| The application of thin film coating material is increasing,The mechanical properties and the application reliability of the film depends largely on the interface bonding strength between the film and the substrate.As a kind of method to evaluate the bonding strength between the film and the substrate is widely used.The scratch test method is simple,the test results can be quantified and test repeatability is well,especially the bonding strength between the hard film and the substrate.The critical load is used as a parameter to evaluate the interface bonding strength between the film and the substrate,which is affected by many non-interfacial factors in the scratches,such as the accurate output of the load and displacement of the test instrument,the mechanical strength,the film and the substrate properties,load loading rate,film thickness and other factors.For this reason,it uses the external standard sensor to carry on the displacement factor and the load factor calibration to the scratches tester used in the experiment,corrects the deviation of the displacement factor and the load factor,and ensures the accurate output of the load and displacement.And the film standard sample scratches test verification,numerical repeatability,indicating that the scratch test instrument is good test state.Secondly,the failure mode and failure mechanism of the hard film under the scratches are analyzed,and the crack and the fracture of the film are always performed before the interface failure of the film.Typical hard films DLC which was deposited in the Si substrate and 304 stainless steel substrate is the main research object.It discuss the non-interfacial factors including substrate properties,film thickness,curvature radius influence on DLC film spalling critical load,and observe the change of the surface crack and the scratch morphology on the films.Since the DLC is deposited directly on the substrate and the bonding strength is not very good,the same thickness of the Ti transition layer is deposited on both substrates.In the scratch test of DLC film,the abrupt change of acoustic emission signal can determine the critical load of film failure.Different substrates interface bonding system shows completely different scratch failure morphology.The film on the Si substrate has a large area spalling failure,and the film on the 304 stainless steel substrate is peeled off.The critical load values of the films were increased and then decreased.The DLC films deposited on different substrates had an optimum thickness value to make the film and the matrix combined with the best strength when the thickness of the transition layer was constant.The thickness of Ti transition layer is 200 nm,and the bonding strength is the best when 500 nm DLC is deposited on Si substrate;and the bonding strength is the best when 800 nm DLC is deposited on the 304 stainless steel.The critical load is increased with the increase of the curvature radius of the indenter for the substrates,using the indenter with different curvature radius in the scratch test.The larger the curvature radius of the indenter is,the more noticeable the crack and the fracture of the film on the surface before the film is peeled off.In this paper,the bond strength of the film substrate,which is represented by the metal thin film,is studied.The scratches show that there is no deformation such as cracking,breaking and falling of the hard film due to the good plastic deformation ability of the metal film.The scratch tester equipped with the acoustic emission signal detection device can not initially determine the critical load of the film separation,and its scratch surface has no obvious failure phenomenon,but it is mainly in the plastic deformation along the scratched direction.The bond strength of the film needs to be determined by combining the depth of scratches and the analysis of surface components,and effective characterization and measurement methods need further study. |
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