Microstructural characterization and mechanical properties of ZTA/ZTA joint brazed by Ni50Ti50 filler metal

Abstract

Obtaining reliable zirconia-toughened alumina (ZTA) ceramics brazed joints is highly crucial for expanding their applications. ZTA ceramics were successfully brazed with Ni50Ti50 active filler metals. The interfacial microstructure of ZTA/Ni–Ti/ZTA joints was characterised through SEM, EDS, XRD and Raman spectroscopy. The effects of holding time on the microstructure and shear strength of the joints were investigated. During brazing, both Al2O3 and ZrO2 reacted with the Ni50Ti50 filler and formed a AlNi2Ti + Ni2Ti4O double layer at the interface. ZrO2 involved in the interfacial reaction transformed into oxygen-deficient ZrO2-x, and ZrO2-x particles were present in the reaction layer because of Al2O3 consumption. NiTi and Ni3Ti compounds precipitated at the centre of a brazing seam. With an increase in the holding time, the thickness of AlNi2Ti and Ni2Ti4O gradually increased and more ZrO2-x particles appeared in the reaction layer. The mechanisms of interfacial microstructure formation and evolution were proposed. The maximum shear strength of 138 MPa was obtained for ZTA brazed at 1320 °C for 45 min. Nano-indentation was conducted to characterize the hardness, elastic modulus and plastic deformability of the reaction products, in order to analyse the fracture mechanism of the joints.