Solid State Phenomena Vol. 197

Abstract: The Zr modified aluminide coatings is an alternative concept for replacing Pt-modified aluminide bondcoat for thermal barrier coatings. In the paper the influence of process parameters on the chemical composition and the thickness of aluminide coatings will be presented. The zirconia-doped aluminide coating was deposited on turbine blades made from ZS6K nickel superalloy during the low-activity CVD process. In recent work the influence of turbine blade geometry on thickness of coating was observed. The thickest coating was observed on the trailing and leading edge on the blade cross-section. In the conducted research, the light and scanning electron microscopy were used as well as the EDS chemical composition microanalysis.

Abstract: The subject matter of the paper is the quantitative evaluation of gaseous and shrinkage porosity in construction elements of a low-pressure aircraft engine turbine using quantitative metallography methods. The research material comprised blades and blade segments with a polycrystalline structure made of IN 713C and MAR M247 superalloys. One of the major problems that occur in the precision castings is their porosity: gaseous, which is the result of emission of dissolved gases from the superalloy during solidification, and shrinkage, being the result of shrinkage of the superalloy and of insufficient feeding of the interdendritic space. The developed practical procedure of selective measurement of gaseous and shrinkage porosity enabling the examination of precision castings made of high-temperature creep resisting nickel superalloys is presented.

Abstract: The aim of the present work was to determine the influence of air plasma spraying (APS) parameters on the microstructure of thermal barrier coatings (TBC) consisting on NiCoCrAlY bond coat and yttria - stabilized zirconia (YSZ) top coat. The scope of the investigation involved macroscopic observation and microstructural analysis by means of light microscopy (LM) and scanning electron microscopy (SEM). For the varied parameters of deposition process quantitative analysis of coatings thickness, porosity, oxide inclusions, metallic inclusions, globular inclusions and cracks were performed. The results of quantitative analysis allowed to establish which APS conditions influence the particular microstructural parameters of TBC coatings.

Abstract: The study describes the mechanism of structure formation in protective coating, growing on iron surface during hot-dip galvanizing. As a first stage of the galvanizing process, immediately after the iron sample has been dipped in galvanizing bath, a layer of frozen zinc is crystallizing on the sample surface. Next, as a result of isothermal solidification, an alloyed layer of the coating; composed of the sub-layers of intermetallic Fe-Zn phases, is formed. At the initial stage of the existence of the alloyed layer, another layer, that of undercooled liquid, is formed on the surface of iron dipped in liquid zinc. As a result of peritectic reactions under metastable conditions, the individual phases are born, forming sub-layers in the expected sequence of Γ1, δ and ζ.

Abstract: This paper provides an analysis of experimental research results and numerical simulation of grain microstructure of turbine blade castings made of the IN-713C nickel superalloy. The numerical simulation was carried out by applying the ProCAST program. The geometric description of model assemblies and three-dimensional ceramic mould enclosure was developed. The boundary conditions as well as the thermal and physical coefficients for alloy and ceramic shell mould were selected for simulation purposes. The parameters of nucleation law based on normal (Gaussian) distribution as well as the values of equation coefficients were established in order to determine the growth rate of dendrite tips for the IN-713C alloy, depending on the undercooling. The experimental verification of boundary conditions for numerical simulation was carried out by comparison with the results of temperature distribution measurements performed in the castings. The analysis of grain microstructure was conducted on the surface and cross-sections of castings. The forecasted grain microstructure was determined using the CAFE module (ProCAST software). The cast microstructure as well as the value of grain growth and nucleation coefficients, which were used for numerical simulation of solidification process, were experimentally verified.

Abstract: STEM-EDX and FIB-SEM tomography studies have been carried out to visualize three-dimensional morphology of the γ’ precipitates in different zones of ex-service turbine blade made of CMSX-4 single crystal superalloy. The results allowed the three dimensional analysis of the changes in microstructure of blade as resulting of operating conditions. Tomographic reconstructions provided quantitative data about γ and γ’ phase shape, size and volume fraction. It was shown that FIB-SEM tomography technique is suitable for 3D reconstruction of the objects of 100 nm in size or even smaller and thus enables the accurate quantitative microstructural analysis of this superalloy.

Abstract: The paper presents the preliminary results of technological tests of aluminizing using a new BPX Pro 325 S CVD equipment. Nickel based cast superalloys: IN 738 and MAR M200+Hf were used as a substrate material. The aluminizing processes with different parameters - pressure, HCl flow and time - were conducted. Microstructure analysis showed coatings whose thickness didn't exceed 20 µm. The authors showed that the changes of parameters values in the analyzed range weakly influenced the coating thickness (about 1-2 µm). It was proven, that it was necessary to decrease the flow of hydrogen chloride and perform the thermodynamic analysis.

Abstract: Some aspects of stochastic nature of the solidification processes are described. Firstly, the influence of the random grains nucleation on the cooling curves repeatability in the thin wall casting is presented. Secondly, the foundations of an average shape prediction for geometry of ele¬mentary diffusion field (concept of the Averaged Voronoi Polyhedron, AVP) are shown for the mi¬cro-modelling of the diffusion limited growth. Stochastic nature of the grains nucleation and growth is taken into account in the solidification modelling based on the Cellular Automaton technique (CA).

Abstract: This paper presents the microstructural characteristics of skull formed during melting of Ti-6Al-4V alloy with 0.5 wt% content of carbon in vacuum induction furnace using water-cooled copper crucible. The microstructure of ingot obtained as a result of skull melting is comprised of TiC carbides evenly distributed in the matrix, which consists of lamellar precipitations of α and β phases. The depth of carbon penetration towards the bottom skull was determined. At the plane section area of bottom skull, three clearly visible zones with diverse area fraction and sizes of carbides that occur in them were found. The effect of area fraction of carbides on hardness of individual zones at the bottom skull with reference to hardness of obtained ingot was also characterized.

Abstract: In this paper, the microstructural characteristics of cast TiAl-based intermetallic alloy were conducted, indicating the average grain diameter and interlamellar spacing as the parameters that determine their functional properties. The possibilities of forming these parameters by changing the crystallisation conditions were also shown. Methods for acquisition of images as well as detection of grain boundaries and lamellar precipitations of phases, necessary in the measurement of stereological parameters of the microstructure of these alloys, were presented