Abnormal deformation behavior in Polysynthetically-twinned TiAl crystals with A and N orientations ---- an AFM study

Polysynthetically-twinned TiAl crystals were deformed by compression with loading axis parallel and perpendicular to the lamellar interfaces. The deformation structures on the free surfaces were scanned using a dimension AFM with scan directions parallel and perpendicular to the lamellar interfaces. Abnormal deformation behaviors were observed to occur in both orientations. When the compression axis is parallel to the lamellar interfaces, the gamma and alpha lamellae deform primarily by shear in planes inclined with the lamellar interface, while the shear vectors lie in the interface. However, in-plane shear, shear in slip planes parallel to the lamellar interfaces, also occurs along the lamellar interfaces. When the loading axis is perpendicular to the lamellar interface, in-plane shear was found to be dominant at the beginning stage of plastic deformation and contributes more to the macroscopic strain. These behaviors are controversial to the Schmid’s Law since the applied resolved shear stress for these deformation systems is zero. The abnormal phenomenon was explained by the large coherency stresses along the lamellar interfaces. Comments Copyright Materials Research Society. Reprinted from MRS Proceedings Volume 842. 2005 Integrative and Interdisciplinary Aspects of Intermetallics. Symposium Materials Research Society Symposium Proceedings Publisher URL: http://www.mrs.org/s_mrs/sec_subscribe.asp?CID=2702&DID=115609&action=detail This conference paper is available at ScholarlyCommons: http://repository.upenn.edu/mse_papers/93 Abnormal deformation behavior in Polysynthetically-twinned TiAl crystals with A and N orientations─── an AFM study Yali Chen and David P. Pope Department of Materials Science and Engineering, University of Pennsylvania Philadelphia, PA 19104-6272, U.S.A