Effects of long-time annealing on the microstructures and shear tensile strengths of diffusion-bonded FeCrAl/N18 clad plates

Abstract

FeCrAl/N18 clad plates were fabricated by solid-state diffusion. The clad plates were hot rolled, and then annealed under vacuum at 800 °C for 480 h. The microstructures and shear tensile strengths of the obtained FeCrAl/N18 clad plates were subsequently investigated. It was found that after annealing, the three samples at the interface were composed of Zr(Cr, Fe)2, Zr3Al, and Zr2Fe phases, as identified by electron probe X-ray microanalysis (EPMA). Transmission electron microscopy (TEM) observations showed that FCC-ZrFe2, Laves phase-ZrFe2, FCC-Fe2(Zr, Nb), and amorphous phases were formed at the diffusion interface. In addition, the diffusion layers thickness of FeCrAl/N18 clad plates with 20, 30 and 50% rolling reduction was 6.5 ± 0.5, 7.0 ± 0.5, and 11.0 ± 0.5 μm, respectively, and the corresponding shear strength was 215, 214, and 317 MPa. Furthermore, the shear strength of the sample with a 50% rolling reduction annealed at 800 °C for a shorter time of 240 h was 310 MPa. It was found that longer annealing times results in the shear strengths initially increasing significantly, prior to reaching to a stable value. The results will be expected to provide possible valuable guidance for the preparation of multilayer fuel cladding materials for nuclear reactor.

Keywords

• FeCrAl alloy
• N18 alloy
• Diffusion
• Annealing
• Microstructure
• Shear tensile strength