Effect of Ion-Plasma Thermocyclic Nitriding on the Fatigue Resistance of ChS70VI Alloy

Abstract

The paper considers one of the topical problems of the targeted control of the properties of the material of products in the zones under critical loads, which lead to their failure or loss of performance. The processes for the diffusion saturation of the surface layers of parts (chemical heat treatment) are an effective method for the strengthening treatment of parts of complex geometric shape. The ion-plasma thermocyclic nitriding technology developed by the Pisarenko Institute of Problems of Strength of the National Academy of Sciences of Ukraine is used for the treatment of specimens of ChS70VI heat-resistant alloy to study its effect on fatigue resistance characteristics. A technology for the ion-plasma thermocyclic nitriding of the surface of specimens and its conditions are presented. In the ion-plasma thermocyclic nitriding technology, heating is effected through glow discharge energy. In this case, the electrical power consumption is greatly reduced (by a factor of ~10) compared with similar chemical heat treatments. Micrographic investigations to determine the surface layer characteristics of specimens after ion-plasma thermocyclic nitriding are presented. The depth distributions of alloying and saturating elements in the specimen were obtained. The micrographic investigations showed that a fairly homogeneous layer 3 μm deep, uniformly distributed over the specimen surface, was formed after treatment by ion-plasma thermocyclic nitriding. To assess the influence of the above technological treatment of specimens, fatigue tests of these specimens and speciments in the initial state were carried out. It was shown that due to the strengthened layer formed on the test surface of specimens, the process of scattered damage accumulation under cyclic loading slows down, and the fatigue resistance characteristics improve: the endurance limit of specimens at the number of cycles to failure N = 107 cycles after technological treatment is 32% higher than that of specimens in the initial state.