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Local atomic correlations of bulk amorphous ZrTiCuNiBe alloys
pp.605-608, 1999 Elsevier Science Ltd 8 1999 Acta Metallurgica Inc. Printed in the USA. All rights reserved 09659773/99/.$-see front matter
NsnoStnwmred Materials, Vol. 12,
Pe:rgamon PII SO965-9773(99)00197-X
LOCAL ATOMIC CORRELATIONS OF BULK AMORPHOUS ZrTiCuNiBe ALLOYS U. Gerald, A. Wiedenmann, R. Bellissent*, M.-P. Macht, II. Wollenberger Hahn-Meitner-Institut, Berlin GmbH, Glienickerstr. 100, 14109 Berlin, Germany * Laboratoire Leon Brillouin, C.E.Saclay (Paris), 91191 Gif-sur-Yvette Cedex, France Abstract -- Samples of bulk amorphous Zr41Ti14Culz.sNiloBe22.5 and two related alloys have been heat treated in the supercooled liquid state and above the crystallization temperature. Wide angle neutron scattering experiments lead to very similar total structure factors S(Q) for both states. They show the characteristic modulations of amorphous material. The total pair correlation functions g(R) obtained by Fourier transformation of S(Q) exhibit three main groups of peaks corresponding to the coordination shells. For all samples and heat treatments the total coordination numbers for the first coordination shell are Z=l2 f 0.7 indicating a dense packing of the atoms. By assigning pair correlations to the different maxima in g(R) parGal coordination numbers of Be and Zr were estimated. 01999 Acta Metallurgica em. Introduction
and Experimental
Zr41Ti14Cu12.5Ni,oBe22.5 (alloy V) belongs to the bulk amorphous alloys which are rather stable against crystallization. Differential Scanning Calorimetry with a heating rate of 20 K/min revealed a wide temperature range for the supercooled liquid (SCL) state between the glass temperature T, = 625 K and T,i = 705 K where the first crystallization step occurs (1). For samples amiealed in the SCL state, X-ray diffraction and transmission electron microscopy gave no significant evidence for crystalline phases (2,3) whereas small angle neutron scattering exhibits a pronounced scattering ‘profile which was attributed to a decomposed nanoscaled microstructure (4). FBWAP indicated anticorrelated fluctuations of Ti and Be concentrations corresponding to compositions of Zr41Tie.7Cu12.5NiloBe27.8 (alloy Dl) and (2) Zr41Ti16.5Cu12.5Niloe*o (alloy D2). The present investigation aims to study the nature of atomic correlations in the as-quenched (a.q.), SCL and the partly crystallized state above Txl. Bulk ingots of the alloys V, Dl and 2 have been prepared by levitation melting, cut into cylindric samples of 11 mm height and 3 mm in diameter and submitted to different heat treatments in high vacuum (p < 10m4Pa). The neutron scattering experiments have been performed at the instrument 7C2 at the LLB Saclay, France, using a wavelength of 0.0705 nm (5). Standard data reduction including background corrections and absolute calibration was performed :in the Faber-Ziman formalism (6) leading to the total structure factor S(Q) as presented in Fig. la.
605
606
FOURTH INTERNATIONAL CONFERENCEON NANOSTRUCTURED MATERIALS
“0
20
40
60
80
100
120
140
160
momentum transfer Q / nm-’
0.2
0.4
0.6
0.8
1.0
Rlnm
FIGURE 1: Total structure factor (a) and total pair correlation function (b) of ZrqITilqCu12.5Ni10Be*2.5 after different heat treatments. Curves above the bottom curve (as quenched) are shifted by 1, respectively.
FOURTH INTERNATIONAL CONFERENCEON NANOSTRUCTURED MATERIALS
607
Results and Discussion The total structure factors S(Q) of the three investigated alloys are very similar presenting the characteristic modulations of amorphous materials. No structural change or relaxation between the a.q. and the SCL state was detected. Above TX,, in addition to the diffuse scattering broadened Bragg reflections occur indicating partial crystallization. Fourier transformation of S(Q) leads to the total pair correlation function g(R), see Fig. lb. Three main groups of peaks centered around 0.28nm, OSnm and 0.72nm are observed corresponding to first, second and third neighbour shells. Only for the first shell reliable values of the total coordination numbers Z are obtainied
according
to 2 = 47rplffM R*g(R)dR
(where RM=0.36nm
is a cutoff radius of
the first shell, and p is the atomic density) and reported in Table 1. For all samples and heat treatments Z = 12 f 0.7 which is indicative for a very dense packing of the atoms in the amorphous state similar to that of the fee lattice. For the first coordination shell g(R) is well described by three Gaussian profiles as shown in Fig. 2 leading to the positions Rl = (0.226~.O.O06)nm, R2 = (0.275&0.007)nm and R3 = (0.320f0.008)nm with only minor variations from sample to sample. The radii are very close to those of published data of pair correlations in binary and ternary systems (7,8) or to values derived from Goldsmith radii of the elements as indicated in Fig. 2. From the area of the Gaussians G(r) the partial coordination numbers are obtained according to Z, = (4np cj I wjk ) j R2 G(R) dR where Wjk=Cjckbjb//2 are the weighting factors and cj the concentration of the ad-atom. Neglecting indissovable pair correlations with wjk
Total and partial coordination R2 and R3 see text.
TABLE 1 numbers of heat treated amorphous
alloys; for values of R 1,
606
FOURTH INTERNATIONALCONFERENCE ON NANOSTRUCTURED MATERIALS
0.10
!r-Be
0.08
0 a3
0.35
0.4
Rlnm
FIGURE 2: Total pair correlation function g(R) of ZT41Ti14Cu12.5Ni10Be22.5 (as quenched state) with fitted gaussian functions and mean correlation distances of the relevant elemental correlations (height of bars indicates value of weighting factors, dashed bar = wa_ri < 0)
In summary, in the multicomponent amorphous alloy a dense random packing of the atoms with strong correlation up to third nearest neighbour shells is present. The total coordination number for the first neighbour shell was evaluated to Z = 12 f 0.7 which is very close to the value expected for long-range ordered fee structures. Local atomic arrangements are not in accordance with those of known crystalline phases. Acknowledgment This work was supported by the European Community via the “Human Capital and Mobility - Access to Large Scale Facilities” program (contract no. ERB CHGECT 920001). References 1. 2. 3. 4. 5. 6. 7. .8.
Johnson, W.L. and Peker, A., Applied Physics Letters, 1993,63,2342. Macht, M.-P., Wanderka, N., Wiedenmann, A.,Wollenberger, H., Wei, Q. Fecht, H.J. and Klose, S.;Materials Science Forum, 1996,225227,65. Wanderka, N., Wei, Q., Doole, R., Jenkins, M., Friedrich, S., Macht, M.-P. and Wollenberger, H., Materials Science Forum, 1998,269-272,773. Wiedenmann, A., Keiderling, U., Macht, M.-P. and Wollenberger, H., Materials Science Forum, 1996,225-227,7 1. Ambroise, J.P., Bellissent-Funel, M.C. and Bellissent, R., Revue de Physique Appliquie, 1984, 19,731. Faber, T.E. and Ziman, J.M., Philosophical Magazine, 1965, 11, 153. Steeb, S. and Lamparter, P., Journal ofNon-Crystalline Solids, 1993, 156-158,24. Wagner, C.N.J., Journal of Non-Crystalline Solids, 1992, 150, 1.
NsnoStnwmred Materials, Vol. 12,
Pe:rgamon PII SO965-9773(99)00197-X
LOCAL ATOMIC CORRELATIONS OF BULK AMORPHOUS ZrTiCuNiBe ALLOYS U. Gerald, A. Wiedenmann, R. Bellissent*, M.-P. Macht, II. Wollenberger Hahn-Meitner-Institut, Berlin GmbH, Glienickerstr. 100, 14109 Berlin, Germany * Laboratoire Leon Brillouin, C.E.Saclay (Paris), 91191 Gif-sur-Yvette Cedex, France Abstract -- Samples of bulk amorphous Zr41Ti14Culz.sNiloBe22.5 and two related alloys have been heat treated in the supercooled liquid state and above the crystallization temperature. Wide angle neutron scattering experiments lead to very similar total structure factors S(Q) for both states. They show the characteristic modulations of amorphous material. The total pair correlation functions g(R) obtained by Fourier transformation of S(Q) exhibit three main groups of peaks corresponding to the coordination shells. For all samples and heat treatments the total coordination numbers for the first coordination shell are Z=l2 f 0.7 indicating a dense packing of the atoms. By assigning pair correlations to the different maxima in g(R) parGal coordination numbers of Be and Zr were estimated. 01999 Acta Metallurgica em. Introduction
and Experimental
Zr41Ti14Cu12.5Ni,oBe22.5 (alloy V) belongs to the bulk amorphous alloys which are rather stable against crystallization. Differential Scanning Calorimetry with a heating rate of 20 K/min revealed a wide temperature range for the supercooled liquid (SCL) state between the glass temperature T, = 625 K and T,i = 705 K where the first crystallization step occurs (1). For samples amiealed in the SCL state, X-ray diffraction and transmission electron microscopy gave no significant evidence for crystalline phases (2,3) whereas small angle neutron scattering exhibits a pronounced scattering ‘profile which was attributed to a decomposed nanoscaled microstructure (4). FBWAP indicated anticorrelated fluctuations of Ti and Be concentrations corresponding to compositions of Zr41Tie.7Cu12.5NiloBe27.8 (alloy Dl) and (2) Zr41Ti16.5Cu12.5Niloe*o (alloy D2). The present investigation aims to study the nature of atomic correlations in the as-quenched (a.q.), SCL and the partly crystallized state above Txl. Bulk ingots of the alloys V, Dl and 2 have been prepared by levitation melting, cut into cylindric samples of 11 mm height and 3 mm in diameter and submitted to different heat treatments in high vacuum (p < 10m4Pa). The neutron scattering experiments have been performed at the instrument 7C2 at the LLB Saclay, France, using a wavelength of 0.0705 nm (5). Standard data reduction including background corrections and absolute calibration was performed :in the Faber-Ziman formalism (6) leading to the total structure factor S(Q) as presented in Fig. la.
605
606
FOURTH INTERNATIONAL CONFERENCEON NANOSTRUCTURED MATERIALS
“0
20
40
60
80
100
120
140
160
momentum transfer Q / nm-’
0.2
0.4
0.6
0.8
1.0
Rlnm
FIGURE 1: Total structure factor (a) and total pair correlation function (b) of ZrqITilqCu12.5Ni10Be*2.5 after different heat treatments. Curves above the bottom curve (as quenched) are shifted by 1, respectively.
FOURTH INTERNATIONAL CONFERENCEON NANOSTRUCTURED MATERIALS
607
Results and Discussion The total structure factors S(Q) of the three investigated alloys are very similar presenting the characteristic modulations of amorphous materials. No structural change or relaxation between the a.q. and the SCL state was detected. Above TX,, in addition to the diffuse scattering broadened Bragg reflections occur indicating partial crystallization. Fourier transformation of S(Q) leads to the total pair correlation function g(R), see Fig. lb. Three main groups of peaks centered around 0.28nm, OSnm and 0.72nm are observed corresponding to first, second and third neighbour shells. Only for the first shell reliable values of the total coordination numbers Z are obtainied
according
to 2 = 47rplffM R*g(R)dR
(where RM=0.36nm
is a cutoff radius of
the first shell, and p is the atomic density) and reported in Table 1. For all samples and heat treatments Z = 12 f 0.7 which is indicative for a very dense packing of the atoms in the amorphous state similar to that of the fee lattice. For the first coordination shell g(R) is well described by three Gaussian profiles as shown in Fig. 2 leading to the positions Rl = (0.226~.O.O06)nm, R2 = (0.275&0.007)nm and R3 = (0.320f0.008)nm with only minor variations from sample to sample. The radii are very close to those of published data of pair correlations in binary and ternary systems (7,8) or to values derived from Goldsmith radii of the elements as indicated in Fig. 2. From the area of the Gaussians G(r) the partial coordination numbers are obtained according to Z, = (4np cj I wjk ) j R2 G(R) dR where Wjk=Cjckbjb//2 are the weighting factors and cj the concentration of the ad-atom. Neglecting indissovable pair correlations with wjk
Total and partial coordination R2 and R3 see text.
TABLE 1 numbers of heat treated amorphous
alloys; for values of R 1,
606
FOURTH INTERNATIONALCONFERENCE ON NANOSTRUCTURED MATERIALS
0.10
!r-Be
0.08
0 a3
0.35
0.4
Rlnm
FIGURE 2: Total pair correlation function g(R) of ZT41Ti14Cu12.5Ni10Be22.5 (as quenched state) with fitted gaussian functions and mean correlation distances of the relevant elemental correlations (height of bars indicates value of weighting factors, dashed bar = wa_ri < 0)
In summary, in the multicomponent amorphous alloy a dense random packing of the atoms with strong correlation up to third nearest neighbour shells is present. The total coordination number for the first neighbour shell was evaluated to Z = 12 f 0.7 which is very close to the value expected for long-range ordered fee structures. Local atomic arrangements are not in accordance with those of known crystalline phases. Acknowledgment This work was supported by the European Community via the “Human Capital and Mobility - Access to Large Scale Facilities” program (contract no. ERB CHGECT 920001). References 1. 2. 3. 4. 5. 6. 7. .8.
Johnson, W.L. and Peker, A., Applied Physics Letters, 1993,63,2342. Macht, M.-P., Wanderka, N., Wiedenmann, A.,Wollenberger, H., Wei, Q. Fecht, H.J. and Klose, S.;Materials Science Forum, 1996,225227,65. Wanderka, N., Wei, Q., Doole, R., Jenkins, M., Friedrich, S., Macht, M.-P. and Wollenberger, H., Materials Science Forum, 1998,269-272,773. Wiedenmann, A., Keiderling, U., Macht, M.-P. and Wollenberger, H., Materials Science Forum, 1996,225-227,7 1. Ambroise, J.P., Bellissent-Funel, M.C. and Bellissent, R., Revue de Physique Appliquie, 1984, 19,731. Faber, T.E. and Ziman, J.M., Philosophical Magazine, 1965, 11, 153. Steeb, S. and Lamparter, P., Journal ofNon-Crystalline Solids, 1993, 156-158,24. Wagner, C.N.J., Journal of Non-Crystalline Solids, 1992, 150, 1.