The centrifugal solid-particle method has proved to be effective in producing functionally
graded materials (FGMs). In this study, Al-Al3Ti FGMs, were produced by this centrifugal method,
from an Al-5 wt % Ti master alloy. Applied centrifugal forces were 30, 60 and 120G (units of
gravity). Samples from the outer surface of each specimen were cut and aluminum matrix texture
analyzed by Schulz reflection method. Analysis of the resulting pole figures indicates a preferred
orientation along the (200) plane for the aluminum matrix crystals. Furthermore, increasing the
applied centrifugal force enhances the orientation effect. Al3Ti platelet orientation and area fraction
at the samples’ outer surface along three observation planes were also measured. The Al3Ti platelets
in the outer region are orientated perpendicular to the centrifugal force direction along two of the
observed planes, also an increase in centrifugal force leads to an increase in orientation in those two
planes. The intermetallic particle volume fraction also increases with higher applied centrifugal
force, although not significantly. A correlation appears to exist between particle orientation and the
preferred orientation of the matrix.(undefined

Rocha, L. A.

Sequeira, P. D.

Watanabe, Y.

Solid State Phenomena

Universidade do Minho: RepositoriUM

  415  Aluminum matrix texture and particle characterization in Al-Al3Ti FGMs produced by a centrifugal solid-particle method P.D. Sequeira 1, 2, a, Yoshimi Watanabe 1, b and L.A. Rocha 2, 3, c  1Department of Functional Machinery and Mechanics, Shinshu University, 3-15-1, Tokida, Ueda 386-8567, Japan 2CIICS - Centro de Investigacao em Comportamento de Superficies, Universidade do Minho, Campus de Gualtar, 4800-058 Guimaraes, Portugal 3DEM – Departamento de Engenharia Mecanica, Universidade do Minho, Campus de Gualtar, 4800-058 Guimaraes, Portugal a pdavid.15163@engmateriais.eng.uminho.pt, b yoshimi@shinshu-u.ac.jp, c lrocha@dem.uminho.pt Keywords: Functionally Graded Material; Texture; Schulz reflection method Abstract The centrifugal solid-particle method has proved to be effective in producing functionally graded materials (FGMs). In this study, Al-Al3Ti FGMs, were produced by this centrifugal method, from an Al-5 wt % Ti master alloy. Applied centrifugal forces were 30, 60 and 120G (units of gravity). Samples from the outer surface of each specimen were cut and aluminum matrix texture analyzed by Schulz reflection method. Analysis of the resulting pole figures indicates a preferred orientation along the (200) plane for the aluminum matrix crystals. Furthermore, increasing the applied centrifugal force enhances the orientation effect. Al3Ti platelet orientation and area fraction at the samples’ outer surface along three observation planes were also measured. The Al3Ti platelets in the outer region are orientated perpendicular to the centrifugal force direction along two of the observed planes, also an increase in centrifugal force leads to an increase in orientation in those two planes. The intermetallic particle volume fraction also increases with higher applied centrifugal force, although not significantly. A correlation appears to exist between particle orientation and the preferred orientation of the matrix. Introduction By a centrifugal solid-particle method [1-4], Al-Al3Ti FGMs have been successfully produced. In this method the alloy is heated up to a temperature located between its solidus and liquidus temperatures, where most of the intermetallic platelets remain solid in the liquid Al-based matrix. The density of the Al3Ti particles is higher than that of the molten Al matrix. Due to this density difference, upon casting under centrifugal force the Al3Ti particles will be segregated in the direction of the applied centrifugal force. This will lead to a graded distribution of the intermetallic particles in the Al matrix [5]. Since the material is composed of two phases its properties depend on the properties of each phase separately as well as on the inter-relationship between those two phases [6]. Furthermore, spatial orientation and distribution of the two phases will also affect the materials properties. In fact, anisotropic wear resistance in an Al-Al3Ti FGM has been studied [7]. Also, in a previous study the crystallographic relationship between the Al matrix and the Al3Ti particles was studied by transmission electron microscopy (TEM) [8]. Selected area diffraction (SAD) taken along a low index direction provided useful information in determining the orientation between the Al matrix and the Al3Ti particles. Diffraction patterns taken at the Al-Al3Ti interface are shown in Fig. 1. The orientation relationship between the Al and the Al3Ti phases is given by                                  _                 _       (111)Al3Ti // (111)Al, [110]Al3Ti // [110]Al       (1)   Solid State Phenomena Vol. 105 (2005) pp. 415-420online at http://www.scientific.net© 2005 Trans Tech Publications, SwitzerlandLicensed to L.A. Rocha (lrocha@dem.uminho.pt) - University of Minho - PortugalAll rights reserved. No part of the contents of this paper may be reproduced or transmitted in any form or by any means without thewritten permission of the publisher: Trans Tech Publications Ltd, Switzerland, www.ttp.net. (ID: 193.137.16.172-08/02/06,18:15:15)   416  A good lattice correspondence is found for the close packed directions and the close packed planes between two crystals [8]. Therefore, it is expected that, due to the existence of a preferred orientation for the intermetallic particles and the above mentioned lattice correspondence, the aluminum crystal would also exhibit an orientation pattern. In order to corroborate this notion, aluminum crystal texture was analyzed by the Schulz reflection method [6]. In this study, results concerning the characterization of Al3Ti particles and the aluminum matrix texture at the surface of produced FGM rings are presented.    Fig. 1 - Diffraction pattern at the Al-Al3Ti interface [8] Experimental Methods Al-Al3Ti FGMs were produced by the centrifugal solid-particle method, from Al-5wt % Ti commercial alloys. Crystal structures and densities are presented in Table 1. Since the relative atomic masses of Al and Ti are 26.98 and 47.88, respectively, the theoretical volume fraction of Al3Ti in the master alloy was calculated to be approximately 11 vol% [7]. In the centrifugal solid-particle method the alloy is heated up to a temperature located between its solidus and liquidus temperatures. Therefore, most of the intermetallic platelets remain solid in a liquid Al-based matrix. It is then poured into a rotating mould in order to obtain ring-shaped samples. The temperature of the melting furnace was 1173 K and applied centrifugal casting forces were 30, 60 and 120G (units of gravity). The FGMs rings have an outer diameter of 90mm, 25mm in height and a length of 20-25mm. A detailed description of the centrifugal method is available elsewhere [1-4,7]. Samples were taken from the rings outer region. Optical micrographs were taken and intermetallic particle size, distribution and orientation were measured along three observation planes, perpendicular to the rotating axis (referred as OP1 in the subsequent text), perpendicular to the rotating direction (OP2) and perpendicular to the centrifugal force direction (OP3), as seen in Fig. 2. For quantitative analysis of the Al matrix texture along OP3, pole figures obtained with the Schultz reflection method [6] were used.  Rotating AxisOP3 OP2OP1 OP2A1OP1A2A3A3A2OP3A1 Fig. 2 - Schematic drawing of the FGM ring. A3 is the centrifugal force direction, A2 is the reference axis for OP1 and OP3, A1 is the reference axis for OP2.  Texture and Anisotropy of Polycrystals II416   417  Table 1 - Crystal Structure and density  Element or compound Crystal Structure Density [Mg/m3] Al fcc 2.7 Al3Ti D022 3.4 Results and Discussion Characterization of the Al3Ti intermetallic particles. As seen in Table 2, the average intermetallic area fraction at the outer surface increases with higher applied centrifugal force. When comparing the 60 and 120G specimens, there is only a very small increase in the measured area fraction. From this fact it is deduced that the maximum particle area fraction packing is around 23-25%.  As seen in Fig.3, the microstructures along OP1 and OP2 for the three samples are very similar while that is not the case with the observed microstructure along OP3. This is due to the nature of the Al3Ti particles and the observation method. Al3Ti particles are platelet in shape and they tend to be oriented perpendicular to the centrifugal force direction. OP1 and OP2 intersect the platelets along its edges while OP3 intersects the platelets face.  Table 2 – Area fraction occupied by the Al3Ti particles at the surface of the FGM specimens  Area occupied by the Al3Ti particles [%] Applied centrifugal force OP1 OP2 OP3 Average 30G 19.5 22.3 21.58 21.13 60G 22.3 22.6 24.58 23.16 120G 26.0 21.2 22.9 23.37  Observation Plane  OP1 OP2 OP3 30G    60G    Applied Centrifugal Force 120G     Fig. 3 - Microstructure at the specimens’ outer surface, dark areas are the Al3Ti particles Solid State Phenomena Vol. 105 417   418  Taking a line perpendicular to the centrifugal force direction as reference axis, the Al3Ti particles’ angle in relation to that axis along the three observation planes was measured. In OP1 the reference axis is the A2 direction, for OP2 it is the A1 direction and along OP3 the reference axis was the A2 direction. Results are presented in Fig. 4. Particles tend to be concentrated between -15° to 15° angle to the reference axis along OP1 and OP2, while along OP3 no pattern is evident. Although it is not entirely clear by the orientation histograms, an increase in applied centrifugal force leads to a higher orientation effect along OP1 and OP2. To quantitatively express this tendency Hermans orientation parameter, fp [9,10], is used (Table 3). An orientation parameter of 1.0 expresses a perfect alignment of the particles with the refence axis and fp = 0.0 a completely random dispersion of particles. Negative values indicate a tendency for the particles to be aligned perpendicularly to the reference axis.  Observation Plane  OP1 OP2 OP3 30G -90 0 90Angle50403020100RelativeFrequency(%) -90 0 90Angle50403020100RelativeFrequency(%) -90 0 90Angle50403020100RelativeFrequency(%) 60G -90 0 90Angle50403020100RelativeFrequency(%) -90 0 90Angle50403020100RelativeFrequency(%) -90 0 90Angle50403020100RelativeFrequency(%) Applied Centrifugal Force 120G -90 0 90Angle50403020100RelativeFrequency(%) -90 0 90Angle50403020100RelativeFrequency(%) -90 0 90Angle50403020100RelativeFrequency(%)  Fig. 4 - Orientation Histograms for Al3Ti platelets at the samples’ outer surface Texture and Anisotropy of Polycrystals II418   419  Table 3 – Hermans orientation parameter Hermans orientation parameter Applied centrifugal force OP1 OP2 OP3 30G 0.839 0.775 0.019 60G 0.808 0.829 -0.074 120G 0.876 0.857 -0.164  Texture of the Al matrix. Aluminum matrix textures at the outer surface of the FGM specimens, along OP3, were studied by using the Schulz reflection method [6]. (200) Pole figures for each specimen, determined by this method, are presented in Fig. 5. As it can be seen non-random patterns appear in all pole figures, indicating a preferred orientation along the (200) plane for the aluminum matrix crystals. Furthermore, increasing the applied centrifugal force enhances this orientation effect. Taking into account the results for particle orientation discussed in the previous section, a correlation appears to exist between Al3Ti particle orientation and the preferred orientation of the Al matrix crystals. This correlation stands in agreement with the lattice correspondence found between the Al matrix crystals and the Al3Ti particles in a previous study [8]. Considering that Al3Ti particles remain, for the most part, solid during processing and have achieved their position as the solidification of the matrix engulfs them it is believed that the Al crystals’ preferred orientation is dependent on the particles’ orientation.   a) Sample cast under 30G b) Sample cast under 60G RDTD30G OP30.84211.47362.10522.7367 RDTD60G OP31.03382.06753.10134.1350 c) Sample cast under 120G  RDTD120G OP31.11532.26033.06703.6247 Fig. 5 - Al matrix (200) Pole figures determined by Schulz reflection method. Rolling direction (RD) corresponds to the A1 direction (Fig. 2) and TD to the A2 direction. Solid State Phenomena Vol. 105 419   420  Conclusions In this study, Al-Al3Ti functionally graded materials (FGMs), were produced by the centrifugal solid-particle method and results concerning the characterization of Al3Ti particles and the aluminum matrix texture at the surface of produced FGM rings are presented. 1) Average intermetallic area fraction at the outer surface increases with higher applied centrifugal force. 2) Orientation of the intermetallic particles perpendicular to the centrifugal force direction was found along two of the observation planes, an effect that is increased with higher applied centrifugal force. 3) Al matrix crystals at the FGMs outer surface exhibit a preferred orientation on the (200) plane, indicating a correlation between the Al crystals’ and the Al3Ti particles’ orientation.  Acknowledgements – This study is partially supported by 21st Century COE Research of the Ministry of Education, Culture, Sports Science and Technology of Japan. References [1]  Y. Fukui: JSME Inst. J. Series III Vol. 34 (1991), p.144 [2]  Y. Fukui and Y. Watanabe: Metal. Mater. Trans. A Vol. 27A (1996), p. 4145 [3]  Y. Watanabe, N. Yamanaka and Y. Fukui: Composites Part A Vol. 29A (1998), p. 595 [4]  Y. Watanabe and Y. Fukui: Aluminum Trans. Vol. 2 (2000), p. 195 [5]  L. Lajoye and M. Suery: Proc. Int. Symp. on Advances in Cast Reinforced Metal Composites, ASM International (1988), p.15 [6]   B.D. Cullity: Elements of X-Ray Diffraction (Addison-Wesley Pub. Co., Boston 1978) [7]  Y. Watanabe, N. Yamanaka and Y. Fukui: Metal. Mater. Trans. A Vol. 30A (1999), p. 3253 [8]  K. Yamashita, Y. Watanabe, N. Yamanaka, Y. Fukui and A. Sato: Proc. JIMIS-8, (1996), p. 371 [9]  S.H. McGee and R.L. McCullough: J. Appl. Phys. Vol. 55 (1984), p. 1394 [10]  L.M. Gonzalez, F.L. Cumbrera, F. Sanchez-Bajo and A. Pajares: Acta Metall. Mater. Vol. 42 (1994), p. 689 Texture and Anisotropy of Polycrystals II420

Aluminum matrix texture and particle characterization in Al-Al3Ti FGMs produced by a centrifugal solid-particle method

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Aluminum matrix texture and particle characterization in Al-Al3Ti FGMs produced by a centrifugal solid-particle method

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