Study of Laser Cladding of Stellite 6 on Nickel Superalloy Substrate with Two Different Energy Inputs

Abstract

Stellite 6 was deposited by laser cladding on a nickel superalloy substrate (NIS) with energy inputs of 1 kW (NIS 1) and 1.8 kW (NIS 1.8). The chemical compositions and microstructures of these coatings were characterized by atomic absorption spectroscopy, optical microscopy and scanning electron microscopy. The microhardness of the coatings was measured and the wear mechanism of the coatings was examined using a pin-on-plate (reciprocating) wear testing machine. The results showed less cracking and pore development for Stellite 6 coatings applied to the nickel superalloy substrate with the lower heat input (NIS 1). Further, the Stellite coating for NIS 1 was significantly harder than that obtained for NIS 1.8. The wear test results showed that the weight loss for NIS 1 was much lower than for NIS 1.8. It is concluded that the lower hardness of the coating for NIS 1.8, together with the softer underlying substrate structure, markedly reduced the wear resistance of the Stellite 6 coating.

Analysis of the Geometry of Wear Tracks in Laser Deposited Stellite 6 Coatings

“…Based on these assumptions, the volume of material removed can be calculated, as well as the C/S area of the wear track and its width. The coating depth was maintained at 0.35 + 0.05 mm for all samples [1][2][3][4][5][6][7] . The estimates of wear depth were compared to the actual coating depth to establish which, if any, wear tests resulted in penetration of the coating.…”

“…Assumption (f) is invalid as the actual coating density would be lower than 8.44 g/cc by an amount that differs for each substrate and for each of the two deposition powers. The maximum difference will be for the coating deposited at 1.8 kW on the Ni-based substrate, which showed 40% dilution [1][2][3][4][5][6][7] . The Ni-based substrate was the alloy IN 718 which has a density of 8.14 g/cc.…”

“…The temperature gradient due to deposition produces a microstructural gradient in the HAZ with solution treated austenite adjacent to the coating and, with depth, austenite containing intermetallics with a range of volume fractions and size distributions depending on the local thermal history. The measured hardness of the substrate was 200 HV and the average HAZ hardness was 240 HV [2,3] . These hardness values are low enough for the substrate material underlying the coating to deform plasticity under the wear loading conditions.…”

“…Dilution by the elements of the substrate alloys is expected to lower this density and therefore, reduce the predicted mass loss. Moreover, the extent of coating dilution varied significantly with the identity of the substrate alloy, with the minimum being about 5% for the mild steel substrate for coating at a laser power of 1 kW, and the maximum being about 40% for the coating deposited on the Ni-based superalloy substrate at 1.8 kW [1][2][3][4][5][6][7] . Therefore, the density of the diluted coating would have varied with the identity of the substrate, as well as the laser deposition power which affects the extent of dilution.…”

“…The sliding wear behaviour of Stellite 6 coated samples produced by laser cladding has been investigated and reported for six high strength alloy substrates in recent publications by the authors [1][2][3][4][5][6][7] .…”