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Global crystallographic textures obtained by neutron and synchrotron radiation
ARTICLE IN PRESS
Physica B 385–386 (2006) 623–625 www.elsevier.com/locate/physb
Global crystallographic textures obtained by neutron and synchrotron radiation Heinz-Gu¨nter Brokmeiera,b, a
Institute of Materials Engineering, Clausthal University of Technical, Agricolastrasse2, 38678 Clausthal-Zellerfeld, Germany b GKSS-Research Center Geesthacht GmbH, Max-Planck-Str. 1, Geb 03, 21502 Geesthacht, Germany
Abstract Global crystallographic textures belong to the main characteristic parameters of engineering materials. The global crystallographic texture is always the average texture of a well-defined sample volume which is representative to solve practical engineering problems. Thus a beam having a high penetration power is needed available as neutron or high energetic X-ray radiation. Texture type and texture sharpness are of great importance for materials properties such as the deep drawing behaviour, one of the basic techniques in many industries. Advantages and disadvantages of both radiations make them complementary for measuring crystallographic textures in a wide range of materials. r 2006 Elsevier B.V. All rights reserved. Keywords: Crystallographic texture; High energetic synchrotron; Thermal neutrons; Global texture; Engineering materials
1. Introduction The crystallographic texture is among others one of the important parameters to describe materials behaviour, anisotropic properties and the history of the material [1]. Moreover, preferred orientations influence the quality of all powder methods used for quantitative phase analyses and for crystal structure determinations. In the case of materials having low crystal symmetry (hexagonal metals) or for multi-phased composites the crystallographic texture is of great importance for the anisotropy of the thermal expansion, which leads often to thermal stresses and to the limitation of the life time of the products. In the case of engineering materials, typical material tests are in practical use to describe materials properties, such as yield point, tensile strength and ultimate stress limit. In order to compare materials properties obtained by a standard material test experiment with the crystallographic texture, one has to average over large sample volumes. Fig. 1 shows some typical sample geometries for global texture work. Institute of Materials Engineering, Clausthal University of Technical, Agricolastrasse2, 38678 Clausthal-Zellerfeld, Germany. Tel.: +49 4152 871207; fax: +49 4152 871338. E-mail address: [email protected].
0921-4526/$ - see front matter r 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.physb.2006.06.117
An ideal sample is shown in Fig. 1a representing a sphere. Spherical samples can have diameters up to 50 mm. In Figs. 1b and 1c, standard samples for a materials test experiment with 6 mm in diameter before (a) and after (b) the test experiment are shown. More complicated sample geometries are usually found for semi-finished products; see as an example in Fig. 1d a Cu–Nb composite ring, where the global texture over the wall thickness (4 mm) and the local texture along the parameter are of basic interest. 2. Global texture measurement In order to measure the crystallographic texture of samples shown in Fig. 1, scattering experiments on nearly identical sample dimensions, which can go up in the cmrange, are necessary on one hand to describe anisotropic behaviour of real products and on the other hand to simulate manufacturing processes. The requirement is a beam with a high penetration power. Based on the high neutron penetration power of thermal neutrons for most materials, neutron diffraction has been established as the standard method for global texture measurements [2]. Short wavelength synchrotron X-rays of about 0.1 A˚ have
ARTICLE IN PRESS 624
H.-G. Brokmeier / Physica B 385–386 (2006) 623–625
scattered beam 5° primary beam
Fig. 2. Schematic view on the beam path of a narrow synchrotron beam in a spherical or cylindrical sample. Fig. 1. Samples geometries for global texture analysis: (a) ideal spherical sample, (b) tensile sample, (c) tensile sample after failure, (d) Cu–Nb ring sample.
similar penetration depths as neutrons. Compared to neutron texture work firstly done by Brockhouse in 1953, texture analyses by synchrotron radiation is rather new. Advantages and disadvantages of both radiations make them complementary for measuring crystallographic textures in a wide range of materials. The main advantage of neutron diffraction is the large beam cross section, so that average textures of spherical samples up to 5 cm in diameter can be analysed where the whole sample takes part in the measurement. A large sample volume guarantees in most cases a sufficient grain statistics even for coarse grained materials. A number of about 104 grains in the scattering volume will provide a high-quality quantitative texture. The typical sample volume of metallic or ceramic neutron samples is between 100 and 3000 mm3, which are due to sample geometry and grain size. A restriction in the material is only for some elements like Cd, B and Li. Less number of grains often present in rocks and ingots yield to pole figures of lower quality, but in all cases no corrections are needed. Similar scattering power of light and heavy elements and the much smaller influence of the scattering angle 2y on the intensity of high h k l reflections are other advantages of neutrons particularly for texture investigations of materials with low crystal symmetry. Due to the necessity of having enough measured pole figures for the quantitative texture analysis, one- or two-dimensional detectors or the time of flight technique are preferred [3]. High energetic synchrotron radiation has a great potential for texture analyses because of the excellent brilliance and the high photon flux [4]. That means, the total counting time for texture measurements can be very short and in situ measurements become possible. For global texture measurements, in situ experiments on a short time scale have been realized to measure the texture under applied load or at high temperatures [5]. Due to the high energy of the used synchrotron radiation, the wavelength is comparably short. That means, the Bragg angles for pole figure measurements are also very small, so that the opening window for additional equipments (furnace or loading device) can be very narrow and consequently the blind area of the non-measurable part of a pole figure is small. Due to the well-known high penetration power of
hard X-rays, investigations on metals such as Fe, Ti, Cu, Al and Mg have been carried out up to 35 mm sample thickness. Restrictions were found for Pt and WC. There is another difference between neutron and synchrotron diffraction for global texture measurements, based on the beam size and the wavelength (Bragg-angle). In neutron diffraction, one tends to average over the whole sample (type I: spherical, cubic or cylindrical shape) or over the whole sample thickness (type II: tensile samples, tubes or ring samples) even for large samples. Up to now this is not possible for high energetic synchrotron work, so that the sample volume changes by rotating or tilting the sample. Fig. 2 shows the influence of such a small primary beam and also the influence of small scattering angle on the experiment. Firstly, a homogeneous texture distribution is required; secondly, one has to correct for absorption and constant volume fraction for non-spherical samples (sheets, semi-finished products, tubes); thirdly, a much smaller effective sample volume needs finer grains to obtain a sufficient grain statistics for a quantitative texture analysis. On the other hand, one can see very clearly that the local resolution using a high energetic synchrotron beam with its excellent brilliance offers the option to measure local textures [6]. Furthermore, high brilliance allows us to measure sharp texture, due to the much smaller pole figure window [7]. It has to be noticed that type II samples need a number of corrections for neutron diffraction too [8]. Local texture investigations on semi-finished products or real components are just on the beginning. Experiments were conducted with both radiations on turbine blades up to 25 mm diameter and 200 mm length, on tubes of 84 mm diameter, 140 mm length, steel rods up to 35 mm diameter and up to 1000 mm length and different extrusion profiles of Mg and Al. The main restriction is the freedom of the goniometer to rotate and tilt the samples.
3. Examples of global texture measurements Local textures of comparably small sample volumes in the bulk and a texture mapping are one of the domains of the synchrotron radiation while global textures of comparably large sample volumes are favoured by neutron techniques. Due to the type of materials and to the target local resolution, both methods are able for investigations of global crystallographic textures of semi-finished products and engineering devices. A wide spread of applica-
ARTICLE IN PRESS H.-G. Brokmeier / Physica B 385–386 (2006) 623–625
625
Fig. 5. Quantitative texture of an annealed Cu wire of 122 mm thickness.
Fig. 3. Comparison of two experimental (10.0) pole figures measured by neutrons and 100 keV X-rays.
4 Pos0Grad Pos30Grad Pos60Grad Pos90Grad Pos120Grad Pos150Grad Pos180Grad
R-value
3
2
1
0 0
15
30 45 60 angle to rolling direction
75
90
Fig. 4. Lankford parameter calculated from quantitative texture data at seven different positions of a niobium tube.
tions has already demonstrated the complementary usage of neutron and synchrotron radiation for global crystallographic texture research. In Fig. 3, two complete (1 0 0) pole figures of an extruded Mg AZ31 rod of 20 mm in diameter are shown. The texture type is identical but the texture sharpness differs, which is due to a different averaging over the whole rod cross section. This rod has a typical texture variation over the cross section [6], which has to be taken into account differently by using neutron or synchrotron radiation. A second example is the non-destructive measurement of the texture variation over the perimeter of niobium tubes. Seamless niobium tubes have been one of the candidates for new accelerator units beside welded materials or Cu–Nb composite tubes. The global texture has to be measured over the whole thickness to describe the materials flow by hydro-forming and the local texture is needed for different positions of the perimeter to describe the equality of the cavity [9]. Fig. 4 indicates the quality of one of 50
different niobium tubes measured at TEX-2 giving the Lankford parameter (R) as a function of the perimeter position. The R-value, which was calculated using the orientation distribution function, describes the deep drawing behaviour. Each tube has a total diameter of 84 mm, a length of 140 mm and a thickness of 6 mm. In the case of small volumes such as thin foils or wires, X-ray diffraction is preferred against neutron diffraction. The energy of the X-rays has to be chosen based on the penetration depth required by the problem, so that laboratory X-ray sources or synchrotron radiation can be used for local and surface texture measurements. Fig. 5 gives an example of an investigation carried out on Cu wires. The experiment was performed at the highenergy beam line BW5 (Hasylab at DESY/Germany). A set of 10 parallel Cu wires with 122 mm thickness each were fixed in a special sample holder to avoid curling, so that an average texture over a total length of 40 mm was obtained. The result was a /1 1 2S fiber texture as shown in the inverse pole figure after ODF calculation using the iterative series expansion method [10]. Acknowledgements This work was funded by the German Ministry for education, science, research and technology (BMBF) under contract numbers 03BRE8CL and 05KS1MCA/2. References [1] H.-F. Kocks, C. Tome, H.R. Wenk, Texture and Anisotropy, Cambridge University Press, Cambridge, 1998. [2] H.-G. Brokmeier, Mater. Sci. Forum 408–412 (2002) 149. [3] S. Vogel, et al., Mater. Sci. Forum 408 (2005) 107. [4] H.J. Bunge, Adv. X-ray Anal. 47 (2004) 359. [5] S.-B. Yi, et al. Mater. Sci. Forum 495–497 (2005) 1585. [6] H.-G. Brokmeier, et al., Adv. X-ray Anal. 46 (2003) 151. [7] K. Moras, et al., J. Appl. Crystallogr. 33 (2000) 1162. [8] V. Luzin, H.-G. Brokmeier, Mater. Sci. Forum 408–412 (2002) 191. [9] H.-G. Brokmeier, W. Singer, H. Kaiser, Appl. Phys. A: Mater. Sci. Process. 74 (2002) s1704. [10] H.-G. Brokmeier, et al., Mater. Sci. Forum 495–497 (2005) 131.
Physica B 385–386 (2006) 623–625 www.elsevier.com/locate/physb
Global crystallographic textures obtained by neutron and synchrotron radiation Heinz-Gu¨nter Brokmeiera,b, a
Institute of Materials Engineering, Clausthal University of Technical, Agricolastrasse2, 38678 Clausthal-Zellerfeld, Germany b GKSS-Research Center Geesthacht GmbH, Max-Planck-Str. 1, Geb 03, 21502 Geesthacht, Germany
Abstract Global crystallographic textures belong to the main characteristic parameters of engineering materials. The global crystallographic texture is always the average texture of a well-defined sample volume which is representative to solve practical engineering problems. Thus a beam having a high penetration power is needed available as neutron or high energetic X-ray radiation. Texture type and texture sharpness are of great importance for materials properties such as the deep drawing behaviour, one of the basic techniques in many industries. Advantages and disadvantages of both radiations make them complementary for measuring crystallographic textures in a wide range of materials. r 2006 Elsevier B.V. All rights reserved. Keywords: Crystallographic texture; High energetic synchrotron; Thermal neutrons; Global texture; Engineering materials
1. Introduction The crystallographic texture is among others one of the important parameters to describe materials behaviour, anisotropic properties and the history of the material [1]. Moreover, preferred orientations influence the quality of all powder methods used for quantitative phase analyses and for crystal structure determinations. In the case of materials having low crystal symmetry (hexagonal metals) or for multi-phased composites the crystallographic texture is of great importance for the anisotropy of the thermal expansion, which leads often to thermal stresses and to the limitation of the life time of the products. In the case of engineering materials, typical material tests are in practical use to describe materials properties, such as yield point, tensile strength and ultimate stress limit. In order to compare materials properties obtained by a standard material test experiment with the crystallographic texture, one has to average over large sample volumes. Fig. 1 shows some typical sample geometries for global texture work. Institute of Materials Engineering, Clausthal University of Technical, Agricolastrasse2, 38678 Clausthal-Zellerfeld, Germany. Tel.: +49 4152 871207; fax: +49 4152 871338. E-mail address: [email protected].
0921-4526/$ - see front matter r 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.physb.2006.06.117
An ideal sample is shown in Fig. 1a representing a sphere. Spherical samples can have diameters up to 50 mm. In Figs. 1b and 1c, standard samples for a materials test experiment with 6 mm in diameter before (a) and after (b) the test experiment are shown. More complicated sample geometries are usually found for semi-finished products; see as an example in Fig. 1d a Cu–Nb composite ring, where the global texture over the wall thickness (4 mm) and the local texture along the parameter are of basic interest. 2. Global texture measurement In order to measure the crystallographic texture of samples shown in Fig. 1, scattering experiments on nearly identical sample dimensions, which can go up in the cmrange, are necessary on one hand to describe anisotropic behaviour of real products and on the other hand to simulate manufacturing processes. The requirement is a beam with a high penetration power. Based on the high neutron penetration power of thermal neutrons for most materials, neutron diffraction has been established as the standard method for global texture measurements [2]. Short wavelength synchrotron X-rays of about 0.1 A˚ have
ARTICLE IN PRESS 624
H.-G. Brokmeier / Physica B 385–386 (2006) 623–625
scattered beam 5° primary beam
Fig. 2. Schematic view on the beam path of a narrow synchrotron beam in a spherical or cylindrical sample. Fig. 1. Samples geometries for global texture analysis: (a) ideal spherical sample, (b) tensile sample, (c) tensile sample after failure, (d) Cu–Nb ring sample.
similar penetration depths as neutrons. Compared to neutron texture work firstly done by Brockhouse in 1953, texture analyses by synchrotron radiation is rather new. Advantages and disadvantages of both radiations make them complementary for measuring crystallographic textures in a wide range of materials. The main advantage of neutron diffraction is the large beam cross section, so that average textures of spherical samples up to 5 cm in diameter can be analysed where the whole sample takes part in the measurement. A large sample volume guarantees in most cases a sufficient grain statistics even for coarse grained materials. A number of about 104 grains in the scattering volume will provide a high-quality quantitative texture. The typical sample volume of metallic or ceramic neutron samples is between 100 and 3000 mm3, which are due to sample geometry and grain size. A restriction in the material is only for some elements like Cd, B and Li. Less number of grains often present in rocks and ingots yield to pole figures of lower quality, but in all cases no corrections are needed. Similar scattering power of light and heavy elements and the much smaller influence of the scattering angle 2y on the intensity of high h k l reflections are other advantages of neutrons particularly for texture investigations of materials with low crystal symmetry. Due to the necessity of having enough measured pole figures for the quantitative texture analysis, one- or two-dimensional detectors or the time of flight technique are preferred [3]. High energetic synchrotron radiation has a great potential for texture analyses because of the excellent brilliance and the high photon flux [4]. That means, the total counting time for texture measurements can be very short and in situ measurements become possible. For global texture measurements, in situ experiments on a short time scale have been realized to measure the texture under applied load or at high temperatures [5]. Due to the high energy of the used synchrotron radiation, the wavelength is comparably short. That means, the Bragg angles for pole figure measurements are also very small, so that the opening window for additional equipments (furnace or loading device) can be very narrow and consequently the blind area of the non-measurable part of a pole figure is small. Due to the well-known high penetration power of
hard X-rays, investigations on metals such as Fe, Ti, Cu, Al and Mg have been carried out up to 35 mm sample thickness. Restrictions were found for Pt and WC. There is another difference between neutron and synchrotron diffraction for global texture measurements, based on the beam size and the wavelength (Bragg-angle). In neutron diffraction, one tends to average over the whole sample (type I: spherical, cubic or cylindrical shape) or over the whole sample thickness (type II: tensile samples, tubes or ring samples) even for large samples. Up to now this is not possible for high energetic synchrotron work, so that the sample volume changes by rotating or tilting the sample. Fig. 2 shows the influence of such a small primary beam and also the influence of small scattering angle on the experiment. Firstly, a homogeneous texture distribution is required; secondly, one has to correct for absorption and constant volume fraction for non-spherical samples (sheets, semi-finished products, tubes); thirdly, a much smaller effective sample volume needs finer grains to obtain a sufficient grain statistics for a quantitative texture analysis. On the other hand, one can see very clearly that the local resolution using a high energetic synchrotron beam with its excellent brilliance offers the option to measure local textures [6]. Furthermore, high brilliance allows us to measure sharp texture, due to the much smaller pole figure window [7]. It has to be noticed that type II samples need a number of corrections for neutron diffraction too [8]. Local texture investigations on semi-finished products or real components are just on the beginning. Experiments were conducted with both radiations on turbine blades up to 25 mm diameter and 200 mm length, on tubes of 84 mm diameter, 140 mm length, steel rods up to 35 mm diameter and up to 1000 mm length and different extrusion profiles of Mg and Al. The main restriction is the freedom of the goniometer to rotate and tilt the samples.
3. Examples of global texture measurements Local textures of comparably small sample volumes in the bulk and a texture mapping are one of the domains of the synchrotron radiation while global textures of comparably large sample volumes are favoured by neutron techniques. Due to the type of materials and to the target local resolution, both methods are able for investigations of global crystallographic textures of semi-finished products and engineering devices. A wide spread of applica-
ARTICLE IN PRESS H.-G. Brokmeier / Physica B 385–386 (2006) 623–625
625
Fig. 5. Quantitative texture of an annealed Cu wire of 122 mm thickness.
Fig. 3. Comparison of two experimental (10.0) pole figures measured by neutrons and 100 keV X-rays.
4 Pos0Grad Pos30Grad Pos60Grad Pos90Grad Pos120Grad Pos150Grad Pos180Grad
R-value
3
2
1
0 0
15
30 45 60 angle to rolling direction
75
90
Fig. 4. Lankford parameter calculated from quantitative texture data at seven different positions of a niobium tube.
tions has already demonstrated the complementary usage of neutron and synchrotron radiation for global crystallographic texture research. In Fig. 3, two complete (1 0 0) pole figures of an extruded Mg AZ31 rod of 20 mm in diameter are shown. The texture type is identical but the texture sharpness differs, which is due to a different averaging over the whole rod cross section. This rod has a typical texture variation over the cross section [6], which has to be taken into account differently by using neutron or synchrotron radiation. A second example is the non-destructive measurement of the texture variation over the perimeter of niobium tubes. Seamless niobium tubes have been one of the candidates for new accelerator units beside welded materials or Cu–Nb composite tubes. The global texture has to be measured over the whole thickness to describe the materials flow by hydro-forming and the local texture is needed for different positions of the perimeter to describe the equality of the cavity [9]. Fig. 4 indicates the quality of one of 50
different niobium tubes measured at TEX-2 giving the Lankford parameter (R) as a function of the perimeter position. The R-value, which was calculated using the orientation distribution function, describes the deep drawing behaviour. Each tube has a total diameter of 84 mm, a length of 140 mm and a thickness of 6 mm. In the case of small volumes such as thin foils or wires, X-ray diffraction is preferred against neutron diffraction. The energy of the X-rays has to be chosen based on the penetration depth required by the problem, so that laboratory X-ray sources or synchrotron radiation can be used for local and surface texture measurements. Fig. 5 gives an example of an investigation carried out on Cu wires. The experiment was performed at the highenergy beam line BW5 (Hasylab at DESY/Germany). A set of 10 parallel Cu wires with 122 mm thickness each were fixed in a special sample holder to avoid curling, so that an average texture over a total length of 40 mm was obtained. The result was a /1 1 2S fiber texture as shown in the inverse pole figure after ODF calculation using the iterative series expansion method [10]. Acknowledgements This work was funded by the German Ministry for education, science, research and technology (BMBF) under contract numbers 03BRE8CL and 05KS1MCA/2. References [1] H.-F. Kocks, C. Tome, H.R. Wenk, Texture and Anisotropy, Cambridge University Press, Cambridge, 1998. [2] H.-G. Brokmeier, Mater. Sci. Forum 408–412 (2002) 149. [3] S. Vogel, et al., Mater. Sci. Forum 408 (2005) 107. [4] H.J. Bunge, Adv. X-ray Anal. 47 (2004) 359. [5] S.-B. Yi, et al. Mater. Sci. Forum 495–497 (2005) 1585. [6] H.-G. Brokmeier, et al., Adv. X-ray Anal. 46 (2003) 151. [7] K. Moras, et al., J. Appl. Crystallogr. 33 (2000) 1162. [8] V. Luzin, H.-G. Brokmeier, Mater. Sci. Forum 408–412 (2002) 191. [9] H.-G. Brokmeier, W. Singer, H. Kaiser, Appl. Phys. A: Mater. Sci. Process. 74 (2002) s1704. [10] H.-G. Brokmeier, et al., Mater. Sci. Forum 495–497 (2005) 131.