Residual stresses in surface layers and coatings

Methods of measurement and mechanisms of formation of residual stresses in the surface layers of metal alloys after ion nitriding, as well as in heat-shielding and refractory coatings are considered. Examples of the application of a technique based on the peculiarities of elastic anisotropy for measuring residual stresses in heterogeneous surface layers, for which the standard technique of diffraction tensometry “sin2Ψ” is not applicable, are given.

Effect of ion nitriding by glow discharge on the physical and mechanical properties of the plastically deformed tool steel R6M5

This work is devoted to the study of the effect of the duration of ion nitriding by glow discharge on the physical and mechanical properties of tool steel with different initial structure. We used specimens of R6M5 tool steel with a coarse-grained structure obtained after annealing at a temperature of 850°C and with a fine-grained structure obtained after severe plastic deformation by torsion discharge. With an increase in the duration of ion nitriding, the thickness of the hardened layer and wear resistance increase. The combination of plastic deformation with ion nitriding by glow discharge increases the adsorption and diffusion rate of the saturating element due to the creation of a highly fragmented and disoriented fine-grained structure and contributed to reduction in processing time.

APPLICATION OF COMBINED TECHNOLOGY FOR RENOVATION AND INCREASED RESOURCE DETAILS OF MEANS OF TRANSPORT

It presents various combinations of primary hardfacing technology for the renovation and improvement of the resource details of ship machinery. Currently, promising are integrated or combined methods hard facing (hybrid technology) coating in conjunction with the modification, the application of multi-layer, multi-functional coatings; development of integrated multioperational technologies. In all conditions, increasing scarcity of expensive alloying materials included in the composition of steels requiring high strength properties of the complex, are promising hybrid technology peening (restore) the surfaces of mild steel Combinations of various primary technologies of application of multipurpose coverings for restoration and increase of a resource of details of knots and units of vehicles are presented. Currently promising are combined methods of application of multifunctional coatings (integrated, hybrid technologies), methods of coating in combination with methods of modification, application of multilayer, multifunctional coatings; development of combined (integrated, hybrid) multioperational technologies. In the conditions of growing shortage of expensive alloying materials which are a part of the steels demanding a high complex of properties of durability, the combined methods of restoration of surfaces are perspective.At present, a methodology for the synthesis of combined multi-operational technologies has not been developed. An empirical-intuitive approach prevails in the combination of multifunctional coating restoration methods. The optimal choice of restoration methods and their sequence is determined by the increase of hardness, complex of mechanical properties, wear resistance, as well as the roughness of the restored surface and the accuracy of the dimensions of the restored part. In the first-best case of combined (hybrid) methods of recovery, the criterion of choice is the comparison of costs and increase the set of mechanical properties of the recoverable parts of components and units of vehicles [13-14]. Each method of recovery has its niche of optimal conditions of use, including even the technological traditions that have developed in a particular enterprise. The decisive factor in the choice of primary methods of applying multifunctional coatings in the combined restoration process is the presence of certain types of equipment at the enterprise and the ability to integrate them intoa single technological cycle. In order to restore vehicle parts with multifunctional coatings with high adhesion strength, hardness and wear resistance, we have proposed a combined (integrated) technology that includes electric arc spraying, electrospark doping and pulsed ion nitriding.

Tribological properties of ion-modified composite coatings

The paper presents the results of a study of one of the ways to increase the wear resistance of “duplex” coatings applied to cutting tools, which are due to preliminary diffusion saturation of the tool surface with nitrogen (known as ion nitriding) followed by physical deposition of a hard coating (Ti, Cr) N. The proposed coating also contains an additional layer with an impurity of ions, deposited on a preliminary nitrided surface of high speed steel before the deposition of a hard coating. Tests were carried out to evaluate the effect of these modified layers on the tool life of the HSS tool. The greatest wear resistance after "triplex" - treatment was achieved during ion implantation of titanium into a pre-nitrided surface. The coefficient of friction of the modified layer was studied at different contact temperatures. Ionic mixing contributes to the appearance of a thin surface layer with an amorphous-like structure, which prolongs the stage of normal wear, which significantly increases the tool life as a result of the self-organization process.

Influence of Glow-Discharge Nitrided Temperatures of Cast Stainless Steel for Cavitation-Erosion Enhancement in Seawater

In this work, corrosion resistance and cavitation-erosion characteristics were investigated by applying plasma ion nitriding technique to cast stainless steels used as materials of high speed rotors under seawater environment. Plasma ion nitriding was performed for 10 h at various temperature parameters with 25% N2 and 75% H2 gas ratio. The cavitation-erosion experiment was carried out under vibration amplitude of 30 °C and sea water temperature of 25 °C according to modified ASTM G32-92. The yN phase that improves corrosion resistance and mechanical properties was formed at the all of experimnetal temperatures after plasma ion nitriding treatment. The crystallite size of phases was calculated through the XRD patterns according to Scherrer formula and obtained smallest nano size of yN phase at 450 °C. Cavitation-erosion resistance was enhanced up to 450 °C but was deteriorated at 500 °C.

The Effectiveness of Active Screen Method in Ion Nitriding Grade 5 Titanium Alloy

The study assessed the effect of ion nitriding on the properties of the surface layer of Grade 5 titanium alloy used, among others, in medicine. Titanium and its alloys have low hardness and insufficient wear resistance in conditions of friction which limits the use of these materials. The improvement of these properties is only possible by the appropriate modification of the surface layer of these alloys. The ion nitriding process was carried out in a wide temperature range, i.e., 530–590 °C, and in the time range 5–17 h. Two variants of nitriding were applied: cathodic (conventional) nitriding and nitriding using the active screen method. The research results presented in this article allow for stating that each of the applied nitriding variants improves the analysed properties (nitrogen diffusion depth, hardness, wear resistance, microstructure analysis and surface topography) of the surface layers in relation to the material before nitriding. The hardness increased in every nitriding variant (the use of the additional active screen increased the hardness to 1021 HK0.025). The greatest increase in titanium abrasion resistance was found for surfaces after cathodic nitriding with an active screen. Each of the applied nitriding variants resulted in surface development.

MODELING AT ION NITRIDING

The paper analyzes the processes occurring in the saturating medium and the processed material, which makes it possible to explain the reasons for the high growth rate of phases during ion nitriding. It is shown that the kinetic coefficient is the link between the technological parameters and the output results of the process. An algorithm for calculating the output parameters of the ion nitriding process is proposed, which, taking into account the principles of similarity and identification, can be used for any steels and alloys.