Stock material or miscellaneous articles – Structurally defined web or sheet – Including components having same physical characteristic in...
Reexamination Certificate
1999-07-27
2001-05-08
Turner, Archene (Department: 1775)
Stock material or miscellaneous articles
Structurally defined web or sheet
Including components having same physical characteristic in...
C427S249300, C427S255120, C427S255290, C427S255360, C427S402000, C427S419100, C427S419200, C427S569000, C427S574000, C427S577000, C427S578000, C428S212000, C428S336000, C428S408000, C428S446000, C428S697000, C428S699000, C428S701000, C428S702000
Reexamination Certificate
active
06228471
ABSTRACT:
FIELD AND BACKGROUND OF THE INVENTION
The invention relates to rigid or flexible substrates covered with a thin coating of diamond-like material which thereby render the substrate surfaces i.a. very hard, corrosion and wear resistant and self-lubricating at the same time. The invention relates also to certain vacuum processes for coating the substrates.
It is generally known to coat substrates with films of diamond-like carbon. Diamond-Like Carbon (DLC) films are amorphous hydrogenated carbon films (a-C:H) that display high hardness and high elasticity combined with good corrosion protection, chemical inertness and a smooth surface. These properties make these films feasible for industrial applications such as hard, wear resistant, self lubricating and corrosion resistant coatings.
However, DLC films show several drawbacks that impede their successful commercial introduction. The most important practical problem is the difficult adhesion to several substrates, particularly steel substrates. This difficulty is caused by the high compressive residual stresses, up to several GPa, present in the material. Other disadvantages are the low thermal stability. limiting the working temperature to about 300° C., the low transmission for visible light and the increase of the coefficient of friction with increasing air humidity. Doping DLC with both metals (Ti, Zr, W, Nb, Ta) and non-metallic elements (Si, F, O, B, N) favourably influences many properties but generally lowers the hardness. Likewise, the interposition of Si, SiO or metal (Al, Ti) between the substrate and a DLC-layer, although improving its adhesion to the substrate, provides only for a soft interface.
It is also known from U.S. Pat. No. 5,352,493 to coat substrates with certain diamond-like nanocomposite compositions (DLN). Diamond-Like Nanocomposite coatings consist of an amorphous structure, comprising generally two interpenetrating networks a-C:H and a-Si:O: DLN, or Dylyn™. DLN exhibits several attractive properties when compared with Diamond-Like Carbon (a-C:H, DLC). Besides the higher temperature stability, the retaining of mechanical properties upon doping with metals and the low internal stress facilitating adhesion. the very low coefficient of friction (<0.1). often even in humid air and under water, is of prime importance for many industrial tribological applications.
However, with the present state-of-the-art deposition technology for DLN using a liquid polyphenylmethylsiloxane precursor, the hardness of the DLN coatings, as measured by depth-sensing indentation. varies generally between 12 GPa and 17 GPa. For several applications. such as abrasive applications, situations of impact erosion or severe tribological applications. this hardness value may be insufficient. In those cases. a hardness of 20 to 25 GPa may be desirable.
OBJECTS AND SUMMARY OF THE INVENTION
There is presently a high demand in the market for substrate coatings which can largely retain the favourable intrinsic properties of DLC-layers throughout the entire coating thickness and thereby avoid its drawbacks, in particular its bad adhesion to the substrates and its sensibility to compressive stresses. It is a first object of the invention to provide such improved coatings.
It is a second object of the invention to provide such coatings which have low stresses throughout their entire thickness, also for substantially thick coatings. It is a third object of the invention to provide such coatings with improved tribological properties, in particular under humid conditions. It is a further object to produce such coatings with controlled wettability or non-sticking properties (low surface energy). In this manner they can become a substitute for teflon which is very soft. or they can be used as a hard release coating in molds. It is another object to produce such coatings with controlled transparency and/or heat or electrical conductivity.
It is also an object to design and produce such coatings—in particular relatively thick coatings—in a flexible manner compared to the conventional vacuum deposition processes for DLC- or modified DLC-coatings.
According to the invention the substrate is covered, at least in part, with a multilayer coating comprising a number of layered structures each such structure comprising
a first diamond like nanocomposite composition layer closest to the substrate, which composition comprises interpenetrating networks of a-C:H and a-Si:O,
a second diamond like carbon composition layer on top of said first layer, and
a transition layer between said first and second layer comprising a mixture of said diamond like nanocomposite and said diamond like carbon compositions. When the number of said layered structures is greater than one, then the coating includes an intermediate layer comprising a mixture of said diamond like carbon and diamond like nanocomposite compositions sandwiched between each pair of such consecutive layered structures.
The building up in this manner of a stack of very thin slices of DLC alternated with DLN allows indeed to deposit thicker coatings which display low stress and which thereby resist better abrasion and wear forces.
According to the invention said first layer can have a thickness of more than 0.10 and up to 3 &mgr;m. Said second layer is thinner than said first layer and has preferably a thickness of between 0.1 and 2 &mgr;m whereas said transition layer has preferably a thickness of between 0.1 and 1 &mgr;m.
Another top layer can be added which comprises a specific diamond like nanocomposite composition at its outer surface in view of controlling in addition the wettability or non-sticking properties of the top surface of said coating.
To improve further the tribological properties of the coating, the nanocomposite compositions will preferably comprise in proportion to their sum of C-, Si- and O-content in at %, 40 to 90% C. 5 to 40% Si and 5 to 25% O. To influence its conductivity, the coating can further be doped with a transition metal (of the Group IV to VII) in at least one of said first, second, transition or intermediate layers. In particular W. Zr and Ti are well suited. Any of said layers can further contain 0.5 to 5 at%, of an inert gas such as N. Ar or Kr.
A flexible process for manufacturing the covered substrate according to the invention comprises the steps of
a) depositing in a vacuum chamber said first layer starting from a continuously introduced fluid organic precursor containing the elements C, H, Si and O to be deposited in a suitable proportion, forming continuously a plasma from said precursor and depositing said composition from the plasma on the substrate to which a negative bias voltage is applied;
b) gradually exchanging said precursor by a hydrocarbon, forming continuously a plasma from the mixture of the precursor and the hydrocarbon and depositing a transition layer from said mixture in plasma form on the negatively charged substrate covered meanwhile with the diamond like nanocomposite composition whereby said mixture composition gradually changes from a diamond like nano-composite composition to a diamond like carbon composition;
c) continuing the plasma deposition of the diamond like carbon composition layer from said hydrocarbon and, when more than one layered structure has to be deposited, then per deposition of another such layered structure;
d) firstly gradually exchanging said hydrocarbon from step c by a suitable organic precursor, forming continuously a plasma from the mixture of the hydrocarbon and said precursor and depositing an intermediate layer from said mixture in plasma form on the negatively charged substrate covered meanwhile with the previous structure whereby said mixture composition gradually changes from a diamond like carbon composition to a diamond like nanocomposite composition and
e) secondly repeating te steps a to c.
This process is quite easy to monitor since changes in only two material flows (precursor and hydrocarbon) have to be kept under control. After all, instead of using Si or a metal bridge layer between a DLC-layer and the s
Neerinck Dominique
Persoone Peter
Foley & Lardner
N.V. Bekaert S.A.
Turner Archene
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