The Effect of Cooling Rate on Microstructure and Mechanical Properties of the Zr-4Hf-3Nb (wt%) Alloy

Abstract

The mechanical properties of Zr-based alloys, such as strength and elongation, are heavily dependent on the cooling rate during heat treatment. Understanding the phase transformation and microstructural evolution in various cooling media can establish the connection between the cooling rate and mechanical properties. The effect of the cooling rate on the phase, microstructure, and tensile properties of Zr-4Hf-3Nb (wt%) alloy is studied in this paper. The results show that the phase composition of the samples transforms from α+β to α+β+ω, and, finally, to α+α’+ω, while the average grain size of α phase decreases from 3.73 μm to 1.96 μm, and the distribution varies from compact to scattering as the cooling rate increases. Hf tends to distribute in β phase, and the slower cooling rate is beneficial to the existence of Hf. The strength and microhardness enhances monotonously, while the elongation ascends first, then decreases as the cooling rate increases. The high strength of water-cooling samples is attributed to the reduction in average grain size and volume fraction of α phase, and the lath α’ martensite and granular ω phase. The fracture pattern of Zr-4Hf-3Nb (wt%) alloy is ductile fracture, and the plasticity gets better with decreasing cooling rate.

The Effect of Cooling Rate on Crystallographic Features of Phase Transformations in Zr-2.5Nb

“…In general, the obtained results of the microstructure characteristics align with the findings from [ 14 , 25 , 26 ]. Some discrepancies, such as differences in alloy chemical compositions, may be attributed to the variation in experimental conditions [ 14 , 26 ], such as the superheating temperature during ST [ 25 ] and annealing in the capsule [ 14 , 25 ].…”

“…In general, the obtained results of the microstructure characteristics align with the findings from [ 14 , 25 , 26 ]. Some discrepancies, such as differences in alloy chemical compositions, may be attributed to the variation in experimental conditions [ 14 , 26 ], such as the superheating temperature during ST [ 25 ] and annealing in the capsule [ 14 , 25 ]. These factors influence both the actual cooling rates and the critical cooling rates, which affect the kinetics of the transformation processes and the size and morphology of the α(α′)-phase crystallites.…”

“…Nuclear reactor technologies are progressing towards fuel conservation, reduced fuel cycle costs, and enhanced reactor safety and reliability. Consequently, higher performance characteristics are demanded for Zr alloys used as fuel rod cladding materials in radiation zones [ 3 , 13 , 14 , 15 ]. Ongoing research into the development of Zr alloys and optimization of their microstructure addresses several key challenges: controlling radiation growth [ 4 , 16 ], increasing corrosion resistance [ 2 , 3 , 6 , 7 ], and reducing hydrogen absorption [ 2 , 3 ].…”

“…Manufacturing zirconium alloy components for nuclear reactors involves numerous thermomechanical treatments, with the resulting microstructure determining the product’s long-term and short-term properties [ 13 ]. The microstructure of Zr alloys, including local and integral texture states, crucially affects functional properties, prompting research into obtaining various microstructures through heat treatments, primarily by altering cooling rates from the β-region [ 14 , 25 , 26 ].…”

“…In [ 14 ], the influence of the microstructure on the mechanical properties is analyzed for the Zr-4Hf-3Nb alloy. It was shown how an increase in the cooling rate changes the mechanism of phase transformation (β→α, ω, α′) due to the refinement of the microstructure and reduction of the fraction of β-phase precipitates with a change in its chemical composition.…”