M. KHAKIAN et al.: MICROSTRUCTURAL EVOLUTION DURING THE TRANSIENT LIQUID-PHASE BONDING ...
365–371
MICROSTRUCTURAL EVOLUTION DURING THE TRANSIENT
LIQUID-PHASE BONDING OF DISSIMILAR NICKEL-BASED
SUPERALLOYS OF IN738LC AND NIMONIC 75
RAZVOJ MIKROSTRUKTURE MED SPAJANJEM S PREHODNO
TEKO^O FAZO NEENAKIH SUPERZLITIN NA OSNOVI NIKLJA
IN738LC IN NIMONIC 75
Meysam Khakian Ghomi, Saeid Nategh, Shamsoddin Mirdamadi
Islamic Azad University, Science and Research Branch, Department of Materials Engineering, Tehran, Iran
khakian-meysam@yahoo.com, nategh@sharif.ir
Prejem rokopisa – received: 2015-04-01; sprejem za objavo – accepted for publication: 2015-05-08
doi:10.17222/mit.2015.072
The joining of dissimilar nickel-based superalloys, i.e., IN738LC to Nimonic 75, using transient liquid-phase bonding with a
Ni-15Cr-3.5B interlayer (MBF-80) was carried out at temperatures of 1080 °C to 1180 °C for different bonding times of 30–150
min. A joint cross-section was surveyed using optical and scanning electron microscopy. Microstructural examinations showed
that after short bonding times, the joint microstructure consists of continuous eutectic intermetallic phases and longer bonding
times lead to a eutectic-free microstructure. It was clear that for all the bonding times and temperatures, boride phases were
precipitated at the interface of the base metal and the interlayer due to boron diffusion in to the base metals. The results also
showed that the morphology of the precipitates in the diffusion-affected zone (DAZ) varies from globular to acicular by
increasing the bonding time. Completion of the isothermal solidification, which prevents the formation of continuous
intermetallic phases at the joint centerline, was studied at different temperatures.
Keywords: IN738LC, Nimonic 75 superalloy, TLP bonding, isothermal solidification, microstructure
Spajanje razli~nih superzlitin na osnovi niklja IN738LC na Nimonic 75, z uporabo prehodno teko~e faze z vmesnim slojem
Ni-15Cr-3,5B (MBF- 80), je bilo izvedeno pri temperaturah od 1080 °C do 1180 °C in pri razli~nih ~asih spajanja od 30 min do
150 min. Pre~ni prerez spoja je bil pregledan s svetlobno in z vrsti~no elektronsko mikroskopijo. Mikrostrukturne preiskave so
pokazale, da pri kratkih ~asih spajanja mikrostruktura sestoji iz zvezne evtekti~ne intermetalne faze, dolgi ~asi spajanja pa
povzro~ijo mikrostrukturo brez evtektika. Izkazalo se je, da se pri vseh ~asih in temperaturah spajanja, boridna faza zaradi
difuzije bora izlo~a na meji z osnovnim materialom v osnovni material. Rezultati so tudi pokazali, da morfologija izlo~kov v
difuzijsko vplivani coni (DAZ) z nara{~anjem ~asa spajanja varira, od globularne do acikularne. Dokon~anje izotermnega
strjevanja, ki prepre~i nastanek zvezne intermetalne faze na liniji spajanja, je bilo prou~evano pri razli~nih temperaturah.
Klju~ne besede: IN738LC, superzlitina Nimonic 75, TLP spajanje, izotermno strjevanje, mikrostruktura
1 INTRODUCTION
IN738LC is one of the most practical casting
nickel-based superalloys. IN738LC is strengthened by
both solid-solution and precipitation-hardening mecha-
nisms.1 Due to the presence of coherent 
’ precipitates in
the alloy with a complex chemical composition and a
high stability at high temperatures, the alloy can keep its
excellent strength in high-temperature operations and
severe conditions, such as gas turbine components.
Because of the mentioned properties, the alloy is a good
choice for utilization in the first rows of gas-turbine hot
sections. Also, this alloy has outstanding strength
accompanied by excellent creep, fatigue, oxidation and
corrosion resistance at high temperatures.2–4
Nimonic 75 is an 80/20 nickel-chromium alloy with
controlled additions of titanium and carbon. Nimonic 75
first introduced in the 1940s for turbine blades as sealing
components and is now mostly used for sheet applica-
tions calling for oxidation and scaling resistance coupled
with medium strength at high operating temperatures. It
is still used in gas-turbine engineering and also for
industrial thermal processing, furnace components and
heat-treatment equipment.5
The weldability of superalloys is very much depend-
ent on the amount of Al and Ti in their chemical compo-
sition. The high precipitation rate of 
’ in alloys with a
large amount of Al and Ti make them susceptible to
crack propagation during welding.6–8 Fusion welding,
diffusion bonding and brazing are the three main me-
thods of joining and repairing superalloys that are widely
used in power plants and aerospace industries. Solid-
state diffusion bonding needs high pressure, time and
temperature. Therefore, the process encounters a lot of
practical and economic limitations, like growth of grains
and precipitates during bonding and lengthy processing
causes it to be uneconomic.9 Brazing is the other method
of joining that uses an interlayer, containing a melting-
point depressant like B, Si and P, as the joining media.
The joining temperature must be precisely arranged to
melt only the interlayer. Brittle boride, silicide and phos-
phate continuous phases may be developed in the joint
Materiali in tehnologije / Materials and technology 50 (2016) 3, 365–371 365
UDK 67.017:621.791/.792:622.785 ISSN 1580-2949
Original scientific article/Izvirni znanstveni ~lanek MTAEC9, 50(3)365(2016)
area during the brazing process and can degrade the
joint’s properties.10,11
Transient liquid-phase (TLP) bonding is a hybrid pro-
cess of brazing and diffusion bonding.1 This method
possesses the advantages of brazing and diffusion
bonding and makes the joint structure very similar to the
base material. In contrast to diffusion bonding, the
process does not need any pressure due to the use of a
liquid interlayer.12,13 The superiority of TLP in compa-
rison with brazing is the completion of isothermal
solidification in the bonding temperature.10 Also, TLP is
widely used in the joining of metals and ceramics.14
In the standard models of TLP, there are three indi-
vidual stages: dissolution, isothermal solidification and
solid-state homogenization. Because of the short-range
diffusion of melting-point depressant elements in the
base metal, the dissolution of the base metal usually
needs several minutes. In the isothermal solidification
stage, long-term diffusion occurs and therefore the pro-
cess needs much more time, depending on the bonding
temperature and the interlayer type and the time varies
from minutes to hours.15 By optimizing the time and
temperature of the bonding, a joint microstructure that is
very similar to the base metal with no discontinuity in
the microstructure can be achieved.16
In this paper, the effect of bonding time and tem-
perature on the microstructure evolution of the transient
liquid-phase bonding of IN 738LC and Nimonic 75
using MBF-80 filler metal was investigated.
2 MATERIALS AND EXPERIMENTAL
PROCEDURES
IN738LC and Nimonic 75 nickel-based superalloys
were used as the base metals in this study. Both super-
alloys were used in the standard solution heat-treated
condition. Commercial Ni-Cr-B in the form of amor-
phous foil (MBF-80) with a 75-μm thickness was used as
the interlayer. The chemical compositions of the base
materials and the interlayer are given in Table 1.
TLP bonding test coupons were cut using EMD
wirecut to a size of 10 mm × 10 mm × 5 mm, then they
were grounded with a pendulum grinding machine, in
order to remove the recast oxide layer from the faying
surface of the coupons, and finally cleaned ultrasonically
in a acetone bath. The interlayer was cut with a size of
11 mm × 6 mm and placed between two faying surfaces
of the base alloys. In order to prevent the movement of
the samples, the assembly was placed in a fixture with-
out any pressure on it. Green stop-off type 1 was used to
prevent the flowing out of the molten interlayer. The
solidus and liquidus temperatures of the interlayer are
1050 °C and 1090 °C, respectively.17 Therefore, the
bonding temperatures were selected above 1050 °C. TLP
bonding was performed in a furnace under a vacuum of
10–5 mbar pressure at different temperatures of (1080,
1120, 1150 and 1180) °C and various holding times of
(30, 60, 120 and 150) min. In order to investigate the
phases formed during the athermal solidification, one
test coupon was bonded at 1120 °C for 5 min. The heat-
treatment cycle of the bonding is illustrated in Figure 1.
The heating rate from 950 °C to the bonding temperature
was set to 20 °C/min. In order to show the effect of time
on the bond strength, a shear test was carried out on all
the samples TLP bonded at 1080 °C.
The TLP-bonded test coupons were cut perpendicular
to the bonding surface, due to brittleness of the inter-
metallic phases formed in the bonding centerline, by
EDM wirecut and then prepared for metallographic
examinations. In order to reveal the microstructure
constituent, the samples were etched with Kalling’s solu-
tion (5 gr CuCl2 + 100 cc HCl +100 cc Ethyl alcohol).18
Metallographic examinations were carried out using
optical and scanning electron microscopy.
3 RESULTS AND DISCUSSION
3.1 Microstructure of the joint
The microstructure of the TLP-bonded specimen at
1120 °C and 5 minutes is shown in Figure 2. As can be
seen, the bonding area can be divided into six distinct
zones:
• Base metal - Nimonic side
• Isothermally Solidified Zone – Nimonic 75 Side (ISZ
– Nimonic Side)
M. KHAKIAN et al.: MICROSTRUCTURAL EVOLUTION DURING THE TRANSIENT LIQUID-PHASE BONDING ...
366 Materiali in tehnologije / Materials and technology 50 (2016) 3, 365–371
Figure 1: Heat-treatment cycle of the TLP bonding test coupons
Slika 1: Potek cikla toplotne obdelave pri TLP spajanju preizku{ancev
Table 1: Chemical composition of base materials and interlayer in mass fractions, (w/%)
Tabela 1: Kemijska sestava osnovnih materialov in vmesne plasti, v masnih odstotkih (w/%)
Alloys Cr Co Al Ti W Mo Ta Nb Fe C B Ni
IN738LC 16.23 8.56 3.41 3.45 3.05 1.73 1.57 0.67 0.08 0.09 0.0063 Bal.
Nimonic 75 20.50 – 0.29 0.55 – – – – 4.78 0.10 – Bal.
MBF–80 14.89 – – – – – – – – – 3.72 Bal.
• Athermally Solidified Zone (ASZ)
• Isothermally Solidified Zone – Inconel 738 Side (ISZ
– Inconel Side)
• Diffusion Affected Zone – Inconel 738 Side (DAZ –
Inconel Side)
• Base metal – Inconel side
As can be seen in Figure 2a, the ISZ zone on both
sides of the ASZ contains a thin layer of 
 solid solution
that formed at the solid/liquid interface during isother-
mal solidification from the base metal to the joint center-
line. The chemical composition of the solid solutions
formed on the ISZ – Inconel Side and ISZ - Nimonic
Side are shown in Table 2. A significant difference bet-
ween these two compositions is related to the chemical
compositions of the Nimonic 75 and the IN738LC. Also,
in Figure 2b, the different phases that are formed during
bonding are specified with A to F.
As the interlayer melts, because the liquid and solid
phases are not in the equilibrium condition, base-metal
dissolution commences. The diffusion of boron into the
base metal and the diffusion of base-metal elements like
Cr, Fe, Co, Al and Ti into the molten interlayer leads to
the equilibrium condition between the liquid and the
solid. A chemical analysis of ISZ shows the diffusion of
the base-alloy elements that were not present in the
primary interlayer. The alloying elements’ diffusion from
the base metal to the interlayer and also boron diffusion
from the interlayer to the base metal increases the
liquidus temperature of the interlayer. The dissolution
stage continues until the liquidus temperature of the
molten interlayer reaches the bonding temperature, and
then the isothermal solidification starts from the
solid/liquid interface to the joint centerline.2, 19
As seen in Table 2, the chemical composition of the
ISZ regions adjacent to the base alloys (Inconel Side and
Nimonic Side) are not similar; therefore, we can
conclude that the time required to reach equilibrium on
each side are not equal. In contrast with the TLP bonding
of two similar alloys, in which the isothermal solidifi-
cation starts simultaneously and the eutectic centerline
forms symmetrically, in dissimilar alloys the TLP
bonding eutectic centerline lies closer to the alloy so that
its equilibrium starts earlier.
A variation of the chemical composition that is due to
the interdiffusion of elements of the base alloy and the
interlayer is the main driving force of solidification for
the ISZ.19 Since the solid and liquid are in an equilibrium
condition during isothermal solidification, the secondary
phases cannot form at this stage.3,20 The solidification
behavior of the remaining liquid during the TLP bonding
of pure nickel using the Ni-Cr-B interlayer, before
completion of the isothermal solidification, was modeled
by K. Ohsasa et al.21 The ternary phase diagram of
Ni-Cr-B, in which the chemical composition of the
interlayer is specified, is shown in Figure 3.22 During the
cooling of the remaining liquid, which is the main
M. KHAKIAN et al.: MICROSTRUCTURAL EVOLUTION DURING THE TRANSIENT LIQUID-PHASE BONDING ...
Materiali in tehnologije / Materials and technology 50 (2016) 3, 365–371 367
Table 2: EDS analysis (x/%) of phase formed in bond line shown in Figure 2
Tabela 2: EDS analiza (x/%) faze, ki je nastala na liniji stika, prikazani na Sliki 2
Al Ti Cr Fe Co Ni Nb Mo Ta W
ISZ - Inconel Side 3.12 0.94 19.41 1.23 3.01 70.43 0.64 0.52 0.28 0.41
ISZ - Nimonic Side 0.57 0.46 22.12 4.26 0.35 71.21 0.34 0.40 0.0 0.28
A (Ni-rich Boride) 1.08 3.83 9.18 0.71 2.28 80.70 0.85 0.56 0.80 0.0
B (
 Eutectic) 0.97 0.53 16.27 1.64 2.47 75.84 0.60 0.66 0.30 0.71
C (Cr-rich Boride) 0.41 0.08 89.72 0.15 0.47 5.37 0.46 2.02 0.0 1.31
D (Cr-rich Boride) 0.04 0.05 87.50 0.40 0.69 5.36 1.37 1.97 1.72 0.89
E 0.75 0.36 73.05 2.34 0.0 22.04 0.63 0.44 0.13 0.25
F 0.56 0.84 40.06 4.11 0.03 52.66 0.66 0.52 0.25 0.30
Figure 3: Liquidus projection of ternary phase diagram Ni-Cr-B
Slika 3: Projekcija likvidusa v ternarnem faznem diagramu Ni-Cr-B
Figure 2: a), b) SEM micrograph of sample bonded at 1120 °C for
5 min
Slika 2: a), b) SEM-posnetek vzorca, spajanega pri temperaturi 1120 °C,
5 min
driving force for ASZ solidification, 
 dendrite is the
first phase that forms at 1100 °C 21 and grows from the
solid/liquid interface towards the joint centerline. Solute
elements with a partition coefficient less than unity (k <
1) are rejected into the liquid. Continuous enrichment of
the liquid from the solute elements leads to the solute
concentration becoming more than the solubility limit of
the solute in the 
 and then the secondary solidification
constituents are formed between the dendrites (Phases E
and F).20 O. Ojo et al.23 and A. Egbewande et al.10 ob-
served the formation of these phases in the TLP bonding
of IN738 and IN600, by use of a Ni-Cr-B interlayer,
respectively.
During the cooling of the liquid and solid-solution
growth additional boron is rejected to the liquid, as a
result of poor solubility and the low partition coefficient
of boron in Ni (0.3 % of amount fractions and ~0.008),24
and then at 1042 °C the solidification path coincides
with the eutectic line that separates the 
 phase stability
region from Ni3B (e8 line in Figure 3) and the 
 solid
solution and nickel boride eutectic phases are formed
simultaneously through a binary eutectic transformation
(L
+Ni3B).
More cooling leads to the growth of the 
 solid
solution and the rejection of boron and the formation of
nickel borides lead to a reduction of the Ni concentration
and an increment in the Cr in the remaining liquid (Cr
solubility in Ni boride is relatively low (10.11 % of
amount fractions).19 Also, the Cr content of the liquid
increases by temperature decrement until at 997 °C the
liquid transforms into three phases of 
 solid solution,
nickel boride and chromium boride through a ternary
eutectic transformation (L
+Ni3B+CrB).21 These
phases are shown in Figure 2b, and its chemical com-
positions are shown in Table 2.
3.2 Effect of time and temperature on the microstruc-
ture of the TLP bonds
In order to investigate the effect of time on the micro-
structure of the TLP bonds, bonding was performed at
1080 °C for 30, 60, 120 and 150 min. It was clear that
the thickness of the intermetallic phases decreases with
the increasing time (Figure 4). The extent of isothermal
solidification during TLP bonding depends on the
amount and rate of boron diffusion into the base alloys.
The thickness of remaining interlayer, which can trans-
form into a continuous eutectic centerline during cool-
ing, decreases for longer bonding times. It was clear that
with an increasing time from 30 to 60 min, the thickness
of the centerline eutectic decreases. After 120 min there
is no continuous eutectic and after a longer time (150
min) there is a negligible amount of intermetallic phases.
The results showed that 150 min is not enough for the
completion of isothermal solidification at 1080 °C.
Figure 5 shows the ASZ thickness and the shear strength
of the bond at different times. It is clear that a dominant
increment in strength can be associated with a decrement
of the ASZ thickness. The shear strengths of Nimonic 75
and IN738 at room temperature are 650 MPa and 860
MPa, respectively. The results showed that the strength
of the TLP-bonded specimen at 1080 °C is less than the
strength of the base metals.
Figure 6 shows the optical microstructure of TLP
bonding at 1120 °C, 1150 °C after 120 min and 1180 °C
after 150 min. It was clear that at bonding temperatures
of 1120 °C and 1150 °C there was no centerline eutectic
micro-constituents, and isothermal solidification was
complete. It can be seen that with increasing bonding
temperatures from 1120 °C to 1150 °C, significant
microstructural changes occurred in the DAZ of IN738,
but no changes happened in the bond line. It is expected
that increasing the bonding temperature and con-
sequently increasing the diffusion rate of boron,
decreases the time required for completing the isother-
mal solidification. But as shown in Figure 6c, at 1180 °C
M. KHAKIAN et al.: MICROSTRUCTURAL EVOLUTION DURING THE TRANSIENT LIQUID-PHASE BONDING ...
368 Materiali in tehnologije / Materials and technology 50 (2016) 3, 365–371
Figure 5: Shear strength and ASZ thickness versus bonding time at
1080 °C
Slika 5: Odvisnost stri`ne trdnosti in debeline ASZ od ~asa spajanja
na temperaturi 1080 °C
Figure 4: Light micrograph of TLP-bonded specimen at 1080 °C:
a) 30 min, b) 60 min, c) 120 min, d) 150 min
Slika 4: Svetlobni posnetek vzorcev, spajanih s TLP, na temperaturi
1080 °C: a) 30 min, b) 60 min, c) 120 min, d) 150 min
there are significant amounts of centerline eutectic in the
bonding after 150 min and isothermal solidification was
not completed yet. O. Idouw et al.25 reported that in TLP
bonding of IN738, increasing the bonding temperature
from 1170 °C leads to the diffusion of aluminum and
titanium into the molten interlayer and a reduction of the
isothermal solidification rate may happen. They reported
that the diffusion of titanium to the molten layer leads to
the formation of a Ni-Ti rich phase, M2SC-type sulpho-
carbide, chromium-rich boride and a 
-
’ centerline
eutectic. These phases are very stable and hard to solute.
Therefore, they can decrease the rate of isothermal
solidification and the completion of the process will be
postponed.
3.3 Precipitation in the diffusion-affected zone (DAZ)
Boride precipitation is expected in the base metal
where the concentration of boron is more than its solu-
bility limit in a 
 solid solution.23 The solubility limit of
boron in nickel is 0.3 % of amount fractions over the
range of 1065–1110 °C, according to the Ni–B binary
phase diagram.26 Therefore, the diffusion of boron into
the base metal during the holding at bonding temperature
leads to the formation of boride precipitates in the DAZ.
These precipitates are shown in Figures 7 and 8 in two
morphologies: globular and acicular.
When the distance between the precipitates and the
interface increases the morphology of the precipitates
changes from globular to acicular. As mention before,
dissolution is the first stage of TLP bonding where the
base-alloys solute elements diffuse into the base alloy
until the equilibrium condition between solid/liquid is
achieved. Therefore, the alloying-elements concentration
in the base metal layer adjacent to the bond is poorer
than the other layers. As shown in Table 3, the amount
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Materiali in tehnologije / Materials and technology 50 (2016) 3, 365–371 369
Figure 7: Variation of precipitates’s morphology in DAZ at 1120 °C
with time from a) 5 min to b) 120 min. The morphology changes from
globular to globular/acicular.
Slika 7: Spreminjanje morfologije izlo~kov v DAZ na temperaturi
1120 °C, v odvisnosti od ~asa od a) 5 min do b) 120 min. Morfologija
se spreminja od globularne do globularno/acikularne.
Figure 6: Light micrograph of TLP-bonded specimens at: a) 1120 °C
for 120 min, b) 1150 °C for 120 min, c) 1180 °C for 150 min
Slika 6: Svetlobni posnetek vzorcev, spajanih s TLP: a) 1120 °C –
120 min, b) 1150 °C – 120 min, c) 1180 °C – 150 min
of alloying elements in the precipitates closer to the
bonding interface (globular precipitates) is less than the
ones further than the bond line (acicular precipitates). As
seen in Table 3, the high chromium content of the
globular precipitates leads to a significant depletion of
the chromium around them. Since the Cr is the main
element for resistance to corrosion of the base alloy, the
depletion of Cr around these precipitates leads to a re-
duction of the matrix’s corrosion resistance.27 Moreover,
a high concentration of 
’-formers in the precipitates
leads to the depletion of Al and Ti in the matrix around
the precipitates, and as seen in Figure 8, there is no 
’
particle around them.
The morphology of the precipitates varies by in-
creasing the bonding temperature from the globular to
the acicular morphology, and at 1150 °C the acicular
morphology is dominant (Figures 6a and 6b). The
reason is probably related to more diffusion of the
alloying elements at the higher temperature and greater
homogeneity of the chemical composition in the DAZ.
The other point that can be gained from Figure 6c is that
the amount of precipitates in the DAZ decreases by
raising the temperature, such that at 1180 °C there is no
acicular and globular precipitate. It can be concluded that
these precipitates may be dissolved at temperatures
lower than 1180 °C.
Figure 7 shows that at 1120 °C, the morphology of
the precipitates varies from globular to globular/acicular
by increasing the holding time from 5 to 120 min. This
phenomenon is related to more diffusion of boron into
the base alloy at longer times and implies that the forma-
tion of acicular precipitates need more alloying elements
than globular precipitates (Table 3).
Figure 8 shows the bond interface in a specimen TLP
bonded at 1120 °C for 150 min. Boron was detected in
all precipitates, but their accurate concentration could
not be reported quantitatively due to X-ray absorption of
the EDS analyzer window. The compositional analyses
shown in Table 3 suggests that globular precipitates are
borides rich in Ni, Cr, Mo, W and Al and acicular
precipitates are borides rich in Ti, Ta, Mo, Nb and W. O.
Ojo et al.22 and O. Idowu et al.24 observed boride
precipitates rich in Cr, W and Mo in TLP bonding of
IN738 by a Ni-Cr-B interlayer at 1130 °C. Also, it can be
seen that there are lots of very fine 
’ around acicular
precipitates. The reason is related to the absorption of Ti
by these precipitates so that the concentration of the 
’
former element is less than normal. Since the Nimonic
75 does not have any boride formers in its chemical
composition, no precipitate was observed in its diffu-
sion-affected zone. Figures 8b and 8c show the different
zones specified in Figure 8a.
4 CONCLUSION
The effect of time and temperature on the TLP bond-
ing of the dissimilar nickel-based super alloys IN738LC
and Nimonic 75 using an MBF-80 interlayer was inve-
stigated. The following conclusions can be drawn from
this study:
• Before completion of the isothermal solidification,
the microstructure of the joint centerline consists of
three eutectic phases: 
 solid solution, Ni-rich boride
and Cr-rich boride.
• DAZ precipitates are formed due to boron diffusion
from the interlayer to the base metal during a
M. KHAKIAN et al.: MICROSTRUCTURAL EVOLUTION DURING THE TRANSIENT LIQUID-PHASE BONDING ...
370 Materiali in tehnologije / Materials and technology 50 (2016) 3, 365–371
Figure 8: a) SEM micrograph of specimen TLP-bonded at 1150 °C for 150 min, b) and c) specified area in a) showed by b) and c) respectively
Slika 8: SEM-posnetek vzorcev, spajanih s TLP, na temperaturi 1150 C, 150 min, b) in c) dolo~eno podro~je a) prikazano na b) oz. c)
Table 3: EDS analysis of phases shown in Figure 8 (x/ %)
Tabela 3: EDS analiza faz prikazanih na Sliki 8 (x/%)
Al Ti Cr Co Ni Nb Mo Ta W
Acicular Precipitates 2.25 39.45 7.99 2.81 18.78 7.49 5.07 11.46 4.69
Globular Precipitates 8.44 3.53 38.70 4.06 34.68 0.57 5.28 0.61 4.12
B 3.71 0.46 25.65 6.32 60.61 0 0.60 1.15 1.49
solid-state transformation. Boride precipitates were
observed in the DAZ at bonding temperatures up to
1150 °C. However, at a bonding temperature of 1180
°C, the boride precipitates were not observed.
• At a given bonding temperature, the morphology of
the DAZ precipitates changes from globular to glo-
bular-acicular with an increasing bonding time.
• Boride precipitation in Nimonic 75 DAZ did not
occur due to a lack of boride-forming elements in its
chemical composition.
• A reduction in the isothermal solidification rate was
observed when TLP bonding at 1180 °C.
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M. KHAKIAN et al.: MICROSTRUCTURAL EVOLUTION DURING THE TRANSIENT LIQUID-PHASE BONDING ...
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