Borroto-Ramírez, A.; Bruyère, S.; Thurieau, N.; Gendarme, C.; Jimenez-Pique, E.; Roa, J.J.; Pierson, J.F.; Mücklich, F.; Horwat, D. Journal of alloys and compounds Vol. 729, p. 137-143 DOI: 10.1016/j.jallcom.2017.09.153 Data de publicació: 2017-12-30 Article en revista
Zr1-xMox thin films were synthesized on glass substrates by co-sputtering molybdenum and zirconium targets in the presence of argon with x in the 0.32–0.95 range. From X-ray diffraction analyses and transmission electron microscopy images it was possible to observe an evolution of the samples structure from a nano-crystalline solid solution of Zr in the bcc lattice of Mo to clusters of Zr(Mo) nano-crystalline in an amorphous matrix. The coherence length deduced from X-ray diffractograms was around 1 nm–8 nm depending on the composition. Mechanical measurements show that the films exhibited high hardness H, low Young's modulus E and therefore high H/E ratio compared with the bulk of Zr and Mo. We also found a low friction coefficient values for all the samples. Finally, an inverse Hall-Petch effect was observed for coherence length lower than 6 nm.
The atomic structure of a Cu13Ni34Pd53 metallic glass was studied by molecular dynamics simulation at different temperatures along a shear deformation cycle. A simulation box of 1 million atoms was deformed in the x axis and then the original orthogonal shape was recovered. Directional pair distribution functions were computed in the coordinate planes and some significant directions along the shear deformation cycle. No anisotropy was found in the initial state, while post-deformation anisotropy was revealed by significant differences of the partial pair distribution functions. The analysis of atomic environments concluded that the remnant anisotropy remains constrained into the shear plane. Low temperature samples showed remnant anisotropy after the full shear sample, while close to the glass transition the anisotropy induced by the initial shear process is removed by the subsequent recovery process.
The effect of minor transition metals and rare earths on glass-forming ability, thermal stability and crystallization of [(Fe0.6Co0.4)0.75Si0.05B0.20]96-xNb4Mx alloys was investigated. The thermodynamic parameters traditionally used to predict the glass-forming ability have been calculated from calorimetric data and tested against mold casting. Only the addition of Zr and Mo allowed to cast 2 mm diameter rods, which does not correlate with predicted results. The microstructural evolution of the different alloys along the crystallization process has been studied by means of transmission Mössbauer spectroscopy showing for all studied compositions (FeCo)23B6 as primary phase that remains stable in the fully crystallized samples. Moreover, the Mössbauer spectra allowed the identification of some paramagnetic phases not identified by conventional x-ray diffraction.
Machado, R.; dos Santos, V.B.; Ochoa, D. A.; Cerdeiras, E.; Mestres, L.; Garcia, J. E. Journal of alloys and compounds Vol. 690, p. 568-574 DOI: 10.1016/j.jallcom.2016.08.116 Data de publicació: 2017-01-05 Article en revista
A systematic study of the functional properties of the (1-x)(Bi0.5Na0.5)TiO3–xBaTiO3 (BNT-xBT) piezoceramic system for 0.05 = x = 0.07 is performed. The samples are obtained through the conventional solid-state route. The expected microstructure for these compounds, with no significant dependence on the composition, is verified by field-emission scanning electron microscopy. The morphotropic phase boundary (MPB) is detected for x = 0.06–0.07 by means of the Rietveld analysis of X-ray diffraction data. The dielectric spectra show a frequency-independent, completely diffuse phase transition with a composition-dependent diffusivity coefficient. The depolarization temperature is effectively evaluated from pyroelectric measurements, the value being strongly dependent on the composition. A significant contribution of the extrinsic effect to elastic, dielectric and electromechanical properties is revealed for MPB BNT-xBT. The Bi3+ substitution by Ba2+ leads to the formation of A-site vacancies, which give rise to the enhancement of domain wall motion, as occurs in other perovskite-type piezoelectrics. Good functional properties are achieved for x = 0.07 (d33 = 180 pC/N), which are similar or even better than those obtained by complex synthesis routes. This system exhibits a remarkable stability in the permittivity that has hitherto not been reported. This fact may open the way for BNT-BT compositions to be used in specific applications in which lead-free piezoceramics have previously been employed with little success, e.g. in high power devices.
Zirconium was used in Al-Mg/B4C composite to improve compocasting efficiency by increasing particle incorporation. Scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS) results revealed that by addition of zirconium a reaction layer containing Zr, Al, B and C is formed on the interface of B4C-matrix. X-ray diffraction (XRD) analysis of extracted particles unveiled that the ZrB2 phase is the main constituent of this layer. Formation of ZrB2 is an exothermic reaction which can rise temperature locally around particles and agglomerates. Rising temperature around agglomerates in conjunction with turbulent flow of melt facilitates agglomerates wetting and dissolving into molten aluminum. As the result, final product contains more uniformly distributed B4C particles. Besides enhancing compocasting efficiency, addition of Zr and formation of reaction layer by improving particle matrix bonding quality, led to increase in ultimate tensile strength and elongation of the composite around 8% and 30%, respectively. SEM observations of the fracture surfaces confirmed that a proper bonding presents at the interface of particles and matrix in presence of Zr.
The thermal stability and microstructure after ageing at 770 K for different times have been studied on six Ni-Mn-Ga-Cu polycrystalline high temperature shape memory alloys, in which Cu substituted Mn, Ga, or both simultaneously. Prior to ageing, those compositions with higher e/a ratio not only show higher martensitic transformation temperatures but also higher thermal hysteresis. The quaternary alloys that contain less Cu show the best thermal stability, almost independently from the element that is substituted by Cu. Nevertheless, all the quaternary alloys studied in this work show notably worse thermal stability than the most stable ternary Ni-Mn-Ga high temperature shape memory alloys reported so far. Increase in ageing time at 770 K promotes the decrease of the transformation temperatures and the c/a ratio of the non-modulated martensite as a consequence of the Cu depletion in the matrix induced by the precipitation of Cu-rich ordered f.c.c. gamma' particles. Although the gamma' precipitates are heterogeneously distributed, the unique alloy with transformation temperatures very close to 770 K also show a high concentration of particles located at some intervariant martensitic boundaries, attributed to an enhanced precipitation process on the habit plane of the retained martensitic planes.
The temperature dependence of the relaxation times of Cu46Zr46Al8 glass was measured by means of mechanical spectroscopy and static stress-relaxation measurements. The weak intensity of secondary relaxation in this alloy allows us to correlate the characteristic times of dynamic and static measurements of primary relaxation. The glassy dynamics of an isoconfigurational state are found to follow an Adam-Gibbs-Vogel expression with the glassy state defined by a fictive temperature. The combination of both measurements proves that, in the frequency domain, the relaxation response can be well described by a single relaxation function above and below the glass transition. The change in relaxation times as function of the fictive temperature and the corresponding effects on the mechanical behavior are estimated and discussed. (C) 2014 Elsevier B.V. All rights reserved.
Zhang, J.; Shan, J.; Li, P.; Zhai, F.; Wan, Q.; Liu, Z.; Qu, X. Journal of alloys and compounds Vol. 643, p. 174-180 DOI: 10.1016/j.jallcom.2015.04.135 Data de publicació: 2015-09-15 Article en revista
Ferrites (CoFe2O4, ZnFe2O4, MnFe2O4 and Mn0.5Zn0.5Fe2O4) nanoparticles can all significantly reduce the desorption temperature of MgH2, and CoFe2O4 shows the best catalytic performance among the four ferrites. After dehydrogenation, new by-products including Mg, Co3Fe7 and MgO phases are found for the CoFe2O4 doped samples, and Mg, Fe3Zn10, Fe and MgO phases are identified for the ZnFe2O4 doped samples. Mg, Fe, Mn and MgO phases are observed for the MnFe2O4 doped samples, while Mg, Fe3Zn10, Mn, Fe and MgO phases appear for the Mn0.5Zn0.5Fe2O4 doped samples. New forming phases Co3Fe7, MgO and Co also have a great catalytic effect on the MgH2 hydrogen storage properties. The onset desorption temperature of MgH2 doped with bimetallic catalysts (20 wt.% Co + 20 wt.% MgO and 20 wt.% Co3Fe7 + 20 wt.% MgO) is lower than that of MgH2 doped with the single catalyst (40 wt.% Co, 40 wt.% MgO and 40 wt.% Co3Fe7), indicating that MgO and Co or MgO and Co3Fe7 have the combination catalytic function. (C) 2015 Elsevier B.V. All rights reserved.
The microstructural and strengthening behavior of two CuMg alloys, with 0.2 and 0.5 m.-% of Mg, were analyzed after severe plastic deformation by Equal Channel Angular Pressing (ECAP). Both alloys were passed through a 90° inner angle ECAP die at room temperature up to 16 passes following route Bc. The EBSD analysis of the deformed microstructure revealed a significant grain refinement after the 2nd pass. Average grain sizes as fine as 0.31 and 0.24 µm for the CuMg0.2 and CuMg0.5, respectively, were obtained after 16 passes. The tensile strength of the ECAPed samples of the present CuMg alloys did not reach a saturation level, attaining 570 and 750 MPa after 16 passes for the CuMg0.2 and CuMg0.5, respectively. The dependence of the yield stress on deformation (i.e. number of ECAP passes) and Mg content was evaluated in terms of the Hall–Petch effect (influence of grain size), dislocation density (through the subgrain hardening effect) and solid solution strengthening. Results indicated that the stronger effect comes from the subgrain microstructure rather than from High Angle Grain Boundaries (HAGB). A minor effect of the chemical composition was also noticed.
We present a temperature investigation of the structural and dynamical evolution of rapidly quenched metallic glasses of Mg65Cu25Y10 at the atomic length scale by means of in situ high energy x-ray diffraction and time resolved x-ray photon correlation spectroscopy. We find a flattening of the temperature evolution of the position of the first sharp diffraction peak on approaching the glass transition temperature from the glassy state, which reflects into a surprising slowing down of the relaxation ynamics
of even one order of magnitude with increasing temperature. The comparison between structural and dynamical properties strengthens the idea of a stress-induced, rather than pure diffusive, atomic motion in metallic glasses
Madinehei, S.M.; Bruna, P.; Duarte, M.; Pineda, E.; Klemm, J.; Renner, F. Journal of alloys and compounds Vol. 615, p. S128-S131 DOI: 10.1016/j.jallcom.2013.12.245 Data de publicació: 2014-12-05 Article en revista
The effect of low amounts of Cr on glass forming ability and corrosion behavior of Fe(65-x)CrxMo14C15B6 (x = 0, 2, 4, 6, 8,10 at.%) ribbons have been studied. It was found that the reduced glass transition temperature (T-rg) do not change significantly with Cr content. The glass forming ability (GFA) of this system is evaluated by the gamma(m), delta and omega parameters and the alloys containing 4 and 6 at.% were found to be the best glass formers in this system. The temperature interval of the supercooled liquid region (Delta T-x) changed with Cr and was enlarged from 35 K at x = 0 to 50 K at x = 4. Corrosion rates measured by immersion tests in H2SO4 decreased with an increase of chromium content in the alloys. The electrochemical measurements indicate that the alloys containing more than 4 at.% of Cr are spontaneously passivated with low current densities in 0.1 N H2SO4 whereas the alloys with Cr content <4 at.% showed transpassive Mo dissolution. In view of these results, the optimal amount of Cr addition in Fe-Mo-C-B amorphous steels is discussed. (C) 2014 Elsevier B.V. All rights reserved.
Zhai, F.; Pineda, E.; Ruta, B.; Gonzalez Silveira, Marta; Crespo, D. Journal of alloys and compounds Vol. 615, p. S9-S12 DOI: 10.1016/j.jallcom.2013.11.120 Data de publicació: 2014-12-05 Article en revista
The structural relaxation, glass transition and crystallization processes of Mg65Cu25Y10 metallic glass are studied by Differential Scanning Calorimetry (DSC) and Mechanical spectroscopy. The relaxation model derived from the mechanical measurements is compared with the kinetics of these transformations obtained from the DSC curves. The structural relaxation kinetics is found to be controlled by the glassy dynamics following an Adams-Gibbs-Vogel function. The glass transition and crystallization kinetics are controlled by the dynamics of the supercooled melt following a Vogel-Fulcher-Tammann behaviour. The results suggest that the microscopic processes responsible of structural relaxation and aging below the glass transition correspond to the same processes generating the a-relaxation peak. (C) 2013 Elsevier B.V. All rights reserved.
A new Fe-based bulk metallic glass with superior glass-forming ability (GFA), Fe46Cr15Mo14C15B6Nb4, was developed based on the Fe-Cr-Mo-C-B alloy system by minor addition of Nb. The effects of Nb addition on glass formation of the Fe-50 xCr15Mo14C15B6Nbx (x = 0, 2, 4 and 6 at.%) alloys were investigated. The optimum addition content of Nb was determined as 4 at.% by X-ray diffraction and differential scanning calorimeter analysis. A fully amorphous rod sample with 3 mm in diameter was produced by using commercial-grade raw materials and a copper mold casting technique. This alloy shows an ultimate compressive strength of 1920 MPa and Vicker's hardness 1360 H-V, which is two to three times that of conventional high strength steel and suggests a promising potential for applications combining outstanding corrosion and wear resistance properties. The crystallization kinetics studies found that the activation energies for glass transition, onset of crystallization and crystallization peak were higher than those of other reported Fe-based bulk metallic glasses. The value of the fragility parameter m for the Fe46Cr15Mo14C15B6Nb4 alloy was calculated to be 34, indicating that the Fe-Cr-Mo-C-B-Nb alloy system is a strong glass former according to the Angell's classification scheme. It is inferred that the more sequential change in the atomic size, the generation of new atomic pairs with large negative heats of mixing and the amount of oxygen in the molten liquid neutralized into Nb oxides provide a synergetic effect for the remarkably improved GFA and thermal stability. (C) 2014 Elsevier B.V. All rights reserved.
Isalgue, A.; Fernandez, J.; Cinca, N.; Villa, M.; Guilemany, J. Journal of alloys and compounds Vol. 577, num. Supplement 1, p. S277-S281 DOI: 10.1016/j.jallcom.2012.05.033 Data de publicació: 2013-11-15 Article en revista
The nanoindentation behavior of wear resistant coatings containing TiC–NiTi is studied. The raw material contained 60%weight of TiC and 40%weight of near equiatomic NiTi. The powder was sprayed by
plasma and HVOF techniques. Higher temperatures in the plasma spraying produced better matrix melting but also more cracks on cooling. The presence of some amorphous or nanocrystalline phase occurs, at least in some coatings, being this related to the good wear behavior. The projection conditions play an important role on the partial transformation because ofthe decomposition and oxidation ofthe NiTi as a
consequence of the temperatures involved during the spray deposition. The nanoindentation measures
suggest that, even with the presence of hard TiC particles, partial oxidation and dissociation of NiTi, there
is some pseudoelasticity.
Fan, J.; Fábrega, C.; Zamani, R.; Shavel, A.; Güell, F.; Carrete, A.; Morante, J.R.; Andreu, T.; Lopez, A.; Arbiol, J.; Cabot, A. Journal of alloys and compounds Vol. 555, p. 213-218 DOI: 10.1016/j.jallcom.2012.11.166 Data de publicació: 2013-04-05 Article en revista
Arrays of vertically aligned ZnO:Cl@ZnS core–shell nanowires (NWs) were grown by a facile low-cost, high-yield and seed-free two-step process. These NWs were used to demonstrate the potential of 3D electrodes based on core–shell heterostructures to enhance charge carrier separation and transfer. With this goal in mind, the photocurrent density of ZnO:Cl@ZnS NWs was characterized as a function of the shell thickness. Although no significant variations in the absorption and photoluminescence spectra were found with the presence of the shell, the photocurrent measured from the core–shell NWs was highly enhanced with respect to bare ZnO:Cl NWs. These photocurrent variations are associated with the control of the band bending in the core–shell NW surface, which modifies the efficiency of charge carrier transfer between the NW and the electrolyte.
Dry mechanosynthesis is an efficient technique to synthesise nanocrystalline calcium deficient hydroxyapatites
(CDHA). The mechanisms underlying a mechanochemical reaction are different from those
triggering a dissolution mediated process, and this can have an effect on the structural features of the
product. In this work, a nanocrystalline CDHA with Ca/P molar ratio of 1.5 obtained by means of dry
mechanosynthesis of calcium oxide and dicalcium phosphate dihydrate was analysed. Spectroscopic
techniques confirmed the presence of hydrogen phosphate (HPO4
2−) groups and a non-apatitic environment
of the phosphate ions and disordered hydroxyl groups due to the nanometric size of the crystals.
Lattice parameters of mechanosynthesised CDHA showed a small increase in the a lattice parameter
(9.4418(20)A˚ ) and a small decrease in the c lattice parameter (6.8745(17)A˚ ), in agreement with the values
reported in the literature for precipitated CDHAs. A prolonged milling resulted in an increase of the
crystallinity of the CDHA and its partial decomposition into -TCP by the loss of OH− and HPO4
Amorphous steels are promising materials with potential structural applications. The glass-forming ability (GFA) and mechanical properties of metallic glasses are intimately related to the local structure. In
Fe-based alloys, Cr andMocontentseemto play a key role in stabilizing the amorphous atomic-level structure. Here we present a study on the effects of changing Mo content in Fe72−xC7Si3.3B5.5P8.7Cr2.3Al2Mox amorphous steels.Westudy the local structure of these alloys by Synchrotron X-ray diffraction and Mössbauer spectroscopy. The results show how the amorphous phase evolves from a ferromagnetic Fe-rich structure to a structure with predominance of paramagnetic environments with the increase of Mo content.
The changes in the distribution of magnetic environments cannot be attributed only to the Fe–Mo substitution but to a change of local configuration in the amorphous phase.
Bruna, P.; Baldi, G.; Pineda, E.; Serrano, J.; Crespo, D.; Monaco, G. Journal of alloys and compounds Vol. 509, p. S95-S98 DOI: 10.1016/j.jallcom.2010.09.065 Data de publicació: 2011-06 Article en revista
Cabrera, J.; S.M. Fatemi-Varzaneh, S.; Zarei-Hanzaki, A. Journal of alloys and compounds Vol. 509, num. 9, p. 3806-3810 DOI: 10.1016/j.jallcom.2011.01.019 Data de publicació: 2011-02 Article en revista
Severe plastic deformation was applied on a wrought AZ31 magnesium alloy by a new method called accumulative back extrusion (ABE). Instabilities of plastic flow in the form of localized shear bands were experimentally observed during ABE processing of the AZ31 alloy. The obtained microstructures show the appearance of shear bands in ABE processed specimens, the extent of which was observed to be decreased by increasing the temperature. The restricted flow (due to the deformation geometry) was discussed as the main cause of the latter behavior. A noticeable grain refinement was observed inside the shear bands which was attributed to the occurrence of continuous dynamic recrystallization inside the bands. To analyze the homogeneity of mechanical properties, the microhardness variations from the deformed bulk to the shear bands were measured and interpreted. The role of shear banding in grain refinement with no harmful effect on material soundness was explained.
The measurement of fragility of glass-forming liquids involves either the determination of viscosity at
different temperatures above the glass transition or the measurement of the dynamic glass–liquid transition
by calorimetry or dilatometry at different heating rates. Significant data dispersion is observed when
comparing fragility parameters obtained by different techniques. Dynamic mechanical analysis (DMA) is
widely used for characterizing glass transition in polymer science while it is still seldom used in metallic
glasses. In this work we determine the relaxation time ( ) vs temperature of a Pd77.5Si16.5Cu6 glass by
means ofDMAmeasurements. The measured range of relaxation times cover the whole region from glass
transition ( > 100 s) to times of the order of 10−2 s. The fragility parameter obtained for this alloy is found
significantly higher than the values obtained from previous viscosity and calorimetric techniques. The
application range, limitations and correctness of the technique are discussed.
Serrano, J.; Pineda, E.; Bruna, P.; Labrado, A.; Le Tacon, M.; Krisch, M.; Monaco, G.; Crespo, D. Journal of alloys and compounds Vol. 495, num. 2, p. 319-322 DOI: 10.1016/j.jallcom.2009.10.250 Data de publicació: 2010-04-16 Article en revista
The effect of partial replacement of Fe by Co (up to 8 %) on thermal stability, structure and magnetic properties of FeNbBCu alloys has been explored in this paper. The results indicate that Co reduces the stability against crystallization of the amorphous alloy and stabilizes the nanocrystalline phase prior to the further precipitation of metastable boride phases. Transmission Mössbauer spectroscopy reveals differences in the hyperfine interactions between the alloys: Co raises the mean hyperfine field of the amorphous state and differences in the nanocrystalline bcc-Fe(Co) environments between the alloys occur depending on the amount of Co near-neighbours in the bcc-Fe structure. The addition of Co has also a notable effect on the magnetic properties of both amorphous and nanocrystalline alloys increasing the Curie temperature, which shows a linear dependence with the Co composition, and the saturation polarization.
Pineda, E.; Hidalgo, I.; Bruna, P.; Pradell, T.; Labrador, A.; Crespo, D. Journal of alloys and compounds Vol. 483, p. 578-581 DOI: 10.1016/j.jallcom.2008.07.194 Data de publicació: 2009-01 Article en revista
Arciniegas, M.; Casals, J.; Manero, J.; Peña, F.; Gil, F.J. Journal of alloys and compounds Vol. 460, num. 1-2, p. 213-219 DOI: 10.1016/j.jallcom.2007.05.069 Data de publicació: 2008-07 Article en revista
Raymond, S.; Piekarz, P.; Sanchez, J.; Serrano, J.; Krisch, M.; Janusova, B.; Rebizant, J.; Metoki, N.; Kaneko, K.; Jochym, P.; Oles, A.; Parlinski, A. Journal of alloys and compounds Vol. 444, p. 104-108 Data de publicació: 2007-01 Article en revista
Gil, F.J.; Picas, J.A.; Manero, J.; Forn, A.; Planell, J. A. Journal of alloys and compounds Vol. 260, num. 1-2, p. 147-152 DOI: 10.1016/S0925-8388(97)00135-7 Data de publicació: 1997-06 Article en revista