Wyniki 1-4 spośród 4 dla zapytania: authorDesc:"Łukasz Frocisz"


  Hypereutectoid cast iron alloys such as G200CrNiMo4-3-3 have a very complex microstructure. The microstructure of these alloys is transformed ledeburite, perlite and secondary carbides precipitates. Proeutectoid carbides can precipitate in different morphologies and areas such as grain boundary precipitates, intergranular precipitates and Widmanstatten shape. Usually Widmanstatten microstructure is treated as a negative microstructural component, because of the possibility of stress concentration on the top of Widmanstatten carbides needles which adversely affect on material properties such as tensile strength and fracture toughness. Tribological measurements show a certain correlation between the amount of Widmanstatten carbides and friction coefficient of the material. Tests presented in this work were performed by the use of T05 block-on ring tribological tester. Various times and loads were used during tests. In addition a pin on disc tests in 750 °C were performed. Two variants of heat treatment, designed to changing the volume fraction and shape of secondary carbides precipitated in Widmanstatten shape, were used. It has been shown that the friction coefficient, increases with a volume fraction and average surface area of Widmanstatten carbides precipitations. Caused by the heat treatment changes in shape of Widmannstatten cementite precipitations results in a decrease in average friction coefficient. Keywords: friction coefficient, cast steel, proeutectoid cementite, Widmanstatten microstructure WPŁYW WYDZIELEŃ CEMENTYTU W UKŁADZIE WIDMANSTATTENA NA WŁASNOŚCI TRIBOLOGICZNE MATERIAŁÓW ODLEWANYCH Nadeutektyczne odlewane stopy żelaza, takie jak staliwo G200CrNiMo4-3-3 mają bardzo złożoną mikrostrukturę, składającą się z ledeburytu przemienionego, perlitu i wydzieleń węglików drugorzędowych. Węgliki drugorzędowe mogą wydzielać się w różnych miejscach i morfologiach, takich jak: wydzielenia na granicach ziarn, w układzie Widmanstattena o[...]

Microstructure and hardness of aged Ti-10V-2Fe-3Al near-beta titanium alloy DOI:10.15199/28.2017.4.1

  1. INTRODUCTION Progress in aerospace is linked with the development and application of the new structural materials. Those materials are characterized by higher strength, lower density and good resistance to environmental factors also at high temperature, while compared with materials which are in use. With the development of materials new technologies are also developed for their processing. They allow the use of the material in real components and lead to improved properties of the elements design, materials savings and reduced manufacturing cost. This applies to both: new and conventional materials used in the construction of aircraft engines [1÷3]. The near-β titanium alloys are characterized by good ductility and low susceptibility to cracking, which classify them as alloys suitable for deformation [4]. One of them, Ti-10V-2Fe-3Al alloy, can be used at elevated temperature and under variable loads, is resistant to atmospheric and sea water corrosion as well [5]. All these aspects along with weight savings facilitated its use in forged components of aircraft structures. According to the literature data, the morphology of microstructure constituents and thus operational properties of the near-β titanium alloys may be changed suitably controlling the heat treatment parameters (temperature and time). Solution treatment from the temperature, where both phases: α and β exist allows to create globular precipitates of phase α. Heating the alloy to a temperature above the phase transformation temperature and the subsequent cooling below the temperature of β phase stability makes possible the precipitation of α phase in the form of needles in an amount dependent on the heat treatment parameters [4]. It is worth to notice that during cooling of near-β titanium alloys the martensitic transformation is possible. This transformation is induced by previous plastic deformation, when the α phase volume fraction materia[...]

Microstructure and phase composition characterization of a Ti–Al intermetallic alloy DOI:10.15199/28.2016.6.8

  Intermetallic Ti-Al alloys are characterized by the unique set of properties which makes these alloys a prospective material for the energy, automotive and aviation industries. The mechanical properties of a intermetallic alloys are strictly related to the microstructure. The refinement of the microstructure can be obtained by the manufacturing process, alloying additions and heat treatment. Microstructure characterization and knowledge about phase transformation mechanisms and their temperature ranges allows to change properties of the bulk material. The aim of this study was the microstructure and phase composition characterization of intermetallic Ti48Al2Cr2Nb alloy. The microstructure was examined using the light and scanning electron microscopy. Identification of phases and their temperature stability were determined by X-ray diffraction, differential dilatometry and calorimetry investigation. The oxidation process was determined by high temperature X-ray diffraction and the thermogravimetric method. The alloy after annealing has a duplex microstructure with precipitations of α2 phase in the γ matrix. Dilatometry and calorimetry allowed us to define the stability of each phase. At first the enriched in chromium α2 phase dissolved, after that the regions depleted in chromium were transformed, and above 775°C the microstructure was only the γ phase. Gamma phase was transformed above 1100°C, the end of transformation γ → α was evaluated as 1250°C. The oxidation investigations allowed us to show that the oxidation process started at 700°C by the oxide layer formation, which was stable till 900°C. Above this temperature the oxide layer started to grow. Key words: intermetallic alloy, microstructure, phase composition, Ti48Al2Cr2Nb, titanium alloy.1. INTRODUCTION Titanium intermetallic alloys due to their unique properties could find possible applications in a wide range of the industries, especially when th[...]

Thermal range of cementite occurrence in hypereutectoid alloys with controlled C, Cr and Mn content DOI:10.15199/28.2018.1.5

  1. INTRODUCTION Hypereutectoid steels are characterized by the high carbon content. High amount of the carbon, above the eutectoid point, resulted in the formation of the secondary carbides in microstructure. This precipitations in a great way influent on the mechanical properties [1÷4]. Cementite is a metastable iron carbide with the rhombic crystallographic structure and structural formula M3C. In cementite particles also could dissolve Cr, Mn, V, Mo, Ti, especially in the case of alloyed steels. It have been shown that the Cr and Mn dissolved in pure cementite increases the temperature of the cementite formation. Additionally, this elements increase the cementite hardness by approximately 3.5 GPa for the 20 mass % of Cr and by 5 GPa for 30 mass % of Mn. The thermal stability of cementite is more significant for the Cr addition than Mn. This alloying elements also increases the Young module of the cementite. It should be noted that with the increase of the alloying elements content also increase a linear expansion coefficient of cementite. Manganese increases resulted in a constant increase of α coefficient with temperature, in pure cementite this relation is opposite. Whereas the 20% mass Cr addition stabilized the α at value 25.5×10-6 K-1 at the temperature range from RT to 1273 K (for a pure cementite 16.2×10-6 K-1 above 481 K). Titanium addition to pure cementite resulted in its destabilization and formation of more thermodynamic stable titanium carbides [5÷7]. It should be noted that the relevant are thermodynamic correlations between the cementite and ferrite/austenite. Enthalpy of the cementite formation in a Fe-C system is about 27.0 kJ/mol [6]. In a Fe-C system in a traditionally used iron alloys, cementite is a part of the eutectoid mixture or could be formed as a precipitations from the liquid/austenite/ferrite. In a case of the eutectoid transformation two main mechanisms of the perlite formation were f[...]

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