Influence of 2 (wt%) titanium addition on the oxidation resistance of tungsten

The oxidation behaviour of W-2Ti (wt%) alloy has been evaluated in dry air at 600, 700 and 800 °C for 100 h and the kinetics compared with those for pure tungsten. Titanium addition exerts a beneficial effect on the oxidation resistance of pure tungsten. The mass gain is almost five times smaller than in the case of commercial tungsten and three times smaller than that of tungsten prepared by powder metallurgy at 600 °C. This effect is even higher at 700 and 800 °C, where the titanium addition suppresses catastrophic oxidation of pure tungsten. Major influence of titanium regards the suppression of massive microcracking in the scale, avoiding the development of the typical non-protective multilayered scale pattern formed on pure tungsten.This research was supported by the Agencia Estatal de Investigación of Spain (PID2019-105325RB-C33/AEI/10.13039/501100011033) and by the Regional Government of Madrid through TECHNOFUSIÓN(III)CM (S2018/EMT-4437) project cofinanced by Structural Funds (ERDF and ESF). The support of the Regional Government of Madrid through the multi-annual agreement with UC3M (Excellence of University Professors-EPUC3M14 and in the context of the V PRICIT - Regional Programme of Research and Technological Innovation) is also acknowledge

On the oxidation mechanism of pure tungsten in the temperature range 600-800 ºC

The oxidation behavior of International Thermonuclear Experimental Reactor (ITER)-reference tungsten grade has been evaluated in dry air in the temperature range 600-800 °C. At 600 °C , the scale remained protective while the integrity of W₁₈O₄₉ layer was kept. Rapid increase in mass gain resulted from massive cracking at local areas in the W₁₈O₄₉ layer. Then, a coarse non-protective columnar WO₂.₉₂ scale was developed which favoured rapid inward oxygen transport into the alloy. At 700 and 800 °C, growth stresses in the scale were released through local cracking. At this stage, WO₂.₉₂ became progressively transformed into WO₃ when the oxygen partial pressure increased across the scale thickness.This investigation was supported by the Spanish Ministry of Science and Innovation (ENE2008 06,403 C06 04). The financial support from the Comunidad de Madrid, through the program TECHNOFUSION, Grant S2009/ENE 1679

Influence of processing route and yttria additions on the oxidation behavior of tungsten

This study is for: The Fifteenth International Conference on Fusion Reactor Materials (ICFRM-15) was held October 16–22, 2011, at the Charleston Marriott Hotel in Charleston, South Carolina (American United States).The oxidation resistance in dry air of pure tungsten and tungsten reinforced with a dispersion of 0.6 wt.% Y₂O₃ nanoparticles has been evaluated between 873 and 1073 K, temperature range that divertor in fusion power plants should endure during long-term times in the case of loss of coolant accident and/or air ingress in the vessel. Both materials were prepared by a powder metallurgy route involving hot isostatic pressing of ball milled tungsten powders and tungsten with dispersed Y₂O₃ nanoparticles. The results have been compared with those of pure tungsten processed by conventional techniques. Thermogravimetric tests at 873 K revealed that the processing route as well as yttria addition considerably affected the oxidation resistance of pure tungsten. Mass gain of W-0.6Y₂O₃ at 873 K was five and two times lower than that of pure tungsten prepared by conventional processing techniques and by powder metallurgy, respectively. This different behavior was related to changes in the structure and composition of the oxide scale. Above 873 K, the kinetics were significantly accelerated for all materials due to the development of a non-protective oxide scale from the earliest oxidation stages, although the kinetics of Y₂O₃-containing material were still the slowest, specially at 973 K. It was analyzed how yttria additions modify the oxidation mechanism of tungsten.Consejería de Educación de la Comunidad de Madrid through the program ESTRUMAT-CM S2009MAT-1585 and by the Ministerio de Innovación y Ciencia (Project ENE2008-06403-C06-04). The additional subvention from EURATOM/CIEMAT association through contract EFDA WP11-MAT-WWALLOY.Publicad

Oxidation behaviour of tungsten with vanadium additions

The effect of vanadium additions on the oxidation behaviour of tungsten has been evaluated at 600 °C in dry air. Mass gain in V-containing tungsten alloys is practically the same than that of pure tungsten processed by a conventional route. The advantage of vanadium alloying arises from the suppression of periodical microcracking described during the oxidation of pure tungsten, although the scale developed during the initial stages is very porous and it is not an effective barrier for inward oxygen ingress. Further protection is conferred when an outermost dense WO3 layer is formed at the air/scale interface by condensation of volatile W and V oxides, turning the kinetics from linear to parabolic

Influence of yttria additions on the oxidation behaviour of titanium prepared by powder metallurgy

The yttria dispersion effect on the oxidation resistance of titanium prepared by powder metallurgy has been evaluated between 700 and 900º C. Yttria additions slightly increase the oxidation rate up to 800ºC and decrease it considerably at 900º C. The multilayered rutile scale formed on pure titanium prepared by conventional techniques is replaced by a denser rutile scale in the case of Titanium prepared by powder metallurgy. Yttria additions raise the temperature at which a more protective dense rutile scale is formedThis work was supported by the Dirección General de Investigación (Ministerio de Ciencia e Innovación of Spain) under grant MAT2006-13005-C03-02, and the Dirección General de Universidades (Comunidad de Madrid) through the program ESTRUMAT-CM (Grant S-0505/MAT/0077).Publicad

Characterization and evaluation of CuCrFeV(Ti, Ta, W) system for High Heat Flux applications

Cu5Cr35Fe35V20-X5, with X = Ti, Ta or W, alloys were produced by arc melting to assess their feasibility to be used as structural materials and as interlayer in cooling systems. The microstructure and mechanical properties of the materials were analyzed in as-cast and aged states. In the as-cast state the structure of the three alloys is BCC, but formation of the intermetallic Fe7Ta3 is observed in Cu5Cr35Fe35V20Ta5. Thermal aging treatment at 700 °C caused significant changes in the microstructure of Cu5Cr35Fe35V20W5 and the formation of the sigma phase. Thermal treated Cu5Cr35Fe35V20Ta5 and Cu5Cr35Fe35V20W5 exhibit high mechanical strength and excellent compressive ductility but show work softening due to the appearance of dynamic recovery mechanisms. Type-A serration behavior is observed for Cu5Cr35Fe35V20W5. Both, the complexity of their microstructures and their differences are responsible for the different mechanical behavior of the three alloys.This research has been supported by the Ministerio de Ciencia e Innovación of Spain (PID2019-105325RB-C33/ AEI/10.13039/501100011033) and by the Regional Government of Madrid through the program TECHNOFUSIÓN(III)CM (S2018/EMT-4437), project cofinancing with Structural Funds (ERDF and ESF). The support of the Regional Government of Madrid through the multi-annual agreement with UC3M ("Excelencia para el Profesorado Universitario"- EPUC3M14) is also acknowledged

Serrated flow in powder metallurgy Al-5%Mg-1.2%Cr alloy processed by equal channel angular pressing

The microstructure, texture and mechanical behavior of the powder metallurgy Al-5 wt.%Mg-1.2 wt.%Cr alloy subjected to equal channel angular pressing (ECAP) has been investigated. The material processed by ECAP, as well as in the homogenized condition, exhibited room temperature serrated flow (SF) up to fracture. The critical stress for the serration onset decreased with increasing strain rate or ECAP temperature. The results indicated that this SF was induced by shear banding. The stress oscillations were attributed to the interaction between shear bands (SBs) and obstacles like second phase particles, and dislocation locks produced by strain hardening. The early stages of the stress-strain sigma-epsilon curves of the ECAP processed samples showed a transition from type B serrations with continuous strain hardening to type B serrations superimposed on a succession of constant stress plateaus when the tensile strain rate was increased from 10⁻4 s⁻1 to 10⁻3 s⁻1. The plateaus in sigma-epsilon curves obtained at a strain rate of 10⁻3 s⁻1 were ascribed to the nucleation of a band at one end of the sample gauge region and subsequent propagation towards the opposite end. At a low strain rate of 10⁻4 s⁻1 the sites for band nucleation should be randomly distributed along the sample gauge region. The disappearance of the plateaus in the sigma-epsilon curves are attributed to the activation of a new moving band before the completion of the deformation banding cycle of the preceding band.The experimental work has been carried out at the LMNM (LM 290) laboratory supported by Madrid Community through the project TECHNOFUSION (S2009/ENE 1679) and Spanish Ministry of Science and Innovation (contract ENE2008 06403 C06 04)

Mechanical properties and microstructure of W/CuY and W/CuCrZr composites produced by hot isostatic pressing

Fully dense W-15 wt%CuY and W-15 wt%CuCrZr composites have been produced by a powder metallurgy route and hot isostatic pressing. The consolidated materials show homogeneous distributions of pre-alloyed CuY and CuCrZr embedded in W phase. Y-enriched particles were found inside the CuY phase. Their mechanical behavior was studied under uniaxial compression from room temperature to 500 °C. W/CuY exhibited a higher value of the yield strength, but W/CuCrZr presented a larger compressive deformation. Both composites manifested strain hardening during plastic deformation. The deformed microstructure at 250 °C and 500 °C was characterized by electron backscatter diffraction (EBSD) measurements and nanoindentation. The correlation between the plastic deformation, grain size and misorientation distributions, has been revealed

Microstructure and temperature dependence of the microhardness of W-4V-1La₂O₃ and W-4Ti-1La₂O₃

This study is presented of: The Fifteenth International Conference on Fusion Reactor Materials (ICFRM-15) was held October 16–22, 2011, at the Charleston Marriott Hotel in Charleston, South CarolinaW–4V–1La₂O₃ and W–4Ti–1La₂O₃ (wt.%) alloys have been produced by mechanical alloying and subsequent hot isostatic pressing. Electron microscopy observations revealed that these alloys exhibit a submicron grain structure with a dispersion of La oxide nanoparticles. Large V or Ti pools with martensitic characteristics are found segregated in the interstices between the W particles of the respective alloys. Microhardness tests were carried out over the temperature range 300–1073 K in vacuum. The microhardness–temperature curve for W–4V–1La₂O₃ exhibited the expected decreasing trend with increasing temperature although the microhardness stayed constant between ~473 and 773 K. The W–4Ti–1La₂O₃ presented quite different temperature dependence with an anomalous microhardness increase for temperatures above ~473 K.The Spanish Ministry of Economy and Competitiveness (project ENE2012-39787-C06-05), the Comunidad de Madrid through the program ESTRUMAT-CM (Grant S2009/MAT-1[5]85), and the European Commission through the European Fusion DevelopmentPublicad

Production and characterization of the Cr35Fe35V16.5Mo6Ti7.5 high entropy alloy

The microstructure, thermal stability, and mechanical properties of a novel Cr35Fe35V16.5Mo6Ti7.5 high-entropy alloy were studied. The mechanical properties were mapped by nanoindentation, and the results correlated with the microstructure and the Vickers microhardness measurements. The alloy was produced by arc melting in a low pressure He atmosphere. Thermal treatments were performed to study the thermal stability of the alloy. The as-cast microstructure of the alloy exhibited a body-centered cubic phase with morphology of dendrites, outlined by a very thin interdendritic phase with a crystallographic structure compatible with Fe2Ti. The presence of the intermetallic particles was predicted by a free-energy based model, in contrast with the single solid solution alloy predicted by a parameter-based model. The volume fraction of the dendrites in the alloy is ∼ 94 % after arc melting. A small fraction of sparse Ti-rich particles, ∼0.4 vol%, was observed. The thermal treatments produced an increase of the population of Ti-rich particles, the formation of a σ-phase and nucleation of precipitates enriched with Fe and Ti into the previous dendrites. The material in as-cast condition exhibited a microhardness value of 6.2 ± 0.3 GPa, while the alloy aged at 960 °C resulted in 7.1 ± 0.4 GPa. Nanoindentations maps showed an excellent correlation with the microstructure, and their statistical analyses yielded a nanohardness mean value of 8.2 ± 0.4 GPa in the dendritic BCC regions of the as-cast and thermal treated samples and 14.1 ± 0.6 GPa for the σ-phase. The onset of the plastic behavior has been studied by analyzing the pop-in phenomenon observed in the nanoindentation loading curves. For the as-cast alloy, this analysis showed that the elastic-to-plastic transition seems to be triggered by dislocation nucleation. The alloy has a low thermal diffusivity in the measured temperature range that increases on increasing temperature.This research has been supported by the Agencia Estatal de Investigación of Spain (PID2019-105325RB-C33/AEI/10.13039/501100011033) and by the Regional Government of Madrid through the program TECHNOFUSIÓN(III)CM (S2018/EMT-4437), project cofinancing with Structural Funds (ERDF and ESF). The support of the Madrid Government (Comunidad de Madrid-Spain) through the Multi-annual Agreement with UC3M ( Excellence of University Professors – EPUC3M14 and in the context of the V PRICIT - Regional Programme of Research and Technological Innovation) is also acknowledge