The composite of nitrided steel of H13 and TiN coatings by plasma duplex treatment and the effect of pre-nitriding

In order to improve the adhesion behavior of TiN coatings deposited on H13 steel, a layered composite structure has been developed by plasma nitriding and plasma-enhanced CVD in the present studies. Effects of the nitriding process on the microstructure, adhesion and microhardness, as well as the residual stress of composite nitrided H13/TiN coatings were investigated. Experimental results showed that the adhesion of TiN coatings to substrate could be remarkably enhanced by an optimized plasma nitriding process conducted at a 25% flow ratio of N2/(H2+N2) for 1 h. The formation of a new compound layer during a nitriding process at a 50% flow ratio of N2/(H2+N2) deteriorates the adhesion of TiN coatings due to premature brittle fracture between the coating and the substrate. The surface hardness of nitrided H13/TiN coatings and compressive residual stress in the diffusion interlayer increase with increasing pre-nitriding time, but the adhesion of the coatings decreases to some extent.