Development of a Cr-based hard composite processed by spark plasma sintering

This investigation analyzes the feasibility of processing a composite material comprising WC particles randomly dispersed in a matrix in which Cr is the main metallic binder. Thus, a new composite material is processed using a commercial, economic, and easily available Cr-based alloy, assuming that there is a certain Cr solubility in the WC particles acting as reinforcement. The processing route followed includes mechanical milling of the powders and consolidation by spark plasma sintering.Publicad

Wear resistance of nanostructured Cr-based WC hardmetals sintered by spark plasma sintering

Erratum to 'Wear resistance of nanostructured Cr-based WC hardmetals sintered by spark plasma sintering' [International Journal of Refractory Metals and Hard Materials Volume 87, February 2020, 105121]. DOI: https://doi.org/10.1016/j.ijrmhm.2020.105206Nanostructured Cr-based WC hardmetals are successfully sintered by spark plasma sintering. The wear behaviour of these Cr-based WC hardmetals with different C contents ranging from 5.57 wt% to 6.91 wt%, is evaluated performing sliding wear tests under two different wear conditions. This work analyses the influence of the C content on the wear performance through the study of the phase formation and WC grain size. The Cr-based hardmetal with 5.57 wt% C content exhibits a lower wear rate than Co-based WC hardmetals tested under similar dry ball-on-plate wear conditions, even considering that these Co-based WC hardmetals have higher WC content (90 wt%) than Cr-based WC hardmetals (83.2 wt%). The combination of a nanosized WC grain and the avoidance of brittle (Cr,Fe)7C3 or soft graphite phases leads to a superior wear performance. Thus, the use of Cr-based binders in the hardmetal industry, alternatively to Co-based binders, is promising in applications in which high wear resistance is needed

Effect of mechanical alloying on the microstructural evolution of a ferritic ODS steel with (Y-Ti-Al-Zr) addition processed by Spark Plasma Sintering (SPS)

The high-energy milling is one of the most extended techniques to produce Oxide dispersion strengthened (ODS) powder steels for nuclear applications. The consequences of the high energy mill process on the final powders can be measured by means of deformation level, size, morphology and alloying degree. In this work, an ODS ferritic steel, Fe-14Cr-5Al-3W-0.4Ti-0.25Y2O3-0.6Zr, was fabricated using two different mechanical alloying (MA) conditions (Mstd and Mact) and subsequently consolidated by Spark Plasma Sintering (SPS). Milling conditions were set to evidence the effectivity of milling by changing the revolutions per minute (rpm) and dwell milling time. Differences on the particle size distribution as well as on the stored plastic deformation were observed, determining the consolidation ability of the material and the achieved microstructure. Since recrystallization depends on the plastic deformation degree, the composition of each particle and the promoted oxide dispersion, a dual grain size distribution was attained after SPS consolidation. Mact showed the highest areas of ultrafine regions when the material is consolidated at 1100 degrees C. Microhardness and small punch tests were used to evaluate the material under room temperature and up to 500 degrees C. The produced materials have attained remarkable mechanical properties under high temperature conditions.Authors want to acknowledge Ferro-Ness project and Ferro- Genesys project funded by MINECO under National I + D + I program MAT2016-80875-C3-3-R and MAT2013-47460-C5-5-P

Analysis of the interface and mechanical properties of field-assisted sintered duplex stainless steels

The development of duplex stainless steels produced by powder metallurgy represents an interesting alternative to conventional fabrication routes, since typical routes imply a strict control of composition and temperature during the processing path in order to avoid undesirable brittle phases. This work proposes a sintering route, designated as field-assisted hot pressing technique, in which an alternating current is applied to consolidate duplex stainless steels with different initial austenite percentages, always higher than ferrite. In all the cases, a thin and hard planar interface composed by two different microconstituents is generated between austenite and ferrite, growing inside the ferritic phase. The good mechanical properties achieved by these field-assisted sintered duplex stainless steels, in terms of nanohardness, elastic modulus, yield strength, ultimate tensile stress and ductility, establish these steels as promising candidates to be introduced in the market.This research did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors. The authors wish to express their gratitude to Dr. M.A. Monclús and Dr. M. Castillo-Rodríguez for their experimental and technical suppor

Study and suppression of the microstructural anisotropy generated during the consolidation of a carbonyl iron powder by field-assisted hot pressing

Published OnlineA spherical carbonyl iron powder was consolidated by the field-assisted hot pressing technique using graphite tools at two different temperatures, both above the austenitizing temperature. The microstructures obtained exhibited a compositional gradient in carbon along the consolidated material. Thus, the outer rim of the cylindrical samples was composed of cementite and pearlite that gradually turned to pearlite, leading to a fully ferritic microstructure at the core of the sample. The increase in the temperature has led to a higher introduction of carbon within the sample. The interposition of a thin tungsten foil between the graphite die/punches and the powders has significantly reduced the diffusion of the carbon through the iron matrix and has suppressed the microstructural anisotropy.Publicad

Estudio de la evolución microestructural de un acero ferrítico ODS de grupo 4 (Y-Al-Ti-Zr) consolidado por consolidación Spark Plasma Sintering (SPS)

Trabajo presentado al VI Congreso Nacional de Pulvimetalurgia y I Congreso Iberoamericano de Pulvimetalurgia, celebrado en Ciudad Real (España) del 7 al 9 de Junio de 2017.[ES]: Los aceros ferríticos ODS son extraordinarios candidatos para su uso en los nuevos reactores nucleares de tipo IV debido a su buen comportamiento a fluencia y bajo irradiación. El uso de elementos de aleaciones como el Ti, Al, Y favorecen la aparición de nanoclusters y nanoprecipitados que limitan el movimiento de dislocaciones, endureciéndolos y mejorando así su comportamiento a fluencia. Con la incorporación del Zr se pretende mejorar la estabilidad térmica de los óxidos precipitados y con ello la temperatura de trabajo. En este caso, el acero ferrítico ODS se ha desarrollado por molienda mecánica de alta energía. Este método proporciona estructuras cristalinas con una gran cantidad de energía almacenada que, al encontrarse heterogéneamente distribuida, produce una recristalización no homogénea durante la etapa de consolidación. La microestructura final obtenida por consiguiente, presenta un tamaño de grano heterogéneo. Con el fin de estudiar este fenómeno, se consolidaron las piezas por SPS haciendo uso de distintas condiciones de consolidación. Se seleccionó una temperatura de sinterización, 1373 K y distintas velocidades de calentamiento (de 100 a 600 °C/min). La estructura obtenida se ha caracterizado mediante difracción de rayos x y microscopía electrónica. Además, con el fin de analizar las propiedades mecánicas del material, se han llevado a cabo ensayos de dureza Vickers y de tracción en probetas subdimensionadas a temperatura ambiente.[EN]: Oxide Dispersion Strengthened (ODS) ferritic Steels are extraordinary candidates for nuclear applications due to their good behavior at high temperature and under irradiation conditions .ODS ferritic steel was produced by mechanical alloying and SPS to obtain a complex nanostructure. A four group elements (Y-Ti-Al-Zr) was selected to improve the stability of the precipitates since they are the main responsible for the thermal stability of fine structure. The heterogeneous distribution of stored energy due to the high energy attrition of MA powder will produce an inhomogeneous recrystallization during the consolidation step. After SPS consolidation a heterogeneous grain size distribution was attained, as recrystallization depends on the plastic deformation degree, on the composition of each particle and on the oxide dispersion promoted. Therefore sintering cycle was performed at 1373 K following fast heating rates (from 100 to 600 °C/min) to minimize porosity. The final microstructures were characterized by XRD and electron microscopy (SEM and TEM). In addition, Vickers microhardness and tensile tests was performed to analyze the mechanical response at R.T.La financiación obtenida por el proyecto MAT2013-47460-C5-S-P ha posibilitado esta investigación.Peer Reviewe

Effect of the heating rate on the microstructure of a ferritic ODS steel with four oxide formers (Y-Ti-Al-Zr) consolidated by spark plasma sintering (SPS)

The proposed ODS ferritic steel alloyed with (Y-Ti-Zr-Al) was produced by mechanical alloying (MA) and spark plasma sintering (SPS) to obtain a complex nanostructure. To densify the material, a sintering cycle by SPS was performed at 1100 degrees C using fast heating rates (from 100 to 600 degrees C/min). During the attrition of MA powders, the uneven distribution of deformation level and of alloying elements has produced an inhomogeneous recrystallization during the consolidation step. Influence of processing condition was studied by modifying the heating rate of SPS to promote a heterogeneous material with bimodal grain size distribution. The final microstructures were characterized by X-ray diffraction and electron microscopy (SEM and TEM). The mechanical behaviour at R.T. was characterized by means of the Vickers microhardness and micro tensile tests. The good balance obtained between ductility (similar to 22-26%) and yield stress (800-910 MPa) at room temperature is provided by the bimodal grain size distribution. To predict the experimental values depending on the processing conditions, a yield strength model is presented. This model covers the contribution of different strengthening mechanism from solid solution, grain size, dislocation density and oxides precipitation. The model indicates the dislocation density as the major strengthening contribution. In addition, small punch (SP) tests were performed to analyse the response of the material at high temperatures where remarkable properties have been achieved.Authors want to acknowledge Ferro-Ness project and Ferro-Genesys project funded by MINECO under National I+D+I program MAT2016-80875-C3-3-R and MAT2013-47460-C5-5-P.Publicad

Microstructure and Mechanical Properties of Spark Plasma Sintered and Severely Deformed AA7075 Alloy

In this paper, the microstructure and mechanical properties of AA7075 with a coarse-fine-grained laminated microstructure produced by spark plasma sintering (SPS) and the cyclic extrusion severe deformation (KOBO) technique were investigated. It was found that an inhomogeneous grain microstructure was formed from coarse and fine grains by the SPS process and then was transformed into a coarse-fine-grained laminated microstructure by means of KOBO extrusion at room temperature. The grain refinement during KOBO extrusion resulted in a fine grained laminated microstructure created due to the formation of low-angle grain boundaries (LAGBs), followed by dynamic recrystallization, leading to high-angle grain boundaries (HAGBs). The EBSD analysis results reveal the formation of a deformed and partially recrystallized ultrafine grain microstructure owing to the generation and development of shear bands during KOBO extrusion. The ultimate tensile strength (UTS) of the AA7075 alloy rose after SPS-KOBO severe deformation up to 422 MPa, with high strains of about 33%. The obtained results clearly show that the SPS-KOBO extrusion technique allows a bimodal laminated fine gradient grain microstructure to be obtained due to deformation and dynamic recrystallization, which result in both high strength and good ductility. The new heterogeneous AA7075 alloys obtained by the SPS-KOBO combined techniques demonstrate that microstructural heterogeneities can assist in overcoming the strength–ductility trade-off

Microstructure and Electrical Conductivity of Cement Paste Reinforced with Different Types of Carbon Nanotubes

Over the last few years, the addition of small amounts of carbon nanotubes (CNTs) to construction materials has become of great interest, since it enhances some of the mechanical, electrical and thermal properties of the cement. In this sense, single-walled and multi-walled carbon nanotubes (SWCNTs and MWCNTs, respectively) can be incorporated into cement to achieve the above-mentioned improved features. Thus, the current study presents the results of the addition of SWCNTs and MWCNTs on the microstructure and the physical properties of the cement paste. Density was measured through He pycnometry and the mass change was studied by thermogravimetric analysis (TGA). The microstructure and the phases were analyzed using scanning electron microscopy (SEM) and X-ray diffraction (XRD). Finally, the electrical conductivity for different CNT concentrations was measured, and an exponential increase of the conductivity with concentration was observed. This last result opens the possibility for these materials to be used in a high variety of fields, such as space intelligent systems with novel electrical and electronic applications.Sin financiación3.748 JCR (2021) Q2, 28/69 Physics, Condensed Matter0.604 SJR (2021) Q2, 147/427 Condensed Matter PhysicsNo data IDR 2021UE