Microstructure characterization and formation mechanism of functionally graded Al-TiAl3 insitu composite by liquid-solid interaction

In this paper, microstructure and formation mechanism of functionally graded Al-TiAl3 insitu composite fabricated by solid-liquid interaction was investigated. Mechanism of formation and distribution of the intermetallic particles was determined and it was in good agreement with computational thermodynamic calculations results. It was found that the gradient microstructure for Al-TiAl3 insitu composite was obtained at 1173 K (900 °C) holding for 180 min which included blocky and plate particles. The Al/Ti interface was changed from flat to irregular form at 1173 K (900 °C) due to diffusion of Al in solid Ti. The role of temperature and holding time was found to be important for formation and distribution of both blocky and plate TiAl3 particles. A critical solute value equal to 2.7 wt% was determined for dissolved Ti. Higher concentrations than the critical value led to the formation of blocky particles (mainly during heating) while lower concentrations led to the formation of plate particles (mainly during cooling). The gradient distribution of intermetallic particles in Al matrix led to a gradient hardness.