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A. Szczotok

Abstract

Microstructural characterization is an important tool to optimize the properties of engineering materials. Quantitative metallography is a common technique, which provides three-dimensional estimations of phases and structure elements from two-dimensional images. Metallography has been described as both a science and an art [1].

Superalloys are high-performance alloys which exhibits excellent mechanical strength and creep resistance at high temperatures, good surface stability, and corrosion and oxidation resistance. Temperature and corrosion resistant materials such as nickel-based superalloys are prepared mostly with standard metallographic techniques. However, the results can be significantly improved by using finely graded CMP (chemical mechanical polish) polishing solutions on a high napped polishing pad.

Sample preparation requires a certain degree of skills and experience, due to the high chemical resistance of most superalloys. Some chemical solutions are able to dissolve the γ matrix and recover the γ' residue, and some others solutions can be used to obtain a contrary effect – dissolve the γ' phase precipitates and recover the γ matrix residue. The aim of the presented research is to describe qualitatively and quantitatively the as-cast microstructure of CMSX-6 SC superalloy. The author’s attention has been concentrated on the γ' phase precipitates morphology. The results of using optical and scanning electron microscopy (SEM) are presented.

Open access

A. Szczotok, J. Pietraszek and N. Radek

Abstract

The study describes the influence of a surface modification in cored, thin-walled castings of blades from IN-713C nickel superalloy on γ' phase precipitates. The blades were produced by using the investment casting process in the laboratory conditions as parts for a low-pressure turbine rotor. The microstructural observations of the γ' phase precipitates on the cross sections of the blades were performed. The observations were followed by quantitative metallography evaluation, and finally, a comparison of the precipitates between one blade with the conventionally applied ceramic core and one with the core covered layer contained a surface modifier (5% of CoAl2O4) was made.

Open access

A. Szczotok, J. Nawrocki and J. Pietraszek

Abstract

In the study the wall thickness of ceramic shell mould influence on (γ + γ′) eutectic in the IN713C nickel-based superalloy airfoil blade casting was described.

Two castings formed as a blade from two wax pattern assemblies were analysed. In the experiment in one pattern the thick ceramic layer was obtained on pressure side and in another one on suction side of the airfoil blade. The microstructure of the cross-sections of the castings were observed on polished and etched metallographic specimens. The microstructure and phases chemical compositions of specimens was analyzed by using the scanning electron microscope Hitachi S-4200 equipped with EDS. It was established, that wall thickness of ceramic shell mould affect size, shape and volume fraction of (γ + γ′) eutectic islands in airfoil blade made from IN713C superalloy.

The analysis was provided in accordance to the typical statistical methodology [1].

Open access

J. Pietraszek, A. Szczotok and N. Radek

Abstract

The primary objective was to test a usefulness of the specific fixed-effect model for the analysis of quantitative relationships gathered from the image analysis of the material microstructures. The dataset was obtained from the investigation of turbine blades made from superalloy IN713C. The analysis based on the general linear model resulted in informative plots revealing mutual relationships between secondary dendrite arm spacing and the mean plane section area of carbides in the material. Directions for further research also were obtained.