Evolution of the beta Phase Flux Dissolution during Quasicrystal Formation

This study focuses mainly on the veri cation of a peritectic reaction during the crystallization of quasicrystals. The and phases apparently provide the necessary material for crystallization of the quasicrystalline phase. We present results of an experimental visualization of the evolution of the ux dissolution process of the high temperature phase. Solidi ed droplets of the phase, formed primarily by the surface tension of the liquid within a bubble or a shrinkage, after crumbling during the ux dissolution may contribute to the quasicrystal formation process according to a peritectic reaction: c + + L ! , where c denotes the crumbled phase immersed in the liquid

Correlation between the Dendritic Structure and Lattice Parameter of γ′- Phase in Single-Crystalline Turbine Blades Made of Superalloys

The dendritic structure and the distribution of the γ′-phase lattice parameter (aγ′) along selected lines of the longitudinal section in a model single-crystalline blade made of CMSX-4® nickel-based superalloy were studied. It was established that there is a correlation between the value of the aγ′ and the predomination of initial or ending fragments of the secondary dendrite arms. It is most noticed for the areas where the dendrite growth conditions are similar to steady. They are located in the center and near the root’s selector extension (SE) area. The correlation has been related to the dendritic segregation mechanism. It was shown that in the single-crystalline blades obtained by the directional crystallization using a spiral selector, the “walls” of the primary dendrite arms that grow at a low angle to the blade axis are created. It was found for the first time that the value of the lattice parameter aγ′ is decreased near such “walls”. Additionally, it was found that competitive growth of the dendrites may occur at a distance of even several millimeters from the bottom surface of the root. The first-time applied X-ray diffraction measurements of aγ′ made in a single-pass along the line allow the analysis of the dendritic segregation in the whole blade cast

The influence of the cooling bores on the dendritic structure and crystal orientation in single-crystalline cored CMSX-4 turbine blades

Single-crystalline cored CMSX-4 blades obtained at a withdrawal rate of 3 mm/min by the vertical Bridgman method were analyzed. The dendritic structure and crystal orientation near the cooling bores of the blades were studied through Scanning Electron Microscopy, the X-ray diffraction measurements of and angular components of the primary crystal orientation, and the angular component of the secondary crystal orientation. Additionally, the primary arm spacing (PAS) was studied in areas near and far from the cooling bores. It was found that in the area approximately 3–4 mm wide around the cooling bores, changes occurred in the , , and angles, as well as in the PAS. The PAS determined for the transverse section of the root and the linear primary arm spacing (LPAS) determined for the longitudinal sections, as well as their relationship, have been defined for the areas located near the cooling bores and those at a distance from them. The vertical temperature gradient of 29.5 K/cm was estimated in the root areas located near the cooling bores based on the PAS values. The value of this gradient was significantly higher compared to the growth chamber operating gradient of 16 K/cm. The two-scale analysis applied in this study allowed for the determination of the relationship between the process of dendrite array creation proceeding on a millimeter scale, which is associated with the local changes in crystal orientation near the cooling bores, and that which proceeds on a scale of tens of millimeters, associated with the changes in crystal orientation in the whole blade cast

Mould walls inclination and dendritic morphology of CMSX-4 blades airfoils

The airfoils of single-crystalline turbine blades were studied. The blades made of industrial CMSX-4 superalloy were obtained by the Bridgman technique. Five different withdrawal rates (1–5 mm/min) were used. Series of as-cast samples were prepared by cutting the airfoils at different distances from the blade root. The metallographic sections, prepared for each cutting planes, were subjected to scanning electron microscopy observations and Laue diffraction studies. Macrostructure images of whole area of airfoil cross-sections were obtained by stitching several obtained SEM images. Morphology of dendrites in different area of cross-sections were analysed. The crystal orientation of each sample were determined by analysis of Laue pattern. It was found that the morphology of dendrites changes in the area, where the dendrite growth is limited by inclined mould walls

Primary crystal orientation of the thin-walled area of single-crystalline turbine blade airfoils

The thin-walled airfoil areas of as-cast single-crystalline turbine blades made of CMSX-4 superalloy were studied. The blades were produced by the industrial Bridgman technique at withdrawal rates of 2, 3 and 4 mm/min. The angle between the [001] crystallographic direction and blade axis, related to the primary orientation, was defined by the Ω-scan X-ray diffraction method at points on the camber line located near the tip of an airfoil and at points of a line located in parallel and near the trailing edge. Additionally, primary crystal orientation was determined by Laue diffraction at the selected points of an airfoil. The influence of mould wall inclination on the primary crystal orientation of the thin-walled areas is discussed. The effect of change in the [001] crystallographic direction, named as "force directing", was considered with regard to the arrangement of primary dendrite arms in relation to the trailing edge and the camber line. It was stated that when the distance between the mould walls is less than the critical value of about 1.5 mm the "force directing" increases as the distance between the walls of the mould decreases. The effect may be controlled by selecting an appropriate secondary orientation using a seed crystal in the blade production process. The model of dendrite interaction with the mould walls, including bending and "deflection", was proposed

Characterization of casting defects in the single crystal turbine blade airfoil

In the paper turbine blades made from single crystal CMSX-4 superalloy were investigated by X-ray diffraction methods (topography, -scan mapping) complemented by scanning electron microscopy observations. By the X-ray diffraction topography method several misorientation defects were visualized as well as dendrites arrangement. It was discussed that tip of the airfoil and thin walled area of the turbine blades located near the trailing edge can accumulate more growth defects than other airfoil part, due to the complex shape of the mould

Crystal perfection studies of single crystal superalloy turbine blades by X-Ray diffraction methods

In the paper the crystal structure of single crystal CMSX-4 blade casts, applied in high pressure turbine of aircraft engines was analyzed. The longitudinal section of blade, cast at withdrawal rate of 3 mm/min was used as a sample. During the conducted research, following X-ray diffraction methods were applied: EFG -scan, Auleytner X-ray topography and analysis of diffraction reflex profile (“rocking curve”). The authors determined crystal orientation in entire blade casts on the basis of set criterion concerning values of angle — deviation of [001] direction from the direction of cast withdrawal. Conclusions concerning the crystal structure quality of the blade were drawn based on results from three different research methods. Local changes in crystal orientation on the surface of blade cast, also areas with significant structure defect degree and the presence of internal stresses were characterized

Surface Decorations of Al-Cu-Fe and Al-Cu-Co Single Quasicrystals

We studied surface decorations of faceted icosahedral Al Cu Fe and decagonal Al Cu Co single quasicrystals by the scanning electron microscopy using primary and secondary electrons. Both types of single quasicrystals exhibited decorations on their facets, however the character of the decorations was totally di erent. Three kinds of decorations has been developed. On icosahedral Al60Cu26Fe14 quasicrystals we found three kinds of decorations: cellular, cavity type and fractal-like. There was no evident di erence in chemical composition between the inner dodecahedra and the decorations of all types. Surface decorations found on decagonal Al73:5Cu17:5Co9 quasicrystals formed a kind of irregular dendritic stars on the separate bright islands

The low-angle boundaries misorientation and lattice parameter changes in the root of single-crystalline CMSX-4 superalloy blades

The relationship between the angles of misorientation of macroscopic low-angle boundaries (LABs) and changes in the lattice parameter of the 0-phase around the LABs in the root of singlecrystalline (SX) turbine blades made of CMSX-4 superalloy were studied. The blades with an axial orientation of the [001] type were solidified using an industrial Bridgman furnace with a 3 mm/min withdrawal rate. X-ray diffraction topography, the EFG W-scan X-ray diffraction method, scanning electron microscopy, and Laue diffraction were used to study the thin lamellar samples with a thickness of 0.5 mm and orientation of the surface perpendicular to the [001] direction. It is found that in the areas with a width of a few millimetres around LABs, decreases in the lattice parameter of the 0-phase occur. These lattice parameter changes are related to the internal stresses of the 0-phase caused by local changes in the concentration of alloying elements and/or to the dendrite bending near the LABs. X-ray topography used on two surfaces of thin lamellar samples coupled with the lattice parameter measurements of the 0-phase near the LAB allows separating the misorientation component of LAB diffraction contrast from the component and visualising the internal stresses of the 0-phase

Dendrite growth in selector-root area of single crystal CMSX-4 turbine blades

The single crystal turbine blades made of CMSX-4 nickel-based superalloy were studied. The turbine blades were obtained by the Bridgman technique with withdrawal rate of 5 mm/min. The samples, cut-off from root part of blades and containing the fragment of the selector, were studied. The effect of selector geometry on the dendrites growth and defects formation in the selector-root area of the blade were analyzed. The Laue diffraction, scanning electron microscopy, and X-ray diffraction topography were applied. It was found that, during crystallization of the selector, the dendrite cores, after reaching the surface of mould, may bend, if the angle between dendrite cores and the mould surface was equal to 12 . When the angle was equal to 24 the growth of dendrites has been stopped. It can be stated that the defects, which appeared in the selector were inherited by the root part