DIFFUSION BONDING OF INTERMETALLIC COMPOUND TIAL

This study was carried out in order to develop a satisfactory technique for joining TiAl intermetallic compounds. Ti-38mass%Al binary cast alloys were bonded in a vacuum of 26 mPa using the solid state diffusion bonding method by varying the bonding conditions, viz. the bonding temperature varied from 1 273 to 1 473 K, the bonding pressure varied from 10 to 30 MPa and the bonding time varied from 0.96 to 3.84 ks. From metallurgical point of view, the diffusion bonding diagrams with bonding conditions were produced in order to obtain a sound joint without microvoids and oxides such as TiO2 or Al2TiO5 at the bonding interface. According to these diagrams, the joints for mechanical testing were produced at the temperature of 1 473 K for 3.84 ks with 15 MPa. The joint tensile strength at room temperature was about 225 MPa and the joints fractured in the base metal zone. However, the joints at the testing temperatures of 1 073 and 1 273 K fractured at the bonding interface and the joint tensile strength was about 40 MPa lower than that of the base metal, because minimal bonding interface migration occurred. The joints recrystallized at the bonded zone were produced in order to promote the migration of the bonding interface and sequently improved the tensile property at 1 273 K for the joint with the previous bonding conditions and with the post-bonding heat-treatments. The joint tensile strength at 1 273 K with recrystallized grain size of around 130-mu-m was about 210 MPa and the joints fractured in the base metal zone departed from the bonded zone even at 1 273 K.