Development of Indirect Laser Peening Process for forminga micro dimple and making powder deposition on the substrate# 1903
Muneharu KUTSUNA1, Hiroki INOUE1, and Haruki MIZUTANI1
1

School of Engineering, Nagoya University, 1 Furo-cho Chikusa-ku, Nagoya, 464-8603, Japan

Abstract

to machinery part such as car engine piston and piston
ring as shown in Fig.1..

A modification of laser peening process has been
carried out for forming a micro-dimple andintroducing compressive residual stress in thematerials and making powder deposition on thesurface of substrates such as metal, polymer andwood using a metal foil.
In the present work, Q-switch pulsed YAG laser with amax. pulse energy of 650mJ as a wave length of
532nm has been used to generate ultra-high plasmapressure of around 5GPa in 8-10ns. The diameter anddepth of dimple formed can be controlled by the beam
spot size, max. pulse energy and thickness of metal foilin the range of 200μｍ 〜700μｍ in diameter and in
the range of 5 〜50μｍ in depth, respectively. A trialof indirect laser peening was carried out to deposit
MoS2 powders on A6061 aluminum alloy substrate toreduce the friction energy loss of piston for car engine.
Process parameters such as laser intensity, type ofmetal foil and thickness of metal foil have been
investigated to characterize this new process.
Introduction

Fig.1 Application of ILP process to piston head
The mechanism of indirect laser peening (ILP process)is shown in Fig.2. ILP process is carried out under thewater. Therefore, second harmonic wave of YAG laser(λ＝532 nm) is recommended to get effective plasmapressure for surface modification[5].

Laser peening is a kind of laser surface treatment that
introduces compressive residual stress on the material
surface. The compressive residual stress is very
effective for improvement of fatigue strength [1-2] andstress corrosion cracking of structures [3-4]. On theother hand, Indirect Laser Peening is a new laser
peenng process. Developed by prof. M.Kutsuna andMr. K.Saito in 2005 (Japanese patent No.4058448). In
this process, a metal foil is used to generate ultra-highplasma pressure and to make micro-dimples on thesurface of substrate with deposition of metal or nonmetallic particles.
.In the present work, process parameters of indirectlaser peening (ILP) process has been investigated forthe characterization of the process for the applications

Fig.2 Experimental setup of indirect laser peening .

High intensity laser beam with short pulse is required
to get ultra-high plasma pressure in 8 -10 ns in theprocess. Many kinds of metal foil are used as a basesheet to absorb the laser power and to generate ultrahigh plasma pressure of 5GPa. The plasticallydeformed base sheet is used for put the high pressure
upon the substrate to make a micro dimple. In theconventional laser peening, base sheet is not used tomake micro-dimples on the substrate. It can be called
as a direct laser peening. In addition,, metallic/nonmetallic particles is put on the back surface of basesheet to make metallic or non metallic
deposition/coating on substrate before indirect laser
peening.

bath, work piece holder, optics (focal distance =150mm) and controller. The typical condition ofindirect laser peening is as follows;
Laser intensity: 5 〜 30GW/cm2 , Beam spot
diameter: from 200μｍ to 700μｍ, Thicknessof metal foil: from 15μｍ to 45μｍ
Experimental Result and discussion
The effects of process parameters such as laser
intensity, type of metal foil and thickness of metal
foil on the shape of dimple and deposition of Mos2
powder have been investigated. Fig.4 shows

Experimental Procedure
Materials used are SK85 tool steel foil, AISI 304 typestainless steel foil, AISI 410 type stainless steel foil
and SS400 mild steel foil (the thickness: 15,25,35 and45μｍ) as metal sheet, MoS2 powder for reduction offriction energy loss , and A6061 aluminum alloy plate
as a substrate.
In the present work, Q-switch pulsed YAG laser with amax. pulse energy of 650mJ as a wave length of
532nm has been used to generate ultra-high plasmapressure of around 5GPa in 10-20ns. The beam spot
diameter is from 200μｍ to 700μｍ. The diameterand depth of dimple formed can be controlled by thebeam spot size, max. pulse energy and thickness ofmetal foil in the range of 200μｍ 〜 700μｍ in
diameter, in the range of 10mJ 〜 650mJ in pulse
energy and in the range of 15μｍ 〜 45μｍ in metal
foil thickness. Fig.3 shows the experimental setup ofindirect laser peening system in Advanced Laser
Technology Research Center Co.

Fig.4 Dimples on the AISI 304 metal foil

Fig.3 Indirect laser peening system used
The peening system including the Q-switch YAG laserof 1.5J pulse energy (λ＝1064nm), X-Y table , water

Fig.5 Shape of dimple on A6061 substrate (unit:μm)

the example of dimples on the metal foil and Fig.5
shows the shape of dimples on the A6061 substrate.
The diameter is about 420μｍ and the max. depth
is 79 μｍ. The green laser (λ=532nm) is effective
to make a dimple on the base sheet under the water
as shown in Fig. 6.

Fig.6 Photo of indirect laser peening on the piston formotorcycle under the water

The diameter and depth of dimple on the metal foil
is 661μm and 22μm ,respectively.

Fig. 7 Dimple on 15 μ ｍ thick metal sheet
formed by ILP process of 9.9GW/cm2Effects of type and thickness of metal foil
(1) Using SK85 tool steel foil
The effect of thickness of SK tool steel foil on theformation of dimple has been investigated under thecondition A shown in Table 1. The one of results isshown in Fig.7. The laser intensity was 4.9GW/cm2.
〜29.7GW/cm2
Table 1 The peening condition A
Pulse energy (mJ)

50,100,200,300

Spot diameter (μm)

400Power(GW/cm2)

density

Number of shot

Thickness of metal
foil (μm)

4.9〜29.7
115,25,35,45

Fig. 8 Dimple and MoS2 powders on A6061
substrate formed by ILP process of
9.9GW/cm2 using 15μｍ thick metal
foilThe dimple on the A6061 substrate is 233μｍ indiameter and 8μｍ in depth was formed by ILP
process as shown in Fig.8. Using 25μm thickmetal foil , dimple was formed as shown in Figs.
9.and 10. The dimple on the metal foil is morethan 481μm in diameter and 12μm in depth andthe dimple on the A6061 alloy substrate is 158μm and 2μm in depth. The higher the thickness ofmetal foil is ,the higher laser intensity is required .

6μm in depth and the dimple on the A6061 alloy
substrate is 158μm and 2μm in depth.

Fig.11 Dimple on 35 μｍ thick SK85 steel foil
formed by ILP process under the 19.8GW/cm2

Fig.9 Dimple on 25 μｍ thick metal foil formed byILP process under the 19.8GW/cm2

Fig.10 Dimple and MoS2 powders on A6061
substrate formed by ILP process under the19.8GW/cm2 using 25 μ ｍ thick metalfoil
Using 35μm thick SK steel foil , the dimple wasformed as shown in Figs. 11.and 12. The dimple on
the steel foil is more than 481 μm in diameter andFig.11 and 12 shows the The 35μｍ thick SK85
steel foil is too heavy and hard for indirect laser
peening (ILP) process as shown in Fig.12. Nodimple was formed on the substrate.

Fig.12 No dimple and MoS2 powder on A6061
substrate formed by ILP process under the19.8GW/cm2 using 35μｍthick metal foil.35μｍthick SK85 steel foil is too hard and is notductile for ILP process as shown in Fig.12.

(2) Using AISI 304 stainless steel foil
The effect of thickness of AISI 304 stainless steel
foil on the formation of dimple has been
investigated under the condition A shown in Table 1.
The results are shown in Figs.13,14,15 and 16. The
laser intensity was 4.9GW/cm2.〜29.7GW/cm2.

Fig.15 Dimple on A6061 substrate using 304
type stainless steel foil of 15 μm in thickness byILP process at a laser intensity of 9.9GW/cm2

Fig.13 Dimple on the 304 type stainless steel foilof 15 μm in thickness by ILP process at a laser
intensity of 9.9GW/cm2

Fig.16 Dimple on A6061 substrate using 304 typestainless steel foil of 15 μm in thickness
by ILP process at a laser intensity of
19.7GW/cm2
Fig.14 Dimple on the 304 type stainless steel foil of15 μ m in thickness by ILP process at a laserintensity of 19.7GW/cm2
AISI 304 stainless steel foil is useful for ILP process
to put MoS2 powder on the substrate as shown inFigs. 15 and 16. Dark particles in the photo shownin Figs.15 and 16 are MoS2 powder. If thethickness of the stainless steel foil increase, theamount of the powder deposited decrease as shownin Fig.17.

Fig.17 Dimple on A6061 substrate using 304 typestainless steel foil of 35μm in thickness by ILP
process at a laser intensity of 9.9GW/cm2(3) Using AISI 410 stainless steel foil

Fig.19 Dimple and MoS2 powder on A6061 alloy
substrate by ILP process using the 410 typestainless steel foil of 15μm in thickness ata laser intensity of 4.9GW/cm2

The effect of thickness of AISI 410 stainless steel
ｆoil on the formation of dimple and deposition ofMoS2 powder has been investigated under thecondition A shown in Table 1. The results areshown in Figs.18,19,20 and 21. The laser intensity
was 4.9GW/cm2.〜29.7GW/cm2

Fig.20 Dimple and MoS2 powder on A6061 alloy
substrate by ILP process using the 410 typestainless steel foil of 15μm in thickness ata laser intensity of 19.7GW/cm2Fig.18 Dimple on the 410 type stainless steel foil of
15 μ m in thickness by ILP process at alaser intensity of 4.9GW/cm2
At a low laser intensity of 4.9GW/cm2, a deep
dimple with MoS2 powder can be formed as shownin Fig.19.

Gray particle in the dimple on the substrate is also
MoS2 in Figs.20 and 21. The diameter of dimple
are about 185- and 191μm and the depth of dimple
are 11μm and 7μm, respectively.

suggests that ductile metal foil can be easily
deformed and put the powder into the substrate.

Fig.21 Dimple and MoS2 on A6061 alloy substrateby ILP process using 410 type stainless steel
foil of 25 μ m in thickness at a laser
intensities of 4.9GW/cm2 (a), 9.9GW/cm2(b),19.7GW/cm2(c),29.7GW/cm2(d)Deposition of MoS2 powder on A6061 substrateusing AISI 410 stainless steel foil is more desirable
than that by 304 stainless steel foil.
(4) Using JIS-SS400 mild steel foil
The effect of thickness of SS400 mild steel foil on
the formation of dimple and deposition of MoS2
powder has been investigated under the condition B
shown in Table 2. The results are shown in Figs.23.
The laser intensity was changed also from4.9GW/cm2.to 29.7GW/cm2.

Fig.22 Dimple and MoS2 on A6061 alloy substrateby ILP process using 410 type stainless steel
foil of 45 μ m in thickness at a laser
intensity of 4.9GW/cm2

Table 2 Indirect Laser Peening Condition B
Pulse energy (mJ)

50,100,200,300

Spot diameter (μm)

400Power density (GW/cm2)

4.9〜29.7

Number of pulse
Thickness of sheet (μm)

135,45The dimple formation and deposition of MoS2
powder by ILP process using SS400 mild steel foilsof 45 μ m are possible as shown in Fig.23. It

Fig.23 Pimple and MoS2 on A6061 alloy substrateby ILP process using SS400 mild steel foilof 45μm in thickness at a laser intensity of
4.9GW/cm2

Summary

Indirect laser process has been developed fordeposition of particles such as metallic , nonmetallic materiales on the metal substrate andmachinery part, and for the dimple formation tointroduce the compressive residual stress for
improving the fatigue strength and corrosion
resistance of conpornents. One of target for
application of this process is a piston for car andmotorcicle engine.

Meet the Author
Dr. Muneharu Kutsuna was a professor of University,
Dept. of Material Science and Engineering of Graduate
School of Engineering, Nagoya University. He has
retired from Nagoya University end of March 2008
and established“Advanced Laser Technology

Research Center (ALTREC)” April 1st 2008.He wasgraduated from Nagoya University in 1974. He had

Acknowledgement
The present work has been supported by theGovernment Research and Development programmefor Creation of Local Inovation Industry. The tiltle is“ Development of Special Laser peening Technology”

been worked for Kawasaki Heavy Industry Co., Ltd forten years from 1972 to 1982. He has studied at MIT asa visiting researcher. He has been worked for Nagoya
University from 1982. His research fields include
welding technology, welding metallurgy, laser material

References

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