An Investigation into the Adhesion Strength of Diamond Like Carbon Multilayer Coating (DLC/TiN/Ti/Cu/Ni)

Advancement in vacuum technologies and vapor deposition processes during last decades has led to the introduction of many modern coatings on metal cutting tools. Even in such an advanced vacuum coating techniques, the failure is not due to the wear of the coating but rather due to the lack of coating adhesion to the substrate. In this work, the coating adhesion test results were performed which is based on the Rockwell indentation tests. This coating adhesion tests were performed as per VDI standards 3198, 1991 for d.c. magnetron sputter deposition of diamond like carbon multilayer coating (DLC / TiN/ Ti / Cu / Ni) on tool substrate. Multilayer coating was deposited on tool substrates at different sputtering parameters/conditions such as power density, partial pressure, substrate temperature and reactive gases. The coated multilayer films were characterized by experimental techniques such as X-ray diffractometer which measures the material deposited, micro Raman spectroscopy and TEM to check DLC, Rockwell indentation to examine adhesion strength, optical profilometer to measure thickness of coating. Ni increases the Cu adhesion on tool substrate. Cu accommodates the shear stress induced by the films / substrate and the mismatch in thermal expansion coefficient, while Ti and TiN promote better DLC bonding. As the target power was increased the adhesion strength, micro hardness and deposition rate were observed to improve. Increase in target power and substrate temperature enhances adhesion strength. Proper substrate preparation and sequence of cleaning processes are the crucial factors for the enhancement of adhesion strength. The sputter deposition conditions for the above mentioned multilayer coatings are identified in this work to get improved quality with particular reference to adhesion and surface finish.