Combinating surface treatments improves surface/subsurface properties by taking advantage of the best attributes of each technique compared with those of the individual method by itself.
The process using a combination of two surface engineering techniques is commonly referred to as duplex surface engineering. An example is the thermochemical surface treatment of a steel substrate prior to the deposition of a hard surface coating. Thermochemical treatments such as nitriding and carburizing inherently form a graded hardness from the surface to the substrate, which creates a gradual transition in properties across the coating-substrate interface and provides a tough and supportive subsurface for the hard coating [1, 5]. There are numerous examples in the literature of the benefit of nitriding, nitrocarburizing or carburizing steels prior to the formation of a hard layer by physical or chemical vapor deposition [1, 5-14].