Control of Laves Precipitation in a FeCrAl-based Alloy Through Severe Thermomechanical Processing

Abstract

In recent years, the development of nuclear grade FeCrAl-based alloys with enhanced accident tolerance has been carried out for light water reactor (LWR) fuel cladding to serve as a substitute for zirconium-based alloys. To achieve excellent microstructure stability and mechanical properties, the control of precipitation particles is critical for application of FeCrAl-based alloys. In this paper, the effect of thermomechanical processing on the microstructure and precipitation behavior of hot-rolled FeCrAl alloy plates was examined. After hot rolling, the FeCrAl alloy plates had typical deformation textures. The rolling direction (RD) orientation gradually rotated from <100> to <110> along with increasing reduction. Shear bands and cell structures were formed in the matrix, and the former acted as preferable nucleation sites for crystallization. Improved deformation helped to produce strain-induced precipitation. The plate with 83% reduction had the most homogeneous and finest precipitation particles. Identification results by TEM indicated that the Laves precipitation was of the Fe2Nb-type crystal structure type, with impurities including Mo, Cr, and Si. The plate with uniform Laves particles displayed favorable heat stability after a long period of aging at 800 °C. The microstructure evolution of the aged sample was also observed. The deformation microstructure and the strain-induced precipitation mechanism of FeCrAl alloys are discussed.

Effect of Rolling Deformation on Creep Properties of FeCrAl Alloys

“…The larger the rolling thickness reduction was, the more energy was provided to the crystal and the more grains completed the dynamic recrystallization process. Similar results were also found by Yamamoto et al, (2015) and Zheng et al, (2019). In addition, the tiny black dots were defects or inclusions which were produced during metallurgy.…”

Laves phase formation in Fe-based alloys from strengthening particle to self-healing agent: a review

“…According to the above, the thermomechanical treatment has a beneficial effect on the nucleation of Lavesphase since the precipitation on a dislocation decreases the associated free energy (equation ( 52)) due to the destruction of the defect ( mb r 0.4 , 2 with μ the shear modulus and b the Burgers vector), resulting in the reduction of the energy barrier for nucleation (equation ( 53)). In addition to the effect on the diffusion through dislocations, there is a notable increase in the nucleation rate for the Laves phase, so the application of the thermomechanical treatment would result in a finely dispersed Laves phase [141].…”