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Microalloying effects on the microstructure and kinetics of nanoscale precipitation in Ni-Al-Fe alloy

The aim of this study is to investigate the influence of 3d transition metal (Co, Mn and V) microalloying on the microstructural evolution, thermomagnetic properties and kinetics of nanoscale precipitation in Ni-25Al-25Fe alloy. The three phase solidification microstructure comprising of dendritic beta-phase (ordered bcc) and interdendritic beta + gamma (disordered fcc) + gamma' (ordered fcc) phases in the as-cast state is significantly altered by annealing. Needle-like disordered gamma-phase precipitates are observed within beta-phase dendrites, and, dissolution of ordered gamma'-phase into the gamma matrix promotes the growth of beta-phase particles in the interdendritic region of Mn- and Co-modified alloys. Disappearance of dendritic microstructure and formation of large volume fraction needle-like disordered gamma-phase precipitates within beta-matrix are observed in V-modified alloy. In all studied alloys, annealing at an intermediate temperature promotes significant hardening of the beta-phase associated with bcc alpha-phase precipitation at the nanoscale. Isothermal precipitation kinetics of the ferromagnetic alpha-phase is studied by a magnetic monitoring approach via magnetically assessed time temperature-transformation diagrams. It is found that V microalloying suppresses the growth of alpha-phase precipitates at high temperatures and large transformed fractions serving as a promising route to maintain balanced mechanical properties for long-term high temperature applications.