Influence of plasma arc currents on the microstructure and properties of Stellite-20 alloy coatings through plasma transfer arc cladding

The effects of cladding currents on the microstructure and mechanical properties of Stellite-20 coatings formed via plasma transferred arc (PTA) cladding were investigated. The Stellite-20 coatings were prepared at the cladding currents of 50, 55, 60, and 65 A. Stellite-20 coatings were composed of columnar dendrites and equiaxed crystals with cobalt-based solid solution and carbides. As the heat input increased, the amount of carbides and precipitated carbides at the grain boundaries increased continuously, enhancing the hardness of Stellite-20 coatings. The amount of carbide precipitation at the grain boundaries was continuously increased with the increase of the cladding current. The maximum value of carbide precipitation in the coating reached 42.94 ± 2.11 % when the cladding current was 65 A. From SLU (single load-unload) indentation testing, the results of all investigations with chromium and molybdenum carbide forms revealed a sequence of increasing hardness values: Cr 23 C 6 < Mo 2 C < Cr 7 C 3 < Cr 3 C 2 . In accordance with MPU (multiple-partial-unload) indentation testing, the fracture toughness of the coatings at different cladding currents was as follows: 50 A > 55 A > 60 A > 65 A, the fracture toughness of the matrix phase decreased with the increase of cladding current, which indicated that the growth in carbide size and the increase of carbide content significantly reduced the toughness of the material. These findings can provide essential understanding and direction about how cladding currents affect the microstructure and mechanical properties of coatings.