A theoretical and numerical investigation of residual stress in thermally sprayed WC-Co coating using nanoindentation technique

Abstract

Thermally sprayed cermet coating has become a potential substitution for hard chrome plating as it possesses promising mechanical and tribological properties that are greatly pompous by the residual stress. The prospect of nanoindentation technique to assess the residual stress in WC-based coating is extremely limited. In the current investigation, a large number of nanoindentation experiments are conducted on the HVOF deposited WC-Co coating to assess the indentation behaviours of WC phases. A theoretical model based on the constant indentation load approach is established to evaluate the residual stresses from the indentation characteristics. It is observed that the contemplated model has the proficiency to evaluate the residual stress certainly for thermally sprayed WC-Co coating with a mean error of around 13 %. A slight difference in measured residual stress using nanoindentation technique with theoretical model and XRD technique is noted. This is ascribed to the existence of prismatic and basal planes of WC phases that possess different nanoindentation characteristics. On the other hand, FEM-reverse algorithm coupled with MATLAB optimaization tool is employed to evaluate the stress-strain relationship of WC phase from its nanoindentation responses. Based on those results, 2D axisymmetric FE models for both stress-free and samples with compressive stress are developed. By performing the sensitivity analysis, it is conceived that a mesh size of 10 nm can lead to a more defined and uniform stress field. The residual stress obtained from numerical analysis are verified with the experimental findings and an average error of around 15 % is observed. Furthermore, nanoindentation technique is a promising approach that is accomplished to perform residual stress depth profile of the coating. Measurements can be conducted on polished cross-section of coating without affecting the coating integrity. Therefore, the proposed technique represents a convenient and non-destructive approach for residual stress depth profiling of thermally sprayed WC-Co coating.