Novel Fusion Technology for Faster Deposition of

Wear Resistant Alloys on Steels using ‘Flexible Metal Cloth’

Siva Purushothaman1,a, Vilas Hippargi2,b and Hiren Patel3,c
1,2,3
EWAC Alloys Ltd (An Associate of Larsen & Toubro Ltd),
Plot 7917, GIDC, Ankleshwar, Gujarat, India
a b c
P.Siva@larsentoubro.com, Vilas.Hippargi@larsentoubro.com, Hiren.Patel2@larsentoubro.com

Keywords: Surface engineering, Cladding, Fusion, Flexible metal-alloy cloth, Wear,

Metallography, Alloys.

Abstract: Selection of surface engineering process and surfacing alloy (consumable) for
protection of metallic surfaces depends on service conditions involved for a particular
industrial operation. Every surface engineering technique (flame spray, laser cladding, PTA,
HVOF etc.) is associated with certain limitations such as coating thickness, substrate
thickness, coating on both sides, surface finish, hardness, accessibility for complex geometry,
deposition efficiency, production rate etc. A novel ‘flexible metal-alloy cloth’ containing
nickel based alloy and hard constituents such as tungsten carbide or chromium carbide is
developed ‘in-house’ as surfacing consumable addressing above limitations including
productivity. High wear resistant coatings for high temperature applications are achieved
using this ‘flexible metal-alloy cloth’ by fusion process at 1050 – 1150 °C. This ‘in-house’
developed surfacing technology can bring huge business to EWAC by defining new market
(niche applications), differentiating from conventional welding solutions and differentiation
from competitors.

Introduction

Industrial components and machineries undergo wear and tear due to their continuous
operation in service. Wear mechanisms generally encountered in the industries include
abrasion, erosion, impact, cavitation, friction, corrosion or combination of two or more of
these factors. Moreover, the severity of the wear depends on service conditions and process
parameters such as abrasive particle size, shape and its velocity, chemical medium and its
concentration, erosive slurry, temperature etc. These wear factors impose critical issues to the
components, which affects the plant’s function and efficiency and thereby increases the
maintenance cost. Replacement of worn-out components is very costly and time consuming.
Thus, it is imperative for a maintenance engineer to look for surface engineering solutions
based on temperature-stable, anti-corrosion and anti-wear materials for the best performance
to protect inexpensive carbon steel components. These surface engineering solutions are
expected to extend the lifecycle of components and machineries.

Recent technological advancements in the field of surface engineering brought drastic

improvements in equipment capability and also exotic surfacing consumables with a focussed
attention to enhance both product performance and productivity. Globally, maintenance and
reclamation engineers witnessing change in trend for surfacing consumables switching over
from conventional flux-coated electrodes containing expensive alloying elements to flux-
cored continuous wire systems based on cost-economic nano-alloys. Similarly, value added
engineering solutions are offered through tailor-made ‘ready-to-use’ wear plates instead of
conventional repair work, which is a time consuming process. Though surface overlaying by
welding process produce a strong metallurgical bonding, but results in stress-relief cracks and
deformations thereby restricting its usage for thin sections and applications demanding
erosive wear resistance against fine particles at high temperature.
Wear resistant solution using metal powder alloys is another interesting surfacing engineering
field, especially for the protection of large surface area where conventional welding processes
fails to meet technical requirements including productivity due to their inherent process
limitations. Powder alloys based on iron, nickel and cobalt can be deposited by thermal spray,
plasma transferred arc (PTA), high velocity oxy-fuel (HVOF), plasma spray and laser
cladding processes. The choice of surfacing process and surfacing alloy depends on service
conditions. However, most of these techniques have process limitations such as cladding on
thin sections, non-uniform cladding thickness, rough surface finish, accessibility issues for
intricate shapes, low deposition rate, use of exotic materials etc.
EWAC Alloys Ltd manufactures different grades of ‘ready-to-use’ welded wear plates using
flux-cored continuous wires for more than a decade. However, there are certain limitations
associated with this existing technology such as presence of stress relieving cracks, rough
surface, high cladding thickness, incapability of deposition on both sides of the plate and low
productivity. These limitations restrict EWAC wear plates for wider usage.
The objective of this paper is to demonstrate a novel ‘in-house’ developed fusion technology
for faster deposition of high performance wear resistant alloys on steel surfaces in two steps.
In the first step, preparation of a novel ready-to-use ‘flexible metal-alloy cloth’ containing
ultra-hard constituents (tungsten carbide / chromium carbides) of different morphology and
volume-fraction in Nickel-based alloy matrix is described. In the second step, fusion of this
flexible cloth on steel surfaces in reducing atmosphere is explained. This paper also narrates
metallography studies, wear resistance evaluation and outstanding features. Some of the
critical and potential applications of this technology especially in Cement, Steel and Power
industries are highlighted, which can open up new business opportunities for EWAC.

Experimental

Free flowing powder alloy materials used in this work are (i) Ni-Cr-Fe-B-Si-C alloy with
grain size in the range of 45 -180 µm (refer Fig.1), which is manufactured ‘in-house’ through
furnace melting and water atomisation process, (ii) fused tungsten carbide (W2C/WC) with
grain size in the range of 45 – 150 µm (refer Fig. 2) and (iii) chromium carbide (Cr7C3/Cr3C2)
with particle size in the range of 125 – 230 µm (refer Fig. 3).

Fig.1: Ni-Cr-Fe-Si-C alloy particles Fig.2: Fused tungsten carbide particles Fig.3: Chromium carbide particles

Two-roll Machine (roll dia 320 mm and roll length 500 mm) is used to manufacture ‘flexible
metal-alloy cloth’ with high metal powder density in the range of 0.5 - 3 mm thickness. (refer
Fig. No.4). Gap between the rolls can be adjusted between 0 and 8 mm. Fusion is carried out
on continuous ‘mesh-belt’ furnace (refer Fig. 5) under reducing atmosphere (75% H2 and
25% N2 generated from NH3 cracking unit).

The fused samples are cut and the cross section is ground and polished using standard
metallographic techniques for micro-structural observation. The morphology and thickness of
the coatings are determined on the polished cross sections by optical microscope (Nikon -
Epiphot 670607) integrated with image analysis software (Olympus 5.1 Build-2640). The
macro-hardness on the surface of the deposits is measured using Rockwell hardness tester
under 150 kg load and micro-hardness is measured using Mitutoyo make micro-hardness
tester (Model MVK-H11) at a constant load of 200 gm and dwelling time of 15 s. Abrasion
resistance of fused samples (dimension 75 x 25 x 5 mm) are carried out as per ASTM G65 on
dry sand abrasion tester (refer Fig.6). The test conditions are as follows: the deposit portion
of the sample is pressed (13.6 kgf) against rotating (6000 revolutions) rubber wheel (60 Shore
A hardness). Ottawa River quartz sand (particle size 200 – 300 µm) is directed between
rotating wheel and the sample at the flow rate of 300 gm/min. Weight of the sample is noted
before and after the experiment to determine weight loss and the wear factor is calculated as
(1 / volume loss).

Fig.5: Continuous ‘mesh-belt’

furnace with reducing atmosphere Fig.6: Dry sand Fig.7: Hot air-jet
Fig.4: Two-Roll Machine erosion tester
abrasion tester

Erosion resistance of fused samples (dimension 15 x 15 x 3 mm) is evaluated on air-jet

erosion tester (refer Fig.7) as per ASTM G76. The test conditions are as follows: air jet (30
m/s) carrying Al2O3 (50 µm particles introduced at the rate of 2 g/min) is allowed to impinge
on the top surface of fused deposit at 90°. Weight of the sample is measure before and after
the experiment to determine weight loss and the erosion rate is calculated as (volume loss /
total mass of quartz sand impinged the sample).

Surfacing alloys in the form of Powders

Boride containing nickel-based alloys is well known for its outstanding wear and corrosion
resistance properties especially at elevated temperatures and are being widely employed for
surface engineering applications by flame spray or laser cladding. Ni-Cr-Fe-B-Si-C system is
of particular interest not only for wear and corrosion properties but also its convenient
processing temperature window and self-fluxing properties. Presence of metalloids such as
boron and silicon in the alloys not only reduces the melting point of the alloy to the range of
1000 - 1150 °C but also reduce oxides on the substrate to form boro-silicates. Ni-alloy
powers can be reinforced with intermetallic compounds such as titanium carbide, chromium
carbide, tungsten carbide, chromium boride, etc. to further enhance wear resistance
properties. The extent of improvement depends on the carbide/boride type, particle size and
distribution and its content in the composite alloy.
EWAC Alloys Ltd manufactures and supplies flame spray grades of nickel-based powder
alloys in different compositions and also as composite alloy with intermetallic compounds for
wear resistance applications. EWAC also executes spray jobs on original and/or worn-out
components.

Surfacing consumable in the form ‘Flexible Metal powder-alloy Cloth’

Nickel-based powder alloy is conveniently converted into ‘flexible cloth’ and the approach
and methodology adopted is explained in detail. Several polymer based binders are evaluated
during the development and the best one is selected meeting the following requirements:

 The binding agent is fully combustible and leave negligible residue

 Thickness range achievable from 0.5 to 3 mm
 Easily cut with knife and scissors
 Long storage life
 Fusion in vertical and horizontal positions

Initially, a binder solution is prepared by dissolving the polymer in an organic solvent. Then a
powder mixture (refer Fig.8 and Fig.9) containing nickel based alloy and tungsten carbide or
chromium carbide in the desired ratios (in two different ratios 70 : 30 & 60 : 40 for Ni-alloy +
W2C/WC and 70 : 30 for Ni-alloy + Cr7C3/Cr3C2) is added along with other additives to the
polymer binder solution and the resulting mixture is kneaded to obtain a uniform paste. The
paste is then poured on silicone coated paper placed in a tray and allowed to stand for few
hours to evaporate solvent. The dried mass is collected and passed through a pair of rolls (set
4 mm apart) couple of times in one direction. The first formed sheet is folded and rolled in a
direction which is 90° to the axis of the first rolling (i.e., cross rolled) to maximise
densification of powder in the sheet. Rolling, folding and cross-rolling steps are repeated 3 to
4 times to obtain a sheet with good green strength and high metal powder. The distance
between the rolls are gradually reduced to further reduce the sheet thickness and increase
powder packing. This is continued until the desired thickness is obtained. Flexible sheets
(refer Fig.10) with good strength are produced with ease within few cross rolling steps in our
work.

Fig.9: Mixture of Ni-Alloy

Fig.8: Ni-based alloy powder and WC powders Fig.10: Flexible metal-alloy cloth

Optimum binder content in the cloth is essential for handling strength, flexibility and defect-
free fused deposits. Similarly, the particle size distribution is also optimised in such a way
that the interstitial spaces between the larger particles are filled with smaller particles for
powder densification in the cloth and minimize voids.
Fusion Process
Mild steel base plates of dimension 250 x 350 x 3.2 mm are wire brushed manually. The
flexible metal-alloy cloth can either be directly placed on the cleaned surface or an adhesive /
double sided adhesive tape may applied on the surface for improved adhesion of flexible
sheet to the substrate for safe handling and transport.

Fusion of flexible metal-alloy sheet can be carried out in any of the following atmospheres:
(i) inert (argon) atmosphere, (ii) vacuum and (iii) reducing atmosphere. Though all three
types of atmosphere are employed during development work, continuous ‘mesh-belt’ furnace
with reducing atmosphere is most preferred for faster deposition of wear resistant surfacing
alloys using ‘flexible metal-alloy cloths’ on steel surfaces. Both vacuum and inert atmosphere
furnaces are batch type with a cycle time of 10 hrs for complete fusion process, whereas the
continuous furnace with reducing atmosphere has a cycle time of just 2 hrs.
When the substrate with powder-alloy sheet (refer Fig.11) is heated between 100 and 250 °C,
the organic binder in the sheet soften and adhere to the substrate. But when the substrate is
further heated between 300 and 750 °C, the organic binder starts decompose, volatile gases
evaporate and sintering of the powder-alloy takeplace. Further heating to 1050 – 1100 °C, the
nickel based alloy melts and wets the tungsten carbide or chromium carbide powders and
upon coolingn the fused deposit exhibits sound metallurgical bond on the steel surface (refer
Fig.12).

Fig. 12: Flexible metal-alloy

Fig.11: Flexible metal-alloy sheet before fusion sheet fused on a mild steel plate

It is expected that at high temperaures, the binder is decomposed by heat and the adhesive
power of the alloy sheet is lost. Thus, the sheet may not be held in position at high
temperatures especially when attached to a slanted surface, curved surface or a downward
surface. However, this can be addressed (i) by including additives in the form of fine metal
powders in the formulation, which starts sintering at 300 °C and significant extent of
sintering progresses at 500 °C and (ii) by controlling the rate of heating especially in the
intial stages.
Initial heating rate is important due to low softening point and decomposition temperature of
polymer binder. When the rate of heating is greater than 50 °C/min, the organic binder has
the tendency to abruptly soften, shrink and burnt, which may lead to swelling, blistes and
cracks in the sheet, which may cause the powder-alloy sheet to fall off from the substrate
during the fusion process. To avoid such defects during fusion especially in continuous
furnaces, it is preferred to pre-heat the sheet on the substrate at 200 – 350 °C for 15 minutes.
This pre-heating produces a tar-pitch like substances through pyrolytic condensation of the
binder in the powder-alloy sheet. The tar-pitch like subtance is responsible to provide an
adhesive power sufficient to hold the powder-alloy sheet on the substrate even in different
positions at 300 °C and above (refer Fig.13 and Fig.14).
 Fig.13: Coating applied on slant Fig. 14: Cross-section of the fused
surface deposit applied on slant surface

During fusion process especially at final processing temperatures (1050 – 1150 °C) both
boron and carbon diffuse from the surfacing alloy into the substrate surface. This diffusion
process lowers the melting temperature of the base metal surface and increases the re-melting
temperature of the coatings.

Microstructure
Microstructure of (Ni-alloy + W2C/WC) fused deposit is shown in Fig. 15 in three different
magnifications. Three different regions viz., substrate, interface and the deposit are clearly
seen in Fig.15 (a). This microstructure reveals (i) continuous and sound interface between
substrate and deposit without any defects and (ii) uniform distribution of tungsten carbide
particles in the deposit. The microstructure of the matrix consists of dendrites of γ-Ni solid
solution phase and several hard phases such as nickel boride (Ni3B), nickel silicide (Ni3Si),
chrome borides and chrome carbides (Cr7B3) dispersed in interdendritic eutectic.

Fig. 15: Microstructure of Ni-alloy+W2C/WC under different magnification (a) 100X (b) 400X (c) 1000X

Similarly, the microstructure of (Ni-alloy + Cr7C3/Cr3C2) fused deposits is shown in Fig 16.
The microstructure consists of uniform distribution of chromium carbides in the deposit and
there is no evidence of any defects at the interface and in the coating.

Fig. 16: Microstructure of Ni-alloy + Cr7C3/Cr3C2 (a) Interface (b) Top layer
Macro and Micro Hardness

The bulk hardness on the top surface of fused deposits of Ni-alloys containing tungsten
carbide and chromium carbide systems along with microhardness values of the matrix and
carbides are presented in Table 1. Both bulk hardness and matrix microhardness for the
coating containing chromium carbide is lower than those of tungsten carbide system. The
carbide microhardness hardness values are in agreement with the values reported in the
literatures for these types of carbides.

The microhardness profile of the deposits across the cross-section covering all three regions
viz., substrate, interface and coating layers for both the systems are presented in Fig.17 and
Fig.18. Matrix microhardness of 700 HV is achieved for the tungsten carbide reinforced Ni-
alloy system at a distance of 0.4 mm from the interface, whereas the same level of
microhardness is achieved at a distance of 0.5 mm from the interface for chromium carbide
reinforced Ni-alloy system.

Ni-Alloy + W2C/WC
1000
Ni-Alloy + Cr7C3/Cr3C2
900
900
800

Fusion line
Microhardness (HV0.2)

Fusion line

800
Microhardness (HV 0.2)

700
700
600
600
Substrate

500
500
400 400
300 300 Substrate Coating
200 Coating 200
100 100
0 0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0
-0.5
-0.4
-0.3
-0.2
-0.1
0.2
0.3
0.4
0.5
0.6
0.7

1.1
1.2
1.3
1.4
0

1
-0.5
-0.2
-0.1

0.15

Distance across interface, mm Distance across the interface, mm

Fig. 17: Microhardness profile of Ni-alloy + W2C/WC Fig. 18: Microhardness profile of Ni-alloy + Cr7C3/Cr3C2

Wear Properties

Abrasive and erosive wear resistance of (Ni-alloy+W2C/WC) and (Ni-alloy+Cr7C3/Cr3C2)

systems are evaluated by conducting dry sand abrasion and air jet erosion tests respectively.
Dry sand abrasion is a three-body abrasion test, which is one of the most frequently used test
methods for evaluation of surface engineered samples for development, screening and
comparison purposes. The surface of the coated sample is pressed against rotating (144
m/min) rubber wheel to cover a total wear path distance of 4.3 km and a steady of stream of
quartz sand (9 kg during 30 minutes test time) falls at the point of contact between sample
and rubber wheel. Weight loss is determined in milligrams and converted to volume loss for
calculation of wear factor as explained in experimental section. Higher the wear factor, better
the wear resistance. A weight loss of 0.165 g (wear factor 60) observed for Ni-alloy
containing 40wt% W2C/WC and 0.22 g (wear factor 45) for Ni-alloy containing 30 wt%
W2C/WC as summarised in Table 1. These results indicate that the abrasive wear resistance
increases with increasing tungsten carbide content in the powder-alloy mixture. Ni-alloy
containing 30wt% chromium carbide experienced a weight loss 0.193 g (wear factor 40). It is
interesting to note that the wear factor of chromium carbide system is more or less similar to
tungsten carbide system eventhough tungsten carbide particles have superior wear resistance
properties. This may be explained by the fact that the density of tungsten carbide is more than
double that of chromium carbide. Therefore, for the same level of loading (30 wt% in this
case), the volume fraction of tungsten carbide in the Ni-alloy matrix is only half that of
volume fraction of chromium carbide in Ni-alloy.

Table 1: Hardness and Wear properties of Ni-alloy+W2C/WC and Ni-alloy+ Cr7C3/Cr3C2 deposits

Properties Ni-alloy + W2C/WC Ni-alloy + Cr7C3/Cr3C2

Deposit thickness 1.5 mm 1 mm

Bulk Hardness (HRc) 56 - 58 53 - 56

Micro-hardness (VPN, 200 g)

 Matrix 750 - 850 650 – 800
 Carbide 1700 - 1800 1300 - 1500

Dry Sand Abrasion test

 Wear Factor 45 – 60 40

Air Jet Erosion Test

 Erosion Rate @ RT 6.03 x10-3 mm3/g 8.24 x10-3 mm3/g
 Erosion Rate @600 ⁰C 1.84 x10-3 mm3/g 2.92 x10-3 mm3/g

Microstructure Uniform distribution of Uniform distribution of

tungsten carbide grains in chromium carbide particles
Ni-Cr-Fe-B-Si-C matrix in Ni-Cr-Fe-B-Si-C matrix

Micro-porosity < 2% <3%

Erosive wear resistance of the deposits are evaluated at ambient temperature and 600 °C in
air. Interestingly, erosion rate of the deposit at high temperature is lower that of the deposit at
room temperature. At high temperatures, the base mild steel surface is oxidised to certain
extent, which led to increase in weight of the sample. Thus, the difference in weight of the
sample before and after the test at 600 °C is lower compared to the weight loss observed for
the sample at ambient temperature. All the tests were conducted under similar test conditions
including size of the specimen and hence the oxidation effect is expected to be the same and
hence, high temperature test results can well be considered for comparison, screening and
development purposes. However, future experiments are planned to perform the test in inert
atmosphere and/or having temperature-stable plating on the mild steel surface of the sample
to eliminate oxidation at high temperature.

Unique Features, Potential Applications and Business Potential

Some of the unique features of powder deposits obtained through ‘in-house’ developed
‘flexible metal-alloy cloth’ and ‘fusion’ technology are as follows:

 Smooth and crack-free surface finish.

 Coatings from 0.5 to 3mm on thin substrates of 1.6 mm.
 Fusion process resulting in low dilution with base metal.
  Good metallurgical bonding between base metal and the fused coating as well
as between hard particles and alloy matrix.
 100% deposition efficiency.
 Applications demanding coating on both sides of the substrate.
 ‘Rready-to-use’ thin wear plates, especially for dynamic applications such as
fan blades, resulting in energy savings.
 High productivity on a continuous furnace (approx. 4 sq.m area of base plates
with dimension 500 x 1000 x 4 mm can be coated with 2 mm powder-alloy in
an hour), which is 3 – 4 times faster than PTA / laser cladding and other
conventional and non-conventional processes.
 Mild steel and stainless steel base plates can be coated.
 Excellent resistance to all kinds of wear - corrosion, erosion and abrasion.
 Easy cutting by plasma.

This novel “Flexible cloth’ & ‘Fusion’ technology is specifically developed to address niche
applications such as erosion applications at high temperatures, friction-free smooth coatings,
double side protection of substrates, ‘ready-to-use’ thin wear plates etc.

Fig.18: Some of the applications of wear resistant deposits (a) Fan blades, (b) Ducts, (c) Baffle plates, (d) Cyclones

Potential surfacing applications in steel, cement and power industries include cladding of fan
blades, fan casing, liners, chutes, hoppers, cyclones, baffle plates, dampers, louvers, guides,
etc., as shown in Fig.18. Each of these applications has a business potential of more than 100
crores.

Conclusion

In order to address niche applications such as fine particle erosion at high temperatures, there
is a need for a special surfacing consumable and process to overcome the limitations of
existing conventional and non-conventional processes. EWAC R&D has developed a novel
surfacing consumable along with a process for faster deposition of wear resistant alloys of
uniform thickness on steel surfaces.

 Surfacing consumable in the form of ‘flexible metal-alloy cloth’ consisting of nickel-

based alloy powder and hard constituents such as tungsten carbide and chromium
carbide is successfully formulated and manufactured.

 Smooth and crack-free deposits are achieved by fusion of ‘flexible cloths’ on steel
plates in a continuous ‘mesh-belt’ furnace under reducing atmosphere with high
productivity.
  Microstructure revealed sound interface and uniform distribution of tungsten carbides
/ chromium carbides in the Ni-alloy matrix. The matrix also contains borides of nickel
and chromium hard phases.

 Both the systems exhibited excellent wear resistance properties, which increased with
increasing tungsten carbide content. Ni-alloy with tungsten carbide exhibited high
erosion resistance at elevated temperature.

This technology has an edge over EWAC competitors featuring high quality and high
deposition rate and can open up new business avenue especially in steel, power and cement
industries with a market size more than 500 Cr.

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