Interfacial Dislocations and Deformation Twinning in Fully Lamellar TiAl
Deformation twinning, which takes place abnormally within lamellar TiAl subjected to creep deformation at strain rates as low as 10{sup -7}, has been found to be intimately related to the motion, pileup and dissociation of interfacial (Shockley partial) dislocations. In this study, results of in-situ TEM observations are presented to verify the motion and pileup of interfacial dislocations. Since the interfacial (Shockley partial) dislocations are energetically unfavorable to undergo cross-slip or climb, under normal conditions they can only move conservatively along interfaces. Consequently, the pileup configuration once generated cannot be easily dissipated and thus remain in place even at elevated temperatures.The dislocation pileup eventually leads to the emission of deformation twins from the interfaces into {gamma} lamellae when a local stress concentration due to the dislocation pileup becomes so great. Deformation twinning of {l_brace}111{r_brace}<11{bar 2}>- and {l_brace}11{bar 2}{r_brace}<111>-type (both generate {Sigma}3 twin boundaries) have been observed. Both types of twinning can be rationalized by dislocation mechanisms involving the core dissociation of interfacial dislocations: 1/6[{bar 1}2{bar 1}]{sub (111)} {yields} 1/6[011]{sub (100)} + 1/6[{bar 1}1{bar 2}]{sub ({bar 1}11)} and 1/6[1{bar 2}1]{sub (111)} {yields} {_}[0{bar 1}0]{sub (001)} + 1/6[111]{sub (11{bar 2})}, and the emission of 1/6<{bar 1}1{bar 2}> and 1/6<111> twinning dislocations into {gamma} lamellae to form the ({bar 1}11)[{bar 1}1{bar 2}]- and (11{bar 2})[111]-type twins, respectively. The critical shear stress for the {l_brace}111{r_brace}<11{bar 2}>-type twinning is evaluated using Peach-Koehler formula based upon the pileup configuration of interfacial dislocations.
- Research Organization:
- Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)
- Sponsoring Organization:
- USDOE Office of Defense Programs (DP) (US)
- DOE Contract Number:
- W-7405-Eng-48
- OSTI ID:
- 792728
- Report Number(s):
- UCRL-JC-137471; TRN: US200223%%884
- Resource Relation:
- Journal Volume: 329-331; Conference: 5th International Conference on Structural and Functional Intermetallics, Vancouver, British Columbia (CA), 07/16/2000--07/20/2000; Other Information: PBD: 13 Jul 2000
- Country of Publication:
- United States
- Language:
- English
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