High-temperature mechanical properties and fracture mechanisms of Al-Si piston alloy reinforced with in situ TiB₂ particles

In order to assess the high-temperature performance of aluminum-silicon alloy reinforced with titanium diboride particles as potential piston material, the tensile behaviors and fracture mechanisms of in situ 4wt% TiB₂/Al-Si composite were investigated in the temperature range 25-350°C. The tensile results revealed that the composite exhibited higher modulus than the matrix alloy at all testing temperatures, but both the matrix alloy and the composite presented similar strength levels above 200°C. The ductility of the composite was found to be lower than that of the unreinforced matrix alloy at 25 and 200°C, but no obvious distinction was observed at 350°C. The effects of temperature and the presence of TiB₂ particles on tensile properties of the composite had been evaluated. Fractographic morphology studies were done using scanning electron microscope, which indicated that the fracture of the composite altered from brittle to ductile mode with temperature increasing. At 25 and 200°C, fracture was dominated by cracked silicon particles and separated TiB₂ particles, while decohesion at particle-matrix interface was prevalent at 350°C. Analysis of the fracture surfaces also showed that regions of clustered TiB₂ particles were found to be the locations prone to damage in the composite at both room and high temperatures.