production bias may be obtained.
The new severe plastic deformation technique known as high-pressure tube twisting (HPTT) is a con... more The new severe plastic deformation technique known as high-pressure tube twisting (HPTT) is a continuous process to obtain grain refinement in bulk metallic materials of tubular geometry. HPTT was applied to commercially pure aluminum up to a shear strain of 24. The mechanical properties were enhanced markedly and were characterized by compression and ring-hoop tensile tests. It was shown that the axial force during HPTT does not contribute to the plastic flow of the material; it is only controlled by the shear component of the applied stress. The microstructure and the crystallographic texture were examined in detail by electron backscatter diffraction, transmission electron microscopy, and X-ray diffraction, and these showed the existence of a gradient within the cross-section of the tube. The next-neighbor grain misorientation distribution showed a bimodal nature, of which the small-angle peak was attributed to the "internal" new grains originating from the interior of the initial grains and the second one from the new grains situated at the grain boundaries of the initial grains. The measured textures were typical shear textures with specific tilts in the sense of the shear direction at large strains, which can be attributed to the effect of strain rate sensitivity of slip. The main component of the textures was the C component, which continuously strengthened with the shear. The results obtained suggest that HPTT is an efficient processing way to transform the microstructure of Al tubes into ultra-fine-grained structures in one single operation.
In this communication we report on the results of an investigation of steady state mechanical res... more In this communication we report on the results of an investigation of steady state mechanical response of Alloy 800H to cyclic tension-compression. The investigation covered the temperature range of 973 K to 1228 K, which included the temperatures of interest for most current and potential applications of the alloy [ 1 ]. Phenomenological relations between the pertinent mechanical quantities were established. The observed regularities of cyclic deformation, condensed in a simple mathematical expression given below, may provide a convenient tool for users of the alloythe more so as the literature data on cyclic deformation behaviour of the alloy available so far are scarce [2-5]. The tension-compression results are complemented with those on steady state deformation in monotonic tensile tests. The Material The compositon of the batch of Alloy 800H studied is as follows (in wt.%): 32.7 Ni, 21.1 Cr, 0.39 Si, 0.95 Mn, 0.38 Ti, 0.42 Al, 0.006 S, 0.34 Cu, Fe balance. The carbon content (0.08 wt.%) is bound in Ti and Cr carbides [6,7]. The material was supplied by Wiggin Alloys in solution annealed condition as hot rolled bars. The average grain size was 8O Inn. Testing Details Cyclic tension-compression tests were carried out in a screw-driven 1484 Zwick testing machine under strain control. Cylindrical specimens with gauge length of 7 mm and diameter of 5 mm were used. Specimen length measurements were performed using LVDTs. A numerical data acquisition system was used for recording the measurements and for strain control. The plastic strain amplitude ea and the magnitude of the cross-head velocity were kept constant in each test, i.e. the sign of the crosshead velocity was reversed each time the plastic strain reached the value of +e a. The plastic strain amplitude e~ and the total strain rate ~ were varied between 8.10-4 and 8-10-3 and between 5.10-4 and 7.10-3 s-l, respectively. The tests were conducted at 973 K, 1073 K, 1123 K, 1173 K and 1228 K which corresponds to the homologous temperatures between about 0.59 and 0.74. At the same temperatures complementary monotonic tensile tests were conducted in the same testing machine. Typically, four strain rates were used at each temperature. Results Cyclic Deformation Cyclic variation of stress with plastic strain under tension-compression is represented by hysteresis loops exemplified by Fig. 1. The shape of the hysteresis loops evolves with the cycle number N but saturates very quickly to a steady state hysteresis loop.
Severe plastic deformation processes involve large grain rotations due to the action of different... more Severe plastic deformation processes involve large grain rotations due to the action of different modes of plastic deformation and other microstructural changes which lead to characteristic texture formation. The present review deals with the evolution of texture during the most important severe plastic deformation processes, namely Equal Channel Angular Pressing (ECAP), High Pressure Torsion (HPT), Friction Stir Processing (FSP), Accumulative Roll Bonding (ARB) and Multi-Axial Forging (MAF). First three of the processes are shear based, while the latter two are plane-strain based. The textures formed during ECAP are visually different from simple shear textures due to (i) the inclination of the shear plane, (ii) additional contribution of non-shear based deformation. The relative intensities of texture components are function of deformation micro-mechanisms, amount of straining and configuration of the strain path. The texture evolved during HPT is very similar to simple shear texture, with additional consequences of microstructural changes that occur due to very large deformations. The textures formed in FSP process also resemble shear textures. On the other hand, texture evolution during ARB and MAF can be described using plane strain deformation. The present review deals with texture evolution during severe plastic deformation as a function of nature of processes and type of materials.
It is proposed to use a miniaturized version of equal channel angular pressing (ECAP) as a means ... more It is proposed to use a miniaturized version of equal channel angular pressing (ECAP) as a means of producing micro electro-mechanical systems (MEMS) parts. The benefits of such a processing technique are the possibility to reach the desired grain refinement down to the micron scale and to enhance the strength of the material at the same time. The viability of
Abstract High-manganese FeMnC and FeMnAlC austenitic twinning-induced plasticity (TWIP) steel exh... more Abstract High-manganese FeMnC and FeMnAlC austenitic twinning-induced plasticity (TWIP) steel exhibits excellent strain-hardening properties due to the gradual reduction of the mean free path for dislocations glide resulting from deformation twinning. Serrated ...
The work focuses on experimental examination of the fatigue behavior of magnesium alloy AZ31 prod... more The work focuses on experimental examination of the fatigue behavior of magnesium alloy AZ31 produced by three different procedures: squeeze casting (SC), hot rolling (HR), and equal-channel angular pressing (ECAP). The microstructures produced were studied by light and transmission electron microscopy (TEM). Squeeze-cast AZ31 had low porosity and coarse grains, while hot-rolled material showed microstructure with grain size of 3
The purpose of this work is to model the mechanical behavior of nanocrystalline materials. Based ... more The purpose of this work is to model the mechanical behavior of nanocrystalline materials. Based on previous rigid viscoplastic models proposed by Kim et al. (Acta Mater, 48: 493, 2000) and Kim and Estrin (Acta Mater, 53: 765, 2005), the nanocrystalline material is described as a two phase composite material. Using the Taylor–Lin homogenisation scheme in order to account for elasticity, the yield stress of nanocrystalline materials can be evaluated. The transition from a Hall–Petch relation to an inverse Hall–Petch relation is defined and is related to a change in plastic deformation mode in the crystallite phase from a dislocation glide driven mechanism to a diffusion-controlled process.
Given the increasing number of antibiotic-resistant bacteria and the need to synthesize new antim... more Given the increasing number of antibiotic-resistant bacteria and the need to synthesize new antimicrobials, silver has attracted interest in the scientific community because of its recognized antimicrobial activity. This study aimed to evaluate the antimicrobial effects of silver nanoparticles (NP) obtained by a new method and tested at concentrations of 6 μg/ml and 60 μg/ml against the species Staphylococcus aureus, Listeria innocua, Salmonella Choleraesuis, Pseudomonas aeruginosa, Escherichia coli, and Bacillus cereus. The ability of these nanoparticles to remove or kill vegetative cells adhered to stainless steel surfaces was also evaluated. We observed that the NP obtained with the new method, concentrated silver nanoparticles (CNP), and silver nanoparticles with added sodium chloride (NPNaCl) had high antimicrobial activities (P < 0.05). We also verified that the most effective condition for the removal of P. aeruginosa cells on stainless steel coupons (10 by 10 mm) was imme...
Dislocation patterning driven by interactions of dislocations with deformation-induced point defe... more Dislocation patterning driven by interactions of dislocations with deformation-induced point defects is considered. The effect of concurrent irradiation-induced production of point defects is also included. The uniform time-dependent solution of the set of equations describing the evolution of the system is "probed" by small periodic perturbations. A linear stability condition obtained in this way as well as the preferred wavelength of the emerging pattern depend on the values of the parameters reflecting biases in the production and annihilation of vacancies and interstitial atoms. It is proposed that by studying the effect of different types of radiation and different irradiation intensities on the occurrence and the wavelength of the dislocation pattern information about the deformationinduced point defect production bias may be obtained.
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