Investigation of adhesion of diamond films on Mo, W and carburized W substrates

Abstract

Abstract A four-factor, three-level, fractional factorial experiment design was used to investigate systematically the influences of substrate pretreatment, deposition parameters, residual stress and substrate material on the adhesion strength of diamond films produced by a microwave plasma CVD process. The experimental results revealed that pretreatment of the substrates with diamond powder scratching was necessary for growing continuous diamond films on Mo, W and carburized W substrates. Statistical analysis showed that the substrate pretreatment had strong influences on film adhesion and, in particular, that the films on the substrates pretreated with Murakami's reagent demonstrated improved adhesion. The methane concentration in the hydrogen/methane gas source had significant effects on the diamond crystallite size and film surface morphology. Neither methane concentration nor deposition temperature in the ranges studied, however, showed significant influences on film adhesion. The total residual stress in the film was shown to be affected by substrate material and deposition temperature. The high mean residual tensile stress in the films deposited on pure W substrates was probably responsible for the poor film adhesion observed in this case. The decrease of the total stress in the films on carburized W substrates correlated well with the improved film adhesion. Carburization of the W substrates before diamond film deposition appeared to lessen the intrinsic stress in the film due to a better structure match between the diamond and tungsten carbide, thus enhancing film adhesion.