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The effect of high fluence helium implantation for different implant conditions and complementary techniques are used in order to separate the different contributions of swelling in silicon carbide (SiC). The elastic diffraction to swelling are obtained by integration of the strain profile determined by x-ray diffraction simulations.

In situ compression tests combined with neutron diffraction were performed on Ti2AlN MAX polycrystals with lamellar anisotropic microstructure: the diffraction peak evolution (position and profile) with applied stress reveals that lamellar grains parallel to compression axis remain elastic while lamellar grains perpendicular to compression plastify, both families being subjected to strong variations of heterogeneous strains (types II and III). We demonstrate that this behavior originates from the complex response of the very anisotropic lamellar microstructure and explains the observation of reversible hysteretic loops when cycling MAX polycrystals even in the elastic regime. [ABSTRACT FROM AUTHOR]

A compression setup fully integrated in an ultra high vacuum chamber is presented. The system has been designed to combine in situ mechanical test together with near field microscopy at variable temperature, from 90 to 600 K. Compressive stress can be applied on the samples up to 500 MPa at different strain rates ranging from 10-6 s-1 to 10-2 s-1. The setup performances are highlighted through investigations on Au and Ni3(Al,Ta) single crystals. In particular, it is demonstrated that the high mechanical stability of the original apparatus allows us to follow in situ the evolution of the same area of interest over a large range of temperature and to keep the high spatial resolution offered by near field microscopy, even at high strain levels. [ABSTRACT FROM AUTHOR]

Statistics on nanoindentation experiments performed on a fourth-generation Ni-based single-crystal superalloy reveal a bimodal hardness distribution, with two mean hardness values only 2.5% away from each other. Using a hardness cartography technique combined with the statistical analysis proved that the hardness values are not randomly distributed but correspond exactly to the dendrites and the interdendritic regions. In this context, hardness cartography is shown to push back the resolution limit of the nanoindentation test. [ABSTRACT FROM AUTHOR]

The HIPing of Ti-Al-1.9TiC and Ti-Al-0.2Sn-1.8TiC reactant mixtures yields Ti3AlC2 and Ti3Al0.8Sn0.2C2 solid solutions, respectively. Rietveld refinement gives a = 3.0786 ± 0.0001 Å and c = 18.589 ± 0.001 Å lattice parameters for Ti3AlC2 and a = 3.0837 ± 0.0001 Å and c = 18.621 ± 0.002 Å for Ti3Al0.8Sn0.2C2. Furthermore, about 2-3 vol% of Ti x Al y intermetallics is detected in Ti3Al0.8Sn0.2C2 solid solution. The intrinsic hardness, measured by nanoindention tests, is 11.4 ± 0.7 GPa for Ti3AlC2 and 10.2 ± 0.6 GPa for Ti3Al0.8Sn0.2C2. Furthermore, hardness values, measured by microindentation tests, are compared with the ones measured by nanoindentation. It is shown that microindentation and nanoindentation performed with large loads lead to underestimated hardness values as several grains are involved in the deformation process. Finally, Young's modulus of Ti3AlC2 and Ti3Al0.8Sn0.2C2 is 260 ± 10 and 250 ± 10 GPa, respectively. [ABSTRACT FROM AUTHOR]

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 changes in anisotropic hardness and indentation modulus induced by plasma nitriding at 400°C of a 316L polycrystalline austenitic stainless steel are analyzed. The dependence of hardness and elastic modulus modifications on the crystallographic orientation is investigated through instrumented indentation and electron backscattering diffraction. Both hardness and indentation modulus exhibit an inverted anisotropy compared to the untreated 316L, likely associated with the presence of the N atoms in interstitial sites. [ABSTRACT FROM AUTHOR]

Abstract: The changes in microstructure and mechanical properties of 4H-SiC implanted at room temperature with 50keV helium ions have been studied. Up to 1×1016 cm−2, no significant change in mechanical properties is observed. Nevertheless, the as-created damage that induce a normal strain profile of few percents, enhance the dislocation nucleation. The compressive in-plane stress impedes the crack formation. At medium fluences, when a buried amorphous layer is created, the hardness curve against penetration depth can be divided into three stages showing “constraining coating” effects. Indents are surrounded by large hillocks resulting from the flowing of the amorphous state. When the entire part of the implanted crystal is amorphous a large decrease is measured for both the hardness and elastic modulus. [Copyright &y& Elsevier]

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]

A correlation between the grain orientation and the out-of-plane magnetic properties of nitrogen-enriched polycrystalline austenitic stainless steel surface is performed. Due to the competition between the magnetocrystalline anisotropy, the exchange and dipolar interactions, and the residual stresses induced by nitriding, the resulting effective magnetic easy-axis can lay along unusual directions. It is also demonstrated that, by choosing an appropriate stainless steel texturing, arrays of ferromagnetic structures with out-of-plane magnetization, embedded in a paramagnetic matrix, can be produced by local plasma nitriding through shadow masks. [ABSTRACT FROM AUTHOR]

Amorphous Fe0.55Zr0.45 films, having thickness of 400 nm, were grown on silicon substrates by co-deposition using ion beam sputtering. Limited surface roughness makes this system particularly suitable for fine-scale scanning force microscopy analysis and nano-indentation. The samples were irradiated with MeV C60 clusters, and the surface morphology of single impacts was found to have a “doughnut” shape, i.e. hillocks having a central crater. Quantitative evaluation of the deformation was achieved by measuring their height and diameter. When C60 projectiles deviate from normal incidence, a tail emerges along the direction of the incident beam. The height of the hillock and length of the tail are increasing with the incidence angle, and the magnitude of the deformation indicates that the damage mainly occurs due to a radial coherent mass transport outwards from the track core by a compression shockwave-like mechanism. The residual compressive in-plane stress, ∼−0.4 GPa for the as-deposited films, was found to notably influence the C60 induced plastic deformations. Indeed, stress relaxation results in a marked decrease in height combined with a significant widening of the surface features. This “flat” surface morphology is attributed to an enhanced radial efficiency of the pressure pulse, owing to a significant reduction of the hardness of the amorphous film after stress relaxation. The overall picture outlined from our observations suggests that the surface damage induced by single MeV C60 ions possibly is the signature of plastic deformation induced at large distances by an energetic radial pressure pulse. This unsteady shockwave allows the energy transfer outwards from the localised region along the ion path that experiences a sudden transient heating. [Copyright &y& Elsevier]

We present a detailed experimental study on Mo1-xSix thin films, an archetypal alloy system combining metallic and semiconductor materials. The correlations between structure and elastic response are comprehensively investigated. We focus on assessing trends for understanding the evolution of elastic properties upon Si alloying in relation to the structural state (crystalline vs amorphous), bonding character (metallic vs covalent), and local atomic environment. By combining picosecond ultrasonics and Brillouin light scattering techniques, a complete set of effective elastic constants and mechanical moduli (B, G, E) is provided in the whole compositional range, covering bcc solid solutions (x<0.20) and the amorphous phase (0.20

We comparatively study the elastic properties of the two existing polytypes of tantalum, α-Ta (ground state bcc structure) and β-Ta (metastable tetragonal structure), using density functional theory (DFT) calculations and thin film growth experiments. The lattice parameter and the single-crystal elastic constants c ij for the two allotropic structures were computed using pseudo-potentials with generalized gradient approximation. Sound velocity measurements on single-phase, highly-textured (001) β-Ta and (110) α-Ta films deposited by magnetron sputtering were carried out using picosecond laser ultrasonic and Brillouin light scattering techniques, while hardness H and Young's modulus E were measured using nanoindentation. We found that the β-Ta phase is significantly harder (H ~18.0 GPa) than α-Ta (H ~10.3 GPa), while their elastic stiffness properties and Cauchy pressure p are similar, C 33 ~285–310 GPa, E ~ 188 GPa, p ~ 70–80 GPa, and agree well with the computed values. However, the out-of-plane shear modulus G of the β-Ta film is softer by 28% with respect to that of α-Ta film and DFT values (50 vs. 69 GPa). The present findings reveal that, contrarily to common claims, the β-Ta phase is not at all brittle but elastically and plastically deforms in a compliant way. Its toughness and elastic strain to failure ability is further comprehended from low G / B (0.205) and high H / E (≈0.1) ratios and the absence of radial cracks around indents, which suggests that β-Ta is also a suitable phase for use as wear-resistant coating in biomedical applications. • Sound velocities measured from picosecond acoustics and Brillouin spectroscopy. • Computed elastic constants agree with measured ones for α-Ta. • A significant softening (25%) of C 44 is measured for β-Ta. • Despite being harder, the β-Ta film is found to be more ductile. [ABSTRACT FROM AUTHOR]