Novel In Situ Nanostructure-Dendrite Composites in Zr-Base Multicomponent Alloy System

Abstract The evolution of a nanostructure-dendrite composite microstructure of two Zr-base alloys solidified through different casting routes is presented. The alloys were designed by adding different amounts of Nb to the Zr-based multicomponent glass-forming alloy system. The refractory metal Nb promotes the formation of a primary phase having dendritic morphology, whereas the residual melt solidifies to a nanostructured/amorphous matrix. The volume fraction and the morphology of the dendritic phase varied with the Nb content and the adopted casting route. A correlation between the alloy composition and adopted casting method with evolved microstructures and mechanical properties is revealed. These composites exhibit a unique combination of high fracture strength up to 1922 Mpa, as well as plastic strain over 15.8% under uniaxial compression testing at room temperature. The high strength of these composites is imparted by the nanostructured matrix, whereas the large plastic strain is a consequence of the retardation of excessive localized shear banding in the matrix by ductile dendrites. The significant work hardening of the composites prior to fracture is attributed to dislocation multiplication in the solid solution-strengthened dendritic phase. Keywords: Zr-based BMGCompositeMicrostructureNanostructureDendriteSecondary arms spacingCasting routeCooling rateYoung's modulusYield stressUltimate compressive stressPlastic strainStrain hardening exponentFracture strainShear banding Acknowledgments The authors want to thank M. Frey, H. Grahl, R. Günther, G. He, H. Kempe, U. Kühn, G. Kumar, H. G. Lindenkreuz, A. Güth, H. J. Klaus, C. Mickel, and M. Stoica for providing technical assistance and stimulating discussions. One of the authors, J. Das, is grateful for the financial support provided by Deautcher Akadmicher Austauschdienst (DAAD) to carry out this investigation at the IFW Dresden.