Interfacial segregation of Ti in the brazing of diamond grits onto a steel substrate using a Cu-Sn-Ti brazing alloy

Diamond grits were brazed onto a steel substrate using, a prealloyed Cu-10Sn-15Ti (wt pet) brazing alloy at 925 degreesC and 1050 degreesC. Due to the relatively high concentration of Ti in the brazing alloy, the braze matrix exhibited a composite structure, composed of beta-(Cu,Sn), a Cu-based solid solution, and various intermetallic compounds with different morpholoories. The reaction of Ti with diamond yielded a continuous TiC layer on the surfaces of the diamond grits. On top of the TiC growth front, an intermetallic compound, composed of Sri and Ti, nucleated and grew into a randomly interwoven fine lacey structure. An interfacial structure developed as the interwoven fine lacey phase was semicoherently bonded to the TiC layer, with the Cu-based braze matrix filling its interstices. The thickness of such a composite layer was increased linearly with the square root of isothermal holding time at 925 degreesC, complying with the law of a diffusion-controlled process. However, at 1050 degreesC, the segregation behavior of Ti and Sri to the interfaces between the TiC layer and the braze matrix diminished, due to the increased solubility of Ti in the Cu-based liquid phase. The enhanced dissolution of Ti in the Cu-based liquid phase at 1050 degreesC also caused the precipitation of rod-like CuTi with an average diameter of about 0.2 mum during cooling. SnTi3 was the predominant intermetallic compound and existed in three different forms in the braze matrix. It existed as interconnected grains of large size which either floated to the surface of the braze matrix or grew into faceted grains. It also exhibited a nail-like structure with a mean diameter of about 1 mum for the rod section and a lamellar structure arising from a eutectic reaction during cooling.