Evaluación de las transformaciones estructurales en recubrimientos de WC10Ni depositados por laser cladding sobre acero para herramienta EN 12379

[ES] Los materiales compuestos de matriz metálica reforzados con carburos, son conocidos por su elevada resistencia a todos los tipos de desgaste, debido a la combinación de las partículas duras en una matriz metálica tenaz. Diferentes tipos de estos materiales, se han empleado en el desarrollo de nuevas herramientas de corte de altas prestaciones. La técnica de láser cladding(LC), permite obtener recubrimientos libres de defectos sobre zonas muy concretas, con un aporte de calor muy localizado. Pero en el caso de carburos de wolframio (WC), debido a la enorme absorción de energía y la diferencia de propiedades entre el metal base y la cerámica, puede producir una gran cantidad de defectos tales como grietas, poros, gran dilución de carburos, falta de adherencia, etc. El objetivo de este trabajo, es estudiar las transformaciones metalúrgicas que aparecen durante el procesado por láser de recubrimientos tipo cermet de WC10Ni, sobre acero de herramienta para trabajo en frío (EN 12379). Además se ha relacionado los parámetros de proceso con la generación de defectos. Para ello, se analiza su microestructura, composición y se obtienen perfiles de dureza en el recubrimiento y en el acero afectado por el calor. Los resultados muestran, que aunque el control de los parámetros del proceso reduce la generación de defectos, al depositar recubrimientos por solape de cordones, se produce gran cantidad de transformaciones debido a la disolución masiva de las partículas de WC y la difusión de elementos de aleación, desde el sustrato hacia el recubrimiento.[EN] Carbide metal matrix composite materials are known for a high resistance to all types of wear. It is due to a beneficial combination of properties given by hard phase particles included in a tough matrix. Different kinds of those materials have been employed in the development of new high properties cutting tools. Laser cladding (LC) technique allows obtaining an accurate defect-free coating with a low thermal affectation of the component. But in the case of WC cermet coatings due to its high laser absorption and the different mechanical and thermal properties between substrate and coating can appear a wide range of different defects as cracks, pores, massive carbide dilution and lacks of adherence. The aim of the present work is to study the metallurgical transformations during LC process of WC cermet coating on cold work tool steel substrate (EN 12379). Also it has been related process parameters with defects generation. Microstructure and composition of the coating and the heat affected zone have been analysed. Microhardness evolution profile has been obtained. Results show that although process parameters control reduce the generation of defects, in the deposition of overlapped layers appear different metallurgical transformations related with massive WC decomposition and the diffusion of alloying elements from substrate to the coating.Candel Bou, JJ.; Amigó Borrás, V.; Sampedro, J.; Bonache Bezares, V. (2011). Evaluación de las transformaciones estructurales en recubrimientos de WC10Ni depositados por laser cladding sobre acero para herramienta EN 12379. Revista de Metalurgia. 47(4):355-364. doi:10.3989/revmetalm.0964S355364474Zhang, H., Wang, G., Luo, Y., & Nakaga, T. (2001). Rapid hard tooling by plasma spraying for injection molding and sheet metal forming. Thin Solid Films, 390(1-2), 7-12. doi:10.1016/s0040-6090(01)00910-5Cadenas, P., Rodriguez, M., & Staia, M. H. (2007). Effect of the post heat treatment on the sliding wear resistance of a nickel base coating deposited by high velocity oxy-fuel (HVOF). Revista de Metalurgia, 43(1). doi:10.3989/revmetalm.2007.v43.i1.51Vilar, R. (1999). Laser cladding. Journal of Laser Applications, 11(2), 64-79. doi:10.2351/1.521888Vicario, I., Soriano, C., Sanz, C., Bayón, R., & Leunda, J. (2009). Optimización del proceso de aporte de recubrimientos anticorrosión de Stellite 6 producidos mediante plaqueado láser. Revista de Metalurgia, 45(1), 14-19. doi:10.3989/revmetalm.0708Chen, C.-C. A., & Duffie, N. A. (1996). Development of an automated surface finishing system (ASFS) with in-process surface topography inspection. Journal of Materials Processing Technology, 62(4), 427-430. doi:10.1016/s0924-0136(96)02447-8Lim, L. ., Ming, Q., & Chen, Z. . (1998). Microstructures of laser-clad nickel-based hardfacing alloys. Surface and Coatings Technology, 106(2-3), 183-192. doi:10.1016/s0257-8972(98)00525-8Wang, P.-Z., Qu, J.-X., & Shao, H.-S. (1996). Cemented carbide reinforced nickel-based alloy coating by laser cladding and the wear characteristics. Materials & Design, 17(5-6), 289-296. doi:10.1016/s0261-3069(97)00025-3Hidouci, A., Pelletier, J. M., Ducoin, F., Dezert, D., & El Guerjouma, R. (2000). Microstructural and mechanical characteristics of laser coatings. Surface and Coatings Technology, 123(1), 17-23. doi:10.1016/s0257-8972(99)00394-1Sidhu, B. S., Puri, D., & Prakash, S. (2005). Mechanical and metallurgical properties of plasma sprayed and laser remelted Ni–20Cr and Stellite-6 coatings. Journal of Materials Processing Technology, 159(3), 347-355. doi:10.1016/j.jmatprotec.2004.05.023St-Georges, L. (2007). Development and characterization of composite Ni–Cr+WC laser cladding. Wear, 263(1-6), 562-566. doi:10.1016/j.wear.2007.02.023Przybyłowicz, J., & Kusiński, J. (2001). Structure of laser cladded tungsten carbide composite coatings. Journal of Materials Processing Technology, 109(1-2), 154-160. doi:10.1016/s0924-0136(00)00790-1Wu, P., Du, H. M., Chen, X. L., Li, Z. Q., Bai, H. L., & Jiang, E. Y. (2004). Influence of WC particle behavior on the wear resistance properties of Ni–WC composite coatings. Wear, 257(1-2), 142-147. doi:10.1016/j.wear.2003.10.01

Study of erosion behaviour of conventional and nanostructured WC-12Co coatings sprayed by atmospheric plasma

Thermal sprayed WC-Co coatings are used extensively to enhance the wear resistance of a wide range of engineering components. In this paper, erosive resistance of plasma atmospheric sprayed WC-12Co coatings has been evaluated. Solid particle erosion tests were conducted on these coatings at different angles of impact with silica and alumina abrasives of size 250 µm. Coatings have been deposited by using micrometric and nanometric agglomerated powders, employing H2 and He as plasmogen gas. In order to determine the erosion regime (ductile or brittle), the influence of impact angle on the erosion rate has been studied. Optical microscope and FESEM have been used to analyze the eroded surface. The influence of the plasmogen gas and the powder employed on the erosive behaviour of the coating has been evaluated. An attempt to connect the erosive behaviour with mechanical properties and microstructure has been made. Hardness has been determined by means of several measurements of Vickers microhardness; fracture toughness has been estimated through indentation method. Identification of phases has been made by means of X Ray diffractio

Nanoindentation study of the mechanical and damage behaviour of suspension plasma sprayed TiO2 coatings

TiO2 coatings can be used as self-cleaning surfaces owing to their photocatalytic and hydrophilic properties. Suspension plasma spray (SPS) has proven to be a feasible and cheap technique for producing self-cleaning surfaces with acceptable photo-activity. This paper presents a nanoindentation study of the mechanical properties (hardness. Young's modulus and scratch resistance) of photoactive layers of suspension plasma sprayed TiO2 coatings applied on to glass substrates. Microstructure observation showed that the rutile grains were surrounded by fine anatase crystals. Under the same spraying conditions, the resulting anatase/rutile concentrations varied depending on the cooling rate (the substrate being either cooled with water or in air). The results showed that higher concentrations of anatase, which is softer than rutile, reduced the scratch damage and increased the friction coefficient. (C) 2011 Elsevier B.V. All rights reserved.The study was financially supported by the Spanish Ministry of Science and Innovation (PID-600200-2009-5 and MAT2009-14144-C03-01 -02).Rayón Encinas, E.; Bonache Bezares, V.; Salvador Moya, MD.; Bannier, E.; Sánchez, E.; Denoirjean, A.; Ageorges, H. (2012). Nanoindentation study of the mechanical and damage behaviour of suspension plasma sprayed TiO2 coatings. Surface and Coatings Technology. 206(10):2655-2660. doi:10.1016/j.surfcoat.2011.11.010S265526602061

Mg–1Zn–1Ca alloy for biomedical applications. Influence of the secondary phases on the mechanical and corrosion behaviour

An as-cast Mg–1Zn–1Ca alloy has been soundly characterized to be used as a biodegradable material in biomedical applications. Ca and Zn additions have a great influence in the microstructure, mechanical properties and corrosion behaviour of Mg alloys. SEM examinations revealed that most of the Ca and Zn atoms form Mg2Ca and Ca2Mg6Zn3 precipitates, which distribute preferentially along the grain boundaries forming a continuous network of secondary phases. The results of nanoindentation tests show differences in hardness and elastic modulus between the α-Mg matrix and the secondary phases. The results of three-point bending tests shows that cracks propagate following the network formed by the intermetallic compounds at the grain boundaries (GBs). The evolved hydrogen after immersion in Hank’s solution of the alloy has been also estimated, showing a change in the corrosion mechanism after 160 h. The intermetallic compounds act as a barrier against corrosion, so that it progresses through the α-Mg matrix phase

Clinical consequences of BRCA2 hypomorphism

Altres ajuts: Asociación Española contra el Cáncer (LABAE16020PORTT)Altres ajuts: Asociación Española contra el Cáncer (ERAPERMED2019-215)The tumor suppressor FANCD1/BRCA2 is crucial for DNA homologous recombination repair (HRR). BRCA2 biallelic pathogenic variants result in a severe form of Fanconi anemia (FA) syndrome, whereas monoallelic pathogenic variants cause mainly hereditary breast and ovarian cancer predisposition. For decades, the co-occurrence in trans with a clearly pathogenic variant led to assume that the other allele was benign. However, here we show a patient with biallelic BRCA2 (c.1813dup and c.7796 A > G) diagnosed at age 33 with FA after a hypertoxic reaction to chemotherapy during breast cancer treatment. After DNA damage, patient cells displayed intermediate chromosome fragility, reduced survival, cell cycle defects, and significantly decreased RAD51 foci formation. With a newly developed cell-based flow cytometric assay, we measured single BRCA2 allele contributions to HRR, and found that expression of the missense allele in a BRCA2 KO cellular background partially recovered HRR activity. Our data suggest that a hypomorphic BRCA2 allele retaining 37-54% of normal HRR function can prevent FA clinical phenotype, but not the early onset of breast cancer and severe hypersensitivity to chemotherapy

Effect of CNFs content on the tribological behaviour of spark plasma sintering ceramic-CNFs composites

Alumina-carbon nanofibres (CNFs) and silicon carbide-CNFs nanocomposites with different volume fraction of CNFs (0-100vol.%) were obtained by spark plasma sintering. The effect of CNFs content on the tribological behaviour in dry sliding conditions on the ceramic-carbon nanocomposites has been investigated using the ball-on-disk technique against alumina balls. The wear rate of ceramic-CNFs nanocomposites decreases with CNFs increasing content. The friction coefficient of the Al 2O 3/CNFs and SiC/CNFs nanocomposites with high CNFs content was found to be significantly lower compared to monolithic Al 2O 3 and SiC due to the effect of CNFs and unexpectedly slightly lower than CNFs material. The main wear mechanism in the nanocomposite was abrasion of the ceramic and carbon components which act in the interface as a sort of lubricating media. The experimental results demonstrate that the addition of CNFs to the ceramic composites significantly reduces friction coefficient and wear rate, resulting in suitable materials for unlubricated tribological applications. © 2011.This work has been carried out with financial support of National Plan Projects MAT2006-01783 and MAT2007-30989-E and the Regional Project FICYT PC07-021. A. Borrell acknowledges the Spanish Ministry of Science and Innovation for her FPI Ph.D. grant. We would like to thank the people from Institute Technological of Materials (ITM) of the Polytechnic University of Valencia for helping us with the tribology experiments during A. Borrell's short stay in 2009.Borrell Tomás, MA.; Torrecillas, R.; Rocha, VG.; Fernandez, A.; Bonache Bezares, V.; Salvador Moya, MD. (2012). Effect of CNFs content on the tribological behaviour of spark plasma sintering ceramic-CNFs composites. Wear. 274:94-99. https://doi.org/10.1016/j.wear.2011.08.013S949927

Fabrication of full density near-nanostructured cemented carbides by combination of VC/Cr3C2 addition and consolidation by SPS and HIP technologies

The aim of present work is to study the effect of VC and/or Cr3C2 in densification, microstructural development and mechanical behavior of nanocrystalline WC-12wt.%Co powders when they are sintered by spark plasma sintering (SPS) and hot isostatic pressing (HIP). The results were compared to those corresponding to conventional sintering in vacuum. The density, microstructure, X-ray diffraction, hardness and fracture toughness of the sintered materials were evaluated. Materials prepared by SPS exhibits full densification at lower temperature (1100 degrees C) and a shorter stay time (5 min), allowing the grain growth control. However, the effect of the inhibitors during SPS process is considerably lower than in conventional sintering. Materials prepared by HIP at 1100 degrees C and 30 min present full densification and a better control of microstructure in the presence of VC. The added amount of VC allows obtaining homogeneous microstructures with an average grain size of 120 nm. The hardness and fracture toughness values obtained were about 2100 HV30 and close to 10 MPa m(1/)2, respectively. (C) 2010 Elsevier Ltd. All rights reserved.The work is supported financially by the Spanish Ministry of Science and Innovation by means of the project MAT 2006-12945-C03-C02 and MAT 2009-14144-C03-C02.Bonache Bezares, V.; Salvador Moya, MD.; Fernández Valdés, A.; Borrell Tomás, MA. (2011). Fabrication of full density near-nanostructured cemented carbides by combination of VC/Cr3C2 addition and consolidation by SPS and HIP technologies. International Journal of Refractory Metals and Hard Materials. 29(2):202-208. https://doi.org/10.1016/j.ijrmhm.2010.10.007S20220829

Careers of highly educated self-initiated expatriates : observations from studies among Finnish business professionals

This chapter reviews existing literature about the careers of self-initiated expatriates and analyzes the different studies carried out among university level educated Finnish business professionals. A series of studies carried out among members of the Finnish Association of Business School Graduates during the last 15 years was cross-analyzed. The studies are based on three surveys and further interviews among their expatriate members (1999, 2004 and a follow-up study in 2012) also involving SIEs. Therefore, this chapter provide an overview of what we know about the careers of Finnish SIEs and show evidence of (1) their career motives, (2) the role of family considerations in the career decision making of SIEs, (3) the development of career capital and social capital during SIE-experiences, and also (4) longer-term career impacts of SIE-experiences. Based on the literature review and analysis of above mentioned studies we highlight the gaps in in the knowledge about SIEs and suggest areas where further research is needed.fi=vertaisarvioitu|en=peerReviewed

Improving tribological properties of cast Al-Si alloys through application of wear-resistant thermal spray coatings

Flame Spray Thermal Spray coatings are low-cost, high-wear surface-treatment technologies. However, little has been reported on their potential effects on cast automotive aluminum alloys. The aim of this research was to investigate the tribological properties of as-sprayed NiCrBSi and WC/12Co Flame Spray coatings applied to two cast aluminum alloys: high-copper LM24 (AlSi8Cu3Fe), and low-copper LM25 (AlSi7Mg). Potential interactions between the mechanical properties of the substrate and the deposited coatings were deemed to be significant. Microstructural, microhardness, friction, and wear (pin-on-disk, microabrasion, Taber abrasion, etc.) results are reported, and the performance differences between coatings on the different substrates were noted. The coefficient of friction was reduced from 0.69-0.72 to 0.12-0.35. Wear (pin-on-disk) was reduced by a factor of 103-104, which was related to the high surface roughness of the coatings. Microabrasion wear was dependent on coating hardness and applied load. Taber abrasion results showed a strong dependency on the substrate, coating morphology, and homogeneity