Increasing the wear resistance of the pump-controlled hydraulic drive units

Due to the lack of 63.5 mm balloons in Ukraine in the first layout of Hop-900 hydraulic transmission sample, the balls of the PBG company (Precision Ball and Gauge Co., England) were used. However, the trials of hydraulic transmission showed increased wear and cracks on the surface of the balls. Goal. The purpose of the work is to increase the wear resistance of the units of a pump-controlled hydraulic drive. Methodology. The coating on the TICRN ball was carried out at the Bu-Lat-3T installation. The coating modes were chosen using a methodology for mathematical planning of an experiment by evaluating microhardness of molded coating and the material use factor. Metallographic studies of the structure of the materials studied and sprayed coatings were performed on the digestive and non-digestive grinds on the MIM-8M microscope. The phase composition of the spray coatings was determined on a Don-1.5 diffractometer in monochromatic CUKα radiation. Results. Following the wear resistance of all investigated materials showed the largest wear resistance of the balls with ion-plasma coating on the surface. Originality. The tests of the samples of radial ball-piston hydraulic transmission of GOP-900 type allowed to conclude that their reliability and further improvement is largely due to the reliability of the piston ball, to which there are high requirements for wear resistance, minimum volume of force and temperature deformation. Practical value. Taking into account the negative experience of using imported steel balls from chrome steel, positive experience of using balloons from Steel SH-15CG, mastered by the production of OJSC HARP, and at the same time, the need to increase the heat resistance and wear resistance of balls should be considered as promising research when using beads from powder, rapid steels of type P6M5F3-MP, ceramic balls having high strength properties.

Study and comparison of wear behaviour of Ni-Al2O3 coatings deposited by hot and cold spray

The sliding wear of hot and cold spray nickel-alumina coatings on SA 213-T 91 boiler steel has been evaluated and compared. The investigation was conducted with pin-on-disc apparatus. The wear testing was done by varying normal loads of 30, 40, and 50N at a constant sliding velocity of 1 ms-1. Then another set of experimentation was done at different sliding velocities of 0.5, 1, and 2 ms-1 at a constant normal load of 30 N. This experimentation was designed to study the effect of varying normal loads and sliding velocities on the wear performance of coatings developed with hot and cold spray techniques. The variation of friction coefficient and wear rate with variation in normal loads and sliding velocities were plotted and analyzed. The evaluation of wear mechanisms and characteristics of Ni-Al2O3 coatings is done with the help of weight change measurements and FE-SEM analysis. The wear resistance of hot spray coatings was found better at high normal loads and sliding velocities in comparison to cold sprayed coatings.

Water-droplet erosion behavior of high-velocity oxygen-fuel-sprayed coatings for steam turbine blades

The water-droplet erosion of low-pressure steam turbine blades under wet steam environments can alter the vibration characteristics of the blade, and lead to its premature failure. Using high-velocity oxygen-fuel (HVOF) sprayed water-droplet erosion resistant coating is beneficial in preventing the erosion failure, while the erosion behavior of such coatings is still not revealed so far. Here, we examined the water-droplet erosion resistance of Cr3C2–25NiCr and WC–10Co–4Cr HVOF sprayed coatings using a pulsed water jet device with different impingement angles. Combined with microscopic characterization, indentation, and adhesion tests, we found that: (1) both of the coatings exhibited a similar three-stage erosion behavior, from the formation of discrete erosion surface cavities and continuous grooves to the broadening and deepening of the groove, (2) the erosion rate accelerates with the increasing impingement angle of the water jet; besides, the impingement angle had a nonlinear effect on the cumulative mass loss, and 30° sample exhibited the smallest mass loss per unit area (3) an improvement in the interfacial adhesion strength, fracture toughness, and hardness of the coating enhanced the water-droplet erosion resistance. These results provide guidance pertaining to the engineering application of water erosion protective coatings on steam turbine blades.

Influence of heat treatment on surface properties of HVOF deposited WC and Ni-based powder coatings: A review

Post-spray treatments have recently been popular as a means of improving the overall quality of thermally sprayed coatings, particularly those done using the HVOF technique. Thermally assisted surface treatment of deposited coatings is an effective way to improve the characteristics of coated components for specific applications. The tribomechanical properties of post-treated WC and Ni-based coatings deposited with high-velocity oxy-fuel (HVOF) technique have been addressed. The structure-property correlations concerning the as-sprayed and post-treated coatings have been considered to understand the various mechanisms responsible for improved performance in terms of wear and corrosion resistance. The recent advancement in the post-treatments such as post-processing using microwave hybrid heating, laser-assisted processing and Stationary friction processing have been incorporated in the current review. Comparative studies have been presented to understand the structure-property relationship and performance of WC and Ni-based HVOF sprayed coatings with the help of various characterization techniques in this review article.

Effect of Laser Processing Parameters on Microstructure, Hardness and Tribology of NiCrCoFeCBSi/WC Coatings

In the present study, pulsed laser post-processing was applied to improve the properties of the thermally sprayed NiCrCoFeCBSi/40 wt.% WC coatings. The powder mix was deposited onto a mild steel substrate by flame spray method and then the as-sprayed coatings were processed by Nd:YAG laser. The peak power density applied was between 4.00 × 106 and 5.71 × 106 W/cm2, and the laser operating speed ranged between 100 and 400 mm/min, providing processing in a melting mode. Scanning electron microscopy, energy dispersive spectroscopy, Knop hardness measurements, and “ball-on-disc” dry friction tests were applied to study the effect of the processing parameters on the geometry of laser pass and microstructure, hardness, and tribology of the processed layers. The results obtained revealed that pulsed laser processing provides a monolithic remelted coating layer with the microstructure of ultrafine, W-rich dendrites in Ni-based matrix, where size and distribution of W-rich dendrites periodically vary across remelted layer depth. The composition of W-rich dendrites can be attributed to a carbide of type (W, Cr, Ni, Fe)C. The cracks sensitivity of coatings was visibly reduced with the reduction of power density applied. The hardness of coatings was between ~1070 and ~1140 HK0.2 and correlated with microstructure size, being dependent on the processing parameters. The friction coefficient and wear rate of coatings during dry sliding were reduced by up to ~30% and up to ~2.4 times, respectively, after laser processing.

FORMATION OF FUNCTIONAL PLASMA SPRAYED COATINGS WITH COMPLEX OF IMPROVED PHYSICAL, MECHANICAL AND OPERATIONAL PROPERTIES

The possibility of increasing the complex of physical, mechanical and operational properties of plasma sprayed coatings from powders of the PG-19M-01 and PRH18N9 grades due to the electric pulse effect on the heterophase high-temperature flow during spraying and next surface plastic deformation of the deposited coatings by shot blasting has been investigated. It is shown that shot blasting provides the formation of a hardening layer with a thickness of up to 180...200 μm, while the maximum level of microhardness is observed at a depth of about 60 μm. The microhardness of the coating from PG-19M-01 powder at the point of maximum hardening increases by 35%; steel coatings from PR-H18N9 powder – by 48% compared to the state after spraying. Experimental studies of the effect of this treatment on the bond strength and wear resistance of the obtained coatings have been carried out. It is shown that after shot-blasting the bond strength of the coatings decreases by 10...15%, and the wear resistance increases by 32...38%.