Size and structure evolution of yttria in ODS ferritic alloy powder during mechanical milling and subsequent annealing

• Published in: Powder technology Vol. 217; pp. 281 - 287
• Main Authors: Dai, Lei, Liu, Yongchang, Dong, Zhizhong
• Format: Journal Article
• Language: English
• Published: Amsterdam Elsevier B.V 01.02.2012; Elsevier
• Subjects: alloys; Annealing; Applied sciences; Austenitic stainless steels; Chemical engineering; chromium; Dispersion hardening alloys; energy; Evolution; Exact sciences and technology; Ferritic alloy; Ferritic stainless steels; Heat resistant steels; iron; Mechanical milling; microstructure; milling; Miscellaneous; Nanocrystalline; Nanocrystals; Nanostructure; Oxide dispersion strengthening; Oxides; particle size; plastic deformation; Solid-solid systems; temperature; transmission electron microscopy; vibration; Yttrium oxide; Nanostructure; Mechanical milling; Ferritic alloy; Oxide dispersion strengthening; Nanocrystalline; Grain size; Strengthening; Particle size; Annealing; Vibration; Plastic deformation; Steel; Rotation; Dispersion; Powder; Transmission electron microscopy; Production; Microstructure
• ISSN: 0032-5910; 1873-328X
• DOI: 10.1016/j.powtec.2011.10.039

Oxide dispersion strengthening ferritic steels are fascinating materials for future high temperature energy production technologies. Mechanical milling with the aim of a fine dispersion of oxides in the metal matrix becomes the main process for the production of ODS steels. The mixed powder which is composed of iron, chromium and yttria (Fe-9Cr-15%Y2O3) was mechanically milled for a maximum period of 100h. Size and structure evolution of Y2O3 and the microstructure changes of the mixed powder during mechanical milling and subsequent annealing were studied. The powder is fractured and welded with rotation and vibration of container during mechanical milling. The results show that the particle size and the grain size decrease with increasing milling time. Nanocrystalline of Y2O3 is gradually formed by severe plastic deformation. It can be explained that the long-range order structure of Y2O3 is damaged by mechanical milling. The formation processes of nanocrystalline in ordered oxides may follow the sequence: ordered phase→disordered phase (loss of long-range order)→fine-grained (nanocrystalline) phase. Growth of nanocrystalline Y2O3 occurs at about 891K during subsequent annealing and the nanostructure of Y2O3 after mechanical milling and annealing was observed by TEM and HRTEM. [Display omitted] ► Y2O3 still remains in the milled powders. ► The combination between yttrium atoms and oxygen atoms isn't fractured by MM. ► Y2O3 exists in nanocrystalline after MM. ► Growth of nanocrystalline Y2O3 has occurred during subsequent annealing.