Zheng Wei

Bio: Zheng Wei is an academic researcher from Hohai University. The author has contributed to research in topics: Thermal spraying & Coating. The author has an hindex of 3, co-authored 10 publications receiving 40 citations.

Influence of the high-velocity oxygen-fuel spray parameters on the porosity and corrosion resistance of iron-based amorphous coatings

Abstract: In this paper, the high-velocity oxygen-fuel (HVOF) spraying technology was used to prepare the iron-based amorphous coatings onto the substrate of 45 steel. Three parameters of spray distance, oxygen flow and kerosene flow were optimized by the Taguchi method, with the porosity of the coatings as object. The statistical tools including orthogonal experimental design, signal-to-noise ratio and analysis of variance were used to optimize the spray parameters. The results indicated that the kerosene flow showed the highest effect on the porosity of the coatings, while the oxygen flow exhibited the least influence. It was found that the coating with lowest porosity was deposited under the spray distance of 380 mm, the oxygen flow of 1840 scfh, and the kerosene flow of 6.8 gph. The potentiodynamic polarization and electrochemical impendence spectroscopy (EIS) results manifested that the iron-based amorphous coating prepared with proper spray parameters exhibited superior corrosion resistance to the hard chromium coating. Besides, the coating with lower porosity exhibited better corrosion resistance than the coating with higher porosity.

Ultrasonic cavitation erosion behaviors of high-velocity oxygen-fuel (HVOF) sprayed AlCoCrFeNi high-entropy alloy coating in different solutions

Abstract: In this study, an AlCoCrFeNi high-entropy alloy (HEA) coating was fabricated by HVOF spraying process. The HEA coating was consisted of the BCC phase (Al-rich phase) and FCC phase (Al-poor phase). The BCC phase was main phase. The mechanical performances and corrosion resistances of the coating and 06Cr13Ni5Mo martensitic stainless steel were analyzed in detail. The cavitation erosion behaviors and mechanisms of the HEA coating and 06Cr13Ni5Mo steel were investigated in distilled water and 3.5 wt% NaCl solution. The effects of microstructures, mechanical properties and corrosion properties on cavitation erosion mechanisms were discussed through the observation of eroded surface morphologies. The results showed that the cavitation erosion resistance of the AlCoCrFeNi coating was about 3.5 times that of the 06Cr13Ni5Mo steel in both solutions. In the 3.5 wt% NaCl solution, corrosion damage aggravated cavitation erosion damage, although the enhancement effect of corrosion on cavitation was limited. The corrosion environment did not change the cavitation erosion mechanisms of the two materials. The cavitation erosion mechanism of the HEA coating was lamellar spalling caused by the extension of the interlaminar cracks. Due to the lower plastic deformation resistance, the cavitation erosion mechanism of the 06Cr13Ni5Mo steel was material spalling caused by plastic deformation and fatigue fracture.

Effect of WC-10Co on cavitation erosion behaviors of AlCoCrFeNi coatings prepared by HVOF spraying

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.

Long-term corrosion behavior of HVOF sprayed Cr3C2–NiCr coatings in sulfide-containing 3.5 wt.% NaCl solution

Abstract: In this work, Cr3C2–NiCr coatings were fabricated by high-velocity oxygen-fuel (HVOF) spraying. Under the help of scanning electron microscope (SEM), energy dispersive spectroscopy (EDS), X-ray diffraction (XRD) and optical microscope (OM), the phase compositions and microstructure of the coatings were characterized. The long-term corrosion behavior of HVOF sprayed Cr3C2–NiCr coating (HC) and Q345 steel was probed in 3.5 wt.% NaCl solution (S1) and 3.5 wt.% NaCl solution containing 20 ppm Na2S (S2). With the extension of immersion time, the corrosion rate of HC in different solutions showed an overall trend of increasing first and then decreasing. The corrosion rate of Q345 steel in both of the solutions showed a growing trend, while the trend in the sulfide-containing solution was even sharper. The corrosion rates of HC in S1 and S2 were both lower than those of Q345 steels, especially in S2. Owing to the generation of the dense protective film on the HC surface as well as the accumulation of corrosion products, after 70 d of immersion, HC exhibited better corrosion resistance in S2 than that in S1.

Electrochemical properties and cavitation erosion behaviors of HVOF sprayed (AlCoCrFeNi)1-X(WC-10Co)X composite coatings in NaCl medium

Abstract: The (AlCoCrFeNi)1-X (WC-10Co)X composite coatings were fabricated on 06Cr13Ni5Mo steel by high-velocity oxygen-fuel (HVOF) spraying. The coatings' microstructure, mechanical properties, and corrosion performance were characterized, and the cavitation erosion resistance of the coatings was tested in 3.5 wt% NaCl medium. The influence of the microstructure, mechanical properties, and corrosion resistance on cavitation erosion resistance were discussed. The microhardness and local plastic deformation resistance of the coatings were increased by WC-10Co, while the corrosion resistance of the composite coatings was decreased by severe galvanic corrosion. The cavitation erosion mechanism of the coatings was lamellar spalling. In NaCl medium, the (AlCoCrFeNi)75(WC–10Co)25 (HEA75/WC25) coating showed lower cavitation erosion resistance than the AlCoCrFeNi (HEA) coating, which was caused by the galvanic corrosion, uncoordinated deformation and the low bonding strength of the HEA/WC-10Co interface. For the HEA75/WC25 coating and (AlCoCrFeNi)50(WC–10Co)50 (HEA50/WC50) coating, the cavitation erosion damage of the HEA75/WC25 coating was higher than that of the HEA50/WC50 coating. When the microstructure and corrosion resistance of the coatings were similar, the cavitation erosion resistance was mainly affected by the mechanical property.

A review on laser cladding of high-entropy alloys, their recent trends and potential applications

Abstract: High-Entropy Alloys (HEAs) are a promising class of metallic materials that have allured the world of material science and engineering. These intriguing materials are proving their worth in the coatings for severe ambient and demanding conditions. Laser cladding (LC) is a non-linear complex, multidisciplinary and modern technology applied for surface modification. Nobler properties of HEAs as compared to traditional alloys permitted the research community to explore Laser-Cladded High-Entropy Alloy Coatings (LC-HEACs). Here, this article provides a review and recent trends of LC-HEACs, aiming to address the use of LC technology for HEA materials, the influence of process parameters on the geometric and metallurgical characteristics of the LC-HEACs. Common defects not limited to microcracks and residual stresses, and techniques to improve the quality of the LC-HEACs are elucidated. Furthermore, thermo-kinetics effect, thermomechanical behavior, microstructural evolution, and strengthening mechanisms are illustrated for a better understanding of laser-material interaction. The potential applications of the LC-HEACs are outlined considering wear, corrosion, erosion, and oxidation resistance and their corresponding substrates. The article also highlights the research gaps, current trends, and possible future directions in the context of critical challenges that need to be catered, before the actual implementation of LC-HEACs in industries. Owing to the variety of element constitution for HEAs design as well as excellent mechanical and functional properties, LC-HEACs will blossom in the years to come.

Multi-scale mechanical properties of Fe-based amorphous/nanocrystalline composite coating synthesized by HVOF spraying

Abstract: Fe-based (Fe–Cr–B–P–C) amorphous/nanocrystalline composite coatings were synthesized by high velocity oxy-fuel (HVOF) thermal spray method with varying powder feed rates and the multi-scale wear behaviour of the coatings’ is reported here. Microstructural characterization of the composite coating envisaged the presence of embedded nanocrystalline phases in the amorphous matrix. The porosity content decreased, whereas the amorphicity of the coating increased gradually with increment in the feed rate. The combined effect of (i) splat morphology and (ii) extent of devitrification on the mechanical and tribological properties of the various coatings was investigated. Increasing the powder feed rate resulted in higher hardness of the coating, which was attributed to better inter-splat bonding and reduction in α-Fe content in the amorphous matrix of the coating due to lower extent of devitrification. Nanotribology test on a single-splat revealed increment in wear resistance at elevated feed rate due to the reduction in volume fraction of softer nanocrystalline α-Fe phases. Besides, dry sliding wear investigated the coatings’ wear behaviour on a global basis and revealed decreasing trends for both wear rate and coefficient of friction with increasing feed rate. Most importantly, the Fe-based composite coatings exhibited low wear volume during nanotribology and lower friction coefficient, low wear rate of dry sliding wear study, compared to an SS316L coating, prepared using industrially optimized parameters. The enhanced wear resistance of the composite coating compared to that of the stainless steel coating makes it an effective method of surface protection for metallic substrates.

Effects of heat treatment on the microstructure, mechanical properties and corrosion resistance of AlCoCrFeNiTi0.5 high-entropy alloy

Abstract: AlCoCrFeNiTi0.5 high-entropy alloy was fabricated, and the effects of heat treatment on the microstructure, mechanical properties and corrosion resistance of this alloy were investigated. The results indicate that heat treatment can not only refine as-cast dendrites and change the morphology of precipitation from long strip to short rod-like structure but also control the ratio of BCC to FCC. The volume fraction of the BCC phase at 1100 °C is 34.8%, which is 9.2% higher than that under the as-cast conditions (25.6%). The highest compression fracture strength and fracture strain of 2785 MPa and 30.7%, respectively, are achieved when the heat treatment temperature and time are 1100 °C and 6 h, respectively. The highest Vickers hardness values of FCC and BCC are 687 HV0.5 and 782 HV0.5, respectively. The order of corrosion resistance is 800-2 h 900-2 h, as-cast, 1000-2 h, 1100-2 h, and 1200-2 h, which is contrary to the trend of the BCC volume fraction. The potential of dendritic FCC is higher than that of interdendritic BCC, and the potential difference is rising because of dendrite decomposition and atom diffusion. The corrosion mechanism is also discussed in this study. Corrosion occurs preferentially on the phase interface and interdendrites, and subsequently connects with each other. As the corrosion intensifies, dendritic FCC begins to be corroded and develops into a large corrosion area.

Mechanistic insight into the role of amorphicity and porosity on determining the corrosion mitigation behavior of Fe-based amorphous/nanocrystalline coating

Abstract: Fe-based in-situ amorphous/nanocrystalline composite coatings were prepared from an amorphous/crystalline powder (Fe63Cr9P5B16C7) using high velocity oxy-fuel thermal spraying of optimized parameters. To investigate the individual effects of amorphicity and porosity on corrosion performance, two melt spun ribbons with no porosity having different amorphous content viz. (i) fully amorphous (FA-Rib) and (ii) partially amorphous (PA-Rib) structure with similar amorphicity as that of the coatings, were synthesized. Potentiodynamic polarization and electrochemical impedance spectroscopy studies revealed a greater influence of the reduced amorphicity on the increased passive current density and decreased polarization resistance, than that of the porosity in the fully amorphous matrix. Besides, extent of pitting increased, whereas fraction of protective phases (chromium oxide and Cr substituted hematite) in the corrosion products of post-polarized samples decreased gradually in the order of FA-Rib to PA-Rib to the coating. Moreover, results of Auger electron spectroscopy revealed that depletion of Cr and thinning of passive film increased significantly with crystallization of amorphous structure, compared to additional porosity effect. These results confirmed that corrosion mitigation ability of the coating was primarily affected by reduced amorphicity. Role of both these microstructural features in governing the corrosion mechanism of the amorphous coating was elucidated.

Evaluation of cavitation/corrosion synergy of the Cr3C2-25NiCr coating deposited by HVOF process

Abstract: Wear processes are always present in components exposed to different work situations. Hydraulic turbines in electric power generation and ship propellers are good examples of components subject to wear and corrosion. One way to protect these components, for example, is the deposition of coatings by thermal spray processes. Indeed, there are several wear or corrosion mechanisms acting simultaneously, and the validation of the mechanisms separately, is not the best way to select the better material. When materials have passivation as protective mechanism against corrosion, the mass loss due erosion can affect the materials selection. This paper study the combined effect of the corrosion on the cavitation mass loss, as well as, the cavitation mass loss influence on the corrosion properties of a chromium carbide Cr3C2-25NiCr coating. Despite of the modification of the erosion mechanism on the cavitated samples under 3,5% NaCl solution, the volume loss did not show any significant alteration. Cavitation mass loss increase the corrosion process, reducing significantly the corrosion potential and raising the corrosion current. It was observed that the cavitation of the Cr3C2-25NiCr HVOF coating influences much more the corrosion kinetics, than the corrosion affects the cavitation resistance.