Characterization of microstructures with sizes from the sub-nm to the μm-range by extended small-angle neutron scattering

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  • ELSEVIER Physica B 241 243 (1998) 98 100

    Characterization of microstructures with sizes from the sub-nm to the pro-range by extended small-angle neutron scattering

    P. Staron*, D. Bellmann, R. Kampmann, M. Klatt, R. Wagner Institute ~?/" Materials Research, GKSS Research Center, 21502 Geesthaeht, Germany

    Abstract

    Conventional SANS facilities cover scattering vectors q between about 0.01 and 3 nm ~ and are well suited for analyzing microstructures in materials with sizes from 1 to about 100 nm. At the Geesthacht neutron facility (GeNF), this range has been greatly extended. Larger values ofq (up to 25 nm 1) are made accessible at the pin-hole facility SANS-2 by means of a second area detector, which can be rotated around the sample. Smaller q-values down to 10- 3 rim- 1 can be covered at the SANS-2 by means of the beam broadening (BB) technique. With the use of a double-crystal diffractometer (DCD) still smaller q-values down to 10- 4 nm i become accessible. Investigations of extremely small structures (clusters with radii of only 0.3 nm), and extremely large ones (creep pores in ceramics with sizes up to some pro) are presented. 1998 Elsevier Science B.V. All rights reserved.

    Keywords: Small-angle neutron scattering (SANS); Double-crystal diffractometry (DCD)

    1. Introduction

    lnhomogeneities with sizes below 1 nm as well as between about 100 and 500 nm can rarely be deter- mined reliably by means of SANS due to the lim- ited range of scattering vectors q accessible with pin- hole cameras and DCD facilities. Therefore, the analysis of important microstructures such as clus- ters which develop during the early stages of de- composition reactions in alloys or creep pores in ceramic materials requires advanced experimental techniques. In the following, we introduce examples

    * Correspondence address: GKSS Forschungszentrum, Max Planck-Str, 21502 Geesthacht, Germany. Fax: + 49 4152 87 1338: e-mail: staron(aiGKSS.de.

    of such investigations which were performed using the pin-hole facility SANS-2 and the DCD at GeNF in Geesthacht.

    2. Analysis of small clusters in a Ni-13 at% AI alloy

    The determination of the size distribution and volume fraction of Ni3AI clusters which are formed during the early stages of decomposition reactions is of key importance in determining the character of the reaction, and in particular, for distinguishing whether a spinodal reaction or nucleation and growth has taken place [1]. In the early stages, the critical radius and the radius of clusters already formed during ageing are well below 1 nm in size.

    0921-4526/98/$19.00 ~ 1998 Elsevier Science B.V. All rights reserved PII S09"~1.~ -45~6(97)00521-8_

  • P. Staron et al. / Physica B 241 243 (1998) 98 100 99

    09

    0,1

    0,01

    0,003

    Ta = 450o C ~ 6h 2h

    ~, 45 min ~4~,~ ~ 15 min

    o 5 ~n [] Horn

    ' ' ' ' l ' ~ ' ' ' ' '~[

    0,5 1 10 30

    q [nm -11

    Fig. 1. Scattering curves ofa SSNi-13 at% AI alloy during aging at 450 'C.

    3. Analysis of creep pores in alumina

    Creep pores are formed in materials if they are exposed to mechanical stresses at elevated temper- atures [3]. They are of great technological import- ance because they may initiate failure of compo- nents such as turbine blades.

    Extended SANS from creep pores in liquid-phase sintered (lps-) alumina after 4% deformation ( T = 1350C, a = 100 MPa) has been measured over four orders of magnitude in q using DCD and SANS-2. The latter was also used to perform BB measurements which depend on heavy multiple scattering (Fig. 3) [4]. From the extensive scatter- ing data obtained, a very broad volume distribu- tion f(R)= 4~R3n(R)/3 of pores ranging from

    1102~ 1 T A = 450 C

    Y-~ 1011

    101~ . . . . .

    0,0 0,5 1,0 1,5 2,0

    R[nm]

    Fig. 2. Size distribution of Ni3AI precipitates after aging for 6 h as derived from the correspondent scattering curve (Fig. 1).

    This is illustrated in the SANS analysis of a bi- nary Ni-13 at% AI alloy after ageing at 450C (Fig. 1). The measurements were performed using the SANS-2 which was run with a second area detector that was rotated around the sample for recording both the scattering from precipitates (up to q = 7 nm -1) and some short-range order scattering (up to q = 25 nm- 1). The size distribu- tions of extremely tiny clusters with radii as small as 0.3 nm were derived (Fig. 2) [2]. This would not have been possible using a standard pin-hole cam- era with maximal accessible scattering vector of about q = 3 nm- 1.

    10 ~'"_-:':-:-:-1-:...... ,.

    CC

    "6

    rr

    1 0 -

    .~ 10 -t t -

    10 4. e"

    m 10 -s- CC

    DCD

    rocking curve "..,... ",,,~ndeformed ' '~"" ' I ' ~ 'L"" I ' ' " t ' " '~ ' ' " ' " ' I ' ' ' " ' "

    . . . . . . ,

    BB ..... c...

    eformed

    primary beam ',,. ,~flndeformed

    ' ' " " '1 ' ' " " "1 ' ' '"'"1 ("' '~'"~1 ' ' ' " ' " 104- ,k,

    SANS ',,,~rmea '~ 10 3-

    "v E 102- X \ ~, 1011 undefor

    104] ' '"'"'1 ' ' " ' '1 .. . . . . . '1 ' ' " ' " ' l ' ' 10 -s 10 .4 10 -3 10 .2 10 "1 10

    q [nm"]

    Fig. 3. Scattering curves of liquid-phase sintered alumina, measured with the SANS-2 and the DCD before and after creep deformation. BB spectra were measured using the SANS-2 with- out a beam catcher.

  • 100 P. Staron et al. /" Physica B 241 243 (19981 98-100

    10-~

    E .=.

    10 -~

    0 500 1000 1500 2000

    R [nm]

    Fig. 4. Size distribution of creep pores as derived from the scattering curves shown in Fig. 4.

    about 50 to 2000 nm was derived (Fig. 4). The data analysis was performed taking into account both the slit height smearing of the DCD and the strong multiple scattering causing the BB spectra [5,6].

    4. Summary

    The size distribution of microstructural compo- nents with radii well below 1 nm and up to several

    micrometers can be determined by the joint use of the SANS-2 and DCD at GeNF. BB experiments at SANS-2 substan tiate the deter- mination of size distributions between 100 and 500 nm. Data evaluation programs accounting for multiple scattering as well as different scattering geometries of SANS-2 and DCD are available at GeNF.

    References

    LI] R. Wagner, R. Kampmann, in: R.W. Cahn, P. Haasen, E.J. Kramer (Eds.j, Materials Science and Technology, vol. 5, VCH, 1991.

    [2] P. Staron, Doctoral Thesis, University of Hamburg, 1997.

    [3] K.S. Chan, R.A. Page, J. Am. Ceram. Soc. 76 (1993) 803.

    [4] M. Klan, Doctoral Thesis, Technical University of Ham- burg-Harburg, 1996.

    [5] M. Klatt, D. Bellmann, R. Kampmann, R. Wagner, C. Wolf, H. Hfibner, Physica B, in press.

    [6] M. Klatt, D, Bellmann, R. Kampmann, R. Wagner, C. Wolf, H. Hiibner, Mat. Res. Soc. Symp. Proc. 376 (19951 707.