Volume 18 Preprint 41
Effect of Friction Welding Process Parameters on Oxidation and Hot corrosion behaviour of Incoloy 800 H
K.Anand, P. Sreeraj, K.Tamilmannan, S. P. Kumaresh Babu, P. Sathiya
Keywords: Incoloy 800 H, Friction welding, hot corrosion, XRD, SEM&EDS.
High temperature corrosion studies were carried out on friction welded Incoloy 800 H in air and molten salt of Na2SO4-60%V2O5 at 7000C under cyclic condition for 50 cycles. Results indicate when heating pressure increase, hot corrosion resistance of the weld decrease. The hot corrosion resistance increases when upsetting pressure increases. Measurement of weight gain or loss were done by Thermogravimetric analysis. It is found that molten salt atmosphere was more corrosion resistance than air oxidation atmosphere. The oxide scales formed on weldment were analysed by XRD, SEM/EDS. The influence of welding parameters on hot corrosion under different environments were discussed in this paper.
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Effect of Friction Welding Process Parameters on Oxidation and
Hot corrosion behaviour of Incoloy 800 H
K.Anand, 2P. Sreeraj, 1K.Tamilmannan, 2S. P. Kumaresh Babu, 3*P. Sathiya
School of Engineering and Technology, Indira Gandhi National Open University,
New Delhi 110016, India.
Department of Metallurgical and Materials Engineering, National Institute of Technology,
Tiruchirapalli-620015, Tamilnadu, India.
Department of Production Engineering, National Institute of Technology,
Tiruchirapalli-620015, Tamilnadu, India.
*Corresponding author: psathiya @ nitt.edu; Tel.:+91 431 2503510; Fax: +91 431 2500133
High temperature corrosion studies were carried out on friction welded Incoloy 800 H in air
and molten salt of Na2SO4-60%V2O5 at 7000C under cyclic condition for 50 cycles. Results
indicate when heating pressure increase, hot corrosion resistance of the weld decrease. The
hot corrosion resistance increases when upsetting pressure increases. Measurement of weight
gain or loss were done by Thermogravimetric analysis. It is found that molten salt
atmosphere was more corrosion resistance than air oxidation atmosphere. The oxide scales
formed on weldment were analysed by XRD, SEM/EDS. The influence of welding
parameters on hot corrosion under different environments were discussed in this paper.
Keywords: Incoloy 800 H, Friction welding, hot corrosion, XRD, SEM&EDS.
Incoloy 800 H alloy is commonly used above 6000C where resistance to creep and rupture is
the prime requirement. Incoloy 800 H is a Fe-Ni superalloy used in a variety of applications
involving exposure to corrosive environments and high temperatures such as heat treating
equipment, chemical and petrochemical processing industry, nuclear power plants and paper
pulp industry [1-3]. Heat treating equipments such as baskets, trays, fixtures employ Incoloy
800 H and chemical and petrochemical industry use incoloy 800 H in heat exchangers and
piping system in nitric acid media especially where resistance to chloride stress corrosion
cracking required. Incoloy 800 H will not become brittle even after a long period of usage in
the 6000C-9000C range where many stainless steels become brittle. Incoloy 800 H can welded
by common techniques used on stainless steels. Friction welding is a solid state joining
process and it is the most economical and also feasible method in joining similar and
dissimilar metals . It is used extensively due to the advantages such as low heat input,
production efficiency, ease of manufacture and environment cleanliness. Friction welding
does not involve melting and solidification and so it gives uniform weld bead without any
microsegregation within the dendritic structures which give less corrosion susceptibility .
The major problem encountered in dissimilar welding of Incoloy 800 H and stainless steel is
the formation of brittle intermetallics at weld interface which reduces corrosion resistance of
weld joint . In hot corrosion, molten salt(s) forms a film on a metal surface that fluxes and
destroys the normal protective oxide layer [8-10]. In fossil fuel, during combustion impurities
like Na, V and S melt or vaporise and get deposited on metal parts. Combustion product
involves Na2SO4 which attacks the metals protective layer and undergo fluxing and metal
consumption . Vanadium the impurity from fuel oil, forms V2O5 having melting point
6700C that produces serious corrosion . The problem gets compounded by the formation
of V-Na mixed oxides having melting point at 5450C. It was reported that Incoloy 800 H
showed better oxidation resistance than Incoloy 825 when both exposed to 10000C and
12000C [13-16]. Tan et al.  conducted the grain boundary examination (GBE) on Incoloy
800 H employed in supercritical water to evaluate the air oxidation behaviour at 550° C. It
was found that GBE resulted in the spallation resistance of the Incoloy 800H and also
reduced the corrosion rate. Dehmolaeib et al.  studied the microstructure and mechanical
properties of Incoloy 800 H after exposing it to 15 years of use. It was observed, the
improvement in hardness and strength and decrease in ductility and toughness were due to the
formation of primary carbides and secondary precipitates after a long time exposure.
A review of the available literature, clearly indicates that only a very limited work was
carried out on hot corrosion studies on welding of Incoloy 800 H joints. So far no visible
work has been focused on friction welding of Incoloy 800 H joints particularly under Na2SO4
- V2O5 environments.
The main objective of this work is to study the hot corrosion behaviour of friction welding of
Incoloy 800 H in molten salt of Na2SO4-60%V2O5 and air oxidation under cyclic conditions
at 7000C. And also to find the effects of welding parameters on hot corrosion resistance of the
weldments. Thermogravimetric technique was used to plot corrosion studies. The hot
corroded weldments were further analysed by XRD, SEM and EDAX.
2. Experimental Procedure
2.1 Friction welding
Friction welding was done by a 150-kN continuous drive friction welding machine. Friction
welding parameters were fixed based on the optimized results . The optimized friction
welding parameters are shown in Table 1. The friction welded specimens are shown in
Table. 1 Welding parameters
Figure 1. Friction welded samples
Base material chemical composition is presented in Table 2.
Table 1 Base material chemical composition (wt.%)
0.06 0.29 0.93 20.14 0.08 30.28 0.58 0.18 0.03 0.56 45.1
2.2 Macrostructure and Microstructure
The weld samples were cut in to the required size (10X10 mm) and the samples were
prepared as per the Metallographic standards. The joint regions were polished by emery
sheets of SiC with grit size varying from 220 to 1000 µm and then subjected to disc polishing
using alumina to obtain mirror polish up to 1µ. Then electrolytic etching (10% oxalic acid
solution; 6 V DC supply and 1 A/Cm2) was used to examine the macro and microstructure of
the joint interface.
2.3 Hot corrosion test
The samples were cut into dimensions of 20X7X2 mm by wire cut EDM for conducting the
hot corrosion studies. The weld zone was located in the mid span of the specimen. Mirror
polished specimens were coated with salt Na2SO4-60%V2O5 uniformly over the surface with
3-5 mg/cm2 by a hair line brush on the calculated surface area of the specimen. The samples
were kept in ceramic boats and preheated up to 2500C in tubular furnace to eliminate
moisture content in salt and weighed for initial mass along with boats. Then they were placed
in the furnace at 7000C. After each cycle, weight changes were measured along with boat by
electronic weighing balance having sensitivity up to 1 mg. Each cycle had 1 hr heating and
20 min cooling. This was undergone up to 50 cycles. Thermogravimetric plots were created
based on the results. The samples after corrosion test were subjected to SEM /EDS, XRD.
3.1 Macrostructure and Microstructure of the weld joints
The typical macrograph of the friction joint is shown in Figure 2. It is observed that the joint
interface is clearly visible and particles are also evenly distributed on the both side of the
Figure 2 Typical Macrograph of the friction joint
The microstructure of the base metal and weld metal with different welding parameters are
shown in Figure 3 (a-d). From Figure 3 (a), well defined grain boundaries and fully austenitic
matrix are observed. Cubic precipitates are also found to be present along the grain
boundaries. It may be due to the presence of titanium and nitrogen, and it may lead to form
nitride or carbonitride of titanium. The spherical precipitates are rich in titanium and carbon
and may be identified as titanium carbide (TiC). And additionally annealing twins are also
observed in the base metal.
(a) Base material
(c) weldmetal- Sample 2
(b) weldmetal-Sample 1
(d) weldmetal - Sample 3
Figure 3 (a-d). Friction weld microstructure of Incoloy 800 H
Figure 3 (c) revels a very fine grain size in the weld metal microstructure. This is due to
higher upsetting pressure. When friction components undergo the high upsetting pressure, the
metal particles are crushed (rubbing action) and they become finer. In comparison to base
material microstructure, all three friction weld microstructures obtained are of fine grain size
with well indentified grain boundaries. The weld metal microstructures are homogenous with
particles precipitated along the grain boundary. All weld metal joint interface microstructure
mainly consisted of austenite phase. The weld joint interface grains are mainly elongated
structure with a very few equiaxed grains.
3.2 Thermogravimetric analysis of Friction weldments of Incoloy 800 H
Thermogravimetric plots are constructed for molten salt environment and air oxidation
environment as shown in Figure 4 and Figure 5 respectively. The x-axis is a function of time
(number of cycles) and y-axis is a function of weight changes per unit surface area (mg/cm2).
It is observed from Figure 4, that when number of cycles increases, weight gain per surface
area is also increases. The uniform weight gain obtained in each and every two cycles is
increased. This may be due to uniform corrosion rate happening in all the weld samples.
Figure 4. Weight change (mg/cm2) in cyclic air oxidation with respect to exposed time (hr)
Figure 5. Weight change (mg/cm2) in cyclic hot corrosion with respect to exposed time (hr)
3.3 XRD Studies
The XRD analysis of the corroded samples of Incoloy 800 H is conducted. The images of the
six samples are shown on Figure 6. From the XRD it is identified that the scales containing
CrO2, CrO3, TiO2, Al2O3 are commonly seen in all samples both in air oxidation and molten
salt environment. All samples in molten salt environment contain an additional NiCr2O4 and
Fe3O4 oxide scale. Samples in air oxidation contain an additonal oxide scale of NiO. Out of
all three hot corroted samples, in air oxidation the first sample set of weld contains Fe3O4
oxide in the scale and in molten salt environment it contains additional MnO oxide.
(a)Sample 1 air oxidation
(c) Sample 2 air oxidation
(e) Sample 3 air oxidation
(b) sample 1 in molten salt
(d) sample 2 in molten salt
(f) sample 3 in molten salt
Figure 6 (a-f) XRD diffraction plots for hot corroded friction welds under different
From Figure 6 (a-f), it is observed that CrO2, CrO3, NiCr2O4, Al2O3 have been predominated
with lower intensities of TiO2, NiO and Fe3O4. Higher amount of CrO2, CrO3, NiCr2O4, Al2O3
are present in molten salt environments compared to air oxidation at 7000C.
3.4 SEM/EDS analysis
SEM images of hot corroded samples along with elemental energy dispersive spectroscopy
(EDS) analysis are shown in Figure 6 (a-g). Here strong and weak peaks of EDS spectrum
reveal the presence of elements diffused from substrate to upper most part of scale during hot
corrosion. Globular and needle like features mainly associated with iron and chromium
oxides are observed in all the samples Figure 6 (a-g). No sulfidation attack is observed on the
top scale of all samples. But the flaky and cuboids shaped structures are mainly associated
with iron and chromium oxides with little amount of nickel. The presence of titanium oxides
are seen in sufficient quanitity.
(a) base metal under molten salt
(b) sample 1 weldment under air oxidation
(c) sample 1 weldment under molten salt
(d) sample 2 weldment under air oxidation
(e) sample 2 under molten salt
(f) sample 3 under air oxidation
(g) sample 3 under molten salt environment
Figure 6 (a-g) SEM images & EDS plots of weld samples under different environments
The results obtained in air oxidation at 700°C (Figure 4 & 5) have been a better corrosion
resistance as compared to molten salt environment. The weight change observed in air
oxidation is less compared to mixed salt environment. Slight change in weight is observed in
air oxidation while a gradual increase is observed in mixed salt. This is due to the molten
deposit on the metal surface at high temperature which causes the formation of passive oxide
layers and diffusion of oxygen through fused salt to metal surface. Initially chromium ions
are transported over the surface of sample to form chromia scale. After some cycles the
additional chromium ions get diffused through depleted layer to meet oxide-metal boundary.
Thermogravimetric curve of molten salt environment studies shows the tendency of multi
stage weight-gain growth rate to be uniform at regular intervals. It could be due to changes in
reaction rate which are associated with the formation of a laminated inner-oxide layer made
up of fine and coarse grain spinal oxide as suggested by Hurdus et al . In a molten salt
environment, sulfur was incorporated into scale and leads to a sulfide formation in the alloy
substrate. Therefore, as the formation of protective oxide scale was inhibited by the presence
of NaCl, chlorides and sulfides tend to form in the alloy substrate as indicated leading to the
propagation of hot corrosion as suggested by Charng et al., . When thermogravimetric
plots are analysed it is found that sample welded with higher heating pressure has lower
corrosion resistance under condition that upsetting pressure remain same. Hence when
upsetting pressure increased, the corrosion resistance will also increase even though the
sample has higher heating pressure. From this it is understood that upsetting pressure has
higher influence than the friction pressure when corrosion resistance is considered. The
presence of oxides like CrO2, CrO3, Cr2O3, NiO, NiCr2O4, Al2O3, and TiO2 are identified
from XRD analysis. In hot corrosion studies no trace of FeO is found because when Cr
content increases it suppresses the formation of FeO. The formation of Chromium oxides,
NiO, NiCr2O4 will protect the surface. But as corrosion time increases the rapid cyclic
heating and cooling of metal may cause thermal shock and affect the protective oxide layer to
cracking and spallation. The presence of Ti, Mn, and Al in the weld zone also forms
protective layer in addition to regular oxide which will increase corrosion resistance to the
On the basis of this investigation, the following conclusions can be drawn.
From thermogravimetric analysis, it is seen that molten salt atmosphere had more
corrosion resistance than air oxidation atmosphere.
Hot corrosion resistance of the weld decreases when heating pressure increases.
Hot corrosion resistance of the weld will increase when upsetting pressure increases.
It is understood that upsetting pressure has higher influence than friction pressure
when corrosion resistance is considered
At higher upsetting pressure, the weld metal microstructure has very finer grains.
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