Mechanical properties evaluation of MMCs via multi-scale nanoindentation and GMM: A case study on induction-cladded in-situ TiC/Ti coatings

The inhomogeneous spatial distribution and size effect of multi-scale reinforced phases makes it challenging to characterize and analyze the surface mechanical properties of metal matrix composites (MMCs). Therefore, a multi-scale hybrid nanoindentation testing strategy integrated with the Gaussian mixture model (GMM) was developed to evaluate the surface mechanical properties of induction-cladded in-situ TiC/Ti multi-phase composite coating in this study. The coating consisted of α-Ti, a small amount of β-Ti and a diffusely distributed TiC reinforced phase. The microhardness stabilized at ∼ 600 HV_0.2, and the TiC phase exhibited a “shallow hard − deep soft” behavior. The mechanical properties of within the TiC region (WTR) were between those of TiC and the matrix phase, and the β-Ti matrix phase exhibited superior performance to that of α-Ti. A correlation model between microhardness and single nanoindentation hardness was constructed using the modified rule of mixtures (ROM) method, revealing the evolution of the phase structure with an increase in the TiC volume fraction. GMM-based decoupling of nanoindentation data indicated that hardness and elastic modulus followed a three-peak Gaussian distribution, corresponding to TiC, WTR, and matrix phases. This study provides a theoretical foundation for the optimization of MMCs properties.