Article
The Hardness Evolution of Cast and the High-Cycle Fatigue
Life Change of Wrought Ni-Base Superalloys after Additional
Heat Treatment
Juraj Belan
1,
* , Lenka Kuchariková
1
, Eva Tillová
1
, Miloš Matvija
2
and Milan Uhríˇcik
1
Citation: Belan, J.; Kuchariková, L.;
Tillová, E.; Matvija, M.; Uhríˇcik, M.
The Hardness Evolution of Cast and
the High-Cycle Fatigue Life Change
of Wrought Ni-Base Superalloys after
Additional Heat Treatment. Materials
2021, 14, 7427. https://doi.org/
10.3390/ma14237427
Academic Editors: Arkadiusz Gola
and Izabela Nielsen
Received: 28 October 2021
Accepted: 1 December 2021
Published: 3 December 2021
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4.0/).
1
Department of Materials Engineering, Faculty of Mechanical Engineering, University of Žilina, Univerzitná
8215/1, 010 26 Žilina, Slovakia; lenka.kucharikova@fstroj.uniza.sk (L.K.); eva.tillova@fstroj.uniza.sk (E.T.);
milan.uhricik@fstroj.uniza.sk (M.U.)
2
Institute of Materials and Quality Engineering, Faculty of Materials, Metallurgy and Recycling, Technical
University of Košice, Letná 9, 042 00 Košice, Slovakia; Milos.Matvija@tuke.sk
* Correspondence: juraj.belan@fstroj.uniza.sk; Tel.: +421-41-513-2631
Abstract:
Concerning the use of modern technologies and manufacturing systems in the production
of high-stress components from Ni-base superalloys and the optimization of the production pro-
cess, knowledge of the microstructure–mechanical properties relationship is very important. The
microstructure of Ni-base superalloys is very closely related to the chemical composition. With
the high number of alloying elements, various phases are presented in the structure of Ni-base
superalloys, which have a predominantly positive effect on the mechanical properties, but also
phases that reduce, in particular, the heat resistance of these materials. The aim of the presented
paper is the quantification of structural parameters of two types of cast alloys, ZhS6K and IN738,
where the effect of dwell at 10 and 15 h at 800
◦
C on the change in morphology and volume fraction
of the
γ
0
-phase precipitate was studied. The detected changes were verified by the Vickers hardness
test. The IN718 superalloy was chosen as a representative of the wrought superalloy. This alloy was
also annealed for 72 h at a temperature of 800
◦
C, and the quantification of structural parameters
was performed by EDS mapping and TEM analysis. Another partial goal was to assess the effect of
changes in the volume fraction of the
γ
0
-phase and
δ
-phase on the change in the high-cycle fatigue
life of superalloy IN 718. This superalloy was tested by dynamic cyclic loading with cycle asymmetry
parameter
R = −1
at an ambient temperature of 22
±
5
◦
C and at a temperature of 700
±
5
◦
C and
with cycle asymmetry parameter R < 1 (three-point bending load) after annealing at 700
◦
C/72 h.
The results of the quantitative analyses and fatigue tests will be further used in optimizing the design
of Ni-base superalloy components by modern technologies such as additive technologies for the
production of turbine blades and implemented within the philosophy of Industry 4.0.
Keywords:
manufacturing engineering of material; advanced engineering material; Ni-base
superalloys; heat treatment; SEM analysis; TEM analysis; phases in superalloys; Vickers hardness;
fatigue test
1. Introduction
Superalloys are the materials most commonly used in environments characterized by
a combination of high operating temperatures and mechanical stress. In general, they can
be divided according to the basic element that forms a solid solution into three basic groups:
superalloys based on nickel, cobalt, and iron. All types of superalloys are characterized
by a basic matrix crystallizing in a cubic, face-centered FCC lattice with different types of
precipitated phases that provide secondary hardening of the basic solid solution. However,
of these superalloy-forming elements, only nickel retains the FCC lattice throughout the
temperature range—it is not a polymorphic metal. Other superalloy-forming elements are
polymorphic, which means that they have allotropic modifications. Iron crystallizes in
Materials 2021, 14, 7427. https://doi.org/10.3390/ma14237427 https://www.mdpi.com/journal/materials
