Coatings for metal casting parts

Abstract

The method is disclosed for coating or impregnating a metal tool with a metal oxide to render the metal part more resistant to liquid metal attack or micro-welds. The method includes the steps of applying a liquid metal carboxylate composition, or a solution thereof, to a substrate material, and exposing the substrate to an environment that will cause vaporization or dissipation of any excess carboxylic acids in the liquid metal carboxylate composition while the metal carboxylates are being converted to metal oxides.

1 . A metal part comprising:
 a surface coating, the surface coating comprising an oxidation product of a liquid metal carboxylate composition disposed on the surface, wherein the surface coating penetrates the metal part to a depth of about 200 Angstroms to about 600 Angstroms.   
   
   
       2 . The metal part of  claim 1 , wherein the metal part comprises a steel alloy. 
   
   
       3 . The metal part of  claim 1 , wherein the liquid metal carboxylate composition comprises a solution of a metal salt of a carboxylic acid in a solvent. 
   
   
       4 . The metal part of  claim 3 , wherein the solvent comprises a carboxylic acid. 
   
   
       5 . The metal part of  claim 3 , wherein the solvent comprises at least one carboxylic acid that corresponds to a carboxylate moiety in the liquid carboxylate composition. 
   
   
       6 . The metal part of  claim 3 , wherein the carboxylic acid has the formula R—C(R″)(R′)—COOH 
     wherein:
 R is selected from the group consisting of H and C 1  to C 24  alkyl groups; and 
 R′ and R″ are each independently selected from the group consisting of H and C 1  to C 24  alkyl groups. 
 
   
   
       7 . The metal part of  claim 6 , wherein the carboxylic acid is alpha-branched, wherein at least two of R, R′ and R″ are not H. 
   
   
       8 . The metal part of  claim 6 , wherein R is H, R″ is C 2 H 5  and R′ is C 4 H 9 . 
   
   
       9 . The metal part of  claim 3 , wherein the carboxylic acid is a mixture of carboxylic acids. 
   
   
       10 . The metal part of  claim 9 , wherein the average molecular weight of the acids contained in the mixture is from about 130 to 420. 
   
   
       11 . The metal of  claim 9 , wherein the average molecular weight of the acids contained in the mixture is from about 220 to 270. 
   
   
       12 . The metal part of  claim 9 , wherein the mixture of carboxylic acids contains 2-ethylhexanoic acid as its lowest boiling acid constituent. 
   
   
       13 . The metal part of  claim 1 , wherein the liquid metal carboxylate composition comprises a mixture of metals. 
   
   
       14 . The metal part of  claim 1 , wherein the liquid metal carboxylate composition comprises one or more metals selected from the group consisting of Lithium, Beryllium, Sodium, Magnesium, Potassium, Calcium, Scandium, Titanium, Chromium, Manganese, Iron, Nickel, Cobalt, Copper, Zinc, Gallium, Rubidium, Strontium, Yttrium, Zirconium, Silver, Cadmium, Tin, Cesium, Cerium, Barium, Lanthanum, Hafnium, Tantalum, Gold, Thallium, Lead, Bismuth, Cerium, Praseodymium, Neodymium, Samarium, Europium, Gadolinium, Terbium, Dysprosium, Holmium, Erbium, Thulium, Ytterbium, Lutetium, Thorium and Uranium. 
   
   
       13 . The metal of  claim 1 , wherein the liquid metal carboxylate composition comprises Zirconium. 
   
   
       14 . The metal part of  claim 1 , wherein the liquid metal carboxylate composition comprises a mixture of metals comprising:
 up to 10% by weight of yttrium;   up to 5% by weight of chromium; and   the balance zirconium;   wherein the minimum total amount of yttrium is at least 3% and the minimum total of chromium is at least 2%.   
   
   
       15 . The metal part of  claim 1 , wherein the liquid metal carboxylate composition comprises a mixture of metals comprising:
 7 to 8% by weight of yttrium;   2 to 3% by weight of chromium; and   89 to 91% by weight of zirconium.   
   
   
       16 . The metal part of  claim 1 , wherein the liquid metal carboxylate composition comprises a mixture of metals comprising:
 14-15% by weight of yttrium;   the balance cerium.   
   
   
       17 . The metal part of  claim 1 , wherein the oxidation product comprises a zirconia. 
   
   
       18 . The metal part of  claim 17 , wherein the zirconia is in cubic form. 
   
   
       19 . The metal part of  claim 18 , wherein the zirconia has an average crystallite size of about 3 nm. 
   
   
       20 . The metal part of  claim 1 , wherein the surface coating has a thickness between about 0.2 μm and about 1 μm. 
   
   
       21 . The metal part of  claim 1 , wherein the metal part comprises a tool. 
   
   
       22 . The metal part of  claim 21 , wherein the tool is used in die-casting metal. 
   
   
       23 . The metal part of  claim 21 , wherein the tool is a thermocouple, a sheath, a die-casting die, a ladle or a pin. 
   
   
       24 . The metal part of  claim 21 , wherein the tool is a stamp, die, punch or cutting tool.