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This study aims to evaluate the mechanical behavior of nanostructured and conventional alumina–titania coatings by means of combining four-point bend tests monitored with acoustic emission. Determination of bending strength, along with information received from acoustic emission signal, such as quantity, amplitude, energy and length of events gives a better understanding of failure mechanisms in coatings. This information has been complemented with optical analysis of fracture surfaces. Failure of coatings has been observed to follow four stages that are clearly defined in the acoustic emission data. This fracture behavior has been observed for all three types of coating tested, but the nanostructured coating presented the best combination of hardness and strength, due to its duplex microstructure.

Powders of K0.5Na0.5NbO3 lead-free piezoelectric ceramics were successfully synthesized via conventional and microwave-assisted heating. A single-mode microwave equipment was used to perform the synthesis following the mixed oxide route and then sintering at different temperatures. The synthesized powders obtained and then sintered by microwave and conventional methods were evaluated by thermogravimetry analysis, X-ray diffraction, field emission scanning electron microscopy and electrical properties. Microwave synthesis processing for 10 min at 650 °C using a heating rate of 30 °C/min promotes the formation of K0.5Na0.5NbO3 particles in the range of 100–300 nm. Perovskite structure formed during calcination shows the coexistence of tetragonal-orthorhombic geometry according to X-ray diffraction patterns. The microwave-obtained particles are consistent with the theoretical stoichiometry. Particle size increases up to 1 µm as the reaction temperature is increased from 650 to 800 °C. An intermediate phase (K,Na)2Nb4O11 is formed in the entire range of synthesis temperatures studied. The samples obtained by microwave sintering show a structure similar to the samples sintered by the conventional method. However, the porosity observed (~ 8–6%) in the microstructure of the microwave-sintered piezoelectric materials affects the density of the material, and these defects cause a decrease in the dielectric values. The highest d33 value of 126 pC/N was obtained for samples obtained by conventional at 1100 °C-2 h compared to the microwave samples (~ 25 pC/N).

Dense alumina toughened zirconia nanocomposites (ATZ, 3Y-TZP with 20 wt% Al2O3) were densified by non-conventional microwave sintering technology at relatively low temperatures (1200 and 1300 °C). The sintering method and its effect on densification, microstructure, mechanical properties and tribological behaviour were investigated. The outcomes demonstrated that the density rose as the sintering temperature was higher, and therefore the mechanical properties were enhanced, reaching a maximum hardness (18.4 ± 0.4 GPa) and fracture toughness (5.7 ± 0.3MPa· m1/2). In addition, the samples were subjected to a tribological test in dry and wet conditions, using artificial saliva. In both cases, the coefficient of friction and wear volume for samples obtained by microwave sintering are lower than conventional samples, with the wear volume being two times higher in dry conditions than in wet conditions., The authors are grateful to the Government of Valencia for the funding received for the project PROMETEU/2016/040. A. Borrell thanks to the Spanish Ministry of Economy and Competitiveness for her RyC contract (RYC-2016-20915). A. Dalmau acknowledges to the Valencia Government for the financial support (APOSTD/2017/051).

The incorporation of AlO-NbC-nanopowder reinforcement in a 3Y-TZP matrix, and its influence on the mechanical properties of 3YTZP/AlO-NbC nanocomposites, obtained by conventional and spark plasma sintering (SPS), was investigated. Nanometric powders of AlO-NbC were prepared by reactive high-energy milling, deagglomeration, and leaching with acid, and added to the 3Y-TZP matrix, at a proportion of 5 vol%. The final powders were dried under airflow, compacted, and sintered in the temperature range of 1300–1500 °C. The effects of the sintering technique and final temperature, on the microstructure and mechanical properties, such as hardness, toughness, and Young's modulus, were analysed. Fracture toughness of the material reinforced with AlO-NbC nanopowders, which is one of its most important properties, differed significantly from that of the 3Y-TZP monolith (5.2 MPa m). The nanocomposites, sintered conventionally at 1450 °C, showed higher fracture toughness (8.7 MPa m). Microstructure observations indicated that NbC nanoparticles were dispersed homogeneously within the 3Y-TZP matrix, and limited its grain growth. However, partial oxidation of the NbC on the nanocomposite surface, at the conventional sintering temperature of 1500 °C, caused a reduction in the fracture toughness., The authors acknowledge the Brazilian institutions CAPES-PVE (grant number 23038.009604/2013-12), FAPESP (grant number 2015/07319-8), Fundação Araucária (grant number 810/2014), European Union/Erasmus Mundus for doctorate mobility (grant number EB15DM1542), and the Spanish Ministry of Economy and Competitiveness (grant number IJCI-2014-19839).

[EN] A simple, soft, and fast microwave-assisted hydrothermal method was used for the preparation of nanocrystalline cobalt ferrite powders from commercially-available Fe(NO3)(3)center dot 9H(2)O, Co(NO3)(2)center dot 6H(2)O, ammonium hydroxide, and tetrapropylammonium hydroxide (TPAH). The synthesis was conducted in a sealed-vessel microwave reactor specifically designed for synthetic applications, and the resulting products were characterized by XRD, FE-SEM, TEM, and HR-TEM. After a systematic study of the influence of the microwave variables (temperature, reaction time and nature of the bases), highly crystalline CoFe2O4 nanoparticles with a high uniformity in morphology and size, were directly obtained by heating at 130 degrees C for 20 min using the base TPAH. Dense ceramics of cobalt ferrite were prepared by non-conventional, microwave sintering of synthesized nanopowders at temperatures of 850-900 degrees C. The magnetic properties of both the nanopowders and the sintered specimens were determined in order to establish their feasibility as a permanent magnet., This work has been carried out with financial support from the Spanish Ministry of Economy, Industry and Competitiveness (MINECO) and CSIC through the Projects MAT2015-67586-C3-R and NANOMIND, respectively. A. Borrell acknowledges MINECO for a Juan de la Cierva contract (IJCI-2014-19839).

[EN] Zirconates with pyrochlore structure, such as Gd2Zr2O7, are new promising thermal barrier coatings because of their very low thermal conductivity and good chemical resistance against molten salts. However, their coefficient of thermal expansion is low, therefore their thermal fatigue resistance is compromised. As a solution, the combination of yttria-stabilised zirconia (YSZ) and Gd2Zr2O7 can reduce the thermal contraction mismatch between the thermal barrier coating parts. In the present study, two possible designs have been performed to combine YSZ/Gd2Zr2O7. On the one hand, a multilayer coating was obtained where YSZ layer was deposited between a Gd2Zr2O7 layer and a bond coat. On the other hand, a functionally-graded coating was designed where different layers with variable ratios of YSZ/Gd2Zr2O7 were deposited such that the composition gradually changed along the coating thickness. Multilayer and functionally-graded coatings underwent isothermal and thermally-cycled treatments in order to evaluate the oxidation, sintering effects and thermal fatigue resistance of the coatings. The YSZ/Gd2Zr2O7 multilayer coating displayed better thermal behaviour than the Gd2Zr2O7 monolayer coating but quite less thermal fatigue resistance compared to the conventional YSZ coating. However, the functionally-graded coating displays a good thermal fatigue resistance. Hence, it can be concluded that this kind of design is ideal to optimise the behaviour of thermal barrier coatings., This work has been supported by the Spanish Ministry of Economy and Competitiveness (project MAT2015-67586-C3-R). A. Borrell acknowledges the Spanish Ministry of Economy and Competitiveness for her Juan de la Cierva-Incorporacion contract (IJCI-2014-49839) and the Program to Support Research and Development (PAID-00-15) of the Universitat Politecnica de Valencia. P. Carpio acknowledges the Valencia Government for his post-doc contract (APOSTD/2016/040).

This study aims to investigate the dry sliding wear behavior of AlO–5vol%NbC nanocomposite sintered by conventional and spark plasma sintering at temperatures from 1450 to 1600 °C. The tests were performed using WC–6 wt%Co balls as a counterpart material, a load of 30 and 60 N, a sliding distance of 2000 m and a sliding speed of 0.1 m/s. The consolidation techniques influenced the friction coefficient, wear rates and patterns. Samples tested at 30 N showed better wear resistance than the samples tests with 60 N. The nanocomposites obtained by SPS at 1500 °C exhibited a lower friction coefficient and wear rate compared to all other materials. The results indicated that AlO-NbC nanocomposites show promise as material for cutting tool applications., This work has been financial support by the Brazilian institution CAPES for the project CAPES-PVE A086/2013 (project No 23038.009604/2013-12). A. Borrell acknowledges the Spanish Ministry of Economy and Competitiveness for her Juan de la Cierva-Incorporación contract (IJCI-2014–19839).

[EN] The LZS glass-ceramic (19.58 Li2O center dot 11.10ZrO(2)center dot 69.32SiO(2)) have a high coefficient thermal expansion (CTE) which can be a limitation in some applications. The addition of alumina in a LZS glass-ceramic matrix is able to reduce the CTE significantly. This happens because of the alumina affinity with respect to lithium silicates to form beta-spodumene (LiAlSi2O6), a crystalline phase having a CTE nearly zero (0.9 x 10(-6) degrees C-1).In this work, (1-5 vol%) Al2O3 nanoparticles (13 nm) were added to a LZS (3.5 mu m) glass-ceramic matrix to prepare composites with the main goal of evaluation the influence of Al2O3 on their mechanical, thermal and electrical properties. Each composition was wet homogenized and then dried at 110 degrees C for 48 h for disaggregation. The composites, sintered at 900 degrees C for 30 min, with relative densities between 92% and 98%, showed zircon and beta-spodumene as main crystalline phases. The incorporation of increasing additions of nanosized alumina progressively decreases the final density. This makes the properties to slightly decrease, also. The Young's modulus significantly decreases from 111 to 78 GPa of hardness due to the exponential variation with porosity, but the changes of toughness and hardness are much lower. The electrical conductivity was maintained within +/- 10-7 S. cm(-1), and the dielectric constant ranged from 5 to 6 for all compositions. Thermal conductivity ranged around 4.2 to 3.5 W/mK. (C) 2017 Elsevier B.V. All rights reserved., This work has been supported by CAPES in the frame of the International Cooperation Program Science without Borders for Special Visiting Researcher PVE (MEC/MCTI/CAPES/CNPq/FAPs/ No 71/2013), Project No A011/2013 (Brazil) and CNPq (National Council for Scientific and Technological Development, Brazil). This work has been also supported by Ministerio de Economia y Cornpetitividad and FEDER Funds under grant No MAT2016-67586-C3-R and grant ENE2013-49111-C2-1-R. A. Borrell acknowledges the MINECO for her Juan de la Cierva-Incorporacion contract (IJCI-2014-19839).

[EN] Li2O-SiO2-ZrO2 (LZS) glass-ceramics have high mechanical strength, hardness, resistance to abrasion and chemical attack, but also a high coefficient of thermal expansion (CTE), which can be reduced adding alumina nanoparticles. The conventional glass-ceramic production is relatively complex and energy consuming, since it requires the melting of the raw materials to form a glass frit and a two-step milling process to obtain particle sizes adequate for compaction. This study describes the preparation of LZS glass-ceramics through a colloidal processing approach from mixtures of SiO2 and ZrO2 nanopowders and a Li precursor (lithium acetate obtained by reaction of the carbonate with acetic acid). Concentrated suspensions were freeze-dried to obtain homogeneous mixtures of powders that were pressed (100 MPa) and sintered conventionally and by spark plasma sintering. The effect of the alumina nanoparticles additions on suspensions rheology, sintering behavior and properties such as thermal expansion, thermal conductivity, hardness and Young's modulus were evaluated. (C) 2017 Elsevier Ltd. All rights reserved., This work has been supported by Ministerio de Economia y Competitividad (MINECO) and FEDER Funds under grant No MAT2016-67586-C3-R. Authors greatly acknowledge the financial Support of CAPES in the frame of the International Cooperation Program Science without Borders for Special Visiting Researcher PVE (MEC/MCTI/CAPES/CNPQ/FAPs/No 71/2013), Project no. A011/2013. A. Borrell acknowledges the MINECO for her Juan de la Cierva-Incorporacion contract (IJCI-2014-19839).

The sintering behavior of AlO-NbC nanocomposites fabricated via conventional and spark plasma sintering (SPS) was investigated. The nanometric powders of NbC were prepared by reactive high-energy milling, deagglomerated, leached with acid, added to the AlO matrix in the proportion of 5 vol% and dried under airflow. Then, the nanocomposite powders were densified at different temperatures, 1450–1600 °C. Effect of sintering temperature on the microstructure and mechanical properties such as hardness, toughness and bending strength were analyzed. The AlO-NbC nanocomposites obtained by SPS show full density and maximum hardness value > 25 GPa and bending strength of 532 MPa at 1500 °C. Microstructure observations indicate that NbC nanoparticles are dispersed homogeneously within AlO matrix and limit their grain growth. Scanning electron microscopy examination of the fracture surfaces of dense samples obtained at 1600 °C by SPS revealed partial melting of the particle surfaces due to the discharge effect., This work has been financial support by the Brazilian institution CAPES for the project CAPES-PVE A086/2013 (project no. 23038.009604/2013-12). A. Borrell, acknowledges the Spanish Ministry of Economy and Competitiveness for her Juan de la Cierva-Incorporación contract (IJCI-2014-19839).

[ES] En el presente trabajo se ha estudiado la influencia de cada uno de los parámetros de la proyección térmica por plasma atmosférico (atmospheric plasma spraying, APS) en la deposición de dos polvos comerciales de YSZ, uno convencional y otro nanoestructurado. En primer lugar se ha estudiado cómo afecta la variabilidad de los diferentes parámetros en el comportamiento de las partículas durante la proyección. Para tal fin, se ha utilizado un sensor que permite determinar la temperatura y la velocidad de las partículas en el interior del plasma. Una vez conocido cómo influyen los parámetros de proyección se han depositado ambos polvos sobre sustratos de acero inoxidable mediante APS modificando aquellos parámetros con un mayor impacto en el comportamiento de las partículas. Estos recubrimientos han sido caracterizados y se ha analizado la influencia del comportamiento de las partículas durante la proyección en la microestructura y propiedades del recubrimiento final. En este trabajo se concluye que la variación de los parámetros de proyección afecta en la velocidad y temperatura de las partículas en el interior del plasma y este comportamiento influye a su vez, y de forma diferente al emplear los distintos polvos (micro- y nanoesctructurado) en las características de los recubrimientos finales., [EN] In the present work, the influence of atmospheric plasma spray (APS) parameters on the deposition of two commercial YSZ feedstocks, one conventional and one nanostrcutured, has been studied. First the study focused on how the variability of the different parameters affects the particle behaviour during spraying. For this purpose, a sensor which enables to measure the particle temperature and velocity inside the plasma was used. Once the spraying parameters influence was known, both powders were deposited by APS onto stainless steel substrates modifying the higher influencing parameters. These coatings have been characterised and the influence of the particle behaviour on the coating microstructure and properties has been analysed. This work concludes the spraying parameters variation affects on the particle velocity and temperature inside the plasma plume and this behaviour influences, in turn but in a different way, on the final coating characteristics when using different powders (micro- and nanostructured)., Este trabajo ha sido financiado por el Ministerio Español de Economía y Competitividad (MAT2012-38364-C03) y el Plan de Promoción a la Investigación de la Universidad Jaume I, acción 2.4 (ref. E-2012-04) y acción 3.1 (ref. PREDOC/2009/10). Los autores están agradecidos con el Servicio Central de Soporte a la Investigación Experimental (SCSIE) de la Universitat de Valencia por el uso del MEB. A. Borrell agradece al Ministerio Español de Ciencia e Innovación su contrato Juan de la Cierva (JCI-2011-10498).

[ES]: La técnica de sinterización no convencional de microondas permite obtener materiales de ß-eucriptita en estado sólido cristalino con densidades cercanas a la teórica (~99 %). Se ha observado una diferencia considerable en estos materiales respecto a la técnica convencional en términos de densificación, microestructura, coeficiente de expansión térmica y propiedades mecánicas. Los valores de dureza y módulo de Young obtenidos mediante sinterización por microondas a 1200 ºC-5 min han sido relativamente altos, 6.8 GPa y 101 GPa, respectivamente, en comparación con el material obtenido mediante horno convencional (3.9 GPa y 58 GPa, respectivamente). Los datos dilatométricos obtenidos, incluyendo el intervalo de temperatura criogénica (-150 ºC a +150 ºC), muestran un coeficiente de expansión térmica controlado y negativo en todo el rango de temperaturas. La combinación de un calentamiento rápido junto con la reducción drástica en el tiempo de ciclo y el ahorro energético, hace que la técnica de microondas sean una clara alternativa a otro tipo de calentamientos., [EN]: Microwave non-conventional sintering technique allows obtaining fully dense glass-free β-eucryptite bulk material (∼99 %). A considerable difference in the densification, microstructure, coefficient of thermal expansion behaviour and mechanical properties, between conventional and non-conventional sintered specimens was observed. The hardness and Young’s modulus values obtained by microwaves at 1200 °C-5min have been relatively high, 6.8 GPa and 101 GPa, respectively, compared to conventional sintering (3.9 GPa and 58 GPa, respectively). Very low thermal expansion materials have been obtained in a wide temperature range including cryogenic temperatures (from -150 ºC to 150 ºC). The high heating rate along with the lower energy consumption makes microwave technique a clear alternative to other types of sintering methods., Los autores desean agradecer el apoyo financiero recibido de la UPV dentro de los proyectos SP20120621 y SP20120677 y, al gobierno español a través del proyecto (TEC2012-37532-C02-01). A. Borrell, agradece al Ministerio de Ciencia e Innovación su contrato de Juan la Cierva (JCI-2011-10498).

The present work aims are to study the dry sliding wear behavior of WC-12wt%Co materials, with or without addition of Cr3C2/VC grain growth inhibitors, and to sinter them by two different consolidation techniques: conventional sintering and spark plasma sintering (SPS). The dry sliding wear tests were performed on a tribometer with a ball-on-disc configuration using a WC-Co ball as a counterpart material with a normal contact load of 60N, a sliding distance of 10,000m and a sliding speed of 0.1m/s. The influence of the grain growth inhibitors and the consolidation techniques in sintered samples were related to the friction coefficient, wear rates and wear pattern damage. Samples sintered by non-conventional technique (SPS) show the best wear resistance and lower friction coefficient. The addition of inhibitors reduces the wear rates in materials consolidated by both techniques. The differences in the wear damage are related to microstructural parameters, mechanical properties and wear rates. © 2013., The work is supported financially by the Spanish Ministry of Science and Innovation by the project MAT2009-14144-C03-C02. L. Espinosa-Fernández, acknowledges the AECI program for the realization of the Ph.D in the ITM-UPV. A. Borrell, acknowledges the Spanish Ministry of Science and Innovation for her Juan de la Cierva contract (JCI-2011-10498).

In recent years, intense research has shown that thermal spray techniques, especially atmospheric plasma spraying (APS), can be used to obtain nanostructured TiO2 coatings with effective photocatalytic activity. This study compares the photocatalytic activity of APS coatings obtained from different powders: two nanostructured TiO2 powders produced by spray-drying of two TiO2 nanosuspensions with different solids contents, one spray-dried powder obtained from a suspension comprising a mixture of submicronic and nanometric TiO2 particles and finally one commercial, nanostructured, TiO2 spray-dried powder. All powders were characterised by XRD, FEG-ESEM, granule size distribution, and a flowability evaluation. Feedstock powders were then deposited on austenitic stainless steel coupons using APS. Hydrogen or helium was used as secondary plasma gas. Coating microstructure and phase composition were characterised using FEG-ESEM and XRD techniques; coating anatase content was quantified by the Rietveld method. A significant amount of anatase to rutile transformation was found to take place during the plasma spraying process. In general, the coatings had a bimodal microstructure characterised by the presence of completely fused areas in addition to non-molten areas consisting of agglomerates of anatase nanoparticles. Results also showed that anatase content and porosity of the coatings largely depend on the secondary plasma gas nature, as well as on the characteristics of the feedstock. Finally the photocatalytic activity of the coatings was determined by measuring the degradation of methylene blue dye in an aqueous solution. A reasonably good fit of a first-order kinetic model to the experimental data was found for all coatings. The values of the kinetic constant were related to feedstock characteristics as well as to plasma spraying conditions. (C) 2012 Elsevier B.V. All rights reserved.

As starting materials two commercial nanosized zirconias doped with 3 mol% of Y 2O 3 were used: a powder of about 100 nm (TZ3YE, Tosoh, Japan) and a colloidal suspension of about 15 nm (Mel Chemicals, UK). Colloidal stability in water was studied for both zirconias in terms of zeta potential as a function of deflocculant concentration and pH. Concentrated suspensions were prepared by dispersing the powder in the colloidal suspension to solids loadings ranging from 5 to 30 vol.% using a sonication probe to achieve dispersion. The rheological behavior was optimized in terms of solids content, deflocculant content and sonication time. Optimized suspensions with up to 25 vol.% solids showed a nearly Newtonian behavior and extremely low viscosities and maintain stable for long times (days) which is an important drawback of conventional nanoparticle suspensions. Samples obtained by slip casting in plaster moulds were used for dynamic sintering studies and dense, nanostructured specimens were obtained at temperatures of 1300-1400°C., This work has been supported by Spanish Ministry of Science and Innovation (Projects MAT2009-14144-C03-02 and MAT2009-14369-C02-01). R. Moreno thanks to Universidad Politecnica de Valencia for the concession of a grant in the frame of its Programme of Support to R + D (PAID-02-11, R-1752).

The effect of adding Cr3C2, VC or a mixture of both as a grain growth inhibitors to cemented carbides obtained from WC-12 wt.%Co nanocrystalline mixtures on the behaviour of friction and dry sliding wear have been studied. All the wear tests were performed on a tribometer with ball on disc configuration, using a WC-6 wt.%Co ball as a counterpart with normal contact loads of 40 and 60 N, sliding distance of 2000 m and a sliding speed of 0.1 m/s. A significant reduction in the wear rates was observed by the effect of the aforementioned additives, in particular for the VC, which showed an increase in the wear resistance of the order of 90%. The analysis of wear and surface damage were correlated to the observed behaviour., The authors would like to thank the Ministry of Education and Science, and the support received through the Projects MAT2006-12945-C03-02 and MAT2009-14144-C03-02, as well as the AECI for the realization of the doctoral thesis by L. Espinosa in the ITM of the UPV.

In this work ultrafine and nanocrystalline WC–Co mixtures were obtained by low energy milling in planetary ball mill. The effect of the processing conditions on the reduction and distribution of the grain sizes and the internal strains level were studied. The characterisation of the powder mixtures was performed by means of scanning and transmission electron microscopy and X-ray diffraction analysis. Observations through SEM and TEM images showed a particle size below 100 nm, after milling. The X-ray diffraction profile analysis revealed a WC phase refined to a crystallite size of 19 nm. ƒThe mixtures obtained have been consolidated and mechanical and microstructurally characterised. The results show improvements in resistant behaviour of the material consolidated from nanocrystalline powders, in spite of the grain growth experienced during the sintering. The best results were found for the material obtained by wet milling during 100 h, which presents values of hardness higher than 1800 HV.

Nanocrystalline tungsten carbide has been obtained by reduction/carburization at low temperature from precursors obtained by freeze-drying of aqueous solutions. Nanocrystalline WC powders with a adequate content of carbon were mixed with submicrometric Cobalt powder (12 wt.%), obtained by same synthesis method, and sintered in vacuum furnace. The cemented carbides fabricated from experimental powders were compared with both commercial ultrafine and nanocrystalline WC-12Co mixtures consolidated by the same route. The synthesised powders were characterized by X-ray powder diffraction, elemental analysis and scanning and high resolution transmission electron microscopy. On the other hand, density, microstructure, hardness and fracture toughness together with X-ray diffraction analysis of the sintered materials were evaluated. The cemented carbides obtained from synthesised powders exhibited a WC platelet-based homogeneous microstructure. This anisotropic growth might be due to the presence of stacking faults parallel to the basal plane in the starting WC powder, which would promote the defect-assisted preferential growth. These materials showed excellent mechanical properties, with a superior hardness/fracture toughness combination compared to materials prepared from commercial mixtures.

[EN] With the development of finer hardmetals, the study of mechanical properties of the different constituents down the micrometric level is a question of concern for materials optimization. Nanoindentation has been developed in last years in order to cope with mechanical characterisation at the nanolevel, but difficulties on phase detection are an issue. In the present work, individual hardness and Young's modulus of the constituents of WC-12Co composite were obtained by the use of very shallow nanoindentations (30 nm depth), with the aid of in situ 3D imaging to identify these. By this method three different phases at the sub-micrometric level have been identified and characterised: namely cobalt matrix, tungsten carbide and eta phase. The presence of the latter phase and its characterisation is of paramount importance in understanding the behaviour of hardmetals. Values of hardness from 8 (cobalt matrix) to 25 GPa (eta phase) have been obtained. Also, for these phases Young's modulus varied from 250 to 400 GPa respectively. Furthermore, it is firstly reported these values for the WC prismatic planes (1 0 1 0) being in the range of 40-55 and 700-900 GPa respectively. These values decrease to a hardness in the range of 25-30 GPa and modulus in the range from 450 to 550 GPa for the WC basal plane {0 0 0 1}. (C) 2010 Elsevier B.V. All rights reserved., This work has been supported by CICYT, Spain, through project number MAT2006-12945-C03-02 and Generalitat Valenciana, through project number ACOMP/2009/221.

WC-12%Co coatings were deposited by atmospheric plasma spraying using conventional and nanostructured powders and two secondary plasmogenous gases (He and H2). Coating microstructure and phase composition were characterized using scanning electron microscopy (SEM), transmission electron microscopy (TEM), and x-ray diffraction techniques (XRD) techniques. This study examined wear and friction properties of the coatings under dry friction conditions. SEM was used to analyze abraded surface microstructure. Coating microhardness and fracture toughness were also determined. All coatings displayed strong decarburization as a result of WC decomposition, which gave rise to the formation of secondary phases (W2C and W). A very fine undissolved WC crystalline dispersion coexisted with these new phases. TEM observation confirmed that the matrix was predominantly amorphous and filled with block-type, frequently dislocated crystallites. Wear was observed to follow a three-body abrasive mechanism, since debris between the ball and the coating surface was detected. The main wear mechanism was based on subsurface cracking, owing to the arising debris. WC grain decomposition and dissolution were concluded to be critical factors in wear resistance. The level of decomposition and dissolution could be modified by changing the plasmogenous gas or feed powder grain size. The influence of the plasmogenous gas on wear resistance was greater than the influence of feedstock particle size.

This study deals with the feasibility of using boron carbide (B4C) as reinforcement for aluminum matrix composites (AMCs) obtained by solid-state processes (powder metallurgy and extrusion). Two different reinforcements were considered: B4C as the object of this study and SiC for direct comparison of results. Aluminum alloy AA6061 was used as matrix in all cases. Comparative analysis between both SiC and B4C composites was focused on mechanical and tribological properties and correlated to microstructural features. Hardness and strength increased for composites together with volume fraction of reinforcement, reaching its maximum value to 10% B4C. Regarding tribology, composites showed an increased dynamic friction coefficient but a lower wear rate than the unreinforced aluminum alloy. Applications as brake disks for automotive industry are foreseen.

Al2O3-13%TiO2 coatings were deposited on stainless steel substrates from conventional and nanostructured powders using atmospheric plasma spraying (APS). A complete characterization of the feedstock confirmed its nanostructured nature. Coating microstructures and phase compositions were characterized using SEM, TEM, and XRD techniques. The microstructure comprised two clearly differentiated regions. One region, completely fused, consisted mainly of nanometer-sized grains of c-Al2O3 with dissolved Ti+4. The other region, partly fused, retained the microstructure of the starting powder and was principally made up of submicrometer-sized grains of a-Al2O3, as confirmed by TEM. Coating microhardness as well as tribological behavior were determined. Vickers microhardness values of conventional coatings were in average slightly lower than the values for nanostructured coating. The wear resistance of conventional coatings was shown to be lower than that of nanostructured coatings as a consequence of Ti segregation. A correlation between the final properties, the coating microstructure, and the feedstock characteristics is given

By evaluating the behavior of unsaturated polyester used in marine environments at room temperature, it is possible to determine its degradation using mechanical characterization parameters. There is a considerable decrease in its mechanical resistance due to the degradation effects. It must also be taken into account that the curing rate of a thermoset resin is one of the most important parameters in its behavior. This study will examine the correlation between the amount of water absorbed at room temperature, the curing rate, and the loss of mechanical properties.

Particulate reinforced titanium composites were produced by PM route. Different volumetric percentages of TiN reinforcements were used, 5,10,15 vol%. Samples were uniaxially pressed and vacuum sintered at different temperatures between 1200-1300°C. Density, porosity, shrinkage, mechanical properties and microstructure were studied. Elastic properties and strength resistance were analysed by flexural strength and tension tests, and after the test, fractured samples were analysed as well to obtain the correlation between the fracture, interparticular or intraparticular, and the level of reinforcement addition. Hardness and microhardness test were done to obtain a better understanding of its mechanical properties. In order to study wear resistance pinon- disc tests were conducted. In addition, the influence of temperature, the reactivity between matrix and reinforcement on microstructural development were observed by optical and electron microscopy.

[EN] The friction and dry sliding wear behavior of alumina and alumina-titania near-nanometric coatings were examined. Coatings were obtained by the suspension plasma spraying technique. Dry sliding wear tests were performed on a ball-on-disk tribometer, with an Al2O3 ball as counterpart material, a normal load of 2 N, a sliding distance of 1200 m and a sliding speed of 0.1 m/s. The effect of including TiO2 in the fabricated coatings on friction coefficient behavior, wear rates and wear damage patterns was determined. The addition of TiO2 to the coatings was found to greatly increase wear resistance by, for example, 2.6-fold for 40 wt% of TiO2. The analysis of the wear surface was correlated with microstructural parameters, mechanical properties and wear rates., The authors wish to thank for the Spanish Ministry of Economy and Competitiveness (MAT2012-38364-C03) and the Autonomous Government of Valencia for funding for the stay in SPCTS-UMR CNRS (France), and the French FCENANOSURF consortium funded by the French Ministry and Industry and local governments of Region Centre and Region Limousin.

Al2O3-TiO2 coatings have been deposited by atmospheric plasma spraying from agglomerated, nanostructured powders showing better properties than those of their conventional (microstructured) counterparts. These nanostructured coatings can be also obtained by suspension plasma spraying however the research on suspension plasma sprayed Al2O3-TiO2 is still scarce. Consequently, it is crucial to study the effect of the suspension characteristics on the coating properties and to optimize the deposition process. In this work, Al2O3-13 wt.% TiO2 tribological coatings were successfully deposited by suspension plasma spraying from three different feedstocks: a nanometric suspension and two bimodal suspensions with different solid contents made up of titania nanoparticles and alumina submicron-sized particles. The coating microstructure and phase composition were characterized using scanning electron microscopy and X-ray diffraction analysis. Moreover, nanoindentation technique was used to determine the nanomechanical properties of coatings. The influence of the feed suspension characteristics on the final coating quality was analyzed. Findings showed that similar microstructures and phases were developed after depositing the different feedstocks. In addition suspension feedstock made up of nanoparticles resulted in a coating with better mechanical properties. However the use of submicron-sized particles in the suspension feedstocks gives rise to some technical and economic advantages in the process which should be taken into account when a suspension plasma spraying process is to be setup. (C) 2014 Elsevier B.V. All rights reserved., This work has been supported by the Spanish Ministry of Science and Innovation (project MAT2012-38364-C03) and it has been co-funded by ERDF (European Regional Development Funds).

A fast approach based on microwave technology was employed for the sintering of novel composites of alumina and using graphene oxide (GO) as susceptor. The thermal stability and structure of GO materials produced by chemical oxidation of graphite were characterized. The morphology, structure and mechanical properties of the composites sintered by microwave approach were reported to the counterparts sintered by conventional method. The results indicated the formation of an interconnecting graphene network promoted the electrical conductivity in the composite having only 2 wt.% GO. Hardness and elastic modulus decreased significantly in samples sintered by conventional method due to lower values of density while microwave technology allowed to achieve a positive effect on the densification and showed a smaller grain size when compared to the one achieved by conventional heating. (C) 2014 Elsevier Ltd. All rights reserved., Financial support from European Commission (project no. NMP3-SL-2010-246073), Universidad Politecnica de Valencia (project SP20120677) and Ministerio de Economia y Competitividad - MINECO (project TEC2012-37532-C02-01, co-funded by ERDF (European Regional Development Funds) is gratefully acknowledged. A.B. acknowledges the Spanish Ministry of Science and Innovation (contract JCI-2011-10498). A.P. acknowledges support from Romanian Authority for Scientific Research - UEFISCDI (project no. PN-II-RU-PD-2012-3-0124).

In this work, five different concentrations of a mixture of TiO2/Al2O3 nanopowders in an alcoholic suspension at 10wt.% solid content were sprayed by Suspension Plasma Spraying on steel discs. The influence of the presence of TiO2 at 0, 13, 40 and 75wt.% in Al2O3 was analysed by studying the properties of the sprayed coatings. Microscopy analysis of the projected coatings revealed a homogeneously distributed microstructure, where the densification of the coating increases with TiO2 content, while the original nanostructure is maintained. A nanoindentation study revealed an increment of nanohardness and elastic modulus due to the densifying effect of TiO2. The addition of significant amounts of TiO2 has been revealed as necessary in order to favour the fusion of Al2O3 in the SPS process.

We have developed composite materials from AA6061 aluminium alloy powders used as matrix and ceramics powders of boron carbide, silicon carbide and boron nitride, used as reinforcements in 2.5, 5.0, 1.5 and 10 % vol. by mechanical mixing and milling in planetary mill at 360 rpm vial velocity for 4 h followed of hot stamping and extrusion process on green compacts. Mechanical properties obtained from tensile tests are influenced by the heat treatment, reinforcement fractions and nature. Moreover, these mechanical characteristics are dependent from the processing route. Optical and Scanning Electron Microscopy analysis revealed the microstructure of materials and let describe the tripartite relation; structure-processing-properties, of the developed materials.Partiendo de polvos de aleación de aluminio AA6061 empleada como matriz y de polvos cerámicos de carburo de boro, carburo de silicio y nitruro de boro, utilizados como refuerzo en fracciones volumétricas de 2,5, 5,0, 7,5 y 10 %, se ban desarrollado materiales compuestos, mediante la mezcla y molienda mecánica de estos polvos, en molino planetario a 360 rpm durante 4 h y posterior estampación y extrusión en caliente de compactos en verde. Las propiedades mecánicas se determinaron mediante ensayos de tracción, observándose gran influencia del tratamiento térmico, contenido y naturaleza del refuerzo, sobre estas propiedades. Por otro lado, se encontró que estas características son igualmente dependientes de la ruta de producción de estos materiales. Los análisis llevados a cabo mediante microscopía óptica y microscopía electrónica de barrido, permitieron describir la relación tripartita, estructura-procesamiento-propiedades, de los materiales aquí desarrollados.

[EN] Many researchers have undertaken studies into the mechanical behaviour of the welded bond,1,2 others have devoted their attentions to metallurgical phenomena, whether concerning phenomena inherent to the area immediately surrounding the weld interface or concerning models or simulations of the welded structure;3,4 in addition, there are those who have made comparisons between different welding methods2 or who have dedicated their time to post-welding treatments.5 However, very few researchers have devoted their attentions to studying microstructural change throughout the HAZ on welded test pieces.

In this paper is compared the stability of different contents of intermetallic particles (Ti3Al and TiAl) in an aluminium alloy (AA6061). A powder metallurgy route combined with a secondary hot extrusion process, was followed to fabricate the composites. The matrix/ reinforcement interaction was enhanced by solubilization heat treatments at temperatures ranging form 470 to 530ºC and times from 1 to 24 h. Scanning electron microscopy was employed to study the microstructure of the composites. The reaction layer thickness and its growing speed were determined by image analysis. The stoichiometric composition was obtained by dispersive energy diffraction of X ray.La presente comunicación compara la estabilidad que presentan diferentes refuerzos intermetálicos (Ti3Al y TiAl) adicionados a una matriz de aluminio (AA6061), empleándose para ambos refuerzos diferentes contenidos del mismo. El método de fabricación elegido combina una vía pulvimetalúrgica con un proceso secundario de extrusión en caliente. Para estudiar la interacción del refuerzo con la matriz, se llevan a cabo tratamientos térmicos de solubilización en estufas con atmósfera controlada, a una temperatura de 530ºC y variando el tiempo entre 0 y 24 h. Se utiliza la microscopía electrónica de barrido (MEB) para el estudio microestructural de los compuestos, calculándose el espesor y la velocidad de crecimiento de las capas de reacción mediante técnicas de análisis de imagen. La estequiometría de las capas formadas se determina mediante microanálisis por energías dispersivas de rayos X (EDX).

The aim of the present study is to evaluate the changes through the HAZ, analyzed under two different but complementary techniques. These are Transmission Electronic Microscopy (TEM) and Differential Scanning Calorimetry (DSC). The results shown that there are remarkable changes in size and morphology of the precipitates, being in accordance with the results obtained by DSC.El presente estudio evalúa los cambios acaecidos a lo largo de la zona afectada por el calor, ZAC, bajo dos ópticas diferentes pero complementarias: la microscopía electrónica de transmisión (TEM) y la calorimetría diferencial de barrido (DSC). Se han obtenido cambios claros y definidos en cuanto a la morfología y tamaño de los precipitados observados por TEM a lo largo de la ZAC, los cuales se correlacionan con los diferentes barridos de DSC. Palabras clave Aleación de aluminio.

Alumina-titania coatings are widely used in industry for wear, abrasion or corrosion protection components. Such layers are commonly deposited by atmospheric plasma spraying (APS) using powder as feedstock. In this study, both Al2O3 and Al2O3-13 wt% TiO2 coatings were deposited on austenitic stainless steel coupons by suspension plasma spraying (SPS). Two commercial suspensions of nanosized Al2O3 and TiO2 particles were used as starting materials. The coatings microstructure and phase composition were fully characterised using FEG-SEM and XRD techniques. Nanoindentation technique was used to determine the coatings hardness and elastic modulus properties. Results have shown that the addition of titania to alumina SPS coatings causes different crystalline phases and a higher powder melting rate is reached. The higher melted material achieved, when titania is added leads to higher hardness and elastic modulus when the same spraying parameters are used. (C) 2014 Elsevier B.V. All rights reserved., This work has been supported by the Spanish Ministry of Economy and Competitiveness (INNOBAR Project, reference: MAT2012-38364-C03) and it has been co-funded by ERDF (European Regional Development Funds).

The aluminium matrix composites materials reinforced by ceramic particles can be elaborated by powder metallurgy techniques, with extrusion processes. These can provide new materials, with a better mechanical behaviour and moreover when we need those properties at higher temperatures. Aluminium alloy reinforced composites with silicon nitride particles by powder extrusion process was done. Their mechanical properties were characterised at room and elevated temperatures.La obtención de materiales compuestos de matriz de aluminio por técnicas pulvimetalúrgicas junto a procesos de extrusión, permite desarrollar materiales reforzados con partículas cerámicas, con propiedades mecánicas mejoradas y más si se demanda un trabajo a elevada temperatura. Se han desarrollado materiales reforzados con nitruro de silicio por extrusión de polvos, realizándose la caracterización de sus propiedades mecánicas a temperatura ambiente y elevada.

Composite materials have been subjected to moderate temperature and high sunlight doses of radiation for long periods of time. All tensile mechanical characteristics increase at moderately high temperature, in accordance with a damped increasing exponential model. Sunlight exposition yields ageing on all mechanical properties, in agreement with a damped decreasing exponential model. These mechanical properties loses in fire-resistant composites are less than standard resin composites ones. Toughness characteristics show loses stronger than strength ones.Se han sometido diversos materiales compuestos a exposiciones prolongadas a temperatura moderadamente alta y a fuertes dosis de radiación solar. Se ha comprobado que todas las características mecánicas a tracción aumentan por efecto continuado de temperaturas moderadas, de acuerdo a un modelo exponencial creciente amortiguado. La exposición prolongada a la radiación solar produce un envejecimiento de todas las características a tracción. Éstas disminuyen según un modelo exponencial amortiguado. Las pérdidas son menores en compuestos con resinas ignífugas que con resinas normales. Los indicadores tenaces experimentan pérdidas más intensas que los indicadores resistentes.

Summary Medium strength AW7XXX aluminium alloys are widely used as welded structures and in transportation. The applications of these alloys are limited by the behaviour of the welded joints. There is no agreement on the joint geometry that must be used on 5 mm welds. The microhardness evolution is one of the most important strength indicators. For this reason, the aim of this work is to study the influence of welded joint geometry on microhardness profile and on the microstructure of a MIG welded AW7020 aluminium alloy, using AW5256 filler.