Spark Plasma Sintering of Cryomilled Nanocrystalline Al Alloy - Part II: Influence of Processing Conditions on Densifica
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t years, spark plasma sintering (SPS) technology has emerged as a viable approach to consolidate nanostructured metallic materials, composites and ceramics. In this process, a pulsed direct current is used concurrently with a uniaxial pressure to sinter powders into fully dense, bulk materials. In comparison with traditional methods such as hot pressing, where the samples are heated externally, the thermal energy during SPS is generated by the resistivity of the materials, i.e., mold components and powder in the case of conductive DONGMING LIU, Visiting Assistant Researcher, is with the Department of Chemical Engineering and Materials Science, University of California, Davis, CA 95616, and also Associate Professor with the Department of Materials Science and Engineering, Shandong University, Jinan 250061, P.R. China. YUHONG XIONG, Post Doctoral Researcher, TROY D. TOPPING, PhD Candidate, YIZHANG ZHOU, Associate Researcher, JULIE M. SCHOENUNG, Professor, and ENRIQUE J. LAVERNIA, Distinguished Professor, are with the Department of Chemical Engineering and Materials Science, University of California, Davis. Contact e-mail: jmschoenung@ ucdavis.edu CHRIS HAINES, Senior Metallurgist, JOSEPH PARAS, Materials Engineer, DAROLD MARTIN, Senior Materials Engineer, and DEEPAK KAPOOR, Group leader, are with the U.S. Army, RDECOM-ARDEC, Picatinny Arsenal, NJ 07806. Manuscript submitted March 4, 2011. Article published online August 9, 2011 340—VOLUME 43A, JANUARY 2012
samples. This technique possesses the advantage of sintering samples at a high heating rate [up to 1000 K/min (1000 C/min)] and under high pressure. Consequently, samples can be consolidated at a relatively low temperature and in a shorter period of time, making it more likely to retain the starting microstructure compared with conventional consolidation methods.[1–3] Nanostructured (NS) (e.g., grain size 50 pct, with relatively high ductility (~11 pct tensile elongation), good weldability, and corrosion resistance.[4] An inspection of the published literature, however, reveals that limited information is available on the behavior of NS or UFG metal powders consolidated via SPS, and hence systematic information on the influence of processing parameters on microstructure and mechanical behavior is nonexistent. In view of this lack of information, the current study was motivated by the following questions. First, what is the behavior of NS and UFG Al during SPS? Second, what is the METALLURGICAL AND MATERIALS TRANSACTIONS A
influence of processing parameters on the mechanisms that govern microstructure and mechanical behavior? In Part I (Spark Plasma Sintering of Cryomilled Nanocrystalline Al Alloy I: Microstructure Evolution), we studied the microstructural evolution during SPS consolidation on the basis of a numerical simulation scheme. In this article (Part II), we focus on fundamental studies to investigate the influence of SPS processing conditions on the densification behavior of cryomilled nanostructured Al 5083 powders and on the mechanical behavior of consolid
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