Journal
MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING
Volume 648, Issue -, Pages 61-71Publisher
ELSEVIER SCIENCE SA
DOI: 10.1016/j.msea.2015.09.037
Keywords
Aluminum (Al); Alumina (Al2O3); Metal matrix composite (MMC); Powder metallurgy (PM); Thermal stability; Ultrafine-grained (UFG) materials
Categories
Funding
- Fulbright Fellowship
- SRDA [APVV-0556-12]
- SAS-NSC JRP project [2011/06]
- VEGA [2/0025/14]
- CONICET-SAS RD [182/13]
- U.S. Office of Naval Research [N00014-12-1-0237]
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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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