Method and Apparatus for Depositing Stable Crystalline Phase Coatings of High Temperature Ceramics

Abstract

Producing high temperature coatings on ceramics using a high enthalpy air plasma spray torch and supplying in at least 3 passes to deposit the coating is advantageous for spraying high temperature ceramics while avoiding formation of undesirable phases, if the stand off distance is chosen such that a width of a bead produced from a single spray pass on the substrate at ˜800° C. is less than 70% of a diameter of a plume of the torch at the stand off, and neither assisted heating, nor forced cooling, nor subsequent heat treatment is used. The rapid cooling endemic to thermal spray that leads to amorphous, metastable and other undesirable phases of alkaline earth aluminosilicate (e.g., barium-strontium aluminosilicate (BSAS)), rare earth silicates (RESs), mullite, etc. can be mitigated sufficiently by the close stand off and high enthalpy torch to provide highly crystalline and stable phase coatings.

1 . A method of producing a high temperature coating on a ceramic substrate, the method comprising:
 operating a high enthalpy plasma spray torch and supplying the torch with a feedstock powder comprising a high temperature ceramic with a melting point above 1600° C., forming undesirable solid phases when rapidly cooled below about 900° C.;   spraying the ceramic substrate with the torch in at least 3 passes to deposit the coating;   wherein a stand-off distance is maintained during the deposition such that a width of a bead produced from a single spray pass on the substrate at ˜800° C. is less than 70% of a diameter of a plume of the torch at the stand-off,   whereby the coating contains less undesirable solid phase without requiring assisted heating, forced cooling or subsequent heat treatment.   
     
     
         2 . The method according to  claim 1  wherein the substrate surface temperature centred on the plume during deposition exceeds 1000° C. because of the proximity of the torch, and the absence of assisted heating and forced cooling. 
     
     
         3 . The method according to  claim 1  wherein the substrate surface temperature is raised prior to deposition by scanning with the torch over the substrate, immediately prior to deposition, to raise the surface temperature above ˜500° C., more preferably from ˜800-1000° C. 
     
     
         4 . The method according to  claim 1  wherein spraying the ceramic substrate with the torch in at least 3 passes; comprises moving a surface of the substrate to be coated in a direction perpendicular to the spray jet at a speed of 0.1-5 m/s; or exposes each region of the substrate to the plume for about 8 s per coating. 
     
     
         5 . (canceled) 
     
     
         6 . The method according to  claim 1  wherein the stand-off distance is:
 chosen where the width of a single spray bead on a substrate at ˜800° C. is 20-70% of the diameter of the plasma plume at the same stand-off distance; 
 chosen where the width of a single spray bead on a substrate at ˜800° C. is 35-65% of the diameter of the plasma plume at the same stand-off distance; 
 chosen where the width of a single spray bead on a on substrate at ˜800° C. is 40-60% of the diameter of the plasma plume at the same stand-off distance; 
 chosen where the width of a single spray bead on a on substrate at ˜800° C. is from ˜0.5 cm to ˜2.5 cm, and the plume diameter is from ˜1 cm to ˜5 cm, the former being at most 70% of the latter; or 
 chosen where the width of a single spray bead on a on substrate at 800° C. is from ˜0.5 cm to ˜2.5 cm, and the plume diameter is from −1 cm to ˜5 cm, the former being at most 40-60% of the latter. 
 
     
     
         7 . The method according to  claim 1  wherein operating the high enthalpy torch comprises:
 supplying a power of 60-200 kW; 
 supplying a power of 80-150 kW; 
 supplying a power of 10-140 kW; 
 supplying a total plasma gas flow at 100-500 slpm; 
 supplying a total plasma gas flow at 150-400 slpm; 
 supplying a total plasma gas flow at 250-310 slpm; 
 supplying plasma gas including N 2 ; 
 supplying plasma gas including 10-90% N 2 ; 
 supplying plasma gas consisting of 10-80% Ar, 5-40% H 2 , and/or He, and 30-80% N 2 ; or 
 supplying plasma gas consisting of 0-25% H 2 , 25-45% Ar and 45-50% N 2 . 
 
     
     
         8 . The method according to  claim 1  wherein the feedstock powder:
 consists of 80% or more of the high temperature ceramic with a melting point above 1600° C.; 
 consists essentially of the high temperature ceramic with a melting point above 1600° C.; 
 consists of 80% or more of the high temperature ceramic with a melting point above 1600° C., the high temperature ceramic having a preferred phase preferentially formed only at a temperature above 900° C.; 
 consists essentially of the high temperature ceramic with a melting point above 1600° C., the high temperature ceramic having a preferred phase preferentially formed only at a temperature above 900° C., 
 consists of 80% or more of the high temperature ceramic with a melting point above 1600° C., the high temperature ceramic having a preferred phase preferentially formed only at temperatures between 900-2000° C.; 
 consists essentially of the high temperature ceramic with a melting point above 1600° C., the high temperature ceramic having a preferred phase preferentially formed only at temperatures between 900-2000° C.; 
 consists of 80% or more of the high temperature ceramic with a melting point above 1600° C., the high temperature ceramic having a preferred phase preferentially formed only at temperatures between 900-1600° C.; or 
 consists essentially of the high temperature ceramic with a melting point above 1600° C., the high temperature ceramic having a preferred phase preferentially formed only at temperatures between 900-1600° C. 
 
     
     
         9 . A method of producing a coating of an alkaline earth aluminosilicate or rare earth silicate (RES) on a ceramic substrate, the method comprising:
 providing a feedstock of an alkaline earth aluminosilicate or RES powder and the ceramic substrate;   plasma spraying the feedstock onto the ceramic substrate with a high enthalpy plasma spray torch to deposit the coating in at least 3 passes;   wherein a stand-off distance is maintained during the deposition such that the width of a bead produced from single spray pass on the substrate at ˜800° C. is less than 70% of a diameter of a plume of the torch at the stand-off,   whereby the coating consists essentially of a desirable stable crystalline phase without assisted heating, forced cooling, or subsequent heat treatment.   
     
     
         10 . The method according to  claim 9  wherein the substrate surface temperature centred on the plume during deposition exceeds 1000° C. because of the proximity of the torch, and because of the absence of assisted heating and forced cooling. 
     
     
         11 . The method according to  claim 9  wherein the substrate surface temperature is raised prior to deposition by scanning with the torch over the substrate, immediately prior to deposition, to raise the surface temperature above ˜500° C., more preferably from ˜800-1000° C. 
     
     
         12 . The method according to  claim 9  wherein depositing the coating in at least 3 passes comprises moving a surface of the substrate to be coated in a direction perpendicular to the spray jet at a speed of 0.1-5 m/s. 
     
     
         13 . The method according to  claim 9  wherein the stand-off distance is:
 chosen where the width of a single spray bead on a substrate at ˜800° C. is 20-70% of the diameter of the plume at the stand-off distance, 
 chosen where the width of a single spray bead on a on substrate at ˜800° C. is 35-65% of the diameter of the plume of the plume at the stand-off distance, chosen where the width of a single spray bead on a on substrate at ˜800° C. is 40-60% of the diameter of the plume at the stand-off distance, 
 chosen where the width of a single spray bead on a on substrate at ˜800° C. is from ˜0.5 cm to ˜2.5 cm, and the plume diameter at the stand-off distance is from ˜1 cm to ˜5 cm, the former being at most 70% of the latter, or 
 chosen where the width of a single spray bead on a on substrate at ˜800° C. is from ˜0.5 cm to ˜2.5 cm, and the plume diameter at the stand-off distance is from ˜1 cm to ˜5 cm, the former being 40-60% of the latter. 
 
     
     
         14 . The method according to  claim 9  wherein plasma spraying comprises:
 supplying a power of 60-200 kW; 
 supplying a power of 80-150 kW; 
 supplying a power of 110-140 kW; 
 supplying a total plasma gas flow at 100-500 slpm; 
 supplying a total plasma gas flow at 150-400 slpm; 
 supplying a total plasma gas flow at 250-310 slpm; 
 supplying plasma gas including N 2 ; 
 supplying plasma gas including 10-90% N 2 ; 
 supplying plasma gas consisting of 10-80% Ar, 5-40% H 2 , and/or He, and 30-80% H>; or 
 supplying plasma gas consisting of 10-25% H 2 , 25-45% Ar and 45-50% N 2 . 
 
     
     
         15 . The method according to  claim 9  wherein the alkaline earth aluminosilicate or RES powders:
 consists of 80% or more of the alkaline earth aluminosilicate or RES and has a melting point above 1600° C.; 
 consists essentially of the alkaline earth aluminosilicate or RES and has a melting point above 1600° C.; 
 consists of 80% or more of the RES and has a melting point above 1600° C., the alkaline earth aluminosilicate or RES having a preferred phase preferentially formed only at a temperature above 1000° C.; 
 consists essentially of the alkaline earth aluminosilicate or RES and has a melting point above 1600° C., the alkaline earth aluminosilicate or RES having a preferred phase preferentially formed only at a temperature above 1000° C.; 
 consists of 80% or more of the alkaline earth aluminosilicate or RES and has a melting point above 1600° C., the RES having a preferred phase preferentially formed only at temperatures between 1000-2000° C.; 
 consists essentially of the alkaline earth aluminosilicate or RES and has a melting point above 1600° C., the alkaline earth aluminosilicate or RES having a preferred phase preferentially formed only at temperatures between 1000-2000*0; consists of 80% or more of the alkaline earth aluminosilicate or RES and has a melting point above 1600° C., the alkaline earth aluminosilicate or RES having a preferred phase preferentially formed only at temperatures between 1200-1600° C.; 
 consists of the alkaline earth aluminosilicate or RES and has a melting point above 1600° C., the alkaline earth aluminosilicate or RES having a preferred phase preferentially formed only at temperatures between 1200-1600° C.; 
 consists of 80% or more of BSAS; or 
 consists essentially of BSAS. 
 
     
     
         16 . A method of producing a mullite coating on a ceramic substrate, the method comprising:
 providing a feedstock of mullite powder and the ceramic substrate; and plasma spraying the feedstock onto the ceramic substrate with a high enthalpy plasma spray torch to deposit the coating in at least 3 passes;   wherein a stand-off distance is maintained during the deposition such that a width of a bead produced from a single spray pass on the substrate at ˜800° C. is less than 70% of a diameter of a plume of the torch at the stand-off,   whereby the desirable stable crystalline phase of the coating is maintained without requiring assisted heating, forced cooling or subsequent heat treatment.   
     
     
         17 . The method according to  claim 16  wherein the localized temperature of the substrate surface within the plasma plume spot during deposition exceeds 1000° C. because of the proximity of the torch in the absence of assisted heating and forced cooling. 
     
     
         18 . The method according to  claim 16  wherein the substrate surface temperature is raised prior to deposition by scanning with the torch over the substrate, immediately prior to deposition, to raise the surface temperature above ˜500° C., more preferably from ˜800-1000° C. 
     
     
         19 . The method according to  claim 16  wherein depositing the coating in at least 3 passes comprises moving a surface of the substrate to be coated in a direction perpendicular to the spray jet at a speed of 0.1-5 m/s. 
     
     
         20 . The method according to  claim 16  wherein the stand-off distance is:
 chosen where the width of a single spray bead on a substrate at ˜800° C. is 20-70% of the diameter of the plume at the stand-off distance, 
 chosen where the width of a single spray bead on a on substrate at ˜800° C. is 35-65% of the diameter of the plume at the stand-off distance, 
 chosen where the width of a spray bead on a on substrate at ˜800° C. is 40-60% of the diameter of the plume at the stand-off distance, 
 chosen where the width of a spray bead on a on substrate at ˜800° C. is from ˜0.5 cm to ˜2.5 cm, and the plume diameter at the stand-off is from ˜1 cm to ˜5 cm, the former being at most 70% of the latter, or 
 chosen where the width of a spray bead on a on substrate at ˜800° C. is from ˜0.5 cm to ˜2.5 cm, and the plume diameter at the stand-off is from ˜1 cm to ˜5 cm, the former being 40-60% of the latter. 
 
     
     
         21 . The method according to  claim 16  wherein plasma spraying comprises:
 supplying a power of 60-200 kW; 
 supplying a power of 80-150 kW; 
 supplying a power of 110-140 kW; 
 supplying a total plasma gas flow at 100-500 slpm; 
 supplying a total plasma gas flow at 150-400 slpm; 
 supplying a total plasma gas flow at 250-3 0 slpm; 
 supplying plasma gas including N 2 ; 
 supplying plasma gas including 10-90% ivfe; 
 supplying plasma gas consisting of 10-80% Ar, 5-40% H 2 , and/or He, and 30-80% N 2 ; or 
 supplying plasma gas consisting of 10-25% H 2 , 25-45% Ar and 45-50% N 2 . 
 
     
     
         22 . The method according to  claim 16  wherein the mullite powder:
 consists of 80% or more of the mullite; or 
 consists essentially of the mullite. 
 
     
     
         23 . A system for thermal spraying to produce a high temperature coating on a ceramic substrate, the system comprising:
 a high enthalpy air plasma spray torch;   a feed supply containing a feedstock powder comprising a high temperature ceramic that has a melting point above 1600° C., the feed supply operably coupled to the torch;   a plasma gas supply operably coupled to the torch;   an electrical power supply operably coupled to the torch;   a ceramic substrate; and   a support for controlling a stand-off distance between the ceramic substrate and torch, while permitting a spray jet of the torch to scan across a surface of the substrate to be coated,   wherein the stand-off distance is chosen so that the width of a single bead on a substrate at ˜800° C. is less than 70% of a diameter of a plume of the torch.   
     
     
         24 . The system according to  claim 23  wherein the localized temperature of the substrate surface within the plasma plume spot during deposition exceeds 1000° C. because of the proximity of the torch, and because of an absence of assisted heating or forced cooling. 
     
     
         25 . The system according to  claim 23  wherein the support permitting scanning comprises a computer numerical controlled subsystem for spraying the ceramic substrate with the torch in at least 3 passes by moving a surface of the substrate to be coated in a direction perpendicular to the spray jet at a speed of 0.1-5 m/s. 
     
     
         26 . The system according to  claim 23  wherein the stand-off distance is:
 where the width of a single bead on a on substrate at ˜800 C is 20-70% of the diameter of the plume at the stand-off, 
 where the width of a single bead on a on substrate at ˜800° C. is 35-65% of the diameter of the plume at the stand-off, 
 where the width of a single bead on a on substrate at ˜800° C. is 40-60% of the diameter of the plume at the stand-off, 
 where the width of a single bead on a on substrate at ˜800° C. is from ˜0.5 cm to ˜2.5 cm, and the plume diameter is from ˜1 cm to ˜5 cm at the stand-off, or where the width of a single bead on a on substrate at −800̂0 is from ˜0.5 cm to ˜2.5 cm, and the plume diameter is from ˜1 cm to ˜5 cm at the stand-off, the former being 40-60% of the latter. 
 
     
     
         27 . The system according to  claim 23  wherein:
 the electrical supply applies a power of 60-200 kW; 
 the electrical supply applies a power of 80-150 kW; 
 the electrical supply applies a power of 110-140 kW; 
 the plasma gas supply supplies a total plasma gas flow at 100-500 slpm; 
 the plasma gas supply supplies a total plasma gas flow at 150-400 slpm; 
 the plasma gas supply supplies a total plasma gas flow at 250-310 slpm; 
 the plasma gas supply supplies plasma gas including N 2 ; 
 the plasma gas supply supplies plasma gas including 10-90% N 2 ; 
 the plasma gas supply supplies plasma gas consisting of 10-80% Ar, 5-40% H 2 , and/or He, and 30-80% N 2 ; or 
 the plasma gas supply supplies plasma gas consisting of 10-25% H 2 , 25-45% Ar and 45-50% N 2 . 
 
     
     
         28 . The system according to  claim 23  wherein the feedstock powder:
 consists of 80% or more of a alkaline earth aluminosilicate or rare earth silicate; consists essentially of a alkaline earth aluminosiiicate or rare earth silicate; consists of 80% or more of BSAS; 
 consists essentially of BSAS; 
 consists of 80% or more of mullite; 
 consists essentially of mullite; 
 consists of 80% or more of the high temperature ceramic with a melting point above 1600° C.; 
 consists essentially of the high temperature ceramic with a melting point above 1600° C.; 
 consists of 80% or more of the high temperature ceramic with a melting point above 1600° C., the high temperature ceramic having a preferred phase preferentially formed only at a temperature above 90 Q° C.; 
 consists essentially of the high temperature ceramic with a melting point above 1600° C., the high temperature ceramic having a preferred phase preferentially formed only at a temperature above 900° C.; 
 consists of 80% or more of the high temperature ceramic with a melting point above 1600° C., the high temperature ceramic having a preferred phase preferentially formed only at temperatures between 900-2000° C.; 
 consists essentially of the high temperature ceramic with a melting point above 1600° C., the high temperature ceramic having a preferred phase preferentially formed only at temperatures between 900-2000° C.; 
 consists of 80% or more of the high temperature ceramic with a melting point above 1600° C., the high temperature ceramic having a preferred phase preferentially formed only at temperatures between 900-1600° C., or 
 consists essentially of the high temperature ceramic with a melting point above 1600° C., the high temperature ceramic having a preferred phase preferentially formed only at temperatures between 900-1600° C. 
 
     
     
         29 . A method of producing a high temperature coating on a ceramic substrate, the method comprising operating a high enthalpy air plasma spray torch and supplying the torch with a feedstock powder comprising a high temperature ceramic with a melting point above 1600° C., that forms undesirable solid phases when rapidly cooled below about 900° C., wherein a cumulative deviation from the following norms is less than 20%: |[N 2 ]|=47.5±2.5%, |[H 2 ]|=17.5+7.5%, |[Ar]|=35±10%, |TGF|=280±30 slpm, |P|=110±23 kW, |D|=8±2 cm, where [N 2 ], [H 2 ], and [Ar] are respectively the percentages of N 2 , H 2 , and Ar in the plasma plume, TGF is the total gas flow, P is the torch power, and D is the stand-off distance measured in cm. 
     
     
         30 . The method according to  claim 29  wherein the cumulative deviation is less than 10%. 
     
     
         31 . (canceled) 
     
     
         32 . The method according to  claim 29  wherein the cumulative deviation is less than 1%. 
     
     
         33 . The method according to  claim 29  wherein:
 operating the torch comprises spraying the ceramic substrate with at least 3 passes, by relative movement of a surface of the substrate to be coated perpendicular to the spray jet at a speed of 0.1-5 m/s: 
 spraying the ceramic substrate with the torch in at least 3 passes exposes each region of the substrate to the plume for about 8 s per coating; or 
 the substrate surface temperature is raised prior to deposition by scanning with the torch over the substrate, immediately prior to deposition, to raise the surface temperature above ˜500° C., more preferably from ˜800-1000*C. 
 
     
     
         34 . (canceled) 
     
     
         35 . (canceled) 
     
     
         36 . The method according to  claim 29  wherein the feedstock powder:
 consists of 80% or more of the high temperature ceramic with a melting point above 1600° C.; 
 consists essentially of the high temperature ceramic with a melting point above 1600° C.; 
 consists of 80% or more of the high temperature ceramic with a melting point above 1600° C., the high temperature ceramic having a preferred phase preferentially formed only at a temperature above 900° C.; 
 consists essentially of the high temperature ceramic with a melting point above 1600° C., the high temperature ceramic having a preferred phase preferentially formed only at a temperature above 900° C.; 
 consists of 80% or more of the high temperature ceramic with a melting point above 1600° C., the high temperature ceramic having a preferred phase preferentially formed only at temperatures between 900-2000° C.; 
 consists essentially of the high temperature ceramic with a melting point above 1600° C., the high temperature ceramic having a preferred phase preferentially formed only at temperatures between 900-200 Q° C.; 
 consists of 80% or more of the high temperature ceramic with a melting point above 1600° C., the high temperature ceramic having a preferred phase preferentially formed only at temperatures between 900-1600° C.; or 
 consists essentially of the high temperature ceramic with a melting point above 1600° C., the high temperature ceramic having a preferred phase preferentially formed only at temperatures between 900-1600° C.