Oriented nucleation and selective growth dependence on annealing temperature for Nb521Y alloy

Abstract

Niobium (Nb) is a candidate material for heat pipes in space nuclear reactors, and it would suffer recrystallization when used at high temperatures. Usually, recrystallization is accompanied by texture evolution, which is related to mechanical properties and irradiation resistance. Thus, it's necessary to evaluate the texture evolution mechanism during recrystallization. In this work, a deformed Nb alloy named Nb521Y with 70 % reduction was annealed at 1100, 1150, 1200, 1250, 1300, 1350, and 1400 °C for 1 h, and then the recrystallization temperature was determined as 1300 °C. During annealing, oriented nucleation and selective growth occurred, both of which exhibited a temperature dependence. Recrystallization nucleation occurs via strain-induced boundary migration and sub-grain coalescence, initiating at deformed grain boundaries and sub-grain networks. The deformed Nb521Y presented {001} 〈110〉, {112}〈110〉, especially {111}〈110〉 textures. Oriented nucleation of {111} 〈112〉, {110} 〈100〉, and {001}〈110〉 occurred, and the latter two were nucleated until temperatures were above 1150 °C. After 1250 °C annealing, selective growth of {111}〈112〉, {225}〈5–54〉and {115} 〈–3–72〉occurred in sequence. After 1300 °C annealing, selective growth of {111}〈112〉 also occurred firstly then growth of {110}〈100〉 and {331} 〈1−10〉 from {111}〈112〉took place. Selective growth sequence and its dependence on annealing temperature were related to misorientation angles, of which close to 30° were preferred to grow at lower temperatures.