Influence of the spray process parameters and the thermal exposure on the mechanical properties of the free-standing air-plasma sprayed thermal barrier coating

The tensile and the 4-point bending tests of the free-standing air plasma sprayed thermal barrier coating (APSed TBC) were carried out in order to evaluate the mechanical properties. The effects of the process variables in the APS and the isothermal exposure on the mechanical properties were investigated. The experimental results indicated that the mechanical properties of the TBC ceramic top coating were significantly changed by the process variables and the isothermal exposure. The elastic modulus evaluated from the unloading curve was much higher than that from the initial loading curve. The microstructural and analytical investigations were also carried out and the relationship between the mechanical properties and the splat structure was discussed. It was cleared that the mechanical properties of APSed TBC was controlled with the change of the splat structure by the initial stage of the sintering

Comparison of Oxidation and Microstructure of Warm-Sprayed and Cold-Sprayed Titanium Coatings

Thick titanium coatings were prepared by the warm spraying (WS) and cold spraying (CS) processes to investigate the oxidation and microstructure of the coating layers. Prior to the coating formations, the temperature and velocity of in-flight titanium powder particles were numerically calculated. Significant oxidation occurred in the WS process using higher gas temperature conditions with low nitrogen flow rate, which is mixed to the flame jet of a high velocity oxy-fuel (HVOF) spray gun in order to control the temperature of the propellant gas. Oxidation, however, decreased strikingly as the nitrogen flow rate increased. In the CS process using nitrogen or helium as a propellant gas, little oxidation was observed. Even when scanning electron microscopy or an x-ray diffraction method did not detect oxides in the coating layers produced by WS using a high nitrogen flow rate or by CS using helium, the inert gas fusion method revealed minor increases of oxygen content from 0.01 to 0.2 wt.%. Most of the cross-sections of the coating layers prepared by conventional mechanical polishing looked dense. However, the crosssections prepared by an ion-milling method revealed the actual microstructures containing small pores and unbounded interfaces between deposited particles

Cold Spray Powders and Equipment

Chapter 3A particle shock consolidation encountered in the coldspray (CS) process is defined by a highvelocity impact of powder particles onto the substrate. The particle impact results in the generation of high stresses and strains both in the particles and the substrate. As shown in the basic monographs (Champagne, 2007; Papyrin et al., 2007), the powder material to be sprayed must feature sufficient ductility to ensure particle strains and cold welding without its failure. In some cases (at very high particle velocities) Ti alloy particle melting occurs (Vlcek et al., 2002). However, impact of other metallic powder materials is characterized by high stresses and particle shear strains. Because a lot of information is available on various powders and powder mixtures developed and applied for cold spraying (Jeandin et al., 2014; Moridi et al., 2014, and others), the goal of this chapter is to describe and discuss the concept of CS material selection, basic criteria for evaluation of its suitability for cold spraying, and particle behavior during the deposition process (acceleration and formation of interfaces)Book chapterPaolo Matteazzi , Alberto Colella , Volf Leshchynsky , Kazuhiko Sakaki et al. "Chapter 3. Cold Spray Powders and Equipment". Cold Gas Dynamic Spray. Roman Gr. Maev, Volf Leshchynsky, eds. CRC Press, 2016, p.95-118.boo