Add time:09/01/2019         Source:sciencedirect.com

The microstructure of TiTa30 alloys diffusion bonded to a 99.7 wt% AI2O3 ceramic was subdivided into a reaction double layer containing the intermetallic phases TiAl and Ti3AI and the (a + β) Ti microstructure. Excellent fracture toughness data of the TiTa30/AI2O3 joints of about 37 J/m2 were obtained after welding at 1200°C for 1 h. The fracture energies of the joints were strongly dependent on the welding temperature which also influenced the thickness of the reaction double layer. The uptake of aluminium and oxygen into the reaction layer and the metal caused an embrittlement and decreased the yield stress and ductility of the metal. Introducing an Nb or Ta layer between pure Ti and AI2O3 before welding resulted in high fracture energies of 40 J/m2 for the Ti/AI2O3 joints. The thermal-induced stresses at the metal-ceramic interface were reduced by the occurrence of an Nb- or Ta-enriched region. The intermediate metal foils also decreased the O and AI uptake of the metal and therefore reduced the brittleness of the reaction zone and the adjacent metal. The thermal-induced stresses at the metal-ceramic interface caused a deflection of the crack into the ceramic during fracture mechanical testing in four-point bending.

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