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Abstract: Correlations between the grain orientations and elastic properties of plasma-nitrided polycrystalline 316L austenitic stainless steel are investigated. The grain orientations (h k l) in a delimited area were obtained from electron backscatter diffraction and related to hardness (Hhkl ) and elastic modulus (Ehkl ) maps obtained from large nanoindentation matrices. The influence of nitrogen concentration on the local mechanical properties has been studied by repeating these indentation matrices in the same area after successive partial removals of the nitrided layer. This nanoindentation tomography allowed the orientation, the shape and the surroundings of individual grains to be taken into account. The results show that plasma nitriding leads to a complete reversal of the elastic behaviour anisotropy: while the non-nitrided 316L austenitic stainless steel shows the typical elastic anisotropy of face-centred-cubic-type metals with a maximum of Ehkl for the oriented grains, the maximum of Ehkl is observed for the oriented grains in the nitrided layer. A similar anisotropy reversal is observed for the hardness Hhkl . These observations are discussed on the basis of the microstructural changes induced by the nitrogen incorporation. [Copyright &y& Elsevier]

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 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]

Abstract: Mechanical property changes of 4H–SiC implanted at room temperature with helium ions at fluences ranging from 7×1015 to 1×1017 cm−2 and at an ion energy of 50keV were investigated by using nano-indentation tests and subsequent atomic force microscopy investigations. Degradation of the mechanical properties of the near-surface due to helium implantation was analysed and correlated with the microstructure evolution examined through transmission electron microscopy cross-section and X-ray diffraction experiments. Up to 1×1016 He+ cm−2 no significant change in mechanical properties is seen whereas a normal strain profile of few percents is generated all along the ion path. Nevertheless, the as-created implantation damage enhance the dislocation nucleation. At intermediate fluences, when a buried amorphous layer is created, the hardness curve against penetration depth can be divided into three stages showing ‘constraining coating’ effects. When the entire part of the implanted crystal is amorphous a decrease of about 50% is measured for hardness value. [Copyright &y& Elsevier]

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]

Abstract: Incipient plasticity in magnesium oxide single crystals has been investigated by nanoindentation with a spherical indenter. For very low loads, the surface deformation can be limited to a single slip line, making modelling of the deformation easier. The recently developed nanoetching technique has been used to investigate the corresponding dislocation structure. Single pile-ups of a few dislocation half loops have been observed and fully characterised. A simple elastic model, based upon the calculation of the Peach Koehler force induced by the pile-ups and the spherical indenter stress field, has been used to determine the equilibrium positions of dislocations in these pile-ups. A comparison between the experimental and calculated structures has led to the determination of the lattice friction stress for edge and screw dislocations in magnesium oxide single crystals. This stress is found to be 65MPa for edge dislocations and 86MPa for screw dislocations. [Copyright &y& Elsevier]

He+ ions were implanted in 4H–SiC at 750 °C with a fluence of 1×1017 cm−2. Bubbles that appear in strata parallel to the surface are readily formed in the as-implanted state. The bubble formation and the dilatation of the c-axis all over the ion track induce the swelling of the implanted surface. Upon annealing at 1500 °C–30 min, the structure is relaxed, the density of cavities decreases and their mean diameter increases. The increase of the step height after annealing suggests the migration of both the interstitials and vacancies. [Copyright &y& Elsevier]

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]

In this paper, it is shown that combining AFM, chemical etching and controlled polishing, progressively removing thin layers of material, allows a three-dimensional reconstruction of the volume distribution of dislocations about and under nanoindentation imprints. To illustrate the method, results obtained in MgO, a material known for its simple plasticity, have been selected. It is shown, comparing surface deformation and etching pattern, that the entire dislocation distribution associated with small indents can be analysed in terms of individual dislocations, leading to a better understanding of the elementary mechanisms of plasticity associated with the early stages of indents formation in crystalline material. [Copyright &y& Elsevier]

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]

Grit blasting with alumina particles offers a conventional substrate surface preparation method intended to improve the adhesion of thermal spray coatings. However, the associated microstructural modifications to the substrate may, in fact, reduce the integrity of the interface. In this paper, we use nanoindentation cartography methods to characterize the local mechanical properties of the interface of a HVOF coating deposited on an alumina grit blasted 17-4PH stainless steel substrate. The results show a hardness gradient in the substrate, which we evaluate within the context of the refinement of the substrate microstructure. We show that nanohardness mapping, combined with Atomic Force Microscopy and Scanning Electron Microscopy analysis provides a viable approach to study this unique contribution of the microstructural relationship between the beneficial and detrimental impacts of grit blasting on the adhesion of thermal spray coatings. [ABSTRACT FROM AUTHOR]

Abstract The mechanical properties of materials usually depend on the size of the considered object. Silicon, for instance, undergoes between the macroscopic and nanometer scales, a brittle-to-ductile transition at room temperature. Although essential for the constantly developing Si-based nanotechnologies, the origin of this remarkable behaviour change remains undetermined for several years. The observation of the mechanisms responsible for plastic deformation in nano-objects is indeed highly challenging at the microscopic scale. One needs controlling the deformation while identifying induced individual plastic events at the smallest scale during the first stages of plasticity. This work describes nano-compression experiments on 100 nm-diameter Si nanopillars followed by post-mortem analysis of the deformed specimens through SEM and atomic resolution TEM imaging. The observed plastic deformation disrupts the usual description of low-temperature undissociated-dislocations-mediated plasticity and is comforted by molecular dynamics calculations. These results shed a new light on the transition between ductile and brittle regimes in silicon by introducing the missing link between plasticity and fracture. Graphical abstract Image 1 [ABSTRACT FROM AUTHOR]

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]

Titanium alloys are widely employed in aerospace applications due to an outstanding combination of properties. The variety of loading conditions and microstructures encountered in industrial components is urging the development of microstructure sensitive modeling capabilities. In particular, reliable predictions require a good knowledge of operating deformation mechanisms. The present study aims at providing a thorough characterization of deformation mechanisms in the near-α Ti-6Al-2Sn-4Zr-2Mo alloy using experiments and simulations. The sequential activation of deformation mechanisms in the α phase was monitored in situ during a tensile test carried out in a scanning electron microscope using a combination of slip traces analysis and electron back-scattered diffraction. Basal slip is activated first, and prismatic slip activity, which proceeds at a higher macroscopic stress level, is needed for a significant creep/relaxation to occur. While little evidence of 〈 a 〉-type pyramidal slip was found, 〈 c + a 〉 pyramidal slip involved first-order pyramidal planes and operates at stress levels near or above the 0.2% proof stress. Atomic force microscopy characterization of the features of the different slip modes revealed that 〈 a 〉 slip is coarser and wavier than 〈 c + a 〉 slip. Twinning, which is usually neglected in such alloys within this strain regime, was observed to be slip stimulated at a plastic strain as low as 0.5%. Crystal plasticity parameters leading to an accurate simulation of the activation sequence of deformation mechanisms were then determined. For this purpose, critical resolved shear stress values were derived for the different slip and twinning modes using specific approaches and subsequently validated using crystal plasticity simulations based on fast-Fourier transforms. [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 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]

Abstract: Multilayer coatings with layer thicknesses in the nanometer range have been shown to exhibit original mechanical properties: these include pronounced softening of some elastic moduli, large increase in yield strength and hardening effect. Such original properties are related to the high interface density and reduced grain sizes associated with these systems. In the first part of this article, the elastic and plastic properties of metal/metal, metal/nitride and nitride/nitride nanoscale multilayers are briefly outlined. The origin of large compressive stress commonly observed in PVD films grown with energetic particles is then presented and illustrations given for the case of epitaxial multilayers for which different stress sources exist. The second part focuses on recent experimental results obtained for three multilayered systems, Mo/Ni, TiN/Cu and ZrN/W, corresponding to different crystal structure and lattice mismatch combinations. Two issues will be addressed: the interdependence between interfacial mixing and elastic softening in Mo/Ni superlattices and the mechanical behaviour of TiN/Cu and ZrN/W multilayers combining ‘hard’ and ‘soft’ materials. These multilayers were grown epitaxially on either MgO (001) or Al2O3(112¯0) substrates by a dual ion beam sputtering technique. Low-angle and high-angle X-ray diffraction experiments as well as Transmission Electron Microscopy observations were used to characterize the microstructure and crystalline orientation, structure of interfaces and type of growth defects. Elastic properties were studied by Brillouin light scattering and hardness values determined from nanoindentation tests. For selected samples, a combined FIB-TEM technique was implemented to image the deformed nanolaminates beneath the indentor. [Copyright &y& Elsevier]

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]

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]

Single crystals 4H-SiC were implanted with 50 keV helium ions at temperatures up to 600 °C and fluences in the range 1×1016–1×1017 cm-2. The helium implantation-induced swelling was studied through the measurement of the step height. The different contributions of swelling were determined by combining simulations of x-ray diffraction curves and transmission electron microscopy observations. At room temperature, amorphization occurs between 1 and 2×1016 cm-2, inducing the decrease in density of about 15%. For high-temperature implants, amorphization does not occur. The strain profiles show saturation in the near-surface region, indicating that a threshold concentration of defects is reached. All the additional point defects created during the implantation have been supposed to annihilate. In the region of high-energy deposition density, the value of strain increases with fluence up to values larger than 6%. The elastic contribution to swelling has been obtained by integration of the strain profile determined by x-ray diffraction simulations. Then, the contribution of helium bubbles to the step height is found to be linear with the fluence: 0.8 nm/1016 He/cm2. [ABSTRACT FROM AUTHOR]

The role of topologically close packed (TCP) phases in deformation of superalloys and steels is still not fully resolved. In particular, the intrinsic deformation mechanisms of these phases are largely unknown including the active slip systems in most of these complex crystal structures. Here, we present a first detailed investigation of the mechanical properties of the Fe 7 Mo 6 μ-phase at room temperature using microcompression and nanoindentation with statistical EBSD-assisted slip trace analysis and TEM imaging. Slip occurs predominantly on the basal and prismatic planes, resulting also in decohesion on prismatic planes with high defect density. The correlation of the deformation structures and measured hardness reveals pronounced hardening where interaction of slip planes occurs and prevalent deformation at pre-existing defects. [ABSTRACT FROM AUTHOR]

The ω-Al 70 Cu 20 Fe 10 phase formation processes have been investigated for two types of samples synthesized by Spark Plasma Sintering: model samples with planar Al/Al-Cu-Fe interfaces produced from Al and icosahedral i-Al-Cu-Fe powder beds superimposed in a graphite die and Al/Al-Cu-Fe composites. For reactively sintered model samples, the ω-Al-Cu-Fe phase formation was studied using Field Emission Scanning Electron Microscopy coupled with Energy-Dispersive X-ray spectroscopy. In-situ Field Emission Scanning Electron Microscope with a heating stage was used to observe the microstructure evolution of initial Al/i-Al-Cu-Fe composites from room temperature up to 823 K. Observations and chemical analyses performed on the different types of samples show the presence of secondary phases such as θ-Al 2 Cu and AlCu together with the presence of an eutectic microstructure which indicate the formation of a transient liquid phase, during the formation of the ω-Al-Cu-Fe phase. The formation processes of the ω-Al-Cu-Fe phase suggested in this work highlight two different scenarii involving the Al enrichment of pre-existing i-Al-Cu-Fe particles and the filling of initial porosities via a liquid mediated reaction involving θ-Al 2 Cu and AlCu intermediate phases. [ABSTRACT FROM AUTHOR]

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

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]

Abstract: Effects of annealing on surface swelling in helium implanted 4H–SiC were studied for different implant conditions. The significant increase of surface swelling observed upon high temperature annealing of samples implanted under severe implant conditions (high temperature and fluence) is observed to be concomitant with the growth of cavities and the formation of other extended defects in the highly damaged zone. Frank loops resulting from the drift of interstitials only form in the highly damaged zone. These loops promote the formation of Shockley partial dislocations leading to stacking fault pile-up. For less severe conditions of implantation, low temperature and fluence, the formation of dislocations is avoided upon post-annealing, and the recovery of swelling progressively occurs. Under intermediate conditions of implantation, the compensation between elastic recovery of the implantation-induced strain and the limited formation of cavities and interstitial-type clusters result in a constant swelling. [Copyright &y& Elsevier]

Abstract: A thin cobalt layer is deposited by electron beam evaporation onto a germanium substrate after an in situ cleaning annealing at 400 or 700°C. The effect of these pre-treatments on the Co/Ge Schottky barrier properties and on the germanide formation is investigated by using different techniques. A strong influence of the pre-treatment is observed. The pre-treatment at 700°C removes the native oxide but enhances the diffusion of contaminants. After post-metal deposition annealing, the sample pre-treated at 700°C shows a double layer structure due to interdiffusion, whereas some large isolated islands are present in the sample pre-treated at 400°C. [Copyright &y& Elsevier]

Abstract: A thin cobalt layer is deposited by electron beam evaporation onto a germanium substrate after an in situ cleaning annealing at 400 or 700°C. The effect of these pre-treatments on the Co/Ge Schottky barrier properties and on the germanide formation is investigated by using different techniques. A strong influence of the pre-treatment is observed. The pre-treatment at 700°C removes the native oxide but enhances the diffusion of contaminants. After post-metal deposition annealing, the sample pre-treated at 700°C shows a double layer structure due to interdiffusion, whereas some large isolated islands are present in the sample pre-treated at 400°C. [Copyright &y& Elsevier]

Currently, kinematic field measurements for studying the mechanical behavior of materials and structures use common optical methods, such as mark tracking techniques, grid methods and correlation techniques. These techniques are employed over a region of interest ranging from micro to millimeter scale. However, when studies need to be conducted on even smaller scales such as sub-micrometric scale, the use of more complex means of observation is required. In this case, the work can be achieved using the scanning electron microscope (SEM), and the Focused-Ion-Beam (FIB) as marking technique. An adaptation of Digital Image Correlation (DIC) method Heaviside-based Digital Image Correlation (H-DIC) is chosen to investigate the mechanical behavior and taking into account local fractures. As the studied problem is to extract strains from a fractured material using a displacement field measurement method, derivative computation for strain determination is not well adapted. The proposed approach consists in extracting the residual strains from local first gradients of H-DIC, which are less perturbed by the fractures. Various tests were performed to evaluate the validity of this new proposed approach. An application to study the mechanical behavior of a metallic composite (Al/ ω -Al-Cu-Fe) is proposed. A particular exploitation of all field lies in the good separation of the strain fields and the cracked part. A discussion that focus on the comparison between a conventional DIC analysis and its extension was presented on the zones without or with fractures. Compression test on a two-phase material Al/ ω -Al-Cu-Fe, Maps after second loading/unloading cycle, and for tow zones (Z1, Z4). (a, d) SEM image, (b, e) equivalent strain H-DIC ε eq ∂ U ∂ X and (c, f) norme of displacement jump vector ║ U′ ║. Unlabelled Image • Coupling Scanning Electron Microscope, Focused-Ion-Beam, and Digital Image Correlation in a metrological process • Separation of strains and fracture properties using an extended DIC • Extracting residual strains from a fractured material for an ex-situ compression test • Application to study the microstructure and the mechanical behavior of a composite metallic material [ABSTRACT FROM AUTHOR]

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]