Abstract
Si3N4 was brazed to Si3N4 with Cu-Ti alloys containing Ti content up to 50 at% at 1373 K for 1.8 ks in vacuum, where pressureless sintered Si3N4 were used. The strength of Si3N4/Si3N4 joints were measured by 4-point bending test at room temperature and elevated temperature. The microstructures and elemental distribution and reaction phases in the joining layers were investigated by means of electron probe micro-analyser and X-ray diffract-meter. The main results obtained are summarized as follows.
(1) The addition of Ti content from 5 to 20 at% to the alloys effectively increases the strength of around 200 MPa for Si3N4/ Si3N4 joint. The strength of the joint extremely rises with further addition of Ti, and reaches the maximum of 500 MPa or more.
(2) Ti in the alloys reacts with Si3N4 and forms TiN and Ti5Si3 for Ti content from 5 to 50 at%. The formation of the compounds at the interface between Si3N4 and the alloy imparts the superior strength to the joint, and the distribution of Ti, Si3 in the alloys gives rise to the improvement of the mechanical properties of the Si3N4/Si3N4 joints.
(3) The Si3N4/Si3N4 joint brazed with Cu-34 at% Ti alloy represents the high strength of 500 MPa up to testing temperature of 773 K, and the degration of strength with further increasing the temperature.
