AMMJ - Library

Laser Cladding
A Versatile Proactive and Reactive Technology
M. Rombouts 1 , J. Meneve 1 , D. Robberecht 2, E. Geerinckx 1 , J. Gedopt 1
1 Flemish Institute for Technological Research (VITO), Laser Centre, Mol, Belgium 2 Maintenance Partners Heavy Duty nv, Belgium
Paper presented at COMADEM 2009 (The full Proceedings of COMADEM 2009 are available for sale – please contact aarnaiz@tekniker.es)
Laser cladding is an additive process wherein a laser source is used to melt metal-based powder or
wire on to a metal substrate. The result is a thick metal or metal matrix composite coating (order of 1
mm thickness) of a high quality: it has an excellent bonding to the substrate and is completely dense.
The laser cladding process enables the treatment of heat sensitive materials and deformation sensitive
components, which cannot be processed by conventional techniques like surface welding.
The technique is increasingly being used in industry as a pro-active technology for corrosion and wear
protection and as a reactive technology for repair of worn components. In both aspects, laser cladding
is a technology contributing to cost-effective maintenance.
Various research efforts are devoted to customised coating development with the aim to reduce
maintenance. This paper will discuss the advantages and limitations of laser cladding as a repair
and coating technique. The capabilities of the process will be illustrated by industrial case studies
performed by VITO.
INTRODUCTION
The functionality of components can often be ameliorated by
combining materials with optimised properties. The bulk material
can be chosen as a function of formability, strength, stiffness and
cost. The surface of this component can then be adapted to satisfy
demands in the field of friction, wear, and corrosion.
A possible process to optimise the surface of metal components
is laser cladding [1,2]. The process can also be used as a repair
technique. During laser cladding, additive material is supplied in the
form of wire or powder to the substrate to be treated. A laser beam
melts the additive material together with a thin surface layer of the
substrate resulting in a coating with a typical thickness of 0.5-1 mm
(Figure 1).
Figure 1 Principle of laser cladding
In most cases powder is used as feedstock and transported in an argon gas flow. It is possible to use an
additional protective gas flow to minimise oxidation during laser cladding. Due to the superficial melting of the
substrate, a strong metallurgical bond is formed between substrate and coating. This is an important benefit
compared to thermal spraying where only a mechanical bond is formed between the coating and substrate.
Another advantage compared to thermal spraying is the higher powder yield, which is typical 75%.
Thanks to the low and local heat input, laser cladding is very well suited for the treatment of heat sensitive
materials and components, deformation is limited and the heat affected zone is small. Moreover, the high
cooling rate during laser treatment results in coatings with a fine microstructure. After deposition, machining of
the component to its final dimensions is mostly required.
As laser source, different types of lasers can be used: CO2, Nd:YAG, diode, disk or fiber laser. The former
two lasers are the most commonly used lasers in materials processing by laser welding and cutting. However,
there is currently a strong development in new, more compact and more efficient lasers including the diode,
disk and fiber lasers. The results presented in this paper are obtained using a diode laser as processing tool.
Laser cladding is a relatively new process, which is being used in industrial sectors like petrochemical,
aerospace, machine and die building, automotive, energy production, to: repair damaged high-value machine
components like turbine blades, shafts, motors, etc. improve the corrosion and/or wear resistance of metallic
components like tooling, pumps, valves, off-shore pipes, etc
The possibilities of laser cladding as a repair and surface treatment technology in energy production industry
is illustrated with two case studies carried out for the company Maintenance Partners. Maintenance Partners
is leader in the Benelux for the repair and revision of mechanical and electrical rotating machines. The case
studies presented in this paper are the repair of a compressor shaft, and the repair of turbine wheels.
EXPERIMENTAL SETUP
Figure 2 shows the experimental setup used for laser cladding in this study. It uses a 3 kW fiber-coupled
diode laser (Laserline), using specific optics to obtain a circular spot with a diameter of about 3,7 mm at the
substrate. A powder supply unit of Medicoat, which is commonly used for thermal spraying, is used. The
powder is supplied in an argon gas flow to the coaxial cladding head. A CCD camera, which looks through a
semi-transparent mirror coaxial with the laser beam, enables aligning of the cladding head to the area to be
treated.
Vol 24 No 1