Joining of austenitic stainless steel and ferritic stainless steel to sialon

Joining of ceramics to metal is not easy due to the difference in the therm al expansion of the two materials. In this research work, the joining of si alon to austenitic stainless steel and ferritic stainless steels were compa red. At above a joining temperature of 1200 degreesC, sialon will react wit h steel to form iron silicide and nitrogen is given off. Thus to counteract this effect, a high nitrogen content in the steel is one way of overcoming this problem by nitriding both austenitic and ferritic stainless steels at 1200 degreesC. These materials were then joined to sialon using a hot pres s at 1250 degreesC. The results show that inter-reaction and interdiffusion on both sides of the materials occur in the layer. Good interfaces were fo und between sialon and steels. Analyses on the joinings were carried out us ing a scanning electron microscope, an optical microscope, a hardness teste r, and XRD. The analysis also indicated different morphology of the interfa ces that were formed. A ductile interlayer was formed between the ferritic stainless steel and sialon, which enabled good joining. However, this layer is absent in the joining of austenitic stainless steel to sialon. In both cases of joining, the chemical reactions between the steels and sialons pro duce an intermediate hardness in the reaction layer. Thus the interfaces ha ve the important role in reducing the effect of thr thermal mismatch betwee n the sialon and steel, where the formation of a composite interlayer provi des properties that are intermediate between those of the steel and sialon. However, the joining of sialon to ferritic stainless steel is more success ful compared to joining to austenitic stainless steel. (C) 2001 Elsevier Sc ience B.V. All rights reserved.