Influence of stacking fault energy on microstructural development in equal-channel angular pressing
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Influence of stacking fault energy on microstructural development in equal-channel angular pressing Shogo Komura, Zenji Horita, and Minoru Nemoto Department of Materials Science and Engineering, Faculty of Engineering, Kyushu University, Fukuoka 812-8581, Japan
Terence G. Langdon Departments of Materials Science and Mechanical Engineering, University of Southern California, Los Angeles, California 90089-1453 (Received 31 August 1998; accepted 12 July 1999)
Equal-channel angular (ECA) pressing is a procedure having the capability of introducing an ultrafine grain size into a material. Experiments were conducted to examine the effect of the low stacking fault energy in pure Cu on microstructural development during ECA pressing at room temperature. The results show that the low stacking fault energy and the consequent low rate of recovery lead to a very slow evolution of the microstructure during pressing. Ultimately, a stable grain size of −0.27 m was established in pure Cu but the microstructure was not fully homogeneous even after pressing to a total strain of ∼10. It is shown by static annealing that the as-pressed grains are stable up to ∼400 K, but at higher temperatures there is grain growth. These results lead to the conclusion that a low stacking fault energy is especially favorable for the introduction of an exceptionally small grain size using the ECA pressing procedure.
I. INTRODUCTION
Equal-channel angular (ECA) pressing is a processing method which may be used to refine the grain size of a material to the micrometer, submicrometer, or possibly nanometer level.1–3 Recently, experiments were conducted to examine the influence of the addition of magnesium in solid solution on the ECA pressing of samples of aluminum.4 The results from this investigation revealed two important findings. First, the addition of Mg leads to an increase in the total strain that is needed to establish a homogeneous microstructure of equiaxed grains within the material. Second, the ultimate stable equilibrium grain size decreases with increasing additions of Mg: specifically, the equilibrium grain sizes were ∼1.3, ∼0.45, and ∼0.27 m, established after strains of ∼4, ∼6, and ∼8, for samples of pure Al (99.99%), Al–1% Mg, and Al–3% Mg, respectively. Since the recovery rates are reduced in Al–Mg alloys by comparison with pure Al, it was concluded that materials exhibiting low rates of recovery will be especially attractive for use in ECA pressing for the fabrication of samples with exceptionally small grain sizes. The present investigation was initiated in order to examine the effect of the stacking fault energy (SFE) on microstructural development and the ultimate equilibrium grain size in ECA pressing. Copper was selected as 4044
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J. Mater. Res., Vol. 14, No. 10, Oct 1999 Downloaded: 11 Mar 2015
the test material because the SFE is very low (∼40 mJ m−2) by comparison with pure Al (∼200 mJ m−2), and it is well established that this low SFE leads to low
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