Anti-atmospheric resistance of ceramics and metals joints -effect of sulfuric acid solution on fracture strength of silicon nitride ceramics nickel joints

摘要

The nickel metal joined to silicon nitride ceramics using silver-copper-titanium brazing and titanium filler was placed In a sulfuric acid solution at 323K for up to 214 hours. Joining strengths were measured by the 4-point bending test. Microstructures of the reaction layer and porous layer were investigated with a scanning electron microscopy and an electron probe microanalyzer. Fracture strength of the normal joint was 245 MPa before soaking and decrease to 17O MPa after 16 hours and to 100 MPa after 144 hours in 1N-H{sub}2SO{sub}4. Three regions were observed on the fracture surface; the region I at the reaction layer/brazing layer interface, the region II at the bonding interface neighborhood in porous layers (in silicon nitride) and the region III at the silicon nitride/reaction layer interface. As a result of electron probe microanalysis of the porous layer on the nickel-side fracture surface, the silicon and nitrogen were detected with high intensity, however, the intensities of yttrium, aluminium and oxygen were low. These results suggest that yttrium-oxide and aluminium-oxide elute as the sintering aid in the grain boundary of silicon nitride. The growth of the porous layers occurred on the joint surface of silicon nitride ceramics with different roughness due to the ground surface roughness of the test piece. In addition, the wedgeshaped porous layers were fromed a residual stress on the interfacial side of the silicon nitride ceramics joints.