Formation mechanism of micro-spikes on AISI 4340 steel with femtosecond laser pulses at near-threshold fluence

We report on the mechanism for the formation of conical micro-spikes on an AISI 4340 steel surface under femtosecond irradiation at near-threshold fluence and at a high repetition rate. We establish that the conical micro-spikes formed in this way are unique and result from a completely different fo...

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Bibliographic Details
Published in:Journal of micromechanics and microengineering 2015-04, Vol.25 (4), p.45007-7
Main Authors: Kam, Dong-Hyuck, Kim, Jedo, Song, Lijun, Mazumder, Jyoti
Format: Article
Language:English
Subjects:
Density
Energy density
Femtosecond
femtosecond laser
Fluence
Formations
high fluence
high repetition rate
High strength steels
micro-spikes
near threshold fluence
Nickel chromium molybdenum steels
Particulates
Steels
Valleys
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Summary:We report on the mechanism for the formation of conical micro-spikes on an AISI 4340 steel surface under femtosecond irradiation at near-threshold fluence and at a high repetition rate. We establish that the conical micro-spikes formed in this way are unique and result from a completely different formation mechanism compared to previously reported formations which are characterized by a random evolution of re-condensed oxide particulates. An experimental micro-spike formation map demonstrates how random micro-spike formations progress to uniform micro-spikes as the fluence increases and how the scan-speed affects the size of the spikes. Apart from fluence, we show that a change in focal position can help to fine-tune the energy density, resulting in identical random conical micro-spikes. The fabricated surfaces show an extraordinary absorption coefficient of up to 0.91 resulting from multiple reflections in the valleys between the micro-spikes. Finally, we find that the relationship between cone number density and scan speed for near-threshold fluence is caused by reduced heat accumulation, increasing the survival rate of cone formation sites.
ISSN:0960-1317
1361-6439
DOI:10.1088/0960-1317/25/4/045007