UDK 669.15:57.012.3:539.53 ISSN 1580-2949
Original scientific article/Izvirni znanstveni ~lanek Mater. Tehnol.
A. GANDA PUTRA et al.: MICROSTRUCTURAL EVOLUTION AND HARDNESS OF FERRITIC SUPERALLOYS ...
235–242
MICROSTRUCTURAL EVOLUTION AND HARDNESS OF
FERRITIC SUPERALLOYS CONTAINING NiAl-B2 AND
L21–Ni2TiAl PRECIPITATES
MIKROSTRUKTURNI RAZVOJ IN TRDOTA FERITNIH
SUPERZLITIN, KI VSEBUJEJO IZLO^KE NiAl-B2 in L21–Ni2TiAl
Adi Ganda Putra1, Selly Septianissa2*, Pawawoi3, Manty Aldilani Ikaningsih3,
Martoni2, Martijanti1, Mohammad Zaki Mubarok4, Hafizh Ridwanulloh3,
Jodi Irawan1, Ba’adilla Akhista Gamara3
1Machine Engineering, Faculty of Manufacturing Technology, Universitas Jenderal Achmad Yani, Bandung 40281, Indonesia
2Department of Mechanical Engineering, Faculty of Engineering, Widyatama University, Bandung 40125, Indonesia
3Metallurgical Engineering, Faculty of Manufacturing Technology, Universitas Jenderal Achmad Yani, Bandung 40281, Indonesia
4Department of Metallurgical Engineering, Faculty of Mining and Petroleum Engineering, Institut Teknologi Bandung,
Jl. Ganesha 10, Bandung 40132, Indonesia
Prejem rokopisa – received: 2025-10-03; sprejem za objavo – accepted for publication: 2026-02-03
doi:10.17222/mit.2025.1575
This study investigates the effect of homogenization and aging treatments on the microstructure and hardness of ferritic superal-
loys containing NiAl-B2 and L21–Ni2TiAl precipitates. Two alloy compositions were prepared using an electric arc furnace,
with Ti additions of 2 w/% (Alloy I) and 4 w/% (Alloy II). The ingots were homogenized at 1150 °C for 10 h followed by fur-
nace cooling, and subsequently aged at 800 °C for 8 h. Characterization was conducted using scanning electron microscopy
(SEM) with energy-dispersive spectroscopy (EDS), X-ray diffraction (XRD), and Vickers hardness testing. The as-cast alloys
exhibited the highest hardness, averaging 650.8 HV for Alloy I and 625.6 HV for Alloy II, due to the presence of metastable
precipitates formed during rapid solidification. Homogenization reduced the hardness to 487.2 HV (Alloy I) and 522.6 HV (Al-
loy II) as a result of precipitate dissolution and redistribution of the alloying elements, while aging increased the hardness to ap-
proximately 525 HV in both alloys through secondary precipitation of the NiAl-B2 and L21–Ni2TiAl with finer and more homo-
geneous distributions. SEM-EDS confirmed that Alloy I exhibited a more uniform dispersion of precipitates, whereas Alloy II
contained a greater quantity of Ni2TiAl, but with local agglomerations. In conclusion, homogenization and aging treatments
strongly influenced the precipitation behavior and hardness of ferritic superalloys, with Alloy I showing superior homogeneity
and Alloy II favoring greater Ni2TiAl formation, highlighting the effect of Ti content on phase stability and mechanical perfor-
mance.
Keywords: aging; ferritic superalloy; hardness; homogenization; L21–Ni2TiAl; NiAl-B2; SEM; XRD
Namen {tudije, predstavljene v ~lanku, je bil raziskati vpliv homogenizacije in staranja na mikrostrukturo in trdoto feritnih
superzlitin, ki vsebujejo izlo~ke NiAl-B2 in L21–Ni2TiAl. Avtorji so pripravili dve zlitini v elektrooblo~ni pe~i z dodatkom Ti v
vi{ini 2 w/% (zlitina I) in 4 w/% (zlitina II). Ingote obeh zlitin so 10 ur homogenizirali pri 1150 °C, jih ohladili v pe~i in nato
starali 8 ur pri 800 °C. Za karakterizacijo izdelanih zlitin so uporabili vrsti~no elektronsko mikroskopijo (SEM) s prigrajenim
energijskim disperzijskim spektroskopom (EDS), rentgensko difrakcijo (XRD) in Vickersov merilnik trdote. Ulite zlitine so
imele najvi{jo trdoto, zlitina I v povpre~ju 650,8 HV in zlitina II povpre~no 625,6 HV, zaradi prisotnosti metastabilnih izlo~kov,
ki so nastali med hitrim strjevanjem. Homogenizacija je zmanj{ala trdoto na 487,2 HV (zlitina I) in 522,6 HV (zlitina II) zaradi
raztapljanja izlo~kov in prerazporeditve legirnih elementov, medtem ko je staranje pove~alo trdoto na pribli`no 525 HV v obeh
zlitinah zaradi sekundarnega izlo~anja NiAl s strukturo B2 in Ni2TiAl s strukturo L21 z bolj fino in homogeno porazdelitvijo.
SEM-EDS analiza je potrdila, da ima zlitina I bolj enakomerno porazdelitev izlo~kov, medtem ko je zlitina II vsebovala ve~jo
koli~ino Ni2TiAl izlo~kov, vendar z lokalnimi aglomeracijami. Avtorji ugotavljajo, da sta homogenizacija in staranje mo~no
vplivala na na~in izlo~anja in trdoto feritnih superzlitin, pri ~emer je zlitina I pokazala bolj{o homogenost, zlitina II pa je dajala
prednost ve~ji tvorbi Ni2TiAl, kar poudarja vpliv vsebnosti Ti na fazno stabilnost in mehanske lastnosti.
Klju~ne besede: staranje, feritna superzlitina, trdota, homogenizacija, izlo~ki L21–Ni2TiAl, NiAl-B2, SEM, XRD
1 INTRODUCTION environments where conventional steels fail.3,4 The de-
mand for more efficient power generation and renewable
Superalloys have been developed as high-perfor- energy systems has further increased the need for ad-
mance materials due to their ability to maintain strength, vanced superalloys with superior mechanical and chemi-
stability, and corrosion resistance at elevated tempera- cal stability.5–7
tures.1,2 These alloys are extensively applied in turbines,
energy-conversion systems, and other high-temperature Among the various types, ferritic superalloys have at-
tracted considerable attention because of their lower
*Corresponding author's e-mail: cost, higher thermal conductivity, and lower coefficient
selly.septianissa@widyatama.ac.id (Selly Septianissa) of thermal expansion compared to nickel-based superal-
© 2026 The Author(s). Except when otherwise noted, articles in this jour- loys.8–10 These characteristics make ferritic alloys partic-
nal are published under the terms and conditions of the Creative Com-
mons Attribution 4.0 International License (CC BY 4.0). ularly suitable for structural applications exposed to cy-
Materiali in tehnologije / Materials and technology 60 (2026) 2, 235–242 235
A. GANDA PUTRA et al.: MICROSTRUCTURAL EVOLUTION AND HARDNESS OF FERRITIC SUPERALLOYS ...
clic thermal loads.2 However, one of the limitations of (XRD). Vickers hardness testing was conducted to evalu-
ferritic alloys is their relatively lower creep and corro- ate the mechanical response.
sion resistance at elevated temperatures. To overcome The objective of this work was to clarify the influ-
this, alloying strategies and precipitation strengthening ence of heat treatment on the precipitation of NiAl-B2
have been introduced. and L21–Ni2TiAl in ferritic superalloys and to establish
The addition of elements such as Ni, Al, and Ti plays the relationship between alloy composition, micro-
a crucial role in forming intermetallic precipitates that structure, and hardness. The findings provide essential
enhance high-temperature performance. In particular, insights into precipitation-strengthening mechanisms and
NiAl-B2 precipitates are known to provide effective highlight the role of Ti content in controlling the phase
strengthening through their coherent dispersion in the stability. This study contributes to the broader develop-
ferritic matrix.11–13 Furthermore, the formation of ment of ferritic superalloys for high-temperature applica-
L21–Ni2TiAl precipitates contributes additional stability tions by providing fundamental knowledge of heat-treat-
and resistance against dislocation motion, thereby im- ment–microstructure–property relationships.
proving both the mechanical strength and potential cor-
rosion resistance. The balance between these precipitates
is strongly influenced by the alloy composition and the 2 EXPERIMENTAL PART
applied heat treatments.13–15
The ferritic superalloys were synthesized by electric
Previous studies have shown that the ratio of Ni to Ti arc melting under an argon atmosphere to minimize any
and the homogenization conditions determine the stabil- oxidation. Two compositions were designed with varia-
ity and morphology of these precipitates.16,17 While tions in titanium content, denoted as Alloy I (2 w/% Ti)
NiAl-B2 tends to form during rapid cooling in the and Alloy II (4 w/% Ti). The nominal chemical composi-
as-cast condition, L21–Ni2TiAl usually emerges more tions of the alloys are presented in Table 1. High-purity
prominently after controlled aging treatments.18 The raw materials of Fe, Ni, Cr, Al, Ti, Mo, and Zr (%99.5 %)
challenge lies in optimizing the precipitation sequence to were used as starting elements. Each alloy was produced
achieve both uniform distribution and desired volume in button ingot form with a mass of approximately 15 g
fraction, since excessive or uneven precipitation can lead per button.
to microsegregation and localized weaknesses.19–22
Heat treatment is a critical step in tailoring the Table 1: Nominal chemical compositions of the ferritic superalloys
microstructure of ferritic superalloys.23 Homogenization (w/%)
eliminates chemical segregation and promotes the diffu- Alloy Fe Cr Ni Al Mo Ti Zr
sion of alloying elements, but it may reduce hardness I 68 10 10 6.5 3 2 0.25
temporarily due to precipitate dissolution. Aging, on the II 66 10 10 6.5 3 4 0.25
other hand, refines and redistributes precipitates, restor-
ing hardness through precipitation-hardening mecha- The melting was conducted in a water-cooled copper
nisms.24 Therefore, a systematic study on the homogeni- crucible under continuous argon flow. Each ingot was
zation–aging sequence is necessary to understand the flipped and remelted at least three times to ensure the
microstructural evolution and its effect on mechanical compositional homogeneity. The resulting as-cast sam-
properties.25–27
ples were subsequently cut into smaller specimens for
Recent reports have mainly focused on nickel-based heat treatment and characterization.
or austenitic superalloys, while fewer works have ad- The heat treatment was performed in two stages.
dressed ferritic systems reinforced with Ni–Al–Ti pre- First, homogenization was conducted at 1150 °C for 10 h
cipitates.11 Moreover, the majority of studies emphasized followed by furnace cooling to room temperature. This
creep or oxidation resistance, with less attention given to treatment was designed to minimize microsegregation
the correlation between microstructure, hardness, and and to redistribute alloying elements within the ferritic
controlled precipitation of NiAl-B2 and L21–Ni2TiAl in matrix. Second, aging was performed at 800 °C for 8 h
ferritic alloys. This creates a knowledge gap, particularly followed by furnace cooling. This process was intended
regarding how different Ti additions affect precipitation to promote secondary precipitation of NiAl-B2 and
behavior during homogenization and aging.12 L21–Ni2TiAl phases with refined morphology and im-
In this context, the present study investigated ferritic proved distribution.
superalloys with two Ti variations (2 w/% and 4 w/%) The homogenization temperature of 1150 °C was se-
prepared via electric arc melting. The alloys were sub- lected based on previous studies on Fe–Ni–Al–Ti ferritic
jected to homogenization at 1150 °C for 10 h and aging superalloys, where this temperature was reported to ef-
at 800 °C for 8 h to examine the evolution of precipitates fectively dissolve coarse intermetallic precipitates and
and their effect on hardness. Microstructural analysis minimize chemical segregation without excessive grain
was performed using scanning electron microscopy growth. The subsequent aging treatment at 800 °C for
(SEM) with energy-dispersive spectroscopy (EDS), and 8 h was chosen to promote the controlled secondary pre-
phase identification was carried out by X-ray diffraction cipitation of NiAl-B2 and L21–Ni2TiAl phases, which are
236 Materiali in tehnologije / Materials and technology 60 (2026) 2, 235–242
A. GANDA PUTRA et al.: MICROSTRUCTURAL EVOLUTION AND HARDNESS OF FERRITIC SUPERALLOYS ...
known to contribute to precipitation strengthening in
similar alloy systems.
Microstructural characterization was carried out us-
ing scanning electron microscopy (SEM, JEOL
JSM-IT200) equipped with energy-dispersive spectros-
copy (EDS) to analyze elemental distribution and phase
composition. X-ray diffraction (XRD, GGAS) with Cu
K radiation (
 = 0.15406 nm) was employed for phase
identification in the range 2 = 20–90° with a step size
of 0.02°.
The mechanical properties were evaluated by Vickers
hardness testing (HV) using a load of 9.81 N (1 kgf) ap-
plied for 10 s. At least five measurements were taken for
each sample, and the average values with standard devia-
tions were calculated.
3 RESULTS Figure 2: X-ray diffraction patterns of ferritic superalloys after ho-
mogenization: a) Alloy I (2 w/% Ti), b) Alloy II (4 w/% Ti)
The hardness measurements of the ferritic superal-
loys under different conditions are summarized in Ta-
ble 2. In the as-cast state, both alloys showed relatively Table 2: Hardness values of ferritic superalloys (HV) in as-cast, ho-
high hardness values, with Alloy I reaching an average mogenized, and aged conditions
of 650.82 HV and Alloy II reaching 625.60 HV. These
values are considerably higher than conventional ferritic Condition Alloy I (HV) Alloy II (HV)
steels, which generally exhibit hardness below 300 HV. As-cast 650.82 625.60
Homogenized 487.16 522.60
After homogenization at 1150 °C for 10 h, a decrease Aged 525.60 525.00
in hardness was observed. Alloy I decreased to
487.16 HV, while Alloy II decreased to 522.60 HV. This The X-ray diffraction results of the alloys after ho-
reduction indicated that the homogenization process in- mogenization are shown in Figure 2. Both alloys exhib-
fluenced the dissolution of precipitates and resulted in ited FeAl, Ni2Al, and Ni2TiAl phases. Alloy I showed a
softer matrices. Nevertheless, Alloy II maintained a lower diffraction intensity for Ni2TiAl, while Alloy II ex-
higher hardness compared to Alloy I after homogeniza- hibited stronger diffraction peaks for this phase, suggest-
tion, showing the influence of higher titanium content. ing a higher volume fraction of Ni2TiAl due to the
Following the aging process at 800 °C for 8 h, both greater Ti addition. This difference highlighted the effect
alloys experienced an increase in hardness. Alloy I of composition on the precipitation behavior after ho-
reached 525.6 HV and Alloy II reached 525.0 HV. Al- mogenization.
though these values did not exceed the as-cast condition, After aging at 800 °C for 8 h, the diffraction patterns
the hardness became more stable and uniform. The trend (Figure 3) revealed a noticeable increase in the intensity
of hardness variation across different heat-treatment con-
ditions is illustrated in Figure 1.
Figure 1: Hardness comparison of Alloy I and Alloy II in as-cast, ho- Figure 3: X-ray diffraction patterns of ferritic superalloys after aging
mogenized, and aged conditions at 800 °C for 8 h: a) Alloy I (2 w/% Ti), b) Alloy II (4 w/% Ti)
Materiali in tehnologije / Materials and technology 60 (2026) 2, 235–242 237
A. GANDA PUTRA et al.: MICROSTRUCTURAL EVOLUTION AND HARDNESS OF FERRITIC SUPERALLOYS ...
Figure 4: SEM micrographs of ferritic superalloys: a) homogenized Alloy I, b) homogenized Alloy II, c) aged Alloy I, d) aged Alloy II
of the Ni2TiAl peaks for both alloys, indicating the for- Phase identification was performed by comparing the
mation and growth of secondary precipitates. Alloy II diffraction patterns with standard reference data
maintained stronger Ni2TiAl reflections compared to Al- (ICDD/JCPDS) and by correlating the XRD results with
loy I, confirming that a higher Ti content promotes fur- compositional information obtained from SEM-EDS
ther precipitation during aging. Meanwhile, Alloy I ex- analysis. Due to the potential overlap of diffraction peaks
hibited a slight enhancement in the NiAl-B2 phase, among FeAl, NiAl-B2, and L21–Ni2TiAl phases, qualita-
implying improved phase stability and homogeneity. The tive phase discrimination was supported by combined
combined heat treatment process (homogenization fol- microstructural and elemental analysis, rather than rely-
lowed by aging) thus facilitated both phase refinement ing solely on peak intensity.
and precipitation strengthening, which correlated with The microstructural features of the alloys observed
the increase in hardness observed experimentally. by SEM are presented in Figure 4. After homogeniza-
Figure 5: EDS elemental mapping of Alloy I after aging
238 Materiali in tehnologije / Materials and technology 60 (2026) 2, 235–242
A. GANDA PUTRA et al.: MICROSTRUCTURAL EVOLUTION AND HARDNESS OF FERRITIC SUPERALLOYS ...
Figure 6: EDS elemental mapping of Alloy II after aging
tion, Alloy I showed relatively uniform ferritic grains matrix. In Alloy II, however, there were localized regions
with a fine dispersion of precipitates, while Alloy II ex- enriched in Ni and Ti, corresponding to Ni2TiAl precipi-
hibited a larger number of precipitates that were distrib- tates. These observations suggested differences in pre-
uted less uniformly. After aging, the microstructures cipitate formation between the two alloys depending on
changed significantly. Both alloys exhibited refined Ti content.
grains and denser precipitate distributions. Alloy I dis- Quantitative EDS point analysis further clarified the
played a more uniform and finer dispersion of precipi- microstructural differences, as presented in Figures 7
tates, while Alloy II showed a larger quantity of precipi- and 8. In Alloy I, Point 1 revealed the presence of
tates, some of which tended to form clusters in localized Ni–Al–Ti enriched regions, whereas Point 2 showed
regions. Fe-rich ferritic regions. In Alloy II, Point 1 indicated en-
The results of the EDS mapping are shown in Fig- richment of Zr together with Ni and Ti, while Point 2
ures 5 and 6. In Alloy I, the main elements (Fe, Ni, Al, showed predominantly Fe with limited amounts of Ni
and Ti) were distributed relatively uniformly within the and Ti. These results demonstrated that Alloy II con-
Figure 7: EDS point analysis of Alloy I (Point 1 and Point 2) after aging
Figure 8: EDS point analysis of Alloy II (Point 1 and Point 2) after aging
Materiali in tehnologije / Materials and technology 60 (2026) 2, 235–242 239
A. GANDA PUTRA et al.: MICROSTRUCTURAL EVOLUTION AND HARDNESS OF FERRITIC SUPERALLOYS ...
tained not only higher Ti-related precipitates but also the phases after homogenization. The stronger Ni2TiAl peaks
localized segregation of secondary alloying elements observed in Alloy II confirmed that higher Ti addition fa-
such as Zr. vored the formation of this ordered intermetallic phase.
Previous studies have also emphasized the role of Ti in
stabilizing L21–Ni2TiAl, which enhances high-tempera-
4 DISCUSSION
ture performance but requires careful control of distribu-
The evolution of hardness across different heat-treat- tion to avoid microsegregation. The balance between
ment conditions can be directly correlated with the ob- NiAl-B2 and Ni2TiAl is therefore essential to achieve a
served microstructural changes. In the as-cast condition, desirable combination of strength and stability.29
the presence of metastable precipitates formed during After aging at 800 °C for 8 h, the XRD results re-
rapid solidification provides strong resistance to disloca- vealed a clear increase in the intensity of Ni2TiAl peaks
tion motion, resulting in high hardness values. Homoge- for both alloys, indicating the continued precipitation of
nization leads to precipitate dissolution and elemental re- this phase during thermal exposure. This finding sug-
distribution, reducing hardness, while aging promotes gests that the diffusion of Ni, Ti, and Al atoms was en-
the formation of finer and more stable NiAl-B2 and hanced during aging, promoting the formation of fine
L21–Ni2TiAl precipitates, which restore the hardness and ordered L21–Ni2TiAl precipitates within the ferritic
through precipitation-hardening mechanisms. matrix. The appearance of stronger and sharper diffrac-
The results demonstrated that the hardness of ferritic tion peaks also reflected an improvement in crystallinity
superalloys was strongly influenced by both the compo- and a reduction of lattice strain compared to the homoge-
sition and heat treatment. The highest hardness values nized condition. The presence of FeNi and Fe3Al peaks
were obtained in the as-cast condition, with Alloy I in minor proportions indicates a partial redistribution of
reaching 650.82 HV and Alloy II reaching 625.60 HV. Fe and Ni during the thermal treatment, a phenomenon
These high values were attributed to the rapid-solidifica- consistent with typical diffusion-controlled phase evolu-
tion process, which promoted the formation of tion in Fe–Ni–Al–Ti systems.
metastable NiAl-B2 precipitates that effectively hindered
dislocation motion. Such a phenomenon has been widely Comparing both alloys, Alloy II showed a higher
reported in ferritic and Ni–Al-based alloys, where rapid fraction and intensity of Ni2TiAl after aging, confirming
cooling leads to supersaturation and metastable strength- that Ti content has a direct influence on the precipitation
ening phases.28 kinetics. The excess Ti provided a higher driving force
During homogenization at 1150 °C for 10 h, the for the formation of L21–Ni2TiAl, which contributes to
hardness of both alloys decreased significantly. This re- enhanced high-temperature strength. However, this ad-
duction was caused by the dissolution of metastable pre- vantage may be offset by a tendency toward local com-
cipitates and the redistribution of alloying elements into positional inhomogeneity, as excessive Ti can lead to
the ferritic matrix. Alloy I dropped to 487.16 HV, while microsegregation and the coarsening of intermetallics. In
Alloy II maintained a slightly higher value of 522.60 HV. contrast, Alloy I exhibited a more balanced micro-
The results indicated that higher Ti addition delayed the structure, where NiAl-B2 and Ni2TiAl precipitates were
complete dissolution of Ni2TiAl precipitates, which pro- more uniformly distributed, leading to better structural
vided partial strengthening even after homogenization. stability and moderate hardness improvement.
Similar observations were reported by Wang et al. The synergistic role of homogenization and aging
(2021), who found that Ti-rich ferritic alloys retain a treatments can therefore be interpreted as a two-step pre-
fraction of Ni2TiAl precipitates after high-temperature cipitation process. Homogenization at 1150 °C for 10 h
homogenization, resulting in moderate hardness reten- dissolved coarse intermetallics and promoted chemical
tion.16 uniformity, while subsequent aging at 800 °C for 8 h fa-
The aging treatment at 800 °C for 8 h restored the cilitated controlled precipitation and refinement of the
hardness values in both alloys, reaching approximately L21–Ni2TiAl phase. This sequence effectively combines
525 HV. This recovery was associated with the second- matrix homogenization with precipitation hardening,
ary precipitation of NiAl-B2 and L21–Ni2TiAl phases. which explains the improved mechanical performance
The finer and more homogeneously distributed precipi- measured experimentally. Such behavior is in agreement
tates improved the hardness by providing effective barri- with previous reports on Fe–Ni–Al–Ti superalloys,
ers against dislocation glide through precipitation hard- where the dual presence of NiAl-B2 and Ni2TiAl contrib-
ening. Alloy I exhibited slightly more uniform hardness utes to a superior strength and oxidation resistance at ele-
values, while Alloy II showed higher scatter due to local- vated temperatures.
ized agglomeration of precipitates. These results con- Overall, the XRD and microstructural observations
firmed that the controlled aging can refine the distribu- demonstrate that the Ti addition plays a key role in tai-
tion of precipitates and compensate for the hardness loss loring the balance between phase fraction and distribu-
caused by homogenization. tion. Alloy I, with lower Ti, favors homogeneity and
The XRD analysis supported these findings by re- structural integrity, while Alloy II, with higher Ti, en-
vealing the coexistence of FeAl, Ni2Al, and Ni2TiAl hances the amount of L21–Ni2TiAl precipitates and po-
240 Materiali in tehnologije / Materials and technology 60 (2026) 2, 235–242
A. GANDA PUTRA et al.: MICROSTRUCTURAL EVOLUTION AND HARDNESS OF FERRITIC SUPERALLOYS ...
tentially improves high-temperature performance. The 5 CONCLUSIONS
combination of these characteristics provides valuable
insight for optimizing future compositions and heat- Ferritic superalloys containing NiAl-B2 and
treatment parameters for ferritic superalloys designed for L21–Ni2TiAl precipitates were synthesized and heat
high-temperature applications. treated with homogenization and aging. The as-cast al-
SEM observations further clarified the differences be- loys exhibited the highest hardness due to the presence
tween the two alloys. After homogenization, Alloy I dis- of metastable precipitates formed during rapid solidifica-
played relatively uniform ferritic grains with fine precip- tion. Homogenization at 1150 °C for 10 h reduced the
hardness as a result of precipitate dissolution and ele-
itates, while Alloy II exhibited larger amounts of
mental redistribution, while subsequent aging at 800 °C
precipitates but with less homogeneous distribution. Af- for 8 h restored the hardness through the formation of
ter aging, both alloys showed refined grains and denser finer and more stable secondary precipitates. Alloy I
precipitate distributions. Alloy I demonstrated more uni- (2 w/% Ti) showed more homogeneous precipitate distri-
form dispersions, while Alloy II presented a higher quan- butions, whereas Alloy II (4 w/% Ti) promoted higher
tity of precipitates that occasionally formed clusters. amounts of Ni2TiAl with local clustering. These findings
These microstructural differences explained the hardness demonstrated that Ti content and heat-treatment se-
trends, as uniform precipitate distributions tend to pro- quence played a decisive role in controlling precipitation
vide more consistent strengthening, while clustered pre- behavior, microstructural stability, and mechanical re-
cipitates may reduce overall efficiency despite their sponse of ferritic superalloys.
higher volume fraction.30–33
EDS mapping and point analysis confirmed these ob-
servations at the compositional level. Alloy I exhibited Acknowledgment
relatively homogeneous distributions of Fe, Ni, Al, and The authors gratefully acknowledge the financial
Ti, while Alloy II revealed localized enrichment of Ni support provided by the Ministry of Education, Culture,
and Ti corresponding to Ni2TiAl precipitates. Point anal- Research, and Technology of the Republic of Indonesia
ysis of Alloy II also revealed significant enrichment of through the BIMA research grant scheme. The authors
Zr in some regions, suggesting that Zr segregation may also thank the research facilities at BRIN and Universitas
influence grain boundary stability and precipitate nucle- Jenderal Achmad Yani for technical assistance and labo-
ation. These findings are in line with the work of Mayer ratory support during this work.
et al. (2024), who reported that minor alloying additions
such as Zr can play a critical role in refining grain size
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