Chemistry: electrical and wave energy – Processes and products – Electrophoresis or electro-osmosis processes and electrolyte...
Reexamination Certificate
1998-12-30
2001-07-10
Gorgos, Kathryn (Department: 1741)
Chemistry: electrical and wave energy
Processes and products
Electrophoresis or electro-osmosis processes and electrolyte...
C204S551000, C204S489000, C204S450000
Reexamination Certificate
active
06258237
ABSTRACT:
FIELD AND BACKGROUND OF THE INVENTION
The invention relates generally to the fabrication of a diamond coating or free standing products and, more particularly, to the fabrication of such coatings on the surface of various substrates, such as of milling cutters, bites (inserts), end mills and drills each having an excellent scale-off (or peeling-off) resistance, various abrasion (wear) resistant members such as valves and bearings, tool steels, as well as substrates acting as heat radiating substrates, such as heat sinks for electronic parts.
As is generally well known, applying a diamond coating to a substrate may be desirable to enhance the performance or to expand the applications of the original (uncoated) substrate.
As used herein, a diamond coating is a coating of carbon primarily in the SP
3
phase.
The unique properties of diamond and the possibility to apply a coating thereof on a substrate offer the potential to exploit these properties in a wide range of applications. The combination of the highest hardness and highest thermal conductivity makes diamond a most effective material for abrasive, cutting, shaping and finishing tools. Its high thermal conductivity, high electrical resistance and low thermal expansion make it a preferred choice for spreading and conducting heat out of high power electronic devices. The chemical stability in corrosive environments and high wear resistance make it possible to use diamond as a protective coating in adverse environments.
Synthetic diamonds are produced by high pressure, high temperature techniques since the 1950's. They are now used in cutting, grinding and polishing. However, the development of techniques to produce diamond films and coatings starting with chemical vapor deposition (CVD) in the early 1980's opened up a vast field of applications. The most relevant applications of diamond coating are in the field of working tools and wear resistant coatings. The high thermal conductivity of these films can decrease wear significantly by rapid heat transfer from hot spots caused by frictional heating. Yet, diamond films have small coefficients of friction particularly in low humidity environments. Examples of wear resistant applications of diamond films include machine tool guides, cutting blades, gears, seals, fuel injection nozzles for internal combustion engines, spindle bearings and shafts of milling machines and lathes, computer discs and turbine blades. Medical applications of diamond coatings include surgical knife edges, precision scalpels and surgical implants. Drilling and cutting tools are a vast potential area for diamond coatings on an cutting tool materials. Diamond coated inserts are used for machining non ferrous metals such as high silicon aluminum alloys, copper alloys green ceramics, composite materials including fiber glass and carbon/carbons. Diamond coated inserts can replace conventional inserts in most turning, milling and round tool applications.
Current processing technologies for thin and thick diamond films include chemical vapor deposition (CVD), such as plasma CVD (e.g., DC plasma, RF induction plasma and microwave plasma CVD); non plasma CVD (e.g., hot filament and laser enhanced CVD); and a hybrid process (vapor-liquid-solid (VLS) growth); and an interactive laser technique, also known as the QQC process. Some of these techniques are addressed hereinunder in greater detail.
The major problem areas in diamond coating in which improvement is still needed are lowering substrate temperatures; increasing growth rates; improved adhesion to a variety of substrate materials; control of thickness uniformity on irregular shapes. These problems are further addressed herein. The present invention is directed at providing a solution to all of these problems.
As already mentioned, one area of particular interest is the application of diamond coating to machine tools (e.g., to machine tool cutting inserts). Diamond is especially a tough (hard) material, wears well, and has thermal qualities which are beneficial in many applications. For many machining applications, the qualities of diamond are seemingly unsurpassed by any other available material.
Carbide has long been an established choice for use in cutting tools and inserts, especially for cutting (machining) ferrous, nonferrous or abrasive materials such as aluminum and its alloys, copper, brass, bronze, plastics, ceramics, titanium, fiber-reinforced composites and graphite. Various forms of carbide are known for tools and inserts, such as cobalt-consolidated tungsten carbide (WC/Co).
CVD Processes:
Fabricating diamond coatings utilizing chemical vapor deposition (CVD) processes are well-known. These CVD processes, however, suffer from various shortcomings, including (i) the requirement for a vacuum chamber in which to carry out the process; (ii) the requirement of performing the process in a gaseous environment (typically methane gas, or the like); (iii) “poisoning” of the coating when forming a diamond coating over a cobalt-containing substrate; (iv) the requirement to preheat the substrate; (v) the requirement of a pressurized environment; and (vi) relatively low rates of deposition.
Certain enhancements to the CVD process have been proposed, including the use of microwave plasma enhanced (MWPE) CVD process which takes place at relatively low temperatures and pressures, as compared with conventional PCD fabrication methods which utilize High Pressure and High Temperature (“HPHT”) techniques. Using these processes, any insert shape can reportedly be uniformly coated, and the coated inserts can have sharp edges and chip-breaker geometries. Hence, these inserts are indexable and can provide from two-to-four cutting corners.
CVD-coated tools tend to have a relatively thin diamond layer (typically less than 0.03 mm), which tends to allow the toughness of the underlying substrate material to dominate in determining overall tool strength, even when shock-loaded. Hence, these CVD inserts tend to be able to handle a larger depth of cut (DOC).
A critical concern with any coated tool or insert is that the coating should exhibit good adhesion to the underlying base material (e.g., carbide).
Concerns with the prior art include (i) delamination (catastrophic failure); (ii) adhesive and abrasive wear resistance (diamond is often used as a milestone for evaluating wear resistance); (iii) toughness (carbide is often used as a milestone for evaluating toughness); (iv) flank wear; (v) Built Up Edge (BUE) heat; and (vi) edge integrity.
The coating should also be compatible with the material contemplated to be machined. For example, polycrystalline diamond coatings tend to have a very low corrosion resistance to the resins in certain composite plastics.
Another area of concern with respect to diamond coatings on tools is that a very hard diamond coating on a softer tool is very prone to failure from stress.
An area of paramount concern is poor adhesion, which would appear to be a result from the reliance of prior art diamond coatings on the mechanism of molecular bonding, as well as from instabilities inherent in formation of the diamond coating.
An example of a CVD coating process is growing diamond by reacting hydrogen and a hydrocarbon gas, such as methane, in a plasma and synthesizing a diamond structure either as a coating or a free-standing blank. Carbide tools may be coated with a thin film of diamond using closed-chamber arc plasma CVD.
There are a number of basic CVD deposition processes currently in use, for depositing diamond coatings. Generally, these processes involve dissociation and ionization of hydrogen and methane precursor gases, which are then passed over and deposited onto a heated substrate.
The need to heat the substrate in order to apply the coatings is, in many ways, counterproductive. Such application of heat can cause distortion of the substrate, and the loss of any temper (heat treatment) that had previously been present in the substrate.
For example, in the hot filament CVD method, a tungsten or tantalum filament is used to heat the pr
Brandon David
Gal-Or Leah
Gilboa Shai
Goldner Rony
Layyous Albir A.
Cerd, Ltd.
Gorgos Kathryn
Maisano J.
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