The interfacial microstructure and fracture toughness of W/Ta multilayer composites

Abstract

The application of tungsten (W) material is limited due to its intrinsic brittleness at low temperature. W-based multilayer composites are one of the solutions to improve the fracture toughness of W. In this study, a series of tungsten/tantalum (W/Ta) multilayer composites are prepared by diffusion bonding. The interfacial microstructure and fracture toughness under different deformation modes are investigated. It has been found that the flexural strength and fracture toughness loading perpendicular to the W/Ta interface are significantly higher than that loading parallel to the interface. The composites bonded at 1000 °C exhibits the highest flexural strength and fracture toughness. Both the flexural strength and fracture toughness decrease as bonding temperature increases. The decrease of flexural strength is due to recovery and recrystallization of the W layers. The decrease of fracture toughness is mainly attributed to the changes of the interfacial microstructure and fracture mechanism. For the composites bonded at 1000 °C, plastic deformation of the Ta layer and interfacial debonding are the main mechanisms for energy dissipation during crack propagation. As the bonding temperature increases, the decomposition of oxide scale and dynamic recrystallization occur at the vicinity of the W/Ta interface. A layer of fine recrystallization grains is developed at the W/Ta interface when the bonding temperature is higher than 1300 °C. As the interfacial bonding defects decreases, the interfacial bonding strength increases. Therefore, the interfacial debonding is inhibited in the composites bonded at a temperature higher than 1200 °C, instead, multiple tunnel micro-cracks appear in the W layers.