Hostname: page-component-77c89778f8-n9wrp Total loading time: 0 Render date: 2024-07-22T18:28:26.086Z Has data issue: false hasContentIssue false
  • English
  • Français

The Interaction Between Dislocations and Lamellar Grain Boundaries in Pst γ Tiai

Published online by Cambridge University Press:  21 February 2011

S. Rao ,
C. Woodward  and
P.M. Hazzledine
S. Rao
Affiliation:
UES Inc., 4401 Dayton-Xenia Road, Dayton, OH 45432
C. Woodward
Affiliation:
UES Inc., 4401 Dayton-Xenia Road, Dayton, OH 45432
P.M. Hazzledine
Affiliation:
UES Inc., 4401 Dayton-Xenia Road, Dayton, OH 45432
Get access

Abstract

In lamellar TiAl the flat-plate geometry of the grains, the barriers to deformation across the grain boundaries and the coherency stresses all contribute to a marked anisotropy in the yield and fracture stresses of the material. Both yield and fracture occur at low stresses when the deformation is within the lamellae (soft mode) and they occur at high stresses when the deformation crosses the lamellae (hard mode). The anisotropy is enhanced by a new effect which can soften the soft mode and harden the hard mode: the geometry of the lamellar boundary produces degeneracies in the planar fault energies at the interfaces which enhance the mobilities of dislocations on these interfaces. These degeneracies modify the core structure of dislocations on or near the interfaces, consequently soft mode dislocations can dissociate widely and move more easily when their glide plane is contained in the interface. Hard mode dislocations can substantially reduce their core energies when intersecting a γ/γ interface, and subsequently become immobilized, by cross slipping on to the interface plane. This paper presents a discussion of the geometry and relative energies of the γ/γ interfaces using elements of Bollman O-lattice theory. In order to investigate the influence of the interfaces on dislocation core structure we have fit an empirical Embedded Atom Method (EAM) potential to the structural and elastic properties of bulk L10 TiAl. The mobility and core structure of the twinning dislocation at the 180° interface and the perfect, 1/2<110] screw dislocation at the 60° and 120° interfaces were calculated using molecular statics within the EAM. We have also studied the influence of one and two atomic step ledges on dislocation mobility in the 120° interface. We find in general that dislocations are more glissile on the γ/γ interfaces, as compared to bulk TiAl and that ledges are weak barriers to dislocation glide. The interfaces themselves are strong barriers to dislocation motion in the hard mode. We find that the 1/2<110] screw dislocations gliding on conjugate {111} planes are trapped at these interfaces, as a result of lower core energies for screw dislocations lying in the interface.

Type
Research Article
Information
MRS Online Proceedings Library (OPL) , Volume 319: Symposia CB – Defect-Interface Interactions , 1993 , 285
Copyright
Copyright © Materials Research Society 1994

Access options

Get access to the full version of this content by using one of the access options below. (Log in options will check for institutional or personal access. Content may require purchase if you do not have access.)

References

[1] The asymmetric notation, <hkl] and {hkl), is used to specify the uniqueness of the c-axis in tetragonal lattice. The notation was introduced by Hug et.al.[17] as a convenience in describing lattice directions and planes in tetragonal TiAl.Google Scholar
[2] Yamaguchi, M. and Umakoshi, Y., Prog. Mat. Sci., 34, 1, (1990).Google Scholar
[3] Yang, Y.S. and Wu, S.K., Scripta Metall. Mater., 24, 1801, (1990); Ibid 25, 255, (1991).CrossRefGoogle Scholar
[4] Inui, H., Nakamura, A., Oh, M.M. and Yamaguchi, M., Ultramicroscopy, 39, 268, (1991).Google Scholar
[5] Kad, B.K. and Hazzledine, P.M., Philos. Mag. Letters 66, 133, (1992).Google Scholar
[6] Frank, F.C. and Merwe, J.H. Van der, Proc. Roy. Soc. A198, 216, (1949).Google Scholar
[7] Hazzledine, P.M., Kad, B.K., Fraser, H.L. and Dimiduk, D.M., in Intermetallic Matrix Composites, edited by Miracle, D.B., Anton, D.L. and Graves, J.A., (Mater. Res. Soc. Proc. 273, Pittsburg, PA 1992) pp 81.Google Scholar
[8] Appel, F., Christoph, U., Beaven, P.A. and Wagner, R., JIMIS-7, (1993).Google Scholar
[9] Inui, H., Oh, M., Nakamura, A. and Yamaguchi, M., Acta Metall. Mater. 40, 3095, (1992).CrossRefGoogle Scholar
[10] Umakoshi, Y. and Nakanao, T., Acta.Metall.Mater. 41, 1155, (1993).Google Scholar
[11] Hazzledine, P.M., Kad, B.K. and Mendiratta, M.G., in Thin Films: Stresses and Mechanical Properties IV, edited by Townsend, P.H., Weihs, T.P., Sanchez, J. Jr., and Borgesen, P., (Mater. Res. Soc. Proc. 308, Pittsburg, PA 1993) pp. 725.Google Scholar
[12] Nakano, T., Yokoyama, A., and Umakoshi, Y., Scripta Metall. Mater., 27, 1253, (1992).Google Scholar
[13] Vitek, V., Crystal Lattice Defects., 5, 1, (1974).Google Scholar
[14] Bollman, W., ‘Crystal Defects and Crystalline Interfaces’, Springer Verlag, New York, (1970).Google Scholar
[15] Rao, S., Woodward, C. and Parthasarathy, T.A., in High Temperature Ordered Intermetallic Alloys IV, edited by Johnson, L., Pope, D.P. and Stiegler, J.O., (Mater. Res. Soc. Proc. 213, Pittsburg, PA 1991) pp. 135.Google Scholar
[16] Daw, M.S. and Baskes, M.I., Phys.Rev.B 29, 6443, (1984).Google Scholar
[17] Hug, G. et al. , Phil Mag A, 57, 499 (1988); W.B.Pearson, ‘A Handbook of Lattice Spacings and Structure of Metals and Alloys - Vols 1 and 2’, Pergamon Press, Oxford(1987); and R.Hultgren, R.L.Orr, P.D.Anderson and K.K.Kelly, ‘Selected Values of Thermodynamic Properties of Binary Alloys’, John Wiley and Sons Inc., New York (1963)Google Scholar
[18] Fu, C.L. and Yoo, M.H., in Alloy Phase Stabilty and Design, edited by Stocks, G.M., Pope, D.P. and Gaimei, A.F., (Mater. Res. Soc. Proc. 186, Pittsburg, PA 1991) pp. 265.Google Scholar
[19] Woodward, C., Mclaren, J.M. and Rao, S., J.Mater Res., 7, 1735 (1992).CrossRefGoogle Scholar
[20] Freeman, A.J. et al. , private communication.Google Scholar
[21] Inui, H., Nakamura, A., Oh, M.H. and Yamaguchi, M., Proc. 1990 Tokyo Meeting Japan Inst. of Metals. Sendai: the Japan Inst. of Metals, p407 (1990).Google Scholar
[22] Simmons, J.P., Rao, S.I. and Dimiduk, D.M., in High Temperature Ordered Intermetallic Alloys V, edited by Baker, I., Darolia, R., Whittenberger, J.D. and Yoo, M.H., (Mater. Res. Soc. Proc. 288, Pittsburg, PA 1993) pp. 335.Google Scholar
[23] Simmons, J.P., Rao, S.I. and Dimiduk, D.M., to be published in Alloy Modelling and Design, edited by Stocks, G.M. et al. , TMS (1994).Google Scholar
[24] Simmons, J.P. et al. , to be submitted for publication in Phil.Mag.A (1994).Google Scholar
[25] Stroh, A.N., Phil.Mag. 3, 625 (1958).Google Scholar