Low Sulfur Nickel Base Substrate Alloy and Overlay Coating System

Abstract

A coated article having an improved coating oxidation life includes a superalloy substrate material having a composition which includes sulfur, herein the sulfur is present in an amount less than 1 ppm; and an overlay coating formed over a surface of the substrate material.

What is claimed is: 
     
         1 - 12 . (canceled) 
     
     
         13 . A process for forming a coated article having an improved coating oxidation life comprising the steps of:
 casting a superalloy substrate material having a composition which includes sulfur, wherein said sulfur is present in an amount less than 1 ppm; and   forming an overlay coating over a surface of said substrate material.   
     
     
         14 . A process according to  claim 13 , wherein said casting step comprises providing a master heat containing active elements in such a way that [wt. ppm of Mg]+[(24/40)×(wt. ppm of Ca)]+[(24/89)×(wt. ppm of Y)]+[(24/atomic weight of any other active element)×(wt. ppm of the said active element)] is greater than or equal to 20 and casting said substrate material as a single crystal having sulfur in an amount less than 0.3 ppm. 
     
     
         15 . A process according to  claim 13 , wherein said casting step comprises using a master heat wherein the other active element is selected from the group consisting of elements in group IIA (Be, Mg, Ca, . . . ), group IIIA (Sc, Y, La, Ac), and group IVA (Ti, Zr, Hf) in the periodic table of elements, with very high affinity to oxygen and sulfur are active elements. It is also understood that elements La and Ac also imply a series of rare earth elements such as Ce, Gd, and Er, referred to as Lanthnides and Actinide series of elements, with atomic numbers ranging from 57 to 71 and 89 to 103, respectively. 
     
     
         16 . A process according to  claim 13 , wherein said overlay coating step comprises forming said overlay coating by EBPVD, cathodic arc, HVOF, or other high-energy or low-energy processes capable of delivering metallic coating alloy of desired composition. 
     
     
         17 . A process according to  claim 13 , further comprising creating a roughened surface area between the coating and the substrate material by rough polishing, grit blasting, oil honing, rough machining, or shot peening. 
     
     
         18 . A process according to  claim 13 , further comprising creating an increased surface area between the coating and the substrate material by introducing particles of an inert second phase into the coating, or the substrate, or between the coating and the substrate material. 
     
     
         19 . A process according to  claim 18 , wherein said introducing step comprises introducing particles selected from the group consisting of alumina, other oxides, nitrides, and carbides. 
     
     
         20 . A process according to  claim 13 , further comprising heat treating said substrate material at a temperature in the range of 1300° F. to 1700° F. to bring sulfur to an outer surface prior to service use. 
     
     
         21 . A process according to  claim 13 , further comprising depositing a ceramic coating over said overlay coating. 
     
     
         22 . A master heat for casting a single crystal nickel based superalloy substrate material, said master heat containing active elements in such a way that [wt. ppm of Mg]+[(24/40)×(wt. ppm of Ca)]+[(24/89)×(wt. ppm of Y)]+[(24/atomic weight of any other active element)×(wt. ppm of the said active element)] is greater than or equal to 20.