Investigations of inhomogeneous mechanical properties and plastic deformations in HIPed P/M nickel-base superalloy FGH96 by using micro-indentation methods

The purpose of this paper is to investigate the influence of non-uniform precipitate distribution on local plastic deformation in HIPed P/M nickel-base superalloy FGH96 by using micro-indentation methods. The micro-indentation tests were conducted in the indenter load range from 100 mN to 450 mN and the loading rate range from 1.94 mN/s to 19.37 mN/s at the room temperature. Then, the load–displacement data of precipitate concentration areas (PCA) and precipitate sparsity areas (PSA) were obtained, respectively. The results show that both PCA and PSA exhibited decreasing micro-hardness during indentations, which proved that the size effect was significant in P/M nickel-base superalloy FGH96 as well. The high micro-hardness of PCA indicates that γ′ precipitate could effectively improve the resistance to deformation. In contrast, the influences of indenter load and loading rate on Young’s modulus were slight. Through plotting test data, it was revealed that a better linear relationship existed between H2 and 1/h. Moreover, the densities of geometrically necessary dislocations (GNDs) and statistically stored dislocations (SSDs) were obtained by data fitting. Like other alloys, the GND density fast decreased with the increase of indentation depth during indentations. The SSD density of PCA was higher than that of PSA when the loading rate was lower than 12.91 mN/s, indicating that the γ′ precipitates could block the dislocation movements and induce strong interactions. However, this mechanism was inconspicuous at high loading rates due to precipitation shearing mechanism. In addition, the FEM method and forward analysis algorithms were used to predict the micro-indentation parameters. Comparing with FEM method, the prediction results were more accurate for forward analysis algorithms. The constitutive equations of PCA and PSA were established by means of reverse analysis algorithms. The microstructural simulation reflected that the interactions between PCA and PSA were significant during uniaxial compression. The high stress concentration existing in PCA between two adjacent PSAs may cause microcracks and void dislocations at the large deformations.