Adhesion of thermal spray using compression technique

An improved surface activation technique improves the adhesion of thermal spray coatings, which is useful for engine cylinder bores. The new method includes compressing the cylinder bore surface to create a surface profile on the surface, such as through rolling a roller along the surface. An engine block is also provided, which includes a plurality of cylinder bores, each cylinder bore having an inner surface, and each inner surface having a surface profile that includes a helical groove and other surface profiles formed in the inner surface. A thermal spray coating is formed on the inner surface of each cylinder bore, the thermal spray coating being adhered to the surface profile of the inner surface. A roller assembly for activating the surface is also provided.

FIELD

The present disclosure relates to improving the adhesion of thermal spray coatings to surfaces and more particularly to surface activation that provides improved adhesion of thermal spray coatings to such surfaces.

INTRODUCTION

Thermal spraying is a coating process which applies material heated and typically melted by combustion or an electrical plasma or arc to a substrate. The process is capable of rapidly applying a relatively thick coating over a large area relative to other coating processes such as electroplating, sputtering and physical and vapor deposition.

The ruggedness and durability of the thermal spray coating would seem to be almost exclusively a feature of the material of the coating and to a lesser extent the quality of application. However, it has been determined that, in fact, typically the most significant factor affecting the ruggedness and durability of a thermal spray coating is the strength of the bond between the thermal spray coating and the surface. A poor bond may allow the thermal spray coating to crack or peel off, sometimes in relatively large pieces, long before the thermal sprayed material has actually worn away, whereas a strong bond renders the thermal spray coating an integral and inseparable component of the underlying surface.

Several approaches have been undertaken to improve the bond between the thermal spray coating and the underlying surface. Some processes involve removing part of the surface material to increase roughness prior to application of the thermal spray. However, these processes can be time consuming (sometimes requiring multiple steps) and can require expensive tools. Furthermore, existing processes may fail to sufficiently improve adhesion.

SUMMARY

The present disclosure provides an improved substrate surface texture, which improves the adhesion of thermal spray coatings. Thus, a method, tool, and engine block are disclosed that provide for improved adhesion of a thermal spray coating.

In one form, which may be combined with or separate from the other forms disclosed herein, a method of activating an inner surface of an engine cylinder bore to achieve better adhesion between a subsequently-applied coating and the inner surface is provided. The method includes compressing the inner surface to create a surface profile on the inner surface.

In another form, which may be combined with or separated from the other forms described herein, an engine block is provided that includes a plurality of cylinder bores. Each cylinder bore has an inner surface, and each inner surface has a surface profile that includes a helical groove formed in the inner surface. A thermal spray coating is formed on the inner surface of each cylinder bore. The thermal spray coating is adhered to the surface profile of the inner surface.

In yet another form, which may be combined with or separated from the other forms described herein, a roller assembly for activating an inner surface of an engine cylinder bore is provided. The roller assembly includes a central shaft defining a central axis and a roller configured to rotate about the central axis. The roller has an activating edge configured to compress a groove into an inner surface of an engine cylinder bore.

Additional features may be provided, such as: the step of compressing the inner surface including rolling a roller along the inner surface; the step of compressing the inner surface including creating a texture on the inner surface; the step of compressing the inner surface further including rolling a second roller along the inner surface; the step of compressing the inner surface further including rolling a third roller along the inner surface; the rolling of the first, second, and third rollers along the inner surface being performed simultaneously to maintain bore concentricity; depositing a thermal spray coating on the inner surface; the first roller is provided as having a first roller pattern configuration and the second roller is provided as having a second roller pattern configuration; the first roller pattern configuration being different than the second roller pattern configuration; the step of compressing the inner surface including creating a helical groove in the inner surface; the step of compressing the inner surface including creating a plurality of dimples in the inner surface; the helical groove being a first helical groove, and creating a second helical groove through a first flank of the first helical groove; creating a third helical groove through a second flank of the first helical groove; the surface profile of each inner surface including a plurality of dimples formed in the inner surface; creating compressive residual stress in the cylinder bore; the compressive residual stress having a magnitude of at least 250 MPa; the helical groove having a helical angle of about 5 to about 20 degrees; the texture including a plurality of rough textures each having radii greater than 10 μm; the textures having a developed interfacial area ratio (Sdr) greater than 100% to enhance coating adhesion; providing each of the helical grooves as having a pitch in the range of about 150 to about 250 μm; providing the first helical groove as having a depth of about 100 to about 250 μm; providing each of the dimples as having a diameter of about 20 to about 30 μm; and the first and the second flanks defining an angle of about 60 to about 75 degrees therebetween.

Further additional features may include the following: each of the inner surfaces of the cylinder bores being formed of aluminum; the roller being a first roller; the roller assembly further comprising a second roller configured to rotate about the central axis and to activate the inner surface of the engine cylinder bore; at least one of the first and second rollers comprising a plurality of micro projections extending from an outer edge; the plurality of micro projections being configured to create a plurality of dimples in the inner surface of the engine cylinder bore; the roller assembly further comprising a third roller configured to rotate about the central axis and to activate the inner surface of the engine cylinder bore; the first, second, and third rollers being spaced about equidistant from each other and from the central axis; a first axle about which the first roller is configured to rotate; a second axle about which the second roller is configured to rotate; a third axle about which the third roller is configured to rotate; a first roller shaft coupled to the first axle; the first roller shaft extending from the central shaft; a second roller shaft coupled to the second axle; the second roller shaft extending from the central shaft; a third roller shaft coupled to the third axle; the third roller shaft extending from the central shaft; the first roller shaft being disposed along a first plane; the second roller shaft being disposed along a second plane; the third roller shaft being disposed along a third plane; the first, second, and third planes being parallel to each other; the first plane being disposed about 50 to about 80 μm from the second plane; the first plane being disposed about 50 to about 80 μm from the third plane; and a second axle about which the second and third rollers are configured to rotate.

DETAILED DESCRIPTION

With reference toFIG. 1, an internal combustion engine block is illustrated and generally designated by the reference number10. The engine block10typically includes a plurality of cylinders12having interior cylinder bores14, numerous flanges16and openings18for threaded fasteners and other features for receiving and securing components such as cylinder heads, shafts, manifolds and covers (all not illustrated).

On the right side ofFIG. 1is an enlarged representation of the cylinder bore14. The cylinder bore14may be a surface of a substrate such as an aluminum engine block10or a surface of an iron sleeve that has been installed in the engine block10. Thus, the cylinder bore14has an inner surface wall19. In either case, the surface finish of the inner surface19of the cylinder bore14may be a machined profile which is mechanically roughened or activated.

It will be appreciated that although illustrated in connection with the cylinder bore14of an internal combustion engine10, with which it is especially beneficial, the present disclosure provides benefits and is equally and readily utilized with other cylindrical surfaces such as the walls of hydraulic cylinders and flat surfaces such as planar bearings which are exposed to sliding, frictional forces.

Referring now toFIG. 2, an enlarged cross-section of a portion of the cylinder bore14schematically illustrates the surface texture20of the activated surface of the inner surface19of the cylinder bore14. The surface texture20is created by compression of the inner surface19. In one example, the surface texture20is created by rolling a roller against the inner surface19of the cylinder bore14to compress the inner surface19and create a groove in the inner surface19, which will be described in greater detail below.

A thermal spray coating22is applied and adhered to the surface profile20of the inner surface19. Typically, the thermal spray coating22for the inner surface19described herein, after honing, may be on the order of about 150 μm and is typically within the range of from about 130 μm to about 175 μm. Some applications may require thermal spray coatings22having greater or lesser thicknesses, however. The thermal spray coating22may be a steel or a steel alloy, another metal or alloy, a ceramic, or any other thermal spray material suited for the service conditions of the product and may be applied by any one of the numerous thermal spray processes such as plasma, detonation, wire arc, flame, or HVOF suited to the substrate and material applied.

Referring now toFIG. 3A, one example of the surface profile20of the inner surface19of the cylinder bore14is illustrated. The inner surface19of the cylinder bore14has a surface profile20that forms at least one helical groove24on the inner surface19. For example, a large main groove24may be rolled or compressed into the inner surface wall19by a first roller (explained in more detail below), resulting in a helical main groove24having a pitch P in the range of about 150 to about 250 μm and a thread height H, or depth, of about 100 to about 250 μm. The main groove24may have a first flank26opposite a second flank28, with an angle A of about 60 to about 75 degrees defined between walls of the first and second flanks26,28. The helical groove24may have a helical angle in the range of about 5 to about 20 degrees, by way of example.

Furthermore, the surface profile20in the inner surface19of the cylinder bore14may include portions forming a plurality of cavities or dimples30in the inner surface19. The plurality of dimples30may be formed along the first and second flanks26,28(and/or in the valley32of the groove24, in some examples, not shown), within the inner surface19. Each dimple30may have a diameter in the range of about 20 to about 30 μm, by way of example.

A secondary helical groove34may be formed through the first flank26of the main groove24. For example, the secondary groove34may be formed through a midpoint M1of the thread height H of the first flank26. Similarly, if desired, a third helical groove36may be formed through the second flank28of the main groove24. The third groove36may be formed through a midpoint M2of the thread height H of the second flank28. The secondary and third grooves34,36may have widths W of about 50 to about 80 μm and depths E of about 50 to about 100 μm, by way of example. The secondary and third grooves26,28may also include their own dimples, if desired (not shown).

After having been compressed, for example by rolling, to create one or more of the grooves24,34,36and/or dimples30, each cylinder bore14comprises compressive residual stress. The resultant compressive residual stress may have a magnitude of at least 250 MPa; in other words, the compressive residual stress may be less than or equal to −250 MPa.

Each valley32can be formed to have a root radius R in the range of about 30 to about 50 μm. The root radius may be determined by the equation:

where γ is the surface tension of the steel or steel alloy coating22, and P is the pressure applied to the liquid steel or steel alloy during the thermal spray application. The root radius R determines the splat size of atomized steel droplets.

The resulting rough textures24,30,34,36that make up the surface profile20may have radii greater than 10 μm and developed interfacial area ratio (Sdr) greater than 100% to enhance coating adhesion. Sdr is computed from the standard equation:

Sdr=Surface⁢⁢Area⁢⁢of⁢⁢the⁢⁢Textured⁢⁢Surface-Cross⁢⁢Sectional⁢⁢AreaCross⁢⁢Sectional⁢⁢Area(2)
For example, a unit of cross sectional area which has two units of area of textured surface has an Sdr percent of 100 ((2−1)/1). Generally speaking, the greater the Sdr, the greater the adhesion strength. Experimentation and life testing has determined that the adhesion achieved for Sdr's below 100% generally provides compromised ruggedness, durability and thus service life. Accordingly, in at least some embodiments of the present disclosure, the Sdr is at or above 100%.

Referring now toFIG. 3B, another example of the surface profile of the inner surface19of the cylinder bore14is illustrated, which is generally designated as20′. It should be understood that the cylinder bore14having the surface profile20′ ofFIG. 3Bmay have the same characteristics as hereinbefore described, except where specifically described as being different from the surface profile20shown inFIG. 3A. The surface profile20′ forms at least one helical groove124on the inner surface19. For example, a large main groove124may be rolled or compressed into the inner surface wall19by a first roller (explained in more detail below), resulting in a helical main groove124having a pitch P in the range of about 150 to about 250 μm and a thread height H, or depth, of about 100 to about 250 μm. The main groove124may have a first flank126opposite a second flank128, with an angle A of about 60 to about 75 degrees defined between walls of the first and second flanks126,128.

Furthermore, the surface profile20′ activated in the inner surface19of the cylinder bore14may include portions forming a plurality of cavities or dimples130in the inner surface19. The plurality of dimples130are formed along the first and second flanks126,128(and/or in the valley132of the groove124, in some examples, not shown), within the inner surface19. Each dimple130may have a diameter in the range of about 20 to about 30 μm, by way of example. The surface profile20′ lacks the secondary and third grooves34,36illustrated inFIG. 3A.

The surface profile20′ may be the entirety of the surface profile activated in a particular engine block10. For example, the surface profile20′ may be created by a single roller wheel. In the alternative, the surface profile20′ may represent an intermediate surface profile that has been rolled by a first roller (described in greater detail below), prior to rolling second and/or third rollers to create the secondary and third grooves34,36shown inFIG. 3A.

Referring now toFIG. 3C, yet another example of the surface profile of the inner surface19of the cylinder bore14is illustrated, which is generally designated as20″. It should be understood that the cylinder bore14having the surface profile20″ ofFIG. 3Cmay have the same characteristics as hereinbefore described, except where specifically described as being different from the surface profiles20,20′ shown inFIG. 3AorFIG. 3B. The surface profile20″ forms at least one helical groove224on the inner surface19. For example, a large main groove224may be rolled or compressed into the inner surface wall19by a first roller (explained in more detail below), resulting in a helical main groove224having a pitch P in the range of about 150 to about 250 μm and a thread height H, or depth, of about 100 to about 250 μm. The main groove224may have a first flank226opposite a second flank228, with an angle A of about 60 to about 75 degrees defined between walls of the first and second flanks226,228.

The surface profile20″ lacks the dimples30,130illustrated inFIGS. 3A-3B. Such a surface profile20″ may provide adequate surface roughness for lower coating adhesion force applications, such as lower power density engines. In the illustrated example, the surface profile20″ also lacks the secondary and third grooves34,36illustrated inFIG. 3A; however, if desired, secondary and third grooves (such as elements34and36shown inFIG. 3A) can be included in the flanks226,228of the main groove224, similar to the secondary and third grooves shown inFIG. 3A.

The surface profile20″ may be the entirety of the surface profile activated in a particular engine block10. In the alternative, the surface profile20″ may represent an intermediate surface profile that has been rolled by a first roller (described in greater detail below), prior to rolling second and/or third rollers to create the secondary and third grooves34,36shown inFIG. 3A.

Referring now toFIG. 4, a method300of activating an inner surface19of an engine cylinder bore14to achieve better adhesion between a subsequently-applied coating and the inner surface19will now be described. The method300includes compressing the inner surface19to create a surface profile on the inner surface. In other words, instead of (or in addition to) removing material from the inner surface19using a tool to remove material, or by erosion through water jetting, for example, the aluminum material of the cylinder bore14is compressed. In some examples, the method300includes compressing the inner surface19by rolling at least one roller along the inner surface.

The method300may include a step302of pre-machining the cylinder bores within an engine block. The method300may then include a step304compressing the inner surfaces of the cylinder bores to activate the surfaces for better adhesion of a subsequently-applied thermal spray. For example, one or more micro rollers may be rolled along the inner surfaces to create grooves, such as one or more of the helical grooves24,34,36,124,224described above. Creating the grooves results in a surface texture on the inner surface of the cylinder bores. The step304may include rolling a first roller, a second roller, and/or a third roller along the inner surface of each cylinder bore, to create a surface profile, such as one of the surface profiles20,20′,20″ described above. Each of the rollers, if more than one are used, can be rolled simultaneously along the inner surface19of the cylinder bore14to maintain concentricity of the cylinder bore.

In step306, the method300may optionally include washing of the cylinder bores14, for example, after compressing the inner surface19with the roller or rollers. The method308then includes a step308of thermal spraying, or depositing a thermal spray coating, on the inner surface19. The method300may then proceed to step310of inspecting the thermally sprayed inner surfaces, if desired.

In order to perform the method300, certain optional steps may be included. For example, the first roller may be provided as having a first roller pattern configuration and a second roller may be provided as having a second roller pattern configuration, where the first roller pattern configuration is different than the second roller pattern configuration. Both rollers can be rolled along the inner surface to create different features in the surface profile. In the alternative, both the first and second rollers can be provided having identical roller pattern configurations. Similarly, a third, fourth, or fifth (or additional) roller may be provided having the same or different roller pattern configurations to create additional surface texture. Each of the rollers can be rolled along the inner surface19to compress material of the inner surface19, either simultaneously or sequentially.

The compressing step304may also include rolling a helical groove into the inner surface19, as shown inFIGS. 3A-3C, by way of example. If multiple rollers are used, each may be used to create its own helical groove, as shown inFIG. 3A, by way of example. Thus, the method300may include creating first, second, and third helical grooves within the inner surface19. The compressing step304may also include creating a plurality of dimples in the inner surface19, as shown inFIGS. 3A-3B, by way of example. The compressing step304may also include creating compressive residual stress in the cylinder bore, having a magnitude of at least 250 MPa (or less than −250 MPa compressive residual stress). The compressing step304of the method300may include creating a plurality of rough textures, each having radii greater than 10 μm and developed interfacial area ratio (Sdr) greater than 100% to enhance coating adhesion. Further, the compressing step304of the method300may include creating one or more helical grooves having a pitch of about 150 to about 250 μm, a depth (or thread height) of about 100 to about 250 μm, and the compressing step304of the method300may include creating dimples having a diameter of about 20 to about 30 μm. Additional details of the method300may be incorporated in the description of a roller assembly, which can be used to perform the method300, as described below.

Referring now toFIG. 5, a roller assembly for activating an inner surface of an engine cylinder bore is illustrated schematically and generally designated at400. The cylinder bore14and inner surface19are sketched in for clarity only, as being see-though, though it should be understood that one would not be able to see through the cylinder bore14or inner surface19in actual application.

The roller assembly400may include a central shaft402defining a central axis C therethrough. In the illustrated embodiment, the central axis C also runs coaxially with a central axis of the cylinder bore14, and thus, the central axis C is the central axis of the cylinder bore14. At least one roller404is provided and configured to rotate about the central axis C.

Referring toFIGS. 6A-6C, additional details of the roller404are shown. The roller404is a main roller or first roller, in this example. The roller404is a wheel that has a main body portion406and an activating edge408configured to compress a groove into the inner surface19of the engine cylinder bore14, as shown inFIGS. 3A-3C. The activating edge408is configured to compress a helical groove into the inner surface19of the cylinder bore14as the roller404is rolled along the inner surface19, as shown inFIGS. 3A-3Cabove. The activating edge408may be disposed on an activating portion409that extends from an outer portion411of the main body portion406of the roller404.

The roller404may also include a plurality of micro projections410extending from the outer edge (activating edge408). The micro projections410are configured to create a plurality of dimples in the inner surface19of the engine cylinder bore14, such as shown and described above inFIGS. 3A-3B, through compression of the micro projections410against the inner surface19as the roller404is rolled along the inner surface19.

The main body406of the roller404may have a height J of about 200 to about 250 μm, or any other desired height to create the helical groove, such as helical groove24, in the inner surface19. Similarly, the activating portion409may have a width K in the range of about 200 to about 250 μm. Further, the micro projections410may be provided as spines, bumps, or any other desired shape, to create dimples, such as the dimples30,130shown inFIGS. 3A-3B.

The roller404has a central aperture412formed through the height J of the main body portion406. A pin or axle414may extend through the aperture412so that the roller404may rotate about the axle414. A roller shaft416is coupled to the axle414. The roller shaft416is also coupled to the central shaft402. A crank418may be coupled to the central shaft402so that the central shaft402is rotatable about the central axis C. Turning the crank418may cause the roller404to be rotated about axle414and about the central axis C to form a groove (such as groove24) in the inner surface19.

In some examples, the roller assembly400also includes a second roller420and a third roller422. The roller assembly400could have any desired number of rollers404,420,422, such as one, two, three, four, five, or six rollers404,420,422. The rollers404,420,422may be spaced equidistant from each other and from the central axis C, to maintain concentricity of the cylinder bore14as the rollers404,420,422are being rolled along the inner surface19of the cylinder bore14. Thus, like the first roller404, the second and third rollers420,422are each configured to rotate about an axle424,426that is coupled to a roller shaft428,430extending from the central axis402, and each roller420,422is configured to rotate about the central axis C to activate the inner surface19. Therefore, the first, second, and third rollers404,420,422may be rolled along the inner surface19simultaneously to maintain bore concentricity by rotating the shaft402.

Along the height M of the central shaft402, each of the roller shafts416,428,430may be positioned about 50 μm from another of the roller shafts416,428,430. For example, the second roller shaft428may be positioned at or near a distal end432of the central shaft402, and the first roller shaft416may be positioned a distance d1from the second roller shaft428, where d1is about 50 μm. Similarly, the third roller shaft430may be positioned a distance d2from the first roller shaft416, where d2is also equal to about 50 μm.

In other words, the roller shaft416may be disposed along a first plane P1, the second roller shaft428may be disposed along a second plane P2, and the third roller shaft430may be disposed along a third plane P2, where the first, second, and third planes P1, P2, P3are parallel to each other. The first plane P1may be disposed about 50 to about 80 μm from the second plane P2, and the first plane P1may also be disposed about 50 to about 80 μm from the third plane P3. Thus, in this example, the first plane P1is located between the second and third planes P2, P3.

The micro projections410extending from the activating surface408of the first roller404are illustrated having a cross section of a trapezoid inFIG. 6C. Accordingly, in a three-dimensional view, the micro projections410could be understood to have a trapezoidal prism shape. Each micro projection410could have a diameter of about 20 to about 50 μm, by way of example.

Referring now toFIGS. 7A-7F, other examples of variations of the micro projections410a-410fare illustrated. Any of shapes of the micro projections410a-410fillustrated could be substituted for the micro projection410illustrated inFIG. 6C, or any other shape not illustrated could be used. In addition, the multiple different shapes for the micro projection410,410a-410fcould be used on a single activating edge408of the roller404. For example, the micro projections410,410a-410fcould alternate in shape along the activating edge408.

Referring toFIG. 7A, for example, any micro projection410on the activating edge408could have a rounded edge and/or the shape of a flattened mountain top, the micro projection labeled as element410ain this variation. Referring toFIG. 7B, any micro projection410on the activating edge408could have a cone shape, the micro projection labeled as element410bin this variation. Referring toFIG. 7C, any micro projection410on the activating edge408could have a combined shape, such as a cone atop a cylinder, the micro projection labeled as element410cin this variation. Referring toFIG. 7D, any micro projection410on the activating edge408could have another combined shape, such as a triangular prism atop a cube or rectangular solid, the micro projection labeled as element410din this variation. Referring toFIG. 7E, any micro projection410on the activating edge408could have a tetrahedron shape, the micro projection labeled as element410ein this variation. Referring toFIG. 7F, any micro projection410on the activating edge408could have a hexagonal shape, such as a hexagonal prism or hexagonal solid shape, the micro projection labeled as element410fin this variation. Though example micro projection shapes410,410a-fare illustrated inFIGS. 6C and 7A-7F, it should be understood that the micro projections410could have any other suitable shape to activate the inner surface19, without falling beyond the spirit and scope of the present disclosure.

Referring now toFIG. 8, one variation of a roller is illustrated and designated at numeral440. This numbering convention indicates that the roller configuration404′,420′,422′ could be used to substitute for any or all of the rollers404,420,422shown and described above. Similarly, the configuration of the first roller404shown inFIG. 6Ccould also be used for the second and third rollers420,422. Any combination of the roller404shown inFIG. 6Cand the roller404′,420′,422′ shown inFIG. 8could be used for one of the roller wheels404,420,422described above. One or more of the rollers404,420,422could be identical, and/or one or more of the rollers404,420,422could resemble the roller404′,420′,422′ that is lacking in micro projections410.

FIG. 8shows a version of a roller440that is a wheel having a main body portion406′ and an activating edge408′ configured to compress a groove into the inner surface19of the engine cylinder bore14, as shown inFIGS. 3A-3C. The activating edge408′ is configured to compress a helical groove into the inner surface19of the cylinder bore14, as the roller440is rolled along the inner surface19, as shown inFIGS. 3A-3Cabove. The activating edge408′ may be disposed on an activating portion409′ that extends from an outer portion411′ of the main body portion406′. The roller440does not have any micro projections410,410a-410f, such as those shown inFIGS. 6C and 7A-7F. Therefore, the roller440is configured to create a helical groove having no dimples, such as the helical groove224illustrated inFIG. 3C. In addition, the roller440may create the helical grooves34,36through the flanks26,28of the first helical groove24shown inFIG. 3A.

The main body406′ of the roller440may have a height N of about 200 to about 250 μm, or any other desired height to create the helical groove, such as helical grooves224,34,36in the inner surface19. Similarly, the activating portion409′ may have a width O in the range of about 200 to about 250 μm.

The roller440may be used as any of the rollers404,420,422described above. In one example, the first roller appears as shown inFIGS. 6A-6C, having micro projections extending from the activating edge408, while the second and third rollers420,422embody the configuration of the roller440illustrated inFIG. 8and having no micro projections410.

Referring now toFIG. 9, an alternate arrangement for a portion of the roller assembly is illustrated and designated at400″, including two of the rollers420″,422″. Instead of one roller404,420,422per axle414,424,426of each roller shaft416,428,430, two rollers420″,422″ may be combined onto a single axle434, which may be coupled to one of the roller shafts416,424,426via coupling portions436. A spacer438may be disposed between the rollers420″,422″ to keep the rollers420″,422″ spaced apart by a distance s, which could be in the range of about half of the pitch width, or about 100 to about 150 μm. The arrangement of two rollers420″,422″ on a single axle434could be substituted for any of the single rollers404,420,422illustrated inFIG. 5, or the combined axle arrangement shown inFIG. 9could take the place of two of the roller shafts416,428,430and associated rollers/axles, if desired. In some variations, three rollers (or any desired number of rollers) could be combined onto a single axle, if desired.

It should be understood the Sdr measurement referred to above is three dimensional. Such surface texture is believed to enhance adhesion of the thermal spray coating by providing connections between the textured surface of the substrate and the thermal spray coating at multiple dimensional sizes or scales from sub-microscopic to microscopic.

The description is merely exemplary in nature and variations are intended to be within the scope of this disclosure. The examples shown herein can be combined in various ways, without falling beyond the spirit and scope of the present disclosure. Such variations are not to be regarded as a departure from the spirit and scope of the present disclosure.