Slurry Erosion Resistance Research Articles

Erosion behavior of hydrophobic polytetrafluoroethylene (PTFE) coatings with different thicknesses

The main purpose of the study is to explore the usage of polytetrafluoroethylene (PTFE) coatings to enhance slurry erosion (SE) resistance of hydro-machinery components. Although PTFE doesn't have enough hardness, however its hydrophobicity and good impact strength make it an interesting material to evaluate whether these properties could help in developing SE resistance in the parent hydro-machinery materials. Polytetrafluoroethylene (PTFE) is one of the leading materials for developing hydrophobic surfaces, which has numerous desirable properties like low friction coefficient, chemically neutral, and considerable thermal firmness. Therefore, in the present study, hydrophobic coatings of PTFE having three different thicknesses were produced (by sintering process) on a hydro-machinery steel SS410. The effect of thickness of hydrophobic coatings on the SE was analysed by conducting SE tests on the coated and uncoated steel SS410 with different combinations of operating parameters; namely average erodent particle size, slurry concentration, impingement angle and impact velocity. A relative study of different thickness of PTFE coatings vis-à-vis the bare steel SS410 was also conducted with respect to hydrophobicity. PTFE coating with minimum thickness showed the lowest erosion rate as compared to its counterparts. Moreover, the PTFE coating with minimum thickness showed superhydrophobic behavior with a contact angle of 159°, which might have also imparted the best SE resistance. With regard to SE of all the candidate materials, impact velocity was found to be the most influencing operating parameter.

Slurry erosion behaviour and mechanism of HVOF sprayed micro-nano structured WC-CoCr coatings in NaCl medium

In this work, we fabricate nanostructured, bimodal, and multimodal WC-10Co4Cr coatings via two high velocity oxy-fuel (HVOF) systems and investigate the coatings’ microstructure, mechanical, electrochemical properties and slurry erosion resistance in 3.5 wt% NaCl solution. The multimodal coating, with a dense microstructure, exhibits lowest decarburization and highest resistance to both corrosion and slurry erosion. The slurry erosion resistance of multimodal coating is enhanced approximately 18% and 11% than the nanostructured and bimodal coatings. However, the performance can easily drop to the worst by changing the HVOF spraying method. The outstanding performance can be attributed to uniform distribution of the multiscale WC grains in the multimodal coating, which effectively reduces the material loss rate during corrosion-accelerated erosion in NaCl solution.

Slurry Erosion Performance of Ni + B4C Microwave Composite Clads

Abstract A composite clad of Ni-based alloy and B4C was developed on austenitic steel substrate through microwave hybrid heating. The B4C was added with Ni-based alloy powder in various weight proportions (0%, 5%, 10%, and 20%). The clads were investigated for the microstructural details, nanohardness and slurry erosion performance. Silt collected from river Uhl was used as the erodent for the slurry erosion test. Slurry erosion performance of the clads was evaluated at an impact angle of 90 deg and jet velocity of 40 m/s. Microstructural characterization confirms the uniform distribution of hard (boride and carbide) phases in the Ni-based matrix of the microwave composite clads. The presence of hard phases in the Ni-based matrix enhanced the slurry erosion resistance performance.

Tribological Investigation of HVOF Sprayed Coated Turbine Steel under Varied Operating Conditions

In the present work, Cr3C2-25NiCr and WC-10Co-4Cr coatings were deposited on AISI304 turbine steel using HVOF-spray process. Performance of these HVOF-spray coated and bare turbines steel was investigated under varied conditions of slurry erosion. Slurry erosion resistance was premeditated by using a laboratory developed slurry erosion test rig. Phases, microstructure and eroded surface were characterized using SEM and XRD analysis. It was observed that HVOF-spray WC-10Co-4Cr coating had shown remarkable erosion resistant feature due to the presence of dense, well bonded structure along with higher hardness followed by Cr3C2-25NiCr coated steel and AISI 304 bare turbine steel. It was observed that under erosion condition, bare steel and Cr3C2-25NiCr coating exhibited ductile followed by brittle mechanisms respectively. Similarly degradation mechanism for WC-10Co-4Cr coating exhibited mainly ductile behaviour

Effect of hot forging on the slurry erosion wear of AISI316 and AISI410 steel

Evaluation of slurry erosion is one of the most important aspects while designing any slurry transportation system as it is a major cause for inefficient functioning and eventually failure of different components of the system. The aim of present work is to investigate the effect of hot forging on the slurry erosion behavior upon two materials namely austenite stainless steel (SS316) and martensitic stainless steel (SS410), experimentally. Hot forging has been done using a Birson Friction Screw Press machine by utilizing a temperature range from 850 °C to 950 °C and maintaining a constant strain rate of 10 s−1. It is observed that the hot forged samples are more erosion resistant than the ‘as received samples’ (ARS). It is also found that the samples hot forged at 950 °C shows the maximum slurry erosion resistance. It is also concluded that the SS410 is more erosion resistant than the SS316 for both ARS and hot forged samples.

HVOF sprayed Inconel 718/cubic boron nitride composite coatings: microstructure, microhardness and slurry erosive behaviour

In the present work Inconel 718 based composite coating with varying cBN were developed on SS304 substrate using high-velocity oxy-fuel (HVOF) technique. The developed coatings were subjected to microstructural, x-ray diffraction, microhardness and adhesion strength studies. The uncoated and composite coatings were subjected to slurry erosion test with varying slurry concentration (10%–40%), slurry rotational speed (500–1500 rpm) and test duration (5–25 h). Cross-sectional analysis of composite coating suggested formation of lamellar structure with good splat/splat bonding as well as with the substrate material. Both microhardness and slurry erosion resistance of Inconel 718/20%cBN coating was found to be significantly higher than that of uncoated and other composite coatings. For all slurry erosion test conditions the composite coatings were found to be superior to that of uncoated substrate. Overall composite coatings showed failure mechanism starting from plastic deformation to spalling while uncoated substrate showed deep crater with heavy ploughing.

Erosion wear analysis of HVOF coated Colmonoy-88 and Stellite-6 micron layers on pump impeller steel by using the Taguchi's approach

PurposeThis paper aims to depict the erosion performance of two HVOF-coated micron layers (Colmonoy-88 and Stellite-6) on pump impeller steel (SS-410) by using Taguchi's method. Taguchi's array (L16) was used to optimize the erosion wear (in terms of weight loss) by using four influencing parameters such as rotational speed, solid concentration, average particle size and time which were varied at four different levels.Design/methodology/approachThe experiments were carried out by using a Ducom slurry tester with rotational speed in the range of 750-1,500 rpm, solid concentration of 35-65 per cent by weight, time period of 75-210 min and average particle sizes in the range of < 53 to 250 µm. Bottom Ash with a nominal size range of < 53 to 250 µm was used as erodent. The process parameters were optimized by using Taguchi's method. The ANOVA method was used to validate the results given by Taguchi's method.FindingsThe results revealed that the presence of both carbides and borides and the additional presence of Cr in Colmonoy-88 coating enhancing the slurry erosion resistance of Colmonoy-88 coating. Moreover, the chromium and tungsten carbide particles help in increasing the bond strength between the coating and the substrate material. Further, it was also found that the time was the most dominant factor as compared to other factors.Originality/valueThe very less work has been reported on optimization of erosion wear response of Colmonoy-88 and Stellite-6 coatings by using different design of experiment techniques. Further, the erosion wear mechanism of both coatings has been studied by using image j analysis software.

Synthesis, characterisation and erosion behaviour of AlCoCrMoNi high entropy alloy coating

AlCoCrMoNi equiatomic high entropy alloy (HEA) powders were prepared by mechanical alloying. High energy planetary ball-mill was employed to mill the powders till single solid solution formation. X-Ray Diffraction (XRD) analysis of as prepared powder was done at 5, 10, 15 and 20 hours of milling. A single BCC phase was formed after 20 h. Field emission scanning electron microscopy (FESEM) was used to study the microstructure of the prepared powder. After 20 hours of milling, a homogenous mixture formed, which was further confirmed by EDAX mapping of as prepared powders. The alloy was coated onto a 316 steel substrate using High-velocity Oxy-fuel (HVOF) coating. Cross-section of the coating was analysed using scanning electron microscope (SEM). The slurry erosion resistance exhibited by the coating was tested using Water-jet Erosion tester with 20 m s−1, 25 m s−1 and 30 m s−1 jet velocity at 30°, 60° and 90° angular impingement. The coating exhibited high ductility along with superior erosion resistance compared to conventional wear resistant coatings.

Evaluation of the Adhesion and Slurry Wear Erosion of Nb2O5 Coatings Applied by Flame Spray

Niobium pentoxide (Nb2O5) has excellent chemical and thermodynamic stabilities, characteristics that have accelerated the applications of this material in the form of coatings to protect against corrosive processes. However, few studies have evaluated its performance in wear protection applications. In this research, the slurry wear erosion resistance of Nb2O5 coatings deposited by flame spray was studied. The microstructural characterization of the coatings was performed by optical microscopy and scanning electron microscopy (SEM) assisted by chemical analysis by energy dispersive X-ray spectroscopy (EDS). Adhesion of the coatings was determined by the adhesion test (ASTM C633-13). Image analysis was used for the quantitative study of the adhesion tested areas and porosity of the coatings. Erosive wear resistance was determined using a container tribometer with erosive mixing at a particle velocity of 9.33 m/s and two particle incidence angles. The thinner coatings had fewer microstructural defects, such as pores and microcracks, and greater adhesive strength. The thicker coatings presented a cohesive failure mode. When the impact angle of the erodent particles was 90 deg, the thickness of the Nb2O5 coatings should not exceed 350 μm. Nb2O5 coatings applied by flame spray showed good resistance to slurry wear erosion, besides inherent low cost and flexibility of the process.

Microwave-Assisted Post-processing of Detonation Gun-Sprayed Coatings for Better Slurry and Cavitation Erosion Resistance

Slurry and cavitation erosion often limits the durability of many fluid machines such as hydroturbines, pumps, and propellers. Despite good resistance against slurry erosion, thermal spray coatings generally exhibit poor resistance against cavitation erosion. The performance of thermal spray coatings under cavitation erosion is limited by the presence of defects such as pores, splat boundaries, and limited adhesion with the substrate. In the present work, we performed post-processing of the WC-10Co-4Cr and Ni coatings deposited using the detonation gun process. For post-processing, microwave technique was used owing to its capability for atomic-level heating. The microstructural characterization of the as-sprayed and post-processed coatings showed significant homogenization for the latter. Compared to the typical lamellar structure of as-sprayed, the processed samples exhibited a columnar structure with metallurgical bonding with the substrate. The mechanical properties of the coatings were significantly improved after post-processing owing to the elimination of splat boundaries and pores which significantly enhanced the cavitation and slurry erosion resistance. Post-processed coatings showed at least ten times higher resistance to cavitation erosion. The slurry erosion resistance of the coatings also improved up to three times depending upon the impingement angle. A significant difference in the erosion mechanism was also observed after post-processing.

Performance evaluation of HVOF sprayed WC-10Co4Cr coatings under slurry erosion

ABSTRACTSlurry erosion is one of the main failure modes of the hydraulic turbine parts, mud pumps and drill pipes. The high velocity oxygen fuel (HVOF) spray process has been widely used for depositing protective coatings especially the cermet coatings that can significantly improve the slurry erosion resistance of substrate materials. In this work, conventional WC-10Co4Cr composite coatings and coatings with bimodal structures were deposited on the 35CrMo steel substrate by HVOF, respectively. Structures of the two kinds of coatings were analysed with SEM and XRD methods, and microhardness, porosity and roughness were also measured. Furthermore, the slurry erosion tests were carried out on the coatings to explore the effect of average particle size, slurry concentration and pH value on the erosion behaviours. The erosion failure mechanisms of the coatings were also explored. The results show that the bimodal coating has a denser microstructure, superior mechanical properties, lower porosity and better slurry erosion resistance than the conventional coating. The erosion-corrosion mechanism of the two kinds of coatings is spalling, caused by crack initiation and propagation under fatigue stress.

Slurry Erosion Behavior of HVOF-Sprayed WC-10Co-4Cr Coated SS 316 Steel with and Without PTFE Modification

Several hydro-machinery components such as impellers of the submersible pump and turbine blades generally suffer from slurry erosion during their operation. High-velocity oxy-fuel (HVOF)-sprayed coatings are promising materials to prevent such components from slurry erosion. Moreover, polytetrafluoroethylene (PTFE) is a well-accepted hydrophobic material, which has several attractive properties such as chemical inertness and considerable thermal stability. Therefore, PTFE coating has been explored as a topcoat for a HVOF-sprayed WC-10Co-4Cr coating, with an aim to enhance the performance of the latter and analyzed with different slurry erosion conditions. A slurry erosion test rig was used for experimentation, and the effect of four different erosion parameters, namely average particle size, slurry concentration, impact angle, and velocity of jet, was investigated. A comparative study between PTFE-modified HVOF-sprayed coating and the standalone HVOF-sprayed coating was also done with respect to slurry erosion behavior and hydrophobicity. The overall results indicate that the slurry erosion of the HVOF-sprayed coated SS 316 steel got enhanced after modification by PTFE topcoat. Furthermore, the topcoat of PTFE on HVOF-sprayed coating resulted in a remarkable improvement in hydrophobicity, showing a superhydrophobic behavior, which might have also provided a better slurry erosion resistance to the HVOF-sprayed steel.

The effect of NbC morphology on the slurry erosion performance of ferrous alloys

It is often proposed that the wear performance of high-chromium white cast irons could be improved by adding Nb to form NbC. However, NbC can form with a needle-like “Chinese-script” morphology and/or as nodular particles, and clear evidence is not available as to which morphology is more beneficial against slurry erosion, a common application for these alloys. The lack of evidence is due to the difficulty of differentiating between the effect of NbC and that of a second type of carbide, M7C3, on slurry erosion resistance. Therefore, we created a martensitic stainless steel resembling the ferrous matrix of a typical high-chromium white cast iron, but without the M7C3 phase, that was reinforced with Chinese-script NbC. A second specimen was prepared by substituting a small amount of Nb for Ti to inoculate the NbC, thus forming nodular particles. An AISI 440C stainless steel was used as a commercial benchmark since it has a similar hardness and microstructure. All three samples were subjected to slurry erosion tests against garnet and sand, with the Chinese-script NbC sample being the worst performer in both cases. Analysis of the worn surfaces revealed that the Chinese-script morphology promoted fracturing, resulting in a higher erosion rate.

An Influence of Factors of Flow Condition, Particle and Material Properties on Slurry Erosion Resistance

Abstract The degradation of materials due to slurry erosion is the serious problem which occurs in the power industries. The paper presents actual knowledge about an influence of individual factors connected with flow conditions, particles and material properties on the slurry erosion resistance. Among the factors connected with operating conditions, an influence of impact angle, and velocity of impact, particle concertation and liquid temperature have been described. In case of the factors connected with solid particle properties, an influence of the size, shape and hardness have been discussed. In the part devoted to the impact of material properties, due to different types of materials, the issues of resistance to erosion of slurries related to the properties of steel, ceramics and polymers are discussed separately. In the paper has been shown that a change of any of mentioned factors causes a change in the erosion rate due to the synergistic effects that accompany to slurry degradation.

Tribological Behavior of Cermet Coatings Deposited from Submicron WC-10Co-4Cr Powders Using HVOF Spraying

In this paper, we prepared cermet coatings deposited from submicron WC-CoCr powders using high-velocity oxygen-fuel (HVOF) spraying process. The detailed microstructures, slurry erosion and sliding wear resistance of as-sprayed coatings were investigated. The slurry erosion test was performed in a rotating disk rig facility with circulating system using distilled water and 3.5 wt.% NaCl slurries. The sliding wear properties were evaluated by a pin-on-disk tribometer under different loads. The results showed that submicron coatings exhibited higher slurry erosion resistance in distilled water slurry than that in 3.5 wt.% NaCl slurry after three tests. The slurry erosion mechanism of the coatings was characterized by scratches and pull-out of carbide particle. With increasing load (from 10 N to 50 N), the coatings showed a reduction in average friction coefficient (from 0.52 to 0.44), and an increase in mass loss (from 3.3 mg to 11.4 mg). The evolution of the sliding wear characteristics of the coatings with the increase of the load was micro-cracks, carbide particle pull-out, spallation, and massive exfoliation. The sliding wear mechanism of the coatings under different loads was primarily abrasive wear. DOI: http://dx.doi.org/10.5755/j01.ms.25.3.19507

Phase transformation of Nb2O5 during the formation of flame sprayed coatings and its influence on the adhesion strength, abrasive wear and slurry erosive wear

The development of research related to the characterization of niobium pentoxide (Nb2O5) has been of great interest in the scientific and commercial community due to promising performances in bio-electrochemical applications, advanced catalysts and corrosive environments. In this work, layers of 250 µm, 350 µm and 550 µm of Nb2O5 were deposited by low-speed flame spray on NiAl-bond coated AISI 1020 steel substrates. The phase transformations of Nb2O5, which occur during the formation of the layers, were studied as a function of deposited thickness and further correlated with adhesion, abrasion and slurry erosion resistance. X-ray diffraction analyzes of the coatings were performed for the study of the phases in the process. Optical Microscopy (OM) and Scanning Electron Microscopy (SEM) with dispersive energy microanalysis (EDS) were used to help microstructural analysis. The adhesive strength of the layers was evaluated by ASTM C633-13 and correlated with abrasion (ASTM G65-16) and slurry erosion wear resistance. From the microscopy analysis, a dense layer was observed with good interconnection at the interface Nb2O5-NiAl, with presence of pores typical of the thermal spray process. The XRD diffractograms of the niobium oxide coated samples show similar results regardless of the coating thickness (250, 350 and 550 µm) presenting superior compatibility with the hexagonal Nb2O5 and the monoclinic NbO2.46 (Nb22O54). The significantly higher intensities of the hexagonal Nb2O5 peaks suggest that it is the predominant phase. The thinner coatings, 250 and 350 µm, had higher adhesive strength, with a mean fracture stress of 16.12 MPa and 15.27 MPa, respectively. Nb2O5 thinner coatings showed also higher abrasive wear resistance when compared to "D2" tool steel and "H13" chrome tool steel. The thicker coatings (550 µm) had a mean adhesive strength of 13.73 MPa. From the abrasive wear tests, thicker coatings showed a greater volume loss of 41.18 mm3. The 550 µm coating presented higher slurry erosion resistance at a 30° particle impact angle, with a lower volume loss (12.93 mm3).

Comparison of the cavitation erosion and slurry erosion behavior of cobalt-based and nickel-based coatings

Cobalt-based and nickel-based coatings were successfully produced using TIG welding and laser cladding technologies as alternative materials with higher cavitation erosion (CE) and slurry erosion (SE) resistance, respectively. Their structure, phase constitution, hardness and elastoplasticity were characterized. Combined with the cumulative mass loss, erosion morphology and roughness, the CE and SE resistances were compared and erosion models were also proposed. The results show that the cobalt-based coating exhibited much better CE resistance and lower SE resistance than the nickel-based coating. The phase transition contributes mostly to the high CE resistance of the cobalt-based coating. While, the combined effects of high hardness, elastoplasticity and hard phases' anchoring and shielding, determine the high SE resistance of the nickel-based coating.

Wear, erosion and corrosion resistance of HVOF-sprayed WC and Cr3C2 based coatings for electrolytic hard chrome replacement

Thermally sprayed carbide-based coatings are nowadays extensively considered as an alternative to electrolytic hard chrome (EHC) coatings to reduce the environmental impact and the overall cost associated with EHC process. In this investigation, high-velocity oxy-fuel (HVOF) spray process was employed to prepare coatings using the traditional carbide powders namely the WC-10Co4Cr, the Cr3C2-25NiCr and a new type of mixed carbide powder WC-40Cr3C2-25NiCr. The Powder deposition rate, basic mechanical properties, abrasive wear, slurry erosion and corrosion resistance of the three coatings were then compared with the EHC coating. The results show that WC-10Co4Cr coating exhibited the highest hardness, abrasive wear and slurry erosion resistance followed by WC-40Cr3C2-25NiCr, EHC, and Cr3C2-25NiCr coating. The deposition efficiency of the powders as per hierarchy was found to be WC-40Cr3C2-25NiCr > WC-10Co4Cr > Cr3C2-25NiCr and all the HVOF sprayed coatings exhibited higher corrosion resistance than EHC coating. The highest powder deposition efficiency coupled with low density, acceptable tribo-corrosion performance, as well as low post processing cost makes the HVOF sprayed WC-40Cr3C2-25NiCr coating a potential candidate to replace the EHC coating.

Mechanical properties and erosive behaviour of 10TiO2-Cr2O3 coated CA6NM turbine steel under accelerated conditions

Purpose This paper aims to evaluate the mechanical properties and slurry erosion behaviour of 10TiO2-Cr2O3 coated turbine steel. Design/methodology/approach Slurry erosion experiments were performed on the coated turbine steel specimens using slurry erosion test rig under accelerated conditions such as rotational speed, average particle size and slurry concentration. Surface roughness tester, Vickers microhardness tester and scanning electron microscope were used to analyse erosion mechanism. Findings Under all experimental conditions, 10TiO2-Cr2O3 coated steel showed better slurry erosion resistance in comparison with Al2O3 coated and uncoated steel specimens. Each experimental condition indicated a significant effect on the erosion rate of both coatings and uncoated steel. The surface analysis of uncoated eroded specimen revealed that plastic deformation, ploughing and deep craters formation were the reasons for mass loss, whereas microchipping, ploughing and microcutting were the reasons for mass loss of coated specimens. Originality/value The present investigation provides novel insight into the comparative slurry erosion performance of high velocity oxy fuel deposited 10TiO2-Cr2O3 and Cr2O3 coatings under various environmental conditions. To form modified powder, 10 Wt.% TiO2 was added to 90 Wt.% Cr2O3.

SiC Particulate Reinforced Aluminium Metal Matrix Composite

Al or Al alloy Metal Matrix Composites have wide range of applications i.e. aerospace, automobile etc. due to its lightweight, high tensile strength, high wear resistance. This review paper characterized the SiC particulate reinforced Al Metal Matrix Composites. The SiC particulates are dispersed in Al or Al alloy by liquid state processing route and solid-state processing route. Stir casting liquid processing route has been followed by no. of researchers due to its simplicity and low processing cost and at the time of reinforcement small amount of Mg is added to increase the wettability of SiC in molten Al or Al alloy. When Al or Al alloy reinforced with SiC, then its mechanical and tribological properties are enhanced. The effect of particle size, weight or volume fraction of the SiC on density, porosity, hardness, impact toughness, tensile strength, ductility, sliding wear resistance, slurry erosion resistance, erosion-corrosion resistance, corrosion resistance and fatigue strength of Al or Al alloy MMCs are reported. The effect of extrusion and machinability of the SiC particulate reinforced Al MMCs are also discussed in this review article.