Surface Roughness Evolution to Identify Incubation Time for Hot Corrosion of Nickel-Base Superalloys: CMSX-4, CM247LC DS
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Surface Roughness Evolution to Identify Incubation Time for Hot Corrosion of Nickel‑Base Superalloys: CMSX‑4, CM247LC DS and IN6203DS at 550 °C Neil Chapman1,2 · Simon Gray2 · Joy Sumner2 · John Nicholls2 Received: 7 June 2020 / Revised: 4 September 2020 / Accepted: 7 September 2020 © The Author(s) 2020
Abstract In the absence of protective scales, nickel-base superalloys have an extremely limited hot corrosion incubation period before increased rates of attack are experienced. This paper reports on the nickel-base superalloys: CMSX-4, CM247LC DS and IN6203DS subjected to 550 °C hot corrosion exposures of durations ranging from 0 to 800 h, during which none of the superalloys developed a fully protective scale. The aim of the research was to identify the incubation period of each superalloy and this was achieved by means of surface roughness evaluations. A metrology exercise was performed on the cross section of test specimens which produced Cartesian data points which were subsequently converted to Ra and Rz data. Statistical analysis of the results suggested the incubation period lasted approximately 400, 500 and 200 h, respectively, for each superalloy. It was concluded that refractory metal phases within the microstructure were associated with the relatively short IN6203DS incubation period. This paper demonstrates that monitoring the changes in surface roughness provides a plausible method to identify the transition from incubation to propagation when studying 550 °C hot corrosion attack. Keywords Liquid sulphate · Solid state · Selective oxidation
Introduction A power generating industrial gas turbine (IGT) comprises three sections: compressor, combustion and turbine [1, 2]. The IGT internal components operating downstream of combustion experience both high temperatures and stresses and are * Neil Chapman [email protected] 1
Siemens Industrial Turbomachinery Limited, Ruston House, Waterside South, PO Box 1, Lincoln LN5 7FD, UK
2
Cranfield University, College Road, Cranfield, Wharley End, Bedfordshire MK43 0AL, UK
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Vol.:(0123456789)
Oxidation of Metals
therefore manufactured from materials, such as nickel-base superalloys, that can endure these conditions. In addition, if corrosive compounds enter the IGT through either the local atmosphere or the fuel used, these materials must be able to cope with the resulting hot corrosion environment. Hot corrosion can be considered a subset of deposit-induced corrosion [1, 2] with the former recognised in aero, marine and IGTs, while the latter is found in many combustion-based power generation systems. Hot corrosion can cause accelerated rates of attack of component alloys [1–4] and as the generic name implies, the presence of deposits such as Na2SO4 is required to induce the attack [1, 2]. The physical condition of the deposits is also an important factor. When deposits accumulate on the components in the molten state, type I hot corrosion occurs [5]. This type of attack is characterised by internal damage/sulphidation and is typically exper
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