Impact Study of Electron-Beam Heating on the Structure and Properties of Boroaluminized Layers Aimed at Producing New Composite Coatings with Special Properties

Abstract

Electron-beam processing is a promising method of surface processing. Electron-beam processing can involve surface melting accompanied by adding alloying elements into the melt (electron-beam alloying), or it can be applied to preliminary obtained diffusion layers on a material’s surface (electron-beam chemical thermal processing). Electron-beam heating both increases the temperature and initiates diffusion processes in the metal. By regulating parameters of electron-beam processing, different types of layers—diffusion, diffusion-crystalized, or liquid phase—are formed. The paper presents the study of the impact of electron-beam heating on the structure and properties of boroaluminized layers in carbon steel 60 (0.6 % carbon), obtained by thermochemical processing (solid-phase boroaluminizing in powder mixture 98 % (70 % aluminum oxide Al2O3) + 10 % boron oxide (B2O3) + 20 % aluminum (Al) + 2 % sodium fluoride (NaF) at T = 950°C, τ = 4 h). The authors studied the influence of electron-heat processing modes on the formation of boroaluminized layers’ structure. The parameters of electron-beam heating were beam current Ic = 20–60 mA and time of impact τ = 15–120 s. The authors conducted metallographic and X-ray microscopic analysis and measured microhardness of boroaluminized layers obtained with a combined method (thermochemical processing and electron-beam heating). It was shown that electron-beam heating of boroaluminized layers leads to changes in the structure and properties as well as in the layer’s morphology. Aluminum is spread evenly in the depth of the layer. The layer’s microhardness changes and the brittleness decreases. The obtained results led to the conclusion that electron-beam heating can be recommended to improve properties of boroaluminized layers and used as a foundation for producing new composite coatings with special properties.