Electro-spark deposition of Fe-based amorphous alloy coatings (original) (raw)
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Surface Modification of 304 Stainless Steel by Electro-Spark Deposition
Journal of Materials Engineering and Performance, 2018
Electrospark Deposition (ESD) is a pulsed micro-welding process that is used to apply surface coatings for repair of damaged high value precision products or modify their surfaces for specific properties. The low heat input, small heat affected zone and the ability to form metallurgical bonding of coating to substrate are some of the major advantages of ESD process. Many applications require the components to have excellent surface performance, such as wear resistance and corrosion resistance. To meet these requirements, some components are built with specific materials, compromising other properties and cost. ESD technique provides an approach to modify the component surface without compromising the bulk properties. Stainless steel is an ideal material for many applications such as industrial equipment, surgical instruments, household hardware etc., due to its resistance to corrosion. Surface modification of stainless steel may improve its performance and may open new applications. In this study, surface modification of 304 stainless steel by ESD was investigated. TiC, WC and Molybdenum (Mo) were employed as coating materials. The ESD processing windows for these coatings were investigated. Scanning electron microscope (SEM) and energy-dispersive X-ray spectroscopy (EDX) analysis was conducted to characterize the microstructure and composition of coated stainless steel. Micro-hardness and wear resistance tests were carried out to evaluate the mechanical properties of coated stainless steel. TiC and WC coatings dramatically increase the micro-hardness of 304 stainless steel. WC coating improves the abrasion wear resistance of stainless steel by more than 5 times, while TiC and Mo coatings also improve it by 2.5 times. Electrochemical tests were conducted to investigate the corrosion resistance of coated stainless steel. Mo coating exhibits significant improvement on corrosion resistance in 5% NaCl solutions, iv which corrodes 350 times slower than stainless steel. TiC coating also increases the corrosion resistance with 10 times slower corrosion rate. WC coating does not show improvement on the corrosion resistance. Electrochemical impedance spectroscopy (EIS) was employed to further investigate the electrochemical behavior of coated stainless steel. The results showed the polarization resistance of Mo coated sample is much larger than that of base metal stainless steel. XRD analysis indicate the phase transformation from austenite to ferrite after ESD of Mo. Comprehensive metallurgical analysis of Mo coated 304 stainless steel is performed after heat treatment at 400ºC, 650ºC and 900ºC. The effects of heat treatment atmosphere are investigated by comparing the sample treated in air and Ar gas. SEM and EDX results show the coating thickness decreases with the increase of heat treatment temperature. Localized Mo rich area is found in heat-treated samples. More cracks, porosities and rougher surface conditions are observed in heat-treated samples. XRD analysis display phase transformation from austenite to ferrite at 400ºC. Mo rich intermetallic is detected at 650ºC under Ar gas. Mo and Cr oxides are found in heat-treated samples above 650ºC in air. XPS results show metallic state Mo disappears after heat treatment in air, while metallic state Mo only disappears at 650ºC in Ar gas. It is suggested that Mo rich intermetallic is formed at specific temperature range around 650ºC. Electrochemical test indicated heat-treated samples, either in Ar or in air atmosphere, have lower corrosion resistance than as-deposited sample. Metallic state Mo and a certain ratio of austenite and ferrite can contribute to better corrosion resistance. EIS analysis with modified equivalent circuit is conducted to further investigate the electrochemical behavior. The results indicate that heat-treated samples introduce more nonuniform coating layers because of oxidation and diffusion of alloy elements. Mo rich intermetallic phase decreases the corrosion potential of the heat-treated sample at 650ºC in Ar, and also decreases the corrosion rate of the sample. v I would like to thank Mr. Nigel Scotchmer, Kevin Chan and Dominic Leung at Huys Industries Ltd. for their assistance and technical support. I would like to thank Huys industries Ltd, Ontario Centres of Excellence (OCE) and National Sciences and Engineering Research Council (NSERC) for providing financial support for this work. I also thank TechnoCoat Co.,Ltd, for materials support. The advice, encouragement and counsel of Dr. Joyce Koo during times of need are the reasons I am capable of finishing this project. I'd like to express my gratitude for her help of getting materials, sharing references and invaluable discussions.
Electrochimica Acta, 2011
The Fe-based amorphous coatings with the composition of Fe 48 Cr 15 Mo 14 C 15 B 6 Y 2 were successfully sprayed on mild steel substrate by the high velocity oxygen fuel (HVOF) spraying process with different feedstock powder sizes (i.e., powder A: −33 + 20 m, powder B: −45 + 33 m, powder C: −55 + 45 m). The coatings were characterized for its morphology, microstructure and thermal stability by using Xray diffraction (XRD), differential scanning calorimetry (DSC), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The corrosion behavior of the coatings in 3.5 wt% NaCl solution was studied with potentiodynamic and potentiostatic polarization test. It was found that the particle size of the feedstock powders had a significant influence on microstructure and corrosion resistance of the resultant coatings. The coatings sprayed with the finest powders show the most compact structure; while the coating with the coarser powders exhibits a better corrosion resistance. It is found that the corrosion resistance of the coatings is closely related to the wetting behavior which is affected by the oxygen content and the roughness of coatings. The coatings with hydrophobicity exhibit a better corrosion. The present result demonstrates that the amorphous coatings with hydrophobicity and excellent corrosion resistant are promising for industrial application in marine environment.
Metallurgical and Materials Transactions A, 2018
Mechanically milled FeCrNbB feedstock powders from commercial precursors were used to produce amorphous coatings through two different industrial thermal-spraying techniques: high-velocity oxygen fuel (HVOF) and flame spraying. Microstructure, thermal behavior, and hardness of the coatings and their corrosion resistances in acidic and alkaline chloride-rich media were comparatively studied. HVOF process was effective to produce~200-lm-thick highly amorphous coatings with hardness over than 700 HV 0.3 and low porosity (~5 pct). Flame-sprayed~220-lm-thick coatings were nanocrystalline, composed of a-Fe, Fe 2 B, FeNbB, and Fe 2 O 3 phases and presented hardness of 564 HV 0.3 and~10 pct porosity. Electrochemical measurements indicated that HVOF coatings exhibit higher corrosion resistance than flame-sprayed ones thanks to the higher amorphous content and lower porosity resulting from the former processing route. Electrochemical impedance spectroscopy results demonstrated that amorphous HVOF Fe 60 Cr 8 Nb 8 B 24 (at. pct) coatings are interesting to protect mild steels such as the API 5L X80 against corrosion in chloride-rich environments.
Journal of Materials Engineering and Performance, 2017
The present work describes a series of new amorphous and nanocrystalline composite coatings (composition: 87.6% Fe, 6.7% Si, 2.5% B, 2.5% Cr, 0.7% C in wt.%) on a mild steel substrate made by high-velocity oxy-fuel thermal spray at different feed rates of 20, 30 and 40 g/min. The microstructure characterization using scanning electron microscopy coupled with energy-dispersive spectroscopy shows uniform and adherent coatings of different thickness depending on the feed rate. The structure of the coating is composite in nature (mixture of amorphous and nanocrystalline phases) as confirmed by the x-ray diffraction and transmission electron microscopy. The hardness of the coating is almost 6-7 times than that of the substrate. Though polarization test of the coating demonstrates corrosion resistance in 3.5% NaCl solution similar to the substrate, the difference of corrosion potentials of the coatings and the substrate is largely negative ($ more than 200 mV against saturated calomel electrode) suggesting anodic nature of the coating as compared to the substrate resulting in sacrificial effect.
Sliding Wear Behavior of Spark-Plasma-Sintered Fe-Based Amorphous Alloy Coatings on Cu-Ni Alloy
Journal of Materials Engineering and Performance, 2018
This paper reports on the processing of Fe 48 Cr 15 Mo 14 Y 2 C 15 B 6 amorphous alloy coatings on Cu-10%Ni (wt.%) alloy using spark plasma sintering. The amorphous alloy coatings were sintered at temperatures ranging from 575 to 675°C at a pressure of 50 MPa. The development of microstructure, phases, and wear properties with sintering temperature of the coatings is investigated. The sintered coatings were found to be near fully dense with hardness close to that of the sintered bulk amorphous alloy. X-ray analysis indicated increasing degree of devitrification of the amorphous coatings with increasing sintering temperature. The wear behavior of the coatings is significantly influenced by the sintering temperature with volume wear rate first decreasing in the temperature range of 575-650°C and then increasing above 650°C. The variation in wear behavior is explained based on relative stability of the protective surface layer and embrittlement of the surface with the sintering temperature.
Corrosion Resistance of Iron-Based Amorphous Metal Coatings
Volume 7: Operations, Applications, and Components, 2006
New amorphous-metal thermal-spray coatings have been developed recently that may provide a viable coating option for spent nuclear fuel & high-level waste repositories [Pang et al. 2002; Shinimiya et al. 2005; Ponnambalam et al. 2004; Branagan et al. 2000–2004]. Some Fe-based amorphous-metal formulations have been found to have corrosion resistance comparable to that of high-performance alloys such as Ni-based Alloy C-22 [Farmer et al. 2004–2006]. These materials rely on Cr, Mo and W for enhanced corrosion resistance, while B is added to promote glass formation and Y is added to lower the critical cooling rate (CCR). Materials discussed in this paper include yttrium-containing SAM1651 with CCR ∼ 80 K/s and yttrium-free Formula 2C with CCR ∼ 600 K/s. While nickel-based Alloy C-22 and Type 316L stainless steel lose their resistance to corrosion during thermal spraying, Fe-based SAM1651 and Formula 2C amorphous-metal coatings can be applied with thermal spray processes without any sign...
Preparation and characterization of highly amorphous HVOF stainless steel coatings
Journal of Alloys and Compounds, 2010
A partially amorphous FeCrMoWBCSi powder has been HVOF sprayed in order to produce highly amorphous coatings. The extinction or retention of crystalline phases due to the spraying process is discussed. Amorphicity in coatings is associated with a high melting degree. The latter is attained by a high particle temperature and sufficient residence time in the flame. Coating properties, such as porosity, microhardness and adhesion strength are evaluated. The lowest coating porosity corresponds to the most amorphous coating. The least crystalline coating presents the highest corrosion resistance in 3.5% NaCl.
Corrosion Resistance of Fe-16%Cr-30%Mo-(C,B,P) Amorphous Coatings Sprayed by HVOF and APS Processes
Two kinds of Fe-16%Cr-30%Mo-(C,B,P) alloy powders having high ability to form an amorphous phase were thermal sprayed onto mild steel substrate using HVOF and APS processes. Perfectly amorphous coating was formed not only by the HVOF process but also by the APS process. The passive current densities of the amorphous coatings sprayed by the HVOF and APS processes were close each other and significantly low compared with that of SUS316L coating in 1 molÁL À1 HCl solution. The coatings of perfectly amorphous phase were little corroded after immersion tests in 1 molÁL À1 HCl solution for one week, though the coatings composed of the mixture of amorphous and crystalline phases corroded markedly.
Properties of the Electro-Spark Deposited Coatings - Technology and Applications
Materials Science Forum, 2015
The paper is concerned with the performance properties of electro-spark deposited coatings, which were determined basing on microstructural and roughness analysis and application tests. The studies were conducted using of the tungsten carbide-ceramic electrodes produced by the powder metallurgy hot pressing route. The anti-wear coatings were electro-spark deposited over C45 carbon steel by means of an EIL-8A. These coatings are likely to be applied to increase the abrasive wear resistance of tools and machine parts.