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Bonding Structure and Mechanical Properties of Ti‐B‐C Coatings
Author(s) -
Abad Manuel David,
Cáceres Daniel,
Pogozhev Yury S.,
Shtansky Dmitry V.,
SánchezLópez Juan Carlos
Publication year - 2009
Publication title -
plasma processes and polymers
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.644
H-Index - 74
eISSN - 1612-8869
pISSN - 1612-8850
DOI - 10.1002/ppap.200930403
Subject(s) - materials science , x ray photoelectron spectroscopy , nanocomposite , amorphous solid , microstructure , titanium , tribometer , amorphous carbon , carbon fibers , composite material , tribology , metallurgy , chemical engineering , crystallography , composite number , chemistry , engineering
Nanocomposite coatings combining hard phases (TiB 2 , TiC) with an amorphous carbon (a‐C) were developed to provide a good compromise between mechanical and tribological properties for M2 steels used in a wide variety of applications such as cutting tools, bearings and gear mechanisms. A combined d.c.‐pulsed and r.f.‐magnetron deposition process was used to deposit nanocomposite TiBC/a‐C coatings with a variable content of carbon matrix phase. Chemical composition was determined by electron energy loss spectroscopy (EELS) and X‐ray photoelectron spectroscopy (XPS). Transmission electron microscopy (TEM) revealed that the coatings microstructure is rather amorphous with small nanocrystals of TiC and/or TiB 2 (not possible to differentiate by diffraction techniques). Investigation of the chemical bonding environment by XPS and EELS allows us to confirm the presence of titanium‐boron and titanium‐carbon bonds together with free a‐C. Coatings exhibited hardness values ( H ) of 25–29 GPa, effective Young modulus ( E *) of 310–350 GPa, H / E * ratios over 0.080 and resistance to plastic deformation ( H 3 / E * 2 ) from 0.15 to 0.20. Tribological properties of the coatings were characterized by a pin‐on‐disk tribometer using steel and WC balls at high contact stresses (1.1 and 1.4 GPa respectively). Friction coefficients were reduced from 0.6 to 0.2 by increasing the content of free carbon without reduction of the hardness (around 28 GPa), by self‐lubricant effects. The tribo‐mechanical data are revised according to the phase composition and chemical bonding inside the nanocomposites.