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Formation of Ti3SiC2–Al2O3 in situ composites with Al2O3 content from 10 to 60 mol% was conducted by self-propagating high-temperature synthesis (SHS) involving the thermite reaction of Al with TiO2. The effect of the Al2O3 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–TiO2 thermite mixture to the Ti–Si–C reaction system substantially reduced the flame propagation rate and reaction temperature, both of which decreased with increasing Al2O3 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 Al2O3 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–TiO2 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% Al2O3-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 Ti3SiC2 and Al2O3 was confirmed and the presence of TiC and Ti5Si3 as the minor phases was also identified. The resulting Ti3SiC2 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 Al2O3 grains about 1–2 μm in the composite is evident. |
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