Recently, environmental concerns have initiated intensive research and development in the field of friction brake systems with the aim to minimize particle emission. First brake systems that include thermally sprayed protective coatings on grey cast iron brake disks have been introduced in automotive industries and have proven suitability to strongly reduce particle emission. However, there is desire to use materials that show better environmental compatibility and lower price and to use processes that permit improved characteristics of protective coatings at reduced production costs. Different approaches concerning choice of base and coating materials as well as production processes are discussed with respect to technological, economic and ecological aspects. Besides grey cast iron also aluminum alloys are considered as base materials. For coating production HVOF spraying and laser cladding offer specific advantages and recent progress concerning the expansion of their production rate limitations is presented. Finally, novel feedstock materials that show excellent compatibility with stainless steel or aluminum alloy matrices have been developed and applied for coating production.

Twin wire arc is a commonly used thermal spray technology for application of steel coatings to cast iron components. Hardness and adhesion strength are critical properties of such coatings, and significant research is available reporting these properties. However, residual stresses and the anisotropic structure of the coatings leads to significantly different behavior in bending applications than in the purely tensile loading of the standard adhesion test. In addition, microstructural features that are controlled by certain process parameters during deposition of the coating can have a significant effect on these properties. This work seeks to relate the hardness and pull-off adhesion strength to the coating microstructure, and to assess the related bending strength and failure mode. Comparisons between bend tests and pull-off adhesion tests show significant differences to consider when evaluating twin wire arc coatings.

This study evaluates the erosion-corrosion performance of thermal spray hardcoats on bronze-coated gray cast iron. In the experiments, gray cast iron plates are coated with a bronze powder by PTA welding and the coatings are characterized based on microstructure and corrosion and wear testing. The bronze coatings provide good corrosion protection, but are shown to be susceptible to cavitation and erosion wear. To compensate, thermal spray hardcoats, including atmospheric plasma sprayed Al 2 O 3 and Cr 2 O 3 and HVOF sprayed WC-Co, were applied over bronze-coated cast iron and corrosion and wear tests were performed. It is shown that the thermal spray hardcoats greatly improve wear resistance, but despite their interconnected porosities, do not affect the corrosion performance of the underlying bronze.

This study aims at evaluating the erosion resistance at temperature of several hard coatings, including: CrC-NiCr by HVOF, Fe-based alloy by Arc Spray, NiCrBSiFe by powder flame spraying. These coatings are to be used for the recovery of highly eroded walls (above 10 mm thickness) of gray cast iron in the exhaust ducts in heavy-fuel engines. The erosion test consists of erosive particles thrown through a high temperature gas jet, for 5 cycles of 5 minutes, according to ASTM G211-14 (modified). Coated samples are subjected to a fuel gas-torch reaching a front temperature of 450ºC and a back temperature of 90ºC (water cooled), simulating the actual application. The eroded samples are characterized using EDS, and SEM. The results show the erosion rate of each material/system, and their corresponding erosion mechanisms. Thus, the results allows for the selection of an optimum coating for this surface recovery application.

The degradation of pump components by corrosion and complex damage mechanisms, e.g. erosion and cavitation leads to high costs through replacement and maintenance of parts. To increase the lifetime of cost-efficient components with superior casting properties, gray cast iron parts are surfaced with duplex stainless steel using an inert shielding gas metal arc welding process. The dilution of the surfacing increases with both increasing heat input and increasing thermal conductivity of the shielding gas. The microstructure is highly affected by the cooling conditions that may enhance diffusion processes and eventually lead to precipitation of deleterious carbides. Higher heat input and prolonged cooling duration during surfacing lead to high dilution and a pronounced carbide network and thus, substantially reduced corrosion resistance in artificial seawater. The corrosion of the surfacings in the potentiodynamic polarization test is driven by selective corrosion of the phase boundary between carbides and chromium-depleted austenite. Passive behavior is observed for coatings with low dilution and higher cooling rates, which showed homogeneous chromium distribution and no interconnected carbide networks. In conclusion, the corrosion behavior of gray cast iron was improved by surfacing with duplex stainless steel.

The wear of piston rings in large marine two-stroke diesel engines is a major maintenance cost. Applying coatings with good oxidation, corrosion resistance and high temperature strength, can lower the total maintenance cost. In the past nickel aluminide with chromium carbide have been applied to pistons by thermal spraying. Using laser cladding a suitable microstructure can be formed while at the same time avoiding cracks and bonding issues. In this report powders and coatings were manufactured in order to be able to investigate the dry-sliding wear behavior. Material with three levels of carbides was atomized. Wear test samples were manufactured by laser cladding. The dry sliding wear-mechanism maps are generated by using block on ring test setup where coated blocks slide against cast iron rings. All alloys exhibited regions of plasticity-dominated wear and oxidational wear with a transition region in-between. The carbide-containing alloys showed lower friction and wear in comparison to the carbide free nickel aluminide alloy.

In this work, the aim is to develop a cost-effective coating to protect cast iron and carbon steel from corrosion and wear. An alloy with a composition of FeCr25Mn10BC was designed that could be readily converted to powder form by gas atomization. Different sized powders were produced, characterized, and subsequently sprayed using a three-cathode air plasma generator. It was found that fine powders with fractions of -25 +10 μm and -10 μm had a much higher affinity to oxidation than coarser ones. Nevertheless, using suitable parameters, dense coatings with low oxide content could be realized even with the finest powder. The results show that full utilization of the powder is achievable due to the wide parameter window of three-cathode plasma spraying and that the average deposition efficiency is more than 70%. In addition to savings in material and processing costs, the new alloy system provides greater wear resistance than stainless steel coatings and exhibits significantly higher corrosion resistance than unprotected cast iron and carbon steel.

Conventional Fe-C-Si alloy cast iron shows good properties at low temperature but at high temperature its properties decrease very sharply. So, to protect this behaviour of cast iron, Si was replaced by Al, since both elements have similar graphitizing effect. In the present study, two types of cast iron, Fe-C-Si and Fe-C-Al, were cast in cold set resin bonded sand mould. After casting, the microstructures were studied using standard metallographic techniques. The wear tests were conducted using “CSM High Temperature Tribometer” following pin-on-disk method at 25 °C, 100 °C, 200 °C and 300 °C. The worn tracks were characterized using optical profilometer, SEM etc.. The results show that abrasive type wear was observed in both types of cast iron and always the Fe-C-Al cast has low wear rate compared to Fe-C-Si. However, after at 100 °C temperature, the wear resistance of Fe-C-Si cast iron starts to decrease whereas at lower temperature, it remains almost unchanged. The wear rates for Fe-C-Si alloy cast iron are 12.42, 16.51, 46.75 and 98.87x10-5mm 3 /N/m whereas the wear rates for Fe-C-Al cast iron are 3.32, 4.23, 4.40 and 8.15x10-5mm 3 /N/m at 25 °C, 100 °C, 200 °C and 300 °C, respectively.

During solidification, the cooling behaviour of materials depends on the heat flow through the mould and the alloy composition. Even though the alloy composition is same; the cooling rate can change the properties of the materials. In the present study, an attempt has been taken to predict the cooling behaviour of gray cast iron into a resin bonded sand mould at various thicknesses using JL FEM analyser software. Using K-type thermocouple, the temperature was measured after every 20 sec. Both, the computer simulated and experimentally investigated cooling curves show the similar nature or pattern of the curves. The microstructure also confirms that the cooling rate changes the structure of the cast iron from gray to white.

This study compares the tribological performance of HVOF and HVSFS coatings applied to gray cast iron and aluminum cylinder liners. Five different materials, including Fe alloy, FeCrMo, CrC-NiCr, NiCrBSi, and WC-Co, were sprayed using a conventional HVOF torch operated by a six-axis robot while the liners were manipulated by means of a rotary table. A similar setup was used to spray TiO 2 -TiC coatings, but the gun was modified for nano-sized particles in a suspension fed axially into the combustion chamber. Coating microstructures were examined using optical and SEM imaging and friction and wear properties were determined through oscillating friction wear tests. The results obtained are compared to state-of-the-art cylinder liners.

In this study, suspension plasma spraying is used to produce cast iron coatings that benefit from a graphite structure. In order to increase the graphite content, different hydrocarbons in the form of liquid suspension (hexane and toluene) and gas precursor (methane) were injected into the plasma stream along with iron powder. Besides promoting the formation of a soot carbon structure, liquid hydrocarbon injection also prevents in-flight particle oxidation, which is a major concern when spraying metals. In addition, it has been observed that using a shroud during spraying significantly increases the amount of soot carbon in cast iron coatings, which can be transformed into graphite by post annealing.

Cast iron coatings containing solid lubricant of graphite are an attractive candidate for wear resistant applications of an aluminum alloy substrate. It is difficult to generate a graphite structure in coatings sprayed with as-atomized cast iron powder which contains a few graphite owing to their high solidification rate. Although a graphite structure is remained in coatings sprayed with fully annealed cast iron powder, graphite carbon becomes lower than that in the annealed powder because of the in-flight oxidation and dissolution of graphite into molten iron. The present study is focused on an increase in graphite carbon through flying droplet diagnostic at a certain spray distance, that is, in-situ measurements of droplet temperature and velocity. Water-atomized cast iron powder which was annealed at 900°C for 3.6ks, was supplied as a spray material. The fully annealed powder was plasma-sprayed onto an aluminum alloy substrate, as well as carrying out flying droplet diagnostic. The amount of graphite carbon can be estimated by flying droplet temperature and velocity, which are controlled by spray parameters such as plasma gas flow rate and plasma current. It is confirmed that droplet velocity exhibits stronger influence on graphite carbon compared with droplet temperature. High velocity causes an increase in graphite carbon, so that it is possible to fabricate graphite-graded cast iron coatings with high amount at the surface and low at the interface.

We investigate the sprayability of various hard metal and composite powder coatings via kinetic spray on cast iron by utilizing both powder and substrate preheat. These coatings include copper, a copper-zirconia composite, nickel, a zinc-nickel composite, and Ti6Al4V alloy. Using the kinetic spray process the coatings were applied to a cast iron substrate which was ground and sand blasted prior to spray. Analysis performed on powders and coating includes: cross-sectional microscopy, hardness of powders and substrate, substrate temperature as a function of heating and cooling times, and adhesion at the coating/substrate level. Results include spray parameters to allow for nickel and copper coatings to be developed on cast iron, adhesion strength as a function of powder hardness, porosity of nickel and Ti6Al4V coatings, and incorporation rates of zirconia in a copper matrix on cast iron. This is an attempt to spray hard powders on a hard substrate. Harder particles are more difficult to spray because they require more energy to plastically deform. Therefore the hardness of the particles plays a significant role in the deposition of a coating. Similarly, harder substrates are more difficult to spray on. This work demonstrates techniques that make spraying hard particles on hard substrates possible.

Graphitization behavior of water-atomized cast iron powder at each thermal spraying step, such as droplet flight, droplet impingement and splat layering, was successively examined. Both as-atomized cast iron powder and coatings sprayed with the powder contain no graphite structure owing to their rapid solidification. A short period of pre-annealing at 1173 K allows the formation of graphite structure in the cast iron powder, in which there exist precipitated graphite of 3.58 mass%. The microstructure observation exhibits that pre-existed pores in the as-atomized powder strongly affect the precipitating sites of graphite, that is, mainly inside the individual powder instead of the surface. However, marked reduction in graphite structure occurs to coatings sprayed with the pre-annealed powder because of in-flight burning and dissolution into molten iron. In-process post-annealing at 773 K for 60 s reveals the formation of graphite structure resulted from the decomposition of iron based metastable carbide in splats and coatings sprayed with the as-atomized powder. Chemical analysis demonstrates that graphitization level of post-annealed cast iron coatings is higher than that of coatings sprayed with the pre-annealed powder. Precipitated intersplat graphite structure of 1.68 mass% appears in cast iron coatings when introducing methane as a powder feeding carrier gas which is liable to decompose in plasma flame. The resultant coatings with graphite structure embedded in hard matrix are anticipated to offer superior wear resistance in comparison to centrifugally cast iron containing flaky graphite of 1.76 mass%.

Thermal sprayed coatings are already used for the wear protection of cylinder bores since more than five years in the automotive industry, primarily in Europe. The adhesion of the coating on the different possible substrates is a key factor for the success of this operation. This paper gives an overview of the different potential processes used for the surface preparation prior to coating deposition. The influence of different substrate materials will be discussed also. Aluminum casting alloys, magnesium base materials, cast iron and also steel substrates will be considered in this paper. The safety and economical aspects of the different processes are considered also. Further, the paper will give an update of the state of the art of the thermal spraying of cylinder bores and the important aspect regarding the saving of energy resource.

Water atomized cast iron powder of Fe-2.17C-9.93Si-3.75Al (in wt%) were deposited onto an aluminum alloy substrate by atmospheric DC plasma spraying to improve its tribological properties. Pre-annealing of the cast iron powder allows to precipitate considerable amounts of graphite structure in the powder. However, significant reduction in graphitized carbon in cast iron coatings is inevitable after plasma spraying in air atmosphere due to the in-flight burning and the dissolution into molten iron droplets. Hexagonal boron nitride (h-BN) powders which have excellent lubricating properties like graphite were incorporated to the cast iron powder as solid lubricant by sintering process (1300 °C) to obtain protective coatings with low friction coefficient. The performance of each coating was evaluated using ring-on-disk type wear tester under paraffin base oil condition in air atmosphere. Conventional cast iron liner which has flaky graphite embedded in pearlitic matrix was also tested in similar conditions in order to make a comparison. Sections of worn surfaces and debris were characterized and wear behaviour of plasma sprayed coatings are discussed.

Since about the year 2000, cast aluminum automobile engine blocks have been coated in production lines using internal plasma spraying technology. Using this approach, the coefficient of friction between the cylinder wall and the piston assembly can be reduced to 30% and oil consumption is reduced of a factor two in comparison with cast iron. The extremely low wear rate of the friction elements increases engine life and reduces maintenance costs. The fuel consumption of the cars can be reduced from 2 to 4% in the case of gasoline and diesel engines. The coating costs are strongly dependent on production volume. For high volume production, the costs can be similar to those for cast iron liners. This paper reviews results from laboratory and field tests evaluating the performance and cost efficiency of plasma sprayed engine block liners.

The excellent wear-resistant performance of cast iron coatings considerably depends on the formation of graphite structure with an inherent self-lubricating property. In the present study, two types of cast iron powders produced by gas- (GA) and water-atomization (WA) were deposited on an aluminium alloy substrate by atmospheric DC plasma spraying. WA powders are generally characterized by high oxygen content, irregular appearance and inexpensiveness compared with those of GA powders. Although alloying elements of silicon and aluminium work as a strong graphitizer and anti-oxidizer, graphite structures are not recognized in coatings sprayed with as-atomized high silicon and aluminium powders. Therefore, either pre-annealing of powders or post-annealing of coatings is required to achieve cast iron coatings containing graphite structure. A marked decrease in graphite occurs to the coatings with pre-annealed GA powder, since there exists precipitated graphite mainly on a GA powder surface. A short period of post-annealing is also valuable for graphitization. The weak oxide layers are observed in coating cross-sections with GA and WA powder, however, their oxidized levels are much lower than those with bearing steel powder containing low silicon and aluminium. Hence, graphitized cast iron coatings sprayed with inexpensive WA powder exhibit a splendid anti-wear performance.

Fundamental aspects of a plasma sprayed cast iron coating on an aluminum alloy substrate are investigated in the present study: focusing on the effects of preheat substrate temperature (T S ) and chamber pressure (P C ) on the splat morphology, the adhesive strength of splats, the formation of a reaction layer and graphite. Splash-type splats appear at low T S but disk and star-shaped splats arise at high T S . Deformed substrate ridges, mainly due to the slight surface melting, are formed adjacent to the splat periphery at high T S . At low T S , pores are observed at the splat/substrate interface, which cause a decrease in the adhesion of splats. In contrast, a reaction layer composed of iron, aluminum and oxygen is ready to form at high T S . The amount of graphitized carbon increases in cast iron splats with T S . At a low P C of 26.3 kPa, disk-type splats are in the majority at a constant T S of 473 K. As P C increases, star-shaped splats appear along with disk splats. The flattening ratio of disk splats decreases with the increase of P C , because of a decrease in the kinetic energy and temperature of molten droplets. An interfacial oxide layer composed of iron, aluminum and oxygen is ready to form at high P C . The number of pores intensively increases with P C , which leads to a decrease in the adhesive strength of splats. The amount of formed graphite in cast iron splats slightly increases with P C , however, that of a rapidly solidified phase of Fe-Si-C decreases because of lowering of the solidification rate.

The focus of this paper is to determine the friction and wear characteristics between conventional metal-metal contacts and cermet-metal contacts. A WC-Co based cermet, applied by the High Velocity Oxy-Fuel (HVOF) process on a carbon steel substrate has been investigated in contact with cast iron pins. That has been compared with conventional carbon steel/cast iron couples. A mineral oil and a mineral oil containing the additive zinc dialkyl dithiophosphate (ZDDP) were used as the lubricants. The formation of a wear film has been shown to vary on the metal and cermet surface. The friction and wear response and the wear film nature are discussed.