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Właściwości mechaniczne i mikrostruktura odkuwek matrycowych ze stopów magnezu DOI:10.15199/24.2016.9.10


  Mechanical properties and microstructure of die forgings magnesium alloys Artykuł obejmuje analizę struktury oraz właściwości mechanicznych odkuwek klamek wykonanych przez Zakład Obróbki Plastycznej Sp. z.o.o. w Świdniku ze stopów magnezu: MgAl4Zn oraz WE43. Klamki odkute zostały przy użyciu prasy śrubowej F1736A oraz młota kuźniczego MPM3150. Badanie właściwości wytrzymałościowych obejmowało pomiary twardości metodą Vickersa oraz statyczną próbę rozciągania. Stwierdzono, że uzyskane odkuwki ze stopu Ma2 (Mg4AlZn) mają właściwości mechaniczne zgodne z warunkami technicznymi odbioru. Określono możliwe przyczyny powstałych wad odkuwek ze stopu WE43. Article microstructure analysis and mechanical properties of forged handles made of magnesium alloys: MgAl4Zn and WE43. Handles was manufactured in Zakład Obróbki Plastycznej Sp. z.o.o in Świdnik. Subjects of evaluation was forged using screw press F1736A and hammer MPM3150. Mechanical properties examination included: Vickers hardness test and tensile test. It was found that forging from Mg4AlZn alloy have comparable properties with technical requirements. Potential reasons of WE43 forgings was determined. Słowa kluczowe: stopy magnezu, kucie matrycowe, właściwości mechaniczne, mikrostruktura Key words: magnesium based alloys, die forging, mechanical properties, microstructure Wprowadzenie. Stopy magnezu już od pierwszej połowy XX wieku zaczęły być stosowane w przemyśle lotniczym. Z uwagi na ich małą masę właściwą i dobre własności wytrzymałościowe są interesującym materiałem dla producentów lotniczych starających się stale obniżać masę swoich produktów. Gęstość stopów magnezu wynosi zaledwie około 1,8 g/cm3 , podczas gdy dla stopów aluminium, które uznawane są za lekkie, wynosi ona około 2,8 g/ cm3, zaś dla st[...]

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[...]

Nowa generacja nadstopów typu γ-γ′ na bazie kobaltu DOI:10.15199/67.2018.8.3


  Głównym kierunkiem rozwoju silników lotniczych oraz turbin w energetyce jest zwiększenie ich temperatury pracy, a co za tym idzie wydajności prowadzącej do mniejszego zużycia paliwa oraz ograniczonej emisji CO2 [31]. Praca tych urządzeń związana jest ze szczególnie trudnymi warunkami, które wymagają od zastosowanych materiałów szeregu odpowiednich właściwości. Pełzanie, korozja wysokotemperaturowa, siarkowa oraz utlenianie są głównymi mechanizmami prowadzącymi do niszczenia w tego typu układach [26]. Obniżenie żywotności elementów może być spowodowane zastosowaniem niskiej jakości paliw, zanieczyszczonych siarką oraz związkami sodu i chloru. Środowisko takie sprzyja powstawaniu ciekłych soli, które są w stanie rozpuścić powłoki ochronne oraz intensyfikować proces degradacji materiału podłoża. Kolejnym niebezpieczeństwem wynikającym z pracy w agresywnym środowisku jest dyfuzja siarki do materiału podłoża i związana z nią korozja w atmosferze tworzących się siarczków [5, 13, 17]. Nadstopy na bazie niklu znalazły szerokie zastosowanie w konstrukcjach silników turbinowych, na elementy takie jak: łopatki turbin, dyski, komory spalania. Duży wachlarz aplikacji zawdzięczają swojej mikrostrukturze typu γ-γ′, która przyczynia się do dużej żarowytrzymałości tych materiałów [7]. Z drugiej jednak strony, ze względu na podatność nadstopów niklu na korozję wysokotemperaturową i siarkową, stosuje się specjalne międzywarstwy, będące elementem powłokowych barier cieplnych. Wadą tego rozwiązania jest cena oraz trudność technologii otrzymywania tego typu zabezpieczeń powierzchni [6, 33]. Następną właściwością, która jest pożądana w kontekście rozwoju żarotrwałych nadstopów jest temperatura topnienia. Odpowiedzią na niedoskonałości nadstopów na bazie niklu wydawał się być kobalt. Metal ten przy jednakowej gęstości wykazuje wyższą temperaturę topnienia (rys. 1). Odporność korozyjna kobaltu i jego stopów w atmosferze siarkowej or[...]

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[...]

The influence of yttrium addition on thermogravimetric behaviour of new Co-10Al-5Mo-2Nb Co-based superalloy DOI:10.15199/40.2018.11.1


  1. Introduction Creep resistant alloys were the most important group of materials and they decide about development direction of materials science in area of chemical and phase constituent designing, modelling and casting technology. Last decades showed that there are impassable limit such as melting temperature and in consequence the further development of those alloys seemed impossible. However, if it is not possible to exceed the melting temperature barrier, it is possible to increase the temperature range of the exploitation of alloys by modifying the alloys microstructure and introducing phases with more stability. The best cachet of such actions is development of new type of Co-based superalloys strengthened by L12 phase, the same like in γ/γ` Ni-based superalloys. This new group of alloys based not on the solid solution and carbide hardening effect such as Haynes 188 and Alloy 255, but is hardened by cubical precipitation of γ`- Co(Al,X)3 phase with L12 type of lattice (where X=W, Mo, Nb, Ta) [1-4]. This group of alloys is basing on Co-Al-W or Co-Al-(Mo,Nb,Ta) systems and the most intensively investigated are alloys such as Co-9Al-9W and Co-7Al-5Mo-2Nb (at. %), as an tungsten-fee alloys [1,4]. This structure is very similar to γ/γ` that is obtained for Ni-based superalloys. The consequences of this differences are related with mainly better creep properties of new L12 strengthened superalloys, but with lower oxidation resistance than conventional Co-based superalloys [5,6]. The oxidation properties of new Co-based superalloys at temperature above 800°C is steel relatively poor what is related with formation of complex multilayered oxide scale based on CoO, CoAl2O4 and CoWO4 oxides [7-16]. The oxidation resistance of Co- Al-W alloys improved by different alloying elements in many publications and revealed beneficial effect of Cr, Si, Ta, B etc. [8-11,13,16]. But in the case of tungsten free alloys [...]

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