Formation of Ti 3SiC 2–Al 2O 3 in situ composites by SHS involving thermite reactions

Abstract

Formation of Ti 3SiC 2–Al 2O 3 in situ composites with Al 2O 3 content from 10 to 60 mol% was conducted by self-propagating high-temperature synthesis (SHS) involving the thermite reaction of Al with TiO 2. The effect of the Al 2O 3 content formed was studied on combustion characteristics and the degree of product conversion. For the elemental powder compacts of Ti:Si:C = 3:1:2, the SHS processes are characterized by the high flame-front velocity ranging between 17.5 and 26.5 mm/s, high combustion wave temperature of 1450–1640 °C, and significant sample deformation caused by a solid–liquid reaction mechanism. The addition of the Al–TiO 2 thermite mixture to the Ti–Si–C reaction system substantially reduced the flame propagation rate and reaction temperature, both of which decreased with increasing Al 2O 3 content in the synthesized composites. It was found that the reaction temperature was below the lowest eutectic point 1330 °C of the Ti–Si system when the composite with Al 2O 3 content higher than 40 mol% was produced. Due to the decrease of the Ti–Si eutectic and addition of the Al powder, the reaction mechanism of the 3Ti–Si–2C–Al–TiO 2 system differs greatly from that of the 3Ti–Si–2C system. As a result, the reaction front velocities as low as 2–5 mm/s were observed in the cases of forming 20–60 mol% Al 2O 3-containing composites, which provides longer reaction time and then leads to an improvement in the product conversion. Based upon the XRD analysis, the formation of Ti 3SiC 2 and Al 2O 3 was confirmed and the presence of TiC and Ti 5Si 3 as the minor phases was also identified. The resulting Ti 3SiC 2 is typically elongated grains in a closely packed pattern and with a size of 10–30 μm in length and 1–3 μm in thickness. Moreover, the dispersion of Al 2O 3 grains about 1–2 μm in the composite is evident.