In the thermal spraying of powder materials, it has been observed in practice that the splat shape changes to a disk type from a splash type with increases in the substrate temperature. However, the details of the substrate surface change due to the heating has not been fully characterized. In this study, an AISI 304 stainless steel substrate surface heated to 673K was analyzed precisely by atomic force microscope (AFM), X-ray photoelectron spectroscopy (XPS), and Auger electron spectroscopy. The results obtained revealed that the change of the substrate surface occurred not in the chemical composition but mainly in the surface roughness, especially surface morphology in nano-meter scale. Hence, substrate heating may bring about the change in substrate surface and this change induces the transition phenomenon.
We have confirmed that in the thermal spraying of practical powder materials, the splat shape changes with increasing substrate temperature to a circular disk shape from a fringe shape with splashing at a critical substrate temperature, Tt. The increase of substrate temperature may accompany a kind of essential change on substrate surface, because the effect is maintained until the substrate is cooled down to room temperature. However, the nature of the substrate surface change due to the heating has not been clearly understood yet. In this study, AISI304 stainless steel was employed as a substrate material, and the substrate was heated in an air atmosphere or laser treated as a pretreatment. Substrate surface topography was analyzed precisely by atomic force microscopy, AFM. We discuss the relationship between surface topography in nano-meter scale and splat morphology. Moreover, in order to evaluate the effect of chemical composition of the substrate surface, gold was coated onto the substrate surface by PVD method after the heat treatment. The effect of adsorbate/condensate on the substrate surface on the flattening behavior of thermal sprayed particles was also verified.
Aluminum nitride (AlN) and iron nitride (Fe4N) coatings were fabricated by reactive plasma spraying using fine feedstock powders. Reactive plasma spraying, in which element particles react with surrounding active species in the plasma, enables to fabricate nitride ceramics which decompose without stable melting phase. However, it is difficult to fabricate the coatings which include higher concentration of nitride phase by reactive plasma spraying using conventional particle size of feedstock powders. Therefore, fine feedstock powders were used in order to enhance the nitriding reaction during spraying. Aluminum or iron particles were injected into Ar/N2 plasma and were deposited onto graphite substrates. It was possible not only to increase the nitride phase content in the coatings but also to densify the microstructure in both materials. Thus, it became clear that using fine feedstock powders are useful for fabrication of nitride ceramic coatings by reactive plasma spraying.
Aluminum nitride (AlN) is one of the attractive ceramics with respect to its excellent mechanical and electrical properties. In this study, AlN coatings were fabricated and the influence of feedstock powders was investigated by reactive RF (Radio Frequency) plasma spraying. Two different particle sizes of commercial aluminum (Al) powders and Al/AlN mixed powders were used as the feedstock powder. The feedstock powder was injected into a RF plasma, and sprayed particles were deposited onto carbon steel or quartz substrates. As a result, it was possible to fabricate thick and dense AlN coating using smaller particle size of Al powders and quartz substrate. However, many agglomerates were formed in the coatings. On the other hand, 50 wt% or above of AlN addition in the feedstock powders was effective to prevent the formation of the agglomerates. Therefore, Al/AlN mixed powder with smaller particle size was useful for fabrication of AlN coatings by reactive RF plasma spraying.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.