AMMJ - Library

AMMJ Laser Cladding 12
REPAIR OF COMPRESSOR WHEELS
Various compressor wheels were worn near the outer diameter. The wheels are made of 30CrNiMo8 steel. The
wheels are manufactured from 2 separate parts that are connected to each other by mechanical fasteners.
In between the upper and lower plates 17 blades are present. This construction makes it impossible to use
conventional welding to repair the wheels since the excessive heat input will result in distortion, which finally
results in loosening of the upper plate from the lower plate. Another phenomenon observed when trying to
repair the wheels by conventional TIG welding is the presence of cracks
near the mechanical fasteners, which are located very close to the area
being welded.
PRELIMINARY TESTS
Prior to treatment of the wheels, laser cladding experiments with stellite
21 powder on a 30CrNiMo8 substrate are performed to evaluate the
absence of cracks in the coating and in the heat affected zone of the
substrate. No cracks or large pores were observed after metallographic
analyses (Figure 5). The Vickers hardness of the stellite 21 coating after
laser cladding is 450-460 HV (0.5 kg load).
REPAIR OF COMPRESSOR WHEELS
The setup used during laser cladding of the wheels is shown in Figure 6. The wheel is mounted on a rotational
axis. To prevent damage of the blades the laser is not placed perpendicularly but at an off-axis position.
Figure 7 shows a close-up of a wheel after
laser cladding. At the outer diameter of the
wheel about 13 laser cladding passes are
applied to ensure an increase in diameter
from 624 mm to 632 mm. The applied scan
speed was 1000 mm/min. No cracking in the
substrate or the coating is observed visually.
After laser cladding and machining, the
wheels are evaluated by a spin test, which
consists in rotating the wheels in vacuum at a
rotation speed of 20.000 rpm. All the treated
wheels survived that test successfully.
CONCLUSIONS
- The local repair of a compressor shaft of
martenstic stainless steel by laser cladding
proved to be successful thanks to the low
heat input of the laser process and high
quality of the resulting laser cladded coating
in terms of metallurgical bonding to the
substrate and high coating density.
- Damaged compressor wheels have been
repaired by laser cladding. The repair
process proved to be successful after spin
testing the wheels at 20.000 rpm in vacuum.
REFERENCES
[1] de Damborenea J., Surface modification of metals by
high power lasers, Surf. Coat. Technol. 100–101;1998.
p.377–382.
[2] Sexton C.L., Byrne G., Watkins K.G., Alloy
development by laser cladding: an overview, J. Laser
Appl. 13 (1); 2001 2–11.
Figure 5 Cross section of stellite 21
coating applied on a 30CrNiMo8 substrate.
Figure 6 Setup used for laser cladding of compressor wheels
Figure 7 Close-ups of compressor wheels after laser cladding
Vol 24 No 1