Effect of WC-10Co on cavitation erosion behaviors of AlCoCrFeNi coatings prepared by HVOF spraying
TL;DR: In this paper, the effects of WC-10Co on the cavitation erosion mechanisms were discussed by compared the differences of volume losses and eroded surface morphologies between the coatings.
Abstract: The (AlCoCrFeNi)1-X(WC-10Co)X composite coatings were fabricated by HVOF spraying and their microstructures, mechanical properties and cavitation erosion behaviors were tested. The effects of WC-10Co on the cavitation erosion mechanisms were discussed by compared the differences of volume losses and eroded surface morphologies between the coatings. The cavitation erosion resistance of the coatings was about 3 times as that of the 06Cr13Ni5Mo steel. With the addition of WC-10Co, the cavitation erosion resistance of the coating was slightly increased. In the initial stage of cavitation erosion test, the cavitation erosion damage was concentrated on the interface, which was caused by the uncoordinated deformation and poor mechanical properties of the interface between HEA and WC-10Co. When the WC-10Co distributed below the HEA region, the WC-10Co played a strong supporting role and improved the impact resistance of the HEA region. The cavitation erosion mechanism of the HEA1 coating was lamellar spalling. The cavitation erosion mechanisms of the HEA2 and HEA3 coatings were particles spalling and lamellar spalling.
TL;DR: In this paper , a gas atomized feedstock was used to fabricate an AlCoCrFeNi HEA coating using the high-velocity oxygen fuel (HVOF) process.
Abstract: In this work, a gas atomized feedstock was used to fabricate an AlCoCrFeNi HEA coating using the high-velocity oxygen fuel (HVOF) process. The coating’s resistance to room temperature surface degradation was evaluated using dry sliding wear and seawater corrosion testing. The coating retained the feedstock phase structure with negligible in-flight oxidation and was composed of a majority BCC phase with a minor B2 phase, resulting in a high micro- and nano-hardness of ~7 GPa. These observed phase compositions were consistent with thermodynamically calculated phase predictions using a CALPHAD model. Microstructure-mechanical property mapping revealed uniform microstructural characteristics. However, the multiscale wear resistance of the coating was critically affected by the presence of the hard BCC/B2 phase composition, which led to severe brittleness. Combinatorial assessment of the worn surface, wear debris and counter body indicated that wear was dictated by a combination of abrasive, surface fatigue, tribo-oxidation and adhesive wear. In addition, the coating exhibited superior general corrosion resistance compared with conventional SS316L, but the selective dissolution of the B2 phase preceded poor localized corrosion resistance, ultimately leading to pitting corrosion.
01 Jan 2017
TL;DR: In this article, wear resistant coatings have been studied as a solution to the problem of corrosion in hydrodynamic components and systems, which reduces the operational efficiency of the system.
Abstract: Cavitation and corrosion on hydrodynamic components and systems reduces the operational efficiency. The use of wear resistant coatings have been studied as a solution to the problem of corrosion an ...
TL;DR: In this article , the phase, layered microstructure, microhardness, and erosion behavior of the coatings were analyzed by performing X-ray diffractometry, scanning electron microscope/energy dispersive spectrometry, Vickers micro-hardness testing, and slurry erosion testing.
Abstract: In this study, AlCoCrFeNi (H1), AlCoCrFeNi+25 wt%WC-10Co (H2), and AlCoCrFeNi+50 wt%WC-10Co (H3) high-entropy alloy (HEA)/tungsten carbide (WC) composite coatings were deposited onto 316 stainless steel substrates by applying the high-velocity oxygen fuel spraying technology. The phase, layered microstructure, microhardness, and erosion behavior of the coatings were analyzed by performing X-ray diffractometry, scanning electron microscope/energy dispersive spectrometry, Vickers microhardness testing, and slurry erosion testing. The effects of WC addition on the erosion behavior and mechanism of the coatings at different flow velocities were investigated. The deposited coatings were compacted and adhered well to the substrate. The AlCoCrFeNi coating was composed of BCC and FCC phases. The porosity of the H1, H2 and H3 coatings were 0.24%, 0.33% and 0.45%, respectively, and were less than 1%. The microhardness of the HEA/WC composite coatings was positively correlated with WC content. The volume loss and rate of volume loss of the coatings decreased with the addition of WC. The erosion mechanism of the AlCoCrFeNi coating was typical ductile wear, with a small amount of interlayer peeling. Furrows, cuttings, and plastic deformation caused by low grazing angles contributed to the failure of the AlCoCrFeNi coating. In the HEA/WC composite coatings, WC protected the HEA from more severe plastic deformation by second-phase strengthening, and the main erosion mechanism of WC was gradual brittle detachment caused by high-grazing-angle erosion in which craters, cracks, and massive spalling were responsible for the erosion process.
TL;DR: In this paper , a simple and environment-friendly composite powder preparation method was proposed, where the surface of the composite powder (WCN2) was modified, leading to the transformation of interfacial bonding between WCN and MWCNTs from mechanical bonding to mechanical bonding accompanied by hydrogen bonding.
Abstract: The WC-20Cr3C2–7Ni/multiwall carbon nanotubes (WCN/MWCNTs) composite powders were prepared by mechanical bonding and surface modification, respectively. In the process of mechanical bonding method (M1), the dispersion of MWCNTs and maintained structural of composite powder (WCN1) were achieved by slurry-based dispersion. On the basis of the M1, a novel, simple and environment-friendly composite powder preparation method was proposed (M2). The surface of the composite powder (WCN2) was modified, leading to the transformation of interfacial bonding between WCN and MWCNTs from mechanical bonding to mechanical bonding accompanied by hydrogen bonding. The distribution of MWCNTs on the surface of WCN2 powder was more uniform than that of WCN1 power. The coatings (WCN, WCN1, WCN2) were prepared by high-velocity oxygen-fuel (HVOF) spraying. Compared with the WCN coating, the homogeneous distribution of MWCNTs not only increased the hardness, elastic modulus and corrosion resistance of the WCN2 coating, but also decreased the brittleness of the WCN2 coating.
TL;DR: In this paper, 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.
Abstract: 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°C, 500°C, and 525°C), 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°C 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.
TL;DR: In this article, the homogenization effect revealed by the microstructure simplification and chemical-segregation reduction leads to the decreased work function variations and the improved corrosion resistance of the AlxCoCrFeNi high-entropy alloys.
Abstract: The present work investigates the homogenization effect of 1250 °C heat treatment on the AlxCoCrFeNi high-entropy alloys (HEAs). The multi-phase microstructures with chemical segregations are inevitable with the increased Al content in the alloys, which cause work function variations and localized corrosion. After heat treatment, the homogenization effect revealed by the microstructure simplification and chemical-segregation reduction leads to the decreased work function variations and the improved corrosion resistance. Thermodynamic calculations that are reliable to predict the phase transformations of the AlxCoCrFeNi HEAs, indicates a further enhancement in corrosion resistance through annealing could be guided for many other HEAs systems.
TL;DR: In this paper, an additive additive manufacturing of a high-entropy alloy, AlCoCrFeNi, was studied with selective laser melting from gas atomized powder, and it was shown that it is possible to modify the microstructure and segregation of element within alloys.
Abstract: Additive manufacturing of a high-entropy alloy, AlCoCrFeNi, was studied with selective laser melting from gas atomized powder. A wide process parameter window in the SLM process was investigated but it was impossible to produce crack-free samples, attributed to stresses that originate during the building processes. The microstructure and elemental segregation in the SLM samples were compared with induction-melted AlCoCrFeNi. The induction-melted sample crystallizes in randomly oriented large grains (several hundred microns). Dendritic and inter-dendritic areas with slightly different chemical composition can be observed. Within these areas a spinodal decomposition occurs with a separation into FeCr- and NiAl-rich domains. Further spinodal decomposition within the FeCr-rich regions into Cr- and Fe-rich domains was observed by atom probe tomography. In contrast, the SLM-samples crystallizes in much smaller grains (less than 20 μm) with a dendrite-like substructure. These dendrite-like features exhibit distinct chemical fluctuations on the nm-scale. During annealing more pronounced chemical fluctuations and the formation of Cr-rich and Cr-poor regions can be observed. The difference in microstructure and spinodal decomposition between the induction-melted and SLM samples is attributed to the significantly higher cooling rate for SLM. This study shows that, by using different synthesis pathways, it is possible to modify the microstructure and segregation of element within alloys. This can be used to tune the materials properties, if the cracking behavior is handled e.g. by change of alloy composition to minimize phase transformations or use of a heating stage.
TL;DR: The TCHEA1 database as mentioned in this paper is suitable for the study of Bcc and Fcc HEA systems and it is also applicable in process simulations when used together with compatible kinetic databases.
Abstract: In this paper we report a thermodynamic database which was developed by using the CALPHAD approach. The TCHEA1 database includes 15 chemical elements (Al, Co, Cr, Cu, Fe, Hf, Mn, Mo, Nb, Ni, Ta, Ti, V, W and Zr). It is suitable for the study of Bcc and Fcc HEA systems. The database is constructed based on the thermodynamic assessment of all binary systems and many key ternary systems where almost all possible metastable and stable phases are considered. It is extensively demonstrated in the present work that TCHEA1 gives satisfactory prediction on the phase equilibria in various HEA systems (quaternary to ennead) and wide temperature ranges (liquidus to subsolidus). Thermodynamic stability calculations of simple solid solutions (Bcc and Fcc) and intermetallics (sigma, Laves, μ-phase etc.) are validated against the available experimental information in as-cast or as-annealed state. Such CALPHAD database focusing on the modelling of Gibbs energy rather than entropy makes reliable predictions of thermodynamic equilibrium and phase transformation, no matter whether the alloy/system has high entropy or not. Cases with miscibility gap in liquid and solid solutions and second-order phase transition at low temperatures are demonstrated. With the volume data included, TCHEA1 is capable to predict the density and thermal expansion coefficient of HEAs as well. This thermodynamic database is also applicable in process simulations when used together with compatible kinetic databases.
TL;DR: In this paper, suspension plasminar spraying (SPS) was used to improve TBC thermal properties and the effect of heat conduction paths, which impact thermal diffusivity values was highlighted for the columnar structure.
Abstract: Improving efficiency of hot section components of aero engines such as turbine blades or nozzle guide vanes is critical for the aircraft industry. Over many years, the development of advanced Thermal Barrier Coatings (TBCs) has been a field of active research to achieve this purpose. Electron Beam Physical Vapor Deposition (EB-PVD) and Atmospheric Plasma Spraying (APS) processes are widely used to apply TBCs on metal substrates. High costs and rather high thermal conductivities of EB-PVD coatings, as well as low thermal lifetime of APS ones, are real drawbacks for next generations of turbine engines. In this study, Suspension Plasma Spraying (SPS) was assessed to improve TBC thermal properties. It was shown that the SPS process allows to perform columnar microstructure easily tunable in terms of both compaction of columnar structure and thermal conductivity. Thermal conductivities were in the 0.7–1.25 W·m− 1·K− 1 range for SPS coatings while values of 0.9 and 1.5 W·m− 1·K− 1 were measured for APS and EB-PVD coatings, respectively. The effect of heat conduction paths, which impact thermal diffusivity values, was highlighted for the columnar structure.
TL;DR: The effects of annealing treatments on the microstructure, elastic and mechanical properties of the coatings were investigated in this article, where the authors showed that the mechanical hardening is accompanied with an increase of the ratio of hardness to elastic modulus (H / E r ), the yield pressure (H 3 /E r 2 ) and the elastic recovery ( η value)
Abstract: FeBSiNb amorphous coatings were synthesized by arc spray processing The effects of annealing treatments on the microstructure, elastic and mechanical properties of the coatings were investigated Annealing below 650 °C induces the formation of α-Fe phase nanocrystals Annealing at 650 °C promotes the formation of Fe 3 B, Fe 23 B 6 phases and α-Fe solid solution The as-sprayed coating displays ultra-high hardness ( H > 16 GPa), high reduced Young's modulus ( E r > 210 GPa) and good wear resistance These properties are further improved after annealing treatments ( H > 20 GPa and E r > 260 GPa are achieved in the fully crystallized coating) The mechanical hardening is accompanied with an increase of the ratio of hardness to elastic modulus ( H / E r ), the yield pressure ( H 3 / E r 2 ) and the elastic recovery ( η value) The different microstructural mechanisms responsible for these annealing-induced changes in mechanical and elastic properties are discussed