Floor covering with inorganic wear layer — Armstrong World Industries, Inc.

Floor covering with inorganic wear layer - Armstrong World Industries, Inc.

Eli Yablonovitch et al. Appl. Phys. Letter, 51(26), Dec. 28, 1987, pp. 2222-2224, Article Entitled «Extreme Selectivity in the Lift-Off of Epitaxial GaAs Films».

L. A. Clevenger et al. Appl. Phys. Letter, 52(10), Mar. 7, 1988, pp. 795-797, Article Entitled «Reaction Kinetics of Nickel/Silicon Multilayer Films».

Ryszard Lamber, Journal of Materials Science Letters 5 (1986), pp. 177-178, Article Entitled «Thin Boehmite Films: Preparation and Structure».

J. C. Huling et al. J. Am. Ceram. Soc. 71[4] C-222-C-224 (1988), Article Entitled «A Method for Preparation of Unsupported Sol-Gel Thin Films».

Trade Literature Entitled, «Interior/Wall Facings From AllianceWall», AllianceWall, Norcross, GA 30092.

Trade Literature Entitled, «Armor-Stat Dissipative Floor Tile», 1988, Trio-Tech International Static Systems, San Fernando, CA 91340.

Primary Examiner:

Ryan, Patrick J.

Claims:

We claim:

1. A floor covering comprising a support and a wear layer deposited on said support by a reduced pressure environment technique selected from the group consisting of sputtering, plasma polymerization, physical vapor deposition, chemical vapor deposition, ion plating and ion implantation, wherein the wear layer comprises a hard inorganic material.

2. A floor covering comprising a support and a wear layer deposited on said support by a reduced pressure environment technique, wherein the support comprises a metal component selected from the group consisting of a foil, a film and a sheet.

3. The floor covering of claim 2, wherein the metal component has a thickness of between 0.007 inches and 0.5 mils.

4. The floor covering of claim 2, wherein the metal component is a steel.

5. The floor covering of claim 2, wherein the support further comprises a decorative layer overlying the metal component.

6. The floor covering of claim 1, wherein the support further comprises a conformable layer capable of inelastic deflection.

7. The floor covering of claim 1, wherein the support comprises plastic, rubber or a mineral/binder system.

8. The floor covering of claim 7, further comprising an ink which diffuses into the support.

9. The floor covering of claim 7, wherein the plastic is a thermoset plastic.

10. The floor covering of claim 1, wherein the wear layer is discontinuous.

11. The floor covering of claim 1, wherein the wear layer is at least 1 micron in thickness.

12. A floor covering comprising a support and a wear layer deposited on said support by a reduced pressure environment technique, wherein the wear layer comprises a hard inorganic material selected from the group consisting of metal oxides and metal nitrides.

13. The floor covering of claim 12, wherein the hard inorganic material is selected from the group consisting of aluminum oxide, silicon oxide, aluminum nitride, silicon nitride and titanium nitride.

14. The floor covering of claim 1, wherein the support is mounted to a base layer, said base layer being capable of conforming to the irregularities of a wood subfloor and capable of accommodating lateral movement of a wood subfloor, the support being mounted whereby the periphery of said base layer is exposed.

15. A floor covering comprising a metal support layer and a wear layer consisting of hard inorganic material.

16. The floor covering of claim 15, wherein the support layer is capable of inelastic deflection.

17. The floor covering of claim 15, wherein the floor covering is capable of supporting a uniform 125 lbs/sq. ft. load with a deflection of not more than one-five hardness of the span.

18. The floor covering of claim 15, wherein the hard inorganic material is a fused ceramic.

19. A method of making a floor covering comprising

(a) providing a floor covering support, and

(b) depositing a wear layer of at least 1 micron in thickness on the support by a reduced pressure environment technique selected from the group consisting of sputtering, plasma polymerization, physical vapor deposition, chemical vapor deposition, ion plating and ion implantation.

20. The method of claim 19, wherein the wear layer comprises a hard inorganic material selected from the group consisting of metal oxides and metal nitrides.

21. The method of claim 19, wherein the wear layer is deposited on the support at a deposition temperature of no greater than 170° C.

22. The method of claim 21, wherein the wear layer is deposited on the support at a deposition temperature of no greater than 150° C.

23. The method of claim 21, wherein the wear layer is deposited in a thickness of at least 3 microns.

Description:

BACKGROUND OF THE INVENTION

The invention relates to a floor covering. More particularly, the invention relates to a floor covering having an inorganic wear layer which preferably has been deposited on a support structure by a low pressure environment deposition technique. Further, the invention is directed to a multilayered floor covering in which each layer contributes to the wear performance and installation characteristics and affects the performance of the other layers.

Floor coverings having wear layers are well known in the art. Such wear layers protect the decorative layer of the floor coverings and lengthen the useful life of the floor covering. With the exception of ceramic tile which are rigid and must typically be installed on a mortar bed and metal floors such as steel plates, neither of which have a wear layer per se, inorganic material is not used as the wear surface of floor coverings. Inorganic materials are typically considered too brittle to be walked on; particularly if a «thin» layer were to be placed over a flexible or conformable support layer. Further, low pressure environment deposition techniques have not been applied to the manufacture of floor coverings.

Reduced pressure environment techniques for depositing films of hard inorganic materials include sputtering, plasma polymerization, physical vapor deposition, chemical vapor deposition, ion plating and ion implantation. Hard inorganic materials which can be prepared using these techniques include metals, metal oxides, metal nitrides and mixtures thereof; such as aluminum oxide, silicon oxide, tin and/or indium oxide, titanium dioxide, zirconium dioxide, tantalum oxide, chromium oxide, tungsten oxide, molybdenum oxide, aluminum nitride, boron nitride, silicon nitride, titanium nitride, and zirconium nitride, as well as metal halides, metal pnictides and metal chalogenides.

Often the partial pressures of key gases in the deposition environment are controlled to effect chemical reactions between depositing metal species. Therefore, a film formed on a substrate by reactive sputtering or reactive deposition can be a compound derived from a metal and a controlling gas, i.e. aluminum oxide produced by sputtering aluminum in oxygen. Sometimes the controlling gases are used to sustain a plasma in the deposition environment. Ion assisted deposition is a technique in which the controlled gas is ionized and is used to bombard the deposition surface to modify the morphology and physical properties of the resulting film.

A critical review of vapor deposition technology related to hard coatings was presented by J. E. Sundgren and H. T. C. Hentzell in J. Vac. Sci. Tech. A4(5), September/October 1987, 2259-2279. A more complete review of techniques involved in formation of thin films in reduced pressure environments is the book edited by J. L. Vossen and W. Kern, Thin Film Processes, Academic, New York, 1978.

Recent articles on thin film preparation include Yabinouitch, E. Gmitter, J. P. Haubison, J. P. and Bhat, R. Appl. Phys. Letter, 51(26), Dec. 28, 1987, 2222-2224 on etching Al/As to form free standing GaAlAs films; Clevenger, L. A. Thompson, C. V. and Cammarata, R. C. Appl. Phys. Letter, 52(10), Mar. 7, 1988, 795-797 on using commercial photoresists as supports; Ryszard Lamber, Thin Boehmite Films: Preparation and Structure; Journal of Materials Science Letters, 5(1986), 177-178; and Huling and Messing, J. Am. Ceram. Soc. 71(4), 1988, C222-C224, on coating on camphor and subliming to obtain free standing mullite.

Patents dealing with thin film deposition include: U.S. Pat. No. 4,604,181 and 4,702,963.

Reduced pressure environment techniques have been used to coat plastics materials such as plastic bags to improve gas impermeability. However, such coatings have been limited to about 0.5 microns in thickness.

While reduced pressure environment techniques have been used to form hard coatings on surfaces such as automobile parts, there has been no suggestion that such coatings could be successfully used as wear surfaces for floor coverings. In fact, such coatings tend to be brittle when applied in a substantial thickness. Thus, one skilled in the flooring art would not expect reduced pressure environment deposited materials to function adequately as a floor covering, particularly in the thickness deemed necessary to protect the decorative layer of a floor covering.

Alliance Wall manufactures and sells wall coverings in which porcelain enamel is fused to a steel sheet. However, use of a material as a wall covering does not suggest that it would be acceptable as a floor covering. Again, one skilled in the flooring art would not expect a thin sheet of ceramic to withstand the long term abuse to which flooring is subjected, particularly when laid over a resilient support structure and walked on by a woman in high heels.

SUMMARY OF THE INVENTION

An object of the invention is to provide a floor covering that has the appearance retention of ceramic tile (including stain resistance and gloss retention), and resists cracking and brittle failure.

A further object is to provide a floor covering having an inorganic wear layer which is flexible enough to be rolled around a reasonably sized mandrel and therefore can be installed in a manner similar to present resilient floor coverings.

Another object is to provide a floor covering laminate having the above listed features and which is conformable to the subfloor on which it is laid.

Such a floor covering has been made by depositing a wear layer of a hard inorganic material on a support by a reduced pressure environment technique. The preferred reduced pressure environment technique is ion assisted physical vapor deposition; and the preferred support is multilayered.

The preferred hard inorganic material is a metal oxide or metal nitride, most preferably aluminum oxide, silicon oxide and silicon nitride. Aluminum oxide, silicon oxide and silicon nitride form films which are colorless, clear and of hardness similar to the dirt to which the floor covering is normally subjected.

Preferred supports include a metal component such as a foil, a film or a sheet. The metal support may be from 0.001″ to 0.25″ thick, preferably 0.003″ to 0.1″ thick. The preferred support is a stainless steel sheet of at least 0.007 inches in thickness. Although a low carbon steel may be used its performance is poorer. Preferably, the support includes a decorative layer of fused glass or ceramic frit overlying the metal component.

Since the glass or ceramic is a metal oxide which can be deposited by a reduced pressure environment technique, the wear layer can be formed from a glass or ceramic material. That is, the decorative layer can be the wear layer.

Depositing a hard inorganic material on surface of a plastic, rubber or mineral/binder system support substrate improves the wear resistance and falls within the scope of the present invention. The plastic may be either a thermoset or thermoplastic. The preferred thermoplastic is polyethylene terephthalate. The preferred thermoset plastic is a crosslinked reinforced polyester such as polyester sheet molding compound sold by Premix, Inc. The thickness of the support should be between 0.0005″ and 0.25″.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a first embodiment of the present invention.

FIG. 2 is a perspective view of a second embodiment of the present invention.

FIG. 3 is a perspective view of a third embodiment of the present invention.

FIG. 4 is a cross-sectional view taken along line 4—4 in FIG. 3.

FIG. 5 is a cross-sectional view of a fourth embodiment of the present invention.

FIG. 6 is a schematic representation of test setup to measure rupture strain.

DETAILED DESCRIPTION OF THE INVENTION

Broadly, the invention is a floor covering having a hard inorganic material wear layer and a support including metal or plastic. While the preferred floor covering is a flexible laminate which has been deposited on a support by a reduced pressure environment technique and which permits installation similar to conventional resilient flooring, including resilient tiles; the invention is intended to include rigid floor coverings having a wear layer of reduced pressure environment deposited hard inorganic material, and conformable floor coverings having a glass or ceramic material applied to a metal support by means other than a reduced pressure environment technique.

Metals and hard inorganic materials such as ceramics have unique properties. Properly selected ceramics are hard enough to resist being scratched by the grit particles in dirt. Properly selected metals should be hard enough to support the ceramic and yet be flexible. Such a laminate can be made in an atomistic deposition chamber by depositing on a thin, properly tempered steel. This laminate could then be mounted on an organic-polymer support layer to form a flooring structure. The support layer conforms to the subfloor irregularities and accommodates lateral movement of the subflooring structure. Although vacuum techniques could be used in making such a flooring structure, current technology would enable it to be made on a continuous, air-to-air production line.

No organic surface, either currently in existence or envisioned, possesses sufficient resistance to loss of gloss and to other physical damage to fully meet desired performance. Thick (1/4inch), hard ceramic tiles (Mohs hardness of at least 7 and preferably 8.5) resist loss of gloss and other physical damage extremely well.

The Mohs hardness of grit particles in dirt probably ranges between 6 (silicates) and 7 (silica). A rule of thumb among tribologists is that if a surface is 1.5 Mohs units harder than a grit particle, the surface will not be scratched by the grit particle. This applies when the grit particle is between two surfaces of equal hardness. In a flooring situation, the grit particle is usually between the relatively soft bottom surface of a shoe and the floor surface. Therefore, the maximum downward force on the grit particle is the resistance the bottom of the shoe offers to penetration by the grit particle. The softer the bottom of the shoe, the less downward force exerted on the particle. Consequently, the difference in hardness between the grit particle and the flooring surface may not need to be quite as large as 1.5 Mohs units. In any case, a Mohs hardness of 8.5 is a reasonable goal for the ceramic film. However, wear layer of Mohs hardness of about 5 or 7 have been shown to retain gloss level despite larger scratches. Prior art organic wear layers have a Mohs hardness of less than 3. Therefore a Mohs hardness of 3 or greater will yield an improvement.

If formed by atomistic deposition, the ceramic-film wearlayer envisioned for the laminate structure would be expected to be essentially stain proof and to retain its gloss extremely well. The film would be expected to be essentially stain proof because such films provide excellent corrosion resistance for the substrates on which they are deposited. The film retains its gloss and resists damage from grit particles because it can be made sufficiently hard, approaching the hardness of the grit particles in dirt, and may be supported on a support having proper stiffness.

Although ceramic film has both stain resistance and gloss retention, its brittleness has prevented it from being used as a wear layer in a resilient floor covering. Brittleness makes the ceramic film susceptible to serious damage. However, by combining the ceramic film with a support such as a sheet of metal or plastic with the proper characteristics, a ceramic film may be used. If the support is sufficiently strong to give the floor covering the ability to support a uniform 125 lbs/sq ft load with a deflection of not more than one-five hundredths of the span, the floor covering may be free standing. The ceramic tile does not have the ability to perform when supported in a free standing manner. Laminate must have the necessary physical properties as discussed below.

In order to understand why such a laminate should solve the problem of brittle damage, it is useful to divide the types of forces causing damage into two categories: (1) localized pressure and (2) impact.

Localized pressure occurs when a grit particle is pressed downward against the ceramic surface. If the particle can force the ceramic film down into the support layer on which it has been deposited, the ceramic film is put into tension and fails. Ceramics, although strong in compression, are weak in tension. To avoid such failure in tension, the support layer must resist being indented when the grit particle is pressed against the ceramic film. Actually, all the ceramic film does in protecting the support layer from indentation is to spread the force over a greater area before that force reaches the support layer. Hardened steel appears to combine the desired hardness (up to a Mohs of almost 7) and flexibility. Although lacking the hardness of steel, some organic polymers, particularly engineering polyesters, have provided adequate support.

A ceramic/metallic laminate also possess the properties needed to resist impact. Impact occurs when a heavy object strikes the floor. Damage is most likely to occur when the pressure (that is force per unit area) is large enough to cause an indentation. Here the tensile strength of the steel should resist putting the ceramic in tension.

An additional property that the support layer should possess is the ability to produce a gradual contour rather than an abrupt contour, both when a grit particle exerts a force on it through the ceramic film and when it is subjected to impact. Calculations nave shown that for a given vertical displacement, a gradual contour subjects the ceramic film to less tension than does the abrupt contour. In order to produce a gradual contour, the support layer should be flexible but not limp. Two materials that possess the desired properties are properly tempered spring steel and polyester based sheet molding compounds.

The ceramic film should have hardness at least of about 6 Mohs and good strength. To possess these attributes, the ceramic must have the proper microstructure. In films formed by atomistic deposition, desirable microstructure can be attained by increasing the temperature and the bombardment energy. One of the advantages of using a steel support layer is that a high enough temperature can be used to get optimum microstructure.

The ceramic film should be applied so that it is under compression. This can be accomplished by depositing the metal-atom portion of the ceramic first and then adding the other element later, either in the same step or in a second step. Using a two-step process allows better control for deposition of the nonmetallic atoms.

The ceramic/metallic laminate is preferably adhered to a conformable support layer. This support layer must be hard enough to support the ceramic/ metallic laminate but must also be able to conform to any irregularities in the subfloor. To perform in a superior manner, the conformable support layer should be capable of inelastic deflection, i.e. capable of permanent deflection with or without residual forces such as applied by adhesives.

In addition, if used in resilient sheet goods it must accommodate some lateral movement of the subfloor. To be able to perform over all subfloors including particleboard, the floor covering should have a rupture strain in excess of 0.3%. Due to seasonal changes including temperature and humidity, particleboard subfloors expand and contract about 0.3% during the year. Plywood expands and contracts about 0.15%. Therefore, to perform adequately over a wooden subfloor, the floor covering including the wear layer should have a critical buckle strain of at least 0.1% and preferably at least 0.3%. Floor coverings of the present invention having plastic support structures meet this requirement.

The support layer preferably is typically made from an organic polymer. It is desirable to select the polymer so that its viscoelastic character will allow it to conform to the floor and still enable it to resist indentation by a rapid impact.

Surface contours can readily be incorporated by embossing the metallic substrate layer before application of the ceramic film. Incorporation of a pattern could be done most readily by printing the pattern on the metallic substrate before deposition of the ceramic film. Some of the ceramic films that can be deposited atomistically are colored, and they may be applied in patterns by use of stencils.

Although the focus of this invention is on atomistically deposited ceramics, the concept of a thin flexible metallic substrate layer could be used with other types of ceramics. Colored ceramic glazes or inks used in conventional ceramic technology could be applied in a pattern on the metallic substrate layer to form a wearlayer in place of the atomistically deposited ceramic film.

The basic concept is combining thin, hard wear surfaces with decorative, support structures to produce unique wear-resistant flexible flooring products. The flooring products have the appearance retention approximating that of ceramic tile but are light weight and easier to install.

A series of inorganic oxides and nitrides (including aluminum oxide and silicon oxide) has been used as the thin, hard inorganic wear layer. The variety of materials used for the support layers include combinations of metals, plastics, rubber and mineral/binder systems. The means of decoration include glass frits, holograms, sublimable dyes and pigmented inks. The plastics, rubber and mineral/binder systems may be through color. Outstanding performance has been demonstrated in an embodiment consisting of three microns aluminum oxide over ten microns glass decorative layer on seven mils tempered steel shim stock bonded either to a filled vinyl tile or a layer of rubber, and also in an embodiment consisting of three microns of aluminum oxide over a sublimable ink decorated polyester sheet molding compound (PSMC). Aluminum oxide coated PSMC resists scratches better than any organic or organic/inorganic coating tested.

Since each layer of the floor covering laminate affects performance, a layer of rotogravure ink will change the appearance retention of a wear layer on a plastic support. Therefore, inks, such as sublimable inks, which will diffuse into the support layer are preferred.

The advantages of the flooring products of the present invention include an appearance retention in traffic environments in a product which can be light in weight, which can be either rigid or conformable, which can be thinner than products currently in the market place, which can be flexible, which can be more resilient than ceramic tile, and which can be installed with conventional resilient-flooring tools.

One preferred embodiment of the floor covering 1 is shown in FIG. 1. The support 2 is a metal, plastic, rubber or mineral/binder system. A wear layer 3 of hard inorganic material is deposited on the support by a reduced pressure environment technique. A decorative layer 4 is deposed between the support layer and the wear layer. The preferred metal is stainless steel. While such metals as ferroplate, brass/ferroplate, steel/ferroplate, chromium-plated brass and 01 steel have been used, any flexible but stiff support can be used.

The preferred thickness of the support is from about three to about nine mil, most preferably about five to about seven mil. Two and four micron alumina wear layers on three, five and seven mil tempered shim steel did not crack even when the resulting laminate was supported by a deformable rubber of Shore hardness 70 and walked on by women in high heels. The three-mil substrate could be pierced by high heels.

The preferred Young’s modulus is about 3×10 7 lbs./inch 2. A modulus of this value or less ensures that the laminate is sufficiently flexible to bend around a 2-inch mandrel without the wear layer cracking, even when the wear layer is on the convex side. Preferably, the floor covering is sufficiently flexible to bend around a 20-inch mandrel without cracking.

The support substrate may also be a decorated or undecorated plastic, rubber or mineral/binder system provided the support layer is sufficiently rigid. The support layers tested include a polyester sheet molding compound (PSMC), rigid polyvinylchloride (PVC) on a tile base, polyethersulfone on a glass base, glass fiber reinforced polyester, fiber filled phenolic, polyetheretherketone with and without a glass base, polyimide on a glass base, polymethylmethacrylate, a photographic polyester on a glass base, Teflon, and PVC on PSMC. A preferred polyester support substrate material is PSMC or polyethylene terephthalate. A fiber filled polyester is more stable and yields fewer cracks.

The thickness of the wear layer must be at least one micron. Preferably the thickness of the wear layer is at least about three microns. Thickness of less than three microns tend to fail more frequently.

Hardness of the wear layer equal to and preferably greater than that of silica also is desirable. Preferably the hardness is at least 6 Mohs, and more preferably 8.5 Mohs.

The invention includes wear layers of metal, metal oxides and metal nitrides. The preferred compositions include Al2 O3. SiOx. AlN, Si3 N4 and TiN. Flooring structures with five to eight microns of Al2 O3 and SiOx supported on an undercoated, reinforced polyester substrate had gloss retention superior to currently marketed wear layer materials. Although individually visible scratches were apparent, the scratches did not affect gloss retention. The scratches can be eliminated or at least minimized by obtaining a good match between the mechanical properties of the substrate and the wear layer. Gloss retention and overall appearance retention is increased by increasing wear layer hardness and substrate hardness. Therefore, Si3 N4 may be a superior wear layer to Al2 O3 .

The decorative layer 4 is a glass or ceramic frit, or pigment. The use of printable inks enables the creation of intricate designs. However, since the wear layer materials may be colored, the wear layer and decorative layer may be combined and a multi-colored wear layer can be deposited with a low pressure environment technique with the use of stencils.

The structure of the FIG. 1 embodiment is acceptable for a resilient flooring structure which is rolled for storage and transport to the installation site, provided the laminate is sufficiently flexible. However, if the flooring structure is a 12×12 inch tile having a rigid support structure, the tile may not be capable of conforming to the irregularities of a wood subfloor and therefore may require installation procedures similar to ceramic or marble.

To overcome this disadvantage the laminate may be bonded to a resilient or conformable layer 5 as shown in FIG. 2. The conformable layer 5 has dimensions slightly greater than the laminate. This allows for the difference in thermal expansion between the subfloor and the laminate. The conformable layer is capable of inelastic deflection under gravitational forces so that over a reasonable length of time, the lower surfaces of the laminate contacts the subfloor over substantially the entire surface area. The conformable layer is capable of conforming to the contour of the subfloor, including a 1/16″ ledge between two plywood sheets forming the subfloor.

The sharp corners of the FIG. 2 embodiment may cause problems since the tiles cannot be laid in a perfectly flat plane. Therefore, the corners tend to snag the soles of shoes. To avoid this problem, the tile may be formed as shown in FIGS. 3 and 4. The laminate of support structure 2, decorative layer 4 and wear layer 3 is formed. Then the laminate is press molded into a cup-shape and bonded to the resilient support base 6. The sides 7 of the laminate are substantially perpendicular to the plane of the conformable layer and are adjacent the sides of the conformable layer.

In another embodiment shown in FIG. 5, the conformable layer 8 has alignment marks 9 on the upper exposed surface. The tiles 1 are bonded to the conformable layer in alignment with the marks to give a pleasing decorative appearance and a discontinuous wear surface. The discontinuities improve flexibility of the floor covering and may extend down to a micron scale.

The following examples, while not intended to be exhaustive, illustrate the practice of the invention. Procedure for the Preparation of Vapor Deposited Coatings Coating Materials. Metals and metal oxides were obtained in 99.9% nominal purity from standard industrial sources. Water was removed from gases using molecular sieve traps. Al2 O3 (99.99%) and SiO2 (99.99%) were obtained from E. M. Industries; ZrO2 (99.7%) and Ta2 O5 (99.8%) was obtained from Cerac, Inc.; TiO2 (99.9%), was obtained from Pure Tech, Inc.

Apparatus.

The deposition system (Denton DV-SJ/26) included a 66 cm wide high vacuum bell-jar assembly; a high speed pumping system (CTI Cryogenics CT-10 cryopump and Alcatel ZT 2033 mechanical pump); an electron-beam vaporization source (Temescal STIH-270-2MB four-hearth «Supersource», with an 8 kWatt Temescal CV-8 high-voltage controller and e-beam power supply and Temescal XYS-8 sweep control); a resistively heated vaporization source (Denton Vacuum, 4 kWatt); a cold cathode ionization source (Denton Vacuum model CC101 with both CC101BPS and CC101PS biased and unbiased power supplies); a residual gas analyzer (Inficon Quadrex 200); a quartz crystal type deposition rate controller (Inficon IC6000); four eight inch circular deposition targets affixed to a planetary rotation sub-system; and a 10″ diameter stainless steel aperture for focusing the e-beam (or thermally) evaporated material and the ion plasma on the same deposition surface. The various power supplies, pressure and gas flow monitors were operated either automatically using Denton’s customized process control system, or manually. Typically, a deposition run began with an automated pump-down process, was followed by a deposition process controlled by the IC6000 and ended with an automated venting cycle.

Deposition Process.

The following general procedure was followed for all deposition runs. Following evacuation to ≤1.0×10 -5 Torr the temperature of the chamber, as measured by a centered thermocouple at planet level, was adjusted to the desired deposition temperature and the planetary rotation was started. Next, Ar gas was admitted to increase the chamber pressure to about 1×10 -4 Torr, and a plasma 300-600 mAmps/300-600 Volts was initiated at the cold cathode source (current density between 95 and 500 u-amps//cm 2 ) which was used to sputter-clean the substrates, in situ, for five minutes. The deposition process was thereafter controlled by an IC6000 process which typically included parameters such as heating rates and times, material densities, desired deposition rates and thicknesses, and the number of layers desired. Prior to deposition, the substrates were shielded from the metal, or metal oxide source. Ion bombardment with an ion plasma began and the shields were removed simultaneously when the IC6000 signaled that the metal or metal oxide had been heated to the temperature appropriate for vaporization. A quartz crystal microbalance provided input for the IC6000 feedback loop system which provided deposition rate control for the remainder of the process. After deposition of a specified thickness, the ion source was turned off, the shields replaced, and the vapor sources allowed to cool.

Rupture Strain Test for Thin Ceramic Coatings

One surprising feature of the present invention is the rupture strain of the thin hard inorganic coatings of the present invention. Obtaining the rupture strain of a thin, hard inorganic film or coating such as a ceramic is a difficult task as the coating is not thick enough to be self-supporting to be tested with conventional apparatus. Among the properties of yield stress, yield strain, modulus of elasticity, rupture or ultimate strain and Poisson’s ratio, the yield strain is of most importance as the wear layer will undergo strain as determined by the underlying load support structure. To create a support structure, it is necessary to determine how much strain can be tolerated by the wear layer and then make design adjustments of the support parameters so that this strain will not be attained in service.

Ceramics are brittle and characteristically, the yield strain is close to, and in a practical sense, is equal to the ultimate or rupture strain. A ductile region does not exist between yield and rupture. This condition makes the test more definitive as rupture is more readily detected than yield, i.e. a crack is observed at the ultimate strain or rupture.

An evaluative test for measuring the ultimate strain to brittle fracture in a thin ceramic film was developed. The test is parasitic in that it relies on a host to produce the elongation strain in the ceramic coating. A thin, highly tempered steel strip is coated with a very much thinner coating of the wear layer (ratio of thicknesses of 250 to 1). The steel strip is bent in a cantilever fashion and being so thick compared to the coating, its bending performance is not affected by the presence of the coating. By measuring the deflection of the cantilever, the surface strain of the bent steel can be calculated by elastic mechanics equations. The coating will experience the same elongation strain as the surface of the steel. The beam is progressively deflected increasing the surface strain of the steel. When the rupture strain of the coating is attained, the coating ruptures by cracking which is visually evident. Measurement of the deflection of the beam and the position along the beam where the crack occurred are sufficient data to calculate the strain when the crack occurred.

The credibility of the test is dependent upon the following items: (1) the coating must be 100% and adhered to the cantilever surface, (2) the deflection of the beam must be small to insure accuracy with use of elastic beam formulae and (3) the yield strain of the cantilever beam must be greater than the rupture strain of the coating.

The detection of a crack and its position must be accurately determined. Detection of a crack in a three micron transparent film requires scrutiny. Observance at 40× magnification and illumination by collimated light appears to be necessary to discover the existence of a typical tension crack.

FIG. 6 depicts the instrument setup to detect and measure the position of the rupture cracks in the wear layer coating. The clamp 10 holds the specimen 11- in a horizontal reference plane indicated by dashed line 12. Micrometer 13 both deflects and measures the distance of deflection ye. The cracks 14 in the wear layer 15 are observed with the aid of microscope 16 and collimated light source 17.

The length of the beam and its thickness are inter-related and wide variations of the two are possible. A length of two inches and a thickness of 0.030 inches has been found suitable for creating observable strain cracking of the wear layer. The test procedure is also usable in evaluating compressive surface strains by simply mounting the beam so that the bending places the coating in compression, i.e. inverting. The unit then deflects up, not down. The percent surface strain at position X, ex, is calculated by the following formula: ##EQU1##

Test evaluation of the method and instrumentation was done on one half inch wide specimens with a standard coating of 3 microns of Al2 O3. Specimens 1 to 4 were coated by the procedure set forth above. A glass decal was also fused to a 0.031 inch thick 302 stainless steel strip to form Sample 5 which had a coating thickness of 10 microns.

Specific values of these coating operations are as follows:

Leave a Reply