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

概要

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Thick titanium coatings were prepared by the warm spraying (WS) and cold spraying (CS) processes toinvestigate the oxidation and microstructure of the coating layers. Prior to the coating formations, thetemperature and velocity of in-flight titanium powder particles were numerically calculated. Significantoxidation occurred in the WS process using higher gas temperature conditions with low nitrogen flowrate, which is mixed to the flame jet of a high velocity oxy-fuel (HVOF) spray gun in order to control thetemperature of the propellant gas. Oxidation, however, decreased strikingly as the nitrogen flow rateincreased. 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 thecoating layers produced by WS using a high nitrogen flow rate or by CS using helium, the inert gas fusionmethod revealed minor increases of oxygen content from 0.01 to 0.2 wt.%. Most of the cross-sections ofthe coating layers prepared by conventional mechanical polishing looked dense. However, the crosssectionsprepared by an ion-milling method revealed the actual microstructures containing small poresand unbounded interfaces between deposited particles.