Phase transformation studies on the a-C coating under repetitive impacts
The phase transformation of hydrogen-free amorphous carbon (a-C) coating on tungsten high speed steel (SKH2) substrates under repetitive impact testing has been studied. The a-C coated disc was impacted by the chromium molybdenum steel (SCM420) pin at several different impact loads and impact cycl...
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my.utem.eprints.81072015-05-28T03:54:12Z http://eprints.utem.edu.my/id/eprint/8107/ Phase transformation studies on the a-C coating under repetitive impacts Abdollah, Mohd Fadzli bin TJ Mechanical engineering and machinery The phase transformation of hydrogen-free amorphous carbon (a-C) coating on tungsten high speed steel (SKH2) substrates under repetitive impact testing has been studied. The a-C coated disc was impacted by the chromium molybdenum steel (SCM420) pin at several different impact loads and impact cycles (up to 100,000) under lubricated conditions. The results show that the sp3 fractions of impacted a-C coating obtained from the surface of impact craters are significantly increased with impact cycles due to decreasing ID/IG ratio. This means that the amorphization of a-C coating also increased after several impact cycles. As for the full-width at half maximum (FWHM) of G peak characterization, it is shown that the hardness of impacted a-C coating is higher than the as-received. From the observation of surface roughness using atomic force microscopy (AFM), it is supposed that increasing sp3 fractions and the hardness of the impacted a-C coating during impact correlate to the reduction of surface roughness. In addition, the tribochemical reaction to the environment during impact occurred at the mating material, where the transfer layer adhered, as well as in the wear debris. This is due to the oxidation of ferrum (Fe) to magnetite (Fe3 O4) and hematite (α-Fe2 O3) phases with predominant peak at about 680 cm−1 and 1317 cm−1 , respectively. The formation of Fe3 O4 and α-Fe2 O3 phases was revealed from Raman spectroscopy and the existence of oxide elements was verified by energy dispersive X-ray spectroscopic (EDS) analysis. Increasing the G peak position, together with a concomitant decrease of their width, it is believed that the structural transformation from sp3 to sp2 is taking place within the wear debris and leads to the graphitization process at a higher contact pressure. It was suggested that the high contact pressure is not just only corresponding to the applied normal impact load, but it is also exerted by an oil lubricant during impact. A high contact pressure can significantly reduce the graphitization temperature and substantially accelerate the graphitization process. However, a significant phase transformation of the transfer layer on the SCM420 pin does not intensely occur because it is mainly coming from the surface layer of the impacted aC coating, where the sp3 content increases and no wear debris is observed inside it. Elsevier 2010-07-24 Article PeerReviewed application/pdf en cc_by http://eprints.utem.edu.my/id/eprint/8107/1/surface.pdf Abdollah, Mohd Fadzli bin (2010) Phase transformation studies on the a-C coating under repetitive impacts. Surface & Coatings Technology, 205. pp. 625-631. ISSN 0257-8972 http://www.journals.elsevier.com/surface-and-coatings-technology/ doi:10.1016/j.surfcoat.2010.07.062 |
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TJ Mechanical engineering and machinery Abdollah, Mohd Fadzli bin Phase transformation studies on the a-C coating under repetitive impacts |
description |
The phase transformation of hydrogen-free amorphous carbon (a-C) coating on tungsten high speed steel
(SKH2) substrates under repetitive impact testing has been studied. The a-C coated disc was impacted by the
chromium molybdenum steel (SCM420) pin at several different impact loads and impact cycles (up to
100,000) under lubricated conditions. The results show that the sp3
fractions of impacted a-C coating
obtained from the surface of impact craters are significantly increased with impact cycles due to decreasing
ID/IG ratio. This means that the amorphization of a-C coating also increased after several impact cycles. As for
the full-width at half maximum (FWHM) of G peak characterization, it is shown that the hardness of
impacted a-C coating is higher than the as-received. From the observation of surface roughness using atomic
force microscopy (AFM), it is supposed that increasing sp3
fractions and the hardness of the impacted a-C
coating during impact correlate to the reduction of surface roughness. In addition, the tribochemical
reaction to the environment during impact occurred at the mating material, where the transfer layer
adhered, as well as in the wear debris. This is due to the oxidation of ferrum (Fe) to magnetite (Fe3
O4) and
hematite (α-Fe2
O3) phases with predominant peak at about 680 cm−1
and 1317 cm−1
, respectively. The
formation of Fe3
O4 and α-Fe2
O3
phases was revealed from Raman spectroscopy and the existence of oxide
elements was verified by energy dispersive X-ray spectroscopic (EDS) analysis. Increasing the G peak
position, together with a concomitant decrease of their width, it is believed that the structural
transformation from sp3
to sp2
is taking place within the wear debris and leads to the graphitization
process at a higher contact pressure. It was suggested that the high contact pressure is not just only
corresponding to the applied normal impact load, but it is also exerted by an oil lubricant during impact. A
high contact pressure can significantly reduce the graphitization temperature and substantially accelerate
the graphitization process. However, a significant phase transformation of the transfer layer on the
SCM420 pin does not intensely occur because it is mainly coming from the surface layer of the impacted aC coating, where the sp3
content increases and no wear debris is observed inside it. |
format |
Article |
author |
Abdollah, Mohd Fadzli bin |
author_facet |
Abdollah, Mohd Fadzli bin |
author_sort |
Abdollah, Mohd Fadzli bin |
title |
Phase transformation studies on the a-C coating under repetitive impacts |
title_short |
Phase transformation studies on the a-C coating under repetitive impacts |
title_full |
Phase transformation studies on the a-C coating under repetitive impacts |
title_fullStr |
Phase transformation studies on the a-C coating under repetitive impacts |
title_full_unstemmed |
Phase transformation studies on the a-C coating under repetitive impacts |
title_sort |
phase transformation studies on the a-c coating under repetitive impacts |
publisher |
Elsevier |
publishDate |
2010 |
url |
http://eprints.utem.edu.my/id/eprint/8107/1/surface.pdf http://eprints.utem.edu.my/id/eprint/8107/ http://www.journals.elsevier.com/surface-and-coatings-technology/ |
_version_ |
1665905358678261760 |
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13.160551 |