The effect of heat treatment on the precipitation hardening in FeNiCoAlTa single crystals

The main goal of this work was to examine the effect of aging process on the precipitation behavior including phase morphology, chemical composition and degree of coherence in Fe-28Ni-17Co-11.5Al-2.5Ta single crystals. The nano-sized and coherent gamma' precipitates were used for strengthening process. The particles were investigated with transmission and scanning electron microscopies along with high energy X-ray diffraction. The single crystalline material of [100] (001) orientation was subjected to three different heat treatments: slowly cooled, quenched and then annealed with various aging conditions. Aging at 973 K for short times results in coherent 2-6 nm-sized gamma' precipitates and fully reversible superelastic strains while annealing at 973 K for 5 h and longer times leads to the precipitation of larger gamma' particles formed together with p phase which significantly reduces the transformed martensite volume fraction.