A study on the kinetic process of reaction synthesis of TiC: Part I. Experimental research and theoretical model
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II.
INTRODUCTION
DIRECT reaction synthesis (DRS), which was developed at the Harbin Institute of Technology (HIT) is a novel in situ process to prepare metal matrix composites (MMCs). By the use of DRS, several composites have been prepared such as Al/TiCp and Al/TiB2.[1,2,3] The results have shown that the tensile strength of the composites have been improved greater than the unreinforced alloy.[4,5,6] During the processing, a preform made of several element or alloy powders by mixing and pressing was put into alloy melt at definite temperature; then a reaction in the melt occurred immediately and ceramic particles were synthesized. After agitating, the MMCs were prepared. The processing of the DRS has been described in detail elsewhere.[4] It has been shown that during the DRS processing, although the preform was put into a Al melt, the preform almost did not react with the Al melt. In fact, the reaction to synthesize TiC happened in the preform.[7] Since the reaction occurring in the preform is the key technique in the composites fabrication process, it is essential to understand the reaction kinetics of reaction synthesis of TiC in the preform in order to control the morphology and size of the TiC particles. Although much research has been done on the thermodynamics of the reaction between Ti and C in Al melt,[8] few studies have been done on the kinetics of the reaction, especially by experiment. In this article, the kinetics of the reaction in the preform has been investigated by the use of the quench experiment and scanning electron microscopy (SEM).
ERLIN ZHANG, Associate Professor, National Key Laboratory of Precision Heat Processing of Metal, E-mail: [email protected], and SONGYAN ZENG and QINGCHUN LI, Professors, YANG BO, Student, and MINGZHEN MA, Associate Professor, School of Materials Science and Engineering, are with the Harbin Institute of Technology (HIT), Harbin 150001, P.R. China. Manuscript submitted July 15, 1997. METALLURGICAL AND MATERIALS TRANSACTIONS A
EXPERIMENTAL
High-purity (99.7 pct) titanium powder, 99.6 pct aluminum powder, and 99.3 pct graphite powder with 325 mesh size were mixed and uniaxially pressed into green compacts having a diameter of 40 mm and an approximate height of 100 mm, corresponding to an approximate 50 to 60 pct of theoretical density. The preform was put on a platen and ignited at the top by an ignition heater (electrical resistant). When the reaction began and propagated to the middle of the preform, the preform was quenched immediately. The X-ray diffraction (XRD) analyses were conducted in a Rikagu Dimax-RB X-ray diffractometer. The microstructures of the quenched preform were observed by the use of a HITACHI S-570 scanning electron microscope with energy-dispersive X-ray (EDX) spectroscopy.
III.
RESULTS AND DISCUSSIONS
Figure 1 shows the macrostructure of the quenched sample. It consisted of three parts, A through C. It can be found that there exist small intervals in part A and many big holes in part C. The XRD analysis results of parts A throu
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