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ЗмістThe microhardness of irradiated samples was ~ 30% higher than for untreated one. Also corrosion resistance enhancement was obser
Table 1 – Parameters of the ion-beam treatment
3 Results and discussion
3.2 Element composition
Fig.3 – Concentration profiles of copper single crystals implanted with Ta ions in planes Cu(100) (a) and Cu(111) (b)
Table2 – Microhardness measured by indentation techniques of mono crystal of copper (100) and (111) with and without Ta implanta
Non-implanted surface of Cu
3.4 Corrosion resistance
This work is performed partially by the STCU Project 1472 as well as a project 2M/0145-2001 of the Ministry of Education and Sci
IMPLANTATION of Ta IONS INTO A COPPER SINGLE
CRYSTAL (100) AND (111)
A.D. Pogrebnjak*, V.T. Shablya*, V.S. Kshnyakin*, O.P. Kul’ment’eva*,**, V.V.Bondarenko ***, B.P.Gritsenko****
* Sumy Institute for Surface Modification, Sumy
** Sumy State University, Sumy
*** Martin-Luther-University of Halle-Wittenberg, Halle/Saale, Germany
****Institute of Strength Physics and Materials Science of RAS, Tomsk, Russia
High-dose implantation (up to 1017 cm-2) of tantalum ions into a copper single crystal has been investigated. Irradiation of the copper crystals was performed in two different planes: (100) and (111). The maximum concentration of the tantalum atoms 5 at. % was observed for sample Cu (100). The Ta concentration in the Cu (111) surface after irradiation was only 1 at.%.
Tantalum implantation was accompanied by surface carbonization and oxidation. Carbon and oxygen atoms were presented in the residual atmosphere of vacuum camber. The concentration of carbon and oxygen atoms on the surface reached 50 at. %.
High dose ion implantation is an effective method of surface modification and improving the servicing characteristics of metals and alloys. This method is developed very intensively due to its advantages in comparison to the traditional methods of surface properties improvement . There are many investigations of processes, which take place in surface layers of metals during ion implantation [2-4], but there exist a lot of contradictory results related to intensive and high-dose implantation of a single crystal using multiple-charged ions. By now, there have been only a few papers on implantation into metal crystals, due to the difficulty of getting good quality surfaces of metal single crystals, and also because of the few research groups having ion sources of high intensity. Such investigations are needed, because processes forming defective profiles and implanted impurities are not well understood.
In the case of high dose (up to 1016 cm-2 per pulse) ion implantation the sputtering processes is of great importance. There have been almost no investigations on surfaces after high-dose ion implantation in a carbon-containing medium, which is used to produce the C-film and carbides in the surface layer . This paper deals with analysis of the changes in the surface layer of Cu (100), (111) which result from high dose (1017 cm-2) Ta+ ion implantation.
Mainly three different types of experiments are presented here, in which the influence of ion implantation on material changes has been investigated. These are: 1) studies of element distribution after Ta+ implantation and its dependence on the plane of the ion treatment; 2) microhardness measurements of samples surface; 3) corrosion resistance studies for treated and untreated samples.
We investigated Cu single samples cut out in parallel to the surface (100) and (111). The single crystals had surfaces of 10103 mm in dimension. The Ta+ ion implantation was carried out with an “Diane-2” implanter. The parameters of the ion treatment are presented in Table1.
The samples were cooled by water and their temperature during the implantation didn’t exceed 473 K.
Element composition and its depth distribution were analyzed by means of Rutherford Backscattering Spectrometry (RBS) of protons with energy of 1745 keV. The spectra were recorded at ?=60° (the angle between the beam and the target) and the scattering angle ?=170°. The concentration depth profiles of the elements were obtained under energy spectra processing using special computer program.
Changes of morphology of samples surface were observed with the help of transmission electron microscopy technique.
Microhardness measurements were performed with nano-indenter PMT-3, where four-faced diamond pyramid was used. The load on the pyramid was 7 g. Microhardness was measured for implanted and non-implanted surfaces of single crystal that made it possible to determine the relative improvement of surface hardness as a result of ion implantation.
Corrosion tests were carried out by means of etching implanted and non-implanted samples in a 2 M solution of H2SO4 acid. The crystals were exposed to the aggressive environment for four hours. Then the mass coefficient of corrosion was calculated for both implanted and non-implanted samples using following expression:
where mB – mass before corrosion test, mA – mass after corrosion tests; S – sample surface area; t – time of corrosion test.
3.1 MORPHOLOGY CHANGES
Ion implantation leads to the certain changes in the surface morphology of the crystals. The pictures of the sample surfaces before and after implantation are shown in fig. 1. (In picture c) we can see drops of metal, which are typical for high-dose ion implantation. This picture corresponds to the plane of irradiation (111). The more interesting is the picture b. In this picture the surface of copper single crystal (100) after implantation is shown. As we can see there are many crystallites on the surface
Fig. 1. Surface morphology of a copper single crystal irradiated with Ta+ atoms in different planes: a) untreated surface; b) Cu(100); c) Cu(111)
The RBS spectra are given in the fig. 2. Fig. 2 demonstrates the energy spectra of back-scattered protons for Cu samples (100) and (111) implanted by the Ta+ ions with a 1017 cm-2 dose. There are two peaks on the both spectra. The first one is in the region of the 590 channel, corresponding to the protons output scattered on the carbon ions. The second one is in the region of 830 channel and corresponds to the resonance output of H+ scattered on implanted Ta atoms. Also on both spectra one can see the shelf in the region of 640 channel. This shelf is a sign of oxygen atoms presenting in the near-surface layer . Ion implantation was accompanied by carbonization and oxidation of the sample surfaces due to poor vacuum
(10-3 Pa) .
Fig. 2 – RBS spectra for single crystal of copper implanted with Ta+ ions in planes:
a) Cu (100); b) Cu (111)
In fig. 3 concentration profiles of elements in surface layer calculated from the RBS spectra are presented.
Fig.3, Sheet 2
As we can see the maximum of the concentration of Ta+ atoms is observed on the surface but not in the depth of a sample.
3.3 HARDNESS TESTS
The results of hardness tests are shown in the Table2.
It may be seen that hardness improvement was observed for both of the implanted samples. For planes (100) and (111) enhancement of hardness was 32,4% and 28,9% respectively.
The surface microhardness of ion-implanted samples is determined by assuming the creation a uniform layer in the material.
It is thought that the increased microhardness is due to the radiation damage, leading to the creation and pinning a big number of dislocations.
Table 3 presents the results of the corrosion studies for the single crystals of copper (100). We can see that ion implantation enhance corrosion resistance properties of the surface of single crystal of copper. The mass coefficient of corrosion for implanted sample is one order lower than for untreated one.
Table3 – Results of the corrosion studies of single crystal Cu (111) in H2SO4 acid
This enhancement occurred due to the formation of carbon and oxide thick film on the surface of sample. The presence of such film is shown in fig. 3, where the concentration profiles of elements are presented. This film protects underlying regions from being chemically attacked by aqueous exposure.
Tantalum ion implantation in a copper single crystal (100), (111) has been studied. The element distribution dependence on the direction of irradiation was observed. The highest concentration of Ta+ was for copper single crystal (100). This plane is a plane of the closest packing, so penetration of Ta+ ions in this direction is the most difficult.
As microhardness tests showed ion implantation induced microhardness enhancement of the copper surface for both of the samples.
A carbon and oxide-containing film formation was observed. This film defends the surface from being attacked by aqueous exposure. So it leads to the increasing of the corrosion resistance of the surface.
Authors would like to thank A.P.Kobzev, V.I.Perekrestov, N.I. Shumakova for help in experiments performing.
Приведены данные исследования высокодозной (до 1017 см-2) имплантации ионов тантала в монокристаллы меди.
Облучаемые медные кристаллы имели 2 различные ориентации: (100) и (111). Максимальная концентрация атомов Та 5 ат. % была обнаружена в Си (100). Концентрация Tа в Cu (111) после облучения составляла только 1 ат. %. Имплантация Та сопровождалась поверхностной карбидизацией и оксидированием. Атомы углерода и кислорода осаждались из остаточной атмосферы камеры имплантера. Концентрация атомов углерода и кислорода на поверхности достигла 50 ат. %.
Микротвердость облученных образцов примерно на 30 процентов выше, чем необлученных образцов. Также было обнаружено увеличение коррозионной стойкости для имплантированных кристаллов.
1 A.N. Valyaev, A.D. Pogrebnjak, N. Kishimoto, V.S. Ladysev. Modification of material properties and synthesys of thin films ander intense electron and ion beams irradiation. Ust-Kamenogorsk: East-Kazakstan Technical University, 2000, 345p.
2 F.F. Komarov, Ionnaya Implantaciya v Metally. Moscow: Metallurgiya, 1990.216 p.
3 A.D. Pogrebnjak, A.M. Tolopa // Nucl. Instrum. Methods, 1990, V.B52. – P.25-43.
4 A.D.Pogrebnjak, V.V. Stayko. Vopr. At. Nauki I Tekh., Ser.: Yad. Konstanty, 1998. - 2.(3) -P.30.
5 A.D.Pogrebnjak, A.P.Kobzev, B.P.Gritsenko,et al.// J. Appl. Phys., 2000. –V.87. P. 3.
6 L. Feldmann, J. Majer. Fundamentals of Surface and Thin Film Analysis. - Moscow: Mir, , 1986.- 342 p.
7 Yu. M. Lakhtin. Engineering physical metallurgy and heat-treatment, Moscow: Mir, 1990. - 422 p.
Поступила в редакцию 10 ноября 2005 г.
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