Many kinds of both metallic and ceramic powder particles were plasma-sprayed onto the mirror-polished metallic substrate surface, and the effect of both substrate temperature and ambient pressure on the flattening behavior of the particle was systematically investigated. In the flattening behavior of the sprayed particle onto the substrate surface, critical conditions were recognized both in the substrate temperature and ambient pressure. That is, the flattening behavior changed transitionally on that critical temperature and pressure range, respectively. We defined and introduced a transition temperature, Tt, and transition pressure, Pt, respectively, for those critical conditions. The role of the related factors (such as solidification of the bottom surface of the splat, desorption of adsorbates on the substrate surface and wetting at interface) on the transition behavior in the flattening was clarified from several points of views. The fact that the dependence both of transition temperature and transition pressure on the sprayed particle material had a similar tendency indicated that the wetting of the substrate by the molten particles seemed to be a domination in the flattening. A three-dimensional transition map by combining both transition temperature and transition pressure dependence was proposed as a controlling principle of the thermal spray process.

In the thermal spraying of practical powder materials, we have confirmed that the splat shape changes to a disk type from a splash type with increasing substrate temperature. Substrate temperature increasing may accompany the change in something on the substrate surface, because the changing effect was maintained till the substrate was cooled down to the room temperature range. Thus, we already pointed out that this non-reversible change in substrate surface due to the heating might be the possible domination for the transition phenomenon of the thermal sprayed particles. However, the essence of the substrate surface change due to the heating has not been clearly understood yet.In this study, SUS304 substrate surface once heated to 673 K was analyzed precisely by atomic force microscope (AFM), X-ray photoelectron spectroscopy (XPS) and auger electron spectroscopy (AES). 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 order. Hence, the substrate heating may bring about the change in the physical way on the substrate surface and this change induces the transition phenomenon.Key Words: substrate, heating, splat, flattening, surface roughness, surface topography, wettability, thermal spraying

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.

an Spstems E)lgt'neeringt lbJehawh' Uim'vetsity of71,ehnalogJg 1-1, 7bunpaku'chq 7byohashi 441'S58a J2rpaq fuktllnoto@tutpsatu4atut, "" thnduate stuciena 7bytthashi' tinj'vetsi'ty oftechnalqgy Abstract: Asplat chape of most meta]]ic and eeramic material onto a flat substrabe surfaee has a transitional ehanging tendency ffom a dmrted wirh splasli to a lenticular without sp]ash at a narTvw temperature range with an increase of the substrate temperature, It has estimated from our results that the physical wetting strongly affects the transitien behffvior with the change ofthe substrate temperature. in this stud}1 the effect of surfaee rnorphclogy ofthe substrate on the flattening behavior of themial spreyed partiele orrto substrate surfaoe was fimdarnenta]]y investigated. The relation between the flattening behavior of the panicle on the substrate surfaee and the surfaoe morphalogy of the substrate was investigated. The morphalogy ofthe substrate was analyzed by Atornie FoTce Microscope: AEM and the surface rDughness was evaluated as a quantitative characteristic of the suhnrate surfeca, Consequentlsc it was rovealed that the surface roughness of the substrate in nm order significantay affects the chape of the sprayed partiele. From the fact, it is inferTed thatthebetterwettingofthesubstratebytheflatteningparticleisinducedbythesurfaceroughnessofthesubstrate.KojJ WtuTls: 7henmal Gbta)[iizg; Suhsttvate 71miperattue; 7}nnsition 71miper:fitua Splasii pmat andDi'sk Elplat

Ni, Ni-Al and Ni-Cr powder particles were plasma sprayed onto the mirror polished metallic substrate surface and the effect of substrate temperature on the particle/substrate interface microstructure was investigated. Sprayed particles were fully melted, sphere in a shape and oxidized on their surfaces during spraying in an air atmosphere. The surface oxide layers were detected as Al or Cr rich thin layer, respectively by electron probe micro analysis (EPMA). After spraying of the particles onto the substrate, cross section microstructures at particle/substrate interfaces were investigated. As a result, almost no oxide layer was detected at the particle/substrate interface when the substrate was kept at room temperature. On the other hand, the oxide layer was apparently recognized at the interface when the substrate was kept at a certain elevated temperature, such as at 673K. The difference in the existence of the oxide layer at interface seems to relate the wettability of the substrate by the liquid particles. The transition temperature, Tt, for each powder material was measured. The meaning of elemental addition to the base metal was considered from the changing tendency in Tt value of each powder material. Through the investigation results obtained, dominating factor on the flattening of the thermal sprayed particles onto the flat substrate surface was estimated.