Prof. Hitoshi Soyama
Department of Finemechanics, Tohoku University, Japan
Title: Mechanical Surface Treatment of Additive Manufactured Ti6Al4V by Cavitation Peening
Abstract:
Additive
manufactured AM titanium alloy Ti6Al4V is attractive metallic materials for
biomedical implants and aviation components, as shape is directly formed from computer-aided
design CAD data with less leading time. However, weak fatigue strength of AM
Ti6Al4V is a big problem for practical applications. Typical method to improve
fatigue strength of metallic components is mechanical surface treatment such as
shot peening. But, an increase of surface roughness due to shot collision
sometimes causes weak spots on the treated surface. Soyama et al. developed
cavitation peening without solid collisions [1],[2], and demonstrated the
improvement of fatigue strength [3]-[5].
Cavitation is a phase change phenomenon from liquid-phase to gas-phase
due to increase of flow velocity. At cavitation bubble collapse, micro-jet and
shock wave are produced, and they produce impacts. Whereas cavitation is harmful
phenomenon for fluid machineries such as pumps and valves, the cavitation impacts
are utilized to improve fatigue properties for metallic components in
cavitation peening.
In
conventional cavitation peening, cavitation is caused by injecting a high-speed
water jet into water. However, “cavitation peening” is different from “water
jet peening”. Note that water column impacts in the high-speed water jet are
utilized in water jet peening. Thus, an expensive high-injection pressure
plunger pump is required. On the other hand, relatively low injection pressure
is good enough for cavitation peening, as cavitation impacts are used in the
cavitation peening. Namely, in the case of cavitation peening, initial cost and
running cost are much cheaper than that of water jet peening.
In
submerged laser peening, it is believed that pressure wave caused by laser
ablation is used for mechanical surface treatment. Note that bubble is
generated after laser ablation at the submerged laser peening. When the
shockwave in water was measured, pressure wave induced by laser ablation was
larger than that of bubble collapse. However, the impact passing through the
material was larger than that of laser ablation, when the impact was measured. Even
though the submerged laser peening, bubble impact is used for the mechanical
surface treatment. Thus, at the present study, bubble induced by the submerged
pulse laser is named as laser cavitation. Namely, the submerged laser peening
is a kind of cavitation peening using laser cavitation.
In the
present keynote speech, fundamental and application of cavitation peening using
a submerged water jet and a submerged pulse laser are explained, and the
improvement of fatigue strength of AM Ti6Al4V is demonstrated comparing with
shot peening.
This work was partly supported by JSPS
KAKENHI Grant Number 18KK0103 and 20H02021.
References
[1] H. Soyama, Key Factors and Applications of
Cavitation Peening, International Journal of Peening Science and Technology,
Vol. 1, (2017), pp. 3-60, http://www.oldcitypublishing.com/wp-content/uploads/2017/11/IJPSTv1n1p3-60Soyama.pdf
[2] H. Soyama, Cavitation Peening: A Review, Metals,
Vol. 10, No. 2, (2020), paper No. 270, pp. 1-27, DOI:10.3390/met10020270
[3] H. Soyama, Comparison between the Improvements
Made to the Fatigue Strength of Stainless Steel by Cavitation Peening, Water
Jet Peening, Shot Peening and Laser Peening, Journal of Materials Processing
Technology, Vol. 269, (2019), pp. 65- 78.
[4] H. Soyama and F. Takeo, Effect of Various
Peening Methods on the Fatigue Properties of Titanium Alloy Ti6Al4V
Manufactured by Direct Metal Laser Sintering and Electron Beam Melting, Materials,
Vol. 13, No. 10, (2020), paper No. 2216, pp. 1-26, DOI:10.3390/ma13102216.
[5] H. Soyama and D. Sanders, Use of an Abrasive
Water Cavitating Jet and Peening Process to Improve the Fatigue Strength of
Titanium Alloy 6Al-4V Manufactured by the Electron Beam Powder Bed Melting
(EBPB) Additive Manufacturing Method, JOM, Vol. 71, No. 12, (2019), pp.
4311-4318, https://rdcu.be/bM66I
Biography: