PurposeThe aim of the current research is to characterize boride coatings on steels and steel alloys produced in a CVD fluidized bed reactor.Design/methodology/approachHeat treatments of alloys in fluidized bed reactors have been carried out for more than 25 years. Recently, this technology has been used for surface engineering applications in the deposition of hard and/or corrosion‐resistant layers. The present paper used fluidized bed technology (FBT) to deposit boride coatings on to ferrous materials. The coatings were examined by means of optical microscopy, Vickers microhardness measurements and X‐ray diffraction in terms of coating thickness and morphology, phase formation and hardness determination. The coating's tribological properties were evaluated under dry wear. Impact tests were also carried out to determine the fatigue resistance of the examined coatings under dynamic impact loading.FindingsBoriding in a fluidized bed reactor is a simple, environmentally friendly and fast‐coating process. The produced iron‐boride coatings are characterized by excellent quality and uniform tooth‐shaped morphology. Fe2B was the predominant boride phase formed, exhibiting superior tribological properties under dry wear conditions. Impact testing investigations revealed high‐fatigue strength of boride coatings in combination with limited deformable substrates.Research limitations/implicationsThe investigated coatings were deposited only on some structural and tool steel substrates.Practical implicationsBoride coatings deposited using FBT are satisfactory abrasive wear‐ and fatigue‐resistant coatings in comparison with those produced using common boride coating methods.Originality/valueThe outcome of the research is of great importance for the industry using abrasive wear coatings.

It is well known that the addition of ceramic phases in an alloy e.g. aluminum, in form of fibers or particles influences its mechanical properties. This leads to a new generation of materials, which are called metal matrix composites (MMCs). They have found a lot of application during the last twenty-five years due to their low density, high strength and toughness, good fatigue and wear resistance. Aluminum matrix composites reinforced by ceramic particles are well known for their good thermophysical and mechanical properties. As a result, during the last years, there has been a considerable interest in using aluminum metal matrix composites in the automobile industry. Automobile industry use aluminum alloy matrix composites reinforced with SiC or Al2O3 particles for the production of pistons, brake rotors, calipers and liners. However, no reference could be cited in the international literature concerning aluminum reinforced with TiB particles and Fe and Cr, although these composites are very promising for improving the mechanical properties of this metal without significantly alter its corrosion behavior. Several processing techniques have been developed for the production of reinforced aluminum alloys. This paper is concerned with the study of TiB, Fe and Cr reinforced aluminum produced by the stir-casting method.

Interactions between solid materials and liquid aluminum lead to a dissolution of solid elements into aluminum, which in turn results in a subsequent growth of intermetallic and intermediate phases. It was established that the growth of the intermetallic phases could be governed by chemical reactions at the interfaces and by interdiffusion of the reacting elements through the different phases. Dissolution on the other hand mainly depends on thermodynamic conditions, experimental parameters such as temperature, stirring time, and reacting holding time and on the degree of the saturation of aluminum as well as on the chemical composition of the solid materials in the reaction zone. The above-mentioned factors play also an important role in the formation of the different phases during dissolution. Nevertheless, a non-uniform distribution of the solute elements may causes a local concentration of these elements into the liquid aluminum, which practically delays the process or alters the equilibrium of the growth of the phases. Thus it is crucial to control the dissolution conditions so that the instabilities induced at the solid materials/aluminum interface are limited. The main objective of this study was to investigate both the formation of intermetallic and intermediate phases in the reaction zone and to examine the development of the diffusion structures of pure aluminum reinforced with TiB particles and to investigate the mechanical properties of the as-produced composite materials.

Impact testing is an efficient experimental procedure that enables the determination of the fatigue resistance of mono- and multi-layer coatings deposited on various substrates, which was not possible with the common testing methods previously available. In this paper an advanced impact tester, able to assess the fatigue failure resistance of coatings working under cyclic loading conditions, is presented. The fatigue failure of the tested coatings was determined by means of scanning electron, optical microscopy, and EDX analysis. The test results are recorded in diagrams containing the impact load versus the number of successive impacts that the examined coatings can withstand. From the experimental results it was concluded that a hard, wear resistant HVOF thermal spray WC-CoCr coating deposited on P91 steel substrate presents a high fatigue resistance.

The impact testing is an efficient experimental method that enables the quantitative and qualitative determination of the fatigue resistance of mono- and multilayer coatings deposited on various substrates, which was not possible with the common testing methods previously available. In this paper the experimental assessment of the fatigue resistance of coatings working under cyclic loading conditions by means of the dynamic impact testing method is presented. The fatigue failure mode, such cohesive or adhesive, of the investigated coatings is determined using scanning electron and optical microscopy, as well as EDX analysis. Critical values of the stress components, responsible for distinctive fatigue failure modes of the coating substrate system are obtained and the fatigue limits of aluminide coatings are illustrated in simple diagrams containing the impact load versus the number of successive impacts that the examined aluminide-P91 system can withstand.