Phase transformation and mechanical behavior of TiFeCoNi alloy during annealing

Adding Ti to FeCoNi alloy modified its microstructure to a two-phased dendritic microstructure, improving its mechanical properties. The phases in the as-cast TiFeCoNi alloy were hard ordered HCP dendrites and soft ordered FCC-interdendrite matrix. Annealing at 1000 °C did not alter the HCP-dendrite structure, but decomposed the FCC-interdendritic matrix and reduced its degree of order. Experimental results indicate that the internal stress due to casting is released in the initial stage of annealing. Then, the phase transformation increases both the ultimate compressive strength and the plastic strain. The TiFeCoNi alloy that was annealed at 1000 °C for 24 h had excellent mechanical properties—a yield strength of 1.33 GPa, an ultimate compressive strength of 2.6 GPa and a plastic strain of 20%.