Vliv vodíku na fyzikálně metalurgické a mechanické vlastnosti superslitin niklu

Abstract

The presented dissertation thesis is focused on the action of hydrogen in some nickel based superalloys that are designed especially for high temperature applications. These highly resistant alloys are often used in very aggressive environments, which can also be a source of hydrogen. The hydrogen can subsequently play an important role in the accelerated degradation of these alloys. The hydrogen effect on the superalloys is quite complex and sometimes even controversial regarding a wide variability of the chemical composition and microstructure Ni based superalloys. The theoretical analysis of the state of art concerning hydrogen impact on the properties of nickel based superalloys is presented in the first part of the thesis. This part also involves main characteristics of these materials. The objective of the experimental part was to analyze the influence of hydrogen on the properties of a Ni based superalloy IN 738LC of a domestic provenance that was rather neglected in the research works devoted to the hydrogen effect. The performed experiments were focused on the influence of higher hydrogen content on the changes of tensile mechanical properties. Changes in failure mode and microstructures were observed using optical, scanning electron and transmission electron microscopies. Four different microstructure modifications of the superalloy resulting of two different castings prepared within several years were studied. The obtained results, in some cases very controversial, illustrate that the solved problem for the studied superalloy IN 738LC was quite complex and challenging due to the dependence of hydrogen effect on many parameters.