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The interfacial adhesion measurement of a ceramic coating on a metal substrate is studied by three-point bending (3PB) technique. In the measurement, interfacial cracks are induced during the 3PB test, and the interfacial energy release rate is calculated from the released energy per unit crack surface area during crack extension under the fixed displacement conditions. A finite element analysis (FEA) model encompassing the plastic behavior of the metal substrate is developed to simulate the 3PB test and extract the energy data. The inputs to the FEA model include the crack length, the maximum and critical loads corresponding to crack initiation, and the mechanical properties of the coating and substrate. A MoB/CoCr ceramic coating/stainless steel substrate system is investigated by the technique for demonstrating the utility of the technique.

A novel thermal spray material of Mo–Co–Cr–B with high durability in molten alloys has been developed to utilise for die casting parts and for galvanising bath parts. In the present paper, detonation gun (D gun) spray technique was used to deposit a Mo–Co–Cr–B alloy coating onto 316L stainless steel substrate, and the microstructures and mechanical properties of the coating system were studied using XRD, SEM, tensile test and Vickers microhardness. The results show that the microstructures of the coating consisted of ternary transition metal borides matrix CoMo2B2, CoMoB, as well as a little amount of binary borides, MoB and CrB. The ternary borides matrix contained both amorphous phase and nanocrystalline grains with a size of 60±35 nm. The bond strength of the coating decreases with increasing thickness of the as sprayed coatings. The anisotropy in the mechanical properties between the cross-section and plan section of the coatings is examined. Comparing the microhardness and bond strength of detonation sprayed Mo–Co–Cr–B coating with those of HVOF sprayed Mo–Co–Cr–B coating, it can be concluded that the detonation spray process has a better performance than HVOF spray process.