International Scientific Journals
of Scientific Technical Union of Mechanical Engineering "Industry 4.0"

In this work the possibilities of reducing the roughness and defects of surfaces obtained by 3D printing with selective laser melting (SLM), via reactive electrospark surface modification (ESD) with low-melting AlSi alloys has been shown. The influence of the energy parameters of the ESD process on the roughness, microstructure, microhardness and performance characteristics of the coatings has been studied. Surfaces with new phases and ultrafine crystal-amorphous structure with particle sizes from micro to nano level, with new relief, with thickness up to 15 μm and microhardness up to 11 GPa were obtained, as the initial SLM roughness from Ra = 8-11μm is reduced to Ra=3-5 μm. Possibilities for control of the characteristics of the coatings and purposeful synthesis of new phases by changing the parameters of the spark discharge have been established. The parameters of the ESD process, which provide simultaneous reduction of SLM surface roughness, removal and erasure of the defects and targeted reactive synthesis of new phases with high performance properties and wear resistance, are defined and optimized.

The research of the technology of obtaining new copper-ferrochrome composite material has been done. The results of its structure and properties analysis are presented. The material structure consists of the copper base, non-dissolved coarse inclusions of ferrochrome, diffused zones, forming around these inclusions and phases, having formed in the place of completely dissolved inclusions of ferrochrome fine particles. The material has good mechanical properties and a high wear resistance due to the formed solid solutions of the carbides in the copper.

Analysis of the structural state and phase composition of surface metal layers after combined treatment of steel which includes preliminary surface plastic deformation of the workpiece, electrospark doping with use of rotating disk electrode 2 mm thick, made of WCCo hard alloy and subsequent surface ball smooth rolling, has been performed. It was shown that the use of combined treatment provides a gradient-layered structure with low surface roughness. Phase composition of the obtained layer consist of ferritic α-Fe phase and a number of carbide phases formed during the interaction of the electrode material with steel: F3W3C, WC and W2C semi-carbide. Wear resistance of the material after treatment exceeds similar properties of the original carbon steel up to 4 times.

This study explores the metal of a coating deposited by a high-chromium flux-cored wire alloyed with a BN-TiB2-ZrB2 complex. We investigated the changes in the durometric properties and fine structure of the coating after tempering and subsequent quenching. It is shown that the hardening of the metal of such a coating after quenching consists in the formation of a complex composite structure with an iron-chromium martensitic matrix, a large amount of eutectic and particles of hardening complexes, which leads to an increase in hardness and wear resistance. It has been established that phase transformations in the metal of such a coating are caused by the formation of an eutectic component based on chromium and iron borides, a framework structure and a large number of dispersed titanium nitride particles up to 2.5 μm in size.

Investigations of wear resistance and tensile strength of steel products with diffusional zinc coating obtained in zinc powders with a nanocrystallized surface of powder particles were carried out. The effect of the structural state of the coating on the wear resistance and adhesive grasping with a steel counterbody was established. The prospects of the nanogalvanizing process to improve the strength of steel products are shown.

The development of technologies in modern machine building aims at improving the mechanical and technological properties of the materials. The present study presents an improvement in the mechanical properties of low carbon steels by thermoffusion coatings with nanofibers obtained under different heat treatment regimes. Depending on the type of heat treatment and the size of the zinc particles, different gradient layers can be obtained in depth. This of course reflects positively on the chemical resistance of the material. In addition, it positively affects the mechanical properties of the material by increasing mechanical strength and technological properties by improving the resistance to plastic deformation. With these first studies, there is an impetus for another look to improve the properties of low-carbon steels that are widely applicable in the field of machine building.

In this paper we study the structure, phase composition, microhardness, wear resistance boride coatings obtained on metals and alloys at complex saturation with boron and copper in various physical and chemical conditions, namely carrying satiation without application of an external magnetic field (EMF) and in its simultaneous imposition . Studies have shown that the use of EMF when applying boride coatings allows in 1.5 – 2 times reduce the duration of saturation detail and get coatings with high hardness and wear resistance.

Established that the application EMF on carbon steels formed a continuous, homogeneous boride layer, thickness is 2 times higher than the boriding without EMF. On the diffraction patterns of the surface layers of boride coatings obtained after boriding at application EMF fixed presence phases FeB and Fe₂B, the redistribution of the proportion of boride phases, the change of the crystal lattices and the decrease in the volume of the unit lattice phase FeB. When the complex is saturated steel 45 with boron and copper diffusion layer is composed of the phases FeB, Fe₂B and Cu. Chemical heat treatment with the simultaneous action of EMF leads to the formation of phases in the diffusion zone FeB and Cu, crack resistance layers obtained after saturation with boron and copper increases to 2.23 MPa · m^0,5 compared to 1.12 MPa · m^0,5 for boride coatings obtained without action EMF .

Formation diffuse boride layers under the action EMF improves tribological characteristics and leads to an increase in wear resistance of 2.2 – 2.6 times.

In this paper was investigated the formation of complex diffusion boride layers on metastable austenite Cr-Mn-N steel powder method. Calculate the value of the diffusion coefficient in different physical – chemical conditions and the thermodynamic potential chemical reactions. Defined phase composition layers obtained on the metastable austenite Cr-Mn-N steel. It is established that the application of an external magnetic field (EMF) leads to a redistribution of the proportion boride phases in the surface layers, changes the period of crystal lattice and increasing the diffusion coefficient.

In this paper we study the structure, phase composition, microhardness, crack resistance, wear resistance boride coatings obtained at complex saturation with boron and copper in the application of an external magnetic field (EMF). Investigations have shown that this method allows the application of boride coatings in 1.5 – 2 times decrease the duration saturation detail, and receive coating with high hardness, wear resistance, crack resistance.

It is established that the application EMF formed a continuous, homogeneous boride layer with thickness coatings in 2 times higher than boride coatings without EMF for the equal duration of the process. When imposing EMF in boride layers observed the redistribution quantitative relation boride phases, namely: decrease of volume phase FeB, and on diffractograms surface layers boride coatings obtained after boriding fixed presence phases FeB and Fe₂B. After complex saturation boron and copper in the application of external magnetic fields fixed phases FeB and Cu.

The researches have shown that the highest spalling stress value is reached in boride phases, obtained in powder environments with copper powder at the application of EMF, and respectively is 420 compared with 225 MPa for coating obtained without EMF. Increased shear stress values in complex layers obtained after saturation with boron and copper caused by the formation of phases more viscosity, for which crack K_1c in 1.4 – 2.0 times higher than the initial boride phases FeB and Fe₂B.

Application of EMF at boriding improves tribological characteristics of coatings: decreases coefficient of friction and increase in 1.5 – 2.5 times wear resistance.

Investigated the wear resistance of coatings obtained by saturation with boron and copper under dry friction – sliding on the air, and found that the coatings obtained by saturation with boron and copper have 2 times better wear resistance than the coating after boriding. Found that the saturation of boron and copper complex provides optimal performance when wear boride phases, namely sufficient microhardness – 15.5 MPa, 0,5 0,5 low porosity, increase in viscosity layer, the value K reaches 2.1 MPa · m to compared with 1.2 MPa · m 1C without complex saturation and increasing stress chipping values to 290 MPa compared to 170 MPa for the boride layers.

Micro arc oxidation (МAО) is one of the advanced methods of obtaining thin-layer oxide ceramic coatings on the elements of machines of different functionality, allowing considerably increasing their life. The work is devoted to investigation of wear resistance and microhardness of coatings formed by micro arc oxidation on aluminium alloys in different electrolyte types. МAО is recommended for application at different engineering and maintenance technical enterprises, that produce, restore and harden elements.

Technique and equipment for plasma spraying of wear-resistant and corrosion-resistant coatings with enhanced adhesive strength was developed. Ceramic powders coated metal thin films were used for plasma spraying. Optimal conditions for deposition of the metal films on the particles of alumina powder (40…63µm fraction) by PVD process were obtained. Deposition of two- layer films on the powder particles was carried out. The first layer was titanium and the second layer was aluminum or copper. The titanium as adhesively-active element capable of wet alumina is necessary for increase the adhesion strength vacuum films as well as plasma sprayed coatings.

A special plasma-spray gun with external arc working in a mode of laminar plasma argon jet generation was designed. Such regime provides melting of the refractory ceramic core, saving metal films as well as localization of thermal effects during spraying process.
The results of testing coated specimens confirmed that the developed technique improves the physical and mechanical properties of the plasma sprayed composite coatings. The sprayed composite coatings were compared with coatings sprayed using pure alumina powders in terms of adhesion, wear and corrosion properties. The shear adhesion strength increases up to about 1.9 times, the wear resistance increases about 5 to 7 times, the corrosion resistance increases about 2.5 to 5 times.

The shear adhesion strength was measured at tension of coated specimen at room temperature by developed adhesion testing technique. The substrate was flat and dog-bone-shaped. The substrate with rectangular cross-section was partially coated with plasma- sprayed coating. The specimens were tested in uniaxial tension under displacement control. The tensile specimens were loaded to adhesion delamination of the coating. Sprayed coating was detached as a result of shear interface stresses.

The impact of current shape during consolidation of Fe – Ti – C – B system materials on the physio-mechanical properties of obtained specimens is studied in present paper. It is experimentally found that the use of method of decrease of voltage surge on output Schottky diodes of SPS device and the decrease of operation time of overcurrent protection in power circuit of SPS generator allowed changing current harmonic composition which lead to an increase of properties of consolidated Fe – Ti – C – B specimens – porosity decreased from 15.8 to 2.8 %, hardness increased from 50 to 55 HRC, loss of mass during abrasive wear decreased from 2 to 0.5 mass. %, and bending strength increased from 750 to 1500 MPa. It is found out that increase of input power during consolidation from 1.3 to 7.5 kJ/s by changing current harmonic composition leads to an increase of physico-mechanical characteristics of Fe – Ti – C – B system metalmatrix composites. Density of consolidated specimens increased from 75 to 95 %, their hardness increased from 35 to 50 HRC, loss of mass during abrasive wear decreased from 10 to 1 mass. % and their bending strength increased from 400 to 1100 MPa.