High temperature oxidation of Ni alloys in CO2 containing impurities

Using alloy 230 as an example, a generalized oxidation lifetime model for chromia-forming Ni-base wrought alloys is proposed, which captures the most important damaging oxidation effects relevant for component design: wall thickness loss, scale spallation, and the occurrence of breakaway oxidation. For deriving input parameters and for verification of the model approach, alloy 230 specimens with different thicknesses were exposed for different times at temperatures in the range 950–1050 °C in static air. The studies focused on thin specimens (0.2–0.5 mm) to obtain data for critical subscale depletion processes resulting in breakaway oxidation within reasonably achievable test times up to 3000 h. The oxidation kinetics and oxidation-induced subscale microstructural changes were determined by combining gravimetric data with results from scanning electron microscopy with energy dispersive X-ray spectroscopy. The modeling of the scale spallation and re-formation was based on the NASA cyclic oxidation spallation program, while a new model was developed to describe accelerated oxidation occurring after longer exposure times in the thinnest specimens. The calculated oxidation data were combined with the reservoir model equation, by means of which the relation between the consumption and the remaining concentration of Cr in the alloy was established as a function of temperature and specimen thickness. Based on this approach, a generalized lifetime diagram is proposed, in which wall thickness loss is plotted as a function of time, initial specimen thickness, and temperature. The time to reach a critical Cr level at the scale/alloy interface of 10 wt% is also indicated in the diagrams.

Predicting Oxidation-Limited Lifetime of Thin-Walled Components of NiCrW Alloy 230

Commercial alloys 282, 230, HR160, HR120 and 188 were exposed to supercritical CO2 and to air at temperatures of 700–1000 °C. Alloy specimens took the form of thick-walled tubes, which were pressurised internally with flowing CO2 to simulate the likely stress conditions in service. All alloys formed protective scales containing continuous chromia layers plus internal oxidation zones. No internal carburisation was ever observed. In most cases, the reaction morphologies and rates were very similar in the two gases. The lack of any significant carbon effect on corrosion is attributed to additional scale layers of manganese spinel and/or silica, which prevent carbon penetration.

Resistance of High-Nickel, Heat-Resisting Alloys to Air and to Supercritical CO2 at High Temperatures

Corrosion behavior and lifetime prediction of VM12, Sanicro 25 and Inconel 617 in supercritical carbon dioxide at 600 °C

High-temperature corrosion research will face a significant change in the near future. Up until now, this research area was dominated by materials issues related to the use of fossil fuels in energy conversion and transportation. Recent political decisions in many of the industrialized countries resulted in a paradigm shift towards the preference of non-fossil renewable energy and CO2 neutral or CO2-free technologies. These political constraints driving the development of new energy conversion technologies in combination with new materials and new manufacturing methods lead to new challenges in high-temperature corrosion research. The availability of advanced investigation techniques as well as increased IT power provides significant potential for the improved in-depth understanding of corrosion mechanisms and the development of comprehensive and reliable lifetime models. The present overview addresses all these aspects and attempts to sketch an outlook, although incomplete, on expected future developments in high-temperature corrosion research.

https://link.springer.com/content/pdf/10.1007%2Fs11085-017-9719-3.pdf

Future Directions in the Field of High-Temperature Corrosion Research

Soybean straw biochar activating peroxydisulfate to simultaneously eliminate tetracycline and tetracycline resistance bacteria: Insights on the mechanism.

An accurate procedure for predicting oxidation-induced damage and lifetime limits is crucial for the reliable operation of high-temperature metallic components in practical applications. In order to develop a predictive oxidation lifetime model for Ni–Cr alloys, specimens of wrought NiCrW alloy 230 with different thicknesses were cyclically oxidized in air at 950–1050°C for up to 3000 h. After prolonged exposure, two types of carbides as well as a Cr-rich nitride (π-phase) precipitated in the γ-Ni matrix. The oxidation-induced loss of Cr from the alloy resulted in the formation of subscale zones, which were free of the Cr-rich carbide and nitride but also of the Ni-W rich M6C. The width of the M6C-free zone was smaller than that free of the Cr-rich precipitates. Thermodynamic and diffusion calculations of the observed time- and temperature-dependent Cr depletion processes identified that back diffusion of C occurred which resulted in an increased volume fraction of M23C6 in the specimen core. With increasing time and temperature, the amount of π-phase in the specimen core increased. The subscale depletion of the initially present Cr-nitrides and the formation of Cr-nitrides in the specimen center is believed to be related to a mechanism which is qualitatively similar to that described for the Cr carbide enrichment. However, with increasing time and decreasing specimen thickness, N uptake from the atmosphere becomes apparent. As a result, the precipitates present in the specimen center eventually consisted almost exclusively of nitrides.

Effect of Specimen Thickness on Microstructural Changes During Oxidation of the NiCrW Alloy 230 at 950–1050°C

Ultra-high low carbon baintic steel strengthened by CuNiAl-rich multistructured particles was studied in this work. The influence of direct quenching and tempering (DQ-T) process on microstructural transformation and precipitation behavior of CuNiAl-rich particles were investigated. The high-density dislocations formed in DQ process provide a large number of nucleation sites for the CuNiAl-rich particles. According to the results of phase field method simulation, the coarsening mechanisms of CuNiAl-rich particles included merger mechanism and Ostwald maturation mechanism. The formation of 9R–B2 core-shell structural CuNiAl-rich particles was owing to the inverse concentration gradient diffusion of Cu between particles with different Cu content. The yield strength was 1228 MPa, because of the co-precipitation of 9R–B2 core-shell structural particles with ∼12.5 nm and B2-ordered particles with ∼3.4 nm. The impact absorbed energy was 44.2J at −40 °C. The small grain size contervailed for toughness reduction from co-precipitation. 

Formation mechanism of CuNiAl-rich multi-structured precipitation and its effect on mechanical properties for ultra-high strength low carbon steel obtained via direct quenching and tempering process

/pdf/structural-color-controllable-humidity-response-chiral-2pw0rkbr.pdf

Ran Duan

Papers

Soybean straw biochar activating peroxydisulfate to simultaneously eliminate tetracycline and tetracycline resistance bacteria: Insights on the mechanism.

Predicting Oxidation-Limited Lifetime of Thin-Walled Components of NiCrW Alloy 230

Effect of Specimen Thickness on Microstructural Changes During Oxidation of the NiCrW Alloy 230 at 950–1050°C

Formation mechanism of CuNiAl-rich multi-structured precipitation and its effect on mechanical properties for ultra-high strength low carbon steel obtained via direct quenching and tempering process

Structural Color Controllable Humidity Response Chiral Nematic Cellulose Nanocrystalline Film