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

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• 作者：Martin Balog^a ; ^b ; ^{martin.balog@savba.sk" class="auth_mail" title="E-mail the corresponding author} ; Tao Hu^b ; Peter Krizik^a ; Maria Victoria Castro Riglos^c ; Brandon D. Saller^b ; Hanry Yang^b ; Julie M. Schoenung^b ; Enrique J. Lavernia^b
• 关键词：Aluminum (Al) ; Alumina (Al2O3) ; Metal matrix composite (MMC) ; Powder metallurgy (PM) ; Thermal stability ; Ultrafine-grained (UFG) materials
• 刊名：Materials Science & Engineering A
• 出版年：2015
• 出版时间：11 November 2015
• 年：2015
• 卷：648
• 期：Complete
• 页码：61-71
• 全文大小：7635 K

文摘

Bulk Al materials with average grain sizes of 0.47 and 2.4 µm, were fabricated by quasi-isostatic forging consolidation of two types of Al powders with average particle sizes of 1.3 and 8.9 渭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 °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 °C for 24 h. In-situ TEM studies revealed that at temperatures ≥450 °C, phase transformation of the am-Al₂O₃ network to crystalline 纬-Al₂O₃ particles occurred. After annealing at 600 °C for 24 h the transformation was completed, whereby only nanometric 纬-Al₂O₃ particles with an average size of 28 nm resided on the high angle grain boundaries of Al. Due to the pinning effect of 纬-Al₂O₃, the Al grain and subgrain structures remained unchanged during annealing up to 600 °C for 24 h. The effect of the am-Al₂O₃→纬-Al₂O₃ transformation on the mechanical properties of ultrafine- and fine-grained Al is discussed from the standpoint of the underlying mechanisms.