Joining of silicon nitride ceramics by hot pressing

Si3N4 ceramics containing Al2O3 and Y2O3 sintering aids have been joined in a nitrogen atmosphere through the application of uniaxial pressure at high temperature, using polyethylene as a joining agent. Four-point bending tests of the joining stress are examined in order to determine the effects of 1400-1600 C temperature, joining pressure, 0.5-8 hour holding time, and surface roughness, on the joined specimens. Greater surface roughness is noted to yield lower joining strength due to smaller contact area, while the higher joint strength obtained with elevated temperatures is attributed to the larger true contact area that is obtained through plastic deformation. (O.C.)