Abstract
We examined physical and mechanical characteristics of multiphase plasma coatings of lamellar structure, which include nanocomponents based on silicon dioxide. Elastic and strength properties of composite materials are explored, connected with peculiarities of the formation of structure and composition of coatings at plasma spraying, based on the proposed calculation–experimental technique, as well as with using results of measurements of internal friction and testing of compositions for the three–point bend. The work presents results of evaluation of the parameters of crack resistance and character of destruction of composite materials, based on examination of energy balance of the system base – plasma at the moment of crack initiation at exfoliation and cracking of coatings. We obtained values of intensity of stresses K 1c of different systems and for the appropriate regions – in the grain body, on the border between the particles, in the area of interphase zone. The parameters of crack resistance (G 1c , K 1c ) are calculated of the coating itself at its exfoliation and / or destruction. We applied the corresponding techniques for determining cohesive strength for some cases of the crack propagation in the coating of dispersed structure depending on the composition of coating and ratio of modules of elasticity of the components of the given composition. The parameters of crack resistance are compared to physical and mechanical characteristics of plasma coatings – their adhesive and cohesive strength. The values of intensity of the released energy and coefficients of intensity of stresses at exfoliation or cracking are compared to such properties as adhesive and cohesive strength of the considered coatings.
Highlights
Coatings, obtained by using the method of metallic plasma spray, are characterized by heterogeneous structure, formed from disk-shaped deformed particles, which are characterized by specific sizes and certain degree of connectedness between themselves
Under conditions of loading a composite material (CM) in the form of the system “matrix-coating”, the nature of crack formation differs significantly from the analogous processes of origin and propagation of cracks that occur in a continuous solid body
Different sections of the curve of deformation are examined, by which the intensity of released energy is calculated or coefficient of intensity of stresses, as well as analysis of adhesive-cohesive strength of the coatings is conducted [12, 14, 15]. It follows from these papers that, in spite of existing, sufficiently large, collection of semi-empirical dependencies for determining parameters of the coatings, there are the differences observed in their values because of difficulty in consideration of mechanisms of deformation and destruction in each particular case
Summary
Coatings, obtained by using the method of metallic plasma spray, are characterized by heterogeneous structure, formed from disk-shaped deformed particles (splats), which are characterized by specific sizes and certain degree of connectedness between themselves. Anisotropy, polyphase structure of plasma coatings, there appear difficulties in selecting methods of studies and further analysis of possibilities of obtaining high physical and mechanical characteristics of the formed coating [4, 5]. In the process of research into mechanical and physical properties, as well as for predicting possible type of destruction of a composition system, it is important, first of all, to analyze elastic characteristics of plasma coatings. Relevant are the questions, connected with the examination of interrelation of combination of properties of the composite material, obtained in the process of plasma spraying This relates, first of all, to adhesive and cohesive properties of coatings, physics and mechanics of their destruction, fracture toughness, which, in turn, depend on elastic characteristics and peculiarities of the laminar disc-shaped structure of coatings. Adhesive-cohesive and strength properties are the most important parameters of coatings and the system “base-coating” as a whole
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