Reaction Behavior and Mechanism during Self-Propagating High-Temperature Synthesis Reaction in an Al-TiO 2 -B 4 C System
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INTRODUCTION
ALUMINA (Al2O3) possesses excellent wear and oxidation resistance and good high-temperature strength, while titanium carbide (TiC) and titanium boride (TiB2) possess high hardness, high elastic modulus, good electric and thermal conductivity, and excellent wear resistance. When TiC or TiB2 is combined with Al2O3, the composite, without a significant drop in hardness, has a better oxidation resistance, superior mechanical strength, and higher fracture toughness than TiC or TiB2 alone.[1,2] Therefore, TiC-Al2O3, TiB2Al2O3, and TiC-TiB2-Al2O3 ceramic or ceramic-reinforced composites are attractive for applications as advanced structural materials. Self-propagating high-temperature synthesis (SHS, also called combustion synthesis) offers many advantages such as process economics and simplicity.[3] A typical application of the SHS is to synthesize advanced ceramic and ceramic-reinforced composites using low-cost raw materials.[4] In the past decades, extensive research has been carried out on the SHS reactions in Al-TiO2-C and Al-TiO2-B2O3 systems for producing (TiC-Al2O3)/Al and (TiB2-Al2O3)/Al composites.[5–15] Unfortunately, the research on the SHS reaction in the Al-TiO2-B4C system was relatively rare. Only recently, Wang et al.[16] reported the preparation of an Al-matrix composite reinforced by multiphases of ceramics, a-Al2O3-TiCTiB2, through the combustion reaction in a 55.6 wt pct Al-36 wt pct TiO2-8.4 wt pct B4C sample in a molten Al (~1100 C) environment. However, the reaction behavior and mechanism in the Al-TiO2-B4C system were not BINGLIN ZOU, Student, PING SHEN, Ph.D., SHIQIANG YIN, Research Scholar, and QICHUAN JIANG, Professor, are with the Key Laboratory of Automobile Materials, Department of Materials Science and Engineering, Jilin University, Changchun 130025, People’s Republic of China. Contact e-mail: [email protected] Manuscript submitted April 1, 2008. Article published online August 20, 2008. METALLURGICAL AND MATERIALS TRANSACTIONS B
systematically investigated, particularly for the effect of the Al content. In practice, the composition of the reactants is an important parameter that influences the SHS reaction as well as the resultant product. For instance, in our recent study, we have indicated that the Al content in the Al-Ti-B4C system exerts a significant effect on both the SHS reaction behaviors and the composition and microstructure of the products.[17] On the other hand, the addition of Al to the Ti-B4C reactants has been found to change the reaction sequence and the phase formation mechanism.[18] In this study, we aim to investigate the effect of the Al content in the reactants on the SHS reaction behavior and mechanism in the Al-TiO2-B4C system. It is expected that the preliminary results would benefit the development of the (a-Al2O3-TiC-TiB2)/Al composites from the Al-TiO2-B4C system.
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EXPERIMENTAL PROCEDURE
The raw materials used were commercial powders of Al (99 pct purity, £29 lm), TiO2 (anatase, 99 pct purity, £0.3 lm), and B4C (‡95 pct purity, £3.5 lm). The impurities
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