Search Results for steel

Superior characteristics of the cold sprayed coating have led to many high-tech applications. Until recently, all these applications were carried out using ‘stationary’ systems only, while some applications such as in-situ repair of aircraft body/engine parts require a portable system. Recently a ‘Portable High Pressure Cold Spray System’ called KINETIKS 2000-2 has been developed. This system is capable of 400 C/20 bars nitrogen/helium jet, and produces dense coatings with clean interfaces of many materials. In order to establish the suitability of this process for producing aluminum alloy coatings for aerospace and other high tech industries, various aluminum alloys (CP-Al, HP-Al, 6061 Al, 7005 Al) coatings were produced over many substrate materials (2024 Al, 7005 Al, 4041 Steel, ZE41A Mg). Coatings were characterized using microstructure, bond strength, bend test, corrosion studies, etc. Microstructural study showed that dense coatings with about 2-4% porosity values were produced with clean and well bonded interfaces. Bond strength of these coatings varied between 20 to 35 MPa, Bend test results showed that the coatings have adequate strengths and could withstand severe strain conditions. Salt fog corrosion studies (ASTM B 117) showed that the coatings impart corrosion resistance to the substrates.

Multilayer high-speed cladding by injection of a M2 steel powder with 0.82%C, 4.7%Mo, 6.4%W, 4.1%Cr, 2.02%V, 0.3%Mn, as chemical composition, in a melted bath produced using a CO 2 continuous wave laser connected to a x-y-z coordinate table was tested in order to increase the wear resistance and heat stability of tool active surfaces made of 0.45%C steel. Layers made by different laser runs were characterized by macro and microstructure analysis, as well as a phase identification analysis by X-ray diffractometry, micro-hardening analysis and hardness testing on the coated layer surfaces in order to establish the optimal cladding condition. Lathe tools made using this technique showed a good ability to maintain their cutting power during steel shaping.

The aim of this study is to achieve, on aluminum alloy substrates, coatings with higher hardness and better dry tribological behavior than that of the substrate. Using atmospheric plasma spraying and a vibratory fluidized bed powder feeder, coatings consisting of a stainless steel matrix with embedded graphite particles were successfully deposited. The dry coefficient of friction of the composite layer is comparable with that of a commonly used stainless steel surface. SEM examinations of polished cross-sections reveal a lamellar structure with randomly distributed graphite inclusions. Paper includes a German-language abstract.

Steel reinforcement corrosion is one of the most serious causes of the premature deterioration of North American bridges and parking garages. Carbon steel rebars are very vulnerable to corrosion in salt contaminated concrete from deicing or coastal environment since the chloride ions induce severe corrosion as they reach the reinforcing steel rebars and depassivate the carbon steel. This paper evaluates the potential of using stainless steel coatings as a means to protect steel rebars from corrosion, especially in a salt contaminated concrete environment. The 316 L stainless steel coated coupons and rebars were prepared using Arc-sprayed and HP/HVOF processes. The corrosion performance of coatings were evaluated using linear polarization, a.c. impedance and salt spray techniques. Metallographic examination was also performed to characterize the coating microstructure.

In this study, stainless steel splats were deposited on preheated stainless steel substrates with oxide scales of different thickness in inert low-pressure plasma spay (LPPS) conditions to examine the effect of in-situ oxidation of prior splats on the morphology and bonding of subsequently formed splats. Splat-substrate interface cross-sections were prepared by focus-ion-beam milling. Splat morphology and bonding state with the substrate were characterized by SEM. The results show that with oxide films up to 35 nm thick, disk-type splats are deposited that bond well to the substrate except in the periphery region. As oxide films become thicker (100 nm) and present a surface with micro-scale roughness, splats take on a finger-like shape with poor bonding at the interface.

The world’s first plant for manufacture of stainless steel clad structural steel is now operational in the USA. The process consists of coating round steel billets with a spray of stainless steel. A metallurgical bond is achieved so that the billets can be reheated and hot worked into long products while retaining the integrity of the coating. The process consists of teeming stainless steel from a ladle into a spray chamber and atomizing the emerging stream with jets of nitrogen to form a spray of semi-liquid particles. The spray is directed onto a 140mm diameter preheated carbon steel billet to form a thick coating (4 – 5mm). The spraying rate of 50Kg/minute produces clad billet at the rate of 15tonnes/hr. Billet is then hot rolled in a conventional bar mill to make corrosion resistant clad steel sections such as rebar and dowel pins. Coating thickness after rolling is in the range 0.5 – 1.0 mm depending on the final section. Clad products have a life expectancy of 75 – 100 years in high chloride environments such as tidal zones, bridge decks and highways treated with de-icing salts. The spray coating process is described together with mechanical properties of the clad bar and results of corrosion tests. The economics of stainless clad steels vs. other corrosion resistant materials are reviewed.

A new process has been developed to incorporate graphite particles in a stainless steel coating during its formation. Four means have been tested to inject the graphite particles outside the plasma jet and its plume : graphite suspension, a graphite rod rubbed on the rotating sample, powder injection close to the substrate with an injector or an especially designed guide. The latter process has been shown to be the most versatile and the best controllable one. It allows to incorporate uniformly between 2 and 12 vol % of graphite particles (2-15 µm) within the plasma sprayed stainless steel coatings. A 2 vol % seems to give the best results : a low decrease (6%) of the coating hardness and the best results in dry friction studied with a pin on disk set up. In this case, depending on the sliding velocity (0.1 to 0.5 m/s) and loads (3.7 to 28 N) the dry friction coefficient against a 100C6 pin is reduced by a factor between 1.5 and 4 compared to that obtained with plasma sprayed stainless steel.

Higher-temperature operation in a gas turbine has urged development of heat-resistant coatings and thermal barrier coatings. We have developed a 2CaO-SiO 2 -CaO-ZrO 2 based thermal barrier coating. This coating should effectively prevent separation of the coating by relieving the shear stress generated due to thermal change of environment between layers with dissimilar properties. The coating was applied to stationary vanes of an actual gas turbine in a 25,000-hour test. This paper describes the results of the field test.

Design, manufacturing, and utilization of efficient heating systems for pipelines and closed-pressure equipment are necessary for cold regions to compensate for heat loss and prevent damages that are caused by freezing of the enclosed liquid. Given large-scale financial losses that stem from failure and bursting of the pipes, the development of novel, efficient, and affordable heaters, which can lead to improved efficiency, cost savings, and environmental benefits across various industries and applications, is of crucial importance. Heating systems have already been produced via different high-temperature thermal spraying techniques to achieve higher efficiency compared to conventional heating cables. In this study, tin, as the heating element, was deposited by using the cold spray process onto alumina coating that was fabricated by flame spraying (FS) to provide electrical insulation. Techno-economic assessment of fabrication and utilization of the coating-based heaters was conducted. It was found that cold-sprayed heater coatings exhibit improved performance compared to other thermally sprayed heater coatings and conventional heater cables. Further, their fabrication and utilization were more economically feasible. The results suggest that the new generations of coating-based heating systems may be competitive with conventional heat tracers that are widely used in industry.

In Laser Cladding, a differentiation must be made between cladding by brazing and cladding by welding regarding process parameters and the resulting material properties. Results of investigations of bronze cladding on steel parts produced by Laser Deposition Brazing will be presented. This means that a strong metallurgical bond is realized by diffusion processes by Laser Deposition Brazing, but the steel base material is not molten. The coatings were characterized by hardness distribution measurements from the bronze cladding to the steel substrate, by measuring the size of the heat-affected zone and by porosity measurements. This combination of a steel substrate and a local bronze coating is used industrially in many tribological applications, such as plain bearings or hydraulic pumps etc. The bronze offers excellent tribological properties. In some cases, the bronze is used as a complete solid part. However, applying the bronze locally to a steel base body instead of using a complete solid bronze component, offers the advantage of the higher modulus of elasticity of the steel, which provides greater stability of shape with regard to possible elastic deformations as these coated parts are exposed to high mechanical loads, it is essential that a high coating quality is achieved by laser cladding and that the properties are extensively and purposefully characterized. The production technology, the characterization and the industrial applications of such bronze coated steel parts are presented and explained in this contribution.

Erosion-corrosion is a severe problem observed in the coal fired thermal power plant boilers which lead to premature failure of boiler tubes. Thermal spray coatings have been applied successfully to check the erosion-corrosion of boiler tubes. In the present research work NiCrTiCRe coating powders were successfully deposited on T22 boiler steel by two different coating processes i.e. high velocity oxy-fuel (HVOF) and cold spray process. The performance of the coatings in actual power plant boiler were investigated and compared. The uncoated and coated T22 boiler steels were subjected the superheater zone of the coal fired boiler for a total of 15 consequent cycles. The thickness loss data and weight change analysis were used to establish kinetics of the erosion-corrosion. X-ray diffraction, surface field emission scanning electron microscope/energy dispersive spectroscopy (FE-SEM/EDS) techniques were used in the present work for the analysis. The results of thickness loss data indicated that the cold sprayed coating performed better in thermal power plant boiler environment.

This work is concentrated on plasma sprayed cermet coatings consisting of stainless steel (SS) (17 wt % Cr and 12 wt % Ni) and chromium oxide (Cr 2 O 3 ). These powders were sprayed simultaneously, however being injected separately to account for the drastic difference in their thermo-physical properties. Chromium oxide was injected internally and stainless steel externally. The plasma parameters (arc current, hydrogen vol %, mass flow rate) were optimized as well as the injector positions. Coatings were achieved with different mass ratios of SS and Cr 2 O 3 . All exhibited a lamellar structure with well distributed Cr 2 O 3 and SS lamellae. They were then systematically characterized by their phase content (XRD), composition (EDS), Vickers micro hardness, morphology (SEM), slurry and dry wear resistances. Finally the best dry linear abrasion resistance was obtained for the pure chromium oxide coatings, while the best slurry wear resistance corresponded to coatings with a mass ratio SS/ Cr 2 O 3 of 56/44.

Fatigue properties of the Al 2 O3 plasma-sprayed SUS316L stainless steel rod specimens coated on different spraying conditions have been studied in a physiological saline solution (0.9 % NaCl solution) to evaluate the potential of surgical implant application. Fatigue tests were conducted in push-pull loading at the stress ratio of R = -1, and frequency of 2 Hz. Microstructure related with fatigue damage was examined by SEM and TEM. The fatigue strength of Al 2 O 3 plasma-sprayed metals significantly depended on spraying conditions: the effects of spraying on fatigue strength decreased with increasing the applied stress amplitude. As-blasted specimens were higher in fatigue strength than Al2O3 plasma-sprayed specimens. It was found that the plasma spraying had significant effects on fatigue crack growth behavior in the early stage of crack propagation. Fatigue cracks preferentially originated from dents that had been caused on the substrata metal surface subjected to grit-blasting. These results are discussed with both the compressive residual stresses due to the grit blasting which was carried out prior to plasma spraying and the corrosion-resistance of the alumina deposit.

In order to increase the wear and corrosion resistance of 0.45% C surface steel layers, a multilayer coating was tested by injection of a powder with 8.9% Cr, 4.5% Fe, 5.1% B, 2.4% Al, 0.6% Cu and all remainder of Ni in the melted bath produced using a CO 2 continuous wave laser. To determine the optimal melting regime, the layers obtained by different laser conditions were characterized by macro and microstructure analysis, as well as a phase qualitative analysis by X-ray diffractometry and microhardness analysis.

Modification of the nozzle of the arc spray equipment was attempted in order to reduce microstructural defects of the spray-formed steel shells since these defects mainly degrade the overall properties of the spray-formed tools. Based on the in-flight particle analysis, a new nozzle design of a gas shrouding concept was proposed. Effects of design factors such as nozzle dimensions and process conditions was investigated by using statistical analysis methods. The results demonstrated that the oxidation of the spray-formed steel shells can be reduced to the one-third levels of the original ones with an optimized design.

In this study, MoB-CoCr composite coatings are deposited on low-carbon steel substrates by HVOF spraying and salt spray tests are conducted to qualitatively evaluate coating density. Test samples with optimized dense coatings showed no rust after 300 hours in a salt spray. Samples with porous coatings, on the other hand, showed signs of rust after just 24-48 hours. Test samples protected by the dense composite coatings, as confirmed by salt spray testing, were undamaged after 90 days of immersion in a Zn-0.2%Al galvanizing bath at 460 °C.

In this study, Ni-20Cr alloy powder was synthesized and deposited on T22 boiler steel by HVOF spraying. Coated and uncoated test samples were placed in a silicon carbide tube furnace and subjected to cyclic oxidation conditions in 900 °C air. Oxidation kinetics were established via weight change measurements and oxidation products were characterized based on XRD and SEM-EDS analysis. The results show that in addition to improving the oxidation resistance of the steel, the Ni-20Cr coatings also reduced spallation due to the formation of a protective Cr2O3 phase.

Cold spray processing of stainless steel coatings, which represent a cost-effective method for wear and corrosion resistance, has been demonstrated as technically feasible. However, these coatings have very low tensile strength in the as-sprayed condition and may also exhibit a marginally higher wear rate. In this study, the cold spraying of 316L stainless steel coatings was investigated to assess the effect of powder size distribution and post-spray heat treatment on strength and wear properties. Coatings on aluminum and steel substrates were produced with a feedstock powder obtained in three particle size distributions. All coatings were deposited under the same conditions using nitrogen as the propellant gas, and then annealed at the optimum temperature. The microstructure and mechanical properties of both as-sprayed and heat-treated coatings were evaluated and the results are presented in the paper.

This study compares the effects of plasma nitriding and nitrocarburizing treatments on HVOF sprayed stainless steel coatings with different crystal structure. The treatments were conducted at 550 °C for 10 h in a gas mixture of N 2 and H 2 for nitriding and N 2 , H 2 , and C 2 H 2 for nitrocarburizing. Optical microscopy, SEM-EDS, and XRD show that the treatments produced thick nitride layers consisting of a compound layer and a nitrogen diffusion layer. The treatments increased not only the surface hardness, but also the load bearing capacity of the coatings due to the formation of CrN, Fe 3 N, and Fe 4 N phases. Plasma nitrocarburized 410 stainless steel had the highest microhardness and load bearing capacity because of the precipitation of Cr 23 C 6 on the surface.

The high velocity combustion wire (HVCW) sprayed coatings have unique structures and properties which are different from the conventional wire / powder HVOF coatings. This paper studies the coatings of 0.8% C Steel formed by the HVCW system. 0.8% C Steel coatings formed by the HVCW system were studied for their wear resistance (pin on desk wear test) and phase composition. Methods like SEM with Wavelength Dispersion Spectroscopy (WDS) attachment were utilized for determining the composition of the coatings. Microhardness and tensile bond strength of the coatings were also ascertained. A set of conventional oxy-acetylene wire flame spray coatings of 0.8% C Steel were also prepared and these coatings were then compared with the HVCW coatings. Possible applications of the HVCW coatings are discussed based upon the properties of the coatings.