Improved Mechanical Properties of Metallic Glass by 2D Gradient Rejuvenation

Abstract

Although metallic glasses have excellent and unique mechanical properties such as high strength, elastic modulus and hardness, they exhibit a poor ductility for the industrial use. Especially in the relaxed metallic glass due to processing or insufficient cooling rate during a manufacturing process, mechanical embrittlement occurs drastically. Therefore, controlling of the relaxation state in metallic glass has been widely evolved by thermal and physical processes. The authors have reported that the less relaxed state can be recovered (rejuvenated) using a thermal process and the rejuvenated metallic glasses actually exhibit the mechanical softening with improved plasticity. Recently, the gradient distribution of rejuvenated structure can be obtained in the cylindrical metallic glass sample using the newly developed asymmetric heat treatment equipment. In such the unique structure, the shear band angle is sensitive to the relaxation state (i.e., amount of local free volume), which develops the formation and propagation of shear band in a very complex manner during the deformation process. As a result, an intrinsic work hardening and an improvement of plastic strain in metallic glass are observed. The results provide a novel way to control the relaxation state functionally and beneficial information on the industrial application of metallic glasses.