Structure Formation in the Combustion Synthesis of Al₂O₃–TiC Composites

Abstract

Structure formation in the combustion synthesis of Al 2 O 3 -TiC composites from TiO 2 , Al, and graphite powders was investigated using cylindrical samples and cone-shaped "quenching samples." It is shown that the phases Ti and Ti 3 Al exist as intermediates in the combustion synthesis process. Titanium carbide forms in a secondary step through reactions between graphite and liquid Ti or Ti 3 Al, then nucleates from a liquid mixture of the three phases Ti, Ti 3 Al, and alumina. The nucleated particles grow in the postcombustion stage. Liquid alumina, containing TiC as a dissolved phase, solidifies into corundum grains in the postcombustion stage. Moreover, it is shown that the temperature gradient in the postcombustion stage markedly affects the microstructures of the products. Higher-temperature gradients, typical at the surface of the samples, give rise to the formation of corundum whiskers and TiC agglomerates. In contrast, lower gradients, typical in the center of the samples, lead to the formation of relatively large TiC particles and corundum grains.

Mechanism of combustion synthesis of Mg2Ni

“…Thus, the microstructural evolution could be observed and analyzed by scanning electron microscopy (SEM) and energy dispersive spectrometry (EDS). The microstructural transitions of TiC-Fe [7], Al 2 O 3 -TiC [8] and NiAl [9] have been observed by using the combustion front quenching method (CFQM). In this paper, the synthesis mechanism of Mg 2 Ni from powders by self-propagating combustion was studied using CFQM.…”

Reaction Behavior and Mechanism during Self-Propagating High-Temperature Synthesis Reaction in an Al-TiO2-B4C System

“…In this case, the reactions in the preheated region could be described by the following equations: The irreversible transformation of anatase to rutile (Eq. [3]) takes place at approximately 918 K. [11] The formation of TiB 2 through the reductive reaction of TiO 2 with B 4 C has been testified by some researchers. [27][28][29] With the increase in temperature as the SHS reaction progressed, the titanium oxides further reacted with Al into the formation of Al 3 Ti, which could be expressed as…”

“…[4] In the past decades, extensive research has been carried out on the SHS reactions in Al-TiO 2 -C and Al-TiO 2 -B 2 O 3 systems for producing (TiC-Al 2 O 3 )/Al and (TiB 2 -Al 2 O 3 )/Al composites. [5][6][7][8][9][10][11][12][13][14][15] Unfortunately, the research on the SHS reaction in the Al-TiO 2 -B 4 C system was relatively rare. Only recently, Wang et al [16] reported the preparation of an Al-matrix composite reinforced by multiphases of ceramics, a-Al 2 O 3 -TiCTiB 2 , through the combustion reaction in a 55.6 wt pct Al-36 wt pct TiO 2 -8.4 wt pct B 4 C sample in a molten Al (~1100°C) environment.…”

Preparation of Al2O3–TiC nanocomposite by mechano-chemical reduction of TiO2 with aluminum and graphite

“…represent a new class of materials with improved mechanical properties, hardness and wear resistance when compared to monolithic ceramics [1][2][3][4][5][6][7]. AT composites are widely used as substrate of magnetic heads and cutting tools due to their attractive mechanical properties and good electrical conductivity [8]. At present commercially available micro-sized AT composites are prepared by pressure-less sintering or hot pressing the direct mixtures of Al 2 O 3 and TiC powders [9,10] during which severe grain coarsening and generation of metal oxides at the interface always take place due to relatively long holding time at high temperature [11].…”