Microstructure and room temperature deformation of Nb-ss/Nb5Si3 in situ composites alloyed with Mo

Room temperature deformation behavior of Nb5Si3 based intermetallics in the ternary Nb-Si-Mo alloy system is investigated by compression testing in re lation to microstructure and compositional effect. The partial ternary phas e diagram of the Nb-Si-Mo alloy system containing phase equilibrium informa tion at 1973 K is determined by metallography, X-ray diffraction and scanni ng electron microscopy (SEM) equipped with wavelength-dispersive X-ray fluo rescence spectroscopy (WDS). A pseudo-binary compound of Nb5Si3-Mo5Si3 is c onfirmed to form at Nb5Si3-rich compositions by Mo addition, without having a solubility range of Si. The phase transformation from alpha -Nb5Si3 to b eta -Nb5Si3 is found to occur at about 5 at.% of Mo content on the Nb5Si3-M o5Si3 pseudo-binary line. The observed yield stresses are largely dependent on not only the volume fraction and morphology of constituent phases but a lso the strength of Nb5Si3 phase equilibrating with Nb solid solution. The in situ composites consisting of alpha -Nb5Si3 phase and bcc solid solution exhibit higher yield stress than those consisting of beta -Nb5Si3 phase an d bcc solid solution when yield stress is compared at the same volume fract ion of bcc phase. It is suggested that room temperature deformability of be ta -Nb5Si3 is superior to that of alpha -Nb5Si3 phase. Room temperature def ormation behavior of the present composites will be discussed in relation t o microstructural evolution. (C) 2001 Elsevier Science Ltd. All rights rese rved.