Thermal Spray Processing of FGMs

Abstract

Functionally gradient materials (FGMs) display continuously or discontinuously varying compositions and/or microstructures over definable geometrical distances. The gradients can be continuous on a microscopic level, or they can be laminates comprised of gradients of metals, ceramics, polymers, or variations of porosity/density. Several processing techniques have been explored for the fabrication of FGMs for structural applications, e.g., powder metallurgy, thermal spraying, in situ synthesis, self-propagating high-temperature synthesis, reactive infiltration, etc. Physical and chemical vapor deposition (CVD) techniques are also being explored to process FGM films with nanometer level gradients in composition. This article addresses the issues related to thermal-spray processing of FGMs and will only peripherally compare the advantages and limitations of thermal spray versus other processing techniques as reported in the literature.In thermal spraying, feedstock material (in the form of powder, rod, or wire) is introduced into a combustion or plasma flame. The particles melt in transit and impinge on the substrate where they flatten, undergo rapid solidification, and form a deposit through successive impingement. Thermal spraying has been traditionally employed to produce a variety of protective coatings of ceramics, metals, and polymers on a range of substrates. More recently, the process has been used for spray-forming structural components.Arc spray, combustion, and plasma are the major techniques comprising thermal spray. These classifications are based on the type of heat source and the method by which feedstock is injected. Arc-spray processes use electrically conductive wire as feedstock, while combustion methods use powder or wire.

High-temperature oxidation of ceramic matrix composites dispersed with metallic particles

“…Ceramic matrix composites dispersed with metallic particles (referred to as M(p)-CMCs) are candidates for high-temperature structure materials as functionally graded materials (FGMs) or nano-composites. Their mechanical and physical properties have been studied as well as their production processes [1][2][3][4]. High-temperature oxidation/corrosion of M(p)-CMCs has, however, not been investigated in any details.…”

Role of Oxide Additives in Stabilizing Zirconia for Coating Applications

“…These techniques are similar to a welding, except that in welding the material is fused to the substrate and stays attached through a metallurgical bond, while thermally sprayed coatings remain attached through a mechanical bond. Further details and information on the various thermal spray techniques can be obtained from references [54][55][56][57].…”

Alumina-based composites strengthened with titanium and titanium carbide dispersions

“…Th us, composites can be constituted in some cases of carbide ceramics, oxide ceramics and metals, and they can be used, for example in application at high temperatures such as in the construction of gas turbine engines in order to increase their thermal cycle effi ciency [4][5]. Th erein, the mechanical and physical properties of such type of composites have been studied, as well as their production processes [6][7][8]. In spite of this, the high temperature cementation of metal-dispersed carbide composites has not been investigated in detail and there are not suffi cient reports on the high temperature cementation of thermal barrier composite-coatings [9].…”