Oxide-forming protective coatings for niobium-based materials

Abstract

Coatings suitable for use as protective oxide-forming coatings on Nb-based substrates exposed to high temperatures and oxidative environments. The coatings contain chromium and/or molybdenum, preferably contains silicon, and optionally contains niobium, titanium, hafnium, iron, rhenium, tantalum, and/or tungsten, which in combination form multiple intermetallic phases, which in combination form one or more intermetallic phases that promote the formation of a slow-growing oxide scale. Depending on the particular coating composition, the intermetallic phases maybe: a silicon-modified Cr 2 Nb Laves phase and optionally a chromium solid solution phase, a CrNbSi intermetallic phase, and/or an M 3 Si intermetallic phase where M is niobium, titanium, and/or chromium; or M 5 Si 3 , MSi 2 and/or M 3 Si 2 where M is molybdenum, niobium, titanium, chromium, hafnium, iron, rhenium, tantalum, and/or tungsten.

1 . A coating capable of promoting the oxidation resistance of a surface of a niobium-based substrate, wherein the coating is formed from a composition containing at least 10 atomic percent molybdenum, silicon, and at least one of niobium, titanium, chromium, hafnium, iron, rhenium, tantalum, and tungsten,
 wherein the coating comprises an M 5 Si 3  matrix containing intermetallic phases comprising at least one of MSi 2  and M 3 Si 2  where M is molybdenum, niobium, titanium, chromium, hafnium, iron, rhenium, tantalum, and/or tungsten,   
     
     
         2 . The coating according to  claim 1 , wherein the coating has an oxide scale on a surface thereof that is a complex oxide containing chromia, titania, niobia, and silica. 
     
     
         3 . The coating according to  claim 1 , wherein the coating contains hafnium. 
     
     
         4 . The coating according to  claim 1 , wherein the composition contains, in atomic percent, about 10 to about 60% molybdenum. 
     
     
         5 . The coating according to  claim 1 , wherein the composition consists essentially of up to about 90 volume percent of the M 5 Si 3  matrix, up to about 50 volume percent of the MSi 2  intermetallic phase, and up to about 90 volume percent of the M 3 Si 2  intermetallic phase. 
     
     
         6 . The coating according to  claim 1 , wherein the coating has an oxide scale on a surface thereof that contains at least one oxide chosen from the group consisting of chromia, titania, niobia and silica. 
     
     
         7 . The coating according to  claim 1 , wherein the coating has fewer than five vertical cracks per linear inch. 
     
     
         8 . The coating according to  claim 1 , wherein the substrate is a component of a gas turbine engine. 
     
     
         9 . The coating according to  claim 1 , wherein the coating is on the surface of the niobium-based substrate, and the niobium-based substrate is formed of a material containing a silicide reinforcement material dispersed in a niobium-based matrix. 
     
     
         10 . The coating according to  claim 9 , wherein the substrate is a component of a gas turbine engine. 
     
     
         11 . A method of forming the coating of  claim 1 , the method comprising:
 an overlay deposition of a molybdenum-containing layer on the substrate by which molybdenum is diffused into the substrate.   
     
     
         12 . A gas turbine engine component comprising:
 a substrate comprising a niobium-based alloy or a niobium-silicide composite;   a coating on the substrate and capable of promoting the oxidation resistance of a surface of the substrate; and   an oxide scale on a surface of the coating;   wherein the coating comprises a composition containing at least 10 atomic percent molybdenum, silicon, and at least one of niobium, titanium, chromium, hafnium, iron, rhenium, tantalum, and tungsten,   wherein the coating is formed from a composition comprising an M 5 Si 3  matrix containing intermetallic phases comprising at least one of MSi 2  and M 3 Si 2  where M is molybdenum, niobium, titanium, chromium, hafnium, iron, rhenium, tantalum, and/or tungsten.   
     
     
         13 . The gas turbine engine component according to  claim 12 , wherein the composition consists essentially of up to about 90 volume percent of the M 5 Si 3  matrix, up to about 50 volume percent of the MSi 2  intermetallic phase, and up to about 90 volume percent of the M 3 Si 2  intermetallic phase, the oxide scale contains at least one oxide chosen from the group consisting of chromia, titania, niobia and silica, and the coating has fewer than five vertical cracks per linear inch. 
     
     
         14 . The gas turbine engine component according to  claim 13 , wherein the composition contains, in atomic percent, about 10 to about 60% molybdenum. 
     
     
         15 . A coating capable of promoting the oxidation resistance of a surface of a niobium-based substrate, wherein the coating is formed from a composition consisting essentially of at least 10 atomic percent molybdenum, silicon, and at least one of niobium, titanium, chromium, hafnium, iron, rhenium, tantalum, and tungsten,
 wherein the coating comprises an M 5 Si 3  matrix containing intermetallic phases comprising at least one of MSi 2  and M 3 Si 2  where M is molybdenum, niobium, titanium, chromium, hafnium, iron, rhenium, tantalum, and/or tungsten.   
     
     
         16 . The coating according to  claim 15 , wherein the coating has an oxide scale on a surface thereof that is a complex oxide containing chromia, titania, niobia, and silica. 
     
     
         17 . The coating according to  claim 15 , wherein the coating contains hafnium. 
     
     
         18 . The coating according to  claim 15 , wherein the composition contains, in atomic percent, about 10 to about 60% molybdenum. 
     
     
         19 . The coating according to  claim 15 , wherein the composition has up to about 90 volume percent of the M 5 Si 3  matrix, up to about 50 volume percent of the MSi 2  intermetallic phase, and up to about 90 volume percent of the M 3 Si 2  intermetallic phase. 
     
     
         20 . The coating according to  claim 15 , wherein the coating has an oxide scale on a surface thereof that contains at least one oxide chosen from the group consisting of chromia, titania, niobia and silica.