Thickness control of TiN network in CoCrFeNi matrix composite with tunable microstructure

Abstract A bottom up approach is designed where a TiN coated CoCrFeNi core- core-shell powder was used as a building block to fabricate CoCrFeNi matrix composites with tunable microstructure. Initially, the core-shell powder was achieved by surface nitriding of mechanically alloyed CoCrFeNiTi powder. By controlling the treatment parameters, powders with variable shell thickness were achieved. Afterwards, the core-shell powder was sintered via spark plasma sintering. The sintered microstructures consisted of CoCrFeNi matrix along with a continuous network of TiN. After sintering of for powders with a thin shell, the matrix phase was Ti rich resulting in the precipitation of intermetallic phase. Additionally, the reinforcement network showed high connectivity. As the shell thickness was increased, the matrix became Ti deficient resulting in the suppression of intermetallic precipitation. The increase in shell thickness also caused discontinuities in the reinforcement network. These microstructural changes impacted the thermal and mechanical properties of the resultant composite. The reinforcement network significantly reduced the coefficient of thermal expansion of the matrix phase. Additionally, all composites showed fracture strength in excess of 1 GPa showing excellent reinforcement efficiency in the designed microstructure.