| Abstract: |
It has been revealed that a regular disk splat can be obtained when the substrate temperature is higher than a transient temperature and increasing the deposition temperature effectively improves the interlamellar bonding in ceramic coatings. With metal alloy splat on a metal substrate of inevitable oxide scale, it is still not clear how the deposition temperature influences splat bonding formation. In this study, Ni20Cr particles were sprayed onto polished diferent metal substrates at different preheating temperatures in argon atmosphere by low pressure plasma spray to reveal the dominating factors over on splat bonding formation. The AISI 304 substrate was used as main substrate and preheated to temperatures of 100 (cooling from heating up to 350 oC), 350 and 550 oC for splat deposition besides the substrates including copper and nickel. The splat morphology, microstructure, splat-substrate interface bonding were characterized by SEM and EBSD. The samples for examination of typical splat interface bonding were prepared by FIB. Results showed the formation of two types of microstructures in splat from the splat surface by SEM and EBSD, including central coarse grain and marginal fine grain. At the interface in the whole central coarse grain zone an effective bonding was observed, while at the marginal fine grain region no effective bonding was observed. The boundary from the bonded zone to unbounded zone corresponds to the transition region of these two microstructures in splat at a deposition temperature higher than 350 oC. The area proportion of effective bonding ratio zone is estimated to be about 41%. In addition, it was found that the average diameter of splats decreased a little with increasing the thermal conductivity of substrates, whereas, the proportion of central coarse grain zone decreased rapidly. As a result, the interface temperature during splatting may play a crucial role on the interface bonding formation.
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