CONTRIBUTION OF RESEARCH AND INNOVATION IN PLASMA ASSISTED
DIFFUSION TREATMENTS TO MEET MODERN TECHNOLOGICAL
CHALLENGES
T. Czerwiec
Institut Jean Lamour (UMR 7198) CNRS – Université de Lorraine, CP2S department Parc de Saurupt, CS 14234 - 54042 Nancy cedex, France
thierry.czerwiec@univ-lorraine.fr
Plasma assisted nitriding (PAN), also known as Ion nitriding, is a thermochemical
treatment involving interaction and diffusion of nitrogen in a metallic material at
moderate to elevated temperatures. It is certainly the oldest plasma assisted surface
treatment process applied at the industrial scale. The potential of the electrical discharges
for plasma assisted nitriding was recognized very early in Germany (1928) and in the
United States (1931), but it was necessary to wait for the Second World War to see the
first industrial applications becoming a reality. Since that time, this technique knew
numerous practical applications induced by technical innovations. This communication
will focus on two main axes. First we will discuss the perspectives in the development of
new plasma assisted diffusion techniques (nitriding, carburizing, nitrocarburizing…) and
on the opportunity to couple different pre-treatments with plasma assisted diffusion
techniques. In a second part, we will discuss the potential of thermochemical treatments
for the functionalization of surfaces by surface patterning or texturing.
Plasma assisted nitriding is usually carried out by a direct current (dc) glow discharge
under rough vacuum (100-1000 Pa) and with moderate substrate voltage (0.3-1 kV). The
dc or pulsed dc potential is applied between the workpieces forming the cathode and the
vessel. In spite of different advantages such as simplicity, robustness, low production and
maintenance costs and the opportunity to treat large pieces, such technology has also
some limitations so that more flexibility and control are required for the development of
innovative thermochemical diffusion processes. The enhanced or intensified PAN
concept results from the recent development of a new generation of low-pressure, high
density plasma sources in the electronics industry. A common feature of these high
density sources is the uncoupling of the plasma generation from the substrate surface, the
so-called “transferred plasma” concept. In such processes, independent substrate biasing
provides a means for independent ion flux and ion energy control.
Improving the diffusion kinetics at low temperature by introducing pre-treatments is
also an exciting challenge that constitutes another aspect of innovation in the field of low
temperature thermo-chemical diffusion treatments of stainless steel and related nickelbased alloys. We will examine recent results concerning mechanical pre-treatment such
as shot peening and surface mechanical attrition treatments. The new concept of surface
patterning on austenitic stainless steel by plasma assisted diffusion treatment will be also
presented. It allows the creation of uniform micro or nano relief with regularly shaped
asperities or depressions. Such engineered surfaces with new functional properties have
potential interesting industrial applications we will present here.