Oxidation behavior of RF magnetron sputtered Cr-SiC-Cr composites coating on zircaloy fuel cladding

Abstract

A three-layered Cr-SiC-Cr sandwich coating was deposited on the zircaloy cladding by RF magnetron sputtering to improve its oxidation resistance in high temperature steam environment. The microstructure and phase composition of the three-layered sandwich structure were confirmed by XRD, EDS, SEM and the glow discharge optical emission spectrometry (GD-OES) analyses, and the oxidation behavior was evaluated at 1200 °C for 2400 s. With an innermost Cr coating on zircaloy cladding, a uniform SiC layer was successfully deposited due to the good adherence of Cr with SiC and zircaloy substrates. The SiC layer was utilized to increase the mechanical strength/ stiffness of the composite coating, and to lower the plastic strain of innermost and outmost Cr layers. In turn, the two ductile Cr layers weakened the tensile and compressive stresses of SiC layer from swelling at high temperature. The results revealed that 1 μm Cr transition/innermost layer was thick enough to alleviate the deformation of the middle SiC layer in high temperature steam environment. The Cr-SiC-Cr coated zircaloy cladding with sequential 1 μm Cr, 1 μm SiC, and 2 μm Cr composites coating, exhibited excellent anti-oxidation property by forming dense and compact Cr2O3/SiO2 protective layers with weight gain of ∼43 mg dm-2, which is one-third of the uncoated zircaloy cladding.