In situ formed Ti-Cu-Ni-Sn-Ta nanostructure-dendrite composite with large plasticity

A group of Ti-Cu-Ni-Sn-Ta multicomponent alloys is prepared by copper mold casting and arc melting, respectively, in which nanostructured (or ultrafine-grained) matrix-dendrite composites can be obtained. With increasing Ti and Ta contents, the volume fraction of the dendritic phase increases. The grain size of the matrix phase depends on the preparation method, and is 30-70 nm for as-cast 2-3 mm diameter cylinders and about 100-200 nm for the as-arc melted samples. Compression test results indicate that fully nanostructured samples exhibit very high yield strength of 1800 MPa with a limited plastic strain of 1.4%. The nanostructured-dendrite composites exhibit high yield strengths of 1525-1755 MPa together with large plastic strains of 4.7-6.0%. The as-arc melted samples exhibit relatively lower yield strengths of 1037-1073 MPa with very large plastic strains of 16.5-17.9% because of the coarser grain size of the matrix. The large plasticity of the composites is attributed to the retardation of localized shear banding and the excessive deformation in the nanostructured matrix due to the in situ formed dendrites. The deformation and the fracture mechanisms of the nanostructure-dendrite composites are discussed based on fractography observations. (C) 2003 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.