Method for processing alloys via plasma (ion) nitriding

2A surface processing method and power transmission component includes transforming a surface region of a metal alloy into a hardened surface region at a temperature that is less than a heat treating temperature of the metal alloy. The metal alloy includes about 11.1 wt % Ni, about 13.4 wt % Co, about 3.0 wt % Cr, about 0.2 wt % C, and about 1.2 wt % Mo which reacts with the C to form a metal carbide precipitate of the form MC. The surface processing temperature, vacuum pressure, precursor gas flow and ratio, and time of processing are controlled to provide a desirable hardened surface region having a gradual transition in nitrogen concentration.