Comparative study on thermal creep resistance of arc ion plated and magnetron sputtered Cr coatings on Zircaloy-4 cladding for accident tolerant fuel

Abstract

The development of accident tolerant fuel (ATF) claddings, particularly coating techniques, has been encouraged to address the urgent need for improved safety measures. Using the two prominent coating technologies—that is, arc ion plating (AIP) and magnetron sputtering (MS)—pure Cr was coated on Zry-4 claddings, and the effect of the Cr coating on low temperature (≤400 °C) creep behavior was investigated. Moreover, their mechanical performance was compared based on the coating method. Creep tests conducted using internal pressurization methods under constant hoop stresses revealed that the AIP Cr coatings reduced the total creep strain by approximately 43–60 %, whereas the MS Cr coatings exhibited an 18–33 % reduction. These improvements on the creep resistance were attributed to the high elastic modulus and limited plasticity of the Cr layer as well as the compressive residual stresses induced during the deposition process. However, ring compression tests (RCTs) performed after creep deformation showed that the residual ductility, characterized by offset strain, decreased in Cr-coated claddings, most notably in the MS Cr-coated specimens, owing to the intrinsic brittleness of the Cr layer. Experimental findings on thermal creep behaviors suggest that while Cr coatings significantly improved the creep resistance and delay gap closure, their mechanical integrity under irradiation and pellet-to-cladding mechanical interaction conditions must be carefully assessed to ensure long–term fuel performance in ATF systems.