On the thermal stability of ultrafine-grained Al stabilized by in-situ amorphous Al2O3 network

MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING

卷:648

Article

Balog, Martin^1,2  Hu, Tao²  Krizik, Peter¹  Castro Riglos, Maria Victoria³  Saller, Brandon D.²  Yang, Hanry²  Schoenung, Julie M.²  Lavernia, Enrique J.² 

[1] Slovak Acad Sci, Inst Mat & Machine Mech, Bratislava 83102, Slovakia

[2] Univ Calif Davis, Dept Chem Engn & Mat Sci, Davis, CA 95616 USA

[3] Ctr Atom Bariloche, RA-8400 San Carlos De Bariloche, Rio Negro, Argentina

关键词: Aluminum (Al);    Alumina (Al2O3);    Metal matrix composite (MMC);    Powder metallurgy (PM);    Thermal stability;    Ultrafine-grained (UFG) materials;   

DOI  :  10.1016/j.msea.2015.09.037

来源: Elsevier

【 摘 要 】

Bulk Al materials with average grain sizes of 0.47 and 2.4 mu m, were fabricated by quasi-isostatic forging consolidation of two types of Al powders with average particle sizes of 1.3 and 8.9 mu m, respectively. By utilizing the native amorphous Al2O3 (am-Al2O3) film on the Al powders surfaces, a continuous, 7 nm thick, am-Al2O3 network was formed in situ in the Al specimens. Systematic investigation of the changes to the am-Al2O3 network embedded in the Al matrix upon heating and annealing up to 600 degrees C was performed by transmission electron microscopy (TEM). At the same time, the stability of the Al grain structure was studied by transmission Kikuchi diffraction (TKD), electron back-scatter diffraction (EBSD), and TEM. The am-Al2O3 network remained stable after annealing at 400 degrees C for 24 h. In-situ TEM studies revealed that at temperatures 450 degrees C, phase transformation of the am-Al2O3 network to crystalline gamma-Al2O3 particles occurred. After annealing at 600 degrees C for 24 h the transformation was completed, whereby only nanometric gamma-Al2O3 particles with an average size of 28 nm resided on the high angle grain boundaries of Al. Due to the pinning effect of gamma-Al2O3, the Al grain and subgrain structures remained unchanged during annealing up to 600 degrees C for 24 h. The effect of the am-Al2O3 -> gamma-Al2O3 transformation on the mechanical properties of ultrafine- and fine-grained Al is discussed from the standpoint of the underlying mechanisms. (C) 2015 Elsevier B.V. All rights reserved.

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