Browsing by Subject "superalloys"

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Access status: Open Access ,
Hot cracking of nickel-based superalloy turbine blade
(2015) Rakoczy, Łukasz; Tuz, Lechosław; Pańcikiewicz, Krzysztof
The aim of this study was to present the hot cracking behavior of a blade originating from a turbine blade segment. The crack was induced by a gas tungsten arc welding process, and the research material was a MAR-M247 nickel based superalloy. This alloy is considered to be difficult to weld because of its high tendency to crack. Light microscopy and scanning electron microscopy show the occurrence of cracking in the melted zone, heat-affected zone, and base alloy. A scanning electron microscopy investigation revealed that cracks are propagated by stresses and liquation of the low temperature constituent.
Access status: Open Access ,
Przyczyny powstawania niedolewów w supercienkościennych elementach odlewanych z nadstopów na osnowie niklu
(2010-07-09) (Data obrony: 2010) Cygan, Rafał
Wydział Odlewnictwa
The research described in this doctoral thesis is a result of a wider project aimed at the description of physical and chemical phenomena occurring at the metal – ceramic mold and ceramic mold – environment boundary during the casting and solidification of investment castings (Research and development project R15 008 03 realized by the AGH in Cracow 2007 – 2010). The physical and chemical phenomena occurring at the metal-ceramic mold interface during the pouring of liquid metal into the mold influence the casting process significantly, and can constitute one of the main reasons for the forming of defects, including misruns and nonfills. In order to efficiently model and, as a result, optimize those technological processes, a series of experiments aimed at the investigation of metal-mold interface phenomena was conducted. The phenomenon of wetting of ceramic materials by liquid metals plays a major role in technological processes involving ceramics and liquid phase. The characteristic used most often to describe the degree of ceramic wetting by a liquid metal is the wetting angle $\theta$. The thermal and physical properties of shelling (molding) materials have a decisive influence on the structure and properties of a casting. That is so because they have the decisive influence on the thermal exchange processes between the casting and the ceramic mold. The exact importance of such properties can be especially appreciated when performing computer simulations of the casting solidification and cooling processes. The solidification process creates the original, primary structure, and the cooling of an already solidified casting creates the final structure of the casting alloy. The course of these processes, which decides about the obtained structure and properties of the casting, is largely dependant on the rate, at which the heat is being removed from the solidifying alloy. Very complicated geometries (super-thin sectioned castings with turbine blade sections measuring at times as little as 0,2 mm), less than perfect casting properties of superalloys and very strict quality standards contribute to the fact, that scrap rates for such castings can be very high. The purpose of a comparison between computer simulations and real-life experiments was to define the preliminary basic physical and chemical parameters, such as the thermal conductivity coefficient between the ceramic mold and insulation or between the ceramic mold and the environment; as well as to perform an initial verification of the ProCast simulation suite ceramic and thermally insulating materials database.