The effect of bonding temperature on the bending behaviors and toughening mechanism of W/(Ti/Ta/Ti) multilayer composites prepared by field activated sintering technique

Abstract

The gradient layered structure is beneficial to improve both strength and fracture toughness of tungsten. In this study, a series of W/(Ti/Ta/Ti) multilayer composites with gradient layered structure are prepared by field activated sintering technique (FAST) with bonding temperatures ranging from 1000 °C to 1400 °C. The results show that both the microstructure and mechanical properties vary with bonding temperatures. Both W and Ta diffuse into Ti layer to stabilize β phase, resulting in the Ti layer with α/β phase. The W/(Ti/Ta/Ti) composites bonded at 1200 °C exhibited the highest flexural strength (1700 MPa) attributed to excellent microstructure combination in the different layers, which are elongated grains and fine recrystallized grains in the W layer, and the martensite basketweave microstructure in Ti layer. Shear bands can be seen in the Ti layer with planar slip-bands and Ta layer with wavy slip-bands. These plastic deformation behaviors cannot be observed in the W layer because it is inherently brittle, similar to ceramic. The toughening mechanism of the W/(Ti/Ta/Ti) composites is as follows: crack deflection and delamination between the interface, multi-crack propagation in the W layer, and local shear deformation in the toughened layer. The bending properties of W/(Ti/Ta/Ti) multilayer composites are related to the interface and the gradient structure of the toughened layer (Ti/Ta/Ti), which can guide the design of the microstructure of the composites and improve its mechanical properties.