Thermally insulated engine components and method of making using a ceramic coating

A component for exposure to a combustion chamber of a diesel engine and/or exhaust gas, such as a cylinder liner or valve face, is provided. The component includes a thermal barrier coating applied to a body portion formed of steel. A layer of a metal bond material is first applied, followed by a gradient structure including a mixture of the metal bond material and a ceramic material, followed by a layer of the ceramic material. The ceramic material includes at least one of ceria, ceria stabilized zirconia, yttria stabilized zirconia, calcia stabilized zirconia, magnesia stabilized zirconia, and zirconia stabilized by another oxide. The thermal barrier coating is applied by thermal spray or HVOF. The thermal barrier coating has a porosity of 2% by vol. to 25% vol., a thickness of less than 1 mm, and a thermal conductivity of less than 1.00 W/m·K.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates generally to internal combustion engines, including insulated components exposed to combustion chambers and/or exhaust gas of diesel engines, and methods of manufacturing the same.

2. Related Art

Modern heavy duty diesel engines are being pushed towards increased efficiency under emissions and fuel economy legislation. To achieve greater efficiency, the engines must run hotter and at higher peak pressures. Thermal losses through the combustion chamber become problematic under these increased demands. Typically, about 4% to 6% of available fuel energy is lost as heat through the piston into the cooling system. One way to improve engine efficiency is to extract energy from hot combustion gases by turbo-compounding. For example, about 4% to 5% of fuel energy can be extracted from the hot exhaust gases by turbo-compounding.

Another way to improve engine efficiency includes reducing heat losses to the cooling system by insulating components of the engine, for example using insulating layers formed of ceramic materials. One option includes applying a metal bonding layer to a metal surface followed by a ceramic layer. However, the layers are discrete and the ceramic is by its nature porous. Thus, combustion gases can pass through the ceramic and start to oxidize the metal bonding layer at the ceramic/bonding layer interface, causing a weak boundary layer to form and potential failure of the coating over time. In addition, mismatches in thermal expansion coefficients between adjacent layers, and the brittle nature of ceramics, create the risk for delamination and spalling.

Another example is a thermally sprayed coating formed of yttria stabilized zirconia. This material, when used alone, can suffer destabilization through thermal effects and chemical attack in diesel combustion engines. It has also been found that thick ceramic coatings, such as those greater than 500 microns, for example 1 mm, are prone to cracking and failure. Typical aerospace coatings used for jet turbines are oftentimes not suitable because of raw material and deposition costs associated with the highly cyclical nature of the thermal stresses imposed.

SUMMARY OF THE INVENTION

One aspect of the invention provides a component for exposure to a combustion chamber of an internal combustion engine, such as a diesel engine, and/or exhaust gas generated by the internal combustion engine. The component comprises a body portion formed of metal, and a thermal barrier coating applied to the body portion. The thermal barrier coating has a thickness extending from the metal body portion to a top surface. The thermal barrier coating includes a mixture of a metal bond material and a ceramic material, and the amount of ceramic material present in the thermal barrier coating increases from the body portion to the top surface.

Another aspect of the invention provides a method of manufacturing a component for exposure to a combustion chamber of an internal combustion engine and/or exhaust gas generated by the internal combustion engine. The method includes applying a thermal barrier coating to a body portion formed of metal. The thermal barrier coating has a thickness extending from the body portion to a top surface, and the thermal barrier coating includes a mixture of a metal bond material and a ceramic material. The step of applying the thermal barrier coating to the body portion includes increasing the amount of ceramic material relative to the metal bond material from the body portion to the top surface.

DETAILED DESCRIPTION OF EXAMPLE EMBODIMENTS

One aspect of the invention provides a component of an internal combustion engine20, such as a heavy duty diesel engine, including a thermal barrier coating22. The thermal barrier coating22prevents heat from passing through the component, and thus can maintain heat in a desired area of the internal combustion engine20, for example in a fuel-air mixture of a combustion chamber24or in exhaust gas, which improves engine efficiency. The thermal barrier coating22is also more cost effective and stable, as well as less susceptible to chemical attacks, compared to other coatings used to insulate engine components.

Various different components of the internal combustion engine20can be coated with the thermal barrier coating22. A corresponding U.S. patent application filed on the same day as the present application and claiming priority to the same provisional patent application No. 62/257,993 is directed to application of the thermal barrier coating22to a piston26. However, as shown inFIG. 1, the thermal barrier coating22can be applied to one or more other components exposed to the combustion chamber24, including a cylinder liner28, cylinder head30, fuel injector32, valve seat34, and valve face36. Typically, the thermal barrier coating22is only applied to a portion of the component exposed to the combustion chamber24. For example, an entire surface of the component exposed to the combustion chamber24could be coated. Alternatively, only a portion of the surface of the component exposed to the combustion chamber24is coated. The thermal barrier coating22could also be applied to select locations of the surface exposed to the combustion chamber24, depending on the conditions of the combustion chamber24and location of the surface relative to other components.

In the example embodiment ofFIG. 1, the thermal barrier coating22is only applied to a portion of an inner diameter surface38of the cylinder liner28located opposite a top land44of the piston26when the piston26is located at top dead center, and the thermal barrier coating22is not located at any other location along the inner diameter surface38, and is not located at any contact surfaces of the cylinder liner28.FIG. 2is an enlarged view of the portion of the cylinder liner28including the thermal barrier coating22. In this embodiment, the inner diameter surface38includes a groove40machined therein. The groove40extends along a portion of the length of the cylinder liner28from a top edge of the inner diameter surface38, and the thermal barrier coating22is disposed in the groove40. Also in this example, the length l of the groove40and the thermal barrier coating22is 5 mm to 10 mm wide. In other words, the thermal barrier coating22extends 5 mm to 10 mm along the length of the cylinder liner28. In the example embodiment ofFIG. 1, the thermal barrier coating22is also applied to the valve face36.FIG. 3is an enlarged view of the valve face36including the thermal barrier coating22.

The thermal barrier coating22could also be applied to other components of the internal combustion engine20, or components associated with the internal combustion engine20, for example other components of a valvetrain, post-combustion chamber, exhaust manifold, and turbocharger. The thermal barrier coating22is typically applied to components of a diesel engine directly exposed to hot gasses of the combustion chamber24or exhaust gas, and thus high temperatures and pressures, while the engine20is running. A body portion42of the component is typically formed of steel, such as an AISI 4140 grade or a microalloy 38MnSiVS5, for example, or another metal material. Any steel used to form the body portion42does not include phosphate. If any phosphate is present on the surface of the body portion42, then that phosphate is removed prior to applying the thermal barrier coating22.

The thermal barrier coating22is applied to one or more components of the internal combustion engine20or exposed to exhaust gas generated by the internal combustion engine20, to maintain heat in the combustion chamber24or in exhaust gas, and thus increase efficiency of the engine20. The thermal barrier coating22is oftentimes disposed in specific locations, depending on patterns from heat map measurements, in order to modify hot and cold regions of the component. The thermal barrier coating22is designed for exposure to the harsh conditions of the combustion chamber24. For example, the thermal barrier coating22can be applied to components of the diesel engine20subject to large and oscillating thermal cycles. Such components experience extreme cold start temperatures and can reach up to 700° C. when in contact with combustion gases. There is also temperature cycling from each combustion event of approximately 15 to 20 times a second or more. In addition, pressure swings up to 250 to 300 bar are seen with each combustion cycle.

A portion of the thermal barrier coating22is formed of a ceramic material50, specifically at least one oxide, for example ceria, ceria stabilized zirconia, yttria stabilized zirconia, calcia stabilized zirconia, magnesia stabilized zirconia, zirconia stabilized by another oxide, and/or a mixture thereof. The ceramic material50has a low thermal conductivity, such as less than 1 W/m·K. When ceria is used in the ceramic material50, the thermal barrier coating22is more stable under the high temperatures, pressures, and other harsh conditions of a diesel engine20. The composition of the ceramic material50including ceria also makes the thermal barrier coating22less susceptible to chemical attack than other ceramic coatings, which can suffer destabilization when used alone through thermal effects and chemical attack in diesel combustion engines. Ceria and ceria stabilized zirconia are much more stable under such thermal and chemical conditions. Ceria has a thermal expansion coefficient which is preferably similar to the steel material used to form the body portions42of the components to which the thermal barrier coating22is applied. The thermal expansion coefficient of ceria at room temperature ranges from 10E-6 to 11E-6, and the thermal expansion coefficient of steel at room temperature ranges from 11E-6 to 14E-6. The similar thermal expansion coefficients help to avoid thermal mismatches that produce stress cracks.

Typically, the thermal barrier coating22includes the ceramic material50in an amount of 70 percent by volume (% by vol.) to 95% by vol., based on the total volume of the thermal barrier coating22. In one embodiment, the ceramic material50used to form the thermal barrier coating22includes ceria in an amount of 90 to 100 wt. %, based on the total weight of the ceramic material50. In another example embodiment, the ceramic material50includes ceria stabilized zirconia in an amount of 90 to 100 wt. %, based on the total weight of the ceramic material50. In another example embodiment, the ceramic material50includes yttria stabilized zirconia in an amount of 90 to 100 wt. %, based on the total weight of the ceramic material50. In yet another example embodiment, the ceramic material50includes ceria stabilized zirconia and yttria stabilized zirconia in a total amount of 90 to 100 wt. %, based on the total weight of the ceramic material50. In another example embodiment, the ceramic material50includes magnesia stabilized zirconia, calcia stabilized zirconia, and/or zirconia stabilized by another oxide in an amount of 90 to 100 wt. %, based on the total weight of the ceramic material50. In other words, any of the oxides can be used alone or in combination in an amount of 90 to 100 wt. %, based on the total weight of the ceramic material50. In cases where the ceramic material50does not consist entirely of the ceria, ceria stabilized zirconia, yttria stabilized zirconia, magnesia stabilized zirconia, calcia stabilized zirconia, and/or zirconia stabilized by another oxide, the remaining portion of the ceramic material50typically consists of other oxides and compounds such as aluminum oxide, titanium oxide, chromium oxide, silicon oxide, manganese or cobalt compounds, silicon nitride, and/or functional materials such as pigments or catalysts. For example, according to one embodiment, a catalyst is added to the thermal barrier coating22to modify combustion. A color compound can also be added to the thermal barrier coating22. According to one example embodiment, thermal barrier coating22is a tan color, but could be other colors, such as blue or red.

According to one embodiment, wherein the ceramic material50includes ceria stabilized zirconia, the ceramic material50includes the ceria in an amount of 20 wt. % to 25 wt. % and the zirconia in an amount of 75 wt. % to 80 wt. %, based on the total amount of ceria stabilized zirconia in the ceramic material50. Alternatively, the ceramic material50can include up to 3 wt. % yttria, and the amount of zirconia is reduced accordingly. In this embodiment, the ceria stabilized zirconia is provided in the form of particles having a nominal particle size of 11 μm to 125 μm. Preferably, 90 wt. % of the ceria stabilized zirconia particles have a nominal particle size less than 90 μm, 50 wt. % of the ceria stabilized zirconia particles have a nominal particle size less than 50 μm, and 10 wt. % of the ceria stabilized zirconia particles have a nominal particle size less than 25 μm.

According to another example embodiment, wherein the ceramic material50includes yttria stabilized zirconia, the ceramic material50includes the yttria in an amount of 7 wt. % to 9 wt. %, and the zirconia in an amount of 91 wt. % to 93 wt. %, based on the amount of yttria stabilized zirconia in the ceramic material50. In this embodiment, the yttria stabilized zirconia is provided in the form of particles having a nominal particle size of 11 μm to 125 μm. Preferably, 90 wt. % of the yttria stabilized zirconia particles have a nominal particle size less than 90 μm, 50 wt. % of the yttria stabilized zirconia particles have a nominal particle size less than 50 μm, and 10 wt. % of the yttria stabilized zirconia particles have a nominal particle size less than 25 μm.

According to another example embodiment, wherein the ceramic material50includes a mixture of ceria stabilized zirconia and yttria stabilized zirconia, the ceramic material50includes the ceria stabilized zirconia in an amount of 5 wt. % to 95 wt. %, and the yttria stabilized zirconia in an amount of 5 wt. % to 95 wt. %, based on the total amount of the mixture present in the ceramic material50. In this embodiment, the ceria stabilized zirconia is provided in the form of particles having a nominal particle size of 11 μm to 125 μm. Preferably, 90 wt. % of the ceria stabilized zirconia particles have a particle size less than 90 μm, 50 wt. % of the ceria stabilized zirconia particles have a particle size less than 50 μm, and 10 wt. % of the ceria stabilized zirconia particles have a particle size less than 25 μm. The yttria stabilized zirconia is also provided in the form of particles having a nominal particle size of 11 μm to 125 μm. Preferably, 90 wt. % of the yttria stabilized zirconia particles have a particle size less than 109 μm, 50 wt. % of the yttria stabilized zirconia particles have a particle size less than 59 μm, and 10 wt. % of the yttria stabilized zirconia particles have a particle size less than 28 μm. When the ceramic material50includes the mixture of ceria stabilized zirconia and yttria stabilized zirconia, the ceramic material can be formed by adding 5 wt. % to 95 wt. % of ceria stabilized zirconia to the balance of yttria stabilized zirconia in the total 100 wt. % mixture.

According to yet another example embodiment, wherein the ceramic material50includes calcia stabilized zirconia, the ceramic material50includes the calcia in an amount of 4.5 wt. % to 5.5 wt. %, and the zirconia in an amount of 91.5 wt. %, with the balance consisting of other oxides in the ceramic material50. In this embodiment, the calcia stabilized zirconia is provided in the form of particles having a nominal particle size range of 11 μm to 90 μm. Preferably, the calcia stabilized zirconia particles contain a maximum of 7 wt. % with particle size greater than 45 μm and up to 65 wt. % of particles less than 45 μm.

According to yet another example embodiment, wherein the ceramic material50includes magnesia stabilized zirconia, the ceramic material50includes the magnesia in an amount of 15 wt. % to 30 wt. %, with the balance consisting of zirconia. In this embodiment, the magnesia stabilized zirconia is provided in the form of particles having a nominal particle size of 11 μm to 90 μm. Preferably, 15 wt. % of the magnesia stabilized zirconia particles have a particle size less than 88 μm.

Other oxides or mixtures of oxides may be used to stabilize the ceramic material50. The amount of other oxide or mixed oxides is typically in the range 5 wt. % to 38 wt. % and the nominal particle size range of the stabilized ceramic material50is 1 μm to 125 μm.

The porosity of the ceramic material50is typically controlled to reduce the thermal conductivity of the thermal barrier coating22. When a thermal spray method is used to apply the thermal barrier coating22, the porosity of the ceramic material50is typically less than 25% by vol., such as 2% by vol. to 25% by vol., preferably 5% by vol. to 15% by vol., and more preferably 8% by vol. to 10% by vol., based on the total volume of the ceramic material50. However, if a vacuum method is used to apply the thermal barrier coating22, then the porosity is typically less than 5% by vol., based on the total volume of the ceramic material50. The porosity of the entire thermal barrier coating22can also be 2% by vol. to 25% by vol., but is typically greater than 5% by vol. to 25% by vol., preferably 5% by vol. to 15% by vol., and most preferably 8% by vol. to 10% by vol., based on the total volume of the thermal barrier coating22. The pores of the thermal barrier coating22are typically concentrated in the ceramic regions. The porosity of the thermal barrier coating22contributes to the reduced thermal conductivity of the thermal barrier coating22.

The thermal barrier coating22is also applied in a gradient structure51to avoid discrete metal/ceramic interfaces. In other words, the gradient structure51avoids sharp interfaces. Thus, the thermal barrier coating22is less likely to de-bond during service. The gradient structure51of the thermal barrier coating22is formed by first applying a metal bond material52to the component, followed by a mixture of the metal bond material52and ceramic material50, and then the ceramic material50.

The composition of the metal bond material52can be the same as the powder used to form the body portion42of the component, for example a steel powder. Alternatively the metal bond material52can comprise a high performance superalloy, such as those used in coatings of jet turbines. According to example embodiments, the metal bond material52includes or consists of at least one of alloy selected from the group consisting of CoNiCrAlY, NiCrAlY, NiCr, NiAl, NiCrAl, NiAlMo, and NiTi. The thermal barrier coating22typically includes the metal bond material52in an amount of 5% by vol. to 33% by vol. %, more preferably 10% by vol. to 33% by vol., most preferably 20% by vol. to 33% by vol., based on the total volume of the thermal barrier coating22. The metal bond material52is provided in the form of particles having a particle size of −140 mesh 105 μm), preferably −170 mesh 90 μm), more preferably −200 mesh 74 μm), and most preferably −400 mesh (<37 μm). According to one example embodiment, the thickness of the metal bond material52ranges from 30 microns to 1 mm. The thickness limit of the metal bond material52is dictated by the particle size of the metal bond material52. A low thickness is oftentimes preferred to reduce the risk of delamination of the thermal barrier coating22.

The gradient structure51is formed by gradually transitioning from 100% metal bond material52to 100% ceramic material50. The thermal barrier coating22includes the metal bond material52applied to the body portion26, followed by increasing amounts of the ceramic material50and reduced amounts of the metal bond material52. The transition function of the gradient structure51can be linear, exponential, parabolic, Gaussian, binomial, or could follow another equation relating composition average to position.

The uppermost portion of the thermal barrier coating22is formed entirely of the ceramic material50. The gradient structure51helps to mitigate stress build up through thermal mismatches and reduces the tendency to form a continuous weak oxide boundary layer at the interface of the ceramic material50and the metal bond material52.

According to one embodiment, as shown inFIG. 4, the lowermost portion of the thermal barrier coating22applied directly to the surface of the body portion42, such as the inner diameter surface38of the cylinder liner28, consists of the metal bond material52. Typically, 5% to 20% of the entire thickness of the thermal barrier coating22is formed of 100% metal bond material52. In addition, the uppermost portion of the thermal barrier coating22can consist of the ceramic material50. For example, 5% to 50% of the entire thickness of the thermal barrier coating22could be formed of 100% ceramic material50. The gradient structure51of the thermal barrier coating22which continuously transitions from the 100% metal bond material52to the 100% ceramic material50is located therebetween. Typically, 30% to 90% of the entire thickness of the thermal barrier coating22is formed of, or consists of, the gradient structure51. It is also possible that 10% to 90% of the entire thickness of the thermal barrier coating22is formed of a layer of the metal bond layer52, up to 80% of the thickness of the thermal barrier coating22is formed of the gradient structure51, and 10% to 90% of the entire thickness of the thermal barrier coating22is formed of a layer of the ceramic material50.FIG. 4is an enlarged cross-sectional view showing an example of the thermal barrier coating22disposed on the inner diameter surface38of the cylinder liner28. Example compositions of the thermal barrier coating22including ceria stabilized zirconia (CSZ), yttria stabilized zirconia (YSZ), and metal bond material (Bond) are disclosed inFIG. 5.FIG. 6is a cross-sectional view showing an example of the thermal barrier coating22disposed on the steel body portion42.

In its assprayed form, the thermal barrier coating22typically has a surface roughness Ra of less than 15 μm, and a surface roughness Rz of not greater than ≤110 μm. The thermal barrier coating22can be smoothed. At least one additional metal layer, at least one additional layer of the metal bonding material52, or at least one other layer, could be applied to the outermost surface of the thermal barrier coating22. When the additional layer or layers are applied, the outermost surface formed by the additional material could also have the surface roughness Ra of less than 15 μm, and a surface roughness Rz of not greater than <110 μm. Roughness can affect combustion by trapping fuel in cavities on the surface of the coating. It is desirable to avoid coated surfaces rougher than the examples described herein.

The thermal barrier coating22has a low thermal conductivity to reduce heat flow through the thermal barrier coating22. Typically, the thermal conductivity of the thermal barrier coating22having a thickness of less than 1 mm, is less than 1.00 W/m·K, preferably less than 0.5 W/m·K, and most preferably not greater than 0.23 W/m·K. The specific heat capacity of the thermal barrier coating22depends on the specific composition used, but typically ranges from 480 J/kg·K to 610 J/kg·K at temperatures between 40 and 700° C. The low thermal conductivity of the thermal barrier coating22is achieved by the relatively high porosity of the ceramic material50. Due to the composition and low thermal conductivity of the thermal barrier coating22, the thickness of the thermal barrier coating22can be reduced, which reduces the risk of cracks or spalling, while achieving the same level of insulation relative to comparative coatings of greater thickness. It is noted that the advantageous low thermal conductivity of the thermal barrier coating22is not expected. When the ceramic material50of the thermal barrier coating22includes ceria stabilized zirconia, the thermal conductivity is especially low.

The bond strength of the thermal barrier coating22is also increased due to the gradient structure51present in the thermal barrier coating22and the composition of the metal used to form the component. The bond strength of the thermal barrier coating22having a thickness of 0.38 mm is typically at least 2000 psi when tested according to ASTM C633.

The thermal barrier coating22with the gradient structure51can be compared to a comparative coating having a two layer structure, which is typically less successful than the thermal barrier coating22with the gradient structure51. The comparative coating includes a metal bond layer applied to a metal substrate followed by a ceramic layer with discrete interfaces through the coating. In this case, combustion gases can pass through the porous ceramic layer and can begin to oxidize the bond layer at the ceramic/bond layer interface. The oxidation causes a weak boundary layer to form, which harms the performance of the coating.

However, the thermal barrier coating22with the gradient structure51can provide numerous advantages. The thermal barrier coating22is applied to at least a portion of the surface of the component exposed to the combustion chamber24or the exhaust gas generated by the internal combustion engine20to provide a reduction in heat flow through the component. The reduction in heat flow is typically at least 50%, relative to the same component without the thermal barrier coating22. By reducing heat flow through the component, more heat is retained in the fuel-air mixture of the combustion chamber and/or exhaust gas produced by the engine, which leads to improved engine efficiency and performance.

The thermal barrier coating22of the present invention has been found to adhere well to the steel body portion42. However, for additional mechanical anchoring, the surfaces of the body portion42to which the thermal barrier coating22is applied is typically free of any edge or feature having a radius of less than 0.1 mm. In other words, the surfaces of the component to which the thermal barrier coating22is preferably free of any sharp edges or corners. According to one example embodiment, the body portion42includes a broken edge or chamfer machined along its surface. The chamfer allows the thermal barrier coating22to radially lock to the body portion42. Alternatively, at least one pocket, recess, or round edge could be machined along the surface of the body portion42. These features help to avoid stress concentrations in the thermal sprayed coating22and avoid sharp corners or edges that could cause coating failure. The machined pockets or recesses also mechanically lock the coating22in place, again reducing the probability of delamination failure.

Another aspect of the invention provides a method of manufacturing the coated component for use in the internal combustion engine20, for example a diesel engine. The component, which is typically formed of steel, can be manufactured according to various different methods, such as forging, casting, and/or welding. As discussed above, the thermal barrier coating22can be applied to various different components exposed to the combustion chamber24or the exhaust gas generated by the internal combustion engine20, and those components can comprise various different designs. Prior to applying the thermal barrier coating22to the body portion42, any phosphate or other material located on the surface to which the thermal barrier coating22is applied must be removed.

The method next includes applying the thermal barrier coating22to the body portion42of the component. The thermal barrier coating22can be applied to the entire surface of the component exposed to the combustion chamber or the exhaust gases, or only a portion of that surface. The ceramic material50and metal bond material52are provided in the form of particles or powders. The particles can be hollow spheres, spray dried, spray dried and sintered, sol-gel, fused, and/or crushed. For example, as shown inFIGS. 1-3, the thermal barrier coating22is applied to the portion of the cylinder liner28and the valve face36.

In the example embodiment, the method includes applying the metal bond material52and the ceramic material50by a thermal or kinetic method. According to one embodiment, a thermal spray technique, such as plasma spraying, flame spraying, or wire arc spraying, is used to form the thermal barrier coating22. High velocity oxy-fuel (HVOF) spraying is a preferred example of a kinetic method that gives a denser coating. Other methods of applying the thermal barrier coating22to the component can also be used. For example, the thermal barrier coating22could be applied by a vacuum method, such as physical vapor deposition or chemical vapor deposition. According to one embodiment, HVOF is used to apply a dense layer of the metal bond material52to the component, and a thermal spray technique, such as plasma spray, is used to apply the gradient structure51and the layer of ceramic material50. Also, the gradient structure51can be applied by changing feed rates of twin powder feeders while the plasma sprayed coating is being applied.

The example method begins by spraying the metal bond material52in an amount of 100 wt. % and the ceramic material50in an amount of 0 wt. %, based on the total weight of the materials being sprayed. Throughout the spraying process, an increasing amount of ceramic material50is added to the composition, while the amount of metal bond material52is reduced. Thus, as shown inFIG. 4, the composition of the thermal barrier coating22gradually changes from 100% metal bond material52along the component to 100% ceramic material50at a top surface58of the thermal barrier coating22. Multiple powder feeders are typically used to apply the thermal barrier coating22, and their feed rates are adjusted to achieve the gradient structure51. The gradient structure51of the thermal barrier coating22is achieved during the thermal spray process.

The thermal barrier coating22can be applied to the entire component, or a portion thereof, for example only the surface exposed to the combustion chamber24or exhaust gas, or only a portion of that surface. Non-coated regions of the component can be masked during the step of applying the thermal barrier coating22. The mask can be a re-usable and removal material applied adjacent the region being coated. Masking can also be used to introduce graphics in the thermal barrier coating22. In addition, after the thermal barrier coating22is applied, the coating edges are blended, and sharp corners or edges are reduced to avoid high stress regions.

As shown inFIG. 4, the thermal barrier coating22has a thickness t extending from the surface of the body portion42of the component, for example the inner diameter surface38of the cylinder liner28, to the top surface58. According to example embodiments, the thermal barrier coating22is applied to a total thickness t of not greater than 1.0 mm, or not greater than 0.7 mm, preferably not greater than 0.5 mm, and most preferably not greater than 0.380 mm. In the example embodiment ofFIGS. 1 and 2, the total thickness t of the thermal barrier coating22disposed along the inner diameter surface38of the cylinder liner28is 0.380 mm. This total thickness t preferably includes the total thickness of the thermal barrier coating22and also any additional or sealant layer applied to the uppermost surface of the thermal barrier coating22. However, the total thickness t could be greater when the additional layers are used.

The thickness t can be uniform along the entire surface of the component, but typically the thickness t varies along the surface of the component, especially if the surface has a complex shape. In certain regions of the component, for example where the component is subject to less heat and pressure, the thickness t of the thermal barrier coating22can be as low as 0.020 mm to 0.030 mm. In other regions of the component, for example regions which are subjected to the highest temperatures and pressures, the thickness t of the thermal barrier coating22is increased. For example, the method can include aligning the component20in a specific location relative to the spray gun and fixture, fixing the component to prevent rotation, using a scanning spray gun in a line, and varying the speed of the spray or other technique used to apply the thermal barrier coating22to adjust the thickness t of the thermal barrier coating22over different regions of the component.

In addition, more than one layer of the thermal barrier coating22, such as 5-10 layers, having the same or different compositions, could be applied to the component. Furthermore, coatings having other compositions could be applied to the component in addition to the thermal barrier coating22. According to one example embodiment, an additional metal layer, such as an electroless nickel layer, is applied over the thermal barrier coating22to provide a seal against fuel absorption, prevent thermally grown oxides, and prevent chemical degradation of the ceramic material50. The thickness of the additional metal layer is preferably from 1 to 50 microns. If the additional metal layer is present, the porosity of the thermal barrier coating22could be increased. Alternatively, an additional layer of the metal bonding material52can be applied over the ceramic material50of the thermal barrier coating22.

Prior to applying the thermal barrier coating22, the surface of the component to which the thermal barrier coating22is applied is washed in solvent to remove contamination. Next, the method typically includes removing any edge or feature having a radius of less than 0.1 mm. The method can also include forming the broken edges or chamfer56, or another feature that aids in mechanical locking of the thermal barrier coating22to the component and reduce stress risers, in the component. These features can be formed by machining, for example by turning, milling or any other appropriate means. The method can also include grit blasting surfaces of the component prior to applying the thermal barrier coating22to improve adhesion of the thermal barrier coating22.

After the thermal barrier coating22is applied to the component, the coated component can be abraded to remove asperities and achieve a smooth surface. In the example embodiment ofFIGS. 1 and 2, the thermal barrier coating22applied to the cylinder liner28requires post-finishing, for example by machining or honing. The method can also include forming a marking on the surface of the thermal barrier coating22for the purposes of identification of the coated component when the component is used in the market. The step of forming the marking typically involves re-melting the thermal barrier coating22with a laser. According to other embodiments, an additional layer of graphite, thermal paint, or polymer is applied over the thermal barrier coating22. If the polymer coating is used, the polymer burns off during use of the component in the engine20. The method can include additional assembly steps, such as washing and drying, adding rust preventative and also packaging. Any post-treatment of the coated component must be compatible with the thermal barrier coating22.