The fracture and fatigue characteristics of alumina coating strengthen with chrome carbide layer, is presented and discussed. The essential aspects of the methodology include acoustic emission monitoring of crack activity and its propagation under cyclic loads. Structural analysis of the alumina revealed an effect of α , γ phases of alumina and CrC thickness on fatigue life of the coating. The fatigue life of the coatings is found to be no longer than 10 3 cycles. None of the coatings resist above 10 3 cycles. It is found to be cracks initiation and propagation in the coating interface that result in the catastrophic failure of the composite. An ultimate load resulted in intensive crack growth in CrC-Al 2 O 3 -Al is found to be about 2 GPa that is higher than that in alumina coating.

Structure and mechanical properties of composite coatings that contain of 5 to 25% (vol.) of ultra-dispersed diamonds, different alumina phases, and components of SiC, AlN have been investigated. Structure, grains morphology, presence of pores and their distribution, interaction zones were investigated with SEM, X-ray-phase analysis and micro-X-ray-spectral analysis. Material was formed by impulse pressing. It is revealed that the material has variable-porosity, high density, microhardness up to 25 GPa and load rating. XRD analysis shows that the structure includes the diamond phase. To investigate load rating of the material Hertzian contact was used. Ultra-dispersed diamonds strength the structure in general as well as mechanical properties and quality of composite coatings.

In this paper fatigue and fracture of the Al-Al 2 O 3 -CrC, coatings have been investigated by in situ experiments performed in a scanning electron microscope. More importantly, micromechanical models using arrays of internal or surface cracks have been developed. The models provide mechanics of deformation and failure for the coating. The models also reveal the role of overloading in crack arrest, which may well be exploited in the safe design of toughened ceramics against fatigue. Initial overloads prior to cyclic loading are found to reduce significantly the crack driving force in post-overload fatigue crack growth. It expected that pre-service overloading has a great potential for improving the fatigue properties of composite coatings based on oxide ceramics and chrome carbide.