Iron ore pellets are sintered and reduced in continuous large industrial oil-fired furnaces. From the furnace, large volumes of hot gas are sucked by powerful fans. Being exposed to gas-borne iron particles and temperatures ranging between 125°C and 328°C fan components are rapidly deteriorated. Extensive part repair or replacement are required for maintaining a profitable operation. The arc spraying technique has been suggested for repair provided it could produce erosion resistant coatings. Commercial wires were arc sprayed using various spray parameters to produce thick coatings. Arc-sprayed coatings and reference specimens were erosion tested at 25°C and 330°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 -300 μm) iron ore particles at a speed of 100 m/s. The volume loss was accurately measured with a laser profilometer. 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 330°C for both 25° and 90° impact angles. Erosion-enhanced oxidation was found responsible for the increase in wastage above room temperature. Though arc spraying can be appropriate for on-site repair, the development of erosion resistant coatings is required for intermediate temperatures.

For applications in which two contacting surfaces are in constant motion relative to each other, materials that are both wear resistant and non-abrasive are often required. Such attributes become even more important when the moving contact occurs with no liquid lubricants present to facilitate sliding. In the present study several WC-based coatings deposited using the HVOF process and containing one or more metal constituents as the binder (or matrix) phase were evaluated to determine their performance under conditions cf sliding wear. Image analysis of the coatings indicated a level of porosity of less than 1%. Hardness measurements found that values for the Vickers microhardness number were in the range of 1100-1500. For the wear tests, the test couple consisted of a coated ring (thrust washer type design) rotating against a stationary carbon disk. For each test, the contact load, speed of rotation and duration were controlled. During the test, the temperature of the carbon disk and the torque were recorded using a data acquisition system. This data was used to determine the coefficient of friction for each couple which, together with the results of measurements of weight change, provided a measure of the comparative performance of the various coatings. The preliminary results indicated that the values for the coefficient of friction for the various couples ranged from 0.15 to 0.29. The three coating compositions consisting of lONi-WC, 12Co-WC and 17Co-WC were found to out-perform other WC-based materials in these sliding wear tests.

Cavitation and erosion damage to hydroelectric turbines and pumps can be a major problem. The effectiveness of thermal sprayed cavitation-erosion resistant coatings for hydroelectric turbine and pumps was evaluated. The coatings evaluated were applied using High Velocity Oxyfuel (HVOF) and Plasma Spray systems. Hard facing cobalt based alloys were evaluated on coupons in the laboratory. Testing was performed using a cavitating jet erosion apparatus utilizing an operating pressure of 27.6 MPa. The results were compared to welded 308 stainless steel. Cavitation resistant austenitic stainless steel weld alloys were also evaluated. The results showed that the cavitation rate of the austenitic stainless steel weld alloys were as low as one third of the rate of the 308 stainless steel. The cavitation rate of the thermally sprayed hard facing coatings were more than three times higher than the rate of the 308 stainless steel. CERHAB glass enamel coatings containing 7 wt % wollastonite fibers were successful applied by using two combustion spray processes. The applied CERHAB coatings were successfully annealed using field portable heaters and may have application as a seal coat for thermal spray coatings applied in the field.

The results of low stress, pin-on-disc and high stress grinding abrasive wear tests on coatings produced by plasma and oxy-acetylene flame spraywelding are presented. FNil5A and FNiWC35 Ni-based self-fluxing alloys were selected as typical spraywelding materials for abrasive wear resistance. The abrasive wear resistance mechanisms of welded overlays produced by various materials and processes were also characterized by hardness tests, microstructural and compositional analyses, and through analysis of the effect of different kinds of abrasive on the wear resistant of Ni-base self-fluxing spraywelding overlays. Results showed that FNiWC35 overlays exhibited improved resistance under low stress abrasion, but the relative wear resistances of FNiWC35 and FNil5A still depended primarily on the type and hardness of the abrasive medium used. For the same material, the abrasive wear resistance of oxyacetylene flame sprayed overlays was higher than that produced by plasma spraywelding. The wear resistance of the plasma spraywelding overlays depended not only on the material, but also strongly on the spraywelding process parameters.

Improvement of the high velocity oxy-fuel deposition (HVOF) process in the last decade has enhanced the microstructure of coatings in order to better perform against wear and corrosion. Indeed cermet and metal HVOF coatings are reliable and have excellent performance under slurry erosion and provide therefore an alternative to the use of high-priced material. This paper presents the results of a study undertaken within the core research program of the National Research Council of Canada technology group in surface engineering, "SURFTEC", in which the performance of ten HVOF erosion-resistant coatings was evaluated. Ten different types of HVOF coatings were studied including: six grades of WC with either Co or a Ni based matrix, one grade of Cr 3 C 2 in a Ni-Cr matrix, and three grade of metallic alloy: Ni alloy, Co alloy and a SS 316- L. The performance of coatings was evaluated with respect to: the volume ratio and composition of metallic binder in carbide coatings, type of carbide, coating microstructure, impinging angle and the size of the erodent particles. All coatings were produced using the HVOF JP-5000 system controlled by the Hawcs-ll controller. Slurry erosion tests were conducted with a jet impingement rig with a 10 %w/w alumina particle/water slurry. The volume loss of material under various slurry erosion conditions was related to the coating properties and microstructure. Results indicate that the behavior of HVOF sprayed materials is dependent on the erodent particle size, to the erosion impinging angle to some extent and to the corrosion resistance of the cermet matrix.

Two grades of stainless steel, 316 and 440-C, in the form of solid wire, and two cored wires, Duocor and 95-MXC, were used. Coatings were made using the Miller BP-400 and TAFA 9000 systems. Slurry jet erosion tests were conducted using a 10 %w/w alumina particle/water slurry. Two alumina particle sizes, 320 and 80 grit (nominal grain diameters 35 μm and 200 μm, respectively) were used at impinging angles of 90° and 20°. The nominal impact velocity of the slurry was 15 m/s and the nozzle-specimen distance 100 mm. The volume loss of material under various slurry erosion conditions was related to the coating properties and microstructure. Results indicate that the wear behavior of arc sprayed materials is dependent on the erodent particle size; for large erodent particle size, the relative erosion is almost independent of the impinging angle, while for the smaller particle size the angle effect is the dominant factor. This behavior can be related to the lamella structure and the relative toughness of the different phases of the coatings.

In corrosive media the wear resistance of ceramic-metallic coatings is dependent on the corrosion resistance of the metal matrix. Other factors that will affect the coating deterioration are the corrosivity of the medium and any galvanic interaction from the surrounding material. This paper presents results from a study where different types of WC(Co/Cr/Mo/Ni) powders have been sprayed by HVOF, Diamond Jet 2600 Hybrid equipment. The properties of the sprayed coatings have been verified by metallographic studies and by erosion-corrosion testing both under corrosive and non-corrosive conditions. The results clearly demonstrate the importance of having a metal matrix at least as corrosion resistance as the surrounding materials. When wear exposed components in pipe systems, pumps or valves are coated with a WC type coating, the corrosion resistance of the metal matrix should be compatible to the material of the rest of the system. This is especially important when the surrounding materials are corrosion resistant alloys as stainless steels, where the coatings otherwise will act as an anode.

Wear property of plasma spray coating in Cr 2 O 3 /TiO 2 powder manufactured of spray dry method on the aluminum substrate was inspected for the application of piston-ring of automotive engine. The plasma spray coatings were varied with feed rate and particle size. Using the ball-on disc type tribometer, wear volume property and surface roughness were investigated. The delamination of the coating layers and wear track were observed with SEM. Also, the cross-section of wear track were investigated, using optical microscopy. As a result of experiment, wear mechanism was addressed.

Protective coatings adapted for titanium alloys which come into frictional contact with one another are described. Among the many coatings investigated, the best ones are cobalt based. The coatings are sprayed only on one of the rubbing surfaces. During rubbing, a small part of the coating transfers to the unprotected titanium alloy surface. The rubbing pair is thus essentially composed of two cobalt alloy-based surfaces. This leads to low coefficient of friction and little or no damage to the rubbing surfaces. The coatings find particular application in the protection from adhesive and fretting wear, galling and seizure of gas turbine and jet engine parts or the like made from titanium alloys.

This work evaluates the potential of using new competitive powders of Fe/TiC system for plasma spraying of wear resistant coatings. To improve coating properties, Cr and Ni were added to the iron matrix. The results of complex investigations of plasma coatings from such materials are presented.

Gas atomized Al 63 Cu 25 Fe 12 powders of varying size fractions were plasma sprayed to study the relationships between coating microstructure and tribological behavior. After spraying, annealing was performed on one of the coatings. Abrasion and sliding wear tests were performed on the coatings. The results indicate a correlation between the abrasion resistance and hardness of the coatings. Furthermore, sliding wear tests reveal lower coefficients of friction for the as-sprayed coatings compared to the annealed coatings.