Fe-activated formation of pseudospinodal alpha phase in TiNbFe based alloys

Abstract

In this project, we aim to investigate the pseudospinodal formation of alpha phase in Ti-Nb-Fe based alloys. The Ti-Nb-Fe ternary system is a relatively low cost system with potential for many future applications. Thermodynamic analyses suggest that properly designed compositions of this system should present homogeneous alpha phase formation when solution-treated and step-quenched to temperatures near 450°C. Such proposition has been the subject of one of our recent works; however, the topic is still open for further interpretations - i.e. a detailed analysis of multiple aging times is required. Additionally, previous studies indicate that other aspects of alpha phase precipitation are controversial in this system: besides having a strong beta-stabilizing effect, Fe accelerates the alpha phase formation during quench-and-aging heat treatments while restricts alpha phase size. Current limitations of the Ti-Nb-Fe system are the relatively high elastic modulus resultant of Fe addition (higher than 80 GPa) and the limited cold-forming ability of the Fe-rich alloys. Many challenges lie ahead. Thereupon, we also aim to investigate the addition of Zr to the Ti-Nb-Fe system to overcome these limitations and improve the microstructure control. Analyzing the solute redistribution during aging in ternary Ti-Nb-Fe and quaternary Ti-Nb-Fe-Zr alloys will be crucial to identify in which conditions the pseudospinodal decomposition actually takes place. It is worth reminding there are no precedents in the literature reporting pseudo-spinodal transformations in Ti-Nb-Fe based alloys. (AU)