Excimer laser processing of tool steel: Tribological effects of multiple pulse processing and titanium alloying Page: 3 of 8
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EXCIMER LASER PROCESSING OF TOOL STEEL: TRIBOLOGICAL EFFECTS
OF MULTIPLE PULSE PROCESSING AND TI ALLOYING
T. R. Jervis, M. Nastasi, A. J. Griffin, Jr., T. G. Zocco, T. N. Taylor, and S. R. Foltyn,
Materials Science and Technology Division,
Los Alamos National Laboratory, Los Alamos, NM 87545
ABSTRACT
Excimer lasers were used to modify the surface of AISI type A-7 tool steel, a high C, high V,
high Cr material used in many cutting applications. Multiple pulses of laser radiation at 248 nm
were used to alter the composition of the surface alloy. Hardness and modulus were not
significantly affected by the treatment, but friction in dry sliding against an alumina pin was
reduced. The reduction was small but persistent for multiply melted and resolidified surfaces.
These surfaces showed a marked increase in the surface Cr concentration. Greater reductions in
friction were obtained from a Ti rich surface layer formed by laser mixing an evaporated Ti layer
into the material. The friction coefficient of the Ti alloyed surface deteriorated after approximately
1,000 cycles, indicating wear-through of the modified surface. The observed properties will be
discussed in terms of the excimer laser modification process and the microstructure and
composition of the resulting surfaces.
INTRODUCTION
AISI type A-7 is an air-hardening, medium-alloy, cold work tool steel used in cutting and
forming dies and in applications that exploit its exceptional abrasive wear resistance. Alloying
additions of C (2.3 wt %), Cr (5.25 wt %), V (4.75 wt %), and lesser amounts of Mo and W (1.1
wt % each) are present in the material. This material is hardened at a solution temperature of 830 C
and tempered at 125 C for several hours to a final hardness. In its fully hardened condition, it is
somewhat brittle so in many applications it is used in a tempered state.
Laser processing was approached to examine the effect of laser processing, specifically
repeated melt-solidification cycles, and to examine the effect of Ti alloying of the surface. Both
laser surface processing an laser Ti alloying with the rapid solidification attendant to excimer laser
processing has been shown to improve tribological properties of other metal alloys and
ceramics1,2.
EXPERIMENT
Experiments were performed on steels tempered to Rockwell hardness of 64 (C-scale). Some
experiments were performed on fully solution hardened materials (RC-68), but because these
materials are subject to brittle failure in applications, we did not examine the tribological effects of
surface alloying on these materials.
Sample materials were obtained in the fully solution hardened and in the tempered condition
and were polished to a mirror finish. For alloying experiments, the polished samples were coated
with 200 nm of Ti using an e-beam evaporation system with a base pressure of less than 10-8 Torr.
The samples were then subjected to varying numbers of pulses of excimer laser radiation at 248 nm
in air at a fluence of 1.1 J-cm2.
Pulses from an excimer laser operating at 248 nm were homogenized in order to produce
uniform illumination on the surface. The homogenizer also produces a square beam spot. The
sample was then moved in front of the beam so that the entire area experienced the requisite
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Jervis, T. R.; Nastasi, M.; Griffin Jr., A. J.; Zocco, T. G.; Taylor, T. N. & Foltyn, S. R. Excimer laser processing of tool steel: Tribological effects of multiple pulse processing and titanium alloying, article, December 1, 1995; New Mexico. (https://digital.library.unt.edu/ark:/67531/metadc670082/m1/3/: accessed April 25, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.