Search

A cored wire formulation, referred to as Alpha 1800, has been developed to produce tailored arc-sprayed coatings that are tough enough to resist particle impacts at 90° and sufficiently hard to deflect eroding particles at low impact angles. One millimeter thick coatings composed of ductile and hard phases with a Knoop hardness reaching 1800 kg/mm2 were easily produced by arc spraying the cored wire with air. Coatings were (1) erosion tested at 25 °C and higher temperatures at impact angles of 25 and 90° in a gasblast erosion rig, (2) slurry erosion tested at impact angles of 25 and 90°, and (3) abrasion wear tested using the ASTM G-65 test procedure. Results show that coatings produced with the new cored wire are at least 5 times more erosion resistant and 10 times more abrasion resistant than coatings produced by arc spraying commercial cored wires. The performance of the new arc-sprayed coating can be compared with that of high-energy WC-based coatings. Maintaining their erosion resistance after being exposed to temperatures up to 850 °C and possessing good oxidation resistance, arc-sprayed coatings produced with the new cored wire are attractive for applications in many industrial sectors involving high temperatures. [ABSTRACT FROM AUTHOR]

Iron ore pellets are sintered and reduced in large continuous industrial oil-fired furnaces. From the furnace, powerful fans extract large volumes of hot gas. Being exposed to gas-borne iron ore particles and temperatures ranging between 125 and 328 °C, fan components are rapidly eroded. Extensive part repair or replacement is required for maintaining a profitable operation. The arc spraying technique has been suggested for repair provided it could produce erosion-resistant coatings. Conventional and cored wires (1.6 mm diameter) were arc sprayed using various spray parameters to produce 250 to 300 µm thick coatings. Arc-sprayed coatings and reference specimens were erosion tested at 25 and 315 °C and impact angles of 25 and 90° in a laboratory gas-blast erosion rig. This device was designed to impact materials with coarse (32 to 300 µm) iron ore particles at a speed of 100 m/s. The coating volume loss due to erosion was measured with a laser profilometer built by National Research Council Canada several years ago. Few arc-sprayed coatings exhibited erosion resistance comparable with structural steel at low impact angles. Erosion of arc-sprayed coatings and reference specimens dramatically increases at 315 °C for both 25° and 90° impact angles. Erosion-enhanced oxidation was found to be responsible for the increase in volume loss above room temperature. Though arc spraying can be appropriate for on-site repair, the development of more erosion-resistant coatings is required for intermediate temperatures. [ABSTRACT FROM AUTHOR]

A pulsed CO-TEA laser was used to melt the surface of plasma-sprayed coatings. An analysis of the laser parameters on the heat transfer is made: the melt depth and the surface temperature were calculated for different laser inputs. It was found that the pulse length must be in the range of 20 to 40 μs in order to fill up the pores of the coating and to keep the surface temperature below the boiling range. Experimental results on surface modification are explained in terms of power density. [ABSTRACT FROM AUTHOR]

A pulsed CO-TEA laser was used to melt the surface of plasma-sprayed coatings. An analysis of the laser parameters on the heat transfer is made: the melt depth and the surface temperature were calculated for different laser inputs. It was found that the pulse length must be in the range of 20 to 40 µ s in order to fill up the pores of the coating and to keep the surface temperature below the boiling range. Experimental results on surface modification are explained in terms of power density. [ABSTRACT FROM AUTHOR]

Thermally sprayed titanium coatings were investigated in the laboratory as anodes for the cathodic protection of reinforced concrete. Three proprietary catalyst systems were used to activate the titanium anode coatings. Some experiments were conducted that applied the catalyst as a precoat on the metallizing wires; in other experiments, the catalyst solution was applied onto concrete blocks before or after arc spraying with titanium. The coated reinforced concrete blocks were powered at a constant current density and in a 95% relative humidity for more than 95 days. The driving voltages measured across the samples demonstrated that precoating the catalyst on the titanium wires had little effect on the driving voltage over the recorded lifetime. In other experiments, where the catalyst was directly applied to the surface of the reinforced concrete blocks, only the cobalt oxide catalyst significantly reduced the driving voltage requirements. The cobalt oxide reduced the driving voltages regardless of whether it was applied on the concrete blocks before or after arc spraying with titanium. [ABSTRACT FROM AUTHOR]

Arc-sprayed coatings are an attractive means to protect components from abrasive wear provided they contain enough hard phases. Because of their hardness and toughness, 316L-TiB2 cermets were selected as the basis for developing wear-resistant coatings. Cored wires composed of type 304 stainless steel sheaths filled with 10 to 65 wt% TiB2,1 to 15 wt% additives, and the balance with 316L stainless steel were fabricated and arc-sprayed with air. The arc-sprayed stainless steel-TiB2 coatings were abrasion tested and the volume loss measured with an optical profiloineter. The volume loss decreased as the proportion of TiB2 increased. However, large differences in volume loss between coatings that contain about the same volumetric proportion of hard phases cannot be explained by a linear relationship. An inverse rule of mixing was proposed and found useful in determining the influence of different additives. Tin, added in the core as a fugitive liquid transfer agent, was the most powerful additive for improving the wear resistance of stainless steel-base coatings. These advanced arc-sprayed stainless steel-TiB2 coatings exhibit greater wear resistance than those obtained by arc spraying commercial solid and cored wires. [ABSTRACT FROM AUTHOR]

The abrasion wear resistance of stainless steel and composite stainless steel/titanium boride coatings arc sprayed with air and argon was evaluated. Stainless steel coatings arc sprayed with air were found to be slightly more resistant than bulk stainless steel, whereas those sprayed with argon were slightly less resistant. The wear resistance of composite stainless steel/titanium diboride coatings was from two to four times greater than that of bulk stainless steel, depending on the cored wire constitution and the type of gas used for spraying. Microstructural analysis, microhardness measurements, and optical profilometry were used to characterize the coatings and wear damage. By considering both the wire constitution and the spraying conditions, it was possible to fabricate composite stainless steel coatings that showed a 400 % increase in wear resistance over bulk stainless steel. [ABSTRACT FROM AUTHOR]

Plasma-sprayed metal-base coatings containing ceramic particles were considered for high-temperature sealing of a moving metal component with a dense silica-base ceramic preheated at 800 ‡C. Selected metal powders (NiCoCrAlY, CuNi, CuNiIn, Ag, Cu) and ceramic particles (boron nitride, Zeta-B ceramic) were agglomerated to form suitable spray powders. Plasma-sprayed composite coatings and reference materials were tested in a modified pinion-disk apparatus in which the stationary disk consisted of a dense silica-base ceramic piece initially heated at 800 ‡C and allowed to cool during tests. The influence of single exposure and repeated contact with ceramic material on coefficient of friction, wear loss, and damage to the ceramic piece was evaluated. [ABSTRACT FROM AUTHOR]

Arc-sprayed zinc coatings can provide cathodic protection against corrosion to steel reinforcement in concrete. Because the adhesion of sprayed zinc on concrete is of major concern, the parameters related to zinc deposition and concrete preparation that affect the adhesion have been previously investigated. However, little attention has been devoted to determining which basic mechanisms are responsible for the adhesion of molten zinc on concrete. Because the interaction of molten zinc droplets with the concrete surface is considered physical, this paper is focused on the influence of surface patterns on the adhesion of arc-sprayed zinc coatings. Concrete surfaces were characterized by image analysis and profilometry techniques to ascertain which surface pattern or components could affect the adhesion of zinc. A modified root mean square (RMS) surface roughness was derived to take into account the different surface mor-phologies seen by sprayed zinc droplets. This modified RMS surface roughness was found to be directly related to the measured bond strength of arc-sprayed zinc on concrete. After the surface profile on con-crete is measured and the surface constituents are considered, the bond strength of arc-sprayed metals on concrete can be forecasted for given deposition parameters. [ABSTRACT FROM AUTHOR]

The dispersion of more than 20 vol.% submicrometer ceramic particles within a metallic matrix and the deposition of such a cermet to form a thick and tough coating presents problems. Most of the coating techniques have failed in attempting to homogeneously disperse very fine and hard particles in large amounts while avoiding their decomposition or reaction with the metal matrix during the deposition process. A simple and efficient method has been developed for producing ceramic-containing composite coatings. It consists in synthesizing cermet-based materials and in depositing them by a rapid solidification process such as thermal spraying. Boride- and carbide-based materials have been successfully obtained by plasma spraying reactive powders comprising the basic reagents. These materials, with a microstructure of submicrometer ceramic particles dispersed in a metallic matrix, exhibit good wear-resistant properties (abrasion and sliding wear). Finally, reactive core wire arc spraying is suggested as a flexible way to produce coatings containing up to 25 vol.% TiB. [ABSTRACT FROM AUTHOR]

The accurate determination of the volume loss of plasma- sprayed coatings submitted to abrasive and erosive wear and the visualization of wear track or crater profiles are of major concern when ranking coatings, developing wear- resistant coatings, or identifying the mechanism responsible for failure. The determination of the volume loss by liquid displacement measurements is impractical when the size of coated pieces is large and the volume loss is small. For evaluating coating damage and directly measuring the volume loss, a three- dimensional surface mapping method is proposed. The three- dimensional image of the worn surface is obtained by a laser triangulation method. The experimental setup is basically composed of an illuminating source and a detecting device. The light source is focused on the sample surface, and the reflected light is then collected on a network of charge couple detectors linked to a computer. Because the spot location on the network is a direct function of the measured height, a three- dimensional image can be obtained after scanning the entire damaged surface so that the volume loss can be calculated easily. Intensity- coded depth images of the worn surface and computerized cross sections of the damaged area can also be obtained. Inspection of coatings damaged by abrasion wear or slurry erosion by optical profilometry reveals that the volume loss measurements by this technique are very accurate as opposed to the volume measured by liquid displacement methods or calculated from weight loss measurements. Moreover, intensity- coded depth images of worn surfaces and computerized cross sections of damaged areas provide relevant information about the coating performance or defects resulting from the deposition process. [ABSTRACT FROM AUTHOR]

Electrotribological applications require materials with both high electrical conductivity and wear resisance. For this purpose, a copper- base plasma sprayed coating containing titanium diboride particles was developed. The process for fabricating this CU- TiB coating consists of plasma spraying reactive powders that contain a Cu- Ti alloy and boron. The reaction between the copper alloy and boron proceeds in different steps going from solid- state diffusion of titanium and copper to the synthesis of TiB in a liquid below 1083 ‡C. Plasma sprayed copper coatings contain finer TiB crystals than Cu- TiB materials synthesized in a furnace at 1200 ‡C. Coatings with 25 vol% TiB2 have hardnesses that are comparable to Cu- Co- Be and Cu- Ni- Be alloys and to Cu- W and Cu- Mo alloys used in spot welding. Their low electrical resistivity of 52 ΜΩ cm could be increased by lowering the oxygen content with coatings and controlling the formation of TiB clusters, the titanium content in solution in copper remaining low after the synthesis reaction. [ABSTRACT FROM AUTHOR]

Titanium carbide-based coatings have been considered for use in sliding wear resistance applications. Carbides embedded in a metal matrix would improve wear properties, providing a noncontinuous ceramic surface. TiC-Fe coatings obtained by plasma spraying of spray-dried TiC-Fe composite powders containing large and angular TiC particles are not expected to be as resistant as those containing TiC particles formed upon spraying. Coatings containing 60 vol% TiC dispersed in a steel matrix deposited by plasma spraying reactive micropellets, sintered reactive micropellets, and spray-dried TiC-Fe composite powders are compared. The sliding wear resistance of these coatings against steel was measured following the test procedure recommended by the Versailles Advanced Materials and Standards (VAMAS) program, and the inherent surface porosity was evaluated by image analysis. Results show that, after a 1-km sliding distance, TiC-Fe coatings obtained after spraying sintered reactive powders exhibit scar ring three times less deep than sprayed coatings using spray-dried TiC-Fe composite powders. For all coatings considered, porosity is detrimental to wear performance, because it generally lowers the coating strength and provides cavities that favor the adhesion of metal. However, porosity can have a beneficial effect by entrapping debris, thus reducing friction. The good wear behavior of TiC-Fe coatings manufactured by plasma spraying of sintered reactive powders is related to their low coefficient of friction against steel. This is due to the microstructure of these coatings, which consists of 0.3 to 1 μm TiC rounded particles embedded in a steel matrix. [ABSTRACT FROM AUTHOR]

An optothermal technique is described for the nondestructive evaluation of thermal barriers, such as ceramic plasma-sprayed coatings. This method is noncontact and requires access from one side only of the sample, thereby making it easier to inspect awkwardly shaped or difficult-to-reach pieces. A laser beam irradiates the coated material, raising its surface temperature to some degrees above ambient. The surface temperature is monitored during or after irradiation by an infrared detector to obtain a characteristic temperature-time curve (thermogram). After appropriate processing, the thermogram provides information on the thermal properties of the coating if its thickness is known. Alternatively, the thickness of the coating can be estimated if its thermal properties are known. In either case, the optothermal analysis allows one to evaluate the degree of thermal insulation provided by the coating. Each measurement is performed nondestructively and within a time period of less than 0.5 sec per point using the single-shot method. [ABSTRACT FROM AUTHOR]