MULTILAYERED COATING FOR DOWNHOLE TOOLS WITH ENHANCED WEAR RESISTANCE AND ACIDIC CORROSION RESISTANCE

Abstract

A coating for protecting a base material from wear and corrosion includes a first layer deposited directly onto an outer surface of the base material. In addition, the coating includes a second layer deposited directly onto the first layer. The first layer is positioned between the base material and the second layer. The first layer includes chromium having a first micro-crack density and the second layer comprises chromium having a second micro-crack density that is less than the first micro-crack density.

Claims

1. A coating for protecting a base material from wear and corrosion, the coating comprising: a first layer deposited directly onto an outer surface of the base material; and a second layer deposited directly onto the first layer, wherein the first layer is positioned between the base material and the second layer; wherein the first layer a comprises a first micro-crack density and the second layer comprises a second micro-crack density, wherein the first micro-crack density is greater than 1000 micro-cracks per inch, and the second micro-crack density is between 400 and 650 micro-cracks per inch; wherein the first layer or the second layer comprises chromium.

2. The coating of claim 1, wherein the first layer has a first thickness measured perpendicular to the outer surface of the base material and the second layer has a second thickness measured perpendicular to the outer surface of the base material; wherein the first thickness of the first layer is substantially uniform and the second thickness of the second layer is substantially uniform.

3. The coating of claim 2, wherein the second thickness of the second layer is less than 0.0050 in.

4. The coating of claim 2, wherein the second thickness of the second layer is between about 0.00050 in. and about 0.0020 in.

5. The coating of claim 2, wherein the first layer has a first hardness greater than 1000 HV and the second layer has a second hardness of about 850 HV.

6. The coating of claim 5, wherein the coating has an inner surface engaging the outer surface of the base material and an outer surface distal the base material, and wherein the coating has a total thickness measured perpendicularly from the outer surface of the base material to the outer surface of the coating, wherein the total thickness is less than 0.030 in.

7. The coating of claim 6, wherein the first layer has a thickness between about 0.00020 in. and 0.0030 in. measured perpendicular to the outer surface of the base material.

8. The coating of claim 1, wherein the first layer comprises chromium and the second layer comprises chromium.

9. The coating of claim 1, wherein the first layer comprises NiP and the second layer comprises chromium.

10. A down-hole tool comprising: a body made of a base material; a protective coating mounted to an outer surface of the base material, wherein the protective coating comprises: a first layer deposited directly onto an outer surface of the base material; and a second layer deposited directly onto the first layer, wherein the first layer is positioned between the base material and the second layer; wherein the first layer a comprises a first micro-crack density and the second layer comprises a second micro-crack density, wherein the first micro-crack density is greater than 1000 micro-cracks per inch and the second micro-crack density is between 400 and 650 micro-cracks per inch; wherein the first layer or the second layer comprises chromium.

11. The tool of claim 10, wherein the first layer has a first thickness measured perpendicular to the outer surface of the base material and the second layer has a second thickness measured perpendicular to the outer surface of the base material; wherein the second layer has a thickness between about 0.00050 in. and about 0.0020 in. measured perpendicular to the outer surface of the base material.

12. The tool of claim of claim 11, wherein the coating has an inner surface engaging the outer surface of the base material and an outer surface distal the base material, and wherein the coating has a total thickness less than 0.030 in. measured perpendicularly from the outer surface of the base material to the outer surface of the coating.

13. The tool of claim 10, wherein the first layer has a first hardness greater than 1000 HV and the second layer has a second hardness of about 850 HV.

14. The tool of claim 10, wherein the first layer comprises chromium or NiP; and wherein the second material comprises chromium.

15. A method for forming a wear and corrosion resistant coating on a surface of a base material, the method comprising: (a) depositing a first layer comprising a first material onto the surface of the base material at a first current density, wherein the first layer has a first micro-crack density greater than 1000 micro-cracks per inch; and (b) depositing a second layer of a second material onto the first layer after (a) at a second current density, wherein the second current density is different than the first current density, and wherein the second layer has a second micro-crack density between 400 and 650 micro-cracks per inch; wherein the first material or the second material comprises chromium deposited at the first current density or the second current density, respectively, of about 3.5 A/in2.

16. The method of claim 15, wherein the first material comprises chromium and the second material comprises chromium.

17. The method of claim 15, wherein the first material comprises NiP and the second material comprises chromium.

18. The method of claim 15 wherein (b) comprises depositing the second layer of the second material until the second layer has a thickness of about 0.0002 in. to 0.0030 in. measured perpendicular to the surface of the base material.

19. The method of claim 15, further comprising (c) heating the first layer after (a) and before (b).

20. The method of claim 15, wherein (c) comprises: (c1) heating the first layer at about 375 F. for about 1.5 hr.; and (c2) heating the first layer at about 500 F. for about 1 hr after (c1).

21. The method of claim 20, wherein (c) comprises increasing the hardness of the first layer to about 50 Rc.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0023] For a detailed description of the disclosed embodiments of the invention, reference will now be made to the accompanying drawings, wherein:

[0024] FIG. 1 is a perspective view of an embodiment of a fixed cutter drill bit made in accordance with principles described herein;

[0025] FIG. 2 is a schematic cross-sectional view of the multilayered protective coating of FIG. 1;

[0026] FIG. 3 is a schematic cross-sectional view of the multilayered coating of FIG. 1, made in accordance with principles described herein;

[0027] FIG. 4A is an SEM image of the surface morphology a conventional hard chromium layer of the prior art comprising a base material 500, and a hard chrome layer 501;

[0028] FIG. 4B is an SEM image of the surface morphology of a multilayered chrome coating made in accordance with principles described herein, and comprising a base material 400, a first chrome layer 401, and a second chrome layer 402;

[0029] FIG. 5 is a process flow chart illustrating an embodiment of a method for making a multilayered chromium coating in accordance with principles described herein; and

[0030] FIG. 6 is a process flow chart illustrating an embodiment of a method for making a protective coating comprising both NiP and chromium layers in accordance with principles described herein.

DETAILED DESCRIPTION OF THE DISCLOSED EMBODIMENTS

[0031] The following discussion is directed to various exemplary embodiments of the invention. However, the embodiments disclosed should not be interpreted, or otherwise used, as limiting the scope of the disclosure, including the claims. In addition, one skilled in the art will understand that the following description has broad application, and the discussion of any embodiment is meant only to be exemplary of that embodiment, and that the scope of this disclosure, including the claims, is not limited to that embodiment.

[0032] The drawing figures are not necessarily to scale. Certain features and components herein may be shown exaggerated in scale or in somewhat schematic form and some details of conventional elements may be omitted in interest of clarity and conciseness.

[0033] Certain terms are used throughout the following description and claims to refer to particular features or components. As one skilled in the art will appreciate, different persons may refer to the same feature or component by different names. This document does not intend to distinguish between components or features that differ in name but not function. The drawing figures are not necessarily to scale. Certain features and components herein may be shown exaggerated in scale or in somewhat schematic form and some details of conventional elements may not be shown in interest of clarity and conciseness.

[0034] In the following discussion and in the claims, the terms including and comprising are used in an open-ended fashion, and thus should be interpreted to mean including, but not limited to . . . . Also, the term couple or couples is intended to mean either an indirect or direct connection. Thus, if a first device couples to a second device, that connection may be through a direct connection, or through an indirect connection via other devices, components, and connections. In addition, as used herein, the terms axial and axially generally mean along or parallel to a central axis (e.g., central axis of a body or a port), while the terms radial and radially generally mean perpendicular to the central axis. For instance, an axial distance refers to a distance measured along or parallel to the central axis, and a radial distance means a distance measured perpendicular to the central axis. As used herein, the term about, when used in conjunction with a percentage or other numerical amount, means plus or minus 10% of that percentage or other numerical amount. For example, the term about 80%, would encompass 80% plus or minus 8%. The term Chromium, Cr and Chrome may be used interchangeably to describe some embodiments of the materials described herein. The terms plating and coating may be used interchangeably to describe embodiments of the materials described herein. The term substantially as used herein (unless specifically defined for a particular context elsewhere or the context clearly dictates otherwise) means nearly totally or completely, for instance, satisfying one or more of the following: greater than 50%, 51% or greater, 75% or greater, 80% or greater, 90% or greater, and 95% or greater of the condition.

[0035] As previously described, hard chromium plating has been used as a protective coating for downhole tools in oil and gas industry to improve the wear and corrosive resistance of bit bodies, a protective coating can be applied to the base metal (steel) of the bit body. While hard chrome plating enhances the wear and corrosion resistance, the conventional plating technique often introduces defects or cracks into the coating, for example when internal stress exceeds the tensile stress of the chromium. Further, in addition to the desired reaction resulting in the metallic chromium formation, many undesired side reactions occur. One of these is the formation of hydrogen gas, which can become entrapped and cause internal stresses, as well as subsequent cracking, as it seeks to escape the deposit. The width, depth, and population density of these cracks varies widely and is influenced by the following: the type of plating chemistry used (single-catalyst, mixed catalyst, proprietary), chromic acid concentration, type and concentration of catalyst, chromium-to-catalyst ratio, plating current-density, bath temperature, concentration of bath impurities (iron, copper, zinc, nickel, trivalent chromium, etc.), and the chromium deposit thickness surface condition of substrate.

[0036] Generally speaking, a micro-crack structure comprised of a high population density of narrow, shallow cracks is preferred because the deposit tends to have a lower stress, higher lubricity, good wearability and better corrosion resistance. If the conditions during plating cause the cracks to be coarse in nature, often referred to as macro-cracks, they may be visible to the naked eye. Usually, chromium with a microstructure comprising macro-cracks exhibits less desirable properties in service. For instance, corrosive fluids can more easily access the underlying substrate material through large macro-cracks than smaller micro-cracks.

[0037] A thin dense chromium (TDC) coating with thickness of 0.0001 in. or 0.0003 in. has less structural defects as compared to hard chrome plating, and is often void of micro-cracks. Thus, TDC usually exhibits better corrosion resistance than hard chrome plating. Thin dense chromium plating has been used in various coating applications such as bearing races, seal surfaces, pump piston, valves and pump housings, due primarily to its high surface hardness, low friction coefficient and high corrosion resistance. However, TDC is typically limited to a maximum thickness of about 0.0005 in., which results in a marked reduction in abrasion, erosion, abrasive wear, scuffing and galling. Therefore, TDC is less than ideal for highly abrasive and corrosive environments.

[0038] Embodiments disclosed herein provide coatings, compositions, and methods to protect and improve the wear and corrosive resistance downhole tools in oil and gas industry while offering the potential to overcome some of the foregoing challenges.

[0039] Referring now to FIG. 1, an embodiment of a downhole tool 100 in accordance with the principles described herein is shown. In this embodiment, tool 100 is a fixed cutter PDC bit adapted for drilling through formations of rock to form a borehole. Bit 100 has a central axis 105 about which it is rotated in a cutting direction 106 to drill the borehole. In addition, bit 100 includes a bit body 110, a shank 111, and an externally threaded connection or pin 112 attached to shank 111. Pin 112 connects bit 100 to a drill string (not shown). Bit body 110 has a bit face 120 formed on the end of the bit 100 that faces the formation and is generally opposite pin 112.

[0040] A cutting structure 121 is provided on face 120 and includes a plurality of circumferentially-spaced blades 130 that extend from bit face 120. In this embodiment, cutting structure 121 includes six angularly-spaced blades 130. Blades 130 are integrally formed as part of, and extend from, bit body 110 and bit face 120. Each blade 130 includes a cutter-supporting surface 131 for mounting a plurality of cutter elements 132. Each cutter element 132 comprises a cutting face 133 attached to an elongated and generally cylindrical support member or substrate 134, which is received and secured in a pocket formed in surface 131 of the corresponding blade 130 to which it is fixed. Each cutting face 133 is made of a very hard material, such as a polycrystalline diamond material, suitable for engaging and shearing the formation.

[0041] Bit 100 also includes circumferentially-spaced gage pads 140 disposed about the circumference of bit 100. In this embodiment, gage pads 140 are integrally formed as part of the bit body 110, with each gage pad 140 extending axially from a corresponding blade 130. Each gage pad 140 has a radially outer gage-facing surface 141 that slidingly engages the borehole sidewall during drilling to help maintain the size of the borehole and stabilize bit 100 against vibration. In certain embodiments, gage pads 140 include flush-mounted or protruding cutter elements embedded in gage-facing surfaces 141 to resist pad wear and assist in reaming the borehole sidewall.

[0042] To enhance the durability and operating lifetime of bit 100, select regions of bit body 110 are provided with a multilayered coating for protecting the base material (for example the metal forming bit body 110) from wear and corrosion, thereby providing enhanced wear resistance and corrosion resistance as described herein. Since formation facing surfaces 131 of blades 130 and gage-facing surfaces 141 of pads 140 are particularly susceptible to wear and damage, in this embodiment, a multilayered protective coating 150 that enhances resistance to wear and corrosion is provided on the entire formation facing surface 131 of each blade 130 and the entire gage-facing surface 141 of each gage pad 140. In other embodiments, additional surfaces of the bit body (e.g., bit body 110) can comprise multilayered protective coatings.

[0043] Referring now to FIG. 2, coating 150 is shown applied to the outer surface 154 of the base metal or material 153 of bit body 110. In general, coating 150 functions to protect underlying base material 153 from wear and corrosion during downhole operations. Coating 150 includes a plurality of layers, and thus, may also be referred to as multilayered. In particular, coating 150 includes a first layer 151 deposited directly onto the outer surface 154 of base material 153 and a second layer 152 deposited directly onto the first layer 151. Thus, first layer 151 is positioned between base material 153 and second layer 152.

[0044] First layer 151 comprises a first material 151a and has a first thickness T.sub.151 measured perpendicular to outer surface 154, and second layer 152 comprises a second material 152a and has a second thickness T.sub.152 measured perpendicular to outer surface 154. In this embodiment, first material 151a and second material 152a each comprise chromium. As will be described in more detail below, each chrome layer 151, 152 is applied via an electrolytic process at a different, discrete current density (e.g., A/in.sup.2).

[0045] In this embodiment, thickness T.sub.151 of layer 151 is substantially constant and uniform moving laterally along coating 150, and thickness T.sub.152 of layer 152 is substantially constant and uniform moving laterally along coating 150. The thickness of each layer 151, 152, respectively, is preferably less than 0.0050 in. More specifically, thickness T151 is preferably between about 0.00020 in. and 0.0030 in. and thickness T152 is preferably between about 0.00050 in. and about 0.0050 in. Each layer 151, 152 includes a plurality of micro-cracks. In general, the micro-cracks in a given layer 151, 152 can be oriented substantially parallel to the outer surface 154 of the base material or substantially perpendicular to the outer surface 154 of the base material 153 and/or oriented substantially perpendicular to the outer surface of the base material. The quantity or volume of micro-cracks in each layer 151, 152 can be characterized in terms of a micro-crack density, which refers to the average number of micro-cracks per unit length (e.g., micro-cracks per inch). A micro-crack is as known in the art, a crack in the material that is not visible to the naked eye, thus requiring a microscope (such as but not limited to SEM) to visualize the crack. A macro-crack in comparison is visible to naked eye (unaided human visual perception), and is thus greater than about 55 micrometers). In general, the micro-crack density of a layer or material can be measured or determined by microscope or such techniques familiar to one skilled in the art. The micro-crack density is inversely related to the current density at which the material is deposited, wherein a low current density will create a high micro-crack density, and high current density will produce a low micro-crack density.

[0046] In this embodiment, first layer 151 has a first micro-crack density, and second layer 152 has a second micro-crack density that is less than the first micro-crack density. In other words, second layer 152 has more micro-cracks per unit length than first layer 151. More specifically, in this embodiment, the first micro-crack density (of layer 151) is greater than 1000 micro-cracks per inch and the second micro-crack density (of layer 152) is between 400 and 650 micro-cracks per inch.

[0047] Referring still to FIG. 2, coating 150 has an inner surface 156 engaging outer surface 154 of base material 153, an outer surface 158 distal to the base material 153, and a total thickness T.sub.150 measured perpendicular to outer surface 154 from inner surface 156 to outer surface 158. Total thickness T.sub.150 is less than 0.030 in. As previously described, thicknesses T.sub.151, T.sub.152 are substantially uniform, and thus, total thickness T.sub.150 is also substantially constant or uniform moving laterally along coating 150. The first layer 151 of protective coating 150 has a first hardness that is greater than 1000 HV and the second layer 152 of coating 150 has a second hardness of about 850 HV.

[0048] Although coating 150 is shown and described as including two layers 151, 152, in other embodiments, the multilayered protective coating (e.g., coating 150) includes more than two layers. However, in such embodiments, each layer preferably has a thickness less than 0.005 in. (measured perpendicular to the outer surface of the underlying base metal or material), and the coating preferably has a total thickness less than about 0.030 in. (measured perpendicular to the outer surface of the underlying base metal or material).

[0049] Referring now to FIG. 3, an embodiment of a multilayered coating 170 for protecting an underlying base metal or material 173 is shown. For example, coating 170 can be used in place of coating 150 previously described to enhance the wear and corrosion resistance of a downhole tool. In this embodiment, coating 170 includes a first layer includes a first layer 171 deposited directly onto the outer surface 174 of base material 173 and a second layer 172 deposited directly onto the first layer 171. Thus, first layer 171 is positioned between base material 173 and second layer 172. First layer 171 comprises a first material 171a and has a first thickness T.sub.171 measured perpendicular to outer surface 174, and second layer 172 comprises a second material 172a and has a second thickness T.sub.172 measured perpendicular to outer surface 174. In this embodiment, first material 171a comprises NiP deposited onto surface 174 via a electroless process, and second material 172a comprises chromium deposited by an electrolytic process directly onto first layer 171 at a discrete current density (A/in.sup.2).

[0050] In this embodiment, thickness T.sub.171 of layer 171 is substantially constant and uniform moving laterally along coating 170, and thickness T.sub.172 of layer 172 is substantially constant and uniform moving laterally along coating 170. Thickness T.sub.171, T.sub.172 of each layer 171, 172, respectively, is preferably less than 0.0050 in. More specifically, thickness T.sub.171 is preferably between about 0.00020 in. and 0.0030 in. and thickness T.sub.172 is preferably between about 0.00050 in. and about 0.0050 in.

[0051] Coating 170 has an inner surface 176 engaging outer surface 174 of base material 173, an outer surface 178 distal to the base material 173, and a total thickness T.sub.170 measured perpendicular to outer surface 174 from inner surface 176 to outer surface 178. Total thickness T.sub.170 is less than 0.030 in. As previously described, thicknesses T.sub.171, T.sub.172 are substantially uniform, and thus, total thickness T.sub.170 is also substantially constant or uniform moving laterally along coating 170. In addition, second layer 172 has a micro-crack density between 400 and 850 micro-cracks per inch, and more specifically between 400 and 650 micro-cracks per inch.

[0052] Although coating 170 is shown and described as including two layers 171, 172, in other embodiments, the multilayered protective coating (e.g., coating 170) includes more than two layers. However, in such embodiments, each layer preferably has a thickness less than 0.005 in. (measured perpendicular to the outer surface of the underlying base metal or material), the coating preferably has a total thickness less than about 0.030 in. (measured perpendicular to the outer surface of the underlying base metal or material), and the layers of NiP and chromium are preferably arranged in an alternating fashion.

[0053] Embodiments described herein also include methods for making or forming a wear and corrosion resistant coating on an outer surface of a base metal or material. In one embodiment, the method comprises: (a) depositing a first layer of a first material onto the surface of the base material; and (b) depositing a second layer of a second material onto the first layer after (a); wherein the first material or the second material comprises chromium and is deposited at a current density of less than about 4.0 A/in.sup.2. In some embodiments, the first material (e.g., material 151a) and the second material (e.g., material 152a) each comprise chromium; wherein (a) comprises depositing the first layer of the first material at a first current density; and wherein (b) comprises depositing the second layer of the second material at a second current density that is different than the first current density. In another embodiment, one of the second current density and the first current density is about 3.5 A/in.sup.2 and the other of the first current density and the second current density is about 1.0 A/in.sup.2. In further embodiments, the first current density may be about 3.0 A/in.sup.2, 2.5 A/in.sup.2, 2.0 A/in.sup.2, 1.5 A/in.sup.2, 1.0 3 A/in.sup.2, and 0.5 A/in.sup.2. In still further embodiments, the second current density may be about 3.0 A/in.sup.2, 2.5 A/in.sup.2, 2.0 A/in.sup.2; 1.5 A/in.sup.2, 1.0 A/in.sup.2, and 0.5 A/in.sup.2.

[0054] In another embodiment, depositing the first layer of the first material may be by pulse current; and depositing the second layer of the second material may also by pulse current.

[0055] In some embodiments of a method of coating a base surface, the second layer formed from a second material is deposited until the layer has a thickness of about 0.0002 in. to 0.0003 in. measured perpendicular to the surface of the base material. Similarly, in some embodiments, the first layer of the first material is deposited until the first layer has a thickness of about 0.00020 in. to 0.0003 in. also measured perpendicular to the surface of the base material. Embodiments of such a method wherein the first material consists of chromium and the second material consists of chromium are illustrated in FIGS. 2 and 4(B).

[0056] Referring now to FIG. 5, an embodiment of a method 200 for making coating 150 as previously described is schematically shown. Beginning in block 201 of method 200, first material 151a comprising chromium is deposited onto base material 153 by a pulsed or alternative current electroplating to form layer 151. The chromium of first material 151a is applied to the base material 153 at a first current density, in for example a Heef 25 bath, where the length of time that the current is applied and the concentration of chromium ions determines the thickness of the layer. Next in block 202, a second material 152a comprising chromium is deposited onto first layer 151 by a pulsed or alternative current electroplating to form layer 152. The chromium of second material 152a is applied to first layer 151 at a second current density that is different than the first current density at which first material 151a is applied, however, each of the current densities is preferably less than 4.0 A/in.sup.2.

[0057] As shown in block 203, blocks 201 and 202 may be repeated as necessary to produce a coating on surface 154 comprising any desired number of discrete layers (e.g., layers 151, 152) of chromium, as well as any desired total thickness (e.g., total thickness T.sub.150) that is preferably less than 0.03 in.

[0058] Referring now to FIG. 6, an embodiment of a method 300 for making protective coating 170 as previously described is schematically shown. Beginning in block 301 of method 300, a first material 171a comprising NiP is deposited onto base material 173 by an electroless process. In block 303, the NiP (first layer 171) is heated at about 375 F. for about 1.5 hr., and further heated at 500 F. for about 1 hr, wherein the first layer 171 is heated for a total of 2.5 hrs. In this embodiment, the resultant layer 171 is about 0.0010 to about 0.0020 inches thick, has an increased hardness of about 50 Rc. Next, in block 303, Second material 172a comprising chromium is deposited on first layer 171 by a pulsed or alternative current electroplating to form second layer 172. The current density at which second material 172a is applied is preferably less than 4.0 A/in.sup.2.

[0059] As shown in block 304, blocks 301, 302, 303 may be repeated as necessary to produce a coating on surface 174 comprising any desired number of discrete layers (e.g., layers 171, 172) of NiP and chromium, and any desired total thickness (e.g., total thickness T.sub.170) that is preferably less than 0.03 in.

[0060] Although coating 150 was shown and described in connection with bit body 110, in general, embodiments of coatings described herein (e.g., coatings 150, 170) can be applied to the surface of any downhole tool such as but not limited to mandrels, mud motor rotors, and agitator rotors. In one embodiment a down-hole tool comprises a body made of a base material and a protective coating is mounted to an outer surface of the base material. The protective coating comprises a first layer deposited directly onto an outer surface of the base material; and a second layer deposited directly onto the first layer, wherein the first layer is positioned between the base material and the second layer; wherein the first layer comprises chromium having a first micro-crack density and the second layer comprises chromium having a second micro-crack density that is less than the first micro-crack density.

[0061] In another embodiment, the first micro-crack density is greater than 2500 micro-cracks per inch and the second micro-crack density is between 1000 and 1500 micro-cracks per inch, in a further embodiment, the first micro-crack density is greater than 1500 micro-cracks per inch and the second micro-crack density is between 500 and 850 micro-cracks per inch, and in a preferred embodiment the first micro-crack density is greater than 1000 micro-cracks per inch and the second micro-crack density is between 400 and 650 micro-cracks per inch.

[0062] In some embodiments of the tool described herein, the first layer has a first thickness measured perpendicular to the outer surface of the base material, and the second layer has a second thickness measured perpendicular to the outer surface of the base material; wherein the first thickness of the first layer is substantially uniform and the second thickness of the second layer is substantially uniform. In another embodiment, the second layer has a thickness between about 0.00005 in. and about 0.020 in. measured perpendicular to the outer surface of the base material, and in a preferred embodiment second layer has a thickness between about 0.00050 in. and about 0.0020 in. measured perpendicular to the outer surface of the base material.

[0063] In a further embodiment of the tool described herein, the coating has an inner surface engaging the outer surface of the base material and an outer surface distal the base material, and wherein the coating has a total thickness less than 0.050 in. measured perpendicularly from the outer surface of the base material to the outer surface of the coating; in a further still embodiment, the coating has an inner surface engaging the outer surface of the base material and an outer surface distal the base material, and wherein the coating has a total thickness less than 0.030 in. measured perpendicularly from the outer surface of the base material to the outer surface of the coating. In another embodiment of the tool the first layer has a first hardness greater than 1100 HV and the second layer has a second hardness of about 500 HV; in a further embodiment the first layer has a first hardness greater than 1000 HV and the second layer has a second hardness of about 650 HV; and in a preferred embodiment the first layer has a first hardness greater than 1000 HV and the second layer has a second hardness of about 850 HV.

EXAMPLES

Example 1: Production of a Wear and Corrosion Resistant Coating on the Surface of a Downhole Tool (e.g., Surface 150) in Accordance with Principles Described Herein

[0064] In one embodiment herein described, a 6.75 inch agitator was hard chrome plated in a Heef 25 bath with alternative current densities of 2.0 and 4.0 A/in.sup.2. The coated agitator was subjected to field runs in conditions: water based mud of 8.4 to 10.25 ppg with pH of 7.8 to 11 at 170-176 F. The mud contained 0.2 to 13.9% solid, 0.25% sand, and 154,000 to 160,000 mg/I of chlorides content. The conventional hard chrome plated agitator rotor is not recommended to run in chloride concentrations of >100,000 mg/I. The total run time of alternated current hard chrome plated agitator rotor was 456 hours of 10 field test runs.

Example 2: Production of a Wear and Corrosion Resistant Coating on a Base Material (e.g., Coating 150) in Accordance with Principles Described Herein

[0065] Alternative current electrolytic plating as described herein was used to create a multilayer Chromium coating (FIG. 5B), and the microstructure of the coating was compared to a single layer hard chrome plating of the prior art (FIG. 5A). The coating comprising of multiple layers of Cr plating can be visualized in the SEM image of FIG. 5(B). Micro-cracks in the cross-sectional polished surface of each of the coatings were enhanced by etching with Mable reagent.

[0066] The Cr plating of the prior art (FIG. 5A) was deposited with current density of 2 A/in.sup.2. The micro-cracks in the conventional hard Cr plating were large, and in the deposition (grow) direction, perpendicular to the surface of the base material.

[0067] In the embodiment of the protective coating described herein, the multilayer Cr plating (the darker layer or first chrome layer) was deposited at 3.5 A/in.sup.2; while the lighter layer or second chrome layer) was deposited at 1.0 A/in.sup.2. The low current density layer (second layer) has a denser microstructure, as evidenced in the FIG. 5B; this is due to the fact that the lower the current density, the slower the metal ion deposit time, the dense the product, and the greater the number of micro-cracks per inch. Further, it can be seen in the first layer that was plated at a current density of 3.5 A/in.sup.2, that some cracks seemed to orientate parallel to the plating surface. As is described herein, the concentration of metal ions, length of deposition, and current density can all be varied to create a coating that satisfies the required wear and corrosion resistance.

SUMMARY OF FEATURES AND ADVANTAGES

[0068] Embodiments of the invention described herein provide for various coatings for application to downhole tools, wherein the coating provides enhanced wear and corrosion resistant coatings. Methods for producing such coatings are also provided.

[0069] Various embodiments of current density are employed to produce a plurality of layers that in some embodiments comprise chrome, each can be of a different thickness and/or micro-crack density. Micro-cracks are thus specific to one layer, rather than to the entire coating (as seen in prior art hard chrome coatings that comprise one layer), and function to reduce the degree to which corrosive fluids (for example from drilling environments) can penetrate the entire thickness of the coating and access the base material of the underlying tool, causing corrosive and wear damage.

[0070] Hence the presence of multiple layers in the coating reduces the degree to which the coating is susceptible to wear and erosion. Further such a microstructure comprising the described micro-crack densities are desirable, because the deposited surfaces also have lower stress, higher lubricity, and enhanced wearability.

[0071] In one embodiment of the method of making a coating for protecting a base material, the base material is a matrix drill body, and in a further embodiment, the coating may be applied to any surface in need of improved corrosive resistance, and or wear resistance, such as but not limited to downhole drilling equipment or tools.

[0072] Therefore it is believed that the protective coatings made by the methods described herein and exemplified in examples described herein, will impart to a surface and such downhole tools as drill bit bodies and wear surfaces to which said materials are applied, improved wear resistance and corrosive resistance as compared to some conventional protective coatings, downhole tools, bit bodies and wear surfaces.

[0073] While preferred embodiments have been shown and described, modifications thereof can be made by one skilled in the art without departing from the scope or teachings herein. The embodiments described herein are exemplary only and are not limiting. Many variations and modifications of the systems, apparatus, and processes described herein are possible and are within the scope of the invention. For example, the relative dimensions of various parts, the materials from which the various parts are made, and other parameters can be varied. Accordingly, the scope of protection is not limited to the embodiments described herein, but is only limited by the claims that follow, the scope of which shall include all equivalents of the subject matter of the claims. Unless expressly stated otherwise, the steps in a method claim may be performed in any order. The recitation of identifiers such as (a), (b), (c) or (1), (2), (3) before steps in a method claim are not intended to and do not specify a particular order to the steps, but rather are used to simplify subsequent reference to such steps.