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Analiza profilowa stali 316L po procesie azotowania jarzeniowego

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Badaniom poddano stal austenityczną gatunku 316L po azotowaniu jarzeniowym w temperaturze T = 430°C przez t = 8 h, oraz po czterech różnych wariantach rozmieszczenia próbek w komorze jarzeniowej. Próbki przeznaczone do azotowania zostały umieszczone na katodzie, na podłożu odizolowanym zarówno od katody jak i anody, czyli w tzw. "potencjale plazmy" oraz dodatkowo próbki umieszczone na katodzi[...]

Korozja lokalna azotowanej stali 42CrMo4 w zakwaszonym roztworze zawierającym chlorkowe jony

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W pracy przedstawiono potencjokinetyczne krzywe polaryzacyjne stali 42CrMo4 oraz żelaza Armco po procesie azotowania jarzeniowego w atmosferze N2/H2 w temperaturze 520°C. Badania potencjokinetyczne wykonano w zakwaszonym (pH = 4) 0,5M roztworze siarczanowym zawierającym jony Cl- o stężeniu 0,02M. Wykorzystując tzw. metodę postępującego ścieniania analizowano kolejne warstwy stali posuwając się od zewnętrznej powierzchni w głąb materiału. Zastosowanie tego typu metody pozwoliło wykreślić głębokościowe profi le wartości potencjałów nukleacji wżerów. Słowa kluczowe: azotowanie jarzeniowe, stal niskostopowa, korozja wżerowa, profi l głębokościowy Pitting corrosion of glow-discharge nitrided AISI 4140 steel in acidifi ed solution containing chloride anions Electrochemical polarization characteristics of glow-discharge, high-temperature (520°C) nitrided AISI 4140 type steel and Fe-Armco are presented in the paper. The potentiokinetic tests were carried out in acidifi ed, 0.5M sulphate (pH = 4) solution containing 0.02M of chloride ions. A method of consecutive thinning of surfacial layers of the treated steel has been applied to determine the depth profi les of its pitting potentials. Keywords: glow-discharge nitriding, low-alloyed steel, pitting corrosion, depth profi le ochrona przed korozja 4-5/2010 XIX Ogólnopolska Konferencja Naukowo-Techniczna SYSTEMY - MATERAŁY - POWŁOKI A N T Y K O R O Z J A 1. Wstęp Azotowanie jest jedną z ważniejszych technologii istotnie podwyższających właściwości eksploatacyjne elementów maszyn [1]. Azotowanie powierzchni stopów żelaza przyczynia się do wzrostu ich właściwości użytkowych takich jak: twardość, odporność na zużycie przez tarcie czy wytrzymałość zmęczeniowa [2]. Jednak warstwy azotowane mają nie tylko korzystne właściwości mechaniczne, zapewni[...]

Influence of strain rate and deformation temperature on the microstructure of Inconel X750 superalloy

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A fundamental feature of plastic deformation is the homogeneity of strain distribution. It is commonly accepted that at low temperatures and high strains, flow localization may develop and affect the material ductility. On the other hand, hot-deformation at intermediate temperatures may also result in localized plastic flow and non- -homogenous deformation. Flow localization, as a result of substructure instability and collective motion of a large number of dislocations characterizes coarse slip or shear banding, Luders bands and the Portevin-LeChatelier effect. Kink bands and mechanical twins may also be considered as a individual form of flow localization. Coarse slip is usually used to describe the localized flow within individual grains, whereas shear bands traverse many grains very often without any significant relation to the position of easy glide systems plane. In pure metals and single phase alloys, shear bands have been found to be preferential sites for the nucleation of both static and dynamic recrystallization. It is widely believed that in age hardenable alloys, shear bands and dislocation substructure produce preferred sites for nucleation of precipitates, thus enhancing the nucleation. These same features also are believed to enhance the particle growth rate during hot deformation as a result of higher vacancy concentration produced by intensive straining as well as increased dislocation pipe diffusion. The study of processes which are associated with dynamic aging of supersaturated solid solution during hot deformation may turn out to be very complicated because of the mutual interaction between dynamic precipitation and the structure resulting from the deformation process. The contribution of flow localization to the strain hardening or flow softening and the flow stress-strain behaviour during hot deformation of precipitation hardenable alloys is still a subject of extensive research. The interaction between [...]

Microstructural evaluation of CMSX-4 superalloy single crystal castings of various geometry

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The turbine blades and combustion chamber belong to critical parts of aircraft jet engines. They work under extreme conditions: very aggressive corrosion environment, high mechanical and thermal stresses. Therefore the creep resistance is very important criterion for selection of critical parts materials and methods of their production [1]. Advances in turbine blade manufacturing were mainly caused by implementation of directional crystallization in casting process. This method enabled obtaining columnar grains in castings, elongated in the main axis direction. This kind of microstructure with no transverse grain boundaries provides higher creep resistance of castings. It was found that much better properties characterize single crystal castings. Casting process of single crystal blades is analogous to casting process of blades having columnar grains. The difference is in the beginning of crystallization process - only one grain properly oriented is selected for further growth [2÷5]. The main parameters controlling single crystal casting quality are temperature gradient and withdrawal rate of mould (vw). Too high cooling rate causes crystallization of grains in front of interface between liquid and solid phases. Whereas too slow mould removal from the heating zone leads to excessive microstructural segregation and defects formation in castings. It is considered that higher temperature gradient (in the accepted range) contributes to improvement of casting quality. The most often applied values of temperature gradient are in the range of 3÷6.5°C/mm and withdrawal rate of about 5 mm/min [6÷12]. Microstructure of most nickel superalloys is mainly composed of gamma (γ) and gamma prime (γ′) phases. The γ′ phase (Ni3(Al, Ti)) - primary strengthening phase - is coherent with the matrix - γ phase. The close match in matrix lattice parameter (~0÷1%) combined with the chemical compatibility allows the ^[...]

Influence of manufacture conditions on the properties of CMSX-4 single crystal castings

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Single crystal turbine blades of the first turbine stages were casted of nickel and cobalt superalloys. Beginning of their production requires significant capital expenditure. It also causes many technological difficulties. Thus, it is essential to have suitable set of casting equipments, vacuum furnaces for the heat treatment and last but not least all the processing know-how. Therefore, only a few foundries are capable to manufacture such turbine blades. Mass production of these single crystal parts of an aircraft engines so far has not been implemented in Poland. The studies performed allow to realize a production technology for single crystal turbine blades casting in Research and Development Laboratory for Aerospace Materials of Rzeszów University of Technology. In practice, precise single crystal casts are obtained via directional crystallization with the use of a block starter and spiral grains selector in a ceramic mould. In the process of monocrystallization the ceramic mould is withdrawn from the heating zone of the furnace to grow the blade. The grains in the cast’s starter grow in a columnar way against their spiral selector. Only one grain survives during competitive growth in the spiral grain selector. The phenomenon of grains growth ‘competition’ is the basis for this process [1÷3]. A single crystal grain nucleus growing from the spiral selectors is the beginning of the single crystal crystallisation consisting in dendrites growth in three orthogonal crystallographic orientations [001]. The direction of [001] axis is parallel to single crystal’s growth axis [4÷10]. Intensive examinations of quality assessment methods were carried out in recent years for single crystal casts of a second generation[...]

Crystallographic orientation of aircraft engines turbine blades made of CMSX-4 single crystal nickel superalloy

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The aircraft engines turbine blades are considered to be so-called Flight Safety Parts (FSP). They are subject to exceptional requirements related to the production process and quality control. They feature narrow dimensional tolerances and perfect surface quality. Requirements with regard to metallurgical purity, permissible casts’ gas and shrinkage porosity, crystallographic orientation, phase composition and relative volume of strengthening phases as well as heat resistance and high-temperature creep resistance are also strict. Single crystal blades of nickel superalloys belong to the group of products most difficult to produce and meeting strictest reliability requirements [1, 2]. Blades of the first turbine stages and guide vanes made of nickel and cobalt superalloys are subject to continual modification both in terms of their chemical composition, heat treatment as well as manufacturing technology. The manufacture of precise casts of single crystal blades of complex shape of the blade and locking piece is a difficult process, belonging to highly advanced technologies. This applies also to the technology of ceramic moulds exposed to especially difficult conditions, including increased time of interaction with a liquid metal. Single crystal blades feature the highest hightemperature creep resistance as compared with blades obtained in the process of directional crystallisation or conventional casts of microstructure composed of equiaxial grains [2÷5]. Single crystal superalloys’ properties depend on the crystallographic direction taken for studies. Hence the assessment of single crystal casts’ quality is related to determination of their crystallographic orientation, which provides the basis for mechanical properties analysis. It has been assumed on the basis of literature review, that the value of the angle of direction [001] deviation from the angle of single crystal superalloys growth cannot exceed 15°.[...]

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