Wyniki 1-3 spośród 3 dla zapytania: authorDesc:"TOMASZ KOZIEŁ"

Mikrostruktura i właściwości nowych martenzytycznych stali 12 % Cr dla nadkrytycznych bloków energetycznych

Czytaj za darmo! »

Badaniom mikrostrukturalnym poddano martenzytyczną stal VM12 zawierającą 12 % chromu, opracowaną przez COST 522 dla elektrowni konwencjonalnych pracujących w temperaturze około 625÷650 °C. Analizowano mikrostrukturę stali w stanie dostawy, po długotrwałym (29 000 godz.) wyżarzaniu, jak i pełzaniu w temperaturze 625 °C. Ilościową analizę obrazu na elektronomikroskopowych zdjęciach mikrostruktury prowadzono w celu określenia gęstości dyslokacji wewnątrz listew martenzytu/podziarn, wielkości podziarn, jak i wielkości (średnia średnica) oraz kształtu (współczynnik kształtu) wydzieleń. Fazy wtórne identyfikowano przy wykorzystaniu selektywnej dyfrakcji elektronów. Badania za pomocą TEM wykazały, że zarówno długotrwałe wyżarzanie, jak i pełzanie w temperaturze 625 °C powoduje zmiany w mikr[...]

The microstructure of rapidly quenched Fe-Cu-based alloy with a liquid miscibility gap

Czytaj za darmo! »

Although superior properties of metallic glasses such as high strength and high elastic limit, its application is very limited due to highly localized shear banding [1, 2] and thus very low ductility. Ductility of metallic glasses could be improved by formation of composite materials consisting of crystalline phases dispersed in the amorphous matrix. Such composites might be produced by in-situ formation of the crystalline phase. In 2004 Kündig et al. [3] for the first time showed two-phase amorphous structure in metallic system. The system he studied included one pair of elements with high positive heat of mixing (La- Zr) while negative heat of mixing of the other elements (Al, Cu, Ni) to both, La and Zr. Positive heat of mixing between two major elements forced liquid phase separation into La-rich and Zr-rich melts during cooling of the homogeneous melt below critical temperature required for decomposition. Negative heat of mixing of the other alloying elements to La and Zr, increased glass forming ability of both separated melts. Rapid cooling enabled formation of two glassy structures, La-rich and Zr-rich, with surface fractal microstructure [3]. This work initiated research of systems based on elements with positive heat of mixing and thus possible formation of two amorphous phases. Several two-phase metallic glasses were reported up to date including Y-Ti-Al-Co [4], Ni-Nb-Y [5], Ag-Cu-Zr [6], Cu-Zr-Al-Y [7] and Nd-Zr-Al-Co [8]. Since two-phase amorphous structure was obtained, one can expect different thermal stability of both glassy phases. Thus formation of amorphous-crystalline composites with nanocrystalline structure is possible by partial devitrification of one of the amorphous phases. This work deals with another system based on two elements, namely Fe and Cu, with positive heat of mixing as high as +13 kJ/mol [9]. Although the Fe-Cu phase diagram does not contain a liquid miscibility gap, Turchanin et al. [10] p[...]

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[...]

 Strona 1