Compressive properties at elevated temperatures of porous aluminum processed by the spacer method
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Yasuo Yamada, Yasumasa Chino, Hiroyuki Hosokawa, and Takeshi Nakajima Materials Research Institute for Sustainable Development, National Institute of Advanced Industrial Science and Technology, Moriyama, Nagoya 463-8560, Japan
Youqing Chen, Hiromu Kusuda, and Mamoru Mabuchi Department of Energy Science and Technology, Graduate School of Energy Science, Kyoto University, Sakyo, Kyoto 606-8501, Japan (Received 11 April 2005; accepted 1 September 2005)
Compressive properties at 573–773 K of porous aluminum produced by the spacer method were investigated and compared with those of bulk reference aluminum with the same chemical compositions. The stress exponent and activation energy for deformation at elevated temperatures in the porous aluminum were in agreement with those in the bulk reference aluminum. In addition, the plateau stress of the porous aluminum was comparable to the stress of the bulk reference aluminum upon compensation by the relative density. Therefore, it is conclusively demonstrated that the mechanism of deformation at elevated temperatures in the porous aluminum is the same as that in the bulk reference aluminum. This is likely due to the homogeneous microstructure in the porous aluminum produced by the spacer method. I. INTRODUCTION
Recently, porous metals have attracted considerable attention as ultralight metals due to their many unique mechanical, thermal, electrical, and acoustic properties.1,2 In certain commercial applications, mechanical properties must be investigated at elevated temperatures. Andrews et al.3 developed the expression for creep bending of cell walls in porous solids and demonstrated the validity of this expression. Cocks and Ashby4 also developed the expression for creep buckling of cell walls in porous solids. These expressions are based on creep of solids, namely, the power-law creep. In general, the stress exponent in the power-law creep is 4–6 for a dislocation creep region. However, much larger stress exponents of 12–15 have been recently reported for porous aluminum.5–7 These larger stress exponents for porous aluminum may be induced by the following:5 the powerlaw breakdown region, permanent damage, and absence of load in severely curved cell walls. Zhang et al.6 observed in their investigations of microstructural evolution during creep that a very high stress is induced locally, resulting in a power-law breakdown region. Also, Haag et al.7 showed that porous aluminum has a lower strength and a larger stress exponent, which results from the
II. EXPERIMENTAL
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Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/JMR.2005.0415 J. Mater. Res., Vol. 20, No. 12, Dec 2005
http://journals.cambridge.org
power-law breakdown region, than predicted by the model for porous aluminum with regular pores. Microstructural inhomogeneity characteristics, such as a significant cell wall curvature and missing cell walls, significantly reduce the strength at elevated temperatures.8,9 Finite element analysis suggested that the missin
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