Features of Boron Behavior during Dynamic Strain Aging in a High Temperature Ni-Based Superalloy Produced by PM HIP Technology: I. High-Temperature Tensile Testing
摘要
The results of a comprehensive multiscale study of the structure and distribution of boron in the fracture zone of high temperature Ni-based superalloy EP741NP, produced by PM HIP technology using rapidly quenched PREP powder, after high-temperature tensile test are presented. A detailed study of the macro-, meso-, and microstructures and distribution of boron in the fracture zone was carried out using the direct nuclear-physical method of track autoradiography on boron in cooperation with metallographic (LM, SEM, EDX) and OIM methods. The effect of dynamic strain aging (DSA) with the engagement of boron at the fracture stage was revealed. It consists in intensive boron migration in the plastic deformation zone of the neck with an abnormally high effective diffusion coefficient and the formation of large allotriomorphic precipitates of the boride phase M3B2 on the mesoscale shear loop and mesoscale shear bands of the Portevin-Le Chatelier (PLC) type in the loop crown, localized around the opening mesoscale crack in the area of localized deformation of the neck. The revealed effect of DSA with the engagement of boron is similar to the effect of DSA with the engagement of carbon and the formation of PLC bands decorated with dispersed carbides in nickel-based superalloys and austenitic stainless steels at the stage of work hardening.