Precipitation induced recrystallisation (PIX) in a Ti-Fe-Mo bcc-superalloy driven by lattice misfit

TL;DR

This study reveals a novel precipitation-induced recrystallisation process in Ti-Fe-Mo bcc-superalloys, where thermal ageing causes grain refinement through boundary precipitation and dislocation activity without external strain.

Contribution

It uncovers the mechanism of precipitation-induced recrystallisation (PIX) driven by lattice misfit in Ti-Fe-Mo bcc-superalloys, a phenomenon not previously documented.

Findings

Grain size reduces from 364 um to 30 um after ageing.

Discontinuous precipitation of beta-prime-TiFe lamellae occurs at boundaries.

Recrystallisation is driven by precipitation and dislocation activity without external strain.

Abstract

Beta-Ti bcc-superalloys, comprising an A2 beta-Ti matrix reinforced by ordered intermetallic B2 beta-prime-TiFe precipitates, exhibit an unusual recrystallisation that occurs with no externally applied strain (i.e. no thermomechanical processing). Thermal ageing at 750 degrees Celsius for 72 h results in refinement of the grain size from 364 um to 30 um. This grain refinement is driven by discontinuous precipitation of beta-prime-TiFe lamellae with the beta-Ti matrix from grain/phase boundaries, which is associated with significant misorientation and increased dislocation density, attributed as precipitation induced recrystallisation (PIX).