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Yalamanchili K.,Linköping University | Forsen R.,Linköping University | Jimenez-Pique E.,Polytechnic University of Catalonia | Jimenez-Pique E.,Center for Research in Nanoengineering | And 6 more authors.
Surface and Coatings Technology | Year: 2014

Zr-Si-N films with varying Si contents were grown on WC-Co substrates by reactive cathodic arc deposition technique. The resulting microstructures of the films correlate to dominant variation in mechanical properties and deformation mechanisms. Si forms a substitutional solid solution in the cubic ZrN lattice up to 1.8at.% exhibiting a fine columnar microstructure. Further Si additions result in precipitation of an amorphous (a)-SiNx phase and evolution of a nanocomposite microstructure (nc ZrN/a-SiNx) which completely suppresses the columnar microstructure at 6.3at.% Si. The rotation-induced artificial layering during film growth is used as a marker to visualize the deformation of the film. A dislocation-based homogeneous plastic deformation mechanism dominates the columnar microstructure, while grain boundary sliding is the active mechanism mediating heterogeneous plastic deformation in the nanocomposite microstructure. Film hardness increases with increasing Si content in the columnar microstructure due to an effective solid solution strengthening. The deformation mechanism of localized grain boundary sliding in the nanocomposite microstructure results in a lower hardness. When cracking is induced by indentation, the fine columnar microstructure exhibits pronounced crack deflection that results in a higher fracture resistance compared to the nanocomposite films. © 2014 Elsevier B.V.

In this paper, we present a combined study of the length-change and tensile strength evolution of highand low-C3A Portland cements. This approach has proven useful to provide an assessment on the performance under severe and moderate sulfate attack. While higher expansion rates are observed in high-C3A samples, tensile strength evolution of both cement types is essentially identical. The simultaneous increase of expansion rate and decrease in tensile strength is strongly suggestive that both processes are related. This is attributed to the formation and development of microcracks that favor the ingress of the sulfate solution in the specimens. These results provide further insights into the commonly accepted idea that standard (accelerated) tests aiming to evaluate the expansion behavior do not provide reliable information on the expected performance (sulfate resistance) and damage potential of Portland cements.

Drozd-Rzoska A.,Polish Academy of Sciences | Rzoska S.J.,Polish Academy of Sciences | Rzoska S.J.,University of Silesia | Pawlus S.,University of Silesia | And 4 more authors.
Physical Review E - Statistical, Nonlinear, and Soft Matter Physics | Year: 2010

Glass transition constitutes one of main problems of condensed matter physics and material engineering that remains unsolved. The common acceptance of the Vogel-Fulcher-Tammann (VFT) equation for portraying the primary relaxation time or shear viscosity indicated a possible phase transition, hidden below the glass transition temperature (Tg). Recently Hecksher [Nat. Phys. 4, 737 (2008)]10.1038/nphys1033 delivered strong empirical arguments that VFT description lacks a direct experimental basis and thus theories not predicting a dynamic divergence should be focused on. We present clear evidence for a superiority of critical-like divergent equation τ (T) = τ0 ( T- TC ) - and TC < Tg for liquid crystalline (LC) glass formers and orientationally disordered crystals (ODIC). Such dependence was already known for spin-glasslike systems and the dynamical scaling model, although the latter was hardly explored so far. The pressure-related behavior is also discussed. Results obtained support arguments for the suggested direct link between critical phenomena and vitrification. LCs and ODICs may be considered as simple experimental model systems for the structural glass formers group. © 2010 The American Physical Society.

Yalamanchili K.,Linköping University | Yalamanchili K.,Polytechnic University of Catalonia | Yalamanchili K.,Center for Research in Nanoengineering | Schramm I.C.,Linköping University | And 7 more authors.
Acta Materialia | Year: 2015

Structure and mechanical properties of nanoscale multilayers of ZrN/Zr0.63Al0.37N grown by reactive magnetron sputtering on MgO (0 0 1) substrates at a temperature of 700 °C are investigated as a function of the Zr0.63Al0.37N layer thickness. The Zr0.63Al0.37N undergoes in situ chemical segregation into ZrN-rich and AlN-rich domains. The AlN-rich domains undergo transition from cubic to wurtzite crystal structure as a function of Zr0.63Al0.37N layer thickness. Such structural transformation allows systematic variation of hardness as well as fracture resistance of the films. A maximum fracture resistance is achieved for 2 nm thick Zr0.63Al0.37N layers where the AlN-rich domains are epitaxially stabilized in the metastable cubic phase. The metastable cubic-AlN phase undergoes stress-induced transformation to wurtzite-AlN when subjected to indentation, which results in the enhanced fracture resistance. A maximum hardness of 34 GPa is obtained for 10 nm thick Zr0.63Al0.37N layers where the wurtzite-AlN and cubic-ZrN rich domains form semi-coherent interfaces. © 2015 Acta Materialia Inc.

Manosa L.,University of Barcelona | Gonzalez-Alonso D.,University of Barcelona | Planes A.,University of Barcelona | Bonnot E.,Polytechnic University of Catalonia | And 7 more authors.
Nature Materials | Year: 2010

The search for materials showing large caloric effects close to room temperature has become a challenge in modern materials physics and it is expected that such a class of materials will provide a way to renew present cooling devices that are based on the vapour compression of hazardous gases. Up to now, the most promising materials are giant magnetocaloric materials. The discovery of materials showing a giant magnetocaloric effect at temperatures close to ambient has opened up the possibility of using them for refrigeration. As caloric effects refer to the isothermal entropy change achieved by application of an external field, several caloric effects can take place on tuning different external parameters such as pressure and electric field. Indeed the occurrence of large electrocaloric and elastocaloric effects has recently been reported. Here we show that the application of a moderate hydrostatic pressure to a magnetic shape-memory alloy gives rise to a caloric effect with a magnitude that is comparable to the giant magnetocaloric effect reported in this class of materials. We anticipate that similar barocaloric effects will occur in many giant-magnetocaloric materials undergoing magnetostructural transitions involving a volume change. © 2010 Macmillan Publishers Limited. All rights reserved.

Yuce S.,University of Barcelona | Yuce S.,Ondokuz Mayis University | Barrio M.,Polytechnic University of Catalonia | Barrio M.,Center for Research in NanoEngineering | And 13 more authors.
Applied Physics Letters | Year: 2012

We report on calorimetric measurements under hydrostatic pressure that enabled us to determine the barocaloric effect in Gd 5 Si 2 Ge 2. The values for the entropy change for moderate pressures compare favourably to those corresponding to the magnetocaloric effect in this compound. Entropy data are complemented with direct measurements of the adiabatic pressure-induced temperature change. © 2012 American Institute of Physics.

Chintapalli R.K.,Polytechnic University of Catalonia | Mestra Rodriguez A.,Polytechnic University of Catalonia | Mestra Rodriguez A.,Center for Research in Nanoengineering | Garcia Marro F.,Polytechnic University of Catalonia | And 3 more authors.
Journal of the Mechanical Behavior of Biomedical Materials | Year: 2014

Sandblasting is a commonly used surface treatment technique for dental crowns to improve the adhesion of the mating parts of a restoration. The goal of this work is to study the effect of different sandblasting conditions on the mechanical properties of 3. mol% yttria stabilized tetragonal zirconia (3Y-TZP), such as biaxial strength, surface elastic modulus, contact hardness and residual stresses induced by sandblasting. The specimens were sandblasted considering two different particle sizes (110, 250. μm), two pressures (2 and 4. bar) and two impact angles (30° and 90°). Biaxial strength of 3Y-TZP increases when sandblasted with 110. μm particles while its decreases with 250. μm particles for impact angle of 90°. Strength increases slightly when sandblasting with 30° impact angle regardless of the size of the particle. Elastic modulus and contact hardness were not affected by sandblasting with 110. μm particles, and compressive residual stresses are produced down to a depth of ~10. © 2013 Elsevier Ltd.

Roa J.J.,Polytechnic University of Catalonia | Roa J.J.,Center for Research in NanoEngineering | Anglada M.,Polytechnic University of Catalonia | Anglada M.,Center for Research in NanoEngineering
Journal of the European Ceramic Society | Year: 2015

The annealing of hydrothermal aged zirconia has been studied by analysing the changes in microstructure and surface mechanical properties in terms of the annealing temperature. In this experimental work, a systematic micro- and nanomechanical study has been conducted in 3. mol% yttria-stabilized tetragonal polycrystalline zirconia (3Y-TZP) aged at 134. °C for 60. h and annealed at 600. °C and 850. °C for 1. h. Advance characterization techniques (micro-Raman, field emission scanning electron microscopy and focused ion beam) have been used to study the near surface microstructural changes induced by these treatments. The mechanical properties and resistance to damage of the near surface are determined by means of nanoindentation and nanoscratch testing. The observed behaviour is discussed in terms of the change in microstructure induced after ageing and annealing. © 2014 Elsevier Ltd.

Yalamanchili K.,Linköping University | Yalamanchili K.,Center for Research in Nanoengineering | Jimenez-Pique E.,Center for Research in Nanoengineering | Pelcastre L.,Lulea University of Technology | And 7 more authors.
Surface and Coatings Technology | Year: 2016

Varying the Si-content in Zr-Si-N coatings from 0.2 to 6.3 at.% causes microstructural changes from columnar to nanocomposite structure and a hardness drop from 37 to 26 GPa. The softer nanocomposite also displays lower fracture resistance. The tribological response of these coatings is investigated under different contact conditions, both at room and elevated temperatures. At room temperature tribooxidation is found to be the dominant wear mechanism, where the nanocomposite coatings display the lowest wear rate of 0.64 × 10− 5 mm3/Nm, by forming an oxide diffusion barrier layer consisting of Zr, W, and Si. A transition in the dominant wear mechanism from tribooxidation to microploughing is observed upon increasing the test temperature and contact stress. Here, all coatings exhibit significantly higher coefficient of friction of 1.4 and the hardest coatings with columnar structure display the lowest wear rate of 10.5 × 10− 5 mm3/Nm. In a microscopic wear test under the influence of contact-induced dominant elastic stress field, the coatings display wedge formation and pileup due to accumulation of the dislocation-induced plastic deformation. In these tests, the nanocomposite coatings display the lowest wear rate of 0.56 × 10− 10 mm3/Nm, by constraining the dislocation motion. © 2016

Rheinheimer V.,Center for Research in Nanoengineering | Casanova I.,Center for Research in Nanoengineering
Cement and Concrete Research | Year: 2012

Thin films of C 3S of a few tens of nanometers were produced by electron beam evaporation. After verification that the chemical composition of the bulk material remained unchanged, the samples were hydrated with water vapor in a reaction chamber under saturated pressure and temperature conditions, and were kept isolated from atmospheric exposure throughout the whole duration of the experiment. Analyses by X-ray photoelectron spectroscopy at different stages of hydration evidence a shift of the Si peaks to higher energies and a subsequent decrease of the Ca-Si binding energy distance, indicating silicate polymerization expected upon formation of C-S-H. The measured molar Ca/Si ratio evolves from that of a jennite-like material, of about 1.55, at the beginning of the experiment (attributed to pre-hydration of the thin films), to a tobermorite-like ratio of 0.85 after 3 h of hydration. © 2012 Elsevier Ltd.

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