2.3 Pregled revije po tipologiji
[tevilo ~lankov, ki spadajo v skupino izvirnih znan-
stvenih ~lankov se je z leti vi{alo, najve~ jih je bilo v letu
2016, najmanj pa v letu 2007. [tevilo strokovnih ~lan-
kov, ki so z letom 2016, po odlo~itvi uredni{tva ukinjeni,
je obdr`alo konstantno {tevilko, od 30 do 40 letno.
Tabela 2: Pregled prispevkov v letih od 2007 do 2017 po tipologiji
Leto Tipologija
1.01
(izvirni znan-
stveni ~lanek)
1.02
(pregledni
znanstveni
~lanek)
1.04
(strokovni
~lanek)
1.20
(predgovor,
spremna
beseda)
2007 39 4 1 0
2008 30 6 8 0
2009 38 3 9 0
2010 43 8 7 0
2011 79 4 14 0
2012 81 0 30 3
2013 98 6 30 0
2014 118 2 39 0
2015 114 6 35 0
2016 125 2 30 2
2017
(do {t. 3)* 46 2 10 1
*podatki pridobljeni pred izidom 4. {tevilke
3 DOSTOPNOST REVIJE
Revija Materiali in tehnologije je `e v devetdesetih
letih prej{njega stoletja, ko se je imenovala {e Kovine
zlitine tehnologije, stopila naproti ideji, da bi bila bolj
odprta in la`je dostopna {ir{i javnosti. V skladu z `eljami
in dejanji uredni{tva in navsezadnje te`njami {ir{e
javnosti ter splo{nih trendov tistega ~asa, je v letu 1998
postala dostopna na svetovnem spletu v celotnem bese-
dilu in jo je bilo sprva mo~ najti na spletni strani
Centralne tehni{ke knji`nice (repozitorij CTK), kasneje
pa na spletni strani www.imt.si, kjer je revija dostopna {e
danes.
Revija (njeni predhodnici @elezarski zbornik in Ko-
vine zlitine tehnologije) je bila v Narodni in univerzitetni
knji`nici (NUK) vklju~ena v projekt digitalizacije in je
danes na voljo v digitalni obliki tako na spletnem portalu
pri Digitalni knji`nici Slovenije pri NUK, kot tudi na
spletni strani revije MIT. Ob petdeseti obletnici izhajanja
revije smo se v uredni{tvu odlo~ili, da na spletni strani
revije uredimo celoten arhiv vseh {tevilk revije, tudi {te-
vilk njenih predhodnic, ki so doslej manjkale: @elezarski
zbornik (ISSN 0372-8633) in Kovine zlitine tehnologije
(ISSN 1318-0010). Revijo Materiali in tehnologije je
mogo~e prelistati kadarkoli in od koderkoli (~e le imate v
bli`ini internet), in sicer od prve {tevilke @elezarskega
zbornika iz leta 1967 pa do vseh ~lankov revije MIT do
danes. Ve~ino {tevilk revije v tiskani obliki hranimo tudi
v knji`nici IMT. Skupno je bilo tako pripravljenih, in v
spletni arhiv dodanih, 123 datotek; 102 {tevilki @elezar-
skega zbornika in 21 {tevilk revije KZT.6
4 ZAKLJU^EK
Za~etki revije in objava ~lankov samo iz podro~ja
`elezarstva in metalurgije pred petdesetimi leti, ko je
industrija jekla in `elezarstva predstavljala najve~ji dele`
tovrstne dejavnosti v gospodarstvu takratne Jugoslavije
in kasneje dr`ave Slovenije, so bili med drugim ravno
tako podlaga za nadaljnje raziskovanje in uveljavljanje
metalurgije kot panoge, ki je do danes po~asi, a vztrajno
pre{la v skoraj vse pore industrije in je v dana{njem ~asu
razvoja tehnologije na izredno visoki ravni. Danes tako z
visoko tehnolo{kimi principi in najnovej{imi tehnolo-
gijami na podro~ju tako kovinskih, kot tudi drugih
materialov, dosegamo zavidljive rezultate. Napredni ma-
teriali, napredne proizvodne tehnologije, nanotehnologije
in biotehnologije so klju~na podro~ja, identificirana v
strategiji pametne specializacije, ki bodo omogo~ala
evropski in slovenski industriji ohraniti mednarodno
globalno konkuren~nost in izkoristiti nove trge. Z njimi
sta metalurgija in kemijska industrija nelo~ljivo povezani
in sta del opredeljenih klju~nih tehnologij. Pri tem razvoj
novih materialov in tehnologij pomeni vstop novih, do
sedaj neznanih mo`nosti, na tr`i{~e, kjer imajo ra-
ziskave, razvoj in inovacije zelo pomembno vlogo.7 Del
raziskav in preizkusov, je predstavljen tudi skozi prispev-
ke in ~lanke v reviji MIT in tudi v drugih medijih,8 ki s
tem {iri nova dognanja, spoznanja in znanja na {ir{i krog
raziskovalcev, znanstvenikov in drugo potencialno publi-
ko. Revija Materiali in tehnologije je danes sicer pri-
znana tudi izven meja Slovenije, vendar pa si v prihodnje
{e vedno `elimo, da bi v reviji objavljalo ve~je {tevilo
strokovnjakov in raziskovalcev iz Slovenije in evrop-
skega prostora.
5 LITERATURA
1 N. Jamar, J. Jamar, Zgodovina znanstvene serijske publikacije
Materiali in tehnologije/Materials and Technology = Historical over-
view of the scientific journal Materiali in tehnologije/Materials and
Technology, Mater. Tehnol., 41 (2007) 1, 13–19
2 http://mit.imt.si/Revija/index-slo.html, 28.7.2017
3 http://mit.imt.si/Revija/information-slo.html, 28.7.2017
4 P. McGuiness, Predgovor urednika=Editor’s preface, Mater. Tehnol.,
50 (2016) 5, str. 639–640
5 http://mit.imt.si/Revija/authors-slo.html, 28.07.2017
6 http://mit.imt.si/Revija/archive.html, 29.07.2017
7 https://www.gzs.si/Novice/ArticleId/58642/srip-matpro, 29.7.2017
8 M. Godec, Najve~ji hit je 3D tisk, Glas gospodarstva, Naj materiali,
pano`na {tevilka, april (2017), 30–31
E. NARED: POMEMBNA OBLETNICA REVIJE MATERIALI IN TEHNOLOGIJE: PETDESET LET IZHAJANJA ...
720 Materiali in tehnologije / Materials and technology 51 (2017) 5, 717–720
MATERIALI IN TEHNOLOGIJE/MATERIALS AND TECHNOLOGY (1967–2017) – 50 LET/50 YEARS
I. SLATKOVSKÝ et al.: INVESTIGATION OF GRAIN BOUNDARIES IN ALLOY 263 AFTER SPECIAL HEAT TREATMENT
721–727
INVESTIGATION OF GRAIN BOUNDARIES IN ALLOY 263
AFTER SPECIAL HEAT TREATMENT
PREISKAVA MEJ ZRN V ZLITINI 263 PO POSEBNI TOPLOTNI
OBDELAVI
Ivan Slatkovský, Mária Dománková, Martin Sahul
Slovak University of Technology Bratislava, Faculty of Materials Science and Technology, Institute of Materials Science,
Bottová 25, 917 24, Trnava, Slovak Republic
ivan.slatkovsky@stuba.sk
Prejem rokopisa – received: 2016-06-20; sprejem za objavo – accepted for publication: 2017-01-24
doi:10.17222/mit.2016.115
Alloy 263 is well known for its very good creep resistance and also for its weldability. These kinds of properties are appreciated
in the power-plant industry where Alloy 263 is used for shafts in a high-pressure circle. One of the possible ways to improve the
properties of superalloys, including Alloy 263, is through the effect of the grain-boundary serration (GBS) which, as research
indicates, is associated with the improvement of the creep resistance that can lead to an increased efficiency of coal power
plants. Grain-boundary serration was observed in different kinds of superalloys although the formation mechanism of serration
has not been clearly explained yet. Some researchers reported that the formation of serration is associated with the change in the
character of the precipitates at grain boundaries. This paper deals with an investigation of the grain boundaries in Alloy 263
using two different kinds of heat treatment. To form serrated grain boundaries in Material A (MA), slow controlled cooling from
the temperature of solution annealing to 800 °C was carried out. Standard heat treatment of Alloy 263 was performed on
material B (MB). Experimental techniques of scanning electron microscopy (SEM) and transmission electron microscopy
(TEM), including electron diffraction, were used to analyze the microstructure, determine the character of the grain boundaries
and identify the secondary particles at the grain boundaries.
Keywords: Alloy 263, grain-boundary serration, precipitates
Zlitina 263 je znana po zelo dobri odpornosti proti lezenju in tudi po dobri varivosti. Te vrste lastnosti so zelo cenjene v
termoelektrarnah, kjer se zlitina 263 uporablja za gredi v visokotla~nem delu turbin. Eden od mo`nih na~inov za izbolj{anje
lastnosti superzlitin, vklju~no z zlitino 263, je tvorba (nastanek) nazob~anih kristalnih mej (angl. GBS). Preiskava je pokazala,
da je ta fenomen povezan z izbolj{anjem odpornosti proti lezenju, kar lahko vodi k ve~ji u~inkovitosti termoelektrarn na
premog. U~inek nazob~anosti mej kristalnih zrn so opazili pri razli~nih vrstah superzlitin, ~eprav mehanizem tvorbe {e ni
popolnoma pojasnjen. Nekateri raziskovalci so ugotovili, da je tvorba nazob~anosti povezana s spremembo lastnosti izlo~kov na
mejah med zrni. Prispevek se ukvarja s preiskavo mej med kristalnimi zrni v zlitini 263 z dvema razli~nima vrstama toplotne
obdelave. Nastanek nazob~anih mej kristalnih zrn materiala A (MA), je bil povzro~en s po~asnim kontroliranim ohlajanjem iz
temperature raztopnega `arjenja, ki je bila 800 ° C. Standardna toplotna obdelava se je izvajala za zlitino 263 - material B (MB).
Za analizo mikrostrukture so uporabili vrsti~ni elektronski mikroskop (SEM) in presevno elektronsko mikroskopijo (TEM),
vklju~no z elektronsko difrakcijo. Na ta na~in so dolo~ili lastnosti mej kristalnih zrn in sekundarnih delcev na mejah zrn.
Klju~ne besede: zlitina 263, nazob~anost mej kristalnih zrn, izlo~ki
1 INTRODUCTION
It is a well-known fact that a reduction in the CO2
emissions produced by coal power plants is one of the
major goals for the countries all over the world. A
possible way to reduce the CO2 emissions is to improve
thermal efficiencies through super critical and ultra-
super critical technologies in power plants, where
efficiencies above 40 % could be reached. Hence, to
achieve this kind of efficiency, the materials like nickel-
based superalloys are considered to be used (Fig-
ure 1).1–3
To prolong the life time of parts when the tempera-
ture exceeds 700 °C, scientists are looking for new paths
of material processing. In the case of heat treatment, one
of the possible ways is a modification of grain boun-
daries (GBs) when the character of the boundaries
changes from straight to zigzag.
The phenomenon of grain-boundary serration (GBS)
was observed in the nickel-based superalloys and in
austenitic stainless steels. The formation of serrations on
grain boundaries (GBs) has not been fully described yet.
However, it is a known fact that in the case of nickel-
based superalloys, the GBS is closely related to the slow
controlled cooling from the temperature of the solution
annealing.
Early studies of serration in the nickel-based alloys
were focused on the interaction between the grain
boundary and ’ phase.4,5 Until now, researchers have
found that the serration is associated not only with the
presence of the ’ phase, but also with other precipitates
like M23C6 carbide, the  phase or the ’’ phase on the
GBs that were observed in different kinds of superalloys.
The formation of these secondary particles could be
highly related to the serrated grain boundaries and their
formation.6–13 Recently, contemporary authors have
Materiali in tehnologije / Materials and technology 51 (2017) 5, 721–727 721
MATERIALI IN TEHNOLOGIJE/MATERIALS AND TECHNOLOGY (1967–2017) – 50 LET/50 YEARS
UDK 669.018:620.1:620.193 ISSN 1580-2949
Original scientific article/Izvirni znanstveni ~lanek MTAEC9, 51(5)721(2017)
found that in some alloys, in the early stages of the
formation, GBS occurred in the absence of the adjacent
coarse ’ particle or M23C6 carbide.12–14 Furthermore, H.
U. Hong et al.15 observed in their research that the
serrations on GBs were formed in the material after a
long solution annealing (2000 min) without any slow
controlled cooling. Also, no secondary particles were
observed.
As reported by the authors of references,10–13 GBS
leads to a morphological change of the carbides on GBs,
from granular to planar. A growth of secondary particles
on the serrated grain boundaries was observed mostly at
a low angle and on special GBs. The authors of referen-
ces10,11 reported that the formation of planar M23C6
carbides is orientated in the {111} plane. Also, the
orientation relationship between the carbides and the
matrix was observed.
Therefore, the purpose of this study is to investigate
the effect of special heat treatment on GBs and identify
the secondary phases formed at the GBs in Alloy 263.
2 EXPERIMENTAL PART
In order to investigate GBS, commercially available
hot-rolled nickel-based superalloy 263 was used in the
study. The chemical composition of the examined alloy
is given in Table 1.
A two-stage special heat-treatment method was
designed to form a GBS in material A, based on the
previous studies.6–13 The solution heat treatment followed
by slow cooling at a carefully controlled rate (until the
aging temperature was reached) was found to be
necessary to generate serrated GB structures.
Material A was solution annealed at 1150 °C for
80 min and cooled slowly to 800 °C at a cooling rate of
3 °C/min, followed by water quenching. After that,
precipitation hardening at 800 °C for 4 h was performed
and followed by air cooling.
On material B, the standard two-stage heat treatment
of Alloy 263 (solution annealing at 1150 °C for 80 min
followed by water quenching and precipitation hardening
at 800 °C for 4 h, cooled in the air) was applied.
For a SEM analysis, the samples were sliced, mecha-
nically grinded and polished. The etching solution for
the SEM observation was a solution containing 5 g
FeCl3, 15 mL HCl, 2 mL HNO3 and 60 mL ethanol used
for 10–15 s in order to reveal the GB configuration and
carbides. A JEOL 7600 F scanning electron microscope
was used for the observation of the GBs.
Thin foils were prepared for a detailed grain-boun-
dary observation using mechanical grinding to a thick-
ness of about 0.1 mm, and then electrolytically etched.
Etching was done on TENUPOL 5 in a solution of
perchloric acid and methanol (1:9). The temperature
during etching was -30 °C and the voltage was 25 V. For
the detailed observation, a transmission electron micro-
scope, JEOL 200 CX with an accelerating voltage of 200
kV, was used. To identify secondary particles at the GBs,
an electron-diffraction analysis was applied.
Extraction replicas were prepared in the following
route: samples were first prepared using standard
metallographic techniques. After that, they were etched
with the above-mentioned solution for 15 s. A thin
carbon film was sputtered onto the etched surface of the
samples. The carbon film (replica) was subsequently
electrolytically extracted, using 8 % perchloric acid, at a
bias of 10 V.
3 RESULTS
Figure 2 shows the microstructure of material A after
the special heat treatment. Light microscopy revealed a
polyhedral grain, the presence of twins as well as the
grain-size heterogeneity in material A. Two types of
grain-boundary morphology were observed with light
microscopy. Straight boundaries with a percentage share
of approximately 38 % of the total of 254 observed grain
boundaries were located in the structure of material A.
Serrated boundaries, as the second type, covered
approximately 39 % of the noticed boundaries. In some
cases, the type of boundary could not be determined
owing to the state of the boundary.
As a reference sample, material B (Figure 3) was
processed with the conventional heat treatment. In
material B, we also observed the base microstructure
I. SLATKOVSKÝ et al.: INVESTIGATION OF GRAIN BOUNDARIES IN ALLOY 263 AFTER SPECIAL HEAT TREATMENT
722 Materiali in tehnologije / Materials and technology 51 (2017) 5, 721–727
MATERIALI IN TEHNOLOGIJE/MATERIALS AND TECHNOLOGY (1967–2017) – 50 LET/50 YEARS
Table 1: Nominal chemical composition of Alloy 263
Chemical-composition limits
Weight % Ni Cr Co Mo C Al Ti Al+Ti Mn
263 Bal 19–21 19–21 5.6–6.1 0.04–0.08 0.60 max 1.90–2.40 2.40–2.80 0.60 max
Weight % Si Fe Cu B Pb S Ag Bi
263 0.40 max 0.07 max 0.020 max 0.005 max 0.0020 0.007 max 0.005 max 0.0001 max
Figure 1: Net efficiency development in the case of hard coal-fired
power plants considering different structural alloys3
with polyhedral grains with the heterogeneity of the
grain size and twins similar to those in material A. As
expected, no serrated boundaries were observed in
material B after the conventional heat treatment.
The grain-boundary details taken with SEM indicate
the presence of precipitates on the serrated and straight
grain boundaries in material A as well as in material B
(Figures 4 and 5). Results of the EDX analysis taken
from material A (Figure 6) reveal the eventual presence
of carbon-rich secondary particles, which could possibly
indicate the presence of carbides at the grain boundaries.
The occurrence of the other elements at the grain boun-
daries was not significant. Comparable results were also
noticed for material B. To confirm the presence of the
secondary particles formed at the boundaries and to
identify the chemical nature of these particles, ED and
EDX using the TEM were taken for materials A and B,
and the results are shown below.
The authors of reference16 predicted and identified
typical kinds of the secondary particles for this alloy,
allowing us to expect mainly the presence of the MC,
M6C and M23C6 carbides.
Figures 7 to 9 summarize the identified phases on the
replicas for material A. Electron diffraction spectra as
well as the EDX analysis of the extracted precipitates
I. SLATKOVSKÝ et al.: INVESTIGATION OF GRAIN BOUNDARIES IN ALLOY 263 AFTER SPECIAL HEAT TREATMENT
Materiali in tehnologije / Materials and technology 51 (2017) 5, 721–727 723
MATERIALI IN TEHNOLOGIJE/MATERIALS AND TECHNOLOGY (1967–2017) – 50 LET/50 YEARS
Figure 5: SEM, material B: a) straight grain-boundary triple point and
b) detail of precipitatesFigure 3: Material B
Figure 4: SEM, material A: a) serrated grain-boundary triple point
and b) detail of precipitates
Figure 2: Material A
found that in some alloys, in the early stages of the
formation, GBS occurred in the absence of the adjacent
coarse ’ particle or M23C6 carbide.12–14 Furthermore, H.
U. Hong et al.15 observed in their research that the
serrations on GBs were formed in the material after a
long solution annealing (2000 min) without any slow
controlled cooling. Also, no secondary particles were
observed.
As reported by the authors of references,10–13 GBS
leads to a morphological change of the carbides on GBs,
from granular to planar. A growth of secondary particles
on the serrated grain boundaries was observed mostly at
a low angle and on special GBs. The authors of referen-
ces10,11 reported that the formation of planar M23C6
carbides is orientated in the {111} plane. Also, the
orientation relationship between the carbides and the
matrix was observed.
Therefore, the purpose of this study is to investigate
the effect of special heat treatment on GBs and identify
the secondary phases formed at the GBs in Alloy 263.
2 EXPERIMENTAL PART
In order to investigate GBS, commercially available
hot-rolled nickel-based superalloy 263 was used in the
study. The chemical composition of the examined alloy
is given in Table 1.
A two-stage special heat-treatment method was
designed to form a GBS in material A, based on the
previous studies.6–13 The solution heat treatment followed
by slow cooling at a carefully controlled rate (until the
aging temperature was reached) was found to be
necessary to generate serrated GB structures.
Material A was solution annealed at 1150 °C for
80 min and cooled slowly to 800 °C at a cooling rate of
3 °C/min, followed by water quenching. After that,
precipitation hardening at 800 °C for 4 h was performed
and followed by air cooling.
On material B, the standard two-stage heat treatment
of Alloy 263 (solution annealing at 1150 °C for 80 min
followed by water quenching and precipitation hardening
at 800 °C for 4 h, cooled in the air) was applied.
For a SEM analysis, the samples were sliced, mecha-
nically grinded and polished. The etching solution for
the SEM observation was a solution containing 5 g
FeCl3, 15 mL HCl, 2 mL HNO3 and 60 mL ethanol used
for 10–15 s in order to reveal the GB configuration and
carbides. A JEOL 7600 F scanning electron microscope
was used for the observation of the GBs.
Thin foils were prepared for a detailed grain-boun-
dary observation using mechanical grinding to a thick-
ness of about 0.1 mm, and then electrolytically etched.
Etching was done on TENUPOL 5 in a solution of
perchloric acid and methanol (1:9). The temperature
during etching was -30 °C and the voltage was 25 V. For
the detailed observation, a transmission electron micro-
scope, JEOL 200 CX with an accelerating voltage of 200
kV, was used. To identify secondary particles at the GBs,
an electron-diffraction analysis was applied.
Extraction replicas were prepared in the following
route: samples were first prepared using standard
metallographic techniques. After that, they were etched
with the above-mentioned solution for 15 s. A thin
carbon film was sputtered onto the etched surface of the
samples. The carbon film (replica) was subsequently
electrolytically extracted, using 8 % perchloric acid, at a
bias of 10 V.
3 RESULTS
Figure 2 shows the microstructure of material A after
the special heat treatment. Light microscopy revealed a
polyhedral grain, the presence of twins as well as the
grain-size heterogeneity in material A. Two types of
grain-boundary morphology were observed with light
microscopy. Straight boundaries with a percentage share
of approximately 38 % of the total of 254 observed grain
boundaries were located in the structure of material A.
Serrated boundaries, as the second type, covered
approximately 39 % of the noticed boundaries. In some
cases, the type of boundary could not be determined
owing to the state of the boundary.
As a reference sample, material B (Figure 3) was
processed with the conventional heat treatment. In
material B, we also observed the base microstructure
I. SLATKOVSKÝ et al.: INVESTIGATION OF GRAIN BOUNDARIES IN ALLOY 263 AFTER SPECIAL HEAT TREATMENT
722 Materiali in tehnologije / Materials and technology 51 (2017) 5, 721–727
MATERIALI IN TEHNOLOGIJE/MATERIALS AND TECHNOLOGY (1967–2017) – 50 LET/50 YEARS
Table 1: Nominal chemical composition of Alloy 263
Chemical-composition limits
Weight % Ni Cr Co Mo C Al Ti Al+Ti Mn
263 Bal 19–21 19–21 5.6–6.1 0.04–0.08 0.60 max 1.90–2.40 2.40–2.80 0.60 max
Weight % Si Fe Cu B Pb S Ag Bi
263 0.40 max 0.07 max 0.020 max 0.005 max 0.0020 0.007 max 0.005 max 0.0001 max
Figure 1: Net efficiency development in the case of hard coal-fired
power plants considering different structural alloys3
with polyhedral grains with the heterogeneity of the
grain size and twins similar to those in material A. As
expected, no serrated boundaries were observed in
material B after the conventional heat treatment.
The grain-boundary details taken with SEM indicate
the presence of precipitates on the serrated and straight
grain boundaries in material A as well as in material B
(Figures 4 and 5). Results of the EDX analysis taken
from material A (Figure 6) reveal the eventual presence
of carbon-rich secondary particles, which could possibly
indicate the presence of carbides at the grain boundaries.
The occurrence of the other elements at the grain boun-
daries was not significant. Comparable results were also
noticed for material B. To confirm the presence of the
secondary particles formed at the boundaries and to
identify the chemical nature of these particles, ED and
EDX using the TEM were taken for materials A and B,
and the results are shown below.
The authors of reference16 predicted and identified
typical kinds of the secondary particles for this alloy,
allowing us to expect mainly the presence of the MC,
M6C and M23C6 carbides.
Figures 7 to 9 summarize the identified phases on the
replicas for material A. Electron diffraction spectra as
well as the EDX analysis of the extracted precipitates
I. SLATKOVSKÝ et al.: INVESTIGATION OF GRAIN BOUNDARIES IN ALLOY 263 AFTER SPECIAL HEAT TREATMENT
Materiali in tehnologije / Materials and technology 51 (2017) 5, 721–727 723
MATERIALI IN TEHNOLOGIJE/MATERIALS AND TECHNOLOGY (1967–2017) – 50 LET/50 YEARS
Figure 5: SEM, material B: a) straight grain-boundary triple point and
b) detail of precipitatesFigure 3: Material B
Figure 4: SEM, material A: a) serrated grain-boundary triple point
and b) detail of precipitates
Figure 2: Material A
extracted at the grain boundaries confirmed the presence
of carbides. The carbides contained minor elements such
as Mo, Cr and Ni (Table 2).
The M6C ((Co,Ni)3Mo3C) carbide was not confirmed
by electron diffraction (confirmed only by the EDX anal-
I. SLATKOVSKÝ et al.: INVESTIGATION OF GRAIN BOUNDARIES IN ALLOY 263 AFTER SPECIAL HEAT TREATMENT
724 Materiali in tehnologije / Materials and technology 51 (2017) 5, 721–727
MATERIALI IN TEHNOLOGIJE/MATERIALS AND TECHNOLOGY (1967–2017) – 50 LET/50 YEARS
Figure 8: a) Extracted small particles of irregular shapes at the grain
boundary, material B and b) point-diffraction spectra of MC carbide
Figure 6: EDX map, carbon-rich grain boundary, material A
Figure 9: Typical EDX spectra of precipitates in material A: a)
carbide MC and b) carbide M6C
Figure 7: a) Detail of a precipitate at the grain boundary, material A
and b) point-diffraction spectra of M23C6 carbide
ysis); a slight difference between the lattice parameters
of the M23C6 and M6C (aM23C6 = 0.1065 nm aM6C = 0.1085
nm) carbides makes the identification difficult.
Table 2: Approximate chemical composition of carbides in Material A
M23C6 MC M6C
Avr. (w/%)  Avr. (w/%)  Avr. (w/%) 
Mo 28.6 ±6.1 64.7 ±6.3 22.9 ±5.0
Ti 4.6 ±3.6 26.0 ±5.0 3.3 ±1.3
Cr 66.8 ±9.6 8.8 ±4.3 27.5 ±3.6
Ni 46.3 ±6.8
Details of the serrated boundaries and precipitates in
Material A, observed with TEM on the foils, can be seen
in Figures 10a to 10b. As shown in the figures, the
asymmetry of the serration was observed on some parts
of the serrated boundaries when the irregularity of the
serration exhibited a high difference in  at the observed
parts of the boundary (on the edges,  = 800–900 nm; in
the middle of the boundary,  = 150–200 nm).
On the serrated grain boundary documented in
Figure 10b, secondary particles of different sizes were
noticed. The shape of the particles copied the serration of
the boundary. Using electron diffraction, the particles
were identified as the M23C6 carbide and the matrix as
the -phase (Figure 11). Electron diffraction also
revealed the existence of the orientation relationship
between the matrix and carbide: {200} || {200}M23C6.
Figure 12a documents a straight grain boundary with
discrete secondary particles in material A. Along the full
length of the boundary, the particles of triangular or
rectangular shapes were observed. As shown in Figure
12b, this kind of particles does not copy the shape of the
boundary as in the case of the precipitates at the serrated
boundaries. The size of the precipitates was approxi-
mately 300 nm. The particles were identified, with elec-
tron diffraction (Figure 13), as M23C6 carbide and the
matrix as phase . However, in the case of the straight
grain boundary, no orientation relationship between the
matrix and the precipitate was spotted.
The precipitates extracted at the grain boundary in
material B as M23C6 carbide were identified on the
replicas using electron diffraction, as documented below
I. SLATKOVSKÝ et al.: INVESTIGATION OF GRAIN BOUNDARIES IN ALLOY 263 AFTER SPECIAL HEAT TREATMENT
Materiali in tehnologije / Materials and technology 51 (2017) 5, 721–727 725
MATERIALI IN TEHNOLOGIJE/MATERIALS AND TECHNOLOGY (1967–2017) – 50 LET/50 YEARS
Figure 12: Detail of straight grain boundary, material A, bright field;
b) detail of precipitates at the grain boundary, material A, dark field;
reflection (2 -2 4)M23C6 was used for the dark-field display
Figure 10: Detail of serrated grain boundary, material A, bright field;
b) detail of precipitates at the grain boundary, material A, dark field;
reflection (2 0 0) M23C6 was used for the dark-field display
Figure 11: Point diffraction spectra – phase  and M23C6 carbide
extracted at the grain boundaries confirmed the presence
of carbides. The carbides contained minor elements such
as Mo, Cr and Ni (Table 2).
The M6C ((Co,Ni)3Mo3C) carbide was not confirmed
by electron diffraction (confirmed only by the EDX anal-
I. SLATKOVSKÝ et al.: INVESTIGATION OF GRAIN BOUNDARIES IN ALLOY 263 AFTER SPECIAL HEAT TREATMENT
724 Materiali in tehnologije / Materials and technology 51 (2017) 5, 721–727
MATERIALI IN TEHNOLOGIJE/MATERIALS AND TECHNOLOGY (1967–2017) – 50 LET/50 YEARS
Figure 8: a) Extracted small particles of irregular shapes at the grain
boundary, material B and b) point-diffraction spectra of MC carbide
Figure 6: EDX map, carbon-rich grain boundary, material A
Figure 9: Typical EDX spectra of precipitates in material A: a)
carbide MC and b) carbide M6C
Figure 7: a) Detail of a precipitate at the grain boundary, material A
and b) point-diffraction spectra of M23C6 carbide
ysis); a slight difference between the lattice parameters
of the M23C6 and M6C (aM23C6 = 0.1065 nm aM6C = 0.1085
nm) carbides makes the identification difficult.
Table 2: Approximate chemical composition of carbides in Material A
M23C6 MC M6C
Avr. (w/%)  Avr. (w/%)  Avr. (w/%) 
Mo 28.6 ±6.1 64.7 ±6.3 22.9 ±5.0
Ti 4.6 ±3.6 26.0 ±5.0 3.3 ±1.3
Cr 66.8 ±9.6 8.8 ±4.3 27.5 ±3.6
Ni 46.3 ±6.8
Details of the serrated boundaries and precipitates in
Material A, observed with TEM on the foils, can be seen
in Figures 10a to 10b. As shown in the figures, the
asymmetry of the serration was observed on some parts
of the serrated boundaries when the irregularity of the
serration exhibited a high difference in  at the observed
parts of the boundary (on the edges,  = 800–900 nm; in
the middle of the boundary,  = 150–200 nm).
On the serrated grain boundary documented in
Figure 10b, secondary particles of different sizes were
noticed. The shape of the particles copied the serration of
the boundary. Using electron diffraction, the particles
were identified as the M23C6 carbide and the matrix as
the -phase (Figure 11). Electron diffraction also
revealed the existence of the orientation relationship
between the matrix and carbide: {200} || {200}M23C6.
Figure 12a documents a straight grain boundary with
discrete secondary particles in material A. Along the full
length of the boundary, the particles of triangular or
rectangular shapes were observed. As shown in Figure
12b, this kind of particles does not copy the shape of the
boundary as in the case of the precipitates at the serrated
boundaries. The size of the precipitates was approxi-
mately 300 nm. The particles were identified, with elec-
tron diffraction (Figure 13), as M23C6 carbide and the
matrix as phase . However, in the case of the straight
grain boundary, no orientation relationship between the
matrix and the precipitate was spotted.
The precipitates extracted at the grain boundary in
material B as M23C6 carbide were identified on the
replicas using electron diffraction, as documented below
I. SLATKOVSKÝ et al.: INVESTIGATION OF GRAIN BOUNDARIES IN ALLOY 263 AFTER SPECIAL HEAT TREATMENT
Materiali in tehnologije / Materials and technology 51 (2017) 5, 721–727 725
MATERIALI IN TEHNOLOGIJE/MATERIALS AND TECHNOLOGY (1967–2017) – 50 LET/50 YEARS
Figure 12: Detail of straight grain boundary, material A, bright field;
b) detail of precipitates at the grain boundary, material A, dark field;
reflection (2 -2 4)M23C6 was used for the dark-field display
Figure 10: Detail of serrated grain boundary, material A, bright field;
b) detail of precipitates at the grain boundary, material A, dark field;
reflection (2 0 0) M23C6 was used for the dark-field display
Figure 11: Point diffraction spectra – phase  and M23C6 carbide
in Figure 14. Other precipitates were not identified,
which does not exclude their presence in Material B.
From the results of the EDX analysis (Figure 15,
Table 3) of the observed precipitates in Material B, the
presence of MC and M6C carbides is also possible.
Figures 16a to 16b document details of straight
boundaries and precipitates at the grain boundary in
material B on the foils. It can be noticed that the
secondary particles extracted at the grain boundaries
have a polyhedral or rectangular shape, and none of the
observed particles copies the shape of the boundary. The
size of these precipitates is in range of 100–200 nm.
I. SLATKOVSKÝ et al.: INVESTIGATION OF GRAIN BOUNDARIES IN ALLOY 263 AFTER SPECIAL HEAT TREATMENT
726 Materiali in tehnologije / Materials and technology 51 (2017) 5, 721–727
MATERIALI IN TEHNOLOGIJE/MATERIALS AND TECHNOLOGY (1967–2017) – 50 LET/50 YEARS
Figure 13: Point diffraction spectra – phase  and M23C6 carbide
Figure 16: Detail of straight grain boundary, material B, bright field;
b) detail of precipitates at the grain boundary, material B, dark field;
reflection (5 -1 -3)M23C6 was used for the dark-field display
Figure 14: Extracted small particle of an irregular shape at the grain
boundary, material A; b) point diffraction spectra of M23C6 carbide
Figure 15: Typical EDX spectra of precipitates in material B: a)
M23C6 carbide, b) M6C carbide
Table 3: Approximate chemical composition of carbides in material B
M23C6 MC M6C
Avr. (w/%)  Avr. (w/%)  Avr. (w/%) 
Mo 27.3 ±6.4 62.9 ±5.6 24.6 ±3.2
Ti 4.3 ±4.9 25.0 ±4.7 4.1 ±1.8
Cr 61.7 ±9.4 10.5 ±3.5 26.0 ±3.1
Ni 42.6 ±5.1
From the diffraction spectra (Figure 17), secondary
particles at the grain boundaries were identified as M23C6
carbide. No relationship between the matrix and preci-
pitate was observed in all the diffraction spectra in
material B.
4 CONCLUSION
To study the serration and precipitates at the grain
boundaries and identify secondary particles in Alloy 263,
both SEM and TEM were used in the research. To form
serrated grain boundaries, material A was heat treated
under special conditions, based on the studies from the
literature. Material A was compared with material B,
which underwent the conventional heat treatment based
on the material list for Alloy 263. The experimental
results can be summarized as follows:
• Serrated and straight grain boundaries were observed
in material A. Approximately 39 % of the observed
boundaries were serrated. In material B, only straight
grain boundaries were observed.
• In both cases, precipitates at the grain boundaries
were identified as carbide M23C6 using electron
diffraction. In material A, carbide MC was also ob-
served.
• The EDX analysis revealed three types of carbides,
based on their chemical compositions, in both ma-
terials: MC, M6C and M23C6.
• Electron diffraction also revealed the orientation
relationship between the matrix and the precipitate at
the serrated grain boundaries: {200} {200}M23C6.
No orientation relationship was observed at the
straight grain boundaries.
Acknowledgments
The authors wish to thank the financial support of the
Slovak Republic Scientific Grant Agency (VEGA)
within Grant No. 1/0402/13.
5 REFERENCES
1 P. J. Maziasz, I. G. Wright, J. P. Shingledecker, T. B. Gibbons, R. R.
Romanosky, Defining the materials issues and research needs for
ultra-supercritical steam turbines, Proc. 4th Inter. Conf. Advances in
Materials Technology for Fossil Power Plants, Hilton Head Island,
USA, 2005, 602–622
2 R. J. Campbell, Increasing the Efficiency of Existing Coal-Fired
Power Plants, https://fas.org/sgp/crs/misc/R43343.pdf, 14.06.2017
3 G. Stein-Brzozowska, D. M. Flórez, J. Maier, G. Scheffknecht,
Nickel-base superalloys for ultra-supercritical coal-fired power
plants: Fireside corrosion. Laboratory studies and power plant expo-
sures, Fuel, 108, (2013), 521–533, doi:10.1016/j.fuel.2012.11.081
4 A. K. Koul, G. H. Gessinger, On the mechanism of serrated grain
boundary formation in Ni-based superalloys, Acta Metallurgica, 31,
(1983) 7, 1061–1069, doi:10.1016/0001-6160(83)90202-X
5 H. L. Danflou, M. Marty, A. Walder, Formation of serrated grain
boundaries and their effect on the mechanical properties in a P/M
nickel base superalloy, Proc. 7th Inter. Symp. on Superalloys, Seven
Springs Mountain, USA, 1992, 63–72, doi:10.7449/1992/ Super-
alloys_1992_63_72
6 R. J. Mitchell, H. Y. Li, Z. W. Huang, On the formation of serrated
grain boundaries and fan type structures in an advanced polycry-
stalline nickel-base superalloy, Journal of Materials Processing Tech-
nology, 209 (2009) 2, 1011–1017, doi:10.1016/j.jmatprotec.2008.
03.008
7 C. L. Qiu, P. Andrews, On the formation of irregular-shaped gamma
prime and serrated grain boundaries in a nickel-based superalloy
during continuous cooling, Materials Characterization, 76 (2013),
28–34, doi:10.1016/j.matchar.2012.11.012
8 A. C. Yeh, K. W. Lu, C. M. Kuo, H. Y. Bor, C. N. Wei, Effect of
Serrated Grain Boundaries on the Creep Property of Inconel 718
Superalloy, Materials Science and Engineering A, 530 (2011),
525–529, doi:10.1016/j.msea.2011.10.014
9 D. H. Ping, Y. F. Gu, C. Y. Cui, H. Harada, Grain boundary segre-
gation in a Ni–Fe-based (Alloy 718) superalloy, Materials Science
and Engineering A, 456 (2007) 1–2, 99–102, doi:10.1016/j.msea.
2007.01.090
10 L. Jiang, R. Hu, H. Kou, J. Li, G. Bai, H. Fu, The effect of M23C6
carbides on the formation of grain boundary serrations in a wrought
Ni-based superalloy, Materials Science and Engineering A, 536
(2012), 37–44, doi:10.1016/j.msea.2011.11.060
11 Y. S. Lim, D. J. Kim, S. S. Hwang, H. P. Kim, S. W. Kim, M23C6
precipitation behavior and grain boundary serration in Ni-based
Alloy 690, Materials Characterization, 96 (2014), 28–39,
doi:10.1016/j.matchar.2014.07.008
12 H. U. Hong, I. S. Kim, B. G. Choi, M. Y. Kim, C. Y. Jo, The effect of
grain boundary serration on creep resistance in a wrought
nickel-based superalloy, Materials Science and Engineering A, 517
(2009) 1–2, 125–131, doi:10.1016/j.msea.2009.03.071
13 H. U. Hong, I. S. Kim, B. G. Choi, Y. S. Yoo, C. Y. Jo, On the role of
grain boundary serration in simulated weld heat-affected zone
liquation of a wrought nickel-based superalloy, Metallurgical and
Materials Transactions A, 43 (2012) 1, 173–181, doi:10.1007/
s11661-011-0837-2
14 H. U. Hong, I. S. Kim, B. G. Choi, Y. S. Yoo, C. Y. Jo, On the
Mechanism of Serrated Grain Boundary Formation in Ni-Based
Superalloys with Low '? Volume Fraction, Proc. 12th Inter. Symp.
on Superalloys, Seven Springs Mountain, USA, 2012, 53–61,
doi:10.1002/9781118516430.ch6
15 H. U. Hong, F. H. Latief, T. Blanc, I. S. Kim, B. G. Choi, C. Y. Jo, J.
H. Lee, Influence of chromium content on microstructure and grain
boundary serration formation in a ternary Ni-xCr-0.1C model alloy,
Materials Chemistry and Physics, 148 (2014) 3, 1194–1201,
doi:10.1016/j.matchemphys.2014.09.047
16 J. C. Zhao, V. Ravikumar, A. M. Beltran, Phase Precipitation and
Phase Stability in Nimonic 263, Metallurgical and Materials
Transactions A, 32 (2001) 6, 1271–1282, doi:10.1007/s11661-
001-0217-4
I. SLATKOVSKÝ et al.: INVESTIGATION OF GRAIN BOUNDARIES IN ALLOY 263 AFTER SPECIAL HEAT TREATMENT
Materiali in tehnologije / Materials and technology 51 (2017) 5, 721–727 727
MATERIALI IN TEHNOLOGIJE/MATERIALS AND TECHNOLOGY (1967–2017) – 50 LET/50 YEARS
Figure 17: Point diffraction spectra – phase  and M23C6 carbide
in Figure 14. Other precipitates were not identified,
which does not exclude their presence in Material B.
From the results of the EDX analysis (Figure 15,
Table 3) of the observed precipitates in Material B, the
presence of MC and M6C carbides is also possible.
Figures 16a to 16b document details of straight
boundaries and precipitates at the grain boundary in
material B on the foils. It can be noticed that the
secondary particles extracted at the grain boundaries
have a polyhedral or rectangular shape, and none of the
observed particles copies the shape of the boundary. The
size of these precipitates is in range of 100–200 nm.
I. SLATKOVSKÝ et al.: INVESTIGATION OF GRAIN BOUNDARIES IN ALLOY 263 AFTER SPECIAL HEAT TREATMENT
726 Materiali in tehnologije / Materials and technology 51 (2017) 5, 721–727
MATERIALI IN TEHNOLOGIJE/MATERIALS AND TECHNOLOGY (1967–2017) – 50 LET/50 YEARS
Figure 13: Point diffraction spectra – phase  and M23C6 carbide
Figure 16: Detail of straight grain boundary, material B, bright field;
b) detail of precipitates at the grain boundary, material B, dark field;
reflection (5 -1 -3)M23C6 was used for the dark-field display
Figure 14: Extracted small particle of an irregular shape at the grain
boundary, material A; b) point diffraction spectra of M23C6 carbide
Figure 15: Typical EDX spectra of precipitates in material B: a)
M23C6 carbide, b) M6C carbide
Table 3: Approximate chemical composition of carbides in material B
M23C6 MC M6C
Avr. (w/%)  Avr. (w/%)  Avr. (w/%) 
Mo 27.3 ±6.4 62.9 ±5.6 24.6 ±3.2
Ti 4.3 ±4.9 25.0 ±4.7 4.1 ±1.8
Cr 61.7 ±9.4 10.5 ±3.5 26.0 ±3.1
Ni 42.6 ±5.1
From the diffraction spectra (Figure 17), secondary
particles at the grain boundaries were identified as M23C6
carbide. No relationship between the matrix and preci-
pitate was observed in all the diffraction spectra in
material B.
4 CONCLUSION
To study the serration and precipitates at the grain
boundaries and identify secondary particles in Alloy 263,
both SEM and TEM were used in the research. To form
serrated grain boundaries, material A was heat treated
under special conditions, based on the studies from the
literature. Material A was compared with material B,
which underwent the conventional heat treatment based
on the material list for Alloy 263. The experimental
results can be summarized as follows:
• Serrated and straight grain boundaries were observed
in material A. Approximately 39 % of the observed
boundaries were serrated. In material B, only straight
grain boundaries were observed.
• In both cases, precipitates at the grain boundaries
were identified as carbide M23C6 using electron
diffraction. In material A, carbide MC was also ob-
served.
• The EDX analysis revealed three types of carbides,
based on their chemical compositions, in both ma-
terials: MC, M6C and M23C6.
• Electron diffraction also revealed the orientation
relationship between the matrix and the precipitate at
the serrated grain boundaries: {200} {200}M23C6.
No orientation relationship was observed at the
straight grain boundaries.
Acknowledgments
The authors wish to thank the financial support of the
Slovak Republic Scientific Grant Agency (VEGA)
within Grant No. 1/0402/13.
5 REFERENCES
1 P. J. Maziasz, I. G. Wright, J. P. Shingledecker, T. B. Gibbons, R. R.
Romanosky, Defining the materials issues and research needs for
ultra-supercritical steam turbines, Proc. 4th Inter. Conf. Advances in
Materials Technology for Fossil Power Plants, Hilton Head Island,
USA, 2005, 602–622
2 R. J. Campbell, Increasing the Efficiency of Existing Coal-Fired
Power Plants, https://fas.org/sgp/crs/misc/R43343.pdf, 14.06.2017
3 G. Stein-Brzozowska, D. M. Flórez, J. Maier, G. Scheffknecht,
Nickel-base superalloys for ultra-supercritical coal-fired power
plants: Fireside corrosion. Laboratory studies and power plant expo-
sures, Fuel, 108, (2013), 521–533, doi:10.1016/j.fuel.2012.11.081
4 A. K. Koul, G. H. Gessinger, On the mechanism of serrated grain
boundary formation in Ni-based superalloys, Acta Metallurgica, 31,
(1983) 7, 1061–1069, doi:10.1016/0001-6160(83)90202-X
5 H. L. Danflou, M. Marty, A. Walder, Formation of serrated grain
boundaries and their effect on the mechanical properties in a P/M
nickel base superalloy, Proc. 7th Inter. Symp. on Superalloys, Seven
Springs Mountain, USA, 1992, 63–72, doi:10.7449/1992/ Super-
alloys_1992_63_72
6 R. J. Mitchell, H. Y. Li, Z. W. Huang, On the formation of serrated
grain boundaries and fan type structures in an advanced polycry-
stalline nickel-base superalloy, Journal of Materials Processing Tech-
nology, 209 (2009) 2, 1011–1017, doi:10.1016/j.jmatprotec.2008.
03.008
7 C. L. Qiu, P. Andrews, On the formation of irregular-shaped gamma
prime and serrated grain boundaries in a nickel-based superalloy
during continuous cooling, Materials Characterization, 76 (2013),
28–34, doi:10.1016/j.matchar.2012.11.012
8 A. C. Yeh, K. W. Lu, C. M. Kuo, H. Y. Bor, C. N. Wei, Effect of
Serrated Grain Boundaries on the Creep Property of Inconel 718
Superalloy, Materials Science and Engineering A, 530 (2011),
525–529, doi:10.1016/j.msea.2011.10.014
9 D. H. Ping, Y. F. Gu, C. Y. Cui, H. Harada, Grain boundary segre-
gation in a Ni–Fe-based (Alloy 718) superalloy, Materials Science
and Engineering A, 456 (2007) 1–2, 99–102, doi:10.1016/j.msea.
2007.01.090
10 L. Jiang, R. Hu, H. Kou, J. Li, G. Bai, H. Fu, The effect of M23C6
carbides on the formation of grain boundary serrations in a wrought
Ni-based superalloy, Materials Science and Engineering A, 536
(2012), 37–44, doi:10.1016/j.msea.2011.11.060
11 Y. S. Lim, D. J. Kim, S. S. Hwang, H. P. Kim, S. W. Kim, M23C6
precipitation behavior and grain boundary serration in Ni-based
Alloy 690, Materials Characterization, 96 (2014), 28–39,
doi:10.1016/j.matchar.2014.07.008
12 H. U. Hong, I. S. Kim, B. G. Choi, M. Y. Kim, C. Y. Jo, The effect of
grain boundary serration on creep resistance in a wrought
nickel-based superalloy, Materials Science and Engineering A, 517
(2009) 1–2, 125–131, doi:10.1016/j.msea.2009.03.071
13 H. U. Hong, I. S. Kim, B. G. Choi, Y. S. Yoo, C. Y. Jo, On the role of
grain boundary serration in simulated weld heat-affected zone
liquation of a wrought nickel-based superalloy, Metallurgical and
Materials Transactions A, 43 (2012) 1, 173–181, doi:10.1007/
s11661-011-0837-2
14 H. U. Hong, I. S. Kim, B. G. Choi, Y. S. Yoo, C. Y. Jo, On the
Mechanism of Serrated Grain Boundary Formation in Ni-Based
Superalloys with Low '? Volume Fraction, Proc. 12th Inter. Symp.
on Superalloys, Seven Springs Mountain, USA, 2012, 53–61,
doi:10.1002/9781118516430.ch6
15 H. U. Hong, F. H. Latief, T. Blanc, I. S. Kim, B. G. Choi, C. Y. Jo, J.
H. Lee, Influence of chromium content on microstructure and grain
boundary serration formation in a ternary Ni-xCr-0.1C model alloy,
Materials Chemistry and Physics, 148 (2014) 3, 1194–1201,
doi:10.1016/j.matchemphys.2014.09.047
16 J. C. Zhao, V. Ravikumar, A. M. Beltran, Phase Precipitation and
Phase Stability in Nimonic 263, Metallurgical and Materials
Transactions A, 32 (2001) 6, 1271–1282, doi:10.1007/s11661-
001-0217-4
I. SLATKOVSKÝ et al.: INVESTIGATION OF GRAIN BOUNDARIES IN ALLOY 263 AFTER SPECIAL HEAT TREATMENT
Materiali in tehnologije / Materials and technology 51 (2017) 5, 721–727 727
MATERIALI IN TEHNOLOGIJE/MATERIALS AND TECHNOLOGY (1967–2017) – 50 LET/50 YEARS
Figure 17: Point diffraction spectra – phase  and M23C6 carbide