Unveiling Relationship Between Crack Evolution Through Long‐Term Ageing and Mechanical Properties of Cold‐Sprayed Ni‐Base Superalloys: Experimental Characterization and Evidence Through Finite Element Modeling

This work examines the effects of prolonged heat‐treatment on the microstructure and mechanical characteristics of cold spray (CS) IN718. The heat treatment reduced coating porosity from 3% to 0.8%. The ageing treatment results in a synergistic effect of precipitation hardening from intermetallic phases and carbides, with a simultaneous reduction in the work‐hardened microstructure through recovery, manifested as reduced dislocation density in the coating. The as‐sprayed coatings exhibit reduced cohesive strength and toughness, along with a significant anisotropy in tensile characteristics, which is a primary objective of the study. The causes of the mechanical anisotropy in the CS coatings have been elucidated. The postprocessing resulted in an increase of ≈120% in cohesive strength and ≈75% in ductility of the coating due to the aforementioned alterations in microstructures. The tensile response of the coatings in both as‐sprayed and heat‐treated conditions has been analysed using numerical modelling, which utilizes crack widths and their densities within the coating. The model clearly shows that cracks perpendicular to the loading affect tensile strength. The model agrees with experimental tensile strength data and accurately predicts crack widths and densities in each anisotropic direction. The finite element models reveal an empirical connection between tensile strength and crack size.