Materials Science and Engineering A282 (2000) 145 – 152
Preliminary study on the laser cleaning of stainless steels after
high temperature oxidation
Pandora Psyllaki, Roland Oltra *
Laboratoire de Recherches sur la Re ´actiite ´ des Solides, UMR 5613 CNRS, Uniersite ´ de Bourgogne, UFR Sciences et Techniques, BP 47 870,
21078 Dijon Cedex, France
Received 1 September 1999; received in revised form 9 November 1999
Abstract
The objective of the present work was to estimate the influence of pulsed laser irradiation on the removal of the oxide layer,
which is developed on the surface of stainless steels during their exposure to high temperature oxidation. In general, this layer is
a protective one, mainly against corrosion. However, in many manufacturing applications or maintenance work, the removal of
the oxides is necessary; for example, the metallic surfaces should be cleaned before welding, otherwise the presence of oxides
increases the tendency to brittle behaviour of the joint. In this study, a pulsed Nd:YAG laser ( =1.064 m, 10 ns) was used for
the surface cleaning of three stainless steels with different chemical compositions and/or surface treatments. The influence of the
laser irradiation on the material, as well as on the mechanisms involved, was investigated by in-situ mass measurements and
post-situ microscopic observations (Scanning Electron Microscopy/SEM, and Energy Dispersion Spectroscopy/EDS). For energy
density applied (1.0–2.0 J cm
-2
), irrespective of the composition and the thickness of the surface layer, the laser irradiation
resulted in the expulsion of the oxide layer, while no material removal of the underlying metal occurred. © 2000 Elsevier Science
S.A. All rights reserved.
Keywords: Stainless steel; High temperature oxidation; Laser cleaning; Q-switched Nd:YAG; In-situ weight measurement; Spallation
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1. Introduction
Stainless steels containing 12wt.% chromium are
widely used for applications at elevated temperatures
(650 – 1050°C), because of their high chemical resistance
in corrosive environments. They owe this ‘non-metallic’
behaviour to the formation of a continuous protective
layer of oxides during oxidation, the exact composition
of which depends on the kind and the concentration of
the alloying elements. In the case of ferritic stainless
steels, containing either Cr ( 17wt.%) or Cr (
10wt.%) and Al ( 5wt.%), the presence of ferrous
oxides in this layer is limited by the formation of Cr
2
O
3
or Al
2
O
3
, respectively [1].
However, in many applications the removal of the
surface oxides is necessary in order to maintain the
good function of a metallic component. For example,
the stainless steel surfaces should be cleaned before
welding because the presence of oxides increases the
tendency of brittle behaviour of the joint and decreases
its mechanical strength. During cyclic thermal loading,
the development of a stress field at the area near the
surface leads to crack initiation and propagation and to
spalling of the protective layer [2]. The fragments pro-
duced can contaminate the environment in which the
component is operating or they can be carriers of
radioactive species when stainless steel has been used in
the construction of a reactor vessel [3]. Thus, the peri-
odical removal of the oxide layer, before its fragmenta-
tion occurs, must be well planned. Chemical and
mechanical techniques have been widely used hitherto
for the removal of these undesirable layers, but they
have many disadvantages, which limit their application:
no selectivity, poor control, introduced stresses, etc.
In recent years, an increasing interest on the use of
laser irradiation for surface cleaning is observed. Com-
pared to the conventional methods of surface cleaning,
laser technique, especially, when combined with an
* Corresponding author. Tel.: +33-3-80396162; fax: +33-3-
80396132.
E-mail address: oltra@u-bourgogne.fr (R. Oltra)
0921-5093/00/$ - see front matter © 2000 Elsevier Science S.A. All rights reserved.
PII:S0921-5093(99)00759-5