In-situ characterisation of plasticity in a cold spray chromium coating at 300 °C

The mechanical response of a cold sprayed chromium coating on a zirconium alloy cladding was studied at both room temperature and 300 °C by in-situ scanning electron microscope (SEM) tensile testing and high-resolution digital image correlation (HRDIC). The coating aims to improve the high temperature oxidation resistance of nuclear fuel assemblies in pressurised water reactors during loss-of-coolant accidents. However, its mechanical behaviour at the nominal operating temperature (~325 °C) must also be evaluated to ensure reliable performance throughout the cladding’s lifecycle. Under quasi-static tensile testing at room temperature, chromium exhibited brittle behaviour, with multiple long parallel cracks forming following little strain localisation, consistent with previous studies. However, at 300 °C the chromium coating showed significant crack resistance, with short and jagged micro-cracks forming instead of long ones. Additionally, distinct strain localisation was observed on the coating’s surface, manifesting as shear strain bands forming mostly at 45° and 135° to the loading direction (LD). The increased plastic deformation of chromium at 300 °C was quantified using nanoscale strain mapping with correlative electron backscattered diffraction and HRDIC. Subsequent slip trace analysis showed that slip in chromium occurs predominantly by either {110} <111> or {112} <111> slip.