A novel and sustainable method to develop non-equiatomic CoCrFeNiMox high entropy alloys via spark plasma sintering using commercial commodity powders and evaluation of its mechanical behaviour

A novel approach to developing high entropy alloys (HEAs) using spark plasma sintering (SPS) was explored in this work where a mix of commercial commodity powders like Ni625, CoCrF75, and 316L was used instead of pre-alloyed powders avoiding the expensive pre-alloying steps like mechanical alloying or gas atomizing. Three non-equiatomic HEAs, based on Co, Cr, Fe, Ni, and Mo were designed and developed by blending the powders which were sintered via SPS and resulted in a single FCC phase after homogenization. The HEAs were microstructurally and mechanically characterized with tensile and hot compression tests up to a temperature of 750oC showing excellent properties. The maximum room temperature tensile strength and ductility demonstrated was 712 MPa and 62% respectively, by the alloy Co23.28Cr28.57Fe25.03Ni21.01Mo2.1. Moreover, the same alloy exhibited a compression strength greater than 640 MPa with a ductility above 45% at a temperature of 750oC. Also, this study paves the way for a novel fabrication route that offers more flexibility to develop new HEAs cost-effectively and efficiently which is crucial for the discovery of new materials over high-throughput techniques. Using such commodity alloys also opens the possibility of developing ingot casting from recycled scraps avoiding the direct use of critical metals

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 small variations in Zr content on the microstructure and properties of ferritic ODS steels consolidated by SPS

Two different zirconium contents (0.45 and 0.60 wt.%) have been incorporated into a Fe-14Cr-5Al-3W-0.4Ti-0.25Y2O3 oxide dispersion-strengthened (ODS) steel in order to evaluate their effect on the final microstructure and mechanical properties. The powders with the targeted compositions were obtained by mechanical alloying (MA), and subsequently processed by spark plasma sintering (SPS) at two different heating rates: 100 and 400 °C·min-1. Non-textured bimodal microstructures composed of micrometric and ultrafine grains were obtained. The increase in Zr content led to a higher percentage of Zr nano-oxides and larger regions of ultrafine grains. These ultrafine grains also seem to be promoted by higher heating rates. The effective pinning of the dislocations by the Zr dispersoids, and the refining of the microstructure, have significantly increased the strength exhibited by the ODS steels during the small punch tests, even at high temperatures (500 °C)This research was funded by Ministerio de Economía y Competitividad, Gobierno de España (grant numbers MAT2013-47460-C5-5-P and MAT2016-80875-C3-3-R). The authors would like to express their gratitude to Daniel Plaza for his kind help during the small punch tests

Portland cement clinkers turned into garnets by spark plasma sintering

The feasibility of sintering Portland cement clinker powders by Spark Plasma Sintering (SPS) has been studied. Different SPSed compacts have been successfully obtained by this technique. The compacts have been characterized by means of X-Ray Diffraction, InfraRed spectroscopy, Scanning Electron Microscopy, Raman Microscopy and Vickers hardness. It is worth noting the finding that slight mineralogical variations in the starting compositions may induce dramatic changes, both in the final mineralogical composition and in the morphology, which can affect the properties of the SPSed compacts. Thus, we find that SPS allows artificial garnets to be obtained in the laboratory by applying pressures as low as 50 MPa, while they are materials that would require much higher pressures in natural environments (2-10 GPa). According to the Selsing model, it has been calculated that the material itself acts as a pressure amplifier at the micrometric level by a factor of 40-200 times. A new model describing the formation of garnets considering the emergence of two transitory eutectic liquids has been explained to justify this phenomenon. This result opens the door to looking for compositions for specific applications with high added value in the field (i.e. high hardness), mainly in the manufacturing of high-pressure (GPa) phases by applying relatively low pressures (MPa).The Authors acknowledge the financial support of the PID2020-119130 GB-I00 project funded by MCIN/AEI/10.13039/501100011033 and by CSIC under grant 201960E103. Thanks to the Official Laboratory for Testing of Construction Materials (LOEMCO, Getafe, Madrid, Spain) for free supply of the clinker sample

Microstructure and Mechanical Properties of Spark Plasma Sintered Mg-Zn-Ca-Pr Alloy

Alloys based on magnesium are of considerable scientific interest as they have very attractive mechanical and biological properties that could be used to manufacture biodegradable materials for medical applications. Mechanical alloying is a very suitable process to obtain alloys that are normally hard to produce as it allows for solid-state diffusion via highly energetic milling, producing fine powders. Powders obtained by this method can be sintered into nearly net-shape products, moreover, their phase and chemical composition can be specifically tailored. This work aims to investigate the effect of milling time on the density, microstructure, phase composition, and mechanical properties of Mg-Zn-Ca-Pr powders processed by high energy mechanical alloying (HEMA) and consolidated by spark plasma sintering (SPS). Thus, the results of XRD phase analysis, particle size distribution (granulometry), density, mechanical properties, SEM investigation of mechanically alloyed and sintered Mg-Zn-Ca-Pr alloy are presented in this manuscript. The obtained results illustrate how mechanical alloying can be used to produce amorphous and crystalline materials, which can be sintered and demonstrates how the milling time impacts their microstructure, phase composition, and resulting mechanical properties

High speed steel matrix composites fabricated by spark plasma sintering

W pracy przedstawiono wyniki badań wpływu temperatury spiekania w zakresie 900–1000°C na mikrostrukturę i wybrane właściwości kompozytów na osnowie stali szybkotnącej M3/2 z 50% dodatkiem wagowym żelaza wytworzonych metodą spiekania iskrowo-plazmowego. Proszek stali szybkotnącej gatunku M3/2 oraz proszek żelaza gatunku NC 100.24 mieszano w mieszalniku Turbula T2F. Przygotowane mieszaniny proszków spiekano z wykorzystaniem urządzenia HP D 25–3. W efekcie spiekania metodą SPS uzyskano kompozyty M3/2–Fe. W mikrostrukturze tych kompozytów występują zarówno ziarna żelaza, jak i ziarna stali szybkotnącej z charakterystycznymi wydzieleniami węglików typu MC i M6C. Osnowa stali szybkotnącej to prawdopodobnie ferryt i bainit. W mikrostrukturze widoczne są także małe pory, w miarę równomiernie rozmieszczone, co świadczy o tym, że temperatura spiekania wynosząca 1000°C jest nieznacznie niższa od optymalnej temperatury spiekania kompozytów M3/2–Fe metodą SPS. Na podstawie wykonanych pomiarów gęstości wykazano, że gęstość względna uzyskanych kompozytów wynosi od 92 do 98% i wzrasta wraz ze wzrostem temperatury spiekania. Ponadto wykazano, że od gęstości względnej zależy twardość oraz wytrzymałość na zginanie. Wraz ze zwiększeniem gęstości względnej od 92 do 98%, uzyskano wzrost twardości od 237 do 367 HBW 2,5/187,5 oraz wytrzymałości na zginanie od 956 do 1107 MPa. Najlepszą relacją gęstość–twardość–wytrzymałość na zginanie odznacza się kompozyt M3/2–Fe uzyskany w temperaturze 1000°C, którego gęstość względna wynosi 98%, twardość wynosi 367 HBW 2,5/187,5, a wytrzymałość na zginanie wynosi 1107 MPa.The paper presents the results of investigations on the influence of sintering temperature in the range of 900–1000°C on the microstructure and selected properties of composites on an M3/2 high speed steel matrix with a 50 wt% addition of iron produced by spark plasma sintering. M3/2 high speed steel powder and NC 100.24 iron powder were mixed in a Turbula T2F shaker/mixer. The prepared powder mixtures were sintered using an HP D 25–3 furnace. As a result of spark plasma sintering, M3/2–Fe composites were obtained. The microstructure of these composites includes both iron grains and high speed steel grains with characteristic precipitates of MC and M6C carbides. The high speed steel matrix is probably ferrite and bainite. Small evenly spaced pores are also visible in the microstructure, which indicates that the sintering temperature of 1000°C is slightly lower than the optimal sintering temperature of M3/2–Fe composites using the spark plasma sintering. Based on the performed density measurements, it was shown that the relative density of the ob-tained composites is from 92 to 98% and grows with increasing the sintering temperature. In addition, it was shown that the relative hardness and bending strength depend on the relative density. Together with the rise in the relative density from 92 to 98%, increases in the hardness from 237 to 367 HBW 2.5/187.5 and the bending strength from 956 to 1107 MPa were obtained. The M3/2–Fe composite obtained at the temperature of 1000°C is characterized by the best density–hardness–bending strength relation, which amounts a relative density of 98%, hardness of 367 HB 2.5/187.5, and bending strength of 1107 MPa

Effect of Sintering Temperature and Iron Addition on Properties and Microstructure of High Speed Steel Based Materials Produced by Spark Plasma Sintering Method

Attempts were made to describe the effect of the sintering temperature and pure iron powder addition on the properties of HSS-based materials produced by the spark plasma sintering method (SPS). After sintering, their density, hardness, flexural strength, and tribological properties were determined. The sintered materials were also subjected to microstructural analysis to determine the phenomena occurring at the particle contact boundaries during sintering. On the basis of analysis of the obtained results, it was found that the mechanical properties and microstructure were mainly influenced by the sintering temperature, which was selected in relation to the previously tested steel M3/2, adjusted upwards due to its chemical composition. The use of the temperature of 1050 °C allows materials to be obtained with a density close to the theoretical density (97%), characterized by a high hardness of about 360 HB. The addition of iron slightly reduces the hardness and also increases the flexural strength to 577 MPa. There was no diffusion of the alloying elements from the steel to the iron due to the short time of exposure to the sintering temperature

DEVELOPMENT OF ALTERNATIVE METHOD FOR MANUFACTURING STRUCTURAL ZIRCONIUM ELEMENTS FOR NUCLEAR ENGINEERING

irconium is used as a structural material for use in aggressive environments, including the core of nuclear reactors. The traditional technology of manufacturing the structural elements of zirconium nuclear reactors is characterized by a long technological process and a significant amount of waste in the form of metal shavings. The paper presents the results of an alternative technology, spark plasma sintering, for manufacturing zirconium products. A complex of microstructural and mechanical studies of the obtained samples was carried out according to the ASTMB-351 standard. The sintering of zirconium powder and options for subsequent processing by various methods, including non-standard ones such as radial shear rolling, are justified. Keywords: zirconium; powder metallurgy; spark plasma sintering; microstructure; rheological; dilatometric studie

Structure and Deformation Behavior of Ti-SiC Composites Made by Mechanical Alloying and Spark Plasma Sintering

Combining high energy ball milling and spark plasma sintering is one of the most promising technologies in materials science. The mechanical alloying process enables the production of nanostructured composite powders that can be successfully spark plasma sintered in a very short time, while preserving the nanostructure and enhancing the mechanical properties of the composite. Composites with MAX phases are among the most promising materials. In this study, Ti/SiC composite powder was produced by high energy ball milling and then consolidated by spark plasma sintering. During both processes, Ti3SiC2, TiC and Ti5Si3 phases were formed. Scanning electron microscopy, energy-dispersive X-ray spectroscopy and X-ray diffraction study showed that the phase composition of the spark plasma sintered composites consists mainly of Ti3SiC2 and a mixture of TiC and Ti5Si3 phases which have a different indentation size effect. The influence of the sintering temperature on the Ti-SiC composite structure and properties is defined. The effect of the Ti3SiC2 MAX phase grain growth was found at a sintering temperature of 1400–1450 °C. The indentation size effect at the nanoscale for Ti3SiC2, TiC+Ti5Si3 and SiC-Ti phases is analyzed on the basis of the strain gradient plasticity theory and the equation constants were defined

Powder metallurgy in Łukasiewicz Research Network – Metal Forming Institute

W artykule przedstawiono metody metalurgii proszków wykorzystywane do wykonywania wyrobów z proszków metalicznych i ceramicznych w Sieci Badawczej Łukasiewicz – Instytucie Obróbki Plastycznej. Do wytwarzania zaawansowanych materiałów metalicznych, ceramicznych oraz kompozytowych zastosowano nowoczesną metodę spiekania iskrowo-plazmowego z wykorzystaniem urządzenia SPS HP D 25-3. Urządzenie to pozwala na realizację procesów spiekania w temperaturze do 2200°C z jednoczesnym prasowaniem z siłą do 250 kN w próżni, atmosferze azotu, argonu lub wodoru. Z kolei do wykonywania wyrobów z proszków na bazie żelaza stosowana jest konwencjonalna metoda prasowania jednoosiowego na zimno i następującego po nim spiekania swobodnego w atmosferze azotowo-wodorowej zdysocjowanego amoniaku z wykorzystaniem gniazda badawczo-doświadczalnego GSMP-75 wyposażonego w piec wgłębny retortowy PSF-12/75. Maksymalna temperatura spiekania wynosi 1200°C. Ponadto omówiono przykładowe prace naukowo-badawcze zrealizowane w ramach zarówno projektów międzynarodowych finansowanych z 7 PR UE oraz Horyzontu 2020, jak i projektów krajowych realizowanych we współpracy z przemysłem. Zaprezentowano wybrane wyniki badań dotyczące kompozytowych sektorów tnących stosowanych w piłach do cięcia kamieni, kompozytowych elektrod nasadkowych stosowanych w zrobotyzowanych stanowiskach zgrzewania punktowego oraz płytek skrawających wykonanych z węglików spiekanych stosowanych w obróbce mechanicznej metali. Poza tym wskazano gałęzie przemysłu, na potrzeby których ŁUKASIEWICZ – INOP wykonuje prace naukowo-badawcze oraz realizuje wdrożenia. Zaprezentowano także ofertę współpracy dla przemysłu.The article presents the powder metallurgy methods used to make products from metallic and ceramic powders in the Łukasiewicz Research Network – Metal Forming Institute. To produce advanced metallic, ceramic and composite materials, the method of spark plasma sintering employing an SPS HP D 25-3 was used. This device allows sintering processes to be performed at temperatures up to 2200°C with simultaneous compaction with a force of up to 250 kN in vacuum, and in a nitrogen, argon or hydrogen atmosphere. On the other hand, to make products from iron-based powders, the conventional method of cold uniaxial pressing and subsequent free sintering in a nitrogen-hydrogen atmosphere of dissociated ammonia employing a GSMP-75 research and testing socket equipped with a PSF-12/75 retort furnace is used. The maximum sintering temperature is 1200°C. In addition, examples of scientific and research work carried out as part of international projects financed from EU FP7 and Horizon 2020, as well as national projects executed in cooperation with industry are discussed. Selected research results concerning composite cutting sectors used in saws for cutting stones, composite cap electrodes used in robotic spot welding stations and cutting inserts made of cemented carbides used in metal machining were presented. In addition, the branches of industry were identified for which the Łukasiewicz Research Network – Metal Forming Institute performs scientific and research works and executes implementations. A cooperation offer for industry was also presented