Fracture and fatigue of Nb alloys and composites

The flow and fracture of engineering materials is controlled by microstructural features as well as the imposed stress state. This paper reviews ongoing work on a number of Nb based systems where the effects of systematic changes in microstructure and stress state on the flow, fracture, and fatigue behavior are being determined. Experiments utilizing notched and fatigue precracked specimens, as well as smooth specimens tested over a range of temperatures from 77K to 773K are described. In-situ fracture experiments conducted inside a scanning electron microscope are also described in order to delineate the sequence of deformation and fracture events occurring in both intermetallic and metallic glass composites, which utilize Nb or a Nb phase as a toughening constituent. In particular, Nb-Nb Silicide composites will be covered and a comparison to the behavior of some other high temperature systems will be provided to highlight some of the potential benefits and problems provided by using Nb/Nb alloys as a toughening constituent. The paper concludes with a summary of more recent work where Nb/Nb alloys have been used to beneficially change the properties of bulk metallic glasses. (AU)