Splat Morphology Research Articles

Effect of splat morphology on the microstructure and dielectric properties of plasma sprayed barium titanate films

In the thermal spray process, the film is built up by impingement of molten droplets onto substrate. Splats are created by flattening and spreading of the impacting droplets. Splat morphology can determine the microstructure, physical and mechanical properties of the coating. In this study, BaTiO3 films were deposited onto a mirror polished stainless steel substrates kept at three different temperatures (25, 300 and 600°C). At the elevated temperatures, the substrate surface topography and the desorbtion of adsorbates and condensate at the substrate surface are two important factors which change the morphology of the individual splats, from splash morphology to disk-like shape. Splat morphology can determine deposit microstructure and improve the coating properties. The morphology of individual splats and the films were studied using scanning electron microscopy. Phase formation of the films was analyzed by X-ray diffraction. The surface topography of the substrates with different temperatures was analyzed using atomic force microscopy. Furthermore, X-ray photoelectron spectroscopy was performed to determine the chemical compositions of the surface substrate. Results indicated that the porosity in the film produced at room temperature was higher than that in the film deposited on the heated substrates. Also, the dielectric coefficient of the films was increased by decreasing the common defects from 120 to 505 for film deposited on as-received and heated substrates, respectively.

Effect of dry-ice blasting on the deposition behavior of molybdenum particles onto aluminum and stainless steel substrates using plasma spraying: From single splat to coating

Molybdenum splats usually exhibit splitting morphology onto aluminum and stainless steel substrates due to substrate melting and their own high surface tension using plasma spraying. In this study, Mo particles were sprayed onto different substrates, which were treated by dry-ice blasting combined with substrate preheating. The splats were studied using detailed microstructural characterization with an emphasis on the splat shape. Moreover, the corresponding Mo coatings deposited onto different substrates were obtained. The results showed that the splitting splat formed on stainless steel was different from that on the aluminum surface. Dry-ice blasting combined with substrate preheating slightly modify the morphology of Mo splat sprayed on aluminum and stainless steel surfaces.

Modeling the impact, flattening and solidification of a molten droplet on a solid substrate during plasma spraying

It is quite important to clearly understand the dynamic process of single splat formation for optimizing the plasma spraying process. In present study, a three-dimensional model including heat transfer and phase change was developed on Ansys Fluent 14 platform to simulate the impact, flattening and solidification of a molten droplet on a solid substrate during plasma spraying. The phase, contact pressure, temperature and velocity fields at different spreading times were presented to gain an insight into splat formation mechanism. The predicted splat morphology was in good agreement with the experimental photos. The effect of mushy zone constant, a parameter dominating the solidification behavior of fluid in Fluent, on the flattening of droplet was further investigated. Through comparing the calculated spread factor from present model with the experimental value, a mushy zone constant of 108 or 109 was found to be more appropriate for simulation on the solidification problem occurring in high-speed impact and flattening process, instead of the range of 104–107 recommended in Fluent.

Feasibility of suspension spraying of yttria-stabilized zirconia with water-stabilized plasma torch

Thermal spraying of suspensions allows preparation of coatings from submicron-sized powders but demands a source of heat with a high enthalpy in order to provide an appropriate thermal treatment of the liquid feedstock during the in-flight stage so that the solvent may be evaporated, dispersed particles melted and accelerated towards the substrate to form a coating. Water-stabilized plasma (WSP) torch developed at the Institute of Plasma Physics AS CR, v.v.i. provides such a heat source with high enthalpy, high velocity of the plasma and, when compared to high-enthalpy gas-stabilized plasma (GSP) torches, relatively cheap operation. In this study, results of our experiments with suspension spraying of yttria-stabilized zirconia (YSZ) with WSP torch are presented and demonstrate that coating deposition with a high feed rate is possible with WSP technology. Formation of both columnar “cauliflower” microstructure and segmentation cracks was achieved. Variation of the deposition conditions was observed to modify coating microstructure in terms of splat morphology, porosity and thickness per pass, which is promising for further coating development.

Deposition Behavior of Semi-Molten Spray Particles During Flame Spraying of Porous Metal Alloy

Porous 316L stainless steel deposits were fabricated by flame spraying semi-molten particles with different melting degrees and spray angles to understand the deposition behavior of semi-molten spray particles. The effects of spray angle relative on the deposition efficiency and deposit porosity were investigated. The morphology of individual splats deposited on flat surface at different angles was examined. The results show that the spray angle had a significant influence on the deposit porosity, pore structure, and deposition efficiency. The slipping of solid core in semi-molten spray particle was clearly observed when semi-molten particles impacted on the polished substrate with an inclined angle. A random model was proposed to simulate the process of particle deposition. It was found that after considering the effects of both solid particle slipping upon impact and particle melting degree, the porosity calculated by simulation with the model agreed well with the experimental observation.

The Effect of CFRP Surface Treatment on the Splat Morphology and Coating Adhesion Strength

Metallization of Carbon Fiber-Reinforced Polymer (CFRP) composites aggrandized their application to aircraft, automobile, and wind power industries. Recently, the metallization of CFRP surface using thermal spray technique, especially the cold spray, a solid state deposition technique, is a topic of research. However, a direct cold spray deposition on the CFRP substrate often imposes severe erosion on the surface owing to the high-impact energy of the sprayed particles. This urges the requirement of an interlayer on the CFRP surface. In the present study, the effect of surface treatment on the interlayer adhesion strength is evaluated. The CFRP samples were initially treated mechanically, chemically, and thermally and then an interlayer was developed by atmospheric plasma spray system. The quality of the coating is highly dependent on the splat taxonomy; therefore the present work also devoted to study the splat formation behavior using the splat-collection experiments, where the molten Cu particles impinged on the treated CFRP substrates. These results were correlated with the coating adhesion strength. The coating adhesion strength was measured by pull-out test. The results showed that the surface treatment, particularly the chemical treatment, was fairly successful in improving the adhesion strength.

Surface modification of air plasma spraying WC–12%Co cermet coating by laser melting technique

Abstract Tungsten carbide cermet powder with 12%Co was deposited on stainless steel substrate by air plasma spraying method. Two types of coatings were produced i.e. thick (430 µm) and thin (260 µm) with varying porosity and splat morphology. The coated samples were treated with CO2 laser under the shroud of inert atmosphere. A series of experimentation was done in this regard, to optimize the laser parameters. The plasma sprayed coated surfaces were then laser treated on the same parameters. After laser melting the treated surfaces were characterized and compared with as-sprayed surfaces. It was observed that the thickness of the sprayed coatings affected the melt depth and the achieved microstructures. It was noted that phases like Co3W3C, Co3W9C4 and W were formed during the laser melting in both samples. The increase in hardness was attributed to the formation of these phases.

Analysis of EMAA Splats on Glass and Mild Steel Substrates

Thermal spray coatings are composed of millions of heated particles driven at high velocities onto a substrate, thereby building up and forming a consolidated coating. Thus, investigating single solidified droplets contributes to the fundamental understanding of the evolution of a surface coating and its properties. In this study, the single splat morphology and thermal characteristics of flame-sprayed ethylene methacrylic acid (EMAA) splats, deposited at various stand-off distances onto glass and mild steel substrates, are investigated using scanning electron microscopy, differential scanning calorimetry, and thermal gravimetric analysis. This study indicates that the microstructure of EMAA coatings can be controlled by judicially selecting the thermal spray parameters rather than by using the trial and error methods that are often used at present.

Ethylene Methacrylic Acid (EMAA) Single Splat Morphology

A single splat is the building block of a thermal spray coating; thus, investigating single splats is essential to understanding thermal spray coatings and their properties. In this study, the morphology of flame sprayed ethylene methacrylic acid (EMAA) splats, deposited at various stand-off distances (SODs) onto glass and mild steel substrates were investigated using a scanning electron microscope, Leica M Stereo-microscope, the WYKO surface profiler and the ContourGT surface profiler. This work analyzed the effect of the process variables on EMAA splat morphology. The modeling of the temperature versus velocity (TV) map, the temperature versus stand-off distance (TS) map and the velocity versus stand-off distance (VS) map of EMAA single splat were presented.

Influence of Parameter Variations on WC-Co Splat Formation in an HVOF Process Using a New Beam-Shutter Device

The formation of single splats is the foundation for any thermal spray coating. Therefore, this study focuses on the investigation of single splat morphologies to determine the influence of spray parameters on the morphological distribution of particles inside the flame. A new method to create a footprint of a spray jet with an extremely short exposure time was used. The resulting field of splats enabled the assignment of each splat to its radial position in the spray jet. The footprints were analyzed and the quantities and morphologies of the splats were correlated to particle in-flight measurements and coating properties. A strong correlation between the particle velocity, the percentage of the so-called pancake-like splats, and the porosity of the coating could be revealed. The influence of the particle temperature was found to be of minor importance to the splat form and the porosity of the coatings. Still, the particle temperature had a good correlation with the coating hardness and the dissolving of the WC. Measurements of the splat size in different areas of the footprints revealed that the percentage of splats larger than 40 μm in diameter was generally higher in the center of the footprint than in the outer regions.

NiTi Splat Features during Vacuum Thermal Spraying onto Several Substrates

Vacuum Plasma Spraying has been used to produce coatings onto steel substrates. This work deals with the study of splat morphology of the NiTi alloy sprayed by VPS onto different substrates (aluminium, copper, stainless steel, glass and alumina). All the previous characteristics are discussed in terms of wettability and thermal conductivities regarding the rapid cooling involved in the process. Although identical conditions were used during thermal spraying, a wide variety of splat formations were observed; commonly, slushy or splash/disc splats are formed depending on whether the particles have partially or fully melted. The thermal effusivity of the substrate material, which is a measure of its ability to exchange thermal energy with its surroundings, seems to play an important role promoting more or less spreading. The higher the thermal effusivity is, the more rapidly the splats are cooled, thus starting the solidification before they come to rest and, changing their morphology.

Study on the Mechanism of Adhesion Improvement Using Dry-Ice Blasting for Plasma-Sprayed Al2O3 Coatings

The mechanisms of adhesion improvement of plasma-sprayed Al2O3 coatings using dry-ice blasting were investigated. In this study, the change of substrate surface characteristics in both the topography and the wettability due to the treatment of dry-ice blasting was mainly studied. The effect of dry-ice blasting on Al2O3 splat morphology with different treatment durations was also examined. The residual stress of plasma-sprayed Al2O3 coatings using dry-ice blasting was measured by curvature method and compared to that of coatings deposited with conventional air cooling. Based on these numerous assessment tests, it could be concluded that the adhesion improvement of Al2O3 coatings could be attributed to the cleaning effect of dry-ice blasting on different organic substances adsorbed on the substrates and the peening effect.

Role of substrate temperature on microstructure formation in plasma-sprayed splats

The flattening nature of the individual splat in thermal spraying is the fundamental process for the coating fabrication process, thus numerous studies have been conducted to understand the splat formation process in thermal spraying. In the present investigation, commercially available pure Cu particles with diameter of several tens of micrometers were thermally sprayed onto mirror polished AISI304 substrates held at various temperatures during the spraying. The top surface, bottom surface, and cross section morphologies of splats collected under designated conditions were observed in detail. According to the observation, different splat microstructures could be found varied with the substrate temperatures. In particular, a typical layer composed of fine grains could be found at splat–substrate interface when the substrate was held at high temperature, which has a close relation with the favorable wetting and enhanced heat transfer from molten droplet to substrate. This layer could induce the rapid decrease of droplet viscosity at the bottom surface and prevent the further spreading of the splat, which promoted the formation of disk-shaped splat.

Fabrication and properties of supersonic plasma sprayed Al2O3 coating on porous Si3N4 substrate

A dense Al2O3 coating was directly deposited on porous Si3N4 substrate by supersonic plasma spraying. The microstructure and interface bonding of supersonic plasma sprayed Al2O3 coating were investigated. The surface of coating displayed explicit splat morphologies with densely packed splats. The molten Al2O3 droplets infiltrated into the inner pores of porous Si3N4, and formed an intermediate layer with rod-like Si3N4 particles at the interface. As-received Al2O3 coating sealed the surface pores of porous Si3N4, and decreased the water absorption of porous Si3N4 obviously from 42.1% to 5.2%, but only with a slight decrease of the total porosity. The mechanical properties of porous Si3N4 were also improved due to Al2O3 coating. The flexural strength of porous Si3N4 increased slightly from 93.7±3.1 to 97.5±3.4MPa, although it decreased obviously at the beginning of spraying due to mechanical erosion of Al2O3 droplets. The Vickers hardness of porous Si3N4 increased gradually from 465±20 to 1023±16MPa with the deposition content of Al2O3 increasing.

Spreading Behavior and Morphology of Ethylene Methacrylic Acid (EMAA) Deposits via the Flame Spray Process

A single splat is the building block of a thermal spray coating; thus, investigating single splats is essential to understanding thermal spray coatings and their properties. In this study, the spreading behavior and the morphology of flame sprayed ethylene methacrylic acid (EMAA) splats, deposited at various stand-off distances (SODs) onto glass and mild steel substrates were investigated using optical microscopy, back scattered scanning electron microscopy and secondary electron scanning electron microscopy. The results of this study indicate that the spread factor increases with an increase in the stand-off distance up to 30 cm for glass and 25 cm for steel substrates. Further increase of the stand-off distance results in a decreased spread factor. The aspect ratio of EMAA single splats on both glass and mild steel substrates decreases with increased stand-off distances, indicating that more circular shapes occur at higher stand-off distances. On mild steel substrates, the minimum unevenness ratio (η) occurs at 35 cm SOD. The unevenness ratio (η) on glass substrates decreases from 1.9 (at 20 cm SOD) to 1.77 (at 25 cm SOD), and from 1.8 (at 30 cm SOD) to 1.3 (at 35 cm SOD). The lowest unevenness ratio (η) is found at 35 cm SOD. The highest unevenness ratio (η) is at 25 cm SOD. This paper discusses the effect of surface chemistry on the underside of an EMAA single splat morphology. It includes Raman spectrum analysis of EMAA and the X-ray diffraction of the EMAA powder. This work analyses the splat morphology and classifies the taxonomy of single splats of EMAA.

Plasma Sprayed Alumina Coating on Ti6Al4V Alloy for Orthopaedic Implants: Microstructure and Phase Analysis

Alumina was coated on Ti6Al4V alloy by atmospheric plasma spraying. Surface and cross sectional analysis of the coating by SEM showed that diameter and thickness of splat was greatly influenced by arc current and stand-off distance. In turn, this variation in splat morphology had effect on evolution of α-Al2O3 and γ-Al2O3 phases as revealed by XRD. Higher proportion of required γ-Al2O3 phase was achieved at stand-off distance of 130 mm and arc current of 500A.

Effect of Thermal Treatment on Nano-Crystallites and Phase Transformation of CaZrO<sub>3</sub>Thermal Barrier Coatings

Thermal barrier coatings (TBCs) are multilayered coatings having the complex structure. In thermal spray coatings characteristic features of deposited molten particle and its microstructure is very important in defining coating properties. In this work stainless steel (AISI 316) was used as substrate material on which bond coat of Ni-20Cr and top coat of CaZrO3 were deposited by air plasma spraying method. Effect of isothermal treatment on the internal microstructure structure of lamella (splat) and phase changes in CaZrO3 coating was studied. The fractured surface of coatings was investigated to observe the splat morphology. It was observed that the nanocrystallites present within the splat grew with increase in temperature. Further, the monoclinic phase was formed as function of temperature and time.

Role of nanocrystalline feedstock in the tribological behaviour of alumina coatings deposited by detonation gun

Alumina coatings were prepared using detonation gun from commercial powder (CP) and high energy ball milled powder (MP) with 83nm crystallite size. The sliding wear rate and wear coefficient of friction were lower in the nanocrystalline powder coating. The coating from the as-received commercial powder consisted of thick splats, and a paucity of nanoparticulate inter-splat regions whereas milled powder coating has thinner splat morphology with nanoparticulate inter-splat regions. The nanoparticulate material in the inter-splat regions and the finer microstructure of the MP coating is believed to be responsible for improved wear resistance.

니켈기 용사코팅의 스플랫 형성에 관한 연구

Thermal spray coatings developed by deposition of splats, it formed by impacting molten droplets on substrates during thermal spray process. In this study, the Ni-based coatings were fabricated by thermal spray process with two different process parameters, oxygen gas flow and acetylene gas flow, with three different levels of each parameters. The morphology of splats and microstructure were observed by optical microscope. Hardness test were performed on the Ni-based coatings. It was confirmed that process parameters of thermal spray process have effect in morphology of splats. These effects also have important implications on the deposit microstructure and properties of Ni-based coatings.

Influence of Substrate Temperature on Structure and Adhesion Strength of Fe–Cr–P–C Amorphous Coating Films Produced by Thermal Spraying Technique

The influence of the substrate temperature on the structure, the pore distribution, and the adhesion strength of Fe-10Cr-based amorphous coating films has been examined. The amorphous coating films have been produced by a thermal spraying technique using our developed cylindrical nozzle on SS400 substrates. The splat morphology of the sprayed particles changed drastically from an irregular splash shape to a disk shape at a transition temperature of about 325°C. When the substrate temperature increased to the transition temperature region, between 325 and 350°C, the porosity in the boundary regions between the sprayed coating films and the substrates drastically decreased to about 6%, which may be due to the drastic increase in the wettability of the sprayed particles accompanied with the change of morphology from the splashed shape to the disk shape. When the substrate temperature increased from the transition temperature of 325°C up to 400°C, the porosity decreased gradually, and the volume fraction of the amorphous phase increased with increasing substrate temperature, resulting in an increase in the adhesion strength up to about 15MPa. [doi:10.2320/matertrans.M2011261]