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Angle-and energy-dispersive X-ray diffraction experiments in a radial geometry were performed in the diamond anvil cell on polycrystalline platinum samples at pressures up to 63 GPa. Observed yield strength and texture depend on grain size. For samples with 70-300-nm particle size, the yield strength is 5-6 GPa at ~60 GPa. Coarse-grained (~2-µm particles) Pt has a much lower yield strength of 1-1.5 GPa at ~60 GPa. Face-centered cubic metals Pt and Au have lower strength to shear modulus ratio than body-centered cubic or hexagonal close-packed metals. While a 300-nm particle sample exhibits the <110> texture expected of face-centered-cubic metals under compression, smaller and larger particles show a weak mixed <110> and <100> texture under compression. Differences in texture development may also occur due to deviations from uniaxial stress under compression in the diamond anvil cell.
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... Another advantage for radial diffraction over axial diffraction is that texture in the radial geometry is sensitive to the active slip systems as well as stress, 32−34 which enables elucidation of the microscopic deformation mechanisms controlling the plastic behavior of the material. 18,35 Through an understanding of the mechanisms by which available slip systems are tuned, we have the potential to rationally design the next generation of ultrahard metal borides. Such ideas have been used previously for a range of superhard metal borides. ...
... 63 Dislocation creep on preferred slip systems has been reported to produce a strong texture, while grain boundary sliding and mechanical twinning usually randomize the texture. 35,61,64 Interestingly, both n-ReB 2 and n-Re 0.52 W 0.48 B 2 exhibit fairly weak texture, with an index of ∼1.3 m.r.d. at the highest pressure reached in our experiment, suggesting that the dislocation-mediated processes are not the dominant mechanism for plasticity. Indeed, the low value indicates that the n-ReB 2 and n-Re 0.52 W 0.48 B 2 maintain a low dislocation density upon non-hydrostatic compression up to ∼60 GPa, a result that also explains why the nanomaterials show a much higher yield strength than their coarse-grained counterparts. ...
Article
Rhenium diboride is an established superhard compound that can scratch diamond and can be readily synthesized under ambient pressure. Here, we demonstrate two synergistic ways to further enhance the already high yield strength of ReB2. The first approach builds on previous reports where tungsten is doped into ReB2 at concentrations up to 48 at.%, forming a rhenium/tungsten diboride solid solution (Re0.52W0.48B2). In the second approach, the composition of both materials is maintained, but the particle size is reduced to the nanoscale (40~150 nm). Bulk samples were synthesized by arc melting above 2500 ºC and salt flux growth at ~850 ºC was used to create nanoscale materials. In situ radial X-ray diffraction was then performed under high pressures up to ~60 GPa in a diamond anvil cell to study mechanical properties including bulk modulus, lattice strain, and strength anisotropy. The differential stress for both Re0.52W0.48B2 and nano ReB2 (n-ReB2) was increased compared to bulk ReB2. In addition, the lattice preferred orientation of n-ReB2 was experimentally measured. Under non-hydrostatic compression, n-ReB2 exhibits texture characterized by a maximum along the [001] direction, confirming that plastic deformation is primarily controlled by the basal slip system. At higher pressures, a range of other slip systems become active. Finally, both size and solid-solution effects were combined in nanoscale Re0.52W0.48B2. This material showed the highest differential stress and bulk modulus, combined with suppression of the new slip planes that opened at high pressure in n-ReB2.
... Although Pt has many excellent properties, its hardness needs to be improved compared with Ir or other hard metals. 16,17 Some alloying elements, such as carbon (C) and silicon (Si) can improve the hardness and strength of alloys. Doping and defect engineering [18][19][20] is a promising and effective way of improving the properties of materials. ...
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Platinum (Pt)-based dilute solid solutions are an important category of hightemperature alloys and bond coatings. In this study, the effects of 33 alloying elements on the mechanical and electronic properties of dilute Pt-based solid solutions are systematically investigated under atom relaxation and full relaxation using firstprinciples calculations based on density functional theory. The negative mixing enthalpy of Pt-dilute solid solutions means that the solubility of the solute elements in the Pt-based dilute alloys is energetically favorable at 0 K. Niobium, rhenium, and scandium are promising candidate elements for increasing the hardness and ductility of dilute Pt-based solid solutions. In addition, the electronic basis for the mechanical properties of Pt-dilute solid solutions is investigated in terms of the electronic density and mean bond population. The results demonstrate that the Pt–X bond lengths are shorter than the Pt–Pt bond length, resulting in greater hardness. Moreover, the model for the composition dependent elastic properties is built based on the CALPHAD approach, which will be used to the Pt-based multiphase alloys in the future. As certain alloying elements improve the hardness and ductility of Pt, this research expands our knowledge of the mechanism of dilute Pt-based solid solutions and provides a basis for next-generation superalloys or bond coatings at higher temperatures.
... This value representing the average lattice strain was obtained using the Triaxial Stress Isotropic E strain model implemented in MAUD and used for a first evaluation of the stress level in plastically deforming aggregates (32). In addition, the stress was also estimated from the platinum foil according to previous reports (49,50). In the cubic phase, the t/G value first increases strongly with pressure and then remains almost stable in a range of pressure between 15.8 and 21.8 GPa, before it begins to decrease with the appearance of the high-pressure phase. ...
Article
The study of orientation variant selection helps to reveal the mechanism and dynamic process of martensitic transformations driven by temperature or pressure/stress. This is challenging due to the multiple variants which may coexist. While effects of temperature and microstructure in many martensitic transformations have been studied in detail, effects of stress and pressure are much less understood. Here, an in situ variant selection study of Mn2O3 across the cubic-to-orthorhombic martensitic transformation explores orientation variants at pressures up to 51.5 GPa and stresses up to 5.5 GPa, using diamond anvil cells in radial geometry with synchrotron X-ray diffraction. The diamonds not only exert pressure but also impose stress and cause plastic deformation and texture development. The crystal orientation changes were followed in situ and a {110} c 〈001〉 c // (100) o 〈010〉 o relationship was observed. Only the {110} c plane perpendicular to the stress direction was selected to become (100) o , resulting in a very strong texture of the orthorhombic phase. Contrary to most other martensitic transformations, this study reveals a clear and simple variant selection that is attributed to structural distortions under pressure and stress.
... High deviatoric stresses can develop in a DAC so it is relevant to check if the Pt grains have not yielded. Dorfman et al. reported that the yielding of platinum strongly depends on the loading conditions [51], the grain size and it can happen at differential stress (S/3 following our definition) values below 1 GPa. In the present experiment, the values of the deviatoric stress are smaller than~300 MPa, and there is no evidence of intensity redistribution along Pt Debye rings, which would have indicated the onset of the plastic deformation. ...
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The existing macroscale models of the calcium (alumino)silicate hydrate (C-(A-)S-H), the main binder of concrete, assume that the nanocrystallites maintain random orientation under any loading conditions. However, using synchrotron-radiation-based XRD, we report the development of preferred orientation of nanocrystalline C-A-S-H, from random at ambient pressure to strongly oriented under uniaxial compression with lateral confinement. The c-axes of the nanocrystals tend to align with the primary load. This preferred orientation is preserved after removing of external loading. The texture, quantified using a standard Gaussian fiber orientation distribution function (ODF), was used to calculate the averaged bulk elastic tensor of oriented C-(A-)S-H. It changes from isotropic (without texture) to transversely isotropic (with texture). Our results provide direct evidence of the reorientation of nanocrystalline C-(A-)S-H as a mesoscale mechanism to the irreversible deformation of cement-based material. The implications of these results for modeling the mechanical property of C-(A-)S-H at the macroscale are discussed.
... Plastic deformation under high stresses also occur in mechanical devices with parts moving at high speeds (e.g., boundary condition lubrication) or for materials submitted to impacts. Thus far, most information on high-pressure plastic deformation mechanisms and yield strengths of oxides, silicates and metals have been obtained from X-ray diffraction techniques on synchrotrons owing to the small sample volumes in the diamond cell (Dorfman et al., 2015;Gleason and Mao, 2013;Merkel et al., 2002Merkel et al., , 2003Miyagi et al., 2006;Shieh et al., 2002;Singh et al., 2008). Some of The Raman frequencies of quartz are used to evaluate deviatoric stresses in rocksaltstructure media in diamond-anvil cell experiments to pressures up to 20 GPa. ...
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This book provides valuable information for all scientists and engineers interested in materials properties. Coverage discusses the measurement and analysis of textures, the prediction of polycrystal properties from measured textures and known single crystal properties, and the prediction of the development of texture and the ensuing anisotropic properties during elastic and plastic deformation. It also gives an overview of observed textures in metals, ceramics and rocks. There is a balance between theoretical concepts and experimental techniques. The book addresses several issues. Part I provides tools and describes methods This book provides valuable information for all scientists and engineers interested in material properties. It describes the measurement and analysis of textures and gives a clear and detailed discussion of the directional dependence of material properties, how they originate, and how they can be modified to improve the material performance. The book also provides an overview of observed textures in metals, ceramics and rocks. There is a useful balance between experimental techniques, theoretical concepts, and applications.
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