Microstructure Features and Mechanical Properties of Casted CoFeB Alloy Target

Abstract

CoFeB alloy, as a promising magneto-resistive material, has attracted extensive attention concerning the magnetic properties of its thin film in the field of magneto-resistive random memory (MRAM). Although there are many studies on the magnetic properties of CoFeB thin films, there is relatively little research on the microstructure and mechanical properties of casted CoFeB alloy. In this work, Co20Fe60B20 (at%) alloy was fabricated through the vacuum induction melting method, and its microstructure features and mechanical performance were studied. Scanning electron microscopy (SEM), electron back scatter diffraction (EBSD), and transmission electron microscopy (TEM) were utilized to characterize the microstructure, which consists of the coarse, needle-like Fe2B phase that crystallizes first, the primary lamellar binary eutectic structure (Fe2B + bcc-Fe), and the ternary eutectic structure (Fe3B + Fe2B + bcc-Fe phase). It is found that Fe3B precipitates on the Fe2B with a core–shell structure. The orientation of bcc-Fe is randomly distributed, while there are two main kinds of textures in Fe2B: {100} <001> and Gaussian texture {110} <001>. In terms of mechanical properties, Co20Fe60B20 alloy’s tensile strength is 140MPa, and the yield strength is 87MPa. Because the cracks are easy to generate and expand along the needle-shaped pre-crystallized Fe2B, the plasticity of Co20Fe60B20 alloy is very poor, only 1%.