Formation of Small Blocky Al 3 Ti Particles via Direct Reaction Between Solid Ti Powders and Liquid Al
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-situ Al3Ti/Al-alloy composites have attracted considerable attention recently due to the excellent properties of Al3Ti phase, such as its high melting point, low density, high Young’s modulus, and good wet ability with aluminum.[1] Particularly, the Al3Ti phase also has an excellent resistance to oxidation and corrosion in the fluoride atmosphere above the melting point of aluminum.[2] Several manufacturing techniques have been developed in the fabrication of in-situ Al3Ti/Al-alloy composites, such as powder metallurgy,[3] the centrifugal solid-particle method,[4] mechanical alloying,[5] and the in-situ casting technique.[6,7] In general, the in-situ casting technique is one of simplicity, economy, and high efficiency and is regarded as a prospective technique for commercial production of aluminum matrix composites.[8] Wang et al.[6] fabricated in-situ Al3Ti/Al-alloy composites by adding K2TiF6 into the molten aluminum alloy at 1223 K to 1323 K (950 °C to 1050 °C). They found that the size and morphology of Al3Ti were largely affected by the temperature, holding time, and composition of the flux. In their research, most Al3Ti particles were rodlike in morphology and longer
Z.W. LIU, Postdoctoral Candidate, and J.G. LI, Professor, are with the School of Materials Science and Engineering, Shanghai Jiao Tong University, Shanghai 200240, P.R. China. Contact e-mail: lzw_ [email protected] Q. HAN, Professor, is with the Department of Mechanical Engineering Technology, Purdue University, West Lafayette, IN 47906. Contact e-mail: [email protected] Manuscript submitted March 5, 2012. METALLURGICAL AND MATERIALS TRANSACTIONS A
than 20 lm. Yu et al.[7] prepared Al-Al3Ti in-situ composites via the direct reaction method by adding the mixture of aluminum and titanium powders into the molten pure aluminum at 1173 K to 1273 K (900 °C to 1000 °C). They found that the size of Al3Ti particles increased with the increase of Al3Ti content. Most Al3Ti particles synthesized in their research were rodlike in morphology and were larger than 50 lm when the Al3Ti content was more than 5 wt pct. In our research, titanium powders were used as the only additive and were added into the pure aluminum melt at 1003 K (730 °C). The aim of the research is to study the evolution of titanium powders in the molten aluminum at a lower temperature and to explore a simple approach of producing in-situ Al composites as well. Pure aluminum (99.5 pct commercial purity) ingot and titanium powders (99.7 pct purity, 40 lm) were used as the matrix and additive, respectively. Some titanium powders wrapped in aluminum foil were added into the molten pure molten aluminum at 1003 K (730 °C) in a graphite crucible in an electrical resistance furnace. Then the aluminum melt was stirred by using a graphite rod to disperse the solid titanium powders in the aluminum melt, preventing the titanium powders being sintered together. The amount of titanium powders added corresponded to the ration of Al-4 wt pct Ti. In order to reflect the evolution process of the solid titanium particles
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