High temperature zirconium alloys Zr-Al-Sn-(Si,Cr,V) by near-α titanium analogy

The use of conventional zirconium alloys at temperatures above 400 °C is limited by high temperature strength and creep resistance. This has prevented the consideration of zirconium alloys for fusion and Generation IV fission plant designs operating at 500 °C–1000 °C. The physical metallurgy of zirconium is similar to titanium which has seen alloying advances allowing application temperatures up to 600 °C. Although the oxidation resistance of zirconium-based alloys is expected to be poor, in a water environment, new Generation-IV and fusion reactors are designed to operate using alternative coolants such as liquid metals and molten salts. Therefore, a new class of zirconium alloys in the Zr-Al-Sn-(Si,Cr,V) system, designed by analogy to near-α titanium alloys, were synthesised by arc melting and processed in a sequence of homogenisation, hot/cold rolling, recrystallisation, and ageing treatments. Microscopy and diffraction identified a refined fully lath grain structure reinforced by nanoscale lamellar or discrete coherent Zr₃Al precipitates, with morphology and crystal structure differing with ageing times. Additionally alloying with Si, Cr, and V respectively leads to Zr₂Si, ZrCr₂, and ZrV₂ incoherent precipitates. Tensile testing revealed a strengthening effect by Al, but with significant changes to ductility on ageing depending on the evolution of Zr3Al. Creep testing showed creep rates orders of magnitude better than conventional Zircaloy-4 and nuclear ferritic/martensitic steels, approaching near-α Ti alloys. The present work offers new insights and perspectives into how high-temperature zirconium alloys might be designed to meet the requirements for fusion and Gen-IV fission.