The morphologies and growth kinetics of the Secondary Reaction Zone (SRZ) formed at the interface between the Pt-Aluminised coating and 4 th generation Ni-base superalloy substrates have been investigated. Three alloys with systematically varying Ru content in the range of 2-5wt% were studied. Each alloy was tested using four different surface finishes prior to Pt coating. At the lowest Ru content sporadic formation of SRZ was observed, whilst in the higher Ru-containing alloys a continuous SRZ was formed. These alloys also showed more rapid SRZ growth, regardless of the original surface finish. The precipitation of TCPs in the substrate inhibited the growth of the SRZ towards the end of the exposure reversing the advantage of early nucleation. The volume fraction of the SRZ formation followed that in the substrate, reducing with Ru content. EBSD analysis revealed that the higher Ru-containing alloys nucleate many more grains of the SRZ but the number of grains adjusts with growth towards a constant grain size. On balance Ru leads to a deeper penetration depth into the substrate.

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Nickel-based self-fluxing alloy coating extends the service life of furnace wall tubes at waste incineration plants due to its excellent corrosion resistance and heat resistance. Fusing of such coatings by induction heating offers improved efficiency and reliability of products. Compared with conventional plasma, flame, and high-velocity oxy-fuel spraying thermal-sprayed coatings, induction-fused coatings provide a far stronger metallurgical bond at the interface, while minimizing the inclusion of pores. In addition, the tubes are less costly than those with welded coatings, and the process reduces the distortion of the products, facilitating easier final assembly. A successful experimental application of 11 units in a waste incinerator revealed virtually no corrosion on the exposed surfaces, and showed an improved water heating efficiency over that of the original tubes. Such units are now being employed in four incinerators in Taiwan, and continuing tests are showing great promise.

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