Seria: NOMATEN Online Seminar

Prelegent i afiliacja: Prof. Sandy Knowles, University of Birmingham, UK

Data: February 25th, 2025, 1 PM

Miejsce: https://meet.goto.com/NCBJmeetings/nomaten-seminar

Streszczenie: Nuclear fusion and generation-IV fission reactor designs aim for operating temperatures in the range 500°C–1000°C. To optimise neutron efficiency, materials with low neutron cross section are sought for the fuel clad, or tritium breeding module. However, conventional zirconium alloys are precluded due to limited oxidation and creep performance at temperatures >400°C. Two approaches have been explored to meet the challenge of high temperature (HT) operation & low neutron cross section: (1) Novel Zirconium Alloys inspired by titanium metallurgy, (2) High entropy alloys.

(1) HT Zirconium alloys, exploiting the similarity in physical metallurgy between titanium and zirconium to make high temperature 500°C–800°C capable Zr alloys. These are based on the Zr-Al-Sn-(Si,Cr,V) system, designed by analogy to near-alpha titanium alloys, e.g. Ti-834. Using advanced microscopy and diffraction, microstructures akin to near-alpha Ti alloys have been demonstrated, specifically a lath grain structure with coherent Zr3Al and incoherent Zr-(Si,Cr,V) based precipitates. A key transformation sequence is described, involving continuous nanoscale precipitation of Zr3Al (D019) in a Zr (HCP) matrix, followed by discontinuous precipitation of Zr3Al (L12). Bending, tensile, and creep tests show greatly improved mechanical performance relative to conventional zirconium alloys. Further work is underway to evaluate the irradiation and environmental resistance of these alloys.

(2) High Entropy Alloys (HEAs) have greatly expanded the compositional design space for alloy design and are promising candidates for advanced nuclear applications due to their exceptional mechanical properties and irradiation damage resistance. This work investigates low density & low neutron cross-section refractory HEAs (RHEAs) for nuclear cladding/structural components. A high throughput computational screening tool, Alloy Search and Predict (ASAP), was used to identify promising RHEA candidates from over 15 million equimolar combinations, such as Zr-Ti-Nb-V type RHEAs. With Thermocalc and first principles modelling then used. Selected compositions were manufactured by arc-melting, thermomechanical deformation, and heat treatments. Techniques including SEM, EBSD, EDX, TEM and diffraction were used to characterise the alloys with a focus on thermal stability and any precipitate evolution, and to link this back to the computational predictions. Mechanical tests, from hardness to creep tests have been performed to evaluate the stability and structural integrity of RHEAs during prolonged reactor operation.