Microstructure characterisation and mechanical behaviour of spark plasma sintered FeCrAl-Y2O3-Ti ODS alloys for nuclear applications

<ns3:p>The paper examines mechanically alloyed and spark plasma sintered FeCrAl-based ODS alloys with different amounts of titanium additions in terms of their potential application in gas-cooled fast nuclear reactors (GFRs). The research aims to elucidate how Ti addition influences the alloys’ microstructural properties and focuses on the microstructural stability characterisation and mechanical properties evaluation of the FeCrAl-ODS alloys at high temperatures up to 800C.In the given study, two compositions of FeCrAl ODS alloys with fixed 9% chromium, 5% aluminium, 0.3% yttrium oxide, and different titanium additions 0.5% and 1%, were mechanically alloyed (MA). The powders were then consolidated via spark plasma sintering (SPS) technique at 1050C, 40 MPa for 10 minutes and finally annealed at 1020C for 30 minutes. The resulting bulk materials were characterised for their microstructure and chemical composition using SEM-EDS and EBSD. Density measurements were conducted using Archimedes’ principle, while mechanical properties were evaluated through Vickers microhardness tests and tensile testing of the miniaturised samples in the range from RT to 800C.The successfully synthesised FeCrAl-Y2O3-Ti ODS alloys achieved a density of approximately 96% and a fine α-ferrite microstructure with most grains under 1 μm. Microstructural analysis revealed α-ferrite grains and the presence of nano- and micro-scale oxide and carbide precipitates. These are expected to stabilise the microstructure and enhance high strength at creep conditions and radiation resistance. Due to mechanical alloying, the crystallite size significantly decreased to about 50 nm, indicating adequate processing conditions. Additionally, the addition of titanium was found to improve the formation of complex oxides and carbides. Moreover, samples with a higher Ti content showed a higher ultimate tensile strength and yield strength at temperatures up to 500C than those with a lower Ti content. Therefore, it seems that Ti positively impacts the strength of the FeCrAl-Y2O3-Ti ODS alloys, and it is entirely consistent with the hardness results that also reveal higher hardness of the sample with higher Ti content.In FeCrAl-Y2O3-Ti ODS alloys, the oxide particles in the matrix should also significantly reduce the effect of ageing embrittlement at elevated temperatures and improve the stability of the microstructure by reducing grain growth under high-temperature operating conditions, thereby positively affecting the strength of the alloys. The results confirmed the homogeneous distribution of complex nanoscale oxide particles and thus improved mechanical properties. Notably, yield strength and tensile strength decrease with increasing test temperature, which was expected, and for samples above 500C and up to 800C, yield strength and tensile strength are almost the same (within the limits of measurement error). Plastic deformation at fracture is similar in both samples (about 10%) up to 500C. Above 600C, plastic deformation generally increases with increasing test temperature, up to about 50% for samples with lower Ti content at 750C. Although both samples show similar strength in the temperature range from 500C to 800C, the higher Ti content appears to reduce ductility.The main research primarily involved the development of new samples of FeCrAl-based materials with yttrium and titanium oxide additives to assess the feasibility of the designated alloys and their processing for further use in Generation IV reactor technologies. The results suggest that the application of the oxide dispersion enhancement effect can significantly increase the strength of FeCrAl alloys, thus qualifying them as materials potentially suitable for the manufacturing of components and subassemblies used under extreme operating conditions in high-temperature or gas-cooled fast nuclear reactors, including, for example, fuel claddings and hot ducts elements.Oxide dispersion strengthened (ODS) alloys, especially those based on FeCrAl, are recognised for their superior high-temperature strength and irradiation resistance, making them promising candidates for structural components in Generation IV nuclear reactors. Despite their potential, detailed experimental data on their mechanical behaviour at elevated temperatures remain limited, particularly for alloys processed by mechanical alloying and spark plasma sintering (SPS). The study provides new insights into the microstructural characteristics and high-temperature mechanical performance (up to 800 C) of miniaturised FeCrAl–Y2O3–Ti ODS alloy specimens. The originality lies in the specific combination of alloy composition, processing route, and advanced testing methodology, enabling the initial verification of the material’s behaviour under its intended operating conditions. The results contribute to a deeper understanding of how such materials perform in environments relevant to advanced nuclear systems, thus supporting the future application of ODS alloy components.</ns3:p>