(1) Background: Boron-based diffusion layers possess great application potential in forging and die-casting due to their favorable mechanical and thermophysical properties. This research explores the enhanced wear resistance of tungsten hot-work steel through boriding and boroaluminizing. (2) Methods: Thermal-chemical treatment (TCT) of steel H21 was carried out. Pure boriding was introduced to the substrate through heating a paste of boron carbide and sodium fluoride 1050 °C for two hours. As for boroaluminizing, 16% of aluminum powder was added to the boriding paste. (3) Results: It was shown that boriding resulted in the formation of an FeB/Fe₂B layer with a tooth-like structure. A completely different microstructure was revealed after boroaluminizing—namely, diffusion layer with heterogeneous structure, where hard components FeB and M_x (B,C) were displaced in the matrix of softer phases—Fe₃Al and α-Fe. In addition, the layer thickness increased from 105 μm to 560 μm (compared to pure boriding). The maximum microhardness values reached 2900 HV0.1 after pure boriding, while for boroaluminizing it was about 2000 HV0.1. (4) Conclusions: It was revealed that the mass loss during wear test reduced by two times after boroaluminizing and 13 times after boriding compared to the hardened sample after five-min testing.

(1) Background: Operational properties and durability of dies in different metal-forming processes significantly depend on their surface quality. Major die failures are related to surface damage due to heat checking cracks, wear, etc. Thereby, strengthening of the working surfaces of dies for hot bending, stamping, forging, and die casting processes is an urgent engineering challenge. Surface alloying with high-energy beams improves the properties of steel products. In these processes, the alloying powders and the treated surfaces can be remelted by electron beam within a short time while the bulk structure of the component remains unchanged, resulting in minimal distortion. The paper presents the results of the electron beam surface alloying (EBSA) of H21 and L6 tool steels with the treatment pastes containing boron carbide and aluminum powders. (2) Methods: Two types of pastes were used for surface alloying: a single-component (B₄C) paste and a two-component (B₄C+Al) one. The microstructure, microhardness, wear resistance, and elemental and phase composition of the layers obtained on steels were investigated. (3) Results: Four layers up to 0.4 mm thick were distinguished on the surface of the steels after the EBSA. Metallographic analysis showed coarse dendrite formation in the layers embedded in matrices of a eutectic or a solid solution. Microhardness of the steels after the two-component EBSA was higher than after B₄C EBSA, which was related to a higher concentration of hard phases, such as iron borides and carbides. In addition, aluminum boride was revealed by the XRD analysis on L6 steel after B₄C+Al EBSA. (4) Conclusions: Wear test indicated that the most resistant samples were H21 steel after single B₄C EBSA and L6 steel after B₄C+Al EBSA. Both samples contained carbon particles in the layer contributing to the high wear resistance as a lubricant. The conducted research is beneficial for mechanical engineering, automotive engineering, medical technology, aerospace engineering, and related industries, where coatings with high microhardness, wear resistance, and surface quality are demanded.

The development of new protective coatings is of great fundamental and applied importance for increasing operational properties of surface layers in machine parts, increasing their durability and expanding their functionality. The study is devoted to the creation of coatings based on boron and aluminum on the surface of alloyed steel using a method, combining diffusion saturation (DS) and subsequent electron beam processing (EBP). DS was carried out in saturating pastes based on boron carbide and aluminum at temperature of 1050 °C for 2 hours. As a result of processing, a diffusion layer with thickness of up to (5.6-5.8) × 10²μm and complex structure with depth-heterogeneous composition was formed on the steel surface. The subsequent EBP led to a complete transformation of the primary diffusion layer and an increase in its thickness to 10³μm. XRD analysis showed significant differences in composition before and after EBP: after EBP tungsten borides (WB, W₂B₉) and iron (Fe₂B) were detected. In addition, it was determined that the distribution of microhardness and elemental composition (B, Al, W) over the depth of the layer after EBP have a more favorable profile without significant fluctuations compared to the sample after DS.

Introduction. Boriding and aluminizing are among the effective methods for improving the performance properties (corrosion resistance, heat resistance and wear resistance) of machine parts and tools. Solid-phase methods of carrying out techniques of thermochemical treatment (TCT) require long-term exposure at elevated temperatures, which negatively affects the structure and properties of the base material. From these positions, the selection of reasonable temperature-time parameters of solid-phase boriding and aluminizing processes is an urgent task. The purpose of this work is to assess the effect of low-temperature boriding and aluminizing processes on the structure and microhardness of diffusion layers on the surface of low-carbon steels. The paper considers two grades of steels with a carbon content of up to 0.4%: low-carbon steel St3 and alloy steel 3Cr2W8V. The use of the second steel is due to the need to identify the effect of alloying elements in steel on the thickness of diffusion layers and its composition. Powder mixtures based on boron carbide and aluminum carbide are selected as sources of boron and aluminum. Results and discussions. It is found at a process temperature of 900 °C and holding for 2 hours after boriding, iron borides are formed on the surface of both steels. At the same time, two borides FeB and Fe2B are detected on St3 steel by X-ray phase analysis (XRD), and only the Fe2B phase is detected on 3Cr2W8V steel. After aluminizing, aluminum-containing phases such as Al5Fe2, Na3AlF6 and Al2O3 are formed in both steels. The thickness of the resulting diffusion layer on St3 after boriding is 35 μm, after aluminizing – 65 μm. The thickness of the diffusion layer on 3Cr2W8V steel is equal to 15 μm after boriding and 50 μm after aluminizing, which is significantly less than on carbon steel and is obviously due to the effect of alloying elements. It is established that TCT leads to a significant increase in the microhardness of the samples surface. Thus, the maximum microhardness of St3 steel increased to 2,000 HV, and the maximum microhardness of 3Cr2W8V steel increased to 1,700 HV after boriding. The microhardness after aluminizing is comparable for both steels and is equal to 1,000-1,100 HV. Elemental analysis of the upper sections of the diffusion layers shows that the content of boron (7-9%) and aluminum (50-53%) corresponds to the detected XRD iron borides and aluminides. In all cases, there is a gradual decrease in the diffusing elements in the direction from the surface to the base.

A mathematical model for predicting the geometric parameters of boron and aluminum-based coatings formed on a steel substrate by laser alloying is presented in the work. The model combines the principles of the theory of experiment planning with an artificial neural network (ANN) apparatus. Coatings were formed by means of laser heating of the steel surface with a pre-applied treatment paste. The ANN was built, trained and tested for the prediction of the width and depth of the molten bath on a steel substrate. The prediction results of the obtained neural network were compared with the corresponding linear models. The efficiency of the considered approach and the possibility of its application for predicting the values of laser treatment of steel parts of machines subjected to surface hardening are shown. The presented approach allows to use one mathematical model for predicting several parameters, thereby reducing the number of experiments.

The paper presents the study of pack boroaluminizing carried out on steel 20 using mathematical planning methods. A mathematical model and nomograms showing the dependence of diffusion layer thickness on basic parameters factors of thermochemical treatment (technological factors such as temperature, treatment time and powder mixture composition) were obtained by means of conducting a full factorial experiment. The degree of impact which technological factors make on the final result and the ranges of their regulation are revealed. The temperature of pack boroaluminizing varied from 900 to 1000 °C, the duration of the process was 2-4 hours, and the ratio of the treatment components of B₂O₃ / Al was 40/60 to 50/50 wt-%. The metallographic analysis has revealed that the depth of the diffusion layer is from 80 to 260 μm, depending on technological factors.