Effect of heat treatments on in-situ Al2O3/TiAl3 composites produced from squeeze casting of TiO2/A356 composites

Abstract

In-situ Al2O3/TiAl3 intermetallic matrix composites were fabricated via squeeze casting of TiO2/A356 composites heated in the temperature range from 700 degreesC to 780 degreesC for 2 hours. The phase transformation in TiO2/A356 composites employing various heat-treatment temperatures (700 degreesC to 780 degreesC) was studied by means of differential thermal analysis (DTA), microhardness, scanning electron microscopy (SEM), electron probe microanalysis (EPMA), and X-ray diffraction (XRD). From DTA, two exothermic peaks from 600 degreesC to 750 degreesC were found in the TiO2/A356 composites. The XRD showed that Al2O3 and TiAl3 were the primary products after heat treatment of the TiO2/A356 composite. The fabrication of in-situ Al2O3/TiAl3 Composites required 33 vol pet TiO2 in Al and heat treatment in the range from 750 degreesC to 780 degreesC. The hardness (HV) of the in-situ Al2O3/TiAl3 composites (1000 HV) was superior to that of nonreacted TiO2/A356 composites (200 HV). However, the bending strength decreased from 685 MPa for TiO2/A356 composites to 250 MPa for Al2O3/TiAl3 composites. It decreased rapidly because pores occurred during the formation of Al2O3 and TiAl3. The activation energy of the formation of Al2O3 and TiAl3 frorn TiO2 and A356 was determined to be about 286 kJ/mole.