Compositionally graded and porosity graded coatings using a solution precursor plasma spray process

Abstract

A solution precursor plasma spray process (SPPS) produces compositionally graded and porosity graded coatings with no discrete interfaces and with reduced coating stress and improved coating durability. The disclosed SPPS process may fabricate superior thick monolithic thermal barrier coatings with engineered microstructural defects (cracks, pores) and thin, dense coatings for a variety of engineering applications. The disclosed coatings may possess a continuous variation of one or more physical properties selected from density, thermal conductivity, emissivity, thermal expansion coefficient, abrasion resistance, erosion resistance, hardness, fracture toughness, gas penetration resistance, liquid penetration resistance, elastic modulus, and strain tolerance. The disclosed coatings may possess a continuous variation of one or more chemical properties selected from corrosion resistance to solids, liquids, and/or gases, reactivity with liquids and prevent further penetration of liquids, reactivity with gases and prevent further penetration of gases, and varying diffusion coefficients for one or more chemical species.

1 . A coating deposited by a solution precursor plasma spray process (SPPS) that is continuously graded throughout a cross-section of the coating as to composition, porosity, or composition and porosity. 
     
     
         2 . The coating of  claim 1  produced by low and high enthalpy thermal spray guns, selected from an air plasma spray, a high velocity oxygen fuel spray, a flame spray, and a detonation gun. 
     
     
         3 . The coating of  claim 1  in which some or all sub-layers are homogeneous as to composition or porosity and for which grading is produced between sub-layers, such that there are no discrete interfaces between sub-layers. 
     
     
         4 . The coating of  claim 1  that is devoid of discrete interfaces based on composition and porosity. 
     
     
         5 . The coating of  claim 1  where the coating possesses a continuous variation of one or more physical properties throughout a cross-section of the coating, wherein the one or more physical properties are selected from density, thermal conductivity, emissivity, thermal expansion coefficient, abrasion resistance, erosion resistance, hardness, fracture toughness, gas penetration resistance, liquid penetration resistance, elastic modulus, and strain tolerance. 
     
     
         6 . The coating of  claim 1  where the coating possesses a continuous variation of one or more chemical properties selected from corrosion resistance to solids, corrosion resistance to liquids, corrosion resistance to gases, reactivity with liquids and prevent further penetration of liquids, reactivity with gases and prevent further penetration of gases, and varying diffusion coefficients for one or more chemical species. 
     
     
         7 . A process for preparing a compositionally graded or porosity graded coating using a solution precursor plasma spray process comprising continuously varying one or more process parameters in the solution precursor plasma spray process, wherein the process parameters are selected from an injection rate of one or more solution precursors being injected into a plasma flame, plasma gun power, plasma gun raster scan rate, plasma gun stand-off distance, an injection rate of a precursor of one or more secondary additives to the solution precursors that can change the plasma flame temperature, and torch gas flow rates, wherein the process produces a coating that is continuously graded as to composition or porosity through a cross-section of the coating. 
     
     
         8 . The process of  claim 7  wherein a plurality of solution precursors of different composition are injected using two or more injectors and wherein a relative proportion of the plurality of solution precursors is varied continuously during deposition of part or all of the coating. 
     
     
         9 . The process of  claim 7  in which sub-layers are homogeneous as to composition or porosity and for which grading is produced between sub-layers, such that there are no discrete interfaces between sub-layers. 
     
     
         10 . The process of  claim 7  wherein multiple injectors are used to produce the coating which is compositionally graded over part or all of the coating thickness. 
     
     
         11 . The process of  claim 7  wherein a plurality of solution precursors are mixed at or near the plasma torch, and wherein relative proportions of the plurality of solution precursors are continuously varied during all or part of the solution precursor plasma spray process to produce a compositionally graded coating. 
     
     
         12 . The process of  claim 7  wherein flow rate and mixing of solution precursors are controlled and varied by a peristaltic pump, a syringe pump with or without switching valves that allow continuous operation, a gear pump, a reciprocating pump, a turbine pump, and a metering orifice and back pressure regulator with or without feedback control from a flow meter. 
     
     
         13 . The process of  claim 12 , wherein the flow rate and mixing of solution precursors are controlled and varied by a metering orifice and back pressure regulator with feedback control from a Coriolis meter.