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Wpływ stanu powierzchni na proces utleniania powłok typu NiCrAlY na stopie Inconel 625

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W artykule przedstawiono wyniki badań dotyczące charakterystyki odporności na utleniania natryskanej plazmowo powłoki NiCrAlY o różnym sposobie przygotowania powierzchni natryskanej plazmowo na stopie Inconel 625. Analizie poddano powłoki w stanie po natryskiwaniu cieplnym oraz po procesie szlifowania. Ocenie poddano odporność na utlenianie obu typu warstw w warunkach testu w temperaturze 1000°C przez czas 1000 godzin. Zakres badań obejmował analizę stanu warstwy wierzchniej powłok przy użyciu badań dyfrakcyjnych składu fazowego oraz badań mikroskopowych pozwalających na ocenę budowy warstwy. Słowa kluczowe: warstwy NiCrAlY, odporność na utlenianie Infl uence of top-surface condition on oxidation resistance of NiCrAlY coating on Inconel 625 alloy The article presents the results of the examination related to characterization of oxidation resistance of NiCrAlY coatings with different types of top-surface conditions, deposited on substrate alloy of Inconel 625 type. Coated specimens with conditions as sprayed and after grinding process were analyzed. Evaluation of oxidation resistance of both types of coatings was made during test of oxidation at temperature 1000°C by 1000 hours of exposure. The range of investigations included analysis of top surface of coatings by XRD characterization of formed oxides types and microscopic investigations of coatings morphology. Keywords: NiCrAlY coating, oxidation resistance 1. Wprowadzenie Trwałość powłokowych barier cieplnych (TBC - thermal barrier coatings) jest związana z wieloma czynnikami, ale większość prac badawczych w tym obszarze wskazuje jednoznacznie, że obserwowane procesy niszczenia powłok TBC są związane głównie ze zjawiskami w strefi e tlenków narastających na powierzchni warstwy podkładowej (TGO - thermally grown oxide) [1]. Nie ma zasadniczych wątpliwości, że główną odpowiedzialność za niszczenie powłok typu ponosi strefa TGA, trwają natomiast dyskusje, co do samego mechanizmu obser[...]

Oxidation behavior of Co-Al-Mo-Nb and Co-Ni-Al-Mo-Nb new tungsten-free y-y' cobalt-based superalloys DOI:10.15199/40.2017.9.5

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Nowadays, the development of heat-resistant materials is crucial for aircraft industry due to the fact that turbine engines performance increasingly depends on high temperature stability of components, therein turbine blades and combustion sectors. From the other site oxidation and hot corrosion, concomitant to high temperature are the main mechanisms leading to faster degradation of materials used it this type of engineering systems [4]. Lifetime of high-temperature elements can be decreased owing to usage of low quality fuels, containing sulphur, sodium and halides impurities. This type of atmosphere promotes formation of liquid flux, which dissolves oxide layers protecting metal and causes increase of oxidation rate. Diffusion of sulphur into alloy results in sulphides formation and the corrosion damage development [2, 5, 9]. The solution providing hot corrosion protection for nickel-based superalloys is utilization of special barrier bond coatings, however this method is expensive and technologically demanding. Protective band coatings enhance hot corrosion resistance, whereas are still not suitable for long exposure at high temperature, therefore development of a new materials with comparable high temperature strength and greater oxidation and hot corrosion resistance is necessary [8]. Nickel-based superalloys are commonly used materials for high temperature applications, whereas cobalt-based alloys are utilized as well. Conventional cobalt-based superalloys exhibit remarkable corrosion resistance, mechanical properties at high-temperature and thermal fatigue resistance [11]. This type of alloys is based on solid solution of refractory elements (W, Mo, Nb, Ta) in fcc cobalt matrix, further strengthened by various carbides, therein M23C6, M7C3 and MC carbides [14]. Further investigations aimed in search of cobalt-based alloys with comparable mechanical properties to γ’ strengthened nickel-based alloys. It was repor[...]

Characterization of primary microstructure of y-y' Co-Al-W cobalt-based superalloy DOI:10.15199/28.2017.5.3


  Cobalt based superalloys are widely employed in various fields of industry, inclusive of turbine engine construction, wherein are used for turbine blades and combustion chamber segments. The usage of these alloys results from remarkable properties at high temperature, particularly creep resistance, fatigue strength as well as resistance to high temperature oxidation and hot corrosion [1]. Conventional Co-based superalloys are commonly applied in as cast state. The microstructure of these alloys consist of solid solution of alloying elements in cobalt fcc matrix. Considerable solid solution hardening of Co-based superalloys is provided by addition of heat-resistant elements. Another utilized strengthening mechanism is precipitation of carbides. Occurrence of MC, M23C6 and M7C3 carbides provides stable service of Co-based components up to approx. 900°C. However, the secondary carbides precipitation during service exposure in elevated temperature greatly decreases low-temperature ductility [2]. The cobalt-based superalloys has considerably developed during the last ten years, resulting in new type of γ/γʹ alloys, strengthened by γʹ phase with L12 crystal structure. Co3Al phase is not present in Co-Al system, due to lack of thermal stability at room temperature and exists only at high pressure. Stability of this phase depends on maximum allowed lattice mismatch, which achieves 1% in this case. However, the ternary compound γʹ-Co3(X, Y) exists in equilibrium conditions and is analogue to Ni3Al phase [3÷5]. In Co-based superalloys containing Ti exists Co3Ti phase, whereas did not meet the expectations concerning strengthening of Co-based superalloys, owing to low temperature of dissolution in cobalt matrix (>750°C) and precipitation in cellular form [6÷8]. In 2006, Sato showed the possibility of Co3Al stability at room temperature as a result of tungsten alloying and γʹ-Co3(Al, W) formatio[...]

Cyclic oxidation resistance of Co-9Al-9W new cobalt-based superalloy DOI:10.15199/28.2019.2.2


  1. INTRODUCTION The main course of turbine engine development is improvement of service temperature concomitant higher efficiency and lower CO2 emission. Elements of turbine engines are exposed to aggressive service environment, which requires utilization of alloys with specific properties. Creep, oxidation, sulphide and hot corrosion are strong contributors to engines elements degradation. Service life of elements working under these conditions may be decreased due to usage of low quality fuels, containing sulphur, sodium and halides impurities. Atmosphere of hot, contaminated gas causes formation of liquid flux, which is able to dissolve protective coatings and accelerate degradation of substrate alloy. Another danger is connected with diffusion of sulphur, resulting in deleterious sulphide corrosion [1]. Although commercial Ni-based superalloys possess excellent creep properties due to γ′ strengthening, their behaviour in hot, corrosive environments is insufficient. Usage of special band coats is a popular way to enhance corrosion resistance of Ni-based superalloys, however, this solution is technologically challenging and considerably consumes financial resources [2÷5]. Another issue connected with development of superalloys is melting temperature. Cobalt seemed to be appropriate replacement for Ni-based alloys due to higher melting point and better corrosion resistance compared to Ni-based alloys. Furthermore these alloys possess appropriate oxidation resistance and excellent thermal fatigue resistance. In past, many research concerning conventional Co-based superalloys have been performed [6÷8]. These alloys are strengthened by carbides and solid solution of refractory metals in fcc cobalt matrix. Unfortunately, their strength at high temperature is considerably lower in comparison to γ′-strengthened alloys from Ni-Al system, therefore conventional Co-based superalloys did not achieve wide recogniti[...]

Odporność na utlenianie warstw krzemkowych na molibdenie i stopie TZM DOI:10.15199/40.2016.2.3


  W artykule przedstawiono wyniki badań charakteryzujące odporność na utlenianie krzemowanego metodą proszkową czystego molibdenu oraz stopu TZM, zawierającego dodatkowo tytan, cyrkon oraz węgiel. Badania odporności na utlenianie przeprowadzono w powietrzu w temperaturze 1200°C w warunkach quasi izotermicznych. Próbki do badań pobierano po 25, 50 i 100 godzinach testu. Wykazano, że o trwałości powłoki krzemkowej na molibdenie i jego stopach decyduje jej jakość, a szczególnie obecność pęknięć i ich zdolność do samozaleczania. W powłokach typu MoSi2 obecność pęknięć penetrujących do materiału podłoża gwałtownie przyspiesza proces niszczenia stopu podłoża, a efekt samozaleczania nie jest obserwowany. W obszarach powłoki wolnych od pęknięć jej trwałość w warunkach utleniania była bardzo dobra. Słowa kluczowe: warstwy krzemkowe, molibden, TZM, odporność na utlenianie. Oxidation resistance of silicide coatings on Mo and TZM alloy Results of investigations characterizing oxidation resistance of pure Mo and TZM alloy (with addition of Ti and Zr) after siliconizing process in activated pack were showed in this article. The oxidation test was made in laboratory air at temperature 1200°C in quasi isothermal conditions. The specimens to microstructural investigations were taken after 25, 50 and 100 hours of exposure. The durability of silicide’s coatings on Mo and TZM alloy is related strongly to their quality and especially to: presents of microracks as well as ability to self-healing process. In the case of MoSi2 type of coatings the presents of deeply penetrating microcracks suddenly increased the failure process of substrate materials, and the self-healing effect was not observed. In the areas of coatings free from discontinuities the durability of silicide layer was very good in oxidation test condition. Keywords: silicide coatings, molybdenum, TZM alloy, oxidation resistance 1. Wprowadzenie Podstawową przyczyną ograniczającą zastosowanie mo[...]

Oxidation performance of Co-Al-W and Co-Ni-Al-W new type of y-y' cobalt-based superalloys DOI:10.15199/28.2017.4.2


  Development of high efficiency turbine engines leads to evolution of heat-resistant superalloys of different types. The nickel-based superalloys are still being the most frequently used in high temperature applications, whereas new types of γ-γʹ cobalt-based analogues are becoming gradually more effective and popular [1÷3]. These alloys exhibit better oxidation, corrosion and wear resistance than Ni-based alloys, although have inferior strength. Solidus temperature of these alloys is 100÷150°C higher than those of commercial nickel alloys, such as CMSX-4 [4, 5]. The microstructure of γ-γʹ Co-based superalloys contains face-centered cubic matrix γ, strengthened by γ′ phase, which is a ternary compound with the L12 structure and usually Co3(Al, W) formula [6]. Furthermore, in the microstructure occurs variety of carbides (M23C6, M7C3 and MC). In fact, formation of γ′ phase is difficult due to required value of lattice mismatch less than 1% [7]. The γ′ Co3(Al, W) exists owing to Al and W content. The alloying elements such as Ti, Ta, Nb, Mo and V promote the γ′ formation and increase solvus temperature. It is also confirmed that the phase stability of the γʹ phase greatly increases by Ni substitution for Co because the Ni3Al with the L12 structure is very stable and the γʹ phase exists in a wide composition range in the Ni-Co-Al ternary phase diagram [8]. One of the most popular alloy from this group is tungsten containing Co-9Al-9W and Co-20Ni-7Al-7W (at. %) alloys [9, 10]. Co-Al-W alloys after high temperature oxidation are characterized by multilayered oxide structure [11, 12]. Surface layer has been characterized as cobalt monoxide, which is harmful to humans and dangerous for the environment. Middle layer consists of mixed oxides of Al, W and other elements present in alloy [13]. Furthermore, several authors reported an external Al2O3 scale in cobalt-based[...]

Charakterystyka powłok krzemkowych na molibdenie i stopie TZM


  W artykule przedstawiono wyniki badań dotyczące charakterystyki powłok dyfuzyjnych otrzymanych w wyniku procesu dyfuzyjnego nasycania krzemem w proszkach aktywowanych blach molibdenowych i ze stopu TZM. Scharakteryzowano morfologię powierzchni zewnętrznej uzyskanych powłok oraz ich skład fazowy i chemiczny. Określono również grubość i budowę wewnętrzną warstw krzemkowych. Stwierdzono, że grubość warstw krzemkowych ok. 40 μm w po 18 godzinach procesu krzemowania. W przypadku stopu TZM jest ona minimalnie mniejsza niż dla czystego Mo. Skład fazowy warstw we wszystkich przypadkach to krzemek typu MoSi2. Słowa kluczowe: warstwy krzemkowe, molibden, TZM, mikrostruktura Characterization of silicide coatings on Mo and TZM alloy The article presents the results of the examination related to characterization of diffusion coatings obtained in pack cementation process on Mo and TZN alloy sheet. Top surface of coatings, their chemical compositions were characterized. The thickness of coatings and their internal structure was evaluated as well. It was revealed that the thickness of silicide coatings was ca. 40 μm, after 18 hours of exposure during diffusion process of siliconizing. In the case of TZM alloy the thickness is little lower than in pure Mo. Keywords: silicide coatings, molybdenum, TZM alloy, microstructure 1. Wprowadzenie Molibden i jego stopy, w tym na przykład stop TZM (Mo-0.5Ti-0.1Zr -0.02C) stosowane są jako materiały do zastosowań wysokotemperaturowych. Wynika to z ich niezwykle korzystnych właściwości użytkowych w wysokiej temperaturze. Do grupy tych właściwości zaliczyć można przede wszystkim wysoką temperaturę topnienia, wysoką wytrzymałość na pełzanie w podwyższonej temperaturze oraz odporność na korozję w środowisku ciekłych metali i ich stopów [1]. Główną słabością molibdenu i jego stopów, jest jego niska odporność na utlenianie w wysokiej temperaturze. Brak odporności na utlenianie spowodowany jest tworzeniem si[...]

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