Activation of diffusion during the formation of boride layers on the surface of steel parts

The features of structure formation of diffusion layers obtained by the technology, including preliminary surface treatment of steel products and subsequent thermal diffusion boriding in powder media, have been investigated. Pretreatment consisted in surface activation by superdeep penetration with a powder composition based on SiC of steel samples made of У8 steel. The features of the activation zones and their distribution over the surface are noted. The features of the activation zones and their quantitative characteristics are noted. A structural analysis of the obtained diffusion layers for the variants of low-temperature (650 °C) and high-temperature (920 °C) boration has been carried out. The chemical composition of the layer and the distribution of the main elements in it are analyzed. In both cases, a change in morphology was noted, consisting in the formation of a more compact diffusion layer and rounding of boride needles in the zone adjacent to the base metal. An increase in the layer thickness by 20–50 % and an increase in the proportion of the high-boron FeB phase relative to the variant of borating without preliminary activation were established.

Boron Diffusion During Carbon Steel Boriding

Protective boride coatings are obtained by chemical-thermal treatment of powder mixtures during induction furnace heating and micro-arc chemical-thermal treatment. Their usage can significantly increase the reliability and durability of steel products. The calculated composition of the saturating charge and the welding flux used to boride steel 20 samples demonstrates that obtained boride diffusion coatings are characterized by high hardness and an extensive diffusion zone. The most optimal composition of the charge that contains iron and boric acid is found to be in the proportion of Fe-25%+H3BO3-75 %. The analysis of the distribution of microhardness over the cross section of coated samples is carried out. The comparative data for the diffusion coefficients and the thickness of the diffusion layers obtained experimentally are presented. The application of the discussed methods makes it possible to intensify the process of diffusion boriding and to ensure the formation of an extensive diffusion zone on the surface of carbon steel products with a high rate of hardening zone formation. The duration of the process is 5 minutes for the induction treatment and 54.05 s for micro-arc chemical-thermal surfacing. It is the main advantage of the experimental techniques mentioned above.

Study of Diffusion Boride Bayers of Steel 20, Obtained by the Micro-Arc Surface

We discuss the results of the study of carbon steel 20 boriding performed by the micro-arc chemical-thermal treatment of a mixture containing iron and boric acid. The study has been carried out in scientific laboratories of the EKSU named after S. Amanzholov. It is found out that boride diffusion coatings obtained by this method are characterized by high hardness of 3.5 GPa and have an extensive diffusion zone. The wide diffusion zone is a surface layer of steel in which the compounds of boron and iron are distributed so that a transition region is formed between the hardened region and the matrix. The material of the diffusion zone is a composite consisting of a plastic а-phase of iron and high strength iron borides. X-ray diffraction studies revealed the formation of Fe3B compounds. It is found that the most optimal composition of the mixture contains iron and boric acid in a ratio of 1:3 (Fe-25% + H3BO3-75 %). The use of the micro-arc surfacing method makes it possible to intensify the process of diffusion boriding in comparison with traditional methods. Also, it ensures that a hardened composite layer with a heterogeneous structure formed by the diffusion-crystallization mechanism is developed on a surface of steel products.

COMBINED TECHNOLOGY OF ELECTRO-SPARK ALLOYING AND THERMAL DIFFUSION BORIDING OF STEEL

The process of thermal diffusion boriding is well known and used throughout the world. It has a number of unique properties, such as high hardness and wear resistance under abrasive wear conditions. Continuous boride layers have increased brittleness, which is related with the elastic properties of borides. In this work, we studied the features of the formation of surface layers onlow-carbon steels after electro-spark alloying, and not by continuous processing of the entire surface of the steel, but only sections and subsequent thermal diffusion boriding from powder medium. Such complex technology enables to form discrete regular and irregular layers, which have a number of advantages, in particular, reduced brittleness. The structure and phase composition of the combined coating growth kinetics of the diffusion layer during the thermal diffusion boriding, are investigated. The creation of the considered composite layers with FeB and Fe2B phases with reduced brittleness will significantly expand their area of application, for example, for working conditions with moderate impact loads.

Chemical reactions at high-speed HFC-boriding

Strengthening of parts and units of machines, increased reliability and longer service life is an important task of modern industry. As an promising materials for protective-strengthening coatings, offered matrix composites based on the ternary system Fe-B-FenB. The article is proposed the complex heating of steel being borated and imbued medium by high frequency currents (HFC), and to combine the diffusion boriding from liquid and solid media and the transition of the diffusion boriding to chemical interaction between the elements of Fe and B. We determined the main components of the reaction-boronizing system, as well as their roles and possible processes that lead to the implementation of topochemical boriding initiated by HFC-heating. Confirmed the course of the reaction leading to the occurrence of reducing agents Ca, Si and active boron in the boronizing mixture.

Surface condition, microstructure and microhardness of boronized layers produced on Vanadis-6 steel after modification by diode laser

The paper presents the study results of surface condition, microstructure and microhardness of Vanadis-6 tool steel after diffusion boriding and laser modification by diode laser. As a result of diffusion boriding the layers consisted of two phases: FeB and Fe2B. A bright area under the continuous boronized layers was visible. This zone was probably rich in boron. As a result of laser surface modification of boronized layers, the microstructure composed of three zones: remelted zone, heat affected zone and the substrate was obtained. The microstructure of remelted zone consisted of boron-martensite eutectic. The depth of laser track (total thickness of remelted zone and heat affected zone) was dependent on laser parameters (laser beam power density and scanning laser beam velocity). The microhardness of laser remelting boronized layer in comparison with diffusion boronized layer was slightly lower. The presence of heat affected zone was advantageous, because it allowed to obtain a mild microhardness gradient between the layer and the substrate.

Microstructure and selected properties of boronized layers produced on C45 and CT90 steels after modification by diode laser

The paper presents the study results of macro- and microstructure, microhardness and corrosion resistance of C45 medium carbon steel and CT90 high carbon steel after diffusion boriding and laser modification by diode laser. It was found that the increase of carbon content reduced the thickness of boronized layer and caused change in their morphology. Diffusion boronized layers were composed of FeB and Fe2B iron borides. As a result of laser surface modification of these layers, the microstructure composed of three areas: remelted zone, heat affected zone (HAZ) and the substrate was obtained. Microhardness of laser remelting boronized layer in comparison with diffusion boronized layer was lower. The presence of HAZ was advantageous, because mild microhardness gradient between the layer and the substrate was assured. The specimens with laser boronized layers were characterized by better corrosion resistance than specimens without modified layer.

Surface Hardening of Titanium Articles With Titanium Boride Layers and its Effects on Substrate Shape and Surface Texture

There is widespread interest in engineering improved properties into the surface layer of manufactured articles. One method for doing so involves a novel boriding process that creates hardened surface layers by the growth of a dual layer TiB2+TiB coating on titanium articles. The objective of the present work was to demonstrate the fundamental feasibility of this process by producing uniform thick boride coating layers on titanium articles and to polish them to a very fine surface texture suitable for biomedical implant bearing surfaces. A powder pack diffusion boriding process was used to grow dual layer TiB2+TiB coatings on simple shapes. Lapping processes were used to polish the borided articles. Evaluation was carried out using measurements of surface texture, geometric form, and hardness, and by metallurgical analysis. Boriding on as-received titanium articles resulted in shape distortion that hampered the subsequent polishing efforts. Hence, further articles were treated with stress-relief annealing prior to boriding, at temperatures below and above the β-transus of the substrate article. Annealing itself caused some form distortion, which was eliminated by lapping. Then, after boriding the annealed articles, varying surface textures and shape distortions were observed. Articles annealed above the β-transus had surface textures with significant peak-to-valley roughness (14–55 μm), and the texture appeared to be patterned upon the substrate microstructure. However, form distortion seemed to be alleviated. For articles annealed below the β-transus, form distortion was not alleviated, and the articles exhibited wavy surface textures with a high peak-to-valley roughness (up to 50 μm). Whether combined or independent, the surface texture changes and shape distortion that occurred during boriding thwarted the polishing processes; the articles could not be uniformly polished to a roughness less than 0.05 μm within the coating thickness. To achieve uniformly polished dual layer TiB2+TiB surfaces on titanium articles using the pack boriding technique, it appears that the substrate raw materials should be free of residual stresses and consist of a fine microstructure.