Microstructures and Mechanical Properties of In Situ Al 2 O 3 /Al-Si Composites Fabricated by Reaction Hot Pressing
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ntly, aluminum matrix composites (AMCs) have been used widely as potential materials in many areas such as automobile, aerospace, and military applications. Moreover, their attractive mechanical and thermal properties including density vs strength, low thermal expansion, wear resistance, and resistance to elevated temperature make AMCs an excellent overcoming means to many technology progresses.[1–4] Reactive hot pressing (RHP) has been suggested to overcome the high concentration of porosity, which occurs during the in situ processing of composites. There, the in situ reinforcements are synthesized by an exothermic conversion of the reactants, followed by hot compaction to obtain near fully dense composites.[5,6] It has been reported that after the aluminum melts, the reduction of silica takes place forming Al2O3 and Si.[7] Based on the following reaction, the in situ Al2O3/Al-Si composite can be synthesized as following: 3SiO2 þ 4Al ! 2Al2 O3 þ 3Si
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In this work, for the first time RHP was employed to fabricate Al2O3/Al-Si composites. Moreover, no reported works were carried out to clarify the effect of EL OUALID MOKHNACHE, Doctor Candidate, G.S. WANG and L.J. HUANG, Associate Professors, and L. GENG, Professor, are with the School of Materials Science and Engineering, Harbin Institute of Technology, Harbin 150001, P.R. China. Contact e-mail: [email protected] Manuscript submitted March 9, 2014. Article published online October 10, 2014. METALLURGICAL AND MATERIALS TRANSACTIONS B
volume fraction of reinforcement in Al-SiO2 system. Three composites reinforced with 10, 20, and 30 vol pct were fabricated by RHP, with the aim to investigate the effect of volume fraction of reinforcement on microstructure and tensile properties at room temperature. The tensile fracture mechanisms were also studied. Pure Al powders (99.6 pct purity) and SiO2 powders (99.2 pct purity), with an average size of 30 and 2 lm, respectively, were used as raw materials. To produce, the in situ composites namely M10, M20, and M30 with different volume fractions 10 pct (i.e., 7.1 vol pct Al2O3 + 2.9 vol pct Si + 90 vol pct Al), 20 pct (i.e., 14.2 vol pct Al2O3 + 5.8 vol pct Si + 80 vol pct Al), and 30 pct (i.e., 21.3 vol pct Al2O3 + 8.7 vol pct Si + 70 vol pct Al) respectively, the stoichiometric starting materials were weighed according to the hypothetical Reaction [1]. The powder mixtures were ball milled using low energy at 160 rpm for 4 hours in a planetary ball mill under an argon atmosphere with a milled media to material ratio of 4:1. The mixture powders were transferred into the graphic mold pre-coated with boron nitride to avoid the reaction between the mold and the reactants. In a vacuum of 4.5 9 102 Pa, different stages were used to fabricate the composites, at the first stage, the powders were heated to 873 K (600 C) and compacted with 25 MPa for 1 hour, at the second stage, the compact was heated to the synthesis temperature [1173 K (900 C)] for 1 hour to complete the reaction. At the final stage, the compact was cooled down to
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