Impact of dilution on the microstructure and properties of Ni-based 625 alloy coatings

Nickel-based alloy IN 625 is used to protect components of aircrafts, power generation and oil refinery due to an association of toughness and high corrosion resistance. These properties are associated with the chemical composition and microstructure of coatings which depend on the processing parameters and the composition of the component being protected. This paper assessed impact of dilution on the microstructure and properties of the Ni alloy IN 625 deposited by Plasma Transferred Arc (PTA) on two substrates: carbon steel API 5L and stainless steel AISI 316L. Differences due to the interaction with the substrate were maximized analyzing single layer coatings, processed with three deposition current: 120, 150 and 180 A. Correlation with a cast Nickel-based alloy sample contributed to assess the impact of dilution on coatings. Dilution was determined by the area ratio and Vickers hardness measured on the transverse section of coatings. Scanning electron and Laser confocal microscopy and X-ray diffraction analysis were carried out to characterize the microstructure. Results indicated the increasing dilution with the deposition current was deeply influenced by the substrate. Dilution ranging from 5 to 29% was measured on coatings processed on the API 5L steel and from 22 to 51% on the low thermal conductivity AISI 316L steel substrate. Differences on the microstructure and properties of coatings can be associated with the interaction with each substrate. Higher fraction of carbides account for the higher coating hardness when processing on API 5L whereas the low thermal conductivity of AISI 316L and the higher Fe content in solid solution contributed to the lower hardness of coatings. Liga de Níquel do tipo IN 625 é usada para proteger componentes de turbinas aeronáuticas ou de geração de energia e de refinarias de petróleo, especialmente devido a uma associação de tenacidade e elevada resistência à corrosão. Estas propriedades são associadas com a composição química e com a microestrutura dos revestimentos que dependem dos parâmetros de processo e da composição do componente a ser revestido. Este artigo avaliou o impacto da diluição sobre a microestrutura e propriedades da liga de Níquel IN 625 depositada por Plasma com Arco Transferido (PTA) sobre dois substratos: aço carbono API 5L e aço inoxidável AISI 316L. Diferenças relacionadas à interação com o substrato foram maximizadas pela análise de revestimentos com cordão único, processados com três corrent