Cobalt chrome etching process

Abstract

Compositions and methods for etching cobalt chromium alloys are disclosed. The compositions generally include at least two mineral acids, certain component metals of the alloy to be etched, and optionally iron (Fe). For example, when etching a cobalt chromium molybdenum alloy, the component metals may include chromium (Cr), molybdenum (Mo), and optionally, cobalt (Co). The at least two mineral acids may include hydrochloric acid (HCl), nitric acid (HNO3), and hydrofluoric acid (HF). The methods provide for etching an entire surface of a substrate or etching a surface of a substrate in a pattern using selective coating patterns and/or coating removal. Thus, unlimited patterns, as well as etch depths and variations in etch depths are achievable using the compositions and methods disclosed. Moreover, the compositions and methods provide cobalt chrome surfaces having very low surface roughness (Ra) that are useful in the aerospace industry.

What is claimed is: 
     
         1 . A composition for etching a cobalt chromium alloy, the composition comprising:
 at least two mineral acids selected from the groups consisting of hydrochloric acid (HCl), nitric acid (HNO 3 ), sulfuric acid (H 2 SO 4 ), and hydrofluoric acid (HF); and   component metals of the cobalt chromium alloy, the component metals comprising at least 0.2 g/l chromium (Cr) and at least 0.1 g/l molybdenum (Mo), wherein the composition etches cobalt chromium alloys at a rate of 0.1 to 1.0 mil/minute.   
     
     
         2 . The composition according to  claim 1 , wherein the component metals comprise at least 3.0 g/l Cr and at least 0.5 g/l Mo. 
     
     
         3 . The composition of  claim 1 , comprising HCl, HF, and HNO 3 , wherein the HCl is included at 1N-10N. 
     
     
         4 . The composition of  claim 1 , comprising HCl, HF, and HNO 3 , wherein the HNO 3  is included at 0.05N-2.0N. 
     
     
         5 . The composition of  claim 1 , comprising HCl, HF, and HNO 3 , wherein the HF is included at 0.1N-2.0N. 
     
     
         6 . The composition of  claim 1 , comprising:
 1N-10N HCl;   0.05N-2.0N HNO 3 ; and   0.1N-2.0N HF.   
     
     
         7 . The composition of  claim 1 , further comprising:
 0.1-400 g/l Iron (Fe), or   0.1-400 g/l cobalt (Co), or   0.1-400 g/l Fe and 0.1-400 g/l Co.   
     
     
         8 . The composition of  claim 1 , wherein the component metals comprise cobalt (Co), Cr, and Mo provided in a native ratio of each metal in the cobalt chromium alloy to be etched. 
     
     
         9 . The composition of  claim 8 , wherein a total amount of the component metals Co, Cr, and Mo in the composition does not exceed 400 g/l. 
     
     
         10 . The composition of  claim 8 , comprising:
 7-355 g/l Co;   3.0-170 g/l Cr;   0.5-40 g/l Mo; and   optionally 0.1 to 400 g/l Iron (Fe).   
     
     
         11 . The composition of  claim 1 , comprising:
 2N-8N HCl;   0.05N-1.1N HNO 3 ;   0.4N-1.3N HF;   50-225 g/l Iron (Fe);   3.0-170 g/l Cr; and   0.5-40 g/l Mo.   
     
     
         12 . The composition of  claim 11 , further comprising:
 7-355 g/l cobalt (Co).   
     
     
         13 . The composition of  claim 1 , comprising:
 1N-10N hydrochloric acid (HCl);   0.05N-2.0N nitric acid (HNO 3 );   0.1N-2.0N hydrofluoric acid (HF).   0.5-355 g/l cobalt (Co);   0.2-170 g/l chromium (Cr);   0.1-40 g/l molybdenum (Mo); and   optionally 0.1 to 400 g/l Iron (Fe).   
     
     
         14 . The composition of  claim 13 , wherein a total amount of the component metals Co, Cr, and Mo in the composition does not exceed 400 g/l. 
     
     
         15 . A method for etching a cobalt chromium alloy work-piece, the method comprising:
 contacting at least one surface of the work-piece with a chemical etching composition according to  claim 1 ,   wherein the contacting step is carried out at a temperature of 20° C. to 150° C. for a time period of 1 minute to 200 minutes, and   wherein the composition etches a surface of the cobalt chromium alloy work-piece at a rate of 0.1 to 1.0 mil/minute.   
     
     
         16 . The method of  claim 15 , further comprising, before the step of contacting the work-piece with the chemical etching composition:
 activating the at least one surface of the work-piece with an activation solution comprising a 10% to 100% (v/v) aqueous solution of a mineral acid.   
     
     
         17 . The method of  claim 15 , wherein the contacting step is carried out within 120 seconds of the activating step. 
     
     
         18 . A work-piece formed by additive manufacturing using a powdered cobalt chromium alloy, the work piece comprising an etched surface that is substantially free of grains of the powdered cobalt chromium alloy, has a surface roughness (R a ) of less than 200 win, and no directional surface scratches. 
     
     
         19 . A work-piece formed of a cobalt chromium alloy having a surface with a surface roughness (R a ) of less than 200 win, no directional surface scratches, and absent cobalt chromium alloy particles. 
     
     
         20 . The work-piece of  claim 19 , wherein the surface roughness (R a ) is less than 100 win, and the work-piece forms at least a portion of a component part of an aerospace vehicle.