Electric Spark Alloying of Structural Alloyed Steel 30HGSNA for Parts of Friction Units

Abstract

The paper analyzes the causes of destruction of parts of friction units of aircraft, which are made of alloy steel 30ХГСНА. It has been established that the following processes develop on the working surfaces of these parts: abrasive wear, stuck, fretting corrosion and fatigue wear.

In laboratory conditions, studies were carried out on the wear resistance of samples made of 30ХГСНА steel, on the working surfaces of which were coated with electrospark alloying. In the research process, a complex technique was used (metallographic, X-ray diffraction and electron microscopy analyzes).

The wear resistance of electrospark coatings was determined on a 2070-СMT-1 universal computerized friction machine according to the disk-block scheme in the environment of MС-20 mineral aviation oil under conditions of boundary friction. Electrospark alloying of the samples was carried out in two stages with a change in the current strength, which made it possible to partially relieve internal stresses and reduce the roughness of the modified surface. A sample was used as a cathode, and electrodes made of sintered self-fluxing powders with titanium and chromium carbide were used as an anode. In the process of coating samples, the collision of electrons with the electrode surface leads to the release of thermal energy and, as a result, to a directed explosion of the anode portion that has received the electron momentum. During the explosion, all liquid and softened material is thrown into the interelectrode gap. A significant part of this material interacts with the surface of the cathode, forming a doped layer. The structure and physicomechanical properties of the resulting coating largely depend on the grain size of carbides. With decreasing grain size of carbides, the coating continuity increases. Due to the fact that in this case the transfer of eroded material in the liquid and vapor phases prevails, and in the presence of large grains, a part of the eroded material is transferred in the form of accumulations of grains. It was found that composite electrospark coatings based on self-fluxing mixtures with fillers of titanium carbide and chromium carbide significantly increase the wear resistance of structural alloy steel 30ХГСНА and are recommended for the implementation of the developed surface hardening technology in production.