Abstract
Surface alloying of AISI 420 steel was carried out in a single vacuum cycle, and consisted of spraying a thin (0.5 μm) film of Zr-Ti-Cu alloy by electric arc spraying of a cathode of the composition Zr-6 at.% Ti-6 at.% Cu, and the subsequent irradiation of the “film (Zr-Ti-Cu alloy) / (AISI 420 steel) substrate” system with an intense pulsed electron beam. It is shown that the concentration of zirconium in the surface layer of steel decreases with an increase in the energy density of the electron beam (ES). It is established that formation of a surface alloy is accompanied by the following: formation of a cellular crystallization structure (the average cell size increases from 150 nm at ES = 20 J/cm2 to 370 nm at ES = 40 J/cm2); decomposition of a solid solution with the release of zirconium carbide particles (particle sizes increase from (10-15) nm at ES = 20 J/cm2 to (30-40) nm at ES = 40 J/cm2). Particles of the carbide phase based on chromium of the composition Cr3C2, Cr7C3 and (Cr, Fe)23С6, along with zirconium carbide particles, are revealed upon the irradiation of the “film (Zr-Ti-Cu alloy) / (AISI 420 steel) substrate” system with an intense pulsed electron beam (ES = 40 J/cm2). Chromium carbide particles have a round shape; their sizes vary from 40 nm to 60 nm. The authors analyzed phase transformation diagrams taking place under equilibrium conditions in Fe-Zr-C; Cr-Zr-C; Fe-Cr-Zr systems. It is established that ultra-high cooling rates that occur during the irradiation of the “film (Zr-Ti-Cu alloy) / (AISI 420 steel) substrate” system with an intense pulsed electron beam impose limitations on the formation of phases of the intermetallic type. It is assumed that the formation of predominantly carbide phases in the surface layer of the material is due to high mobility of carbon atoms in steel.
Highlights
Formation of surface alloys is one of the methods for substantial improvement of the structure of parts and products, as well as an increase in their service life
Based on the study of the phase diagrams of Fe-Cr-Zr, Cr-Zr-C, and Fe-Cr-C systems obtained under equilibrium conditions we shall analyze phase transformations in the given alloy
It has been shown that irradiation of the system “film / (AISI420 steel) substrate” with an intensive pulsed electron beam is accompanied with the following: formation of a surface alloy, whose concentration of doping elements (Zr) decreases with an increase in the energy density of the electron beam; formation of a cellular crystallization structure; decomposition of a solid solution with a release of zirconium carbide and chromium carbides particles
Summary
Formation of surface alloys is one of the methods for substantial improvement of the structure of parts and products, as well as an increase in their service life. This approach avoids the use of expensive, highly alloyed materials which require significant financial and energy costs, both during the production and processing of parts and products. A promising method for formation of surface alloys is the combined treatment, which includes the deposition of thin films of alloying elements and the subsequent irradiation with concentrated energy fluxes (laser radiation [1, 2], high-intensity electron [3,4,5] and powerful ion [6, 7] beams, plasma flows and jets [8,9,10,11]).
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