Features of Boron Behavior during Dynamic Strain Aging in a High Temperature Ni-Based Superalloy Produced by PM HIP Technology: II. High-Temperature Compression Testing
摘要
The results of a detailed study of the structure and behavior of boron in the specimens of the high temperature nickel superalloy EP741NP produced by the PM HIP technology using the rapidly quenched powder PREP after high-temperature compression tests are presented. Compression tests of cylindrical specimens were carried out at a temperature of 1050°C and strain rates of 10–3 and 10–4 s–1. The method of track autoradiography on boron, in combination with methods of metallography (LM, SEM, EDX) and OIM, was used to identify the regularities of influence of changes in structural-phase state during high-temperature deformation on the features of boron distribution. The method of track autoradiography on boron provides an opportunity to study macro-, meso-, and micro-heterogeneity of boron distribution in correlation with the features of the structural-phase state. The effect of dynamic strain aging DSA involving boron in the zone of intensive plastic deformation and the occurrence of dynamic recrystallization DRX with the formation of a “necklace” structure at a deformation rate of 10–3 s–1 has been revealed. This effect consists in the intensive migration of boron in the zone of plastic deformation, resulting in the enrichment of the “necklace” area in boron and the decoration of it with dispersed precipitates of M3B2 boride phase. A decrease in the strain rate to 10–4 s–1 leads to flow instability with the manifestation of the PLC type effect and flow localization with the manifestation of a PLC type serration on the flow curve at the DRX softening stage under conditions of increased heterogeneity of the DRX structure with the formation of PLC type meso shear bands, compared to the DRX “necklace” structure. The revealed effect of DSA involving boron with the formation of meso shear bands of PLC type at the stage of DRX softening is similar to the effect of DSA involving carbon and the formation of PLC type shear bands decorated with dispersed carbides in nickel-based superalloys and austenitic stainless steels at the stage of work hardening.