In-situ high temperature stress analysis of Ti(C,N) coatings on functionally graded cemented carbides by energy dispersive synchrotron X-ray diffraction

• In-situ high temperature X-ray thermal stress analysis of CVD Ti(C,N) coatings
• Effect of functionally graded substrates on thermal cycle stress level
• Measured stresses below theoretical stresses indicating presence of microstructural defects
• FEM simulation combined with bi-linear plasticity model to fit measured strain relationships

We report on in-situ high temperature X-ray thermal stress analysis of chemically graded Ti(C,N) coatings deposited on functionally graded cemented carbide substrates by chemical vapor deposition. The in-situ analyses were performed by energy dispersive X-ray diffraction using synchrotron radiation. The samples were subjected to one individual thermal cycle from room temperature to 800 °C and cooled down to room temperature again. The stresses were determined using the sin2ψ method in the Ψ geometry combined with scattering vector measurements in order to unravel the compositional influences on the lattice strain distributions. It was found that the Ti(C,N) thin film presents a cycling residual stress behavior (tensile–compressive–tensile) connected to the temperature cycle. If top-blasting is applied on the thin film layer after the coating process, compressive stresses are generated. These compressive stresses induced by top-blasting are partially released after the high temperature thermal cycle. The functionalization of the cemented carbide substrate influences the level of stresses developed in the coating. The stress behavior as a function of temperature is discussed with the support of finite element modeling by introducing a bi-linear plasticity model to calculate strain relationships which is in agreement with the synchrotron measurements.

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