Effect of spraying parameters on the microstructural and corrosion properties of HVAF-sprayed Fe-Cr-Ni-B-C coatings

Thermally sprayed Fe-based coatings have been extensively studied as future solution in order to replace more expensive, harmful and environmentally dangerous Ni- and WC-based coatings for several industrial applications where high corrosion and wear resistance are required. The aim of the present study is to investigate the effect of spraying parameters on the microstructure and the corrosion resistance of Fe-based coatings manufactured with the High Velocity Air Fuel (HVAF) thermal spray process. Six sets of thermal spraying parameters have been chosen and their effect on the overall quality of coatings was investigated. All HVAF coatings showed comparably dense microstructure with near-zero oxidation, proving the high quality of the deposition process. However, higher anti-corrosion and mechanical properties were achieved by increasing the spraying air pressure and decreasing the particle feeding rate without altering the thickness and the overall deposition rate. Powder feeding rate was reported to have a remarkable effect on microstructure and corrosion properties. Coatings with beneficial compressive residual stresses were successfully obtained by increasing air pressure during spraying which resulted in improved microstructural and corrosion properties

Properties of arc-sprayed coatings from Fe-based cored wires for high-temperature applications

Equipment of a thermal power plant is subjected to high temperature oxidation and wear. This raises operating costs through frequent repair of worn parts and high metal consumption. The paper proposes a possible solution to this problem through arc spraying of protective coatings. Cored wires of the Fe-Cr-C basic alloying system are used as a feedstock. Additional alloying by Al, B, Si, Ti and Y allows one to create wear- and heat-resistant coatings, which are an attractive substitute of more expensive Co- and Ni-based materials. © 2017 Author(s)

High-pressure cold-sprayed Ni and Ni-Cu coatings - Improved structures and corrosion properties

Cold spraying is a promising technique for the production of dense metallic coatings. In cold spraying, coating formation is based on high velocity impacts of solid particles with high kinetic energy. During the impacts, particles deform plastically and adhere, building-up the coating. This makes it possible to form pure and dense coating structures. Full impermeability of the coatings is required e.g. in corrosion protection applications. Nickel and nickel-copper alloys have good corrosion resistance and therefore, as dense coatings, they have a high potential for employment as corrosion barrier layers. In this study, the structural and corrosion properties of high-pressure cold-sprayed (HPCS) Ni and NiCu coatings are characterized. NiCu alloys are known to have good corrosion resistance e.g. in sulphuric and hydrochloric acids whereas Ni is resistant to e.g. caustic soda and alkaline salt solutions. This study also shows the effect of heat treatments on the coating performances. FESEM studies of cross-sectional samples reveal structural details of dense coatings while corrosion properties are evaluated with polarization measurements. Corrosion behaviors are compared with corresponding bulk materials and substrate material in order to perceive the real corrosion protection potential of the coatings

Porpora trombotico trombocitopenica e plasma exchange: studio di 8 casi

Le procedure venivano inziate il più precocemente possibile dopo la diagnosi e almeno le prime 5 sedute erano effettuatte a intervalli di 24 ore. Sette su otto pazienti hanno ottenuto una risposta completa con un programma intensivo di plasma exchange come terapia elettiva. Con una mediana di FU di 17 mesi (10-50) tutti i pazienti mantengono la remissione senza sequele neurologiche o complicamze infettive dovute alle unità di PFC trasfuse

Wear and corrosion resistance of high-velocity oxygen-fuel sprayed iron-based composite coatings

Thermally sprayed iron-based coatings are being widely studied as alternative solution to conventional hardmetal (cermet) and Ni-based coatings for wear and corrosion applications in order to reduce costs, limit environmental impact and enhance the health safety. The aim of the present work is to study the cavitation erosion behaviour in distilled water and the corrosion properties in acidic solution of four high-velocity oxy-fuel (HVOF) sprayed Fe-based composite coatings. Fe-Cr-Ni-B-C powder was selected for its good sliding wear properties. In addition, a powder composition with an addition of Mo was studied in order to increase the corrosion resistance whereas additions of 20 wt. % and 40 wt. % WC-12Co as blended powder mixtures were investigated in order to increase wear resistance. Improvement of coating properties was significant with the advanced powder compositions. Dense coating structures with low porosity were detected with microstructural characterization. In addition, good cavitation wear resistance was achieved. The cavitation resistance of customized Fe-based coating with Mo addition was reported to be twice as high as that of conventional Ni-based and WCCoCr coatings. The corrosion properties of HVOF Fe-based coatings were also evaluated by studying electrochemical behaviour in order to analyse their potential to use as corrosion barrier coatings. Copyright \uc2\ua9 2013 by ASME

Microstructural characteristics and tribological behavior of HVOF-sprayed novel Fe-based alloy coatings

Thermally-sprayed Fe-based coatings have shown their potential for use in wear applications due to their good tribological properties. In addition, these kinds of coatings have other advantages, e.g., cost efficiency and positive environmental aspects. In this study, the microstructural details and tribological performances of Fe-based coatings (Fe-Cr-Ni-B-C and Fe-Cr-Ni-B-Mo-C) manufactured by High Velocity Oxygen Fuel (HVOF) thermal spray process are evaluated. Traditional Ni-based (Ni-Cr-Fe-Si-B-C) and hard-metal (WC-CoCr) coatings were chosen as references. Microstructural investigation (field-emission scanning electron microscope FESEM and X-Ray diffractometry XRD) reveals a high density and low oxide content for HVOF Fe-based coatings. Particle melting and rapid solidification resulted in a metastable austenitic phase with precipitates of mixed carbides and borides of chromium and iron which lead to remarkably high nanohardness. Tribological performances were evaluated by means of the ball on-disk dry sliding wear test, the rubber-wheel dry particle abrasion test, and the cavitation erosion wear test. A higher wear resistance validates Fe-based coatings as a future alternative to the more expensive and less environmentally friendly Ni-based alloys

Microstructure and Sliding Wear Behavior of Fe-Based Coatings Manufactured with HVOF and HVAF Thermal Spray Processes

The microstructure and micromechanical behavior of thermally sprayed Fe-based coatings manufactured with high-velocity oxygen fuel (HVOF) and high-velocity air fuel (HVAF) processes were investigated. Fe-Cr-Ni-Si-B-C and Fe-Cr-Ni-Mo-Si-B-C powders were used as the feedstock materials. The coatings showed a highly dense microstructure with near-zero oxidation. The microstructure of the feedstock powders was better retained when sprayed with HVAF process. Differential scanning calorimetry revealed two small exothermic peaks at about 600\ua0\ub0C for the HVOF-sprayed coatings, without any increase in weight in thermogravimetric analysis. It suggested the re-precipitation of carbides that were dissolved during spraying due to the higher particle temperature reported by spray diagnostics system during the HVOF process ( 481800\ua0\ub0C) compared to the HVAF one ( 481400\ua0\ub0C). Micro- and nano-indentations helped to show the difference in inter-lamellar cohesive strength and, in turn, in the particle deposition mechanism. Coatings sprayed with Fe-Cr-Ni-Mo-Si-B-C composition possessed higher sliding wear resistance than that of Fe-Cr-Ni-Si-B-C due to higher nano-hardness. More specifically, HVOF-sprayed Fe-Cr-Ni-Mo-Si-B-C coating showed the largest intra-lamellar hardness, the largest elasticity, and high quality of particle interfaces which resulted in lower sliding wear rate

Micromechanical properties and sliding wear behaviour of HVOF-sprayed Fe-based alloy coatings

The tribological performance of two Fe–Cr–Ni–Si–B–C (Colferoloy) alloy coatings manufactured by HVOFthermal spraying was studied by rubber-wheel dry particle abrasion test and ball-on-disk sliding wear tests. The results were compared to those obtained on Ni–Cr–Fe–Si–B–C and Cr3C2–NiCr layers (also manufactured by HVOF-spraying), hard chromium electroplating and bulk tool steel. At room temperature, the sliding wear loss of the Colferoloy coatings against alumina counterpart,caused by a mix of mild abrasion, delamination and tribo-oxidation, was larger than that of Cr3C2–NiCrand tool steel but lower than that of Ni–Cr–Fe–Si–B–C and hard chromium plating. At 400 ◦C and 700 ◦C,Colferoloy coatings mainly suffered abrasive grooving: they were still superior to Ni–Cr–Fe–Si–B–C butinferior to Cr3C2–NiCr. Against steel, Colferoloy coatings, with limited delamination and negligible wearloss, were comparable to Cr3C2–NiCr and superior to Ni–Cr–Fe–Si–B–C, tool steel and electrolytic hardchromium, although they inflicted quite significant wear to the steel counterbody. Colferoloy coatings were therefore validated as alternatives to Ni-based alloys and electroplatedchromium under sliding wear conditions, but appeared unsuitable for particle abrasion resistance. The different sliding wear behaviours of HVOF-sprayed coatings could be explained by coupling micro and nano-hardness to scratch testing, which reflected cracking resistance and plastic deformability