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Application of a quantitative materialography methods for an evaluation of a structure repeatability of turbine blades made of MAR M247 nickel-based superalloy

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The results of studies on inhomogeneity of gas and shrinkage pores volume fraction, size and shape (Tab. 1) as well as size and shape of grains (Tab. 3) revealed during macroscopic analysis of experimental low pressure turbine blades of a jet engine made of MAR M247 nickel-based superalloy were characterized in the present work. The procedures of macro- and microstructure evaluation described[...]

Quantitative evaluation of γʹ phase in CMSX-4 superalloy

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The microstructure of nickel-base superalloys determines their mechanical behaviour. The strength of Ni-base superalloys is dependent on such factors as volume fraction, size, coarsening rate, and composition of γʹ phase precipitates [1]. The content and size of γʹ phase precipitates embedded in a cubic face-centred γ matrix can be adjusted by the alloy design and heat treatments. The composition of the ordered γʹ precipitates does differ, i.e. Ni3(Al, Ti, ...), and depends on the alloy composition and processing [2]. The characterization of γʹ phase precipitates in different nickelbased superalloys has been the subject of extensive research work. Volume fraction of the γʹ phase in Ni-base superalloys is a significant element influencing on working out the superalloys chemical compositions [3]. MATERIAL The measurements of γʹ phase precipitations were carried out on a monocrystalline cylindrical bar of 8 mm diameter made of CMSX-4 nickel-base superalloy [4]. The bar was cast in Laboratory of Material Research for Aircraft Industry in Rzeszów. The material was investigated in the as-cast condition. IMAGE ACQUISITION AND ANALYSIS OF γʹ PHASE PRECIPITATES The bar intended for investigations was cut perpendicularly to the main axis. The procedure of metallographic specimen preparation was described in details in Table 1. Quantitative metallography of CMSX-4 requires the revealing of γʹ precipitates by means of an appropriate etching conditions selection as well as use of appropriate image acquisition in order to observe the γʹ precipitates and register the images of the superalloy microstructure with them. In the previous work two etching methods of the γʹ phase precipitates were described [5]. For a quantitative evaluation of the precipitates etchant caused their etching and leaving the γ matrix is better, so in the ca[...]

Application of EBSD technique to investigation of modern materials for aero engines turbine blades

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Turbine blades, vanes, and other parts of aero engines exposed to high temperature are produced of nickel-based superalloys via investment casting. Directional solidification (DS) allows obtaining excellent mechanical properties of blades [1]. Because turbine blades are flight safety parts, they must be free of any defects. However, directional solidification is very complex and many casting defects may appear during this process [1]. The commonly defects in DS and single crystal (SX) castings are freckles [1÷6] and stray grains [7÷9]. Freckles are casting defects that appear on the surface of DS or SX castings in the form of long chains of equiaxed grains aligned parallel to gravity [1÷6]. Freckle dimensions depend on casting dimensions: the length is usually the same as the casting, but the width is from one to several millimeters. Freckles are enriched with elements segregated to the liquid phase during solidification [2÷4]. Compared with the freckle-free part of a casting, freckled areas are characterized by an increased carbide content, γ + γ′ eutectics, and porosity [4]. Freckle formation is attributed to thermosolutal convection and buoyancy forces in the mushy zone, which are in turn caused by density inversion in the interdendritic liquid [5]. The tendency for various superalloys to freckle is characterized by the freckling index F, which depends on the chemical composition [1]: F C C C C C C = + + - + Ta Hf Mo Ti W 1 5 0 5 0 5 1 2 . . . . Re (1) where CTa, CHf, CMo, CTi, CW, and CRe are the concentration (wt %) of tantalum, hafnium, molybdenum, titanium, tungsten, and rhenium, respectively. In case of F > 1, the freckling tendency is low. The density inversion of interdendritic liquid in the mushy zone is caused by strong segregation of some elements (i.e., W, Re) into the solid phase. Therefore, during directional solidification, these elements are depleted in the liquid alloy in interdendr[...]

Evaluation of sialon ceramics - crack resistance via surface stereometry and multifractal analysis

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One of the most frequently applied parameters in quantitative fractography is the fracture area development coefficient RS. It provides, inter alia, the information on the fracture formation mechanism and the energy consumed for its formation. Sialon ceramics studies confirm this viewpoint [1]. For selected parameters RS qualitative dependencies were developed. A proportional relation betwee[...]

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