In-Service Oxidation and Microstructural Evolution of a Nickel Superalloy in a Formula 1 Car Exhaust

Abstract

The oxidation response and microstructural evolution of an Inconel 625 alloy exhaust manifold exposed to an automobile racing environment has been examined using a range of advanced electron microscopy-based techniques, atom probe tomography and high-sensitivity laser ablation mass spectrometry. The dynamic, corrosive gas conditions result in accelerated oxidation, with the inner exhaust surface also heavily contaminated by multiple species including Zn, P, K and Na. Nb carbides and Ti nitrides identified in stock control samples evolve into mixed (Ti, Nb)N species during exposure, decorated by smaller Mo, Si-rich precipitates. The exposed alloy component therefore reveals unique surface and subsurface features following in-service use.

Microstructural degradation of polycrystalline superalloys from oxidized carbides and implications on crack initiation

“…Ti-rich nitrides were found to form at or near the γ R /γ interface and within the γ precipitate, with a composition given in Table 3. Their stoichiometry does not yet exactly correspond to TiN nitrides often observed in nickel-based superalloys [36], which could be due to the thermal exposure too short to complete the formation of TiN. Similar nitrides were observed in other nickel-based superalloys during oxidation of MC carbides [37].…”

Atom Probe Tomography Investigations of Microstructural Evolution in an Aged Nickel Superalloy for Exhaust Applications

“…4. Niobium and titanium, elements which have been shown to segregate at oxide interfaces, [24] are being depleted from the matrix to form c¢¢ precipitates at markedly shorter aging times than previously reported. This could cause unexpected changes to the corrosion resistance of the alloy when operating in a corrosive exhaust environment.…”

Rapid assessment of structural and compositional changes during early stages of zirconium alloy oxidation

“…Alloys applied in nuclear reactors 1,2 , gas turbines 3,4 , heterogeneous catalysis 5,6 , automotive internal combustion engines 7 , and electronic devices 8,9 are routinely exposed to high-temperature, corrosive, and oxidising environments. Oxidation of alloys in service can degrade material properties and performance, raising significant safety and economic concerns.…”