Attributes of Spark Plasma Sintering on Developing Oxide Dispersion Strengthened Ferritic Steels and Understanding Struc
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Attributes of Spark Plasma Sintering on Developing Oxide Dispersion Strengthened Ferritic Steels and Understanding Structure–Property Relation B. V. Ponraj1 . S. Kumaran1
Received: 23 January 2020 / Accepted: 2 November 2020 The Institution of Engineers (India) 2020
Abstract Ferritic alloys strengthened by oxide dispersoids having a composition of Fe–16Cr–2W–0.3Ti–0.5Y2O3 and Fe–16Cr–2W–0.3Ti–0.75Y2O3 were developed through mechanical alloying followed by spark plasma sintering process. The densification behaviour of ferritic steel was understood while sintering at a temperature of 900 C with soaking for 5 min, at the applied pressure of 50 MPa. X-ray diffraction analysis was done on milled powders and sintered bulk samples to confirm the alloying and crystallographic changes. Field emission scanning electron microscopy (FESEM) was carried out to study the morphology and FESEM-EDS to ascertain the composition of alloyed powders. Transmission electron microscopy study conceded the evolution of nanocrystalline ferritic steel during MA. Distinctive stages of mechanical alloying were observed. System with 0.5 Y2O3 displayed better densification behaviour and possessed higher mechanical properties. Keywords Oxide dispersion strengthening Ferritic steel Mechanical alloying Spark plasma sintering Transmission electron microscopy
& B. V. Ponraj [email protected] S. Kumaran [email protected] 1
Introduction Ferritic ODS steels are quite desirable for application in fast reactor and fusion reactor systems, thanks to their appreciable swelling resistance which retains their dimensional stability, attractive thermal conductivity, superior strength and subdued neutron activation, making repairs cheaper relatively [1–3]. Austenitic steels, characteristic of their fcc structure, tend to suffer from void swelling and stress corrosion cracking, where ferritic ODS steels hold an edge [4, 5]. It is arduous to fabricate ODS steels through traditional methods, for instance casting route because of the low solubility limit and inhomogeneous distribution of the rare earth oxides in solute metal. During conventional casting, oxide particles would aggregate collectively, followed by coarsening [6]. Benjamin was the pioneer in adopting mechanical alloying (MA) route for synthesis of the nickelbased dispersion alloys [7]. This process leads to uniform dispersion of nano-oxides in the metal matrix, becoming an impressive technique for fabrication of oxide dispersed steels [8]. The superior resistance to creep offered by ODS steels at high-temperature is associated with the factor that the dispersoids serve as obstacles against dislocation motion and hinder grain growth through interaction with dispersion [9, 10]. The pinning force generated by the nanosized dispersoids restricts the grain boundary movement to a great extent [3, 11]. Oxide dispersoids with a comparatively small diameter give rise to higher limiting stress, above 300 MPa that can reinforce the dispersion strengthening effect quantitatively
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