Al-TiC Composites Fabricated by a Thermally Activated Reaction Process in an Al Melt Using Al-Ti-C-CuO Powder Mixtures. Part I: Microstructural Evolution and Reaction Mechanism

Abstract

Al matrix composites reinforced with TiC particles are fabricated by a thermally activated reaction of Al-Ti-C powder mixtures in an Al melt. In the presence of CuO, reactant mixtures in the form of a pellet added to molten Al at temperatures higher than 1093 K (820°C) instantly reach the peak temperature over 1785 K (1512°C), followed by combustion wave propagation with in situ synthesizing TiC with a size of approximately 1 lm. Incomplete reaction products such as unreacted C, Al 3 Ti, and TiC aggregates are also observed. The pellet microstructure evolution upon the combustion reaction indicates that preheating temperature, i.e., the initial melt temperature, affects both the thermodynamic and kinetic characteristics of the reaction, and thereby influences the final microstructure of the Al/TiC composites. Based on the experimental and theoretical results, a sequence of the reaction leading upto the in situ synthesis of TiC is illustrated and the corresponding mechanism for the present process is proposed.

Al-TiC Composites Fabricated by a Thermally Activated Reaction Process in an Al Melt Using Al-Ti-C-CuO Powder Mixtures: Part II. Microstructure Control and Mechanical Properties

“…Detailed characterisation of constituent phases in the Al/TiC composites fabricated by the developed process was carried out by analyzing both X-ray diffraction (XRD) and a scanning electron microscopy (SEM) equipped with an energy dispersive spectrometer (EDS), and the results are presented in our earlier studies. [12][13][14] When using Ti with a relatively small size of 50.8 lm and CNT as a C source, even in the absence of CuO, the complete reaction occurs at 1163 K (890°C) and produces no trace of Al 3 Ti (acicular or angular) or unreacted C in the microstructure of Figure 3(a). However, TiC aggregates are occasionally observed as shown in Figure 3(b), which is probably due to the fact that the initial size of Ti is far coarser than that of C. Figure 4 shows that the TiC agglomeration also depends on the particle size of C powder present in pellets containing Ti with a fixed mean particle size of 50.8 lm.…”

“…Our recent study [14] predicted the critical size of Ti and C for their complete conversion into Al 3 Ti followed by the formation of TiC via Eqs. [1] to [4] by calculating the reaction kinetics.…”

“…[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.…”

“…The microstructure of the in situ composites, however, occasionally contains undesirable features of TiC aggregates as well as incomplete reaction products of Al 3 Ti and unreacted C as reported in our earlier study. [14] Kim et al [15] reported that very large Al 3 Ti 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.…”

“…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.…”