Microstructural and elasto-plastic material parameters identification by inverse finite elements method of Ti(1-x) AlxN (0 < x < 1 sputtered thin films from Berkovich nano-indentation experiments

International audienceThe mechanical properties of Ti(1 − x)AlxN (0 b x b 1) films of different thicknesses deposited by r.f. reactive magnetron sputtering on Si b100N and high speed steel substrates have been investigated. The as-deposited coatings have been characterized by X-ray diffraction, atomic force microscopy, four-probe electric resistivity method,mechanical deflection of cantilever beams and Berkovich nano-indentation tests associated with inverse finite elements analysis. The coatings with x b 0.58-0.59 present a cubic structure whereas for x N 0.7 a hexagonal structure is observed. Between these two compositions cubic and hexagonal structures coexist. The roughness depends on the film thickness and on the Al content and a minimumassociated to a very fine microstructure is clearly observed in the two-phase coatings. The electric resistivity sharply increases as soon as the hcp structure appears (x ~ 0.6). The mean residual stresses are compressive, except for the AlN coating, and present a minimum at the neighborhood of x ~ 0.64 where a mixed structure is observed. The indentation modulus MbhklN and the Berkovich hardness HBbhklN greatly depend on the Al content and a progressive decreasing has been observed for 0.58 b x b 0.7. For the MbhklN evolution, a simple model taking into account the stiffness coefficients of TiN and AlN structures, the mean residual stress level and the variations of the lattice parameters in the two structure domains is proposed. Knowing the elastic properties of these films, inverse finite elements analysis of the indentation curves considering a simple isotropic linear elasto-plastic behavior allows, as a function of the composition, the yield stress σY and the linear hardening coefficient Hp⁎ to be estimated. σY and Hp⁎ are in the ranges 4.2 to 6.8 GPa and 60 to 400 GPa, respectively. The maximum value of Hp⁎/σY which characterizes the ability of these coatings to exhibit plastic strain hardening is maximum for x = 0.5 and 0.6. The quality of the estimation was discussed through a practical identifiability study and quantified using an identifiability index. Tip radius and elasticity of the Berkovich indenter are two very relevant parameters to improve identifiability and correctly extract the plastic parameters of the behavior law. Scratch crack propagation resistance shows an evolution similar to those of Hp⁎/σY

Characterization of organic ultra-thin film adhesion on flexible substrate using scratch test technique

International audienceThe mechanical properties of interfaces and more precisely the adhesion are of great importance for the understanding of the reliability of thin film devices. Organic thin film transistors (OTFT) on flexible substrate are a new class of electronic components. Since these devices are flexible and intended for different fields of application like sensors and displays, they will undergo a lot of mechanical and thermal stress during their useful life. Moreover, interfaces play an important role in the electrical stability of these transistors. In this context, the adhesion of two organic submicron thin films, semi conducting and dielectric respectively, deposited on polymeric substrate were investigated by scratch test method. This study demonstrates the feasibility and selectivity of the scratch test as a tool for assessing the adhesion and the damage behaviour of ultra-thin organic film on flexible plastic substrate. The semi-crystalline substrate presents a brittle cracking damage from a given strain, whereas when covered by the semi-conducting thin film, the sample exhibits a more ductile behaviour. Moreover, this technique has proven to be sensitive enough to highlight the effects of a plasma treatment prior to deposition

Influence du mode de polymérisation de composites verre/polyester sur leur comportement mécanique

L’objet de cette communication est d’analyser les propriétés mécaniques de composites unidirectionnels verre/polyester obtenus par deux procédés différents de polymérisation : un procédé conventionnel thermique et un procédé photochimique. Les propriétés mécaniques de surface ont été étudiées par micro-indentation afin d’observer l’influence des conditions d’élaboration sur la réponse du composite à une pénétration. Il apparait que la dureté d’indentation HIT et le taux de conversion de la résine ne sont pas suffisants pour discriminer les échantillons. Les propriétés d’élasticité et de fluage sont également nécessaires pour comparer et comprendre le comportement des différents composites. Le procédé de photopolymérisation de la résine améliore les propriétés mécaniques du composite ainsi élaboré

Un système expert d’analyse de surfaces en tribologie projet Fondation CETIM

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