Friction and wear are influenced by the surface conditions of the material, since there is deformation, segregation, generation of oxide films, among others. Roughness is an important characteristic in tribological studies, where the parameters of skewness and kurtosis have greater influence than the conventional parameters R a and R q. This study is aimed to investigate the influence of the parameters of skewness R sk and R ku kurtosis on the surface of the USI AR 360 steel machining by the milling and turning processes in the pin-on-disc sliding wear test. Results showed that surfaces with the same R a and R q could be distinguished by the skewness parameter. Different behaviors were observed in the analysis of friction curves, where the skewness effect showed a tendency to reduce the friction coefficient. It was also observed that the feed marks orientation in relation to the sliding direction can influence the tribological behavior of the surfaces.

International audienceThe aim of this work is to compare several methods for the determination of very thin films Young's modulus and stress state: the nanoindentation test, the bulge test and the point-deflection method. The tested structures were silicon nitride and silicon nitride/silicon oxide bilayer membranes with different shapes (square or rectangular) and dimensions (from 1 mm to 3 mm). We report new experimental results on submicron thick dielectric membranes with thicknesses down to 100 nm. A Young's modulus of 217 14 GPa have been found for silicon nitride membranes with a residual stress of 411 30 MPa using the bulge test. Using nanoindentation experiments, a Young's modulus higher than 190 GPa has been estimated. The bulge test is still valid for the studied high dimension to thickness ratio membranes and more appropriate to determine the Young's modulus. A mixture law was shown to be possibly applied for SiN/SiO bilayer membranes for the Young's modulus and stress determination. The point deflection method is limited by the very low stiffness of these structures and only the residual stress can be accurately extracted. As the Young's modulus and membrane geometry have no significant influence on the stress determination by means of the point deflection method for the studied membranes (with a high lateral dimension to thickness ratio), more reliable results have been obtained such as 487 40 MPa using an AFM cantilever for load-deflection experiments, for SiN thin films

The development of new coatings in the last years contributed to the improvements of machining industry. In general, it is known that the performance of drilling tools increases with the application of a proper coating, and it is worth remembering that the adhesion is an important condition for the success of any coating. This work presents a performance of cemented carbide cutting tool coated with diamond-like carbon (DLC). The deposition of the coating used in this study has been done using plasma enhanced chemical vapor deposition system. Suitable adhesion between film and the substrate did not occur in the initial deposition parameters tested. To enhance adhesion of the film, an intermediate silicon layer has been added. To evaluate this adhesion, VDI 3198 standard adhesion test was used. Spectra analyses collected using Raman backscattering spectroscopy have been used to characterize the composition and structural information of the film. The silicon layer was evaluated using atomic force microscopy. Drilling tests were performed using workpieces casting in aluminum alloy (SA-323) and roundness, radial deviation, deviation of diameter and roughness of geometries changes were measured as a function of the number of holes produced. The results showed that the DLC coating improves the tool performance, which subsequently improves the drilling quality.

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This paper deals with the design optimization of new high sensitivity microphones in SOI technology for gas sensing applications. A novel geometry of bossed silicon membranes used as mechanical transducer has been studied by Finite Element Modelling. Device fabrication is achieved from SOI substrates through deep backside anisotropic etching and shallow front side RIE to define a bossed sensing membrane with two reinforced areas. Thus, the influence of thin film stresses on the device performance is largely decreased. Polysilicon gauges are located on the reinforced areas to get a better linearity in pressure.

In this paper, the bulge test is used to determine the mechanical properties of very thin dielectric membranes. Commonly, this experimental method permits to determine the residual stress (r 0 ) and biaxial Young's modulus (E/(1 -t)). Associating square and rectangular membranes with different length to width ratios, the Poisson's ratio (t) can also be determined. LPCVD Si 3 N 4 monolayer and Si 3 N 4 /SiO 2 bilayer membranes, with thicknesses down to 100 nm, have been characterized giving results in agreement with literature for Si 3 N 4 , E = 212 ± 14 GPa, r 0 = 420 ± 8 MPa and t = 0.29.

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