Papers by Keyword: HVOF

Abstract: Nickel-based coatings are a vital technology in industrial applications, offering protection to metallic objects against high temperatures, wear, corrosion, and erosion. The current research work examines the deposition of NiCrBSi powder in Stainless steel (AISI SS 304) using the high-velocity oxy-fuel (HVOF) thermal spray coating technique. The effects of HVOF-deposited NiCrBSi coatings on the microstructure, morphology, and mechanical and physical properties of the coated stainless steel. Microstructural and morphological analyses were performed using scanning electron microscopy (SEM), field emission scanning electron microscopy (FESEM), and X-ray diffraction (XRD) to characterize the coating. The coatings were systematically assessed for surface roughness, deposition efficiency, coating thickness, and porosity. Adhesion strength was measured using a pull-off adhesion tester to ensure robust bonding. The results demonstrate that HVOF-sprayed NiCrBSi coatings possess low porosity (2-3%), strong adhesion (45–55 MPa), and increased hardness, making them highly suitable for high-temperature, anti-wear applications, with improved durability and performance under harsh operating conditions.

Abstract: This study investigates the indentation fracture toughness (IFT) of six HVOF-applied cermet coatings. The materials tested were WC-42CrC-16Ni and Cr₃C₂-37WC-18NiCoCr. For each material, three coatings were produced using varying deposition parameters. IFT was measured under a 100 N load, and the K_iC values were calculated using the method proposed by Chicot. For the Cr₃C₂-37WC-18M coating, the K_iC value increased with higher oxygen and kerosene flow rates. Conversely, for the WC-42CrC-16Ni coating, higher K_iC values were observed at lower oxygen and kerosene flow rates.

Abstract: The paper presents a systematic approach to optimize the HVOF deposition technology of Al₂O₃ 40 TiO₂ coatings for the protection of components in the energy industry. Key performance factors evaluated include scratch resistance, surface roughness, and friction coefficient, given their importance for the intended applications. By means of a comprehensive experimental program using the Design of Experiment (DOE) method, the main HVOF process parameters were investigated, such as Fuel-to-Oxygen ratio (F/O), Stand-off Distance (SOD), and Powder Feed Rate (PFR), to identify optimal deposition conditions. Scratch resistance tests revealed that increasing the F/O and reducing the SOD significantly improved the tribological properties of the coatings. Surface morphology analysis through optical and electron microscopy confirmed that optimized HVOF parameters lead to dense coatings with low roughness and minimal defects, essential characteristics for components subjected to wear and severe friction. Additionally, tribological measurements demonstrated a significant reduction in the coefficient of friction for the optimized coatings. The obtained results demonstrate the HVOF technology’s capability to produce Al₂O₃ 40 TiO₂ coatings with superior properties for protecting energy industry components operating under severe conditions. The presented optimization approach can serve as a guide for best practices in developing new coating systems with enhanced performance.

Abstract: The paper presents an optimization approach for enhancing the hardness and adhesion of Al₂O₃-40%TiO₂ coatings produced by High-Velocity Oxi-Fuel (HVOF) thermal spraying, aimed at their application in protecting components subjected to aggressive environments and severe mechanical stresses [1-4]. Through an experimental factorial program, key parameters of the HVOF process such as fuel flow rate, oxygen flow rate, spray distance, and powder feed rate were investigated to identify optimal conditions leading to improved mechanical performance of the deposited layers. Vickers hardness and tensile adhesion tests were utilized to evaluate the properties of the coatings. The results indicated that increasing the fuel and oxygen flow rates, coupled with reducing the spray distance, significantly increased the hardness of the coatings, achieving values up to 244 HV5. Moreover, optimizing these parameters maximized the coating-substrate adhesion, reaching values exceeding 30 MPa. Microstructural analysis using scanning electron microscopy (SEM) revealed that optimized HVOF parameters generated dense layers with low porosity and enhanced adhesion at the layer-substrate interface, thereby explaining the superior mechanical behaviors of the coatings. These findings demonstrate the capability of HVOF technology to produce Al₂O₃-40%TiO₂ layers with optimal mechanical properties, essential for applications requiring resistance to wear, impact, and corrosive environments [5-7].

Abstract: Thermally sprayed NiCrBSi alloys have attracted interest in various fields of protective coating applications due to their good properties, especially for wear and corrosion resistance. Titanium diboride (TiB₂) is an attractive additive particle because of its properties such as high hardness, high melting point, high chemical resistance, high elastic modulus and low density. In this work, the effect of TiB₂ on dry reciprocating wear behavior of NiCrBSi-TiB₂ coating was systematically studied. NiCrBSi alloy powder was mixed with 15, 20, and 25 wt.% TiB₂ powder. Subsequently, mixed powder was coated on the substrate of 316L stainless steel (∅20 mm and 5 mm thickness) by High Velocity Oxygen Fuel (HVOF) technique. The microstructure of the coating was investigated under an optical microscope and scanning electron microscope (SEM). The hardness of the coating was measured by microhardness. In addition, dry sliding friction and wear behavior of coating were performed on a reciprocating ball-on-flat wear tester machine. The high-chromium steel (AISI 52100) ball of 6 mm in diameter was used as the counterpart. The conditions of the tests were 8 mm in stroke, 1 and 2 Hz in testing frequency with 10 N load, and sliding distance of 100 m. The variation of friction coefficient was recorded during the tests. The results indicated that an increase in TiB₂ content within the coating led to the formation of dark gray phases, oxidation layers and porosities in the microstructure. Consequently, reduction in the coating's hardness and wear resistance were discovered. In addition, the addition of TiB₂ in the NiCrBSi coating resulted in the higher material loss on the counterface ball due to abrasive wear mechanism.

Abstract: This bibliographic research explores the field of renewable energy by exploiting the potential of the High Velocity Oxygen Fuel Deposition (HVOF) method, an advanced thermal spray coating technology. HVOF involves propelling powder particles at remarkable speeds onto material surfaces, providing a means of applying protective coatings. This study explores the versatility of HVOF in creating protective coatings tailored for renewable energy applications. Specifically, the main coating targeted is the infrared reflective coating, made using alumina powders renowned for their exceptional attributes such as high strength, hardness, corrosion resistance and heat resistance, making them ideal for various components used in the renewable energy sector.

Abstract: The present research work explores the possibility of use of HVOF sprayed cermet coating Stellite-6 on gas turbine material Titanium Alloy (Ti-31). The coating is investigated for their resistance to erosion under laboratory conditions. Solid particle erosion studies were conducted using silica sand as the erodent. Erosion studies were done with impact angles of 30º, 60º and 90º. Stellite-6 coating performs better under sand erosion conditions. Stellite-6 coatings undergo damage by brittle mode. Erosion behavior of the substrate materials is ductile and resistance is better than the coating material. SEM microstructures were used for scar produced by the erodent, at 30º, 60º and 90º. impact angles, also indicates that the material damage is due to ploughing and entrapment of silica particles.

Abstract: The MCrAlY overlay coatings are widely used for high-temperature protection of hot section part of gas turbines and jet engines. This type of coatings are usually thermally sprayed using APS (Atmospheric Plasma Spraying), LPPS (Low Pressure Plasma Spraying) as well as HVOF (High Velocity Oxygen Fuel) methods. In present article the newly developed ethanol based HVOF gun was used for production of this type of coatings. The stainless steel 18-8 type was used as a base material. The AMDRY 386 (Oerlikon-Metco) NiCrAlY powder was used for coatings production. In the research different oxygen (400, 500, 600 NLPM) and ethanol (16.5, 18.3, 21.3, 23.6 and 26.6 dm³/h) flow ratio were selected for experimental processes. The powder feed ratio was also changed during process. After deposition the microstructural assessment using Scanning Electron Microscopy and chemical composition analysis using EDS method were conducted. The obtained results showed that coating was above 100 μm thick depending on the process parameters. The low concentration of pores and oxides was also observed on coatings cross-section. Using of ethanol HVOF gun enables to form good quality MCrAlY coatings with 50% reduction of oxygen consumption in comparison with conventional HP/HVOF torch using kerosene such as JP 5000. The other benefit of its using is lower CO₂ emission and lower concentration of carbon in coating in comparison with classic JP 5000 HVOF gun. The ethanol HVOF is a promising technology and might be considered as an replacement of LPPS and HVOF process for production of MCrAlY type of coatings.

Abstract: The authors carried out complex studies of a composite multilayer high-entropy coating obtained by HVOF in a protective atmosphere. They also investigated metallophysical properties of the coating (using electron microscopy and X-ray diffraction analysis) in order to obtain new information on its composition, mechanical properties, and phase composition. Functional properties of the high-entropy layer were also determined. The effect of mechanical activation of powders on the structural-phase state and quality of the layered coating has also been studied. On the basis of complex metallophysical studies, they investigated the formation of a structure in a composite multilayer high-entropy coating after HVOF in a protective atmosphere and subsequent thermomechanical treatment. Calorimetric tests of the functional high-entropy layer were carried out to reveal the exo effect corresponding to the manifestation of phase transformation. The mechanical properties of steel with a multilayer composite coating have been determined.

Abstract: Variants of air-plasma sputtering (APS) and supersonic gas-flame sputtering in the HVOF modification of wear-resistant coatings on 30HGSN2A steel, used for the manufacture of rods of liquid dampers, have been worked out. Powder mixture designated as mixture A with chemical composition (wt%): 85 % chromium carbide (Cr₃C₂) powder and 15 % steel powder consisting of 20 % chromium and 80 % nickel were used for spraying. During the quality control of the applied coatings were evaluated: appearance, thickness, adhesion strength, microhardness and porosity. The phase composition of the coatings was also determined. The deposition modes are determined for varying the size and shape of powder mixture particles, as well as the deposition distances, which allow obtaining coatings with the required values of microhardness, adhesion strength and porosity. Such coatings can be obtained by using each of the three powder mixtures studied. The highest microhardness of the coating (11500-12100 MPa) was achieved using the powder mixture C (86%WC + 10%Co + 4%Cr) – and the HVOF method. The phase composition of this coating is represented by WC (base) and W2C carbides. The maximum shear strength (114 MPa) was achieved using a powder mixture A (85% Cr₃ C₂ + 15%X20H80) and the APS method. In the first variant, the porosity of the coating is 1.8-2.0 %, in the second - 5-8 %.