Laser Applications Laboratory
Laser Glazing of Railroad Rails
Project description: Laser glazing of
Category: Project with industrial partner (American Association of Railroads)
Laser glazing treatment is applied on the gage face of the rails to help minimize flange and rail wear, reduce fuel consumption, and decrease the likelihood of derailments caused by flange climb and low-rail rollover.
To maintain the toughness and relative inexpensiveness of rail steel while
reducing wheel/rail friction, an ideal approach is to modify the loading surface
of existing rail in a way that renders it substantially harder yet leaves the
substrate unaffected. Laser treatment can accomplish this by changing the surface
microstructure, and doing so in a such a way that the surface layer undergoes
a smooth transition into the substrate and is well bonded to it. One way to
harden the surface of rail steel is by laser surface hardening, i.e. selective
austenitization and martensitization of the local surface region of rail steel
by rapid heating and cooling. The hard surface layer will resist plastic flow
and reduce friction and wear. This simple process has some minor disadvantages.
Unlike in the case of hard bulk materials, like diamond, o thin hard surface
when loaded substantially will transmit these loads to the soft substrate,
which can deform even if the surface does not. If the surface layer has the
same elastic modulus as the substrate, it can not mitigate stress concentrations
any differently than an untreated surface. However, a surface layer with a
smaller modulus than the substrate can distribute surface stress concentrations
elastically within the layer and mitigate their effect on the substrate. Also,
if the hard surface layer does deform plastically, it will do so in the same
manner as untreated rail steel, producing a damage layer along which separation
can eventually occur leading to delamination. What is needed then is a surface
layer that is hard with respect to plastic flow, is elastically compliant,
and, when it does deform plastically, does not produce a damage layer, Laser
glazing can be an ideal treatment to achieve this goal.
In laser glazing, a thin surface layer is melted and rapidly solidified to
produce an amorphous or quasi-amorphous surface film. The lack of crystalline
order in such materials makes them substantially resistant to plastic flow,
and hence very hard. They exhibit about a 30% or greater reduction in elastic
modulus. If they do deform plastically, localized defects are not involved,
and the more open structure tends to be self healing. Consequently, repeated
plastic flow is less likely to result in debris being deposited in a subsurface
damage layer. For these reasons, the laser glazing process alone is sufficient
to provide satisfactory reductions in friction and wear.
The videos are in QuickTime® format. Download the QuickTime plugin
glazing of 1080 steel wheel
Laser glazing of rotatory parts shown in this movie clip.
[ View this video 00:00:22 (1.8 MB) ]
- Laser glazing of flat steel surface
Laser glazing of flat surface of steel parts is shown in the movie clip by moving the required beam over the surface at a constant speed.
[ View this video 00:00:18 (1.3 MB) ]
Last Modified: Thu, October 10, 2013 4:43 PM