Acquisition of a new LVPS and APS coating system at Delta Air Lines necessitated optimization of the coating parameters on both systems, especially for application of bond coat (LVPS) and top coat (APS) for a TBC coating system. To expedite the coating optimization, it was determined that a design of experiments (DOE) approach would best enable the establishment of the operating window for the two systems. Samples prepared were primarily evaluated for their performance while exposed to a cyclic oxidation cycle. Samples were also evaluated for the microstructure and composition using energy dispersive spectroscopy (EDS) analysis. Samples from the ceramic coating DOE were also evaluated for their erosion characteristics. Results indicate a low correlation between the individual bond coat parameters evaluated to the furnace cycle life. However, the top coat spray parameters were found to have a greater correlation to furnace cycle life and erosion performance.

In this work, a novel liquid fuel HVOF process fueled with ethanol was used to prepare 75wt%Cr 3 C 2 –25wt%NiCr coatings on AISI304 stainless steel substrate. Taguchi method was employed to optimize the spray parameters (ethanol flow rate, oxygen flow rate, powder feed rate and standoff distance) to achieve better erosion resistance at 90° impact angle. The results indicated that ethanol flow rate and oxygen flow rate were identified as the highly contributing parameters on the erosion wear loss. The important sequence of the spray parameter is ethanol flow rate > oxygen flow rate > standoff distance > powder feed rate. The optimal spray parameter (OSP) for minimum erosion wear loss was obtained under ethanol flow rate of 28slph, oxygen flow rate of 420slpm, powder feed rate of 76.7 g/min and standoff distance of 300mm. The phase composition, microstructure, hardness, porosities, and the erosion wear behaviors of the coatings have been studied in detail. Besides, erosion wear testing of the optimized coating was conducted at 30°, 60° and 90° impact angle using air jet erosion testing machine. The SEM images of the erodent samples were taken to analyze the erosion mechanism.

This study assesses the erosive wear performance of hard-phase-reinforced coatings developed for use on hammer drills employed in mining operations. Several laser-clad coatings consisting of a nickel matrix with various tungsten carbides were evaluated along with two Fe-based alloys, FeCrBSi and FeCrNiBSi, and a WC-CoCr reference layer deposited by HVOF spraying. Erosion tests were conducted in 15° steps up to an angle of 90° and coating performance was determined based on volume loss obtained by 3D profilometry. At low angles, the more brittle materials lost significantly less volume, but at 90°, wear-resistant steel performs almost as well as a hard-phase loaded coating. Laser-clad layers with spherical fused tungsten carbides (FTC) performed better overall than coatings with regular (angular) FTC.

This study investigates the cavitation erosion (CE) behavior and fracture morphology of tungsten carbide thermal spray coatings. WC-CoCr and WC-CrC-Ni powders of various sizes were deposited on stainless steel substrates by HVOF spraying using different combustion pressures. Coating samples and Cr steel reference specimens were subjected to vibratory cavitation erosion tests, volume loss was measured, and erosion damages were examined by SEM to assess fracture morphology. The results indicate that CE resistance can be improved by reducing porosity and increasing interparticle bonding strength.

One of the economical and fast solutions for failure against erosive wear in oil and gas industries is the deposition of cermets using HVOF thermal spray. Recently, especially with the new development of bimodal feedstock powders, the composition percentages of the mixed powders have played a key factor in the final coating performance. In the present study, a design of experiment (DOE) software was implemented to study the influence of different powder percentages on the coating performance. The coating mechanical properties and its performance were investigated via dry solid particle erosion tests, hardness measurement and SEM respectively. The results showed that both the hardness and erosion resistance of the coating increases as the composition percentage of the nanostructured WC-12Co increased due to the strong adhesion of WC nano size grains at the substrate/coating interface as a result of improved mechanical interlocking.

HVOF and HVAF deposited coatings of three commercial Fe-based powder alloys have been ranked according to ASTM G76 solid particle erosion testing. The reference was electrolytic hard chrome (EHC) plating. The test results at 30 m/s abrasive particle velocity showed that 6AB powder alloy, when HVAF sprayed, Fe SP586 when both HVOF and HVAF sprayed meet the EHC plating reference erosion rate. 6AB HVOF sprayed and Fe SP529 both HVOF and HVAF sprayed powder alloys achieved two to three times higher erosion rate but were still at the same level of magnitude as the EHC plating reference.

High quality coatings of titanium can be obtained by cold spraying using high process gas temperatures and pressures. However, the performance of cold sprayed coatings is determined not only by the respective material properties and the impact conditions, but also by the temperature and properties of the substrate—including the already deposited— material. In the present study, cold spray of spherical titanium grade II powders was performed on titanium grade II, copper, and stainless steel substrates, using two sets of parameters and three different substrate temperatures. Single impacts and respective particle adhesion were investigated using wipe tests followed by a modified cavitation test. Higher bond strengths were achieved for substrates that were held at higher temperatures during spraying. Moreover, the electrical conductivity of coating, taken as a measure of particle-particle bonding quality within the coating, improved and the porosity decreased for increased substrate temperatures. The findings are discussed in view of the thermal conditions, as well as the mechanical response of the uppermost layer of the substrate/deposit set.

Cavitation erosion is a common phenomenon that occurs in hydraulic turbine blades and result in mass loss. Welding is the most common technique used to recover the geometrical profile of these cavitation eroded turbine blades, however it is known that tensile residual stress can develop. The development of manufacture process that could reduce or eliminate the residual stress level will contribute for a longer service life of this component. It is aimed in this study evaluate cavitation erosion mechanism of Fe- Mn-Cr-Si-Ni arc thermally sprayed coating. Coatings were analyzed by optical and scanning electronic microscopy, microhardness, cavitation tests (ASTMG32-92) and the analysis of eroded surface areas after ultrasonic cavitation tests with DRX and SEM. The results showed that lamellae morphology, oxide volume fraction and porosity modified by changings in parameters deposition, modified cavitation mass loss mechanisms. After ultrasonic cavitation tests, it was verified that mass loss occurred by interlamellae oxide removal and splats surface deformation in initial stages, followed by rupture and finally detachment of the lamellae. Splashing droplets promote greater mass loss in some localized areas because they lower intersplat cohesion.

WC-Co thermal sprayed coatings are mainly used for wear protecting functions in various industries, for which high velocity oxy fuel (HVOF) spray is considered to be the best suited process. However, WC-Co HVOF coatings still have some defects as compared with sintered bulk, such as decarburization of WC and porous structure. Recently, experiments of WC-Co coatings using warm spray (WS) and cold spray processes have demonstrated some improvements in reduction of these defects. In particular, WS process seems to be a more promising process for WC-Co coatings from the previous work. In this study, wear resistant functions of WC-12%Co coatings prepared by HVOF and WS were investigated by abrasion and erosion tests. In addition, in-flight particles were captured and their characteristics such as the amount of decarburization, crystal phase, particle strength and particle size distribution were investigated to clarify the difference between HVOF and WS processes. The result shows that the wear resistances of the WC-Co WS coatings are comparable or superior to those of the HVOF coatings, which can be attributed to the difference in the amount of W 2 C and coatings porosity revealed by the in-flight particles and the coating microstructure. The result of the in-flight particle analysis also indicates that wear resistance of WS coatings can be further improved by optimizing the powder shape and chemical composition.

Damage of marine screw propeller parts made of aluminum bronze cast material caused by cavitation erosion is one of the serious problems. Erosion resistant thermal spray coating on aluminum-bronze material is expected to extend lifetime of such propellers. In this study, Cobalt-based alloy coatings sprayed by; (a) atmospheric plasma spraying (APS), (b) low pressure plasma spraying (LPPS) and (c) high velocity oxy-fuel (HVOF) spraying and aluminum bronze cast material were evaluated by cavitation erosion test using magnetostrictive cavitation test equipment. Fracture morphology of cavitation eroded coating surfaces were analyzed by surface observations with SEM and also the amount of volume loss was measured. Cobalt-based alloy coatings sprayed by LPPS exhibited superior cavitation erosion resistance compared to aluminum bronze cast material and coatings by APS and HVOF. Moreover, mechanical properties of Cobalt-based alloy coatings were investigated in detail by nanoindentation technique. It is found that cavitation erosion resistance of coatings is subjected to interparticle cohesive strength.

WC-Co cermet coatings were fabricated by using Warm Spraying, which is a modification of HVOF spraying to lower the temperature of the propellant gas below the melting point of Co. By changing the processing parameters, specimens were prepared for hardness, abrasion wear and particle erosion tests. Their microstructures were examined by SEM and XRD. The microstructure clearly showed the effects of suppression of the dissolution of WC into the Co phase, which is the major cause of embrittlement of the conventional HVOF sprayed WC-Co coatings. By combinations of adequate feedstock powder and processing parameters, it was possible to take advantage of fine WC grain size to prepare coatings with higher hardness (HV > 1400), smoother surface (Ra < 2 μm), and moderately improved wear performances compared with conventional HVOF coatings.

In this present work, WC-Co coatings with different Co contents were deposited by warm spraying using two different powder sizes and their microstructure, hardness, fracture resistance, and wear properties were investigated. The coatings produced from fine powders showed higher hardness and better wear behavior for all Co contents than those deposited from coarse powders, which is attributed to improved splat-splat bonding and a reduction in porosity that comes with using fine powder.

Erosion-resistant coatings on high-temperature polymer matrix composites are of great interest for turbine blade applications. This study evaluates the erosion resistance of thermal spray coatings using conventional weight loss methods in order to compute net erosion volume loss and assess thermal cycling durability. During erosion tests, coated polymer composite coupons were subjected to runway sand and aluminum oxide erodent at different temperatures and angles of incidence. Erosion test data are reported along with the results of coated polymer matrix composite blades.

The cavitation erosion result mass loss. Welding is the most common technique used to recover the geometrical profile of the blades. However it is known that tensile residual stress can develop. The search for manufacture process that could reduce or eliminate the residual stress level will contribute for a longer life service. The target in this study to evaluate the potential of ASP thermal spray to recover surfaces. The influence of processing parameters on the cavitation resistance and mechanisms was evaluated for three alloys, AWS309LT1, AWS410NiMo and a Co stainless steel known as Cavitec. Coatings were analyzed by optical and electronic microscopy, microhardness and cavitation tests regarding the effect of air pressure. The results showed that lamellae morphology, oxide volume fraction and cavitation resistance were modified by the ASP parameters. The increase in the pressure modified the oxide fraction from 26 to 37% in AWSI309LT1, 23 to 31% for AWS410NiMo and 16 to 23% for Cavitec. Mass loss varied from 3.5 to 4.8 mg/h for AWSI309LT1, 6.65 to 18.19 mg/h for AWS410NiMo, and 3.4 to 4.0 mg/h for Cavitec; the best performance occurred with Cavitec and was associated with higher pressure of deposition and minor oxide volume fraction.

A simulated environment erosion test platform consisting of a control chamber, a modified HVOF gun, and a programmable logic control module is presented. This robust equipment can vary angles of impingement from 0-90 degrees, erodent velocities up to 300 m/s, and temperatures exceeding 2000°C. The erodent velocity, flow rates and temperatures are directly measured employing a high speed camera, and a DPV/CPS 2000 particle flight diagnostic sensor in contrast to estimates typically reported in the literature. It is demonstrated that, although the gas jet type erosion test apparatuses are frequently used in laboratories, quantitative parameter characterization is essential for setting up a test protocol. Both room and high temperature tests have been performed on this test bed. It is believed that the quantitative characterization of test parameters would greatly assist the designer in choosing and developing the appropriate erosion resistant coatings for their application.

Thermal spray coatings were deposited by the HVOF technique using two grades of WC-VC-Co powders (WC- 10VC-12Co and WC-10VC-17Co), produced by agglomeration and sintering, from WC, VC and Co starting powders. The coatings were sprayed by a commercial enterprise producing WC-Co thermal spray coatings, using the same spray parameters as for WC-Co coatings. This paper presents results from the characterization of the powders as well as the results of abrasion and erosion tests performed under identical conditions on the new WCVC- Co coatings and on standard WC-Co coatings of equal cobalt content. Under many conditions, the WC-VC-Co coatings performed better than the standard coatings, despite their deposition conditions not having been optimized.

Particulate erosion tests were conducted on coatings of heat/wear resistant materials (Cr 3 C 2 -NiCr (HVOF), Fe-Cr–Mn-B-Si (Arc spray), Fe-Cr-B-Si (HVOF)) and comparing materials (stainless steel, carbon steel). The erosion test was given under comparatively mild test conditions such as catalyst impinging in consideration of actual plants. In the previous paper, the particle erosion mechanism on using angular particulate erodent has been conjectured that it was similar to a cutting phenomenon of grinding process between the particle and surfaces with plastic/elastic properties. As the shape of erodent is an important factor as well as hardness of erodent and surfaces, the particulate erosion properties were investigated using three types erodent (angular/spherical silica and angular alumina). The materials of erodent were selected commercially available silica-filler and alumina grit. The erosion wastage depends on the shape and hardness of the particles. We considered the erosion mechanism of thermally sprayed coatings and metal materials depending on the shape and hardness of erodent.

Among the WC based cermets coating materials, those using the 10%Co-4%Cr matrix demonstrate excellent wear and corrosion properties. In this paper the erosion behaviors of WC-10%Co-4%Cr HVOF coatings was evaluated under different erosion conditions. The coatings were obtained from the JP-5000 gun using kerosene as fuel and the Diamond Jet gun using propylene and hydrogen. Two types of powder morphology were used: the first type was coarse and angular while the second was smaller, porous and spherical. The coatings were submitted to dry and slurry erosion. Erosion tests were performed at room temperature for both dry and slurry erosion. Dry erosion was evaluated by jet erosion while for slurry erosion, two different tests were performed: Coriolis and jet impingement erosion. Experimental results show that for the same powder, the erosion resistance measured by the Coriolis test exhibits 100% variation while for jet impingement it varies only by 20% depending on gun and spray conditions. The results also show that the powder selection is one of the key factors controlling the coating performance. The selection of powder can affect the Coriolis erosion resistance by more than 300% and the dry and slurry erosion resistance by 75%. The results are analyzed as a function of the processing and coating microstructure.

This work investigates the particle erosion properties of wear protection layers at high temperatures. The materials tested include tungsten and carbide cermets, nickel alloys, and chromium steel applied by different thermal spraying methods. Among key findings: HVOF-sprayed Cr 3 C 2 -NiCr cermet coatings showed the least amount of wear after particle erosion testing. It was confirmed that erosion resistance depends on elastic-plastic conditions between the particles and coating surface, not layer hardness. The impact of solid particles does not cause abrasion in elastic friction areas and only rarely causes abrasion in regions where plastic plowing occurs. Paper includes a German-language abstract.

This study examines the high-temperature erosion characteristics of carbide cermet coatings produced by HVOF spraying. The coating materials tested include three Cr 3 C 2 cermets, WC, and WC-Cr 3 C 2 . A low carbon steel and an arc-sprayed iron-base coating are also tested for reference. A nozzle-type elevated-temperature erosion tester is used to spray bed ashes collected from several coal-fired boilers. Coating samples are analyzed and compared based on composition, surface morphology, erosion wastage, and hardness relative to that of the bed-ash particles. From the comparisons, a number of conclusions are drawn. Paper includes a German-language abstract.