Influence of microstructure on crack initiation and propagation behavior in swaged tungsten heavy alloy during Charpy impact process

Abstract

In this study, microstructure evolution and mechanical properties of 90W–7Ni–3Fe alloy under different swaging levels were systematically examined, with an emphasis on the relationship between the deformed microstructure and impact failure behavior. The deformed microstructure was characterized by scanning electron microscopy (SEM), electron back-scattered diffraction (EBSD) and transmission electron microscopy (TEM), and the impact toughness of specimens were tested using an instrumental Charpy impact machine. Microstructure observations showed that swaging significantly changed shape of W grains and increased the W contiguity. With increasing of deformation levels, microstructure changed from high density dislocations to subgrain structures. Furthermore, pronounced <101> texture is also found in the W phase at the highest deformation level. With increasing of deformation level, the tensile strength sharply increased from 950 to 1313 MPa and the tensile strain decreased from 27% to 9%. The impact test results indicate that the total impact absorbed energy consists of crack initiation energy and crack propagation energy. As deformation level increases, crack initiation energy decreased from 81 J to 23 J, while crack propagation energy first increased to 23 J and then decreased to 10 J. The decrease in crack initiation energy is mainly caused by the increase in dislocation density and W contiguity. The variation of crack propagation energy is relatively complex and influenced by several factors, such as W contiguity, the ability of the matrix phase to resist crack extension, the increased W cleavage event, and so on. Our study provides a deep insight into the relationships between microstructure and impact toughness of swaged tungsten heavy alloys.