Influence of process parameters and initial microstructure on the oxidation resistance of Ti48Al2Cr2Nb coating obtained by laser metal deposition

[EN] Ti6Al4V have been the most important and versatile titanium alloys currently used, due to their excellent combination of low density and good mechanical properties, despite their application temperature being limited to up to 300 °C. In this work, a Ti6Al4V sheet was coated with a Ti48Al2Cr2Nb alloy by laser cladding process, with the process parameters resulting in laser-specific energy densities of 70, 80, 90 and 180 J/mm2, laser power between 600 and 900W and scanning speed of 100 to 300 mm/min. In order to analyze the oxidation resistance at elevated temperature, isothermal oxidation tests were carried out at 800 °C for 5, 10, 25, 50, 100 and 150 h in static air. The oxidized samples were characterized by optical microscopy (OM), scanning electron microscopy (SEM), field emission microscopy (FESEM) with energy dispersive spectroscopy (EDS), and X-ray diffraction (XRD) analysis. Two groups of coatings with similar microstructures were obtained, and their influence on the formation of thermally oxidized growth layers was studied. From the isothermal oxidation tests, it was observed that the Ti48Al2Cr2Nb coatings have good resistance to oxidation in air at 800 °C in comparison with the Ti6Al4V substrate by obtaining layers of oxides up to 12 ¿m thick after 150 h of oxidation. The structure of the oxide layers is complex and comprises the growth of successive layers from the outer surface of the coating. The effect of the microstructure of the coating on the density of the oxide layer formed was evaluated.The authors would like to thank the Ministerio de Ciencia e Innovacion of the Spanish Government for their financial support through research project MAT2011-28492-C03 and the Generalitat Valenciana through grant ACOMP/2014/151.Zambrano Carrullo, JC.; Pereira Falcón, JC.; Amigó, V. (2019). Influence of process parameters and initial microstructure on the oxidation resistance of Ti48Al2Cr2Nb coating obtained by laser metal deposition. Surface and Coatings Technology. 358:114-124. https://doi.org/10.1016/j.surfcoat.2018.11.015S11412435

Caracterización microestructural de recubrimientos NiCoCrAlYTa obtenidos por láser coaxial y por refusión láser sobre AISI 316L

[ES] En este estudio se ha evaluado la microestructura de recubrimientos NiCoCrAlYTa depositados mediante la técnica de laser cladding coaxial, y en recubrimientos obtenidos por proyección térmica de alta velocidad (HVOF) y refundidos por láser, ambos sobre láminas de acero inoxidable AISI 316L. Se ha analizado la microestructura, variación de microdureza y composición química, mediante microscopía óptica, microscopía electrónica de barrido (MEB) y microanálisis por espectroscopía de energía dispersiva (EDS). Los recubrimientos obtenidos no presentan macro defectos importantes y existe una buena unión metalúrgica con el sustrato; no obstante, existe una estructura dendrítica columnar no homogénea que depende del procesado láser. Los análisis evidencian la disolución y mezcla de elementos químicos relevantes con el NiCr que generan una variación gradual entre sustrato y recubrimiento que influye en el endurecimiento observado en la intercara del recubrimiento. Se logra la densificación de los recubrimientos HVOF eliminando la porosidad inicial y mejorando su acabado superficial, diferencias en la disolución de elementos químicos han sido encontradas para las dos técnicas utilizadas, debido al espesor del recubrimiento obtenido y los parámetros láser utilizados.[EN] In this study the microstructure of NiCoCrAlYTa coatings deposited by coaxial laser cladding technique, and laser remelted coatings obtained previously by high velocity oxy fuel thermal spraying (HVOF), both on sheets of stainless steel AISI 316L, were evaluated. Optical microscopy, scanning electron microscopy, and energy dispersive spectroscopy microanalysis have been used to analyze the chemical composition, microstructure, and microhardness. A coatings without cracks or macro pores and a good metallurgical bond with the substrate through the dilution zone was obtained; yet there is no a homogeneous columnar dendrite structure that depends of laser processing parameters. The analysis evidenced the dilution and mixing of relevant chemical elements such as Fe, Co, Al and Ta with Ni-Cr, generating a gradual variation between substrate and coating which influence the hardening observed at the interface of the coating. The densification is achieved by removing HVOF coating initial porosity and improving the surface finish, differences in the chemicals components dissolution have been found for the two techniques employed, influence by the thickness coating and by the laser parameters.Pereira Falcón, JC.; Candel Bou, JJ.; Amado, J.; Amigó Borrás, V. (2014). Caracterización microestructural de recubrimientos NiCoCrAlYTa obtenidos por láser coaxial y por refusión láser sobre AISI 316L. Revista Colombiana de Materiales. Especial(5):127-132. http://hdl.handle.net/10251/91890S127132Especial

Effect of Powder Reuse on Powder Characteristics and Properties of DED Laser Beam Metal Additive Manufacturing Process with Stellite® 21 and UNS S32750

In this work, the influence of powder reuse up to three times on directed energy deposition (DED) with laser processing has been studied. The work was carried out on two different gas atomized powders: a cobalt-based alloy type Stellite® 21, and a super duplex stainless steel type UNS S32750. One of the main findings is the influence of oxygen content of the reused powder particles on the final quality and densification of the deposited material and the powder catch efficiency of the laser deposition process. There is a direct relationship between a higher surface oxidation of the particles and the presence of oxygen content in the particles and in the as-built materials, as well as oxides, balance of phases (in the case of the super duplex alloy), pores and defects at the micro level in the laser-deposited material, as well as a decrease in the amount of material that actually melts, reducing powder catch efficiency (more than 12% in the worst case scenario) and the initial bead geometry (height and width) that was obtained for the same process parameters when the virgin powder was used (without oxidation and with original morphology of the powder particles). This causes some melting faults, oxides and formation of undesired oxide compounds in the microstructure, and un-balance of phases particularly in the super duplex stainless steel material, reducing the amount of ferrite from 50.1% to 37.4%, affecting in turn material soundness and its mechanical properties, particularly the hardness. However, the Stellite® 21 alloy type can be reused up to three times, while the super duplex can be reused only once without any major influence of the particles’ surface oxidation on the deposited material quality and hardness.This research work was supported by the Basque Government (Eusko Jaurlaritza, Department of Economic Development and Infrastructure, Programme ELKARTEK) through EDISON project (grant KK-2022/00070) and through ECOFAST project (grant KK-2024/00018)

Desarrollo y caracterización de recubrimientos MCrAlY obtenidos mediante técnicas láser para aplicaciones de barrera térmica en aceros inoxidables

[EN] The coaxial laser cladding process is an excellent tool to obtain quality coatings, achieving complete melting and deposition of alloys with high melting point on complex 3D surfaces. In this work we have studied the coaxial laser cladding parameters for MCrAlY coatings (where M = Ni, Co, Fe or combinations of these), commonly used as bond coats in thermal barrier systems, among them: NiCoCrAlYTa, NiCoCrAlY, NiCrAlY and CoNiCrAlY; selecting the laser parameters that allow to obtain overlapping coatings with adequate geometrical aspect ratio, minimum dilution, low porosity and good metallurgical bond with the austenitic stainless steel substrate, by using a 2.2 kW Nd:YAG laser equipment and coaxial head with annular nozzle. The laser coatings have been characterized using various microstructural tech-niques, to identify their constituent phases and the type of microstructure obtained with coaxial laser processing. The mechanical properties were determined by three-point bending tests as well as micro hardness and nanoindentation tests. The high temperature oxidation behavior of the laser coatings and austenitic stainless steel substrate were studied through isothermal oxidation tests at 1100 ºC. The morphology and chemical composition of the oxidized surface were evaluated in detail. The oxidation kinetics and the thermal growth oxide scale, thickness, structure and composition of the oxide layers formed according to the oxidation time were also studied. Finally, friction and wear behavior at room temperature and elevated temperature (500 ºC) were studied by dry sliding tribological tests, in order to obtain the friction coefficient and wear resistance of MCrAlY laser cladding coatings and to compare their behavior with the substrate. The experimental results, allowing to analyze the influence of coaxial laser processing on mechanical properties and high temperature behavior of MCrAlY laser coatings, as well as their comparison with the AISI 304 austenitic stainless steel and MCrAlY coatings obtained by thermal spray processes that are currently used in bond coats. The results indicate that the coaxial laser cladding may be a good alternative to thermal spray processes, because microstructural integrity is improved and defects such as porosity and lack of metallurgical bonding were decreased. These facts, along with the enhancement of the oxidation and the wear resistance of MCrAlY alloys at high temperature, make the coaxial laser process potentially useful to obtain MCrAlY bond coats for new generation of thermal barrier systems.[ES] El proceso de plaqueado láser coaxial es una excelente herramienta para la obtención de recubrimientos de calidad, logrando la completa fusión y deposición de aleaciones con elevado punto de fusión sobre superficies 3D complejas. En este trabajo se han estudiado los parámetros de procesado láser coaxial de superaleaciones MCrAlY (donde M = Ni, Co, Fe o combinaciones entre ellos), comúnmente empleadas como recubrimientos de anclaje en sistemas de barrera térmica, entre ellas: NiCoCrAlYTa, NiCoCrAlY, NiCrAlY y CoNiCrAlY; logrando seleccionar una combinación de parámetros que permiten obtener recubrimientos por solape de cordones con adecuada relación de aspecto, mínima dilución, bajo nivel de porosidad y buena unión metalúrgica con el sustrato de acero inoxidable austenítico, utilizando un equipo láser Nd:YAG de 2.2 kW y un cabezal coaxial. Los recubrimientos láser han sido caracterizados microestructuralmente con diversas técnicas, logrando identificar las fases que los constituyen y el tipo de microestructura obtenida con el procesado láser coaxial. Se han determinado sus propiedades mecánicas a través de ensayos de microdureza, nanoindentación instrumentada y de flexión a tres puntos. Se ha estudiado también el comportamiento de oxidación a alta temperatura de los recubrimientos y del acero inoxidable austenítico mediante ensayos de oxidación isotérmica a 1100 ºC, logrando evaluar en detalle la morfología y composición de la superficie oxidada, la cinética de oxidación, así como la evolución del espesor, estructura y composición de las capas de óxido formadas en función del tiempo de oxidación. Por último, se ha realizado el estudio del comportamiento ante la fricción y el desgaste a temperatura ambiente y a elevada temperatura (500 ºC), mediante ensayos tribológicos de desgaste por deslizamiento en seco, con la finalidad de obtener el coeficiente de rozamiento y evaluar la resistencia al desgaste que presentan los recubrimientos láser MCrAlY y su comparación con el comportamiento que presenta el sustrato. Los resultados de la experimentación han permitido analizar la influencia del procesado láser coaxial en las propiedades mecánicas y el comportamiento a alta temperatura de recubrimientos MCrAlY, y su comparación con el acero inoxidable AISI 304 y recubrimientos similares obtenidos por procesos de proyección térmica y utilizados en la actualidad. Los resultados indican que el plaqueado láser coaxial puede ser una buena alternativa a los procesos de proyección térmica, ya que se mejora la integridad microestructural, se disminuyen los defectos como la porosidad y la falta de unión metalúrgica, mejorando también el comportamiento ante la oxidación y el desgaste a elevadas temperaturas de los recubrimientos de anclaje MCrAlY que pueden ser utilizados en nuevos sistemas de barrera térmica.[CA] El procés de plaquejat làser coaxial és una excel·lent eina per a l'obtenció de recobriments de qualitat, aconseguint la completa fusió i deposició d'aliatges amb elevat punt de fusió sobre superfícies 3D complexes. En aquest treball s'han estudiat els paràmetres de processament làser coaxial de superaliatges MCrAlY (on M = Ni, Co, Fe o combinacions entre ells), comunament emprades com recobriments d'ancoratge en sistemes de barrera tèrmica, entre elles: NiCoCrAlYTa, NiCoCrAlY, NiCrAlY i CoNiCrAlY; aconseguint seleccionar una combinació de paràmetres que permeten obtenir recobriments per solapament de cordons amb adequada relació d'aspecte, mínima dilució, baix nivell de porositat i bona unió metal·lúrgica amb el substrat d'acer inoxidable austenític, utilitzant un equip làser Nd:YAG de 2.2 kW i un capçal coaxial. Els recobriments làser han estat caracteritzats microestructuralment amb diverses tècniques, aconseguint identificar les fases que els constitueixen i el tipus de microestructura obtinguda amb el processat làser coaxial. S'han determinat les seves propietats mecàniques mitjançant assaigs de microduresa, nanoindentació i de flexió a tres punts. S'ha estudiat també el comportament d'oxidació a alta temperatura dels recobriments i de l'acer inoxidable austenític mitjançant assaigs d'oxidació isotèrmica a 1100 ºC, aconseguint avaluar en detall la morfologia i composició de la superfície rovellada, la cinètica d'oxidació, així com la evolució del gruix, estructura i composició de les capes d'òxid formades en funció del temps d'oxidació. Finalment, s'ha realitzat l'estudi del comportament davant la fricció i el desgast a temperatura ambient i a elevada temperatura (500 ºC), mitjançant assajos tribològics de desgast per lliscament en sec, amb la finalitat d'obtenir el coeficient de fricció i avaluar la resistència al desgast que presenten els recobriments làser MCrAlY i la seva comparació amb el comportament que presenta el substrat. Els resultats de l'experimentació han permès analitzar la influència del processat làser coaxial en les propietats mecàniques i el comportament a alta temperatura de recobriments MCrAlY, i la seva comparació amb l'acer inoxidable AISI 304 i recobriments similars obtinguts per processos de projecció tèrmica, utilitzats actualment. Els resultats indiquen que el plaquejat làser coaxial pot ser una bona alternativa als processos de projecció tèrmica, ja que es millora la integritat microestructural, es disminueixen els defectes com la porositat i la falta d'unió metal·lúrgica, millorant també el comportament davant l'oxidació i el desgast a elevades temperatures dels recobriments d'anclatge MCrAlY que poden ser utilitzats en nous sistemes de barrera tèrmica.Pereira Falcón, JC. (2015). Desarrollo y caracterización de recubrimientos MCrAlY obtenidos mediante técnicas láser para aplicaciones de barrera térmica en aceros inoxidables [Tesis doctoral no publicada]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/52946TESI

Use of a Holistic Design and Manufacturing Approach to Implement Optimized Additively Manufactured Mould Inserts for the Production of Injection-Moulded Thermoplastics

Injection moulding is one the most familiar processes for manufacturing of plastic parts by injecting molten thermoplastic polymers into a metallic mould. The cycle time of this process consists of the phases of injection, packing, cooling, and ejection of the final product. Shortening of cycle time is a key consideration to increase productivity. Therefore, in this manuscript the adoption of additively manufactured mould inserts with conformal cooling channels by means of selective laser melting (SLM) with the aim to reduce process cycles is presented. The design and manufacture of a mould insert with conformal cooling channels for producing pressure fitting thermoplastic parts is described. Numerical analysis of the injection process and simulation of shape distortions after SLM were conducted providing useful results for the design and manufacture of the mould insert. The results of the numerical analyses are compared with experimental 3D geometrical data of the additively manufactured mould insert. Temperature measurements during the real injection moulding process demonstrating promising findings. The adoption of the introduced method for the series production of injection moulded thermoplastics proves a shortening of cycle times of up to 32% and a final product shape quality improvement of up to 77% when using mould inserts with conformal cooling channels over the conventional mould inserts

Psychometric Properties and Measurement Invariance of the Generalized Tracking Questionnaire-Children

Self-report measures of generalized patterns of rule-following are being developed in the last years including the Generalized Pliance Questionnaire (GPQ) and the Generalized Tracking Questionnaire (GTQ). Specifically, the GTQ is a 11-item self-report developed for adults that has shown excellent psychometric properties, a one-factor structure, and criterion validity in view of its positive correlations with executive functions tests. This study aims to develop the children’s version of the GTQ (i.e., Generalized Tracking Questionnaire-Children, GTQ-C). In so doing, we adapted the vocabulary of some of the GTQ items and added an additional item (i.e., the GTQ-C consisted of 12 items). Afterward, the GTQ for children (i.e., GTQ-C) was administered to a sample of 730 Colombian children and adolescents from 7 to 17 years. A cross-validation study was conducted to analyze the factor structure of the questionnaire. The analysis showed that a one-factor structure showed a good fit to the data. All items of the GTQ-C showed good discrimination indexes and the whole questionnaire showed adequate internal consistency. The GTQ-C showed measurement invariance across gender and age group. In conclusion, the GTQ-C seems to be a valid and reliable measure of generalized tracking for children that might be used to analyze the developmental trajectories of tracking and its relationship with other relevant behavioral processes

Evaluación de la anisotropía en las propiedades mecánicas del acero inoxidable AISI 304 laminado en frío

[EN] The anisotropy is the term used in metallic materials to describe the difference between the mechanical properties according to the direction in which they were evaluated. In this study we determined the variation of the mechanical properties of AISI 304 austenitic stainless steel in annealing state and cold rolled in several passes. Three orientations in the rolling plane with respect to the rolling direction (parallel, diagonal and perpendicular) were evaluated. For each study condition anisotropy in the mechanical properties was observed. The bigger tensile strength and yield strength, and the lower total elongation were obtained for the transverse orientation. For the material in annealing state, a slight anisotropy was observed, and it increases by cold rolling deformation. The anisotropy being greater in magnitude, for the greatest percentage of cold deformation reached. The crystallographic texture of cold rolled material, evaluated by EBSD revealed a predominant fiber texture parallel to the transverse direction, and parallel to the rolling direction, with mayor evolution and intensity in the transverse direction[ES] La anisotrop¿¿a es el t¿ermino usado en los materiales met¿alicos para describir la diferencia que existe entre las propiedades mec¿anicas de acuerdo a la direcci¿on en las cuales fueron evaluadas. En este trabajo se analiz¿o la anisotrop¿¿a del acero inoxidable austen¿¿tico AISI 304 en estado de entrega y laminado en fr¿¿o, tomando en cuenta tres orientaciones en el plano de laminaci¿on con respecto al sentido de laminaci¿on (paralela, diagonal y perpendicular). Para cada condici¿on, se observ¿o anisotrop¿¿a en las propiedades mec¿anicas, obteniendo la mayor magnitud para la resistencia a tracci¿on y resistencia a fluencia, as¿¿ como, el menor alargamiento en la orientaci¿on transversal. Para el material en estado de entrega se observ¿o una ligera anisotrop¿¿a, y ¿esta se incrementa al deformarlo en fr¿¿o, siendo mayor para el mayor porcentaje de deformaci¿on alcanzado. La textura cristalogr¿afica del material laminado en fr¿¿o, evaluada mediante EBSD revel¿o, una textura de fibra predominante en paralela a la direcci¿on transversal, y en paralela al sentido de laminaci¿on, siendo de mayor evoluci¿on e intensidad en sentido transversal.Pereira Falcón, JC.; Torres, M.; Amigó Borrás, V.; Zambrano Carrullo, JC. (2012). Evaluación de la anisotropía en las propiedades mecánicas del acero inoxidable AISI 304 laminado en frío. Ingeniería - Universidad de Carabobo, Facultad de Ingeniería. 19(1):7-15. http://hdl.handle.net/10251/91882S71519

Microstructure and mechanical properties of NiCoCrAlYTa alloy processed by press and sintering route

Nickel-based superalloys such as NiCoCrAlY are widely used in high-temperature applications, such as gas turbine components in the energy and aerospace industries, due to their strength, high elastic modulus, and high-temperature oxidation resistance. However, the processing of these alloys is complex and costly, and the alloys are currently used as a bond coat in thermal barrier coatings. In this work, the effect of cold press and sintering processing parameters on the microstructure and mechanical properties of NiCoCrAlY alloy were studied using the powder metallurgy route as a new way to obtain NiCoCrAlYTa samples from a gas atomized prealloyed powder feedstock. High mechanical strength and adequate densification up to 98% was achieved. The most suitable compaction pressure and sintering temperature were determined for NiCoCrAlYTa alloy through microstructure characterization. Scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), and energy dispersive spectroscopy microanalysis (EDS) were performed to confirm the expected γ-Ni matrix and β-NiAl phase distribution. Additionally, the results demonstrated the unexpected presence of carbides and Ni-Y-rich zones in the microstructure due to the powder metallurgy processing parameters used. Thus, microhardness, nanoindentation and uniaxial compression tests were conducted to correlate the microstructure of the alloy samples with their mechanical properties under the different studied conditions. The results show that the compaction pressure did not significantly affect the mechanical properties of the alloy samples. In this work, the compaction pressures of 400, 700 and 1000 MPa were used. The sintering temperature of 1200 °C for NiCoCrAlYTa alloy was preferred; above this temperature, the improvement in mechanical properties is not significant due to grain coarsening, whereas a lower temperature produces a decrease in mechanical properties due to high porosity and poor solid-state diffusion.The authors would like to acknowledge the economic support of the Spanish Ministry of Science and Innovation of the Government of Spain through research project MAT2011-28492-C03 and the Generalitat Valenciana (ACOMP/2013/114). Furthermore, the authors thank Dr. Jose Luis Jorda for the XRD analysis.Pereira Falcón, JC.; Zambrano Carrullo, JC.; Afonso, CRM.; Amigó Borrás, V. (2015). Microstructure and mechanical properties of NiCoCrAlYTa alloy processed by press and sintering route. Materials Characterization. 101:159-165. https://doi.org/10.1016/j.matchar.2015.02.001S15916510

IFPA Meeting 2010 Workshop Report I: Immunology; ion transport; epigenetics; vascular reactivity; epitheliochorial placentation; proteomics

Workshops are an important part of the IFPA annual meeting. At IFPA Meeting 2010 there were twelve themed workshops, six of which are summarized in this report. 1. The immunology workshop focused on normal and pathological functions of the maternal immune system in pregnancy. 2. The transport workshop dealt with regulation of ion and water transport across the syncytiotrophoblast of human placenta. 3. The epigenetics workshop covered DNA methylation and its potential role in regulating gene expression in placental development and disease. 4. The vascular reactivity workshop concentrated on methodological approaches used to study placental vascular function. 5. The workshop on epitheliochorial placentation covered current advances from in vivo and in vitro studies of different domestic species. 6. The proteomics workshop focused on a variety of techniques and procedures necessary for proteomic analysis and how they may be implemented for placental research.</br