INVESTIGATION OF IMPACT OF IMPLANTED OXIGEN IONS ON
THERMALLY INDUCED PROCESSES IN LAMELLAR SYSTEM IRON-
BERILLIUM
S.A. Nurkenov, S.B. Kislitsin, I.D. Goriachev, V.I. Antonyuk,
V.S. Rusakov*, K.K. Kadyrzhanov
Institute o f Nuclear Physics NNC RK, Almaty 050032, Kazakhstan Lomonosov Moscow State University, Moscow 119899, Russia
ABSTRACT
In the performed work the methods o f Mössbauer spectroscopy and X-ray analysis there were investigated thermally induced processes in lamellar systems a-Fe:O+-B e(0.7 m km )-5 7Fe(0.1 mkm) and a-F e- Be(0.7 m km )-5 7Fe(0.1 mkm), obtained by methods o f magnetron and thermal-vacuum sputtering o f Be and Fe atoms enriched by nuclei 5 7Fe. The sequence o f phase transformations at consistent isothermal annealing has been established. It has been shown that implanted oxygen layer in the matrix a-Fe reduces interdiffusion o f beryllium and iron atoms.
1. INTRODUCTION
Development o f new effective technologies o f obtaining o f material working in conditions o f corrosive mediums at considerable mechanical, thermal, radiation and other loads are o f practical and scientific interest. Thus, the considerable interest is presented with implantation system metal-metalloid. It is connected that, forming phases o f implantation o f irradiated metal in near-surface layers it is possible to improve considerably its strength and anticorrosive properties. Hardly non-equilibrium conditions in implanted material, the changes o f its defective structure and elemental composition during radiation effect create considerable complexities at the description o f these phenomena not only on quantitative, but also on the qualitative level. The thermal stability at high temperatures is important for the obtained coatings /1-3/. Using the methods o f Mössbauer spectroscopy on 57Fe nuclei, in the work /4, 5/ were investigated processes o f phase-generation in lamellar system Fe-Be and the capability o f obtaining o f thermally stable layer o f iron berrylide saturated up to limiting concentration o f beryllium in iron substrate has been performed. In the work /6, 7/ using the methods o f Mössbauer spectroscopy on conversion electrons there was investigated a structural-phase state o f a-Fe surface irradiated by ions o f oxygen. There were revealed the peculiarities o f process o f phase formation in the implantation system F e:0+. Based on /4-7/ we can suggest that the oxygen layer implanted in a-Fe substrate will influence on processes o f interdiffusion o f Fe and Be and will be conductive to more effective generation o f thermally stable layer o f iron beryllide in lamellar system Fe-Be. The purpose o f the present activity was the investigation o f influence o f implanted oxygen ions o f on thermally induced processes in a lamellar system Fe-Be by the methods o f Mössbauer spectroscopy and X- ray phase analysis.
2. METHOD OF EXPERIMENTAL INVESTIGATIONS
At preparing o f samples there was used a-Fe as a substrate, rolled up to depth o f 10 mkm with the subsequent homogenizing annealing at the temperature o f T = 850°C within 3 hours. In one of foils o f a-Fe at heavy ion accelerator UKP-2-1 o f INP NNC RK the were implanted the 0 + ions with energy o f 1,6 MeV to doze 1.15-1018 ion/cm2. Using the methods o f magnetron and thermal vacuum sputtering o f Be and Fe atoms enriched by 57Fe nuclei there were obtained systems a-Fe:O+-B e(0.7 m km )-5 7Fe(0.1 mkm) and a-Fe-Be(0.7 m km )-5 7Fe(0.1 mkm). The control o f sample depth was realized both weight method and method o f Rutherford back-scattering o f protons. The obtained systems were subjected to a consistent isothermal annealing in vacuum 5 1 O' 6 mm Hg at the temperature o f T = 700°C. For investigations o f thermally induced processes in the above-stated systems there were used the methods o f Mössbauer spectroscopy with registration o f y- quanta on “passing” (TMS) and registration o f conversion electrons in back-scattering geometry (CEMS) and X-ray phase analysis. The selection o f the method was caused by swirl reasons: The method TMS gives the information about phase structure gives, averaged on the whole thickness o f a sample; CEMS method the information on thin (~0,1 mkm) near-surface layer o f a sample. X- ray phase analysis gives information about phase structure from the layers up to 4 mkm. Thickness from
investigation surfaces. X-ray phase analysis o f samples was fulfilled on a diffractometer D8 ADVANCE on
CuXa radiation. The measurements were conducted in Bregg-Brentano geometry from both sides o f a
sample. Mössbauer investigations were made on a spectrometer MSI 104ME in geometry «on absorption» at room temperature. 57Co was a source o f y-quanta in a matrix Rh with activity ~5mCi. The calibration o f a spectrometer was realized using a reference specimen a-Fe. The processing o f experimental spectra was conducted using the program complex MSTools /8-10/.
3. RESULTS AND DISCUSSION
The binary Fe-Be system, except for solubility regions Be in Fe and Fe in Be, has several intermetallic compounds: FeBe2, FeBe5 n FeBex / 1 1 -13/. FeBe2 compound or P - phase having HCP crystalline structure such as MgZn2 (P6 3/mmc) is a ferromagnetic. The area o f existence o f this phase is within the limits o f atomic content CBe = 67-1-79 at. %. In this connection we shall mean hereinafter this phase as FeBe2+s (0<S<1,8). At increase o f concentration o f beryllium in P-phase the Curie point decreases from 645 C (at 8=0) to ~300 C (at 8~1,8). FeBe5 compound or 8-phase has a cubical crystalline structure such as UNi5 with a space group o f a symmetry Fm3c /12/ (according to other data - a structure such as MgCu5 with a space group o f a symmetry Fd3m /1 1/). The 8-phase is a ferromagnetic with Curie temperature Tc<20°C, so that at room temperature it is in a paramagnetic state. Beryllides with the greatest content o f beryllium and common formula FeBex (1 1,2<x<1 1,8) have hexagonal structure with a space group P6m2 and are paramagnetic. Figures 1 and 2 perform the Mössbauer spectra o f 57Fe nuclei and the result o f recovery o f distribution function o f hyperflne parameters o f Mössbauer spectra (A) and (B) obtained after sequential isothermal annealings at T = 700°C o f lamellar systems a-Fe-Be(0,7 m km )-5 7Fe(0,l mkm) and a-Fe:O+-B e(0,7 m km)- 5 7Fe(0,l mkm).
Fig. 1. Mössbauer spectra o f 57Fe nuclei and the result o f recovery o f distribution function o f hyperflne parameters o f Mössbauer spectra (A) and (B) after sequential isothermal annealings at T = 700°C o f lamellar system a-Fe-Be(0,7 m km )-5 7Fe(0,l mkm).
The analysis and processing o f Mössbauer spectra was conducted by a method of recovery o f two distribution functions o f hyperflne parameters realized in the program DISTRI included in a program complex MSTools /9, 10/
According to the data on hyperflne parameters fo 57Fe Mössbauer nucleir subspectra iron beryllides reported in the work /14/, we recovered two independent distribution functions p(Hn) and spectra (A) and (B) corresponding to that functions (see fig. 1 (A, B)). As one can see from fig. 1, we did not get to find out partial spectra o f the highest beryllides. However, values o f hyperflne fields for partial spectrum, which is smaller on intensity (190 kOe < Hn < 200 kOe) definitely indicates its belonging to FeBe2 + 5 beryllide, and spectrum (B) in the range from (220 kOe < Hn < 360 kOe) relates to Fe atoms in solution a-Fe(Be) and availability o f Be atoms in its nearest coordination orb.
Fig. 2. Mössbauer spectra of 57Fe nuclei and result o f recovery of distribution function o f hyperflne parameters o f Mössbauer subspectra (A) and (B) obtained after subsequent isothermal annealings at T = 700°C o f lamellar system a-F e:0+-B e (0.7 mkm)- 5 7Fe(0.1 mkm).
Fig. 2 presents Mössbauer spectra and the result o f recovery o f distribution function p(Hn), where the values o f hyperflne parameters o f spectra (A) and (B) coincide with the from data introduced in the work /14/, and characterize P-phase FeBe2 + 5 and solid solution a-Fe(Be). With increase o f time o f isothermal annealing, P- phase FeBe2+s is dissolved in a-Fe(Be) increasing beryllium concentration in the solution. At 0.5 h annealing in the system a-Fe:O+-B e(0.7 m km )-5 7Fe(0.1 mkm) was revealed a Mössbauer line o f paramagnetic type in the center o f a spectrum, that has allowed to use CEMS method, for revelation of high berillides (see fig. 5).
For confirmation o f P-phase FeBe2+s dissolution in solution a-Fe(Be) in investigated lamellar systems (see fig. 3 and fig. 4) there were carried out X-ray investigations. Fig. 3 performs fragments o f X-ray difractograms obtained from the side o f Beryllium coating for the system Be(0.7 m km )-5 7Fe(0.1 mkm) depending on annealing duration. We can see that at 0.5 h annealing there is dissolution o f P-phase FeBe2+s that leads to formation o f solid solution a-Fe(Be). At further increase o f annealing time there is a complete dissolution o f P-phase FeBe2+s and disturbance o f crystalline state in iron structure.
Fig. 3. Fragments o f X-ray diffractograms obtained from the side o f beryllium coating for the system a-Fe-Be(0.7 m km )-57Fe (0.1 mkm) after preliminary isothermal annealings at T = 700°C. From fig. 4 one can see that in the system a-Fe:O+-B e(0,7 m km )-5 7Fe(0,l mkm), the processes o f interdiffusion o f beryllium and iron atoms are realized slowly. P - Phase FeBe2 + 5 is seen distinctly at additional 2.5 h o f annealing and is absent in the system a-Fe-Be(0.7 m km )-5 7Fe(0.1 mkm). The relative intensity o f reflexes (1 0 0), (0 0 2) and (1 0 1) for the phase FeBe2 + 5 after each annealing in both systems is less than the corresponding relative intensity o f partial CEMS spectrum o f the phase FeBe2+5, but more than the relative intensity o f partial spectrum o f the phase FeBe2 + 5 in Mössbauer investigations in the geometry on “absorption”. It is explained by the fact that the depths, where X-ray beams are registered are larger than the depths o f surface layer o f conversion Mössbauer method. As there is less o f beryllium on the depth, the fraction o f the phase FeBe2 + 5 is less and the fraction o f the solid solution a-Fe(Be) is more, respectively.
Fig. 4. Fragments o f X-ray diffractograms obtained from the side o f beryllium coating for the system a-Fe:O+-B e(0.7 m km )-57Fe (0.1 mkm)after sequential isothermal annealings at T = 700°C.
CEMS spectra o f 57Fe nuclei o f lamellar system a-Fe:O+-B e(0,7 m km )-5 7Fe(0,l mkm) taken from the side o f beryllium coating after sequential isothermal annealings at T = 700°C are presented at fig. 5. Analyzing these spectra it was revealed that they represent a superposition o f two partial spectra with different relative intensity. Only one spectrum has an exclusion, which was obtained after initial annealing at T = 700°C within
0.5 hours, when one could observe the third partial spectrum o f paramagnetic type corresponding to the highest beryllide FeBe5. At following increasing o f annealing time the phase FeBe5 was not revealed. Further we can see the considerable decrease o f concentration o f the phase FeBe2+5, which leads to increase o f concentration o f the solid solution a- Fe(Be).
Fig. 5. CEMS spectra o f 57Fe nuclei in lamellar system a-Fe:O+-B e(0.7 mkm)- 5 7Fe(0.1 mkm) taken from the side o f beryllium coating after sequential isothermal annealings at T = 700°C and the result o f reduction o f distribution function o f hyperflne parameters o f Mössbauer spectra
Fig. 6 performs spectra o f the systems a-Fe:O+-B e(0.7 m km )-5 7Fe(0.1 mkm) and a-Fe-Be(0.7 mkm)- 5 7Fe(0.1 mkm) taken from the side o f iron after sequential isothermal annealings at T = 700°C. As one can see from fig. 6 in the system a-Fe-Be(0.7 m km )-5 7Fe(0.1 mkm) within 5-hour annealing there was the complete crystalline fracture o f a-Fe, which is opposite to the system a-Fe:O+-B e(0.7 m km )-5 7Fe(0.1 mkm). The presented experiment data shows the delayed migration o f beryllium atoms in oxygen-containing system and confirm the idea about influence o f implanted oxygen ions.
Fig. 6. Fragments o f X-ray diffractograms o f lamellar systems a-Fe:O+-B e(0.7 mkm) 5 7Fe(0.1 mkm) and a-Fe-Be(0.7 mkm)- 5 7Fe(0.1 mkm) from the side o f iron after sequential isothermal annealings at T = 700°C.
4. CONCLUSIONS
1. The systematic investigations o f influence o f implanted oxygen ions on thermally induced processes in the lamellar system Fe-Be have been carried out for the first time by the methods o f Mössbauer spectroscopy on 57Fe nuclei and X-ray phase analysis.
2. The sequence o f phase transformations in surface layers and sample volume during isothermal annealing has been determined.
3. It has been shown that oxygen layer in the matrix a-Fe implanted 0 + ions reduces interdiffusion o f beryllium and iron atoms, as it is the barrier preventing diffusion o f components in lamellar system multipliers.
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