This paper presents the results an experimental study on ferroalloy-base flux-cored wire coatings. The work conducted shows that it is possible to improve the structure and properties of coatings by adding aluminum to the ferrochromium powder charge and rare-earth elements and calcium to ferroboron. This reduces the oxygen content and porosity of coatings by a factor of 1.5-2. It also reduces residual tensile stresses in outer coating layers and improves coating-substrate adhesion strength as well as abrasive wear resistance.

Residual stresses exert profound influence on the longevity of parts with thermal spray coatings. The distribution and value of the residual stresses depend on method of coating deposition, composition of the applied material, parameters of thermal spraying and methods of post-treatment. Therefore, the study of the influence of the various technological factors on the residual stresses in the plasma spray coatings is very important. Due to heterogeneity of the coating, residual stresses can be determined only by the experimentation by using new methods which take into consideration real values of elastic characteristics and density of elementary layers. Methods and formulas for the calculations of the residual stresses in coatings deposited on bars, rings, discs, cylinders are presented. Experimental results for the various thermal spray coatings are also shown. These results can be used for the optimization of coating deposition and would supplement the existing database.

The experimental results of developing tribological surface coatings for high temperature application are presented. The primary focus of this work was in the area of high output advanced, low heat rejection (LHR) diesel engines, where high temperature lubrication between the piston ring and the cylinder liner wall surface is essential. The target temperature focused upon in our research is an operating top ring reversal temperature of approximately 1000° F. The technology developed typically involves treating a porous thermal spray coating with chemical binders improving coating strength and integrity and eliminating open porosity to form an almost monolithic appearing coating. The effectiveness of the densification through the coating thickness was studied. It has been shown that densification process improves mechanical properties and dramatically extends coating wear resistance. Good results were obtained using densified plasma spray Iron oxide (hematite) for a cylinder liner coating versus plasma sprayed Tribaloy T 800 for piston ring. Single Cylinder LHR engine test successfully demonstrated the feasibility of this tribological pair for the possible future applications.

Future development of thermal spray processes and new composite materials raises an important problem concerning the transition from qualitative to quantitative methods of coatings evaluation. It is well known that thermal spray coating deposition in most cases is accompanied by the formation of temporal and residual stresses through the coating thickness. For proper evaluation of formed stressed state it is extremely important to know the real value of elastic characteristics in different layers of the coating. This problem has become more complicated taking into consideration the variety of materials, different spray parameters, number of coating layers and extreme service conditions. These values can be obtained only from experimentation. Elastic characteristics (EC) could be used in many calculations, such as durability, stiffness, fatigue, vibration and others. This paper describes new methods of experimental determination of elastic characteristics presumed as variable throughout the coating thickness. Influence of coating composition, particle size of initial powders, spray parameters, post-treatment and other factors on elastic modulusses were studied. Obtained experimental data for different materials supplement existing data and can be used for evaluation of residual stresses and other purposes.