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Nanostructural evolution of steel and titanium alloys exposed to glow-discharge plasma
NIM B Beam Interactions with Materials & Atoms
Nuclear Instruments and Methods in Physics Research B 261 (2007) 678–681 www.elsevier.com/locate/nimb
Nanostructural evolution of steel and titanium alloys exposed to glow-discharge plasma I. Tereshko a, V. Abidzina b
a,*
, A. Tereshko a, I. Elkin
b
a Belarusian-Russian University, Prospect Mira 43, 212005 Mogilev, Belarus ‘KAMA VT’ Research and Production Enterprise, Karl Liebknecht Street 3a, 212000 Mogilev, Belarus
Available online 7 April 2007
Abstract We have investigated the formation process of nanostructures with different dimensions and the modification of materials after their treatment by low-energy ion irradiation in glow-discharge plasma. The materials under investigation were armco-iron, high-speed steel and titanium alloys. Low-energy ion impact was carried out in a specially constructed plasma generator, where materials were irradiated by ions of residual gases in vacuum. The ion energy was 1–3 keV. After the low-energy ion treatment, microhardness of the irradiated materials, their fine dislocation structures and electrical resistivity were investigated. Simultaneously, a computer simulation of material behavior after a glow-discharge plasma impact was made. We showed that nanostructures may be formed by self-organizing processes development in nonlinear media after low-energy irradiation. This result is confirmed by computer simulation of the influence of low-energy ions on nonlinear crystal structures. 2007 Elsevier B.V. All rights reserved. PACS: 61.82.Bg; 68.18.Fg Keywords: Nanostructures; Nonlinear effects; Computer simulation; Self-organizing processes
1. Introduction Nanodimensional systems are the most dynamically developing field in modern physics. Development of nanodimensional complexes and nanocluster formation in construction materials, as well as nanostructure surface layers, is an important part of this field. As a rule, increase in strength of construction materials leads to a decrease in their plasticity. These two competitive properties may be combined in materials where nanostructures are formed. In addition, these materials have high durability, corrosion resistance, impact resistance and other improved operational properties that are important for cutting tool production. The conventional strategy of nanodimensional system formation is the clusterization of separate molecules into *
Corresponding author. Tel.: +375 296 466821; fax: +375 222 225518. E-mail address: [email protected] (V. Abidzina).
0168-583X/$ - see front matter 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.nimb.2007.04.021
a structure stabilized by intermolecular forces. That is so called ‘bottom-up strategy’ [1]. But this strategy is ineffective for production of bulky units with embedded nanostructures. Another way to obtain nanocrystal formation is to use intensive plastic deformation [2]. However, this method cannot be used if the dimensions and geometry of the finished products must remain unchanged. It should be taken into consideration that in nanostructure formation process, nonlinear properties have vital importance and a process of self-organization in nonlinear crystal lattices takes place. We have shown [3–7] that nonlinear effects take place during interaction between charged particles and the irradiated surface of crystal materials. These effects are one of the underlying reasons for self-organization of irradiated materials that results in deep modification, often unexplained by classic solid-state physics. This modification is clearly observed after low-energy ion irradiation in glowdischarge plasma. A decrease in ion energy to 1 keV leads
I. Tereshko et al. / Nucl. Instr. and Meth. in Phys. Res. B 261 (2007) 678–681
to a great increase in the depth of the modified layer of the irradiated materials. In fact, a long-range effect bulk modification occurs. Bombardment of solid surfaces by low-energy ions leads to nonlinear oscillations of atom oscillators of crystal lattices. As a result new metastable and long-lived structures form and the nanodimensional structures deserve more attention. The main aims of this paper are the following: – to show experimentally the possibility of nanocluster formation in metals and alloys by low-energy ion irradiation in glow-discharge plasma; – to show using computer simulation how nanocrystal structures may be formed in solids by low-energy ion irradiation in glow-discharge plasma. 2. Experimental methods We investigated armco-iron, M2 high-speed steel and C2 cemented carbide hard alloy (sintered tungsten (79%WC) and titanium (15%TiC) carbides with 6%Co binding base). Samples were placed in a specially constructed plasma generator and were exposed to glow-discharge plasma by ions of the residual gases of the vacuum. The ion energy depended on the voltage in the plasmatron and did not exceed 1.0–2.5 keV. Irradiated fluence was 2 · 1017 ion cm 2. The temperature of the specimens was controlled during the irradiation process and did not exceed 343 K while the irradiation time varied from 15 to 90 min. Dependence of microhardness on the time elapsed after stopping the irradiation was investigated every day for two months. Temperature dependence on resistivity of irradiated samples was similarly measured. The fine structures of the materials were studied layerby-layer using transmission electron microscopy. The simulation was made using molecular dynamics. We chose Morse potential as the potential of atomic interaction [3]. Multi-valleys of the potential are achieved by expanding Morse potential in a Taylor series. Within the investigation a special model for calculating the atom displacement of the crystal lattice under the influence of external low-energy ion irradiation was developed. It was based on the conception of a three-dimensional lattice as a nonlinear atom chain system. It is in this model calculations that in three-dimensional and planar (two dimensional) variants using classical dynamic equation were made. The accuracy of this model and the results of calculations were checked during extracting from threedimensional lattice one atom chain which can be described by the equations for the chain of n-coupled oscillators given in [5] and in which errors in calculations were minimal. The equation system was solved by means of the Runge– Kutta method. The dependence of each atom displacement on time after stopping the ion bombardment was investigated.
679
3. Results and discussion It had been shown earlier in [3–8] that after low-energy ion irradiation modification of materials was observed up to the depth of 10 mm from the irradiated surface. That result was described as a ‘‘long-range effect’’. This is actually a bulk modification. Here ‘‘long-range effect’’ is understood as considerable excess of the modified layer depth of the irradiated materials beyond the ion projected range in the target [9]. Using transmission electron microscopy we showed that for well annealed samples with initially small dislocation density (armco-Fe, Ni3Fe etc.) after irradiation in glow-discharge plasma, a high increase in dislocation density at the maximum at the depth of 6 mm was observed [5,7,8]. For materials with initially increased dislocation density (unannealed copper, M2 high-speed steel, titanium alloys) reorganization of present dislocation structure is the most considerable that consists of intensive formation of dislocation fragments or grinding of fragments with corresponding increase in their disorientation. These reorganizations also take place well below the irradiated surface. In this paper, we would like to focus on the observation one more type of bulk modification of the materials mention above, that is the formation of nanoclusters at big distances from the irradiated surface. Fig. 1 shows the structures of nonirradiated armco-Fe (a), after ion impact at the depth of 6.4 mm (b) and at the depth of 9.8 mm from the irradiated surface (c). The following peculiarities were observed: (1) after low-energy ion irradiation areas with nanostructure dimensions (nanoclusters) are formed. Microdiffraction analysis of these areas shows that they have almost amorphous structure; (2) concentration of nanoclusters decreases with increase in the depth from the irradiated surface (Fig. 2, curve 1); (3) average diameter of clusters increases with the depth from the irradiated surface (Fig. 2, curve 2). The same results were obtained for high-speed steel and titanium alloys but they are difficult to analyze due to high dislocation density. As a result mechanical and physical properties of the irradiated materials are considerable changed. The dependence of M2 high-speed steel microhardness on the time elapsed after stopping the irradiation was investigated [6]. The irradiation was performed in the chamber with 2.5 kV discharge voltage for 90 min. The thickness of the samples was 10 mm and the back surface contacted the cathode. The following peculiarities may be noticed: (a) during long a period of time (up to 1.5 month) after stopping the irradiation large oscillations of microhardness along the time axis are observed that exceed measurement error in many times. These oscillations
680
I. Tereshko et al. / Nucl. Instr. and Meth. in Phys. Res. B 261 (2007) 678–681
Fig. 2. Dependence of nanocluster concentration and average diameter of nanoclusters for armco-Fe on the depth from the irradiated surface. Curve 1 – nanocluster concentration in irradiated condition (full curve), curve 11 – nanocluster concentration in nonirradiated condition (dashed-line curve), curve 2 – average diameter of clusters.
(c) there is an evident tendency for microhardness to increase with increasing time after irradiation in glow-discharge plasma. An increase in microhardness by 80–90% relative to initial state of unirradiated samples is observed approximately in one month. Large oscillations of microhardness were obtained after irradiation of C70 cemented carbide hard alloys. A greater hardening effect was obtained at the voltage of 1 kV i.e. decreasing the energy of ion irradiation, in spite of logic, leads to more alloy hardening. We showed that these oscillations might lead either to hardening or to softening of materials depending on irradiation conditions and the time elapsed after stopping the irradiation. Investigation of the dependence of the resistivity of steel samples on the time after stopping the irradiation in glowdischarge plasma showed the following peculiarities [6]: (a) during long period of time (up to 1.5 month) after stopping the irradiation large oscillations of samples resistivity are observed. (b) there is a tendency resistivity to decrease after irradiation in glow-discharge plasma.
Fig. 1. The fine structure of nonirradiated armco-Fe (a), after low-energy ion irradiation in glow-discharge plasma at the depth of 6.4 mm (b) and 9.8 mm (c) from the irradiated surface.
are observed for both the irradiated and the back surfaces of the sample; (b) microhardness on the back surface of the sample is slightly different than those on the irradiated surface (and sometimes even exceeds them), confirming the presence of a long-range effect;
This last peculiarity contradicts the increase in dislocation density of irradiated materials. None of the results mentioned above can be explained in terms of the well-known ideas about radiation defects in solids [10,11]. Therefore, new concepts about the processes formed in crystal lattices after low-energy ion irradiation are required. Such concepts were presented in [3–7] and they were based on taking into consideration nonlinear effects of translation symmetry breaking of crystal lattices during the bombardment of solids surfaces by charged particles. The authors suggest a hypothesis based on the idea of nonlinear oscillation excitation in crystals which lead to the active self-organizing processes in the ion subsystem of irradiated crystals.
I. Tereshko et al. / Nucl. Instr. and Meth. in Phys. Res. B 261 (2007) 678–681
681
Fig. 3. One-dimensional lattice: (a) initial state; (b) new stable state.
In this paper computer simulation of self-organization process in three-dimensional crystal lattices after external low-energy ion impact presented in the form of random ‘ion rain’ was done. Atoms on the target surface receive random amount and direction impulses from ions that bombarded the surface. Energy transmitted to target atoms is less than the threshold needed to form point defects but sufficient for nonlinear oscillation excitation in ion subsystem of a lattice (for the convenience we shall refer to the ions in crystal lattices as ‘‘atoms’’ or ‘‘atomic oscillators’’). Fig. 3 illustrates the results of a numerical experiment in the investigation of a relaxation process in one-dimensional nonlinear atomic chain in the case that its first atom receives an impulse from an external ion impact. In initial atom chain (Fig. 3(a)) as a result of low-energy ion impulse to atom N1 nonlinear oscillations along the Xaxis excite, which results in the atoms stabilization in new positions that may be interpret as new long-lived metastable atomic groups formation (nanoclusters) (Fig. 3(b)). The time of stabilization is very long. It specifically depends on rigidity of atomic bonding in lattices (nonlinear coefficients are based on them) and on the value of ion energy of external irradiation. The period of the lattice inside the clusters does not correspond to the initial one. It is clusters that provide new complexes of physical and mechanical properties to lattices (irradiated materials). A phase diagram of randomly chosen atom of the chain was made and showed that its new final attractor is a highly displaced state out of the initial state. One can see, as a result high-fragmented structures with nanodimension are formed. We showed using computer simulation method that average size of such fragmented areas should increase with the depth from the irradiated surface in accordance with our experimental results. 4. Conclusions 1. Low-energy ion irradiation of solids in glow-discharge plasma leads to the formation of complex, multilayer nanocrystalline structures in the irradiated volume. These changes cannot be explained within the framework of the classical physics of radiation damages of solids.
2. Computer simulation (using a molecular dynamics method) of nonlinear oscillations in atom oscillator systems of crystal lattices after their low-energy ion irradiation showed the possibility of nanostructures formation and their stability. 3. Nanostructures formations in steels and alloys during low-energy ion irradiation in glow-discharge plasma lead to changes in physical and mechanical properties and may be used to develop new hardening technologies of metals and alloys. Acknowledgement Authors acknowledge partial support from the Center for Irradiation of Materials, Alabama A&M University. References [1] M. Ratner, D. Ratner, Pearson Education Inc, 2003. [2] N.A. Koneva, L.I. Trishkina, E.V. Kozlov, Izv. RAS. Phys. 62 (1998) 1350 (in Russian). [3] I.V. Tereshko, V.I. Khodyrev, V.M. Tereshko, E.A. Lipsky, A.V. Goncharenya, S. Ofori–sey, Nucl. Instr. and Meth. B 80–81 (1993) 115. [4] I.V. Tereshko, V.I. Khodyrev, V.M. Tereshko, E.A. Lipsky, I.V. Romanenko, in: Application of Particle and Laser Beams in Materials Technology, London, 1995, p. 595. [5] I.V. Tereshko, V.I. Khodyrev, E.A. Lipsky, A.V. Goncharenya, A.M. Tereshko, Nucl. Instr. and Meth. B 127–128 (1997) 861. [6] I.V. Tereshko, V.I. Khodyrev, V.V. Glushchenko, G.V. Rimkevich, A.M. Tereshko, A.A. Russian, in: Proceedings of the 36th International Seminar ‘Actual problems of strength’, 2001, p. 648 (in Russian). [7] E.V. Kozlov, I.V. Tereshko, N.A. Popova, Sov. Phys. J. (USA) 5 (1994) 506. [8] E.V. Kozlov, I.V. Tereshko, N.A. Popova, E.A. Lipsky, V.I. Khodyrev, Tsvetn. Met. 7 (1991) (in Russian). [9] A.N. Didenko, U.P. Sharkeev, E.V. Kozlov, A.I. Riabchikov, Longrange Effects in Ion Implanted Metal Materials, STL, Tomsk, 2004, p. 328 (in Russian). [10] J. Williams, J. Poutau, Ion Implantation and Beam Technologies, Navukova Dumka, Kiev, 1988, p. 360. [11] W. Eckstein, Computer Simulation of Ion–Solids Interaction, Springer-Verlag, Berlin, Heidellberg, New York, 1991.
Nuclear Instruments and Methods in Physics Research B 261 (2007) 678–681 www.elsevier.com/locate/nimb
Nanostructural evolution of steel and titanium alloys exposed to glow-discharge plasma I. Tereshko a, V. Abidzina b
a,*
, A. Tereshko a, I. Elkin
b
a Belarusian-Russian University, Prospect Mira 43, 212005 Mogilev, Belarus ‘KAMA VT’ Research and Production Enterprise, Karl Liebknecht Street 3a, 212000 Mogilev, Belarus
Available online 7 April 2007
Abstract We have investigated the formation process of nanostructures with different dimensions and the modification of materials after their treatment by low-energy ion irradiation in glow-discharge plasma. The materials under investigation were armco-iron, high-speed steel and titanium alloys. Low-energy ion impact was carried out in a specially constructed plasma generator, where materials were irradiated by ions of residual gases in vacuum. The ion energy was 1–3 keV. After the low-energy ion treatment, microhardness of the irradiated materials, their fine dislocation structures and electrical resistivity were investigated. Simultaneously, a computer simulation of material behavior after a glow-discharge plasma impact was made. We showed that nanostructures may be formed by self-organizing processes development in nonlinear media after low-energy irradiation. This result is confirmed by computer simulation of the influence of low-energy ions on nonlinear crystal structures. 2007 Elsevier B.V. All rights reserved. PACS: 61.82.Bg; 68.18.Fg Keywords: Nanostructures; Nonlinear effects; Computer simulation; Self-organizing processes
1. Introduction Nanodimensional systems are the most dynamically developing field in modern physics. Development of nanodimensional complexes and nanocluster formation in construction materials, as well as nanostructure surface layers, is an important part of this field. As a rule, increase in strength of construction materials leads to a decrease in their plasticity. These two competitive properties may be combined in materials where nanostructures are formed. In addition, these materials have high durability, corrosion resistance, impact resistance and other improved operational properties that are important for cutting tool production. The conventional strategy of nanodimensional system formation is the clusterization of separate molecules into *
Corresponding author. Tel.: +375 296 466821; fax: +375 222 225518. E-mail address: [email protected] (V. Abidzina).
0168-583X/$ - see front matter 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.nimb.2007.04.021
a structure stabilized by intermolecular forces. That is so called ‘bottom-up strategy’ [1]. But this strategy is ineffective for production of bulky units with embedded nanostructures. Another way to obtain nanocrystal formation is to use intensive plastic deformation [2]. However, this method cannot be used if the dimensions and geometry of the finished products must remain unchanged. It should be taken into consideration that in nanostructure formation process, nonlinear properties have vital importance and a process of self-organization in nonlinear crystal lattices takes place. We have shown [3–7] that nonlinear effects take place during interaction between charged particles and the irradiated surface of crystal materials. These effects are one of the underlying reasons for self-organization of irradiated materials that results in deep modification, often unexplained by classic solid-state physics. This modification is clearly observed after low-energy ion irradiation in glowdischarge plasma. A decrease in ion energy to 1 keV leads
I. Tereshko et al. / Nucl. Instr. and Meth. in Phys. Res. B 261 (2007) 678–681
to a great increase in the depth of the modified layer of the irradiated materials. In fact, a long-range effect bulk modification occurs. Bombardment of solid surfaces by low-energy ions leads to nonlinear oscillations of atom oscillators of crystal lattices. As a result new metastable and long-lived structures form and the nanodimensional structures deserve more attention. The main aims of this paper are the following: – to show experimentally the possibility of nanocluster formation in metals and alloys by low-energy ion irradiation in glow-discharge plasma; – to show using computer simulation how nanocrystal structures may be formed in solids by low-energy ion irradiation in glow-discharge plasma. 2. Experimental methods We investigated armco-iron, M2 high-speed steel and C2 cemented carbide hard alloy (sintered tungsten (79%WC) and titanium (15%TiC) carbides with 6%Co binding base). Samples were placed in a specially constructed plasma generator and were exposed to glow-discharge plasma by ions of the residual gases of the vacuum. The ion energy depended on the voltage in the plasmatron and did not exceed 1.0–2.5 keV. Irradiated fluence was 2 · 1017 ion cm 2. The temperature of the specimens was controlled during the irradiation process and did not exceed 343 K while the irradiation time varied from 15 to 90 min. Dependence of microhardness on the time elapsed after stopping the irradiation was investigated every day for two months. Temperature dependence on resistivity of irradiated samples was similarly measured. The fine structures of the materials were studied layerby-layer using transmission electron microscopy. The simulation was made using molecular dynamics. We chose Morse potential as the potential of atomic interaction [3]. Multi-valleys of the potential are achieved by expanding Morse potential in a Taylor series. Within the investigation a special model for calculating the atom displacement of the crystal lattice under the influence of external low-energy ion irradiation was developed. It was based on the conception of a three-dimensional lattice as a nonlinear atom chain system. It is in this model calculations that in three-dimensional and planar (two dimensional) variants using classical dynamic equation were made. The accuracy of this model and the results of calculations were checked during extracting from threedimensional lattice one atom chain which can be described by the equations for the chain of n-coupled oscillators given in [5] and in which errors in calculations were minimal. The equation system was solved by means of the Runge– Kutta method. The dependence of each atom displacement on time after stopping the ion bombardment was investigated.
679
3. Results and discussion It had been shown earlier in [3–8] that after low-energy ion irradiation modification of materials was observed up to the depth of 10 mm from the irradiated surface. That result was described as a ‘‘long-range effect’’. This is actually a bulk modification. Here ‘‘long-range effect’’ is understood as considerable excess of the modified layer depth of the irradiated materials beyond the ion projected range in the target [9]. Using transmission electron microscopy we showed that for well annealed samples with initially small dislocation density (armco-Fe, Ni3Fe etc.) after irradiation in glow-discharge plasma, a high increase in dislocation density at the maximum at the depth of 6 mm was observed [5,7,8]. For materials with initially increased dislocation density (unannealed copper, M2 high-speed steel, titanium alloys) reorganization of present dislocation structure is the most considerable that consists of intensive formation of dislocation fragments or grinding of fragments with corresponding increase in their disorientation. These reorganizations also take place well below the irradiated surface. In this paper, we would like to focus on the observation one more type of bulk modification of the materials mention above, that is the formation of nanoclusters at big distances from the irradiated surface. Fig. 1 shows the structures of nonirradiated armco-Fe (a), after ion impact at the depth of 6.4 mm (b) and at the depth of 9.8 mm from the irradiated surface (c). The following peculiarities were observed: (1) after low-energy ion irradiation areas with nanostructure dimensions (nanoclusters) are formed. Microdiffraction analysis of these areas shows that they have almost amorphous structure; (2) concentration of nanoclusters decreases with increase in the depth from the irradiated surface (Fig. 2, curve 1); (3) average diameter of clusters increases with the depth from the irradiated surface (Fig. 2, curve 2). The same results were obtained for high-speed steel and titanium alloys but they are difficult to analyze due to high dislocation density. As a result mechanical and physical properties of the irradiated materials are considerable changed. The dependence of M2 high-speed steel microhardness on the time elapsed after stopping the irradiation was investigated [6]. The irradiation was performed in the chamber with 2.5 kV discharge voltage for 90 min. The thickness of the samples was 10 mm and the back surface contacted the cathode. The following peculiarities may be noticed: (a) during long a period of time (up to 1.5 month) after stopping the irradiation large oscillations of microhardness along the time axis are observed that exceed measurement error in many times. These oscillations
680
I. Tereshko et al. / Nucl. Instr. and Meth. in Phys. Res. B 261 (2007) 678–681
Fig. 2. Dependence of nanocluster concentration and average diameter of nanoclusters for armco-Fe on the depth from the irradiated surface. Curve 1 – nanocluster concentration in irradiated condition (full curve), curve 11 – nanocluster concentration in nonirradiated condition (dashed-line curve), curve 2 – average diameter of clusters.
(c) there is an evident tendency for microhardness to increase with increasing time after irradiation in glow-discharge plasma. An increase in microhardness by 80–90% relative to initial state of unirradiated samples is observed approximately in one month. Large oscillations of microhardness were obtained after irradiation of C70 cemented carbide hard alloys. A greater hardening effect was obtained at the voltage of 1 kV i.e. decreasing the energy of ion irradiation, in spite of logic, leads to more alloy hardening. We showed that these oscillations might lead either to hardening or to softening of materials depending on irradiation conditions and the time elapsed after stopping the irradiation. Investigation of the dependence of the resistivity of steel samples on the time after stopping the irradiation in glowdischarge plasma showed the following peculiarities [6]: (a) during long period of time (up to 1.5 month) after stopping the irradiation large oscillations of samples resistivity are observed. (b) there is a tendency resistivity to decrease after irradiation in glow-discharge plasma.
Fig. 1. The fine structure of nonirradiated armco-Fe (a), after low-energy ion irradiation in glow-discharge plasma at the depth of 6.4 mm (b) and 9.8 mm (c) from the irradiated surface.
are observed for both the irradiated and the back surfaces of the sample; (b) microhardness on the back surface of the sample is slightly different than those on the irradiated surface (and sometimes even exceeds them), confirming the presence of a long-range effect;
This last peculiarity contradicts the increase in dislocation density of irradiated materials. None of the results mentioned above can be explained in terms of the well-known ideas about radiation defects in solids [10,11]. Therefore, new concepts about the processes formed in crystal lattices after low-energy ion irradiation are required. Such concepts were presented in [3–7] and they were based on taking into consideration nonlinear effects of translation symmetry breaking of crystal lattices during the bombardment of solids surfaces by charged particles. The authors suggest a hypothesis based on the idea of nonlinear oscillation excitation in crystals which lead to the active self-organizing processes in the ion subsystem of irradiated crystals.
I. Tereshko et al. / Nucl. Instr. and Meth. in Phys. Res. B 261 (2007) 678–681
681
Fig. 3. One-dimensional lattice: (a) initial state; (b) new stable state.
In this paper computer simulation of self-organization process in three-dimensional crystal lattices after external low-energy ion impact presented in the form of random ‘ion rain’ was done. Atoms on the target surface receive random amount and direction impulses from ions that bombarded the surface. Energy transmitted to target atoms is less than the threshold needed to form point defects but sufficient for nonlinear oscillation excitation in ion subsystem of a lattice (for the convenience we shall refer to the ions in crystal lattices as ‘‘atoms’’ or ‘‘atomic oscillators’’). Fig. 3 illustrates the results of a numerical experiment in the investigation of a relaxation process in one-dimensional nonlinear atomic chain in the case that its first atom receives an impulse from an external ion impact. In initial atom chain (Fig. 3(a)) as a result of low-energy ion impulse to atom N1 nonlinear oscillations along the Xaxis excite, which results in the atoms stabilization in new positions that may be interpret as new long-lived metastable atomic groups formation (nanoclusters) (Fig. 3(b)). The time of stabilization is very long. It specifically depends on rigidity of atomic bonding in lattices (nonlinear coefficients are based on them) and on the value of ion energy of external irradiation. The period of the lattice inside the clusters does not correspond to the initial one. It is clusters that provide new complexes of physical and mechanical properties to lattices (irradiated materials). A phase diagram of randomly chosen atom of the chain was made and showed that its new final attractor is a highly displaced state out of the initial state. One can see, as a result high-fragmented structures with nanodimension are formed. We showed using computer simulation method that average size of such fragmented areas should increase with the depth from the irradiated surface in accordance with our experimental results. 4. Conclusions 1. Low-energy ion irradiation of solids in glow-discharge plasma leads to the formation of complex, multilayer nanocrystalline structures in the irradiated volume. These changes cannot be explained within the framework of the classical physics of radiation damages of solids.
2. Computer simulation (using a molecular dynamics method) of nonlinear oscillations in atom oscillator systems of crystal lattices after their low-energy ion irradiation showed the possibility of nanostructures formation and their stability. 3. Nanostructures formations in steels and alloys during low-energy ion irradiation in glow-discharge plasma lead to changes in physical and mechanical properties and may be used to develop new hardening technologies of metals and alloys. Acknowledgement Authors acknowledge partial support from the Center for Irradiation of Materials, Alabama A&M University. References [1] M. Ratner, D. Ratner, Pearson Education Inc, 2003. [2] N.A. Koneva, L.I. Trishkina, E.V. Kozlov, Izv. RAS. Phys. 62 (1998) 1350 (in Russian). [3] I.V. Tereshko, V.I. Khodyrev, V.M. Tereshko, E.A. Lipsky, A.V. Goncharenya, S. Ofori–sey, Nucl. Instr. and Meth. B 80–81 (1993) 115. [4] I.V. Tereshko, V.I. Khodyrev, V.M. Tereshko, E.A. Lipsky, I.V. Romanenko, in: Application of Particle and Laser Beams in Materials Technology, London, 1995, p. 595. [5] I.V. Tereshko, V.I. Khodyrev, E.A. Lipsky, A.V. Goncharenya, A.M. Tereshko, Nucl. Instr. and Meth. B 127–128 (1997) 861. [6] I.V. Tereshko, V.I. Khodyrev, V.V. Glushchenko, G.V. Rimkevich, A.M. Tereshko, A.A. Russian, in: Proceedings of the 36th International Seminar ‘Actual problems of strength’, 2001, p. 648 (in Russian). [7] E.V. Kozlov, I.V. Tereshko, N.A. Popova, Sov. Phys. J. (USA) 5 (1994) 506. [8] E.V. Kozlov, I.V. Tereshko, N.A. Popova, E.A. Lipsky, V.I. Khodyrev, Tsvetn. Met. 7 (1991) (in Russian). [9] A.N. Didenko, U.P. Sharkeev, E.V. Kozlov, A.I. Riabchikov, Longrange Effects in Ion Implanted Metal Materials, STL, Tomsk, 2004, p. 328 (in Russian). [10] J. Williams, J. Poutau, Ion Implantation and Beam Technologies, Navukova Dumka, Kiev, 1988, p. 360. [11] W. Eckstein, Computer Simulation of Ion–Solids Interaction, Springer-Verlag, Berlin, Heidellberg, New York, 1991.