Slip Transfer Across Hetero-Interfaces in Two-Phase Titanium Aluminum Intermetallics
- PDF / 638,257 Bytes
- 8 Pages / 593.972 x 792 pts Page_size
- 21 Downloads / 157 Views
I.
INTRODUCTION
TWO-PHASE TiAl-based intermetallics with a slightly Ti-rich composition (e.g., Ti-48 at pct Al) with microstructures containing large volume fractions of morphologically lamellar grains are promising candidate materials for applications in advanced gas-turbine engines.[1,2] They contain a hexagonal ordered phase a2-Ti3Al with a DO19 structure, which is a minor constituent, and a primitive tetragonal L10-ordered c-TiAl phase, which is the major constituent. However, the widespread use of these alloys is hindered by the limited tensile elongation to failure and problems with cracking during metallurgical processing by forging, for instance. Hence, it is important to develop a detailed understanding of the deformation behavior of the constituent phases c-TiAl and a2-Ti3Al, as well as the interplay between them during plastic straining. The basic deformation accommodating processes in the two phases (i.e., relevant dislocation glide and mechanical twinning) are understood reasonably well.[2–9] However, the synergistic interplay between the deformation processes active in the c and a2 phases in lamellar TiAl requires further attention because for general plasticity of the technologically important polycrystalline materials, both phases must deform compatibly across the heterophase interfaces. The L10-ordered tetragonal c-TiAl phase with a small volume fraction of lamellae of the DO19-ordered JO¨RG M.K. WIEZOREK, Professor, and ANDREAS KULOVITS, Doctor, are with the Department of Mechanical Engineering and Materials Science, Swanson School of Engineering, University of Pittsburgh, Pittsburgh, PA 15260. Contact e-mail: [email protected] XIAO-DONG ZHANG, Doctor, Senior Research Scientist, is with the Center for Materials Science, Bose Corporation, Framingham, MA 01701. HAMISH. L. FRASER, Professor, is with the Department of Materials Science & Engineering, The Ohio State University, Columbus, OH 43210. Manuscript submitted December 21, 2009. Article published online June 12, 2010 METALLURGICAL AND MATERIALS TRANSACTIONS A
hexagonal a2-Ti3Al phase obeys the following crystallographic orientation relationship such that[3]: 110 c 1120 a2 and ð111Þc kð0001Þa2 For the c lamellae, six orientation variants are related by multiple 60 deg rotations around the common lamellar interface normal [111] and coexist with the a2 lamellae, which form crystallographically equivalent heterophase interfaces with each of the c phase variant lamellae[3] (Figure 1). The anisotropic mechanical properties associated with the lamellar grains are well documented in the literature and have been studied from a fundamental point of view using directionally solidified material comprising only a single lamellar grain, so-called polysynthetically twinned TiAl (PST-TiAl).[2,3] The yield strength of PST-TiAl is very high for loading normal to the lamellar interface plane, is still high for loading parallel to the interface plane, and is much lower for intermediate orientations of the loading direction relative to the lamellar interf
Data Loading...
