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Fibre Laser Nitriding of Titanium and its Alloy in Open Atmosphere for Orthopaedic Implant Applications: Investigations on Surface Quality, Microstructure and Tribological Properties
Chan, Chi-Wai Lee, Seunghwan Smith, Graham C. Donaghy, Clare L.
Chan, Chi-Wai
Lee, Seunghwan
Smith, Graham C.
Donaghy, Clare L.
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Other Contributors
EPub Date
Publication Date
2016-12-20
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Abstract
Laser nitriding is known to be an effective method to improve the surface hardness and wear resistance of titanium
and its alloys. However, the process requires a gas chamber and this greatly limits the practicability for
treating orthopaedic implants which involve complex-shaped parts or curved surfaces, such as the tapered surface
in a femoral stemor the ball-shaped surface in a femoral head. To tackle this problem, a direct laser nitriding
process in open atmosphere was performed on commercially pure titanium (grade 2, TiG2) and Ti6Al4V alloy
(grade 5, TiG5) using a continuous-wave (CW) fibre laser. The effects of varying process parameters, for instance
laser power and nitrogen pressure on the surface quality, namely discolouration were quantified using ImageJ
analysis. The optimised process parameters to produce the gold-coloured nitride surfaces were also identified:
40W(laser power), 25mm/s (scanning speed), 1.5mm(standoff distance) and 5 bar (N2 pressure). Particularly,
N2 pressure at 5 barwas found to be the threshold above which significant discolouration will occur. The surface
morphology, composition, microstructure, micro-hardness, and tribological properties, particularly hydrodynamic
size distribution of wear debris, were carefully characterized and compared. The experimental results
showed that TiG2 and TiG5 reacted differently with the laser radiation at 1.06 μm wavelength in laser nitriding
as evidenced by substantial differences in the microstructure, and surface colour and morphology. Furthermore,
both friction andwear properties were strongly affected by the hardness and microstructure of titaniumsamples
and direct laser nitriding led to substantial improvements in their wear resistant properties. Between the two
types of titanium samples, bare TiG2 showed higher friction forces and wear rates, but this trend was reversed
after laser nitriding treatments.
Citation
Chan, C., Lee, S., Smith, G. C. & Donaghy, C. (2016). Fibre Laser Nitriding of Titanium and its Alloy in Open Atmosphere for Orthopaedic Implant Applications: Investigations on surface quality, microstructure and tribological properties. Surface and Coatings Technology, 309, 628-640.
Publisher
Elsevier
Journal
Surface and Coatings Technology
Research Unit
DOI
10.1016/j.surfcoat.2016.12.036
PubMed ID
PubMed Central ID
Type
Article
Language
en
Description
Series/Report no.
ISSN
0257-8972
EISSN
1879-3347