Al-TiC Composites Fabricated by a Thermally Activated Reaction Process in an Al Melt Using Al-Ti-C-CuO Powder Mixtures:
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INTRODUCTION
AL/TIC composites are being developed for application to advanced engineering structural materials due to their several advantages, such as high strength-toweight ratio, wear resistance, and stiffness.[1–6] The In situ process of producing a thermodynamically stable TiC in an Al matrix involves an exothermic chemical reaction and has been extensively performed by selfpropagating high-temperature synthesis (SHS) that enables reactants to be converted into products in a combustion wave after ignition.[7–9] The SHS processing produces a high volume fraction of ceramic reinforcements with submicron size and with a sound interface with the matrix. However, this has been achieved through either a powder metallurgy[7] or ingot metallurgy[1,9–11] routes at high operating temperatures exceeding 1400 K (1127 C). Our recent study introduced a very practical process of SHS combined with conventional casting to fabricate in situ Al/TiC composites.[12,13] It is noted that a certain amount of CuO addition thermally activates a combustion reaction of the Al-Ti-C system and thereby enables the formation of in situ TiC with a large volume fraction in an Al melt at a reasonably low temperature range of 1023 K to 1193 K (750 C to 920 C). The microstructure of the in situ composites, however, occasionally contains undesirable features of TiC aggregates as well YOUNG-HEE CHO, Senior Researcher, and JUNG-MOO LEE and SU-HYEON KIM, Principal Researchers, are with the Division of Light Metals, Korea Institute of Materials Science, 797 Changwondaero, Changwon 642-831, South Korea. Contact e-mail: jmoolee@ kims.re.kr Manuscript submitted April 8, 2014. Article published online January 6, 2015 1374—VOLUME 46A, MARCH 2015
as incomplete reaction products of Al3Ti and unreacted C as reported in our earlier study.[14] Kim et al.[15] reported that very large Al3Ti phases were readily fractured by hot compression, which caused the debonding of the matrix/particle interface. Many attempts at controlling the microstructure of in situ composites have been made by changing various processing parameters, such as initial melt temperature,[13,16] particle size of powders used as reactants,[17,18] contents of excess Al,[9,18,19] flux addition,[16,20] and ultrasonic vibration.[21] More recently, we clarified the mechanism responsible for the formation of such undesirable phases by systematically investigating the microstructure evolution of Al-Ti-C pellets upon the combustion reaction.[14] This importantly suggests an optimum processing parameter that controls the pellet microstructure that directly affects the final microstructure of the Al/TiC composites. Based on our previous study,[14] we aim to develop high-performance Al-based metal matrix composites (MMCs) reinforced with TiC by controlling the final microstructure. The important role of the initial size of elemental powders in the formation of TiC aggregates is further discussed with using various Ti and C sources. Moreover, mechanical properties of Al-Cu-Mg/TiC composites fabricated by t
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