Design of W Buffer Layer for Adhesion Improvement of DLC Films on Tool Steels

Kwang-Ryeol Lee, Kwang Yong Eun, Inyoung Kim and Jongryoul Kim

Diamond-like carbon (DLC) has been a candidate for various applications due to its excellent tribological and mechanical properties.  However, poor adhesion on tool steels limits the applications in wide range.  In the present work, we investigated the effect of W and W-C intermediate layer on the adhesion of DLC films to AISI D2 tool steels.  The intermediate layers were deposited by DC magnetron sputtering and the DLC films were deposited on the various intermediate layers by r.f.--PACVD.  Adhesion of the DLC film was significantly improved by introducing W and W-C intermediate layers.  The adhesion was strongly dependent on the thickness of W layer and the CH₄ fraction in the sputtering gas during the intermediate layer deposition.  TEM cross section revealed that in addition to the chemical compatibility between carbon and the intermediate layer materials, the microstructure of the intermediate layer is also important to improve the adhesion.  Columnar grains of the intermediate layers and structural continuity between W and W-C mixed layer were the significant factors affecting the adhesion of DLC films.