Microstructural evolution of MgAl 2 O 4 oxide-dispersion-strengthened alloy by mechanical milling and hot isostatic pres
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Yongchang Liub) School of Material Science and Engineering, Tianjin Key Laboratory of Advanced Jointing Technology, Tianjin University, Tianjin 300072, People’s Republic of China
Ping Feng and Jun Zhao College of Materials and Chemical Engineering, Three Gorges University, Yichang 443002, People’s Republic of China (Received 6 March 2014; accepted 18 June 2014)
Oxide-dispersion-strengthened (ODS) ferritic alloys are fascinating materials for future high temperature energy production technologies. MgAl2O4 ODS alloy incorporating nanoscale oxide particles were produced by mechanical milling (MM) followed by hot isostatic pressing (HIP). The MgAl2O4 nanoscale oxide particles were formed during the HIP process by the addition of MgO and Al2O3 to the Fe–Cr matrix. Microstructural evolution of ODS alloys was structurally characterized at each step of the elaboration processes by means of scanning electron microscope (SEM), transmission electron microscope (TEM), and x-ray diffraction (XRD). The observations of structure of the mixed powders in ODS alloys after MM indicated that the initial powders, coupled with the original MgO and Al2O3 powders, got fractured by severe plastic deformation and ultrafine bcc grains (;17 nm) of the matrix and amorphous phase composed of Mg, Al, and O were formed during MM. The main driving force for the formation of amorphous phase comes from the increase of volume fraction of bcc Fe grain boundary and the increase of interfacial energy due to the decrease in the size of MgO and Al2O3 powders. The MgAl2O4 nanoscale oxide particles formed at 1173 K which was far below the traditional sintering temperature of the raw material. And the structures of MgAl2O4 nanoscale oxide particles were observed by TEM.
I. INTRODUCTION
Oxide-dispersion-strengthened (ODS) ferritic alloys are believed to be the most promising candidates of structural materials for advanced nuclear systems, such as Generation IV fission systems and the demonstration fusion reactors.1–4 Traditional high Cr ferritic creep resistant alloys, which are used as header and main/reheat steam pipe in thermal power plant, possess enhanced creep strength at the elevated temperatures. Those materials are mainly strengthened by solid solution strengthening and carbide or nitride precipitation strengthening.5 However, these strengthening mechanisms become ineffective above 650 °C as a result of the precipitation coarsening or dissolution. Large drop in creep strength of high Cr ferritic creep resistant alloys was observed in long-term high temperature service condition,6 whereas higher temperature is required to improve the Address all correspondence to these authors. a) e-mail: [email protected] b) e-mail: [email protected] DOI: 10.1557/jmr.2014.144 1440
J. Mater. Res., Vol. 29, No. 13, Jul 14, 2014
http://journals.cambridge.org
Downloaded: 18 Mar 2015
reactor’s efficiency. Compared with traditional high Cr ferritic creep resistant alloys, the advanced ferritic ODS alloys will be served in a more adverse circumstance in which there are hig
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