The results of experimental studies of the structure and properties of steels and alloys subjected to laser chemical-heat treatment of carbide and nitride coatings created by electro-spark alloying and ion-plasma sputtering are achieved. It is shown that laser processing of coatings allows to change purposefully the structural state and set properties of the surface layers of the product, and, therefore, modify the basic characteristics of process operation and control the most important output parameters – wear products, and the quality of the surface layers of the irradiated parts. It is established that a rational choice of chemical composition and method of applying coatings on the surface of metal products of various functionalities helps to improve the quality of the surface layers, to increase the hardness of the irradiated working areas by 30-50%, wear resistance-2-3 times, as compared to volumetric-hardened steels.

No abstract

No abstract

The research depicts structural picture of the steel surface layers after pulsed laser treatment with surface reflow. There are factors contributing to the dispersion of forming crystals to the nanoscale level. There is also found interdependence of nanostructure and laser-irradiated products strength characteristics.

Experimental studies of laser-irradiated layers in a magnetic field (MF) have shown a non-trivial morphology of the surface of handling zone of material in case of reflow. Twisting of a thin layer of liquid metal is observed, irradiated area is getting a crescent appearance, definitely strictly oriented in relation to magnetic flux. This is probably due to the effect of Righi-Leduc, as well as the action of Lorentz forces, which deflect the electrons flow. As a result, there is significant mixing of metal in the irradiation zone, chemical composition equalization, which positively affects the strength properties of the products. One of the important consequences of the MF-effect on the results of laser processing is the phenomenon of magnetostriction. In laser irradiation without MF slide lines were observed on the pre-polished surface patterns resulting from the emerging thermal and structural stresses. By analyzing the topography of irradiated surfaces using modern analysis techniques and computer image processing, it was established that irradiation in MF in conditions of magnetostriction decreases the stress level in irradiated areas and reduces the risk of cracking. The results of temperature measurements at the irradiated spot on cooling stage allow establishing that the cooling rate during laser processing in a MF is considerably higher than without the field. It affects the processes of phase and structural transformations. At laser heating in MF microheterogenic austenite is supercooled with great speed to temperatures of martensite transformation. After that its transformation begins, the sequence of which is determined by the level of local saturation, degree of deformation and is controlled by temperature. The first crystals of martensite are formed in the least saturated areas of austenite, and a very high speed (thousands or tens of thousands of °С/s) of the transformation process beginning γ → α prevents martensite self tempering, which partially can occur when the temperature decreases further due to transformation spread on the remaining volume of austenite, grabbing areas of different saturation. As a result, along with the “fresh-formed” martensite in the areas of laser quenching the martensite is formed, in which segregation of carbon or even ε-carbide may occur and residual austenite with high carbon intensity are formed. Released dispersed carbides contribute to obtaining a sufficiently high hardness values of metals irradiated in a MF.