A Quantitative Study of the Synthesis of TiB 2 Particles via Salts-Metal Reaction at Different Temperatures
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NTRODUCTION
IT is well known that in situ TiB2 particles can be synthesized via the salts-metal reaction by adding the mixed K2TiF6-KBF4 salts into molten Al at high temperatures.[1,2] Due to its unique characteristics, such as low cost, high efficiency and short synthesizing time, the salts-metal reaction has been widely used in practical productions for producing in situ TiB2/Al composites and the existence of TiB2 particles can improve the mechanical properties of the Al alloys significantly.[3,4] This type of material has been obtained more attentions in the aerospace and automobile industries. In nature, the salts-metal reaction belongs to a chemical reaction. The synthesizing temperature is one of the most important factors, which influences the formation of the products during the reaction. Generally, a high temperature is beneficial for the formation of TiB2 particles, and the temperature used in the salts-metal reaction is usually higher than 1073 K (800 °C). It has been reported that a lower temperature can lead to the formation of Al3Ti and AlB2 phases, which decrease the
ZHIWEI LIU, Associate Professor, is with the State Key Laboratory for Mechanical Behavior of Materials, School of Materials Science and Engineering, Xi’an Jiaotong University, Xi’an 710047, P.R. China, and also with the School of Engineering Technology, Purdue University, 401 North Grant Street, West Lafayette, IN 47906. Contact e-mails: [email protected]; [email protected] QINGYOU HAN, Professor, is with the School of Engineering Technology, Purdue University. Contact e-mail: [email protected] ZHIFU HUANG, Associate Professor, and JIANDONG XING, Professor, are with the State Key Laboratory for Mechanical Behavior of Materials, School of Materials Science and Engineering, Xi’an Jiaotong University. Manuscript submitted February 21, 2015. METALLURGICAL AND MATERIALS TRANSACTIONS A
yield of TiB2 phase in the Al matrix.[5] Thereby, using a higher temperature of the Al melt is always recommended in order to improve the production of TiB2 particles in the reaction. Although the salts-metal reaction has become the most common method for synthesizing in situ TiB2/Al composites, the relationship between the temperature and the formation of TiB2, however, has not been investigated clearly. A quantitative study of the effect of temperature on the synthesis of TiB2 regarding the yield of TiB2 particles and their size distribution has not been reported by other researchers. In addition, the understanding of the formation mechanism of TiB2 in the salts-metal reaction is still unclear. So far, two main viewpoints with regard to the formation process of TiB2 have been proposed. One refers that TiB2 particles are formed by a dissolution-precipitation mechanism when the concentrations of Ti and B reach saturation in molten Al (alloys).[6] The detailed mechanism can be summarized as follows. First, K2TiF6 and KBF4 are melted on the Al surface, both of which are separately decomposed to KF (liquid), TiF4 (gas), and BF3 (gas), which are expressed as follo
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