Structure and Corrosion Resistance of Zr–1% Nb and Zr–2.5% Nb Alloys after Equal-Channel Angular Pressing

Equal-channel angular pressing (ECAP) technique induces two simultaneous processes in commercial zirconium (Zr) alloys with low (1%) and high (2.5%) niobium content (Nb): grain refinement and deformation-induced phase transformation. The grain refinement reduces the grain size to the sub-micro scale through increasing the grain boundary (or grain perimeter). The structural elements size is reduced to 169 nm for Zr–1% Nb and to 185 nm for Zr–2.5% Nb. During the phase transformation, β-Nb precipitates dissolve in α-Zr matrix to form a supersaturated solution. To demonstrate the effects of those processes on pitting resistance of zirconium alloys before and after ECAP, cyclic potentiodynamic polarization tests in a chloride-containing solution (Ringer) were performed. The results revealed that the corrosion rate (corrosion current density) decreased for nanostructured zirconium alloys, enhancing the corrosion resistance after ECAP. However, the phase transformation induced during ECAP reduced passivity and pitting resistance to chloride ions in alloys with low Nb content. In contrast, no significant change was observed during the two-phase to single phase transformation in high Zr–Nb alloys.