Adhesion Strength of Titanium Nitride Coatings on 20Kh13 Steel

Primary nanocracks appear in 20Kh13 steel due to the state of stress associated with the relaxation of its surface. The nanocrack size is 1.21 nm. After 100 ns or more, these nanocracks transform 121-nm mesocracks. When titanium nitride is ion-plasma sprayed, its ions diffuse into the steel and form an interphase (transition) layer about 130 nm (121 nm) in size. The size of this layer is experimentally measured on the cleavage of a turbine blade using a MIRA 3 (TESCAN) electron microscope and a Quanta 200 3D system. A TiN coating with a hardness H_TiN ≈ 21 000 MPa is at the top of this layer. 20Kh13 steel with an ultimate tensile strength σ_u = 830 MPa is at the bottom of this layer. H ≈ 3000 MPa of the transition layer should be called the adhesion strength of the titanium nitride coating on a turbine blade made of 20Kh13 steel. To separate the TiN coating from the 20Kh13 steel, it is necessary to do the work of adhesion W_a = 2.620 J/m², which gives σ_a = 2260 MPa for the stress in the transition layer. This stress in the transition layer is close to H ≈ 3000 MPa. This means that we propose a model of primary cracks, which can be used to estimate adhesion strength theoretically.