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.

What is claimed is: 
     
         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 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.   
     
     
         2 . The coating of  claim 1 , 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. 
     
     
         3 . The coating of  claim 2 , 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.   
     
     
         4 . The coating of  claim 2 , wherein the second layer has a thickness less than 0.0050 in. measured perpendicular to the outer surface of the base material. 
     
     
         5 . The coating of  claim 2 , 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. 
     
     
         6 . 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. 
     
     
         7 . The coating of  claim 6 , wherein the coating has an inner surface engaging the outer surface of the base material and an outer surface distal to 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. 
     
     
         8 . The coating of  claim 7 , 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. 
     
     
         9 . 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 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/in2. 
     
     
         10 . The method of  claim 9 , wherein the first material and the second material 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.   
     
     
         11 . The method of  claim 10 , wherein one of the second current density and the first current density is about 3.5 A/in2 and the other of the first current density and the second current density is about 1.0 A/in2. 
     
     
         12 . The method of  claim 10 , wherein (a) comprises depositing the first layer of the first material by pulse current; and
 wherein (b) comprises depositing the second layer of the second material by pulse current.   
     
     
         13 . The method of  claim 10 , 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. 
     
     
         14 . The method of  claim 13 , wherein (a) comprises depositing the first layer of the first material until the first layer has a thickness of about 0.00020 in. to 0.0030 in. measured perpendicular to the surface of the base material. 
     
     
         15 . The method of  claim 9 , wherein the first material consists of chromium and the second material consists of chromium. 
     
     
         16 . The method of  claim 9 , wherein the first material comprises Ni—P and the second material comprises chromium. 
     
     
         17 . The method of  claim 16 , wherein (a) comprises depositing the first layer of the first material by an electroless process. 
     
     
         18 . The method of  claim 17 , 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 16 , further comprising (c) heating the first layer after (a) and before (b). 
     
     
         20 . The method of  claim 19 , 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. 
     
     
         22 . 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 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. 
   
     
     
         23 . The tool of  claim 22 , 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. 
     
     
         24 . The tool of  claim 23 , 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.   
     
     
         25 . The tool of  claim 23 , 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. 
     
     
         26 . The tool of claim of  claim 25 , 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. 
     
     
         27 . The tool of  claim 23 , wherein the first layer has a first hardness greater than 1000 HV and the second layer has a second hardness of about 850 HV.30. 
     
     
         28 . 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 comprises Ni—P and the second layer comprises chromium having a micro-crack density between 400 and 650 micro-cracks per inch.   
     
     
         29 . The coating of  claim 28 , wherein the second layer consists of chromium. 
     
     
         30 . The coating of  claim 29 , 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.   
     
     
         31 . The coating of  claim 28 , 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 is between 0.0005 in. and 0.002 in. and the second thickness is between 0.0002 in. and 0.0030 in.   
     
     
         32 . The coating of claim of  claim 28 , 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.