An experimental trial for the synthesis of α″-(Fe_100-xCo_x) ₁₆N₂ (x = 0-30) martensite films by reactive sputtering

In order to determine the synthesis conditions of α″-(Fe_100-xCo_x)₁₆N₂, Fe-Co nitrided films were fabricated on MgO single-crystal substrates using reactive sputtering. The thermal stability of the α′_Fe-Co phase was evaluated by measuring the temperature dependence of σ_s. It was found that: (1) for the as-deposited (Fe_100-xCo_x)-N films, α′_Fe-Co martensite phase with a stoichiometric N content of 11 at% can be formed up to x = 10, and with increasing x, α′_Fe-Co phase with stoichiometric N content is not formed. (2) The phase decomposition temperature, T_pd, of α′-(Fe_100-xCo_x)-N (x = 0-30) phase depends strongly on the Co and N contents of the α′_Fe-Co phase. The T_pd of α′ phase decreases from 200°C (x = 0) to RT (x = 30) with increasing Co and N contents. (3) The formation at RT of stable α′-(Fe_100-xCo_x)₁₆N₂ (x = 10-30) phase in the Fe-Co alloy system is concluded to be fairly difficult.