CLF-1钢预氧化层的制备及其氢同位素渗透行为OA

Reduced activation ferritic/martensitic(RAFM)steels,such as the CLF-1 steel developed by China,are primary candidate structural materials for the tritium breeding blankets of future nuclear fusion reactors.However,their inherent high hydrogen isotope permeability and significant tritium retention pose critical challenges to fuel self-sufficiency and radiological safety.While dedicated barrier coatings are highly effective,tailored pre-oxidation treatment presents a viable,cost-effective,and procedurally simple synergistic protective strategy that offers excellent thermodynamic compatibility,especially for complex internal components.Furthermore,during actual reactor operation,components are exposed to extremely low oxygen partial pressures rather than ambient air.Therefore,the work aims to systematically investigate the microstructural evolution and deuterium permeation behavior of pre-oxidation layers formed on CLF-1 steel under both oxygen-rich and simulated low oxygen potential environments,so as to elucidate the underlying mitigation mechanisms. CLF-1 steel samples were subjected to varied pre-oxidation treatments at temperatures ranging from 400 to 800℃for durations of 2,10,and 24 hours under atmospheric air and argon environments.The phase compositions,surface and cross-sectional microstructures,and elemental distributions of the resultant oxide films were extensively characterized through X-ray diffraction,field emission scanning electron microscopy,and energy-dispersive X-ray spectroscopy.Subsequently,macroscopic deuterium permeation kinetics were evaluated with a high-temperature gas-driven permeation platform at testing temperatures of 400-500℃.Key kinetic parameters,including the permeation reduction factor,permeation activation energy,and the pre-exponential factor,were quantitatively derived to assess the inhibition efficacy. The structural architecture and subsequent permeation inhibition efficacy of the pre-oxidation layers were jointly dictated by the oxygen partial pressure and the oxidation temperature.Under oxygen-rich conditions at moderate temperatures(400-700℃),a continuous and dense Cr2O3 protective layer preferentially formed.The optimal sample synthesized at 700℃for 2 hours achieved a maximum PRF of 5,accompanied by an increase in the permeation activation energy from 36.37 kJ/mol(bare substrate)to 42.55 kJ/mol,confirming that the dense Cr2O3 lattice introduced an additional energy barrier that effectively impeded the bulk diffusion of deuterium atoms.Conversely,when the oxidation temperature reached 800℃in air,the high mobility of Fe cations in the oxide lattice and the absolute concentration advantage of Fe in the substrate led to the rapid dominant growth of Fe-based oxides.The substantial mismatch in the Pilling-Bedworth ratio between the iron oxides and the substrate,coupled with accumulated thermal stresses during cooling,induced severe multi-layer transverse cracking and massive spalling,rendering the layer entirely ineffective as a permeation barrier. Under trace oxygen conditions simulated by high-purity argon,the severely restricted oxygen flux fundamentally altered the oxidation kinetics.At lower temperatures,the insufficient lateral growth of initial oxide and the rapid outward diffusion of Fe cations resulted in significant vacancy coalescence,producing highly porous layers.However,at 800℃,the increase in Cr bulk diffusion facilitated the formation of a robust double-layer architecture comprising an outer Fe-rich passivation layer(Fe3O4)and an inner Cr-rich spinel layer(FeCr2O4)with a thickness of approximately 20 μm after 24 hours.Remarkably,the sample annealed at 800℃for 2 h exhibited superior barrier performance,yielding a PRF of 11.Moreover,macroscopic kinetic analyses revealed a drastic plunge in the pre-exponential factor and a sharp decrease in the activation energy to 17.75 kJ/mol. Pre-oxidation treatments significantly alter the surface chemistry and hydrogen isotope permeability of CLF-1 steel.While moderate-temperature air oxidation mitigates permeation by elevating the bulk diffusion barrier via a Cr2O3 film,high-temperature oxidation under low oxygen partial pressures realizes enhanced inhibition by the combined effect of a tiny number of internal microscopic and the Fe3O4/FeCr2O4 composite layer defects inhibits deuterium penetration.This work establishes a mechanistic framework for the microstructural evolution of RAFM steels under diverse oxygen potentials and validates the engineering applicability of tailored pre-oxidation as an effective tritium permeation barrier strategy for fusion reactor components.