Inter-particle connections development during sintering of Cr-Mo-alloyed steel powder in N2/H2 atmosphere

Powder metallurgy is one of the oldest metal processing techniques; it is a manufacturing process that is based on the production of metal, ceramic or composite components from powders. Manufacturing of ferrous powder metallurgy precision parts has increased in the last decades, in particular for automotive applications. The properties of a component manufacture by PM techniques may be tailored or improved by the addition of alloying elements; chromium and molybdenum are widely used in conventional metallurgy as alloying elements, but the tendency of chromium to form stable oxides and the decrease in compressibility it produces, have restricted its use in powder metallurgy. However, low chromium alloyed steels meet all the requirements for most structural components and for the market needs, so research and development of these steels is being carried out nowadays. In this study, specimens of the same composition (pre-alloyed water atomized powder of low Cr-Mo content) were sintered in a 90N2/10H2 atmosphere during 3 minutes and at different temperatures from 700°C to 1120°C. Two additional samples were sintered at 1120°C during 15 and 30 minutes each. Impact test was performed in all the specimens in order to produce fracture surfaces, which were studied using High Resolution Scanning Electron Microscopy (HRSEM) and EDX analysis. Microstructural investigation was carried out as well. The objective of this investigation was to evaluate the effect of the sintering temperature and time on both the inter-particle necks development and the inclusions evolution. It was found that Inter-particle necks development is enhanced with sintering temperature and time and that the reduction of the Fe-oxide layer on the powder particles is a pre-condition for the formation of solid metallic contacts. Furthermore, different failure mechanisms were found with increasing sintering temperature. It was also found that the morphology and size of the inclusions change with increasing sintering temperature and time.---------------------------------------------------------------------------------------------La pulvimetalurgia es una de las técnicas de procesamiento de materiales metálicos más antiguas: consiste en un proceso de fabricación para la producción de componentes metálicos, cerámicos o de materiales compuestos a partir de polvos. La fabricación de piezas fabricadas a partir de polvos férreos se ha incrementado en las últimas décadas, en especial en la fabricación de elementos para la industria del automóvil. Las propiedades de un componente fabricado por PM pueden ser ajustadas o mejoradas mediante la adición de elementos de aleación: cromo y molibdeno han sido ampliamente utilizados en la metalurgia convencional como aleantes, pero la tendencia del cromo para formar óxidos de cromo muy estables y el decremento en compresibilidad que produce han limitado su uso en pulvimetalurgia. Sin embargo, los aceros aleados con bajo contenido en cromo cumplen todos los requerimientos necesarios para la mayoría de los componentes estructurales y para las necesidades del mercado, por lo que investigación y desarrollo de este tipo de aceros se está desarrollando en estos últimos años. En este estudio, probetas de la misma composición (polvos pre-aleados fabricados mediante atomización en agua con bajo contenido en cromo y molibdeno) fueron sinterizadas en atmósfera de 90N2/10H2 durante tres minutos y a diferentes temperaturas desde 700 hasta 1120ºC. Asimismo, dos probetas adicionales se sinterizaron a 1120ºC durante 15 y 30 minutos respectivamente. Las probetas fueron sometidas a ensayo de fractura para producir superficies de fractura, que fueron estudiadas mediante microscopía electrónica de barrido (SEM) y microscopía óptica. El objetivo de esta investigación fue evaluar el efecto de la temperatura y tiempo de sinterización en la evolución de los cuellos entre partículas y de las inclusiones. Se ha encontrado que el desarrollo de los cuellos entre partículas se ve incrementado con un aumento en la temperatura y el tiempo de sinterización y que la reducción de la capa superficial de óxido de hierro en las partículas es condición necesaria para la formación de contactos sólidos entre partículas. Además, se han encontrado diferentes mecanismos de fallo al aumentar la temperatura de sinterización. También ha podido comprobarse como la morfología y tamaño de las inclusiones cambia al aumentar la temperatura de sinterización y el tiempo, lo que puede suponer el punto de partida para investigaciones futuras.Ingeniería Industria

Mechanical properties of advanced high-strength steels produced via quenching and partitioning

Mención Internacional en el título de doctorAdvanced high-strength steel (AHSS) grades have been frequently used for applications that require a compromise between cost reduction, mechanical behavior and reliability of components that work under static and fatigue service loading conditions. Quenching and Partitioning (Q&P) is receiving increasing attention as a novel heat treatment to produce AHSSs containing martensite/retained austenite mixtures, with desirable combination of strength, ductility and toughness. However, despite the significant body of research on microstructure and mechanical properties of Q&P steels, there is still a significant lack of knowledge on the effect of microstructural architecture on their mechanical performance. Particularly, no research on fatigue and fracture behavior of Q&P steels has been carried out up-todate. Therefore, the main objective of this PhD thesis is to develop a concept of microstructural design in Q&P steels in order to improve a wide range of mechanical properties (uniaxial tensile, fatigue and fracture), as well as to gain fundamental understanding of their relationship with the microstructure and Q&P processing parameters. It is demonstrated that: (i) tensile mechanical behavior and strain partitioning between phases strongly depend on the microstructure of Q&P steels, which, in turn, can be tuned via manipulation of the Q&P parameters; (ii) matrix conditions play an important role in fracture behavior of Q&P steels and (iii) fatigue life of Q&P steels is also determined by their microstructure and can be enhanced via improvement of strength of interphase boundaries. Based on the analysis of the experimental results, it is shown that tailoring of the microstructure of Q&P processed steels can lead to further improvement of their mechanical performance.Los Aceros Avanzados de Alta Resistencia (AHSSs) se utilizan generalmente en la fabricación de componentes que trabajan en condiciones de servicio estáticas y/o a fatiga. Por lo tanto, es necesario que proporcionen un buen compromiso entre coste, comportamiento mecánico y fiabilidad. En los últimos años, se está prestando una gran atención hacia el novedoso tratamiento térmico conocido en inglés como "Quenching and Partitioning" (Q&P) para la producción de AHSSs con microestructuras multifásicas que consisten en mezclas de martensita y austenita retenida, proporcionando de este modo la combinación de resistencia, ductilidad y tenacidad deseada. Sin embargo, a pesar de que ya se ha realizado un importante trabajo de investigación para avanzar en la comprensión de la microestructura y las propiedades mecánicas de estos aceros, resulta imprescindible profundizar aún más en el efecto que la arquitectura microestructural tiene en los aceros Q&P. En particular, no se ha realizado hasta la fecha ningún trabajo que analice el comportamiento a fatiga y fractura de los aceros Q&P. Por este motivo, el principal objetivo de la presente Tesis Doctoral es desarrollar el concepto de diseño microestructural en los aceros Q&P. De este modo se busca mejorar un amplio rango de propiedades mecánicas entre las que se incluyen la resistencia a tracción, así como a fatiga y fractura. Asimismo, se busca establecer la relación entre las citadas propiedades mecánicas, la microestructura y los parámetros de procesado. En este trabajo se ha comprobado que: (i) el comportamiento a tracción y la partición de la deformación entre distintas fases depende en gran medida de la microestructura de los aceros Q&P que, por otra parte, puede ajustarse gracias a la manipulación de los parámetros de procesado Q&P; (ii) las propiedades de la matriz juegan un papel muy importante en el comportamiento a fractura de los aceros Q&P y (iii) la vida a fatiga de los aceros Q&P también está determinada por la microestructura y puede ser mejorada reforzando los bordes entre fases. En base al análisis de los resultados experimentales obtenidos, se muestra que el rendimiento mecánico de los aceros Q&P puede mejorarse a través del diseño microestructural.Programa Oficial de Doctorado en Ciencia e Ingeniería de MaterialesPresidente: José Manuel Torralba Castelló.- Secretario: José María Cabrera Marrero.- Vocal: Laura Molí Sánche

Healthcare workers hospitalized due to COVID-19 have no higher risk of death than general population. Data from the Spanish SEMI-COVID-19 Registry

Aim To determine whether healthcare workers (HCW) hospitalized in Spain due to COVID-19 have a worse prognosis than non-healthcare workers (NHCW). Methods Observational cohort study based on the SEMI-COVID-19 Registry, a nationwide registry that collects sociodemographic, clinical, laboratory, and treatment data on patients hospitalised with COVID-19 in Spain. Patients aged 20-65 years were selected. A multivariate logistic regression model was performed to identify factors associated with mortality. Results As of 22 May 2020, 4393 patients were included, of whom 419 (9.5%) were HCW. Median (interquartile range) age of HCW was 52 (15) years and 62.4% were women. Prevalence of comorbidities and severe radiological findings upon admission were less frequent in HCW. There were no difference in need of respiratory support and admission to intensive care unit, but occurrence of sepsis and in-hospital mortality was lower in HCW (1.7% vs. 3.9%; p = 0.024 and 0.7% vs. 4.8%; p<0.001 respectively). Age, male sex and comorbidity, were independently associated with higher in-hospital mortality and healthcare working with lower mortality (OR 0.211, 95%CI 0.067-0.667, p = 0.008). 30-days survival was higher in HCW (0.968 vs. 0.851 p<0.001). Conclusions Hospitalized COVID-19 HCW had fewer comorbidities and a better prognosis than NHCW. Our results suggest that professional exposure to COVID-19 in HCW does not carry more clinical severity nor mortality

Now, the part of intuition. Research, Art and Creation, 2018

Catálogo de Exposición del Máster en Investigación en Arte y Creación de la UCM. Muestra celebrada del 25 de septiembre al 10 de octubre de 2018 en la Sala de Exposiciones de la Facultad de Bellas Artes. C / Pintor el Greco 2, Ciudad Universitaria. 28040 Madrid. Comisariado de Javier Mañero Rodicio.Exhibition catalog of the Master in Art and Creation Research of the UCM. September 25 to October 10, 2018 in the Exhibition Hall of the Faculty of Fine Arts. C / Pintor El Greco 2, University City. 28040 Madrid. Curated by Javier Mañero Rodicio.Fac. de Bellas ArtesFALSEFacultad de Bellas Artes. Universidad Complutense de Madrid.pu

Treatment with tocilizumab or corticosteroids for COVID-19 patients with hyperinflammatory state: a multicentre cohort study (SAM-COVID-19)

Objectives: The objective of this study was to estimate the association between tocilizumab or corticosteroids and the risk of intubation or death in patients with coronavirus disease 19 (COVID-19) with a hyperinflammatory state according to clinical and laboratory parameters. Methods: A cohort study was performed in 60 Spanish hospitals including 778 patients with COVID-19 and clinical and laboratory data indicative of a hyperinflammatory state. Treatment was mainly with tocilizumab, an intermediate-high dose of corticosteroids (IHDC), a pulse dose of corticosteroids (PDC), combination therapy, or no treatment. Primary outcome was intubation or death; follow-up was 21 days. Propensity score-adjusted estimations using Cox regression (logistic regression if needed) were calculated. Propensity scores were used as confounders, matching variables and for the inverse probability of treatment weights (IPTWs). Results: In all, 88, 117, 78 and 151 patients treated with tocilizumab, IHDC, PDC, and combination therapy, respectively, were compared with 344 untreated patients. The primary endpoint occurred in 10 (11.4%), 27 (23.1%), 12 (15.4%), 40 (25.6%) and 69 (21.1%), respectively. The IPTW-based hazard ratios (odds ratio for combination therapy) for the primary endpoint were 0.32 (95%CI 0.22-0.47; p < 0.001) for tocilizumab, 0.82 (0.71-1.30; p 0.82) for IHDC, 0.61 (0.43-0.86; p 0.006) for PDC, and 1.17 (0.86-1.58; p 0.30) for combination therapy. Other applications of the propensity score provided similar results, but were not significant for PDC. Tocilizumab was also associated with lower hazard of death alone in IPTW analysis (0.07; 0.02-0.17; p < 0.001). Conclusions: Tocilizumab might be useful in COVID-19 patients with a hyperinflammatory state and should be prioritized for randomized trials in this situatio

Evolving trends in the management of acute appendicitis during COVID-19 waves. The ACIE appy II study

Background: In 2020, ACIE Appy study showed that COVID-19 pandemic heavily affected the management of patients with acute appendicitis (AA) worldwide, with an increased rate of non-operative management (NOM) strategies and a trend toward open surgery due to concern of virus transmission by laparoscopy and controversial recommendations on this issue. The aim of this study was to survey again the same group of surgeons to assess if any difference in management attitudes of AA had occurred in the later stages of the outbreak. Methods: From August 15 to September 30, 2021, an online questionnaire was sent to all 709 participants of the ACIE Appy study. The questionnaire included questions on personal protective equipment (PPE), local policies and screening for SARS-CoV-2 infection, NOM, surgical approach and disease presentations in 2021. The results were compared with the results from the previous study. Results: A total of 476 answers were collected (response rate 67.1%). Screening policies were significatively improved with most patients screened regardless of symptoms (89.5% vs. 37.4%) with PCR and antigenic test as the preferred test (74.1% vs. 26.3%). More patients tested positive before surgery and commercial systems were the preferred ones to filter smoke plumes during laparoscopy. Laparoscopic appendicectomy was the first option in the treatment of AA, with a declined use of NOM. Conclusion: Management of AA has improved in the last waves of pandemic. Increased evidence regarding SARS-COV-2 infection along with a timely healthcare systems response has been translated into tailored attitudes and a better care for patients with AA worldwide

Impact of COVID-19 on cardiovascular testing in the United States versus the rest of the world

Objectives: This study sought to quantify and compare the decline in volumes of cardiovascular procedures between the United States and non-US institutions during the early phase of the coronavirus disease-2019 (COVID-19) pandemic. Background: The COVID-19 pandemic has disrupted the care of many non-COVID-19 illnesses. Reductions in diagnostic cardiovascular testing around the world have led to concerns over the implications of reduced testing for cardiovascular disease (CVD) morbidity and mortality. Methods: Data were submitted to the INCAPS-COVID (International Atomic Energy Agency Non-Invasive Cardiology Protocols Study of COVID-19), a multinational registry comprising 909 institutions in 108 countries (including 155 facilities in 40 U.S. states), assessing the impact of the COVID-19 pandemic on volumes of diagnostic cardiovascular procedures. Data were obtained for April 2020 and compared with volumes of baseline procedures from March 2019. We compared laboratory characteristics, practices, and procedure volumes between U.S. and non-U.S. facilities and between U.S. geographic regions and identified factors associated with volume reduction in the United States. Results: Reductions in the volumes of procedures in the United States were similar to those in non-U.S. facilities (68% vs. 63%, respectively; p = 0.237), although U.S. facilities reported greater reductions in invasive coronary angiography (69% vs. 53%, respectively; p < 0.001). Significantly more U.S. facilities reported increased use of telehealth and patient screening measures than non-U.S. facilities, such as temperature checks, symptom screenings, and COVID-19 testing. Reductions in volumes of procedures differed between U.S. regions, with larger declines observed in the Northeast (76%) and Midwest (74%) than in the South (62%) and West (44%). Prevalence of COVID-19, staff redeployments, outpatient centers, and urban centers were associated with greater reductions in volume in U.S. facilities in a multivariable analysis. Conclusions: We observed marked reductions in U.S. cardiovascular testing in the early phase of the pandemic and significant variability between U.S. regions. The association between reductions of volumes and COVID-19 prevalence in the United States highlighted the need for proactive efforts to maintain access to cardiovascular testing in areas most affected by outbreaks of COVID-19 infection

Çédille, revista de estudios franceses

Presentació