Study on Residual Stress Modulation and Mechanical Properties of Titanium Nitride Coatings

The residual stress is the key factor determining the thickness of PVD hard coatings. In present study, TiN coatings with thickness ranging from 3.7 μm to 15.5 μm are fabricated on high speed steel by multi-arc ion plating (MAIP). As the coating thickness increases, the curvatures of substrate become more pronounced yet the average residual stresses are decreased. Combining the substrate curvature method and finite element analysis (FEA), the dependences of residual stress and adhesion strength on coating thickness have been revealed. The larger interfacial shear stress is the main reason for the lower adhesion strength, which is determined by the integral residual stress over the coating thickness. It is also found that the residual stress is increased with increasing bias voltage and/or lowering the working pressure. The coating with the higher compressive residual stress exhibits a dense columnar structure and pronounced (111) orientation. And meanwhile, it owns the higher hardness, larger fracture toughness and favorable wear resistance. Above research results suggest that the mechanical properties of hard coatings can be improved through the residual stress modulation.