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… Click to show full abstract
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.
               
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