The chloride–sulfate-induced hot corrosion of superheater tubes remains a predominant failure mechanism in waste-to-energy (WTE) plants, resulting in significant downtime and maintenance expenditure. This study investigated the high-temperature corrosion performance and failure behavior of laser-clad Stellite 6 (Co-based) and Inconel 625 (Ni-based) coatings deposited on AISI 304 stainless steel substrates. Coatings were produced using optimized laser cladding parameters (laser power: 1.0–2.5 kW; scanning speed: 600–1400 mm/min) to achieve defect-free, metallurgically bonded multilayered structures with minimal dilution. Corrosion resistance was evaluated at 450 °C for 168 h under simulated WTE superheater conditions, including cyclic exposure to KCl–Na2SO4 salt deposits and a flowing gas mixture of SO2, O2, and H2O. Post-exposure analysis revealed distinct failure mechanisms between the two coatings. Stellite 6 exhibited superior corrosion resistance, with approximately 52% lower mass gain, attributed to the formation of a predominantly compact and relatively adherent <InlineEquation ID="IEq1"> <EquationSource Format="TEX">${\text{Cr}}_{2} {\text{O}}_{{3}} /{\text{CoO}}$</EquationSource> <EquationSource Format="MATHML"><math> <msub> <mrow> <mtext>Cr</mtext> </mrow> <mrow> <mn>2</mn> </mrow> </msub> <msub> <mrow> <mtext>O</mtext> </mrow> <mrow> <mrow> <mn>3</mn> </mrow> </mrow> </msub> <mrow> <mo>/</mo> </mrow> <mrow> <mtext>CoO</mtext> </mrow> </math></EquationSource> </InlineEquation>-rich scale that substantially reduced the penetration of corrosive species under the present test conditions. In contrast, Inconel 625 suffered from more severe degradatiosn, including internal oxidation, localized chlorination, and sulfidation, due to the formation of a less protective duplex NiO–Cr2O3 scale. The failure mode in Inconel 625 was characterized by scale spallation and accelerated corrosion kinetics consistent with an approximately parabolic rate law <InlineEquation ID="IEq2"> <EquationSource Format="TEX">$\left( {k_{{\text{p}}} = 0.464 {\text{mg}}^{2} {\text{cm}}^{ - 4} h^{ - 1} , R^{2} = 0.89} \right)$</EquationSource> <EquationSource Format="MATHML"><math> <mfenced close=")" open="("> <mrow> <msub> <mi>k</mi> <mtext>p</mtext> </msub> <mo>=</mo> <mn>0.464</mn> <msup> <mrow> <mtext>mg</mtext> </mrow> <mn>2</mn> </msup> <msup> <mrow> <mtext>cm</mtext> </mrow> <mrow> <mo>-</mo> <mn>4</mn> </mrow> </msup> <msup> <mi>h</mi> <mrow> <mo>-</mo> <mn>1</mn> </mrow> </msup> <mo>,</mo> <msup> <mi>R</mi> <mn>2</mn> </msup> <mo>=</mo> <mn>0.89</mn> </mrow> </mfenced> </math></EquationSource> </InlineEquation> over the 168-h test period. The enhanced durability of Stellite 6 is linked to its higher Cr content and the stabilizing effect of carbide phases, which promote sustained chromia formation. These findings highlight the critical role of coating composition and microstructure in determining corrosion failure mechanisms and support the use of Stellite 6 laser cladding as a robust surface protection strategy to mitigate high-temperature corrosion failures in WTE superheater tubes.

Enhanced High-Temperature Corrosion Resistance of Laser-Clad Stellite 6 Versus Inconel 625 Coatings in Simulated Waste Incineration Environments

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发表日期：

2026年5月29日

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Duoli Wu,
Mustavi Rafid,
Nahian Sadid,
Hongyu Hu,
Xinlong Wei,
Erjuan Yang,
Yong Li,
Chao Zhang

摘要

The chloride–sulfate-induced hot corrosion of superheater tubes remains a predominant failure mechanism in waste-to-energy (WTE) plants, resulting in significant downtime and maintenance expenditure. This study investigated the high-temperature corrosion performance and failure behavior of laser-clad Stellite 6 (Co-based) and Inconel 625 (Ni-based) coatings deposited on AISI 304 stainless steel substrates. Coatings were produced using optimized laser cladding parameters (laser power: 1.0–2.5 kW; scanning speed: 600–1400 mm/min) to achieve defect-free, metallurgically bonded multilayered structures with minimal dilution. Corrosion resistance was evaluated at 450 °C for 168 h under simulated WTE superheater conditions, including cyclic exposure to KCl–Na₂SO₄ salt deposits and a flowing gas mixture of SO₂, O₂, and H₂O. Post-exposure analysis revealed distinct failure mechanisms between the two coatings. Stellite 6 exhibited superior corrosion resistance, with approximately 52% lower mass gain, attributed to the formation of a predominantly compact and relatively adherent ${\text{Cr}}_{2} {\text{O}}_{{3}} /{\text{CoO}}$ ${Cr}_{2} O_{3} / CoO$ -rich scale that substantially reduced the penetration of corrosive species under the present test conditions. In contrast, Inconel 625 suffered from more severe degradatiosn, including internal oxidation, localized chlorination, and sulfidation, due to the formation of a less protective duplex NiO–Cr₂O₃ scale. The failure mode in Inconel 625 was characterized by scale spallation and accelerated corrosion kinetics consistent with an approximately parabolic rate law $\left( {k_{{\text{p}}} = 0.464 {\text{mg}}^{2} {\text{cm}}^{ - 4} h^{ - 1} , R^{2} = 0.89} \right)$ $(k_{p} = 0.464 {mg}^{2} {cm}^{- 4} h^{- 1}, R^{2} = 0.89)$ over the 168-h test period. The enhanced durability of Stellite 6 is linked to its higher Cr content and the stabilizing effect of carbide phases, which promote sustained chromia formation. These findings highlight the critical role of coating composition and microstructure in determining corrosion failure mechanisms and support the use of Stellite 6 laser cladding as a robust surface protection strategy to mitigate high-temperature corrosion failures in WTE superheater tubes.