Thermal barrier composition, a superalloy machine part provided with a coating having such a composition, a ceramic coating, and a method of fabricating the coating

Abstract

The invention relates to a ceramic thermal barrier composition of low conductivity and high high-temperature strength. In characteristic manner, the composition comprises a zirconia base, at least one trivalent oxide enabling the zirconia to be stabilized and enabling the thermal conductivity of the zirconia to be reduced in optimum manner, and at least one pentavalent oxide enabling the content of oxygen vacancies to be reduced so as to make it substantially equal to that of a partially stabilized zirconia. Preferably, said trivalent oxide is present with a molar content constituted by a first portion enabling the zirconia to be stabilized partially and a second portion which introduces point defects into the lattice said pentavalent oxide is present with a molar concentration equal to said molar concentration of said second portion of the trivalent oxide. The invention is applicable to making a superalloy machine part having a ceramic coating with said composition, and possibly also a bonding underlayer.

1 . A method of fabricating a ceramic coating comprising a thermal barrier on a superalloy substrate, the method comprising the following steps: 
 depositing a bonding underlayer on said superalloy substrate; and    depositing a ceramic coating on said underlayer, the ceramic coating comprising a zirconia base, at least one trivalent oxide enabling the zirconia to be stabilized and enabling the thermal conductivity of the zirconia to be reduced in optimum manner, and at least one pentavalent oxide enabling the content of oxygen vacancies to be reduced as to make substantially equal to that of a partially stabilized zirconia, said trivalent oxide being selected from the group consisting of: erbium oxide, europium oxide, praseodymium oxide, terbium oxide, holmium oxide, and mixtures thereof.    
     
     
         2 . A method of fabrication according to  claim 1 , wherein said trivalent oxide is present at a molar concentration constituted by a first portion enabling the zirconia to be stabilized partially, and by a second portion which introduces point defects into the lattice, and wherein said pentavalent oxide is present at a molar concentration equal to said molar concentration of said second portion of the trivalent oxide.  
     
     
         3 . A method of fabrication according to  claim 1 , including an additional step consisting in oxidizing the bonding underlayer prior to depositing the ceramic coating.  
     
     
         4 . A method of fabrication according to  claim 1 , wherein said pentavalent oxide is selected from the group comprising niobium oxide, tantalum oxide, and mixtures thereof.  
     
     
         5 . A method of fabrication according to  claim 1 , wherein said trivalent oxide is present at a molar concentration lying in the range 4% to 30%.  
     
     
         6 . A method of fabrication according to  claim 1 , wherein said pentavalent oxide is present at a molar concentration lying in the range 2% to 20%.  
     
     
         7 . A method of fabrication according to  claim 1 , wherein said pentavalent oxide is present at a molar concentration lying in the range 4% to 12%.  
     
     
         8 . A method of fabrication according to  claim 1 , wherein said pentavalent oxide is present at a molar concentration lying in the range 3% to 10%.  
     
     
         9 . A method of fabrication according to  claim 1 , wherein the difference between the molar concentration of trivalent oxide and the molar concentration of pentavalent oxide lies in the range 4% to 12%.  
     
     
         10 . A method of fabrication according to  claim 1 , wherein the difference between the molar concentration of trivalent oxide and the molar concentration of pentavalent oxide is substantially equal to 4%.