Methods of making surface hardened medical implants comprising providing a biocompatible alloy with a surface comprising an oxide or nitride layer, diffusing at least a portion of the respective oxygen or nitrogen from the oxide or nitride layer the substrate for a period of time to form a diffusion hardened zone of desired thickness. The period of time is based at least on (1) the diffusivity of a diffusing specie in the oxide or nitride layer, (2) a desired hardness profile of at least a portion of said implant defined by a function selected from the group consisting of: an error function, an exponential function, a near uniform distribution function, and any sequential combination thereof, or (3) a desired thickness of said oxide or nitride layer to be retained.
