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The plasticity of Ti3SnC2, a recently synthesized MAX phase, was investigated. Localized deformation was induced by nanoindentation in a polycrystalline sample, and the resulting surface topography was observed by atomic force microscopy (AFM). For several grains, buckling around the indent was observed, in agreement with the kink band deformation process often reported for MAX-phase materials. For other grains, slip lines have been revealed by AFM. The corresponding slip systems have been identified through the determination of the local crystalline orientation by electron backscatter diffraction. First- and second-order pyramidal slip systems are shown to be active for some grain orientations, as well as dislocation interactions and cross slip from one system to the other. [ABSTRACT FROM AUTHOR]

The nanoindentation test is commonly used for the local determination of mechanical properties (hardness, elastic modulus, etc.) and also to study the initial stages of plasticity (dislocation nucleation, dislocation interaction mechanisms) at the nanometre scale. In the latter case, the determination of the elastic stress field beneath the indenter is of primary interest. An analytical expression is derived for the elastic stress and strain fields beneath an axisymmetric punch. Most solutions, in the literature, are given for simple indenter shapes, such as flat, conical or spherical indenters. The complete solution proposed for an arbitrary indenter profile is described by a power law, in which the exponent can be an integer or not. The stress is given as the real part of complex analytical expressions. [ABSTRACT FROM AUTHOR]

This study investigates the incipient plasticity during a nanoindentation test with a spherical indenter in magnesium oxide single crystals. The load–displacement curves show multiple pop-ins, interspaced by elastic deformation, and reveal the transition from an initial elastic deformation regime to a continuous elastoplastic one. Nanoindentations have been stopped after the first pop-in and the dislocation structures have been three-dimensionally characterized by AFM observations of the surface deformation and by nanoetching. The dislocation pattern shows two activated slip systems. The resolved shear stress has been calculated just before the pop-in, for all of the activated slip systems. The final positions of the dislocations generated during the first pop-in reveal that they were all nucleated at the point of maximum resolved shear stress. [ABSTRACT FROM AUTHOR]

This letter is based on recent progress in the observation of dislocation distributions around nanoindentations by chemical etching. This so-called nanoetching technique is used to determine the dislocation mechanisms associated with the pop-in phenomenon in MgO and LiF. Successive stages of highly controlled chemomechanical polishing have revealed that these dislocations are half-loops lying in the classical slip systems of MgO or LiF. However, they do not extend on the surface in the classical rosette-arms pattern but stay concentrated around the imprint. A mechanism of dislocation interactions, enhanced by the fact that the dislocations are suddenly nucleated in a small volume, is proposed to explain this specific distribution. [ABSTRACT FROM AUTHOR]

Nanoindentations have been performed at very low load in (001) MgO single crystals. The surface deformation has been investigated by atomic force microscopy, and the rosette arms pattern, induced by the glide of only a few dislocations, has been observed. Moreover, surrounding steps, oriented along the <100> directions, have been identified and associated with the early stage of the formation of the square shaped slip lines pattern commonly observed in the case of microindentation performed under very high loads. The fine structure of these surrounding steps has been resolved clearly, and a mechanism has been proposed based upon interaction between dislocations belonging, respectively, to edge and screw rosette arms and upon the activation of a <011>(211) secondary glide system. [ABSTRACT FROM AUTHOR]