Volume 50, Issue 8

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 consisted of 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 from a lack of feeding of the interdendritic space. The comprehensive procedure of porosity evaluation includes: an automatic decimal-to-binary conversion of pores, a selective quantitative evaluation of gaseous and shrinkage porosity, the development of measuring conditions of quantitative metallography parameters, and the application of structural maps showing the varied porosity distribution over the cross-sections of castings of blades and blade segments. The developed practical procedure of selective measurement of gaseous and shrinkage porosity in the examination of precision castings made of high-temperature creep resisting nickel superalloys is presented.

Modern single crystal (SX) turbine blades are fabricated by directional solidification using a grain selector. The grain selection process was investigated by numerical simulation and verified by the experiment. A coupled ProCAST and cellular automaton finite element (CAFE) model was used in this study. According to the latest literature data, we designed the grain selector. Simulation confirmed an optimal grain selection efficiency of the applied selector geometry. The obtained experimental results reveal the possibility of stray grain formation in SX castings with a designed selector, in contrast to the simulation results.

The paper presents the quantification results of the inhomogeneity of phase distribution in intermetallic alloys from the Mg-Al-Sr system after die-casting and gravity casting, the quantification results of phase β of alloy Ti-6-4 after hydrogen treatment and cyclic heat treatment, and of intragranular regions of diverse crystallographic orientation in the copper microstructure in a state of strain and in a recrystallized state. The quantification of the distribution inhomogeneity, based on the concept of directional lacunarity, is effective and precisely detects the size of inhomogeneity and the degree of its intensity, irrespective of the morphology of microstructural components. An analytical description of inhomogeneity allows comparing the results of quantification, regardless of the size of the sets analyzed.