Microscopic deformation mechanism of a Ti66.1Nb13.9Ni4.8Cu8Sn7.2 nanostructure–dendrite composite

Systematic investigations of the microstructural changes upon compression have been performed in order to elucidate the microscopic deformation mechanisms of the high-strength and ductile Ti66.1Nb13.9Ni4.8Cu8Sn7.2 nanostructure-dendrite composite. After 8% deformation, a rotation of beta-Ti dendrites is observed during the interaction of slip and shear bands. This rotation leads to the formation of new slip bands in the dendrites. The beta-Ti dendrites locally transform into omega phase during the interaction between the newly and the previously formed slip bands. The rotation of the dendrites causes local volume changes at the interfacial areas between the dendrites and the matrix, consisting of a mixture of hexagonal close-packed alpha-Ti and body-centered tetragonal Ti2Cu phases. This induces a rotational stress into the nanostructured matrix. After further deformation up to 25%, the shear bands penetrate the dendrite/matrix interfaces, producing extra interfaces. The nanostructured matrix exhibits a sandwiched microstructure in order to accommodate effectively the shear strains. These results suggest that structural coherency of the dendrite/matrix interfaces is important for controlling both the strength and the ductility of the nanostructure-dendrite composite. (c) 2006 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.