Phase transformation and precipitation of Zr-Sn-Nb-Fe alloys at different cooling rates

The phase transformation mechanisms and elemental precipitation behaviors in Zr-1.0Sn-1.0Nb-0.3Fe (N1) and Zr-1.0Sn-0.3Nb-0.3Fe (N2) alloys under varying cooling rates were systematically investigated. As the cooling rates decrease from water cooling (WC) to liquid nitrogen cooling (LNC), air cooling (AC), and finally furnace cooling (FC), the phase transformation progressively shifts from a non-diffusional martensitic mechanism to a diffusional mechanism, accompanied by increasing Nb and Fe segregation. Rapid cooling (WC) retains metastable (beta+omega)-Zr phases with limited Fe enrichment. Intermediate cooling rates (LNC/AC) promote semi-diffusional transformations, leading to the formation of binary Zr-Fe precipitates (Zr2Fe, Zr3Fe). Slow furnace cooling (FC) allows for complete elemental diffusion, resulting in residual beta-Zr and equilibrium Zr(Nb,Fe)(2) phases. Notably, Zr2Fe persists in the low-Nb N2 alloy under these conditions. Phase transformations and precipitate phases nucleate and grow along the low-index habit planes of the parent phase. In addition to the Burgers orientation relationship between alpha-Zr phase and beta-Zr phase, the orientation relationships between Zr2Fe and Zr(Nb,Fe)(2) and the matrix, designated as <0001>alpha//<001>Zr2Fe, {(1) over bar 100}alpha//{110}Zr2Fe and <011>beta//<<(2)over bar>110>Zr(Nb,Fe)2, {21 (1) over bar}beta//{0002}Zr(Nb,Fe)2, have also been characterized.