Abstract Hard-to-cut materials such as stainless steels and nickel-based super alloys are widely applied in different critical areas, e.g., aerospace and automotive components and chemical plants. Complex parts used in these areas are machined by recently developed indexable copy face mills with round inserts. This work aims to apply such inserts for studying machinability and process cost optimization during face milling of several hard alloys including SS 403cb+ (a new grade of stainless steel), Inconel 718, and Inconel 625 with indexable copy face mills. Machining experiments on these alloys are performed at different cutting speed and feed rate combinations, and machinability is studied in terms of tool life and wear, material removal rate, cutting forces, and force coefficients. The extended Taylor's tool life model that includes both the cutting speed and feed rate are also used to determine the model coefficients. Using standard cost optimization model, process parameters are optimized considering the trade-off between material removal rate and tool life. The coefficients estimated for the extended Taylor's tool life model are also validated. Findings reveal that machinability of Inconel 625 is poorest among the three alloy materials considered. Also, machining cost is found to be about 5 and 6 folds for Inconel 718 and Inconel 625, respectively, as compared to that for SS 403cb+ when considering a fixed volume to be removed at the optimized speed and feed combinations of each material.