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Analysis of Fatigue Data For WC-17%co and WC-10Co-4Cr HVOF Thermal Spray Coatings

Analysis of Fatigue Data For WC-17%co and WC-10Co-4Cr HVOF Thermal Spray Coatings. Introduction . Scanning electron microscopy characterization of fracture surfaces at all stress levels. Microstructure characterization of samples at all stress levels. Residual stress characterization:

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Analysis of Fatigue Data For WC-17%co and WC-10Co-4Cr HVOF Thermal Spray Coatings

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  1. Analysis of Fatigue Data For WC-17%co and WC-10Co-4Cr HVOF Thermal Spray Coatings

  2. Introduction • Scanning electron microscopy characterization of fracture surfaces at all stress levels. • Microstructure characterization of samples at all stress levels. • Residual stress characterization: • Hoop stress in substrate and coating. • Axial stress at the interface. • Longitudinal stress in coating. • Correlation of data to form understanding of fracture mechanism.

  3. Current Data • SEM characterization shows that fatigue cracks initiate at imbedded aluminum oxide grit sites

  4. Current Data • The fatigue specimens at high stress levels show delamination of the coating at the interface.

  5. Current Data • No coating cracks are shown to propagate into the base metal, or provide a preferential site for fatigue to initiate. • Microstructural cracks all run axial along the length of the specimen perpendicular to the substrate fracture and appear to be interlamellar in nature. • All coating cracks arrest at the bond line interface and release energy axially causing delamination. • Fracture mechanics analysis always provides that crack energy will propagate along the path of least resistance. The bond line interfacial strength between the coating and substrate is orders of magnitude less than the energy required to break the atomic (crystallographic) bonds in the bulk metal.

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