Establishment of a new method of evaluation for the adhesive strength of thin films by micro-indentation wit two degrees of freedom

This research project aims at the establishment of a new method of evaluation for the adhesive strength of thin films by micro-indentation with two degrees of freedom.We studied the following three points and have succeeded to developed a method which can be generally applicable to various combinations of films and substrates.Trial production of two-freedom indentorA micro-indentation set-up with two degrees of freedom was developed。This is equipped with an optical microscope which enables real-time observation of crack extension behavior for the measurement of interface crack length.Selection of the optimum loading path and shape of indentorVarious loading，configurations were examined by using the indentor developed above。As a conclusion，specimens should be prepared where the film is projected a little out of the cross section of the substrate。This projection is pushed upwards from the interface side by a conical stylus of diamond，which we found the best way to efficiently extend an interface crack.Evaluation of toughness by the computational simulationComputational simulations were carried out according to the loading configuration above。By comparing the crack extension resistance curves obtained by both experiment and simulation，we succeeded to evaluate the toughness of interface。As an example，the toughness of interface between a WC-Co substrate and the diamond film prepared as a wear protection coating was determined to be about14J/m I D 12 I D 1.Although adhesion of wear protection coating is one of the critical problems，this is the first quantitative data ever obtained all over the world for the adhesive strength of diamond coatings on WC-Co cutting tools.This fact proves that our new method is quite a successful one with a significant advantage for industries.

This research project aims at the establishment of a new method of evaluation for the adhesive strength of thin films by micro-indentation with two degrees of freedom. We studied the following three points and have succeeded to developed a method which can be generally applicable to various combinations of films and substrates.Trial production of two-freedom indentorA micro-indentation set-up with two degrees of freedom was developed. This is equipped with an optical microscope which enables real-time observation of crack extension behavior for the measurement of interface crack length.Selection of the optimum loading path and shape of indentorVarious loading, configurations were examined by using the indentor developed above. As a conclusion, specimens should be prepared where the film is projected a little out of the cross section of the substrate. This projection is pushed upwards from the interface side by a conical stylus of diamond, which we found the best way to efficiently extend an interface crack.Evaluation of toughness by the computational simulationComputational simulations were carried out according to the loading configuration above. By comparing the crack extension resistance curves obtained by both experiment and simulation, we succeeded to evaluate the toughness of interface. As an example, the toughness of interface between a WC-Co substrate and the diamond film prepared as a wear protection coating was determined to be about 14 J/mィイD12ィエD1. Although adhesion of wear protection coating is one of the critical problems, this is the first quantitative data ever obtained all over the world for the adhesive strength of diamond coatings on WC-Co cutting tools. This fact proves that our new method is quite a successful one with a significant advantage for industries.