• Metals and materials international
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• v.24 no.6
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• pp.1309-1314
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• 2018

In this study, we investigated the state of $Y_2O_3$, as a major additive element in Fe-based ODS alloys, during mechanical alloying (MA) processes by thermodynamic approaches and experimental verification. For this purpose, we introduced $Ti_2O_3$ that formed different reaction products depending on the state of $Y_2O_3$ into the Fe-based ODS alloys. In addition, the reaction products of $Ti_2O_3$, Y, and $Y_2O_3$ powders were predicted approximately based on their formation enthalpy. The experimental results relating to the formation of Y-based complex oxides revealed that $YTiO_3$ and $Y_2Ti_2O_7$ were formed when $Ti_2O_3$ reacted with Y; in contrast, only $Y_2Ti_2O_7$ was detected during the reaction between $Ti_2O_3$ and $Y_2O_3$. In the alloy of $Fe-Cr-Y_2O_3$ with $Ti_2O_3$, $YTiO_3$ (formed by the reaction of $Ti_2O_3$ with Y) was detected after the MA and heat treatment processes were complete, even though $Y_2O_3$ was present in the system. Using these results, it was proved that $Y_2O_3$ decomposed into monoatomic Y and O during the MA process.

• Journal of Powder Materials
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• v.2 no.1
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• pp.53-62
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• 1995

TLP(Transient-Liquid-Phase) bonding of Fe-base MA956 ODS alloy was performed. As insert metal a commercially available Ni-base alloy(MBF50) and an MA956 alloy with additive elements of 7wt% Si and 1wt% B were used. To confirm the idea that a concurrent use of MA956 powder with Insert metals can enhance the homogenization of constituent elements and thereby reduce the thickness of joint interface, MA956 powder was also inserted In a form of sheet. SEM observation and EDS analysis revealed that Cr-rich phase was formed in the bonded interface in initial stage of isothermal solidification during the bonding process, irrespective of kind of insert metals. Measurement of hardeness in the region of bonded interface and EDS analysis showed that a complete homogenization of composition could not be obtained especially in case of MBF50. Joints using either BSi insert metals only or BSi insert together with MA956 powder interlayer showed, however, a remarkable improvement in a compositional homogenization, even though a rapid grain growth in the bonded interface could not be hindered.

• Proceedings of the Korean Powder Metallurgy Institute Conference
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• 1995.04a
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• pp.38-38
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• 1995

• Journal of Powder Materials
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• v.25 no.4
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• pp.327-330
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• 2018

This study is conducted as a preliminary research to verify the feasibility of Ti-based Oxide dispersion strengthened (ODS) alloy. Pure-Ti powder is mixed with $Y_2O_3$ powder and subsequently, mechanically alloyed at $-150^{\circ}C$. The Ti-based ODS powder is hot-isostatically pressed and subsequently hot-rolled for recrystallization. The microstructure consists of elongated grains and Y excess fine particles. The oxide particle size is larger than that of the typical Fe-based ODS steel. Tensile test shows that the tensile ductility is approximately 25%, while the strength is significantly higher than that of pure Ti. The high-temperature hardness of the Ti-ODS alloy is also significantly higher than that of pure Ti at all temperatures, while being lower than that of Ti-6Al-4V. The dimple structure is well developed, and no evidence of cleavage fracture surface is observed in the fracture surface of the tensile specimen.

• Journal of Powder Materials
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• v.27 no.4
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• pp.311-317
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• 2020

In this study, the effects of Co content on the microstructure and Charpy impact properties of Fe-Cr-W ferritic/martensitic oxide dispersion strengthened (F/M ODS) steels are investigated. F/M ODS steels with 0-5 wt% Co are fabricated by mechanical alloying, followed by hot isostatic pressing, hot-rolling, and normalizing/tempering heat treatment. All the steels commonly exhibit two-phase microstructures consisting of ferrite and tempered martensite. The volume fraction of ferrite increases with the increase in the Co content, since the Co element considerably lowers the hardenability of the F/M ODS steel. Despite the lowest volume fraction of tempered martensite, the F/M ODS steel with 5 wt% Co shows the highest micro-Vickers hardness, owing to the solid solution-hardening effect of the alloyed Co. The high hardness of the steel improves the resistance to fracture initiation, thereby resulting in the enhanced fracture initiation energy in a Charpy impact test at - 40℃. Furthermore, the addition of Co suppresses the formation of coarse oxide inclusions in the F/M ODS steel, while simultaneously providing a high resistance to fracture propagation. Owing to these combined effects of Co, the Charpy impact energy of the F/M ODS steel increases gradually with the increase in the Co content.

• Journal of Powder Materials
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• v.24 no.2
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• pp.133-140
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• 2017

This study investigates the oxidation properties of Fe-14Cr ferritic oxide-dispersion-strengthened (ODS) steel at various high temperatures (900, 1000, and $1100^{\circ}C$ for 24 h). The initial microstructure shows that no clear structural change occurs even under high-temperature heat treatment, and the average measured grain size is 0.4 and $1.1{\mu}m$ for the as-fabricated and heat-treated specimens, respectively. Y-Ti-O nanoclusters 10-50 nm in size are observed. High-temperature oxidation results show that the weight increases by 0.27 and $0.29mg/cm^2$ for the as-fabricated and heat-treated ($900^{\circ}C$) specimens, and by 0.47 and $0.50mg/cm^2$ for the as-fabricated and heat-treated ($1000^{\circ}C$) specimens, respectively. Further, after 24 h oxidation tests, the weight increases by 56.50 and $100.60mg/cm^2$ for the as-fabricated and heat-treated ($1100^{\circ}C$) specimens, respectively; the latter increase is approximately 100 times higher than that at $1000^{\circ}C$. Observation of the surface after the oxidation test shows that $Cr_2O_3$ is the main oxide on a specimen tested at $1000^{\circ}C$, whereas $Fe_2O_3$ and $Fe_3O_4$ phases also form on a specimen tested at $1100^{\circ}C$, where the weight increases rapidly. The high-temperature oxidation behavior of Fe-14Cr ODS steel is confirmed to be dominated by changes in the $Cr_2O_3$ layer and generation of Fe-based oxides through evaporation.

• Nuclear Engineering and Technology
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• v.56 no.7
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• pp.2584-2594
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• 2024

A novel approach to incorporating oxide formers into ferritic ODS production has been developed using the co-precipitation technique. This method enables the tailored design of complex nano-oxides, integrated during Mechanical Alloying (MA) and precipitated during Spark Plasma Sintering (SPS) consolidation. Findings illustrate that co-precipitation effectively produces nano-powders with customised compositions, enriching Y, Ti, and Zr in the ferritic grade to condition subsequent oxide precipitation. While the addition of Y-Ti-Zr-O nano-oxides did not prevent the formation of Y-Al-O and Al-containing nano-oxides, these were refined thanks to the presence of well-dispersed Zr. Additionally, the Spark Plasma Sintering (SPS) parameters were optimised to tailor the bimodal grain size distribution of the ODS steels, aiming for favourable strength-to-ductility ratios. Comprehensive microstructural analyses were performed using SEM, EDS, EBSD, and TEM techniques, alongside mechanical assessments involving microtensile tests conducted at room temperature and small punch tests carried out at room temperature, 300 ℃, and 500 ℃. The outcomes yielded promising findings, showcasing similar or better performance with conventionally manufactured ODS steels. This reinforces the effectiveness and success of this innovative approach.

• Proceedings of the Korean Powder Metallurgy Institute Conference
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• 2004.04a
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• pp.45-46
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• 2004

• Journal of Powder Materials
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• v.24 no.4
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• pp.298-301
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• 2017

In the present work, we use multiwall carbon nanotubes (MWCNT) as the starting material for the fabrication of sintered carbon steel. A comparison is made with conventionally sintered carbon steel, where graphite is used as the starting material. Milling is performed using a horizontal mill sintered in a vacuum furnace. We analyze the grain size, number of pores, X-ray diffraction patterns, and microstructure. Changes in the physical properties are determined by using the Archimedes method and Vickers hardness measurements. The result shows that the use of MWCNTs instead of graphite significantly reduces the size and volume of the pores as well as the grain size after sintering. The addition of $Y_2O_3$.to the Fe-MWCNT samples further inhibits the growth of grains.

• Proceedings of the Korean Powder Metallurgy Institute Conference
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• 2006.09a
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• pp.305-305
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• 2006