Solid-Lubricant Coatings (SLC)
Traditional SLC of metallic type are Cu, Ag, In using in the industry
(turbo-machinery, ball-bearing, etc.). Their application is limited due
to their physic- chemical properties: low plasticity, low service
temperature, high oxidizability.
The
utilization of a new category of SLC made of Metal-Carbon (Me-C)
composites is of good prospects. This category includes:
a)
"SOFT" SLC: both components
serve as lubricant; this is the case when a metal: (i) does not interact
with C at all or (ii) interacts weakly at the level of founding
metastable compounds. This type of SLC covers the following pairs: Cu-C,
Ag-C, Ni-C, Co-C.
b)
"HARD" SLC: there are two
phases: (i) soft – Me-C and (ii) hard – Carbide forming a rigid
carcass/frame. This type of SLC covers the following pairs: W-C, Ta-C,
Mo-C, Nb-C, Cr-C, Hf-C, Ti-C, Zr-C, V-C.
The
rise of Me content increases wear-resistance; such composites can be
successfully applied to strengthen metal-cutting tools. The introduction
of nitrogen or oxygen in the process of depositing the above composites
leads to the growth the percentage of hard phase due to forming Nitrides
or Oxides which, finally, compound Carbonitride-C or Oxycarbide-C that
is rigid carcass + atomic C (non-reacted) as lubricant. This is an ideal
barrier structure which effectively prevents from adhering chips to the
cutting edge of tool which reducing the wear of the cutting edge.
Additionally, the wear-resistance of the tool grows due to forming the
coating with submicrostructure of amorphous type.
The
following applications are recommended: (i) antifriction & plain
bearings, in particular high speed; (ii) cutting tools for stainless
steels and high-alloyed compounds; (iii) the parts of internal
combustion engines; (iv) turbine blades, etc.
The
coatings of Tà2Ñ
, ÒàÑN, NbCN, Ñr3C2,
Mo2C,Ti C, ZrC – are of high service life in the sea water;
high thermo-oxidative resistance shows the coating of 97,3% Ñr3C2
& 0,6%C; Cr-C coatings displays high chemical resistance to HCl,HNO3,
ÍÑlÎ4
during the heating.
