Characterization of Distribution of Microstructure and Micro-mechanical Properties of Nickel-Based Single Crystal Superalloy Within the Shot-Peened Layer

Distributions of hardness, elastic modulus, yield strength, and residual stress within the shot-peened layer of nickel-based single crystal superalloy were measured by instrumented indentation with Berkovich indenter under a constant indentation displacement of 400 nm. Elastic modulus is little affected by shot peening, while yield strength calculated by Nobre’s method is significantly increased. The hardness and residual stress calculated by Vickers hardness testing are also proportional to the results by instrumented indentation. Indentation parameters such as hardness, indentation work, and contact area linearly depend on residual stress. Microstructures observed by SEM and EBSD show that the crystal orientation is severely distorted within 20 μm from the peened surface. The thickness of the plastic deformation layer measured by EBSD is 60 μm. XRD results show that the number of diffraction peaks increases after shot peening, indicating the transformation from single crystal to polycrystalline structure; residual stress, domain size, microstrain, and dislocation density of shot-peened layer are − 837.5 MPa, 12.88–37.68 nm, 4.39–6.17 × 10^–3, and 4.84–8.15 × 10¹⁵ m⁻², respectively. The values of residual stress calculated by different nanoindentation models are different, but they are proportional to one another with a similar variation within the shot-peened surface. David’s model is the most suitable one to assess residual stresses of single crystals by performing nanoindentation tests on the side surface that is perpendicular to the peened surface. The maximum compressive residual stress calculated by David's model is 1.26 GPa at the depth of 38 μm, and the total depth of compressive residual stress is about 130 μm.