Abstract
Oxidation-induced degradation of structural materials employed as exhaust valves within internal combustion engines (ICEs) will be a relevant life-limiting mechanism, in addition to creep and mechanical fatigue, due to ever-increasing severity of operating temperatures and pressures. Ni–Cr-based alloys, which form external chromia-based scales at the relevant operating temperatures are being considered as suitable candidate materials. Thermal cycling of these alloys in water vapor-containing atmospheres, such as those present during hydrocarbon fuel combustion within ICEs, can considerably influence their oxidation behavior. In this study, the role of typical alloying additions such as Mn, Si, Al and Ti on the cyclic oxidation behavior of model NiCr–X (X = Mn,Si,Al,Ti) alloys exposed in dry air and air + 10% H 2O at 800∘C and 950∘C was investigated. Combined additions of Mn and Si reduced scaling rates compared to binary Ni–22Cr alloys. The presence of water vapor possibly suppressed formation of NiMnCr spinel and thereby the Cr depletion in the alloy. Combined Al and Ti additions mainly resulted in accelerated oxidation kinetics due to the Ti doping of chromia scales. More porous external scales were observed in water vapor leading to a much deeper depth of nitridation in the Ni–22Cr–Al–Ti alloys.
| Original language | English |
|---|---|
| Pages (from-to) | 157-187 |
| Number of pages | 31 |
| Journal | Oxidation of Metals |
| Volume | 95 |
| Issue number | 1-2 |
| DOIs | |
| State | Published - Feb 2021 |
Funding
This manuscript has been authored by UT-Battelle, LLC, under contract DE-AC05-00OR22725 with the US Department of Energy (DOE). The US government retains and the publisher, by accepting the article for publication, acknowledges that the US government retains a nonexclusive, paid-up, irrevocable, worldwide license to publish or reproduce the published form of this manuscript, or allow others to do so, for US government purposes. DOE will provide public access to these results of federally sponsored research in accordance with the DOE Public Access Plan ( http://energy.gov/downloads/doe-public-access-plan ) G. Garner and G. Cox assisted with the experimental work at ORNL. V. Cox is thanked for metallographic preparation. T. Lowe is thanked for helping with microstructural characterization. P. Tortorelli and M. Brady are thanked for their valuable comments on the paper. This research was sponsored by the U.S. Department of Energy Office of Vehicle Technologies, Powertrain Materials Core Program.
Keywords
- Alloy composition profiles
- Cyclic oxidation
- Electron back scatter diffraction
- Internal oxidation
- Ni-based alloys
- Water vapor