Evolution of microstructure and crystallographic texture in a novel Zr-4Nb-2Al alloy during hot rotary swaging

Overview & Synopsis

A multi-step induction-assisted hot rotary swaging route was developed for the novel dual-phase Zr-4Nb-2Al alloy to investigate the evolution of microstructure, crystallographic texture, and mechanical properties during sequential deformation. Phase-transformation temperatures determined by electrical resistivity measurements were used to select processing conditions in the single-phase $β$ field at 880°C and the $α+β$ field at 780°C. Induction heating with thermographic temperature control enabled reduction of the initial 12 mm rod to 6.3 mm, corresponding to a total area reduction of 72%. Swaging in the $β$ field refined millimetre-sized prior-$β$ grains to approximately 100 $μ$m, while subsequent cooling produced a fine lamellar $α+β$ microstructure. Further deformation in the $α+β$ field disrupted the lamellar structure, promoted globularisation and recrystallisation of the $α$ phase, and refined the $β$ phase. The microstructural evolution was accompanied by a pronounced $\langle 11\bar{2}0\rangle_α\parallel\mathrm{SD}$ fibre texture in the $α$ phase, whereas the $β$ phase exhibited predominantly $\langle 110\rangle_β\parallel\mathrm{SD}$ together with a $\langle 111\rangle_β\parallel\mathrm{SD}$ component. The phase constitution remained comparatively stable, with approximately 12-15 wt.% retained $β$ throughout processing. Subsequent $α+β$ swaging decreased the compressive yield strength from 1103 to 839 MPa while increasing plastic deformability, with a maximum fracture strain of 32%. Radial hardness heterogeneity was progressively eliminated. These results demonstrate that induction-assisted rotary swaging in selected phase fields provides an effective route for tailoring microstructure, texture, and mechanical response in dual-phase zirconium alloys.