Estudio de la evolución microestructural de un acero ferrítico ODS de grupo cuatro (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, Ciudad Real (España), 7, 8 y 9 Junio de 2017Los 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.La financiación obtenida por el proyecto MAT2013-47460-C5-S-P ha posibilitado esta investigación

Directed energy deposition and characterization of high-carbon high speed steels

Directed energy deposition (DED) of two high-carbon high speed steel alloys Febal-C-Cr-Mo-V and Febal−x-C-Cr-Mo-V-Wx was performed by using a 4 kW Nd:YAG laser source. The purpose of additive manufacturing was design and evaluation of thermally stable – high temperature wear resistant alloys. High temperature (500 °C) pin-on-disc tests were conducted to investigate the effect of carbides phase fraction on friction and wear. Strain scanning of the powder and additively manufactured materials was carried out by Neutron diffraction. Microstructures of both alloys consisted of a martensitic matrix with networks of primary and eutectic carbides. Micro-hardness (0.5 HV) measurement of all multilayer laser deposits, showed a micro-hardness greater than 700 HV, with no detrimental effect of repetitive laser thermal cycling. Febal−x-C-Cr-Mo-V-Wx showed a better high temperature wear resistance due to greater phase fraction of VC and Mo2C carbides. Fracture surfaces of post-heat treated tensile samples of Febal-C-Cr-Mo-V and Febal−x-C-Cr-Mo-V-Wx revealed brittle failures with minimal plasticity. Neutron strain mapping of the metal powders and the additively manufactured materials resulted in a weak diffraction signal and peak widening effect. These results could be explained either by an effect of strong crystallographic texture in the bulk or by the presence of nano- or semi-crystalline phases

Microstructural and mechanical characterisation of ODS ferritic alloys produced by mechanical alloying and spark plasma sintering

Powders with nominal composition Fe-14Cr-2W-0·4Ti were mechanically alloyed (MA) with Y2O3 in a planetary ball mill at two different rotational speeds. Consolidation of the as milled powders was performed by spark plasma sintering (SPS). As milled powders showed a highly deformed microstructure with elongated nanometre grains and, depending upon the rotational speed, different stages of the nanocluster evolution were observed to be produced. In the case of consolidated materials, grain growth occurred during the SPS process and it was possible to observe the influence of the MA parameters, with larger and more homogeneously distributed grains at the higher rotational speed. Additionally, Ti was observed to be incorporated to the nanoclusters after SPS, indicating a further step in their evolution during consolidation. The mechanical behaviour of the SPS compacts was evaluated by tensile and small punch testing also showing the influence of the MA parameters in the material behaviour

Directed energy deposition and characterization of high-carbon high speed steels

Directed energy deposition (DED) of two high-carbon high speed steel alloys Febal-C-Cr-Mo-V and Febal−x-C-Cr-Mo-V-Wx was performed by using a 4 kW Nd:YAG laser source. The purpose of additive manufacturing was design and evaluation of thermally stable – high temperature wear resistant alloys. High temperature (500 °C) pin-on-disc tests were conducted to investigate the effect of carbides phase fraction on friction and wear. Strain scanning of the powder and additively manufactured materials was carried out by Neutron diffraction. Microstructures of both alloys consisted of a martensitic matrix with networks of primary and eutectic carbides. Micro-hardness (0.5 HV) measurement of all multilayer laser deposits, showed a micro-hardness greater than 700 HV, with no detrimental effect of repetitive laser thermal cycling. Febal−x-C-Cr-Mo-V-Wx showed a better high temperature wear resistance due to greater phase fraction of VC and Mo2C carbides. Fracture surfaces of post-heat treated tensile samples of Febal-C-Cr-Mo-V and Febal−x-C-Cr-Mo-V-Wx revealed brittle failures with minimal plasticity. Neutron strain mapping of the metal powders and the additively manufactured materials resulted in a weak diffraction signal and peak widening effect. These results could be explained either by an effect of strong crystallographic texture in the bulk or by the presence of nano- or semi-crystalline phases

Development and characterization of multilayer laser cladded high speed steels

Two high speed steel (HSS) alloys were laser cladded on 42CrMo4 steel cylindrical substrate by using a 4 kW Nd:YAG laser source. After optimization of the laser material processing parameters for single layers, multilayered clads were produced. Microstructural characterization of the laser deposits constitutes studies of the carbides and matrix, which was done by using Scanning Electron Microscopy (SEM), Energy Dispersive Spectroscopy (EDS), Electron Backscattered Diffraction (EBSD) and High Resolution Transmission Electron Microscopy (HRTEM). The strengthening mechanism of LC1 (Fe-Cr-Mo-W-V) was comprised of a martensitic matrix and retained austenite along with networks of VC and Mo2C eutectic carbides. Cr enriched fine carbides (Cr7C3 and Cr23C6) were embedded within the matrix. During laser cladding of the multilayer deposits, cladding of subsequent layers had a detrimental effect on the hardness of previously cladded layers, which was due to tempering of existing lath martensite. To overcome the hardness drop, a new alloy LC2 (Febal−x-Cr-Mo-W-V-Cox) was blended by addition of 3–5% of Co in LC1. The addition of Co resulted in an overall increase in hardness and a reduction in the hardness drop during sequential layer cladding; the latter was due to the presence of Co in the solid solution with Fe. HRTEM was performed to characterize the nanometer-sized precipitates evolved during the re-heating. These carbides were either enriched with V and W or formed from a complex combination of V, Mo, W and Cr with lattice spacings of 0.15 nm to 0.26 nm

Laser metal deposition of vanadium-rich high speed steel: Microstructuraland high temperature wear characterization

A comparative high temperature wear study was conducted between two alloys: laser metal deposited vana-dium-rich (V-rich) high speed steel (HSS) and spun cast carbide enhanced indefinite chilled double poured (CE-ICDP) iron. Laser Metal Deposition (LMD) of V-rich HSS alloy was performed by using a 4.0 kW Nd:YAG laser atthree different laser scan speeds to investigate the effect thereof on the carbide size and morphology, phaseconstitution and mechanical properties (such as micro-hardness and wear resistance) of the laser metal deposits.A comprehensive microstructural characterization of these alloys revealed that the dendritic microstructureof the V-rich HSS alloy consisted of martensitic matrix and VC carbides. Increasing the laser processing speedssignificantly changed the morphologies of VC carbides from square and round to angular and rod-like shapes.The micro-hardness of the V-rich HSS was improved from 760 HV to 835 HV by increasing the laser processingspeed. During high temperature (500 °C) pin-on-disc wear tests, the V-rich HSS showed excellent wear resistancecompared to CE-ICDP iron. It was found that V-rich HSS with square and round shape VC carbides (V-rich10 mm/s) showed the most improved tribological performance with oxidative wear found to be the dominantwear mechanism at this temperature

Notch Impact Behavior of Oxide Dispersion Strengthened (ODS) Fe20Cr5Al alloy

In this paper tensile tests and LS and LT notched Charpy impact tests were performed at the temperature range between -196 and 200 °C on an oxide dispersion strengthened (ODS) Fe20Cr6Al0.5Y2O3 hot-rolled tube. The absorbed energy values in the range of high-temperatures of LS notched specimens is considerably higher than those of LT notched specimens; however such values tend to converge as temperature increases. Ductile fracture on the normal planes to RD with delaminations parallel to the tube surface were observed in the temperature range between RT and 200 °C. Delaminations of crack divider type were observed in LT specimens, whereas delaminations of crack arrester type were observed in LS specimens. The yttria particles in the grain boundaries and the transverse plastic anisotropy are the possible causes of that the delaminations were parallel to the tube surfacePM 2000 is a trademark of Plansee GmbH. The authors acknowledge the financial support of the Spanish Ministerio de Economia e Innovacio´ n (MINECO) in the form of a Coordinate Project in the Energy Area of Plan Nacional 2009 (ENE2009-13766-C04-01). G.P. acknowledges MINECO for financial support in the form of PhD Research Grant (FPI). This research was supported by ORNL’s Shared Research Equipment (SHaRE) User Facility, which is sponsored by the Office of Basic Energy Sciences, U.S. Department of EnergyPeer reviewe