Evaluation of Induction Thermography for the Detection of Cracks Due to Mechanical and Thermal Stress in WC-10Co-4Cr Coatings

Abstract WC–Co-Cr coatings have exceptional mechanical properties including high hardness, wear resistance and corrosion resistance. However, under continuous wear or mechanical/thermal overloads, such as line loads in calender rollers or improper heating/cooling cycles, these coatings can develop defects like cracks and dents. Such damage compromises product quality, particularly in calendering processes where precise roller concentricity (single-figure micrometre range) is critical. This study investigates induction thermography as a non-destructive alternative for defect detection in WC-10Co-4Cr coatings. Coated C60 steel specimens with different surface roughness (conditions: ground and as-sprayed) were subjected to controlled mechanical (strains: 0.12% to 0.4%) and thermal stresses (thermal shock), inducing cracks with widths ranging from approx. 1 to 4.5 µm and depths up to the full coating thickness (≈ 400 µm). Both crack width and depth influenced the thermal contrast, with deeper cracks producing a stronger signal. Using the Fourier transform method and principal component analysis, induction thermography successfully identified cracks down to a minimum resolved width of ≈ 1 µm in ground and ≈ 1.7 µm in as-sprayed specimens, demonstrating its sensitivity to defect detection across different surface conditions. The results highlight the potential of this method to improve process reliability and product quality in high-precision applications by enabling non-invasive inspection.