OPTIMIZATION OF TiNp/Ti CONTENT FOR Si_3N_4/42CrMo JOINTS BRAZED WITH Ag-Cu-Ti+TiN_p COMPOSITE FILLER

摘要

The Si_3N_4 ceramic was brazed to 42CrMo steel by using TiN particles modified braze, and the proportion of TiNp reinforcement and active element Ti was optimized to improve the joint strength. The brazed joints were examined by means of SEM and EDS investigations. Microstructural examination showed that TiN+Ti_5Si_3 reaction layer was adjacent to Si_3N_4, whereas TiC was formed in 42CrMo/filler reaction layer. The Ag-Cu-Ti brazing alloy showed intimate bonding with TiNp and Cu-Ti intermetallics precipitated in the joint. The strength tests demonstrated that the mechanical properties of joints increased and then decreased by increasing the TiNp content when a low Ti content (6wt.%) was supplied. When the Ti content (>6wt.%) was offered sufficiently, the joint strength decreased firstly and then stayed stable with increasing the TiNp content. The maximum four-point bending strength (221MPa) was obtained when the contents of TiNp and Ti were 10vol.% and 6wt.%, respectively.