TiN coating of tool steels: a review

Titanium nitride (TiN) has been used in the coating of tool steels since the mid-sixties. The reasons to coat cutting tools in a production situation are to increase tool life, to improve the surface quality of the product, and to increase the production rate. The advantages of TiN coating include high hardness and adhesion, good ductility, excellent lubricity, high chemical stability and tough resistance to wear, corrosion and temperature. In this paper, the principles, advantages and limitations of various TiN coating processes are summarized, the microstructures and mechanical properties of TiN coatings on tool steel substrates are reviewed and new developments in the property design of TiN coatings are presented. It is concluded that TiN coating of tool steels is a proven way of success in boosting production and curtailing cost. For HSS applications, however, PVD processes are more appropriate than CVD processes although PVD has its own limitations, which need to be addressed in research into and the development of coating processes in the future. With the growing popularity of TiN-coated tools and new development of coating process, and thus better property control, the market of TiN-coated tool steels promises a prosperous future.