The increasing demands for higher performance and more severe application conditions have been the main driver for wider use of titanium alloys for engineering components. The main reason for that is favourable combination of properties like high specific strength, good corrosion resistance and biocompatibility. On the other hand poor tribological properties restricted use of titanium alloys to non-tribological applications.

This drawback can be eliminated by modifying the surface layer of the alloy. Various surface engineering techniques including PVD and plasma nitriding can be used to produce metallic nitride coatings and more recently DLC coatings were successfully applied. However plastic deformation of the substrate leads to premature failure of the usually elastic coating when the high stresses are encountered. That is because coating and substrate materials posses significantly different strength properties i.e. Young's modulus. Additionally the difference in thermal expansion coefficient leads to development of high residual stresses during the process of coating deposition. Cracking of the hard coating leads to stress concentration and localized plastic deformation of the substrate that can modify macroscopic deformation behaviour of the system.

The life of the coating can be increased by introducing intermediate hardened surface layer reducing plastic deformation of substrate material. Main factors controlling deformation behaviour of the material with hard coating are: (i) the difference in Young's moduli between coating and substrate material, (ii) yield strength of substrate material, (iii) coating thickness, (iv) magnitude of residual stresses in the coating, (v) depth of the crack in the coating. In the work influence of these factors on tensile behaviour of titanium alloy with hard elastic coating was investigated by means of FEM method to enable tailoring the resistance to plastic deformation and increase load bearing capacity of this system.

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