Influence of Spray Parameters on the Thickness, Hardness and Porosity of low-pressure Cold Sprayed WC-Ni Coatings

In this study, a 33 full factorial design methodology was used ­­to analyze the effects of spray parameters on the thickness, hardness, and surface porosity of low-pressure cold-sprayed WC-17Ni coatings. Three levels were selected for the spray parameters included in the design which were the powder feed rate (17.1 g/min, 21.1 g/min, and 23.7 g/min), gas temperature (475℃, 500℃, and 525℃), and the nozzle to substrate stand-off distance (3 mm, 5 mm, and 10 mm). It was found that the feed rate was the most significant parameter that affected the coating thickness. The surface porosity was most significantly affected by stand-off distance. The coating hardness was most influenced by the interaction between the feed rate and stand-off distance. An optimization study was then performed to maximize the coating thickness and hardness while minimizing the surface porosity. The optimal spray parameters (OSP) were found to be at a feed rate of 23.7 g/min, 500℃ for the carrier gas temperature, and 10 mm for the stand-off distance. The OSP yielded a coating that was 1.22 ± 0.06 mm thick, with a hardness of 364.5 ± 8.5 HV and porosity of 6.8 ± 0.6%. With a multi-parameter process, the system response is affected by both the variation in the individual parameters and the interaction of the parameters with each other. It was also concluded that the interaction between the parameters significantly affected the coating hardness. These results suggest that variation of the selected parameters produce statistically significant effects on the coating quality of WC-17Ni coatings using a low-pressure cold spray system.

Analysis of the Influence of Different Parameters on Droplet Characteristics and Droplet Size Classification Categories for Air Induction Nozzle

Droplet characteristics are identified as essential factors in agricultural spray application. The aims of this study were to analyse the influence of spray parameters on droplet characteristics and to determine possible candidate sprays that would produce the same droplet size categorizations as the American Society of Agricultural and Biological Engineers (ASABE) standard S-572.1 for air induction nozzles (AINs). Six different orifice sizes of the Billericay Farm Services (BFS) air induction (AI) flat fan hydraulic nozzles (the air bubblejet) were examined at different spray pressures (200 kPa, 300 kPa, 400 kPa, 500 kPa, 600 kPa and 700 kPa) and concurrent air velocities (2 m/s, 3 m/s, 4 m/s and 5 m/s). The influences of spray parameters on the droplet characteristics were analysed using analysis of covariance (ANCOVA) and analysis of variance (ANOVA). Results showed that: (1) The values of droplet characteristics and the results of ANOVA were significantly different before and after eliminate the influence of dynamic surface tension (DST) on droplet characteristics by ANCOVA; (2) (a) the reduction rates of the droplet diameter sizes decreased with increasing spray pressure; (b) air velocities of 2 m/s and 5 m/s resulted in smaller droplets reports, and air velocities of 3 m/s and 4 m/s are more suitable for agricultural spray applications; (c) a larger nozzle orifice size not always result in a larger droplet size and (3) Fine, Medium, Coarse, Very Coarse and Extremely Coarse droplet classification categories as the ASABE S-572.1 standard categorizations were determined to classify AINs.

THE INFLUENCE OF THERMAL SPRAY PROCESS TECHNOLOGICAL PARAMETERS ON THE PROPERTIES OF COATINGS / TERMINIO PURŠKIMO TECHNOLOGINIŲ PARAMETRŲ POVEIKIS DANGŲ SAVYBĖMS

The article deals with the plasma sprayed Ni-based coating on aluminum alloy substrates. Before spraying, the surfaces of substrates were modified employing sandblasting and its combination with preheating. The coatings were sprayed under variation of spray process parameters. The study involves coating microstructure, porosity and adhesion tests. The influence of spray parameters and substrate pre-treatment on the properties of coating were evaluated. Straipsnyje nagrinėjamos plazminio purškimo būdu ant aliuminio lydinio substrato užpurkštos Ni pagrindo dangos. Substrato paviršius prieš purškimą buvo apdorotas smėliavimo būdu, taip pat ir pakaitinant substratą iki 150 °C temperatūros. Naudojant skirtingus plazminio purškimo proceso parametrus, buvo užpurkštos nikelio-aliuminio dangos. Darbe ištirta gautų dangų mikrostruktūra, akytumas ir adhezijos stipris. Įvertintas plazminio purškimo parametrų ir substrato paruošimo poveikis gautų dangų savybėms.

Influence of Spray Parameters on Sliding Wear Properties of HVOF Sprayed Fe-Based Amorphous Coatings

Amorphous powders of Fe-10.7%W-4.5%Cr-4.1%B-3.6%Ni-3.5%Si-2.1%Mo-1.2%C-0.7%Mn were sprayed under six sets of spraying parameters using high velocity oxy-fuel spraying. Phase structure of coatings as well as microstructure is found to be strongly affected by spraying parameters. Sliding wear resistance of amorphous coatings benefits significantly from less porosity and oxides. In addition, evidence correlation is found between amorphous content and wear resistance of coatings. Coating with the best wear resistance exhibits the wear rate of only 2.84×10-6 mm3/(N·m), equals 1.70% and 217% of cast 316L stainless and HVOF-sprayed Cr3C2-NiCr coating respectively.

Plasma Spraying and Characterization of Tungsten Carbide-Cobalt Coatings by the Water-Stabilized System WSP

Tungsten carbide-cobalt powders (WC-17wt% Co) were plasma sprayed by a water-stabilized system WSP. Experiments with variable feeding distances and spray distances were carried out. Thinner coatings were deposited on carbon steel substrates and thicker coatings on stainless steel substrates to compare different cooling conditions. Basic characterization of coatings was done by XRD, SEM, and light microscopy plus image analysis. Microhardness was measured on polished cross-sections. The main focus of investigation was resistance against wear in dry as well as wet conditions. The appropriate tests were performed with set-ups based on ASTM G65 and G75, respectively. The influence of spray parameters onto coating wear performance was observed. The results of mechanical tests were discussed in connection with changes of phase composition and with the quality of the coating's microstructure. The results show that for obtaining the best possible WC-17Co coating with WSP process, from the viewpoint of wear resistance, the desired parameters combination is long feeding distance combined with short spray distance.

Influence of the Spray Parameters on the Transient Pressure within a Molten Particle Impacting onto a Flat Substrate

This paper is devoted to the investigation of the transient pressure occurring at the impact of a molten particle onto a flat substrate surface under different thermal spray conditions. In this paper, the mathematical model developed is based on the following assumptions: laminar, viscous and incompressible fluid; the mixed velocity-pressure model is employed to construct the finite element model. The choice of pressure penalty coefficient, which depends on the Reynolds number, is crucial for the results. This is discussed in this paper. The numerical results show that the pressure at the particle-substrate interface is strongly affected by the processing parameters, especially by the particle density and the impact velocity. The influence of spray parameters and material properties are also discussed.