Effects of hot rolling temperature and aging on the second phase particles of Zr-Sn-Nb-Fe zirconium alloy

Highlights: • The effect of increasing hot rolling temperature is to making the second phase particles(SPPs) grow larger, the distribution of the SPPs more non-uniform, the number of β-Nb particles increase and the average Nb/Fe ratio of Zr-Nb-Fe particles increase firstly and then decrease. • The effects of ageing time during processing is to leading to the mean diameter of SPPs become larger and reduce of Nb/Fe ratio further. • The hot rolling temperature is generally higher than 650℃ in industry production, while the research shows that the lower hot rolling temperature(620℃) is beneficial to the alloy, which can be used as the experimental basis for the improvement of hot rolling process. -- Abstract: Various processes were used to prepare Zr-0.4Sn-1Nb-0.3Fe zirconium alloy plate samples, including hot rolling at 620,650,700℃ without aging and hot rolling at 700℃ after aging with 10 and 50 h at 480℃, respectively. The second phase particles (SPPs) of Zr-0.4Sn-1Nb-0.3Fe zirconium alloy were investigated by SEM and TEM. The results show that the mean diameter of SPPs is within 100 nm under different process conditions. Homogeneous and fine secondary phases distribute dispersively at 620℃, and most of these SPPs are Zr(Nb,Fe)₂ with a C14 hexagonal close packed (HCP) structure. When hot rolling at 650℃, the β-Nb precipitates are also observed in addition to Zr(Nb,Fe)₂ particles, and the distribution of SPPs is bunching and clustering. As the hot rolling temperature increases to 700℃, the SPPs present in a wide variety of sizes and non-uniform distribution, and the number of β-Nb particles increases. Aging prior to hot rolling is helpful to improve the uniform distribution of SPPs, as the aging time extends, the mean diameter of SPPs becomes larger. With the increase of hot rolling temperature, the average Nb/Fe ratio of Zr-Nb-Fe particles increases firstly and then decreases at the range of 620℃ to 700℃, aging processing leads to the further reduce of Nb/Fe ratio. Therefore, homogeneous and fine secondary phases distribute dispersively can be obtained when hot rolling at 620℃, which is beneficial to improve the combination property of zirconium alloys.