In situ hard coatings strain measurement using a commercial strain-gage device

In this work we present a novel technique which can be used to measure in situ the induced substrate strain caused by the depositing film. The technique, based on the application of a commercial strain-gage, was used during the deposition of ultra-hard silicon carbide (SiC) films by RF magnetron sputtering, onto thin (95 μm) martensitic stainless steel substrates. The direct measurement of the electrical resistance of the strain-gage provides the strain values used to find the stress present in the film/substrate interface. Using a value of 480 GPa for the Young modulus of the SiC film, preliminary measurements furnish a value of the residual stress σ varying from 0.7 to 3 GPa, depending on the deposition conditions. These results are in good agreement with other ex situ measurements performed on the same material. The strain sensibility of this technique is about 10 μm/m.