Search

Deformation behavior of an industrial coated cemented carbide (WC-Co substrate coated with CVD multilayer of TiN/Zr(C,N)/Ti(C,N,O)/Al2O3) was investigated by means of micropillar compression method. In addition to the WC-Co substrate pillars, new composite pillar combination consisting of substrate, TiN interlayer and carbonitride hard coating were tested. The study targeted to document and analyze interactions between different phases and components (substrate, interlayer and coating) while subjected to compressive stress. It is found that deformation of the substrate depends mainly on the assemblage and the distribution of WC and Co phases within the pillar. The phase assemblage is subjected to changes after deformation which has an impact on the stiffness. Detailed analysis of plastic deformation within WC coarse grains pointed out that strain energy can be extensively dissipated in this phase by means of single and multiple slip. The composite/hybrid pillar formed by association of the substrate and the coating enhanced the ultimate strength in comparison to their respective individual components, highlighting the effective load-bearing response of coating and substrate acting as a coated system. This assessment was further supported by the excellent interfacial strength attested by the established TiN interlayer between the substrate and the coating. Keywords: WC plasticity, Cobalt deformation, Zr(C,N) (ZrCN) CVD hard coating, TiN interlayer, Interfacial strength, EBSD

The stress corrosion cracking behaviour of Fe-Ni-Cr synthetic alloys was studied in NaOH solutions at 350°C, using a slow strain rate technique. Results were compared with tensile tests in air at 350°C. The influence of composition was investigated in the ranges : Ni (wt %) = 10 to 100 %, Cr (wt %) = 0 to 36 %. The role of C, S and P in ultra pure 600 alloys was studied in detail.

Plane-strain compression tests have been carried out on different orientations of aluminium single and bicrystals for strains up to −1. The stress-strain behaviour and the active slip systems are compared with theoretical predictions for constrained plastic flow. For both high and low symmetry bicrystals, the flow stress levels are in good agreement with the values predicted by averaging the plastic work terms of the component crystals, i.e. grain boundaries appear to have little effect on the plastic flow of aluminium bicrystals for strains between − 0, 05 and − 1. The observed slip systems in the crystals confirm the theory, and also show that extra slip due to possible boundary incompatibilities is not observed for the orientations used. In addition, pronounced deformation banding occurs in certain highly symmetrical orientations.

The experimental lattice rotations, during rolling, of grains in aluminium sheet containing either equiaxed or pancake-shaped grains have been compared with the predictions of both the full and relaxed constraints models of grain deformation. Both grain shape and orientation are found to influence the lattice rotations and hence the grain deformation modes. The results are analysed using a new continuous constraints model which incorporates both grain shape and orientation effects to quantitatively predict a continuous transition, during deformation, from the full to relaxed constraints modes.

International audience; The dynamic interactions between solid solution hydrogen atoms and dislocations in face centred cubic (fcc) crystals are considered. Using strain ageing experiments, the strength of the elastic binding between dislocations and solutes atmospheres is measured. These results support the linearised hydrogen elasticity framework for modelling hydrogen-dislocation interactions. It is used to derive quantitative estimates of hydrogen effects on dislocation properties. Consequences are predicted on the Franck-Read mechanism and the cross-slip probability of screw dislocations. They are compared to the tensile response of nickel single crystals. Cross-slip is the mechanism whose alteration by hydrogen has the most important consequences on deformation. Effects on hydrogen-induced damage are discussed and possible extensions to other classes of metals and alloys are outlined.

Large strain plastic deformation of metallic materials is investigated. By expressing the rate of change of the resolved shear stress applied to a slip system in a grain as a linear function of the slip rates, it is shown that the existing stress plays a significant role at large strain.

A simplified continuum yield surface of the Hill type is derived which gives a ‘best fit’ to the Bishop and Hill polyhedron for cubic crystals. By this means the flow behaviour of anisotropic metals containing several ideal orientations can be readily predicted or described. The method has previously been applied to prediction of the axial stresses generated during fixed end torsion testing; it is here extended to the length changes taking place during free end torsion testing. Plastic strain ratios R(α) are also calculated for rolled sheet containing the most frequently observed texture components; the former are shown to be in good agreement with the experimental observations reported in the literature.