An Assessment of Milling Time on the Structure and Properties of a Nanostructured Ferritic Alloy (NFA)

DiDomizio, Richard; Huang, Shenyan; Dial, Laura; Ilavský, Ján; Larsen, Mike

doi:10.1007/s11661-014-2521-9

Cited by 15 publications

(14 citation statements)

References 24 publications

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“…Empirical observations have also indicated that long milling times of the precursor material [19,40] are needed to achieve a uniform as-milled microstructure. This was also supported by producing 14YWT with additions of Fe 2 O 3 and YH 2 powder instead of Y 2 O 3 powder [41].…”

Section: Discussionmentioning

confidence: 99%

“…This alternative route introduces new parameters on the optimization of the alloy design. In particular, the milling time will have a strong influence on the initial distribution of the solutes, particularly yttrium and oxygen [19]. The tensile properties of a 14Cr NFA are directly associated with the microstructural changes that arise during mechanical alloying, such as the attrition time [19], which provide the starting structure for thermomechanical treatment (extrusion, rolling, etc.).…”

Section: Introductionmentioning

confidence: 99%

“…In particular, the milling time will have a strong influence on the initial distribution of the solutes, particularly yttrium and oxygen [19]. The tensile properties of a 14Cr NFA are directly associated with the microstructural changes that arise during mechanical alloying, such as the attrition time [19], which provide the starting structure for thermomechanical treatment (extrusion, rolling, etc.). Short milling times may not be sufficient to redistribute the solute atoms in all the yttria particles within the solid solution, whereas overly long milling times add unnecessary expense to the fabrication, and introduce additional elements, such as carbon, from wear of the components of the attritor mill [16,20].…”

Section: Introductionmentioning

confidence: 99%

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The role of processing route on the microstructure of 14YWT nanostructured ferritic alloy

Mazumder

Parish

Bei

et al. 2015

Journal of Nuclear Materials

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a b s t r a c tNanostructured ferritic alloys have outstanding high temperature creep properties and enhanced tolerance to radiation damage over conventional ferritic alloys. To achieve these properties, NFAs are fabricated by mechanical alloying of metallic and yttria powders. Atom probe tomography has demonstrated that milling times of at least 40 h are required to produce a uniform distribution of solutes in the flakes. After milling and hot extrusion, the microstructure consists of a-Fe, high number densities of TieY eO-vacancy-enriched nanoclusters, and coarse Y 2 Ti 2 O 7 and Ti(O,C,N) precipitates on the grain boundaries. In contrast, the as-cast condition consists of a-Fe with 50e100 mm irregularly-shaped Y 2 Ti 2 O 7 pyrochlore precipitates with smaller embedded precipitates with the Y 3 Al 5 O 12 (yttriumealuminum garnet) crystal structure indicating that this traditional processing route is not a viable approach to achieve the desired microstructure. The nano-hardnesses were also substantially different, i.e., 4 and 8 GPa for the as-cast and as-extruded conditions, respectively. These variances can be explained by the microstructural differences and the effects of the high vacancy content introduced by mechanical alloying, and the strong binding energy of vacancies with O, Ti, and Y atoms that retard diffusion.Published by Elsevier B.V.

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Section: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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The role of processing route on the microstructure of 14YWT nanostructured ferritic alloy

Mazumder

Parish

Bei

et al. 2015

Journal of Nuclear Materials

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“…This kind of model was previously applied on either HIPed or extruded steels [48,53,54]. Also, DiDomizio et al and Kim et al applied a full quadratic summation of the strengthening contributions in ODS ferritic steels [55,56]. Kim et al showed that a linear superposition model was less relevant to predict the yield strength.…”

Section: Yield Strength Modelingmentioning

confidence: 99%

Tailoring the microstructure and the mechanical properties of ultrafine grained high strength ferritic steels by powder metallurgy

Mouawad

Boulnat

Fabrègue

et al. 2015

Journal of Nuclear Materials

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“…However during thermal exposure at higher temperature and Cr levels due to phase stability or phase separation, high temperature α-BCC may transform into iron rich (BCC) and α'-Cr (BCC) phases. This phase transformation could change corrosion and/or mechanical properties of the alloy and affect performance of the material.In this study an NFA was prepared via a mechanical alloying process and subsequent hot consolidation, the detail of processing has been discussed elsewhere [5]. The chemical composition of the alloy used in this study is given in table 1.…”

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confidence: 99%

Microstrcutural Stability of Nanostructured Ferritic Alloys (NFA)

et al. 2015

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Nanostructured ferritic alloys (NFA), are being developed for various high temperature applications where mechanical strength including creep properties and good resistance to irradiation damage is desired [1,2]. NFAs with a high chromium content (Cr >12%) present a fully ferritic matrix and are envisaged for applications in an extended range of temperature [3]. The high temperature strength is achieved by fine, homogeneously distributed nanoclusters in a ductile matrix that play an important role in enhancing mechanical strength [4]. The balance of chemical composition and most importantly Cr in these alloys is critical in order to maintain a ferritic structure and achieve desired corrosion and oxidation properties. However during thermal exposure at higher temperature and Cr levels due to phase stability or phase separation, high temperature α-BCC may transform into iron rich (BCC) and α'-Cr (BCC) phases. This phase transformation could change corrosion and/or mechanical properties of the alloy and affect performance of the material.In this study an NFA was prepared via a mechanical alloying process and subsequent hot consolidation, the detail of processing has been discussed elsewhere [5]. The chemical composition of the alloy used in this study is given in table 1. The billet was cut into pieces and aged at 427°C (800°F), 482°C (900°F) and 537°C (1000°F) up to 25,000 hrs. Each aged sample was removed from the furnace at a specific time interval and mechanical properties including Vickers hardness and tensile properties were measured. Microstructural evaluation on each sample was carried out using a 200KV Tecni-Osiris TEM equipped with 4 EDS detectors.TEM results showed that phase separation leads to the formation of the chromium-rich α' phase (Fig1,2). Also a tungsten rich laves phase was found at the grain boundaries after 2500hrs exposure at 482°C (Fig.2). Experimental results showed that tensile properties of the alloy are not significantly affected by annealing time (Fig. 3). This behavior is attributed to dislocation/NFA interaction and is under investigation.

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An Assessment of Milling Time on the Structure and Properties of a Nanostructured Ferritic Alloy (NFA)

Cited by 15 publications

References 24 publications

The role of processing route on the microstructure of 14YWT nanostructured ferritic alloy

The role of processing route on the microstructure of 14YWT nanostructured ferritic alloy

Tailoring the microstructure and the mechanical properties of ultrafine grained high strength ferritic steels by powder metallurgy

Microstrcutural Stability of Nanostructured Ferritic Alloys (NFA)

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