Surface and Coatings Technology 125 (2000) 45–48
www.elsevier.nl/locate/surfcoat
Laser cladding of turbine blades
L. Shepeleva a, *, B. Medres a, W.D. Kaplan a, M. Bamberger a, A. Weisheit b
a Department of Materials Engineering, TECHNION - Israel Institute of Technology, Technion City, 32000 Haifa, Israel
b Institute fur Werkstoffkunde und Werkstofftecknik, Agricolastrabe 6, D-38678 Clausthal-Zellefreld, Germany
Abstract
A comparative study of two different techniques for the application of wear-resistant coatings for contact surfaces of shroud
shelves of gas turbine engine blades (GTE ) has been conducted. Wear-resistant coatings were applied on In713 by laser cladding
with direct injection of the cladding powder into the melt pool. Laser cladding was conducted with a TRUMPF-2500, CW-CO
2
laser. The laser cladding was compared with commercially available plasma cladding with wire. Both plasma and laser cladded
zones were characterized by optical and scanning electron microscopy. It was found that the laser cladded zone has a higher
microhardness value (650–820 HV ) compared with that of the plasma treated material (420–440 HV ). This is a result of the
significant reduction in grain size in the case of laser cladding. Unlike the plasma cladded zones, the laser treated material is free
of micropores and microcracks. © 2000 Elsevier Science S.A. All rights reserved.
Keywords: Laser cladding; Plasma cladding; Shroud shelve; Turbine blade
1. Introduction
The operational stability of turbine blades with
shroud shelves depends on the wear resistance of the
shroud shelves. [1,2]. It is known that during operation,
as a result of dynamic contact as well as vibration and
heat, the contact surfaces of shroud shelves undergo
intensive wear. This leads to the formation of a gap
between them and, as a result, increases the amplitude
of alternating loads on the blade critical cross-section
[2]. Thus, the wear of the blade shroud shelves’ contact
area determines the overall service life of the GTE [2,3].
To increase the service life of turbine blades with shroud
shelves, plasma cladding of cobalt stellites supplied in
the form of wire is used. These materials exhibit sufficiently high tribological properties [1,3].
In spite of a significant increase in wear resistance
for cladded blades (compared with non-cladded blades)
plasma cladding technology has some essential
drawbacks:
$ plasma cladding is performed manually, and does not
provide the required uniformity of the coating;
$ the layer contains cracks and pores both at the layer–
substrate interface and in its entire volume;
$ the plasma cladded layer has a sharp boundary with
* Corresponding author.
the substrate, where high stress concentration leads
to the formation of cracks and pores under loading;
and
$ plasma cladding increases the hardness of the coating
by 20– 40 HV above that of the substrate.
These limitations can be overcome by applying coating techniques, such as laser cladding [3–5].
This paper presents a comparison between the microstructure and properties of plasma cladding in which
the clad material is supplied via a wire, and laser
cladding with direct injection of cladded powder into
the melt pool.
2. Experimental methods
Commercially available blades with plasma cladding
were investigated, as well as wear-resistant coatings
produced by laser cladding, using the method of direct
injection of cladding powder into the melt pool. All
tests were performed with alloy In713.
Laser cladding was conducted with a TRUMPF-2500
CW-CO laser operated at a laser power density in the
2
range of 2.8×104–3.6×104 W/cm2 and scanning velocities of 0.5–0.7 cm/s. The powder feed rate was 0.015–
0.02 g/s. Both plasma and laser cladding zones were
0257-8972/00/$ - see front matter © 2000 Elsevier Science S.A. All rights reserved.
PII: S0 2 5 7- 8 9 7 2 ( 9 9 ) 0 0 60 3 - 9
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L. Shepeleva et al. / Surface and Coatings Technology 125 (2000) 45–48
Fig. 1. SEM micrograph of the plasma cladded zone and its interface
with the substrate.
Fig. 3. (a) SEM micrograph of a laser cladded substrate region. (b)
EDS line-scan analysis of the major elemental distribution across the
laser clad–substrate interface.
Fig. 2. EDS line-scan analysis of the major elemental distribution
across the plasma clad–substrate interface
characterized by optical and scanning electron microscopy (SEM ).
3. Results and discussion
3.1. Plasma cladding zone
The plasma-cladding zone and its interface with the
substrate are shown in Fig. 1. In this figure one can see
that the plasma cladded zone is characterized by the
presence of microcracks and pores, which might
adversely affect the wear resistance of contact surfaces
of blades [2]. The low content of Ni, which originates
from the substrate, in the cladding is evident in Fig. 2.
From Figs. 1 and 2 it can be concluded that the boundary between the clad and substrate is very sharp and
contains a large quantity of microcracks and pores. The
sharp boundary can be correlated with the processing
characteristics — e.g. the relative size of the plasmaheating source compared with that of the wire and the
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L. Shepeleva et al. / Surface and Coatings Technology 125 (2000) 45–48
Table 1
The microhardness at various locations in the laser cladded blades by
various power densities
Sample
group
1
2
3
Laser treatment
conditions ×104
( W/cm2)
Microhardness (HV )
Base
Boundary
Cladded layer
3.6
3.2
2.8
400
400
400
572
522
464
824
680–724
542
in the melt due to the intensive mixing. The low viscosity
of the melt bath and the directional dendritic growth,
which nucleated on the cold substrate, result in the
crack- and pore-free interface [6 ] seen in Fig. 4. Table 1
presents the microhardness at various locations in the
laser treated blades by various power densities.
The microhardness for both interface and laser cladded zones increase as a function of laser radiation power
density. The laser cladded zones reveal a significant
grain refinement ( Fig. 5) which raises their microhardness values.
Fig. 4. EDS line-scan analysis of concentration changes of basic elements of a laser cladded layer and substrate in interdendritic regions.
substrate. Therefore, the melted wire, which spreads on
the unmelted surface of the substrate, is not sufficiently
overheated to ensure mixing and/or mutual dissolution
of elements from both components.
This is reflected in the concentration profiles seen in
Fig. 2. The porosity seen in Fig. 1 results from gas
entrapped in the high viscosity melt [6 ]. The microhardness of the plasma cladded layer is 420–440 HV. The
microhardness of the substrate is 400 HV.
4. Conclusions
1. Laser cladding of the contact surfaces of shroud
shelves by direct powder injection provides a cladding
layer with a higher hardness than plasma treated
surfaces.
2. Laser cladded zones, unlike the plasma treated surfaces, are free of microcracks and pores.
3. The laser cladded zone has a smooth interface with
the substrate, which prevents stress concentration at
the clad–substrate interface during operation.
3.2. Laser cladded Zone
The laser cladded zone has a uniform microstructure
with a smooth boundary between the cladded layer and
the substrate ( Fig. 3(a) and (b)).
The crack- and pore-free interface between the laser
cladded zone and the substrate, at higher magnification,
and the enrichment of the cladding with Ni from the
substrate are evident in Fig. 4. The formation of a
smooth interface by laser cladding can be explained by
the fact that the laser beam causes significant heating of
the injected powder and essential overheating of the
molten surface of the substrate, and hence the hot
particles melt on hitting the melt bath. The high temperatures prevail in the melt and the gradient in the surface
tension throughout this melt pool result in dissolution
of constituents from the substrate, and their distribution
Fig. 5. SEM micrograph of a laser clad–substrate interface.
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L. Shepeleva et al. / Surface and Coatings Technology 125 (2000) 45–48
Acknowledgement
Dr. B. Medres and Dr. L. Shepeleva acknowledge
the Center for Absorption in Science, Ministry of
Immigrant Absorption State, Israel for its financial
support.
References
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(1987) 387.
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of GTE blades, Aviazionaya Promishlennost Mag. 2 (1984) 8.
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made of EP-109 alloy, Reports of 1st All-Union Conference on
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