Deformed microstructures of two-phase Zr-2.5Nb alloy: Effects of the second phase hardness

Two types, A and B, of Zr-2.5Nb samples were subjected to compression tests. Both samples consisted of similar microstructure - hexagonal closed packed (hcp) α phase (the primary phase) and grain boundary bcc (body centered cubic) β phase. However, the hardness of the β phase differed between the samples - respectively being hard (sample A) and soft (sample B) relative to the primary phase. This difference was caused by the presence of fine ω precipitates. The relative hardness of β phase determined almost all aspects of deformed microstructure developments. In sample A, the primary phase had higher lattice strain and in-grain misorientation developments. In sample B, on the other hand, the softer β phase was clearly linked to more deformation twinning and associated grain size refinement and 'texturing' of the hcp α phase.