Particularities of the structure and properties of TiC-Al2O3 complex ceramics obtained by combustion in open-air of TiO2-Al-C mixtures and sintering under load

Abstract

The combustion in open-air of complex aluminothermic TiO₂-Al-C mixtures, followed by sintering was used to produce TiC-Al₂O₃ based ceramics. For this purpose, powders mixtures containing [TiO₂-Al-C], [TiO₂ + Al + (90%C + 10%B)], [TiO₂ + (90%Al + 10%Mg) + C] and [(90%TiO₂ + 10%SiO₂) + Al + C], were prepared via the conventional powder metallurgy route. The combustion product was crushed and sieved in order to recover the fractions less than 40 µm. The different mixtures of ceramic powders first underwent cold uniaxial compression followed by a sintering at 2023 K, under a cyclic load of 50 MPa applied for 2.4 ks. X-ray diffraction analysis of the samples revealed the presence of TiC, Al₂O₃ and Al₂TiO₅ spinel. The combustion in open-air is accompanied by an evaporation of aluminum, the presence of unreduced TiO₂ and the formation of new oxides such as Ti₃O₅ and Ti₄O₇ which generate Al₂TiO₅ spinel during the sintering. Microstructural analyses using a scanning electron microscope combined with semi-quantitative evaluation revealed the basic ceramic structure composed of TiC, Al₂O₃ and Al₂TiO₅. The additions of boron, magnesium or silica generate new phases such as TiB₂, MgAl₂O₄ and Ti₃SiC₂ modifying the structure and the ceramic composition. Finally, the aluminothermic mixtures composition therefore has a significant impact on the structure, hardness, micro-indentation results and tribological behavior of the ceramics studied. Thus, the lowest wear rate and friction coefficient were recorded on the ceramic containing 33.81wt.% TiC—51.73wt.% Al₂O₃—3.42wt.% Al₂TiO₅—11.04wt.% Ti₃SiC₂.