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 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 Ni—P 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 Ni—P; 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 Ni—P 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.