Coating Laser
Content
Applied Mechanics and Materials Vols. 152-154 (2012) pp 1239-1243
Online available since 2012/Jan/24 at www.scientific.net
© (2012) Trans Tech Publications, Switzerland
doi:10.4028/www.scientific.net/AMM.152-154.1239
Coating of Ti64 bearings in air by using a Q-sw laser
Justyna Rozwadowska1,a, K. Kida1,2,b, E. C. Santos1,c, T. Honda1,d, H. Koike1,e,
Y.Kashima3,f, Ryo Matsumoto4,g
1
2
Kyushu University, 744 Motooka, Nishi-ku, Fukuoka 819-0395, Japan
Fundamental Studies on Technologies for Steel Materials with Enhanced Strength
and Functions, Consortium of the JRCM, Minato-ku, Tokyo, Japan
3
Kashima bearings corporation, 2-9-21 Himesato, Nishiyodogawa-ku, Osaka 555-0025, Japan
4
Osaka University, 2-1 Yamadaoka, Suita, Osaka, Japan
a
[email protected], [email protected],
c
d
e
[email protected], [email protected], [email protected],
f
[email protected], [email protected]
Keywords: Rolling contact fatigue, Ti64, laser coating in air, Q-sw laser
Abstract. The influence of surface oxidizing using a Q-sw laser on the wear loss of titanium-4Al-6V
(Ti64) alloy during rolling contact fatigue is investigated. Titanium components are widely
appreciated for their superb biocompatibility, high strength to weight ratio and corrosion resistance.
Due to the above mentioned advantages titanium bearings are a popular choice in applications
requiring high strength, light weight, and minimum maintenance (for example, aerospace and defence
industries). In these rolling contact applications however issues such as fretting and wear related
problems are a common occurrence as the tribological properties of titanium alloys are inferior to
those of other metal alloys, such as steel. In an attempt to tackle this problem, a Q-sw laser was used in
this work to coat Ti64 bearings with complex titanium oxide layers in a closed chamber without any
protective gas. Non-coated and coated samples were tested under water by using a thrust-type rolling
contact fatigue machine. The morphology and crystallographic texture of the layers were observed by
laser confocal microscope, scanning electron microscope and X-ray diffraction. The wear loss of the
coated samples was at least fifty-fold lower than that of the non-coated bearings and a 3-fold increase
in the maximum load capacity compared with TiN layers was achieved.
Introduction
Pure titanium can be found in two allotropic crystal forms: α (alpha, hexagonal closed packed) and β
(beta, body centred cubic crystal structure) at transus temperature of 882 °C for the pure metal. Ti64 is
formed by alpha and beta phases. Titanium is highly reactive with interstitial elements: oxygen,
nitrogen, carbon and hydrogen and providing that the atmosphere for the reactions is adequate easily
forms oxides, nitrides, carbides and hydrides during thermal processing even at low temperatures. At
ambient temperature a native oxide layer of the order of 3 nm to 7 nm covers titanium’s surface and is
responsible for the material’s high corrosion resistance. This thin natural oxide layer is however easily
removed by friction. Nitride and carbide layers can have a beneficial effect on titanium’s tribological
properties and hardness, there is however not much research done on the influence of oxide coats.
According to Bell [1] and Bloyce [2], the low tribological properties of titanium are attributed to the
material’s electronic configuration and crystallography. While most hexagonal metals have good
friction and wear properties, the friction coefficient of titanium, that has a hexagonal crystal structure
at room temperature, is relatively high. This fact may be related to a difference in the slip mechanisms
within the material. The α-phase titanium has a ‘c/a’ ratio of 1.587, inferior when compared to the
theoretical ideal of 1.633. Due to this low c/a, the operative slip systems and available twinning planes
in titanium’s crystal lattice increase. As a method of decreasing the undesirably high friction
All rights reserved. No part of contents of this paper may be reproduced or transmitted in any form or by any means without the written permission of TTP,
www.ttp.net. (ID: 165.215.209.15, ProQuest-16/10/13,23:09:40)
Online available since 2012/Jan/24 at www.scientific.net
© (2012) Trans Tech Publications, Switzerland
doi:10.4028/www.scientific.net/AMM.152-154.1239
Coating of Ti64 bearings in air by using a Q-sw laser
Justyna Rozwadowska1,a, K. Kida1,2,b, E. C. Santos1,c, T. Honda1,d, H. Koike1,e,
Y.Kashima3,f, Ryo Matsumoto4,g
1
2
Kyushu University, 744 Motooka, Nishi-ku, Fukuoka 819-0395, Japan
Fundamental Studies on Technologies for Steel Materials with Enhanced Strength
and Functions, Consortium of the JRCM, Minato-ku, Tokyo, Japan
3
Kashima bearings corporation, 2-9-21 Himesato, Nishiyodogawa-ku, Osaka 555-0025, Japan
4
Osaka University, 2-1 Yamadaoka, Suita, Osaka, Japan
a
[email protected], [email protected],
c
d
e
[email protected], [email protected], [email protected],
f
[email protected], [email protected]
Keywords: Rolling contact fatigue, Ti64, laser coating in air, Q-sw laser
Abstract. The influence of surface oxidizing using a Q-sw laser on the wear loss of titanium-4Al-6V
(Ti64) alloy during rolling contact fatigue is investigated. Titanium components are widely
appreciated for their superb biocompatibility, high strength to weight ratio and corrosion resistance.
Due to the above mentioned advantages titanium bearings are a popular choice in applications
requiring high strength, light weight, and minimum maintenance (for example, aerospace and defence
industries). In these rolling contact applications however issues such as fretting and wear related
problems are a common occurrence as the tribological properties of titanium alloys are inferior to
those of other metal alloys, such as steel. In an attempt to tackle this problem, a Q-sw laser was used in
this work to coat Ti64 bearings with complex titanium oxide layers in a closed chamber without any
protective gas. Non-coated and coated samples were tested under water by using a thrust-type rolling
contact fatigue machine. The morphology and crystallographic texture of the layers were observed by
laser confocal microscope, scanning electron microscope and X-ray diffraction. The wear loss of the
coated samples was at least fifty-fold lower than that of the non-coated bearings and a 3-fold increase
in the maximum load capacity compared with TiN layers was achieved.
Introduction
Pure titanium can be found in two allotropic crystal forms: α (alpha, hexagonal closed packed) and β
(beta, body centred cubic crystal structure) at transus temperature of 882 °C for the pure metal. Ti64 is
formed by alpha and beta phases. Titanium is highly reactive with interstitial elements: oxygen,
nitrogen, carbon and hydrogen and providing that the atmosphere for the reactions is adequate easily
forms oxides, nitrides, carbides and hydrides during thermal processing even at low temperatures. At
ambient temperature a native oxide layer of the order of 3 nm to 7 nm covers titanium’s surface and is
responsible for the material’s high corrosion resistance. This thin natural oxide layer is however easily
removed by friction. Nitride and carbide layers can have a beneficial effect on titanium’s tribological
properties and hardness, there is however not much research done on the influence of oxide coats.
According to Bell [1] and Bloyce [2], the low tribological properties of titanium are attributed to the
material’s electronic configuration and crystallography. While most hexagonal metals have good
friction and wear properties, the friction coefficient of titanium, that has a hexagonal crystal structure
at room temperature, is relatively high. This fact may be related to a difference in the slip mechanisms
within the material. The α-phase titanium has a ‘c/a’ ratio of 1.587, inferior when compared to the
theoretical ideal of 1.633. Due to this low c/a, the operative slip systems and available twinning planes
in titanium’s crystal lattice increase. As a method of decreasing the undesirably high friction
All rights reserved. No part of contents of this paper may be reproduced or transmitted in any form or by any means without the written permission of TTP,
www.ttp.net. (ID: 165.215.209.15, ProQuest-16/10/13,23:09:40)
