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Opracowanie metodologii zabezpieczenia powierzchni stopów niklu przed utlenieniem wewnętrznym w podwyższonych temperaturach bazując na powłokach dyfuzyjnych wraz z dodatkiem pierwiastków ziem rzadkich - TANGO IV

Development of high temperature coatings against internal oxidation process in Ni based alloys exposed at elevated temperatures based on diffusion coatings doped with rare elements - TANGO IV

Project Overview

Nickel-based alloys are used in the most severe load and temperature conditions due to their better mechanical properties (creep resistance) than high-chromium austenitic steels, these alloys are used, for example, in aircraft engines for up to 1400 oC, in nuclear and coal power plants where high pressure  and temperature is meet (p = 30 MPa, T = 700 – 760 oC). Currently, Ni based alloys as one, meet the strict criteria related to long-term service life under harsh conditions including oxidation at high temperature.

The Ni based alloys which are used at high temperatures and under the high pressure regime, unfortunately undergo an internal oxidation process. The results of the NCN project showed that nickel-based alloys exhibit increased resistance to steam oxidation at high temperature, however, unlike high-chromium austenitic steels, underwent internal oxidation process. This process consists the oxidation of an alloying elements at the grain boundaries  leading the weakening of the external structure of the material operating at high temperature, this process (internal oxidation) may result in the removal of the outer oxide scale from the material. The internal oxidation process is correlated directly with concentration of alloying elements, oxidation time, oxygen concentration in the atmosphere and finally temperature.

In order to protect these alloys against internal oxidation process, as a goal of the project, it is proposed to develop a methodology for the protection of the surface of the alloys (the same alloys as tested in the project No. 2014/13/D/ST8/03256 of the National Science Centre entitled: “Development mechanism of thermodynamically stable, thin and protective oxide scales formation at high temperatures in pure water steam on the alloys based on Fe and Ni structures with high chromium content“(www.http://hiteco.iod.krakow.pl/), through the use of “pack cementation “coatings: the coatings manufactured using dedicated powder, activator and inert filler. Furthermore, the coatings will be doped with additives of rare earth elements (RE): Gadolinium (Gd), Dysprosium (Dy), Terbium (Tb), Ytterbium (Yb), Rhenium (Re), Lanthanum (La), Yttrium (Y), Cerium (Ce) up to 1.5% by weight. The project is divided into several tasks, the description of the tasks is given below:

OBJECTIVE 1: Development of pack cementation coatings for Ni based alloys

Objective 1 was divided into stages, Stage 1 aims to develop the pack cementation coating on Ni based alloys (alloy 263, Haynes® 282®), these alloys undergo internal oxidation process (based on the National Science Center project results). The coatings will be deposited in temperature range 700 – 1000 oC, using standard horizontal tube furnace. Inside the tube furnace a stainless steel cylinder will be inserted, this cylinder is equipped in additional fittings to provide constant gas circulation to the main chamber during coating deposition. During pack cementation deposition only high purity argon is used. The coatings will be deposited using dedicated powders (µm in size): Al2O3 (96 wt.% – inert filler), Al (active element: 2 – 6 wt. %) and finally activator of the chemical process (AlCl3: 1 – 2 wt. %).

The samples of alloy 263 and Haynes® 282® will be inserted into a ceramic crucible with a lid, the samples inside a crucible will be covered by a powder mixture with addition of rare elements (RE) up to 1 – 2 wt.% . The coatings will be deposited in temperature range 700 – 1000 oC during t = 10, 15, 20 and finally 24 h to optimize process parameters. As mentioned previously, each of the coating will be enriched by addition of a tiny amount of RE: Gadolinium (Gd), Dysprosium (Dy), Terbium (Tb), Ytterbium (Yb), Rhenium (Re), Lanthanum (La), Yttrium (Y), Cerium (Ce). The produced coatings will be examined using standard instruments in order to validate microstructure, chemical composition and phase development of the fabricated coatings. The next Stage of this Objective will be exposure of the fabricated coatings in air and steam atmosphere at high temperature to observed if proposed solution will reduce internal oxidation process. The high temperature exposure in steam and air atmosphere will be carried out at 800 oC for 1000 hours (10 x 100 hours). Every 100 hours, the samples will be withdrawn from the rig and kinetic data will be measured using an electronic balance with a high accuracy (m = 0.01 mg, m = 100 g). To validate proposed hypothesis, the samples with no coating will be exposed as a reference materials. The exposure in steam will be carried out in the rig presented in the previous research [1 – 6], In this rig, water is circulated in a loop, highly distillated water is pumped to the rig via peristaltic pump, before the test, the rig with the samples inside is ventilated by nitrogen in order to vanish impurities and moisture from the cylinder (T = 200 oC). Afterwards, the samples with a coating and without the coating (with RE and without RE) will be heated up to required temperature for 100 hours and cooled down to room temperature, 10 times this process will be repeated to obtain kinetic values. Same procedure will be used in steam atmosphere exposure as well as in air oxidation experiment. In air atmosphere, the samples will be introduced to a rig inside a hot zone in ceramic tube, a ceramic tube on both ends will be closed by iron wool to ensure no moist or air from the outside will be introduced. The samples after exposure in both environments will be examined using standard instruments to observe microstructure, chemical composition and phase development, this process will be carried out using SEM, EDS and XRD respectively. Finally, the last stage (Stage 3) of this project aims to investigate cyclic oxidation resistance of the produced coatings. The coating will be heated up for 3 hours and cooled down to room temperature after 15 min, the coatings again will be introduced to a rig, it is planned to perform 100 cycles at 800 oC or remove the sample if a coating will detached from the base material (Ni based alloy).

References

[1] M. Łukaszewicz, N. J. Simms, T. Dudziak, J. R. Nicholls, Materials at High Temperatures, 29(3), (2012) 210–218
[2] M. Łukaszewicz, T. Dudziak, N.J. Simms, J. R. Nicholls, Oxidation of Metals, 79(5), (2013), 473–483
[3] T. Dudziak, N Simms, M Lukaszewicz, J. Oakey, J. Cockrem, Anti-Corrosion Methods and Materials, 60(6), (2013) 2-2
[4] T. Dudziak, V. Deodeshmukh, L. Backert, N. Sobczak, M. Witkowska, W. Ratuszek, K. Chrusciel, A. Zielinski, J. Sobczak, G. Bruzda, Phase Investigations under Steam Oxidation Process at 800 oC for 1000 h of Advanced Steels and Ni-Based Alloys, Oxidation of Metals, Vol 87, (2016), 139–158
[5] T. Dudziak, K. Jura, A. Polkowska, V. Deodeshmukh, M. Warmuzek, M. Witkowska, W. Ratuszek, K. Chrusciel, Steam Oxidation Resistance of Advanced Steels and Ni-Based Alloys at 700 oC for 1000 h, Oxidation of Metals, DOI 10.1007/s11085-017-9818-1
[6] T. Dudziak, P. Gajewski, B.Śnieżyński, V. Deodeshmukh, M. Witkowska, W. Ratuszek, K. Chruściel, Neural Network Modelling Studies of Steam Oxidised Kinetic Behaviour of Advanced Steels and Ni-based alloys at 800 oC for 3000 hours, Corrosion Science, Vol. 133, (2018), 94-111

OBJECTIVE 2: Commercialisation of the results in energy sector

The main market for commercialization of the produced coatings with addition of RE is the energy sector (coal-fired power plants, combined heat and power plants, municipal waste incineration plants etc.). During the laboratory research conducted in this project (TRL level: 2), the project manager will make every effort to bring industrial partners into cooperation.

The basic criterion for using the product in the energy sector is its reliability of this product in real conditions where coal or municipal waste are fired or burned. The laboratory environment and the results achieved in laboratory may differ a lot from the real conditions, hence it is important to investigate these type of coatings in real power plant sector. For this reason, it should be taken into account that the interest in coatings will be high, as the energy sector is inclined to new technologies, but on the other hand, the energy sector requires very proven solutions, because the costs associated with breakdowns, shutdowns of units or downtime in electricity production are very high and the applied coatings after the test cycle in the laboratory may not be entirely convincing its application. As mentioned previously, the market and demand analysis will be developed throughout the duration of the project, although it should be noted that this analysis is well known to the project manager, as he operates in the energy sector and knows what are the problems in this industry.