The present invention pertains to, among other things, wear-, scratch-, and corrosion-resistant coatings for metal substrates, such as those used to prepare medical implants.
Once installed, metallic orthopaedic implants are vulnerable to deterioration caused by scratching, wear, or otherwise damaging or corrosive processes that can occur in situ. Damaged implants may exhibit diminished performance, and in some cases must be repaired or replaced, and the complex and often physically traumatic surgical procedures necessary for doing so can delay the patient's progress towards rehabilitation. Furthermore, longer-lasting orthopaedic implants are of increasing interest due to demographic trends such as the increased life expectancy of implant recipients and the need for orthopaedic intervention among younger subjects (e.g., due to sports injury, excessive body weight leading to joint stress, or poor health maintenance).
Implants comprising metallic substrates, including such materials as steel, cobalt, titanium, and alloys thereof, are also vulnerable to damage or mechanically-assisted corrosion that can lead to loss of structural integrity, scratching or abrasive wear, increased wear rates and reduction of implant performance.
Traditional approaches for improving the scratch- and wear-resistance of metallic orthopaedic implants have included surface treatments such as ion implantation, gas nitriding, high temperature oxidation, and coating techniques (see, e.g., U.S. Pub. No. 2007/0078521, published Apr. 5, 2007). However, certain limitations such as inability to provide an optimal level of peak hardness, poor adherence of coatings to underlying substrates, and economic feasibility may abridge the utility of some of these traditional methods.
The present invention relates to the discovery that the scratch, corrosion and wear resistance and adhesion of a ceramic coating formed on metallic orthopaedic implant components may be improved by controlling the process parameters used to prepare the metal substrate prior to coating the substrate. The present invention also relates to the discovery that the scratch, corrosion and wear resistance and adhesion of a ceramic coating formed on metallic orthopaedic implant components may be improved by using a coating comprising multiple “thin” layers of ceramic instead of fewer thicker layers. In addition, the present invention also relates to the discovery that the optimal composition of the outer articular surface of a ceramic-coated orthopaedic implant component may advantageously be varied with the material used for the bearing that bears against the outer articular surface. Although these discoveries may be used together to improve ceramic-coated metallic orthopaedic implant components, each discovery, and aspects of each discovery, may also be used independently, as discussed in the Detailed Description.
In one aspect, the present invention provides a method of making an orthopaedic implant component comprising the steps of obtaining a metal orthopaedic implant component that has been HIP'd and homogenized, and depositing a ceramic coating on the HIP'd and homogenized component by depositing a first band of the ceramic coating upon said HIP'd and homogenized metal substrate and depositing a second band of the ceramic coating upon said first band of the ceramic coating.
In one alternative embodiment, the step of obtaining a metal orthopaedic implant component that has been HIP'd and homogenized includes obtaining a metal orthopaedic implant component with a surface that has been HIP'd, homogenized and from which ½-1 mm of HIP'd and homogenized metal has been removed from at least a portion of the metal orthopaedic implant component. In a more particular embodiment, the HIP'd and homogenized metal is removed through at least one of the following material removal processes: grinding; machining; and polishing.
In any of the above alternative embodiments, the step of depositing a first band of the ceramic coating may comprise CVD-depositing a layer of titanium nitride, titanium carbonitride or both titanium nitride and titanium carbonitride.
In any of the above embodiments, the step of depositing a second band may comprise depositing at least one layer of titanium nitride, titanium carbonitride or both titanium nitride and titanium carbonitride.
In any of the above embodiments, the method may further comprise depositing an outer band of the ceramic coating upon the second band, with the outer band defining the outer articular surface of the orthopaedic implant component. In one particular embodiment, the outer band comprises alumina; an additional bonding band may be deposited between the second band and the alumina of the outer band. Alternatively, the outer band may comprise a layer of titanium nitride, titanium carbonitride or both titanium nitride and titanium carbonitride.
In any of the above embodiments, the step of depositing a second band may comprise CVD-depositing a plurality of layers, each layer comprising titanium nitride, titanium carbonitride or both titanium nitride and titanium carbonitride. In this embodiment, the thickness of the layer of the first band may be greater than the thickness of each layer in the second band. In this embodiment, 2-100 layers, 2-50 layers, 5-50 layers or about 30-50 layers may be deposited in the second band, each layer comprising titanium nitride, titanium carbonitride or both titanium nitride and titanium carbonitride.
In another aspect, the present invention provides an orthopaedic implant kit comprising a first component having an outer articular surface and a second component having an outer bearing surface sized and shaped to articulate against the articular surface of the first component. The first orthopaedic implant component includes a metal substrate surface that is substantially free from interdendritic carbides and a ceramic coating on the metal substrate. The ceramic coating defines the outer articular surface of the first component. The ceramic coating has a total thickness of about 3 microns to 20 microns and includes a material selected from the group consisting of titanium carbide, titanium nitride, titanium carbonitride, and both titanium nitride and titanium carbonitride.
In one particular embodiment, the outer bearing surface of the second component is defined by a material selected from the group consisting of metal and ceramic and the ceramic coating of the first component has an outer surface comprising a material selected from the group consisting of titanium carbide, titanium nitride, titanium carbonitride, and both titanium nitride and titanium carbonitride.
In another particular embodiment, the ceramic coating includes a first band and a second band. The first band comprises titanium nitride, titanium carbonitride, or both titanium nitride and titanium carbonitride covering the substrate surface. The second band comprises a plurality of layers of titanium nitride, titanium carbonitride, or both titanium nitride and titanium carbonitride covering the first band. The first band has a thickness greater than the thickness of each layer in the second band. The ceramic coating may include a third band. The third band may have a thickness greater than the thickness of each layer in the second band. In one more particular embodiment the third band comprises titanium nitride, titanium carbonitride, or both titanium nitride and titanium carbonitride covering the second band, with the third band having a thickness greater than the thickness of each layer in the second band. More particularly, the third band may comprise a single layer having a thickness of from about 2-15 microns.
Alternatively, in another particular embodiment, the third band of the ceramic coating comprises alumina covering the second band, and wherein the third band has a thickness greater than the thickness of each layer in the second band. The third band may comprise a single layer having a thickness of from about 2-15 microns.
In a particular embodiment, the second band comprises about 2 to 50 layers of ceramic, each layer comprising titanium nitride, titanium carbonitride, or both titanium nitride and titanium carbonitride. The second band may comprise about 5 to 50 layers of ceramic, each layer comprising titanium nitride, titanium carbonitride, or both titanium nitride and titanium carbonitride. The second band may comprise about 30-50 layers of ceramic, each layer comprising titanium nitride, titanium carbonitride, or both titanium nitride and titanium carbonitride.
In a particular embodiment, the second band comprises a plurality of layers of ceramic, each layer having a thickness less than about 0.5 microns. Each layer in the second band may have a thickness less than about 0.2 microns.
In a particular embodiment, the first band has a thickness of about 2-3 microns. The first band may have a thickness of about 2.5 microns.
In a particular embodiment, the ceramic coating has a total thickness of 14-15 microns. In this embodiment, the first band comprises a single layer of ceramic comprising titanium nitride, titanium carbonitride, or both titanium nitride and titanium carbonitride, the single layer having a thickness of about 2-3 microns. The second band comprises about 30-50 layers of ceramic, each layer comprising titanium nitride, titanium carbonitride, or both titanium nitride and titanium carbonitride, each layer having a thickness less than about 0.2 microns. In this embodiment a third band comprises alumina covering the second band, the third band having a thickness of about 2-10 microns.
In another aspect, the present invention provides an orthopaedic implant component having an outer articular surface. The orthopaedic implant component comprises a metal substrate surface and a ceramic coating on the metal substrate surface defining the outer articular surface of the implant component. The ceramic coating includes a first band and a second band. The first band comprises titanium nitride, titanium carbonitride, or both titanium nitride and titanium carbonitride covering said substrate surface. The second band comprises a plurality of layers of titanium nitride, titanium carbonitride, or both titanium nitride and titanium carbonitride covering said first band. The ceramic coating includes a portion that exhibits no acoustic emission peaks characteristic of Lc2 chipping or buckling spallation type cracking events per millimeter of scratch length from a 200 micron radius diamond indenter under a 20N constant load. Chipping and buckling spallation Lc2 events, together with acoustic emission characteristics are defined per ASTM C1624-05.
In a more particular embodiment, the ceramic coating includes a portion that has fewer than 5 acoustic emission peaks characteristic of Lc2 chipping or buckling spallation per millimeter of scratch length from a 200 micron radius diamond indenter under a 40N constant load as measured per ASTM C1624-05.
In a more particular embodiment, the ceramic coating includes a portion that has fewer than 2 acoustic emission peaks characteristic of Lc2 chipping or buckling spallation per millimeter of scratch length from a 200 micron radius diamond indenter under a 40N constant load as measured per ASTM C1624-05.
In another more particular embodiment, the ceramic coating includes a portion that has no acoustic emission peaks characteristic of Lc2 chipping or buckling spallation per millimeter of scratch length from a 200 micron radius diamond indenter under a 25N constant load as measured per ASTM C1624-05.
In another more particular embodiment, the ceramic coating includes a portion that has no acoustic emission peaks characteristic of Lc2 chipping or buckling spallation per millimeter of scratch length from a 200 micron radius diamond indenter under a 28N constant load as measured per ASTM C1624-05.
In another more particular embodiment, the ceramic coating includes a portion that has no acoustic emission peaks characteristic of Lc2 chipping or buckling spallation per millimeter of scratch length from a 200 micron radius diamond indenter under a 30N constant load as measured per ASTM C1624-05.
In any of the above embodiments, the ceramic coating may also comprise an outer band covering the second band, the outer band defining an articulating surface of the implant component. The outer band may comprise alumina or alternatively may comprise titanium carbide, titanium nitride, titanium carbonitride or both titanium nitride and titanium carbonitride.
In any of the above embodiments, the inner band may include a layer of titanium nitride, titanium carbonitride or both titanium nitride and titanium carbonitride. The thickness of the layer of the inner or first band may be greater than the thickness of each layer of the second band. In embodiments with an outer band, the thickness of the layer of the outer band may be greater than the thickness of each layer of the second band.
In any of the above embodiments, the ceramic coating may have a thickness of 10-20 microns.
In any of the above embodiments, the layer of the first band may have a thickness of about 2-3 microns, the layer of the outer band may have a thickness of about 5 microns, and the second band may have a thickness of about 4-14 microns. In a particular embodiment, the second band has a thickness of about 5 microns.
The present invention may be understood more readily by reference to the following detailed description taken in connection with the accompanying figures and examples, which form a part of this disclosure. It is to be understood that this invention is not limited to the specific products, methods, conditions or parameters described and/or shown herein, and that the terminology used herein is for the purpose of describing particular embodiments by way of example only and is not intended to be limiting of the claimed invention.
In the present disclosure the singular forms “a,” “an,” and “the” include the plural reference and reference to a particular numerical value includes at least that particular value, unless the context clearly indicates otherwise. Thus, for example, a reference to “a material” is a reference to one or more of such materials and equivalents thereof known to those skilled in the art, and so forth. When values are expressed as approximations, by use of the antecedent “about,” it will be understood that the particular value forms another embodiment. As used herein, “about X” (where X is a numerical value) preferably refers to ±10% of the recited value, inclusive. For example, the phrase “about 8” preferably refers to a value of 7.2 to 8.8, inclusive; as another example, the phrase “about 8%” preferably refers to a value of 7.2% to 8.8%, inclusive. Where present, all ranges are inclusive and combinable. For example, when a range of “1 to 5” is recited, the recited range should be construed as including ranges “1 to 4”, “1 to 3”, “1-2”, “1-2 & 4-5”, “1-3 & 5”, and the like. In addition, when a list of alternatives is positively provided, such listing can be interpreted to mean that any of the alternatives may be excluded, e.g., by a negative limitation in the claims. For example, when a range of “1 to 5” is recited, the recited range may be construed as including situations whereby any of 1, 2, 3, 4, or 5 are negatively excluded; thus, a recitation of “1 to 5” may be construed as “1 and 3-5, but not 2”, or simply “wherein 2 is not included.”
In the present disclosure, chemical formulas may be used as shorthand for the full chemical names. For example, “TiN” may be used to denote titanium nitride, “TiCN” to denote titanium carbonitride, “TiC” to denote titanium carbide and Al2O3 to denote aluminum oxide or alumina. It should be noted that the use of chemical formulas is not meant to imply that these materials are of that precise stoichiometry. In some instances, depending on deposition conditions and the like, materials may deviate from nominal stoichiometry. In addition the aluminum oxide layer can be of either kappa alumina, alpha alumina, one or more other crystalline forms of alumina, or a mixture which includes layered structures of each unless expressly limited to a particular form (although, as discussed below, alpha alumina is preferred).
The disclosures of each patent, patent application, and publication cited or described in this document are hereby incorporated herein by reference, in their entirety.
The present invention pertains, in part, to the discovery that the scratch, wear and corrosion resistance of a coated metal implant component can be improved or maximized by: 1) controlling the process used to prepare the metal substrate prior to coating; and/or 2) by using a coating comprising multiple “thin” layers of TiN, TiCN, or both TiN and TiCN beneath an outer layer of Al2O3 (preferably in the alpha form). The improvements related to the use of multiple thin layers of TiN, TiCN, or both TiN and TiCN are disclosed in U.S. application Ser. No. 12/605,756, U.S. Pub. No. 2010/012926A1, which is incorporated by reference herein in its entirety, and in the present application. The present application provides information related to a preferred preparation of the metal substrate prior to coating. In addition, although it may be desirable to include a thicker outer layer of alumina on the coated implant in some applications, in other applications it may be desirable to use a different ceramic material for a thicker outer layer, such as a non-oxide ceramic titanium material.
As discussed above in the Background of the Invention, steel, cobalt, titanium and alloys thereof are common metals used in orthopaedic implants. Steel, cobalt and alloys thereof are expected to be usable in the present invention as the metal substrate. A conventional cobalt chromium alloy useful as the metal substrate is Co-28Cr-6Mo. Co-28Cr-6Mo may be cast, wrought, forged or injection molded, for example. For cast medical devices, Co-28Cr-6Mo may be cast according to ASTM-F75. Such a cast alloy may be used as the metal substrate for a ceramic coating. As discussed in more detail below, the as-cast Co-28Cr-6Mo may advantageously be treated by hot isostatic pressing (HIP) and homogenization prior to coating the substrate, particularly where the outer articular surface of the ceramic coating comprises alumina. It has also been found that in some instances it may be advantageous to grind and polish the HIP'd and homogenized Co-28Cr-6Mo prior to coating the substrate, as discussed in more detail below.
Although the work reported below has been done with Co-28Cr-6Mo, it is anticipated that the principles of the present invention will be applicable to other cobalt chromium alloys and other metals suitable for implantation into the human body, including new materials as they are developed.
As-cast Co-28Cr-6Mo commonly has 50-100 micron diameter interdendritic (Co, Cr, Mo) carbides present as an inherent result of the investment casting process. When such an as-cast substrate is coated, surface carbides may increase the occurrence of defects in a ceramic coating on the substrate; for example, such surface carbides may increase the occurrence of defects in coatings including one or more layers of TiN and TiCN and an outer layer of alumina
It is also believed that the TiN and TiCN layers of an TiN/TiCN/Al2O3 coating nucleate and/or grow more quickly for a given set of deposition parameters on (Co, Cr, Mo) carbides than on the solid solution matrix phase of the CoCrMo substrate. Parts of the TiN and TiCN layers above such carbides may be exposed at the surface of the coating when the Al2O3 layer is polished after coating. Thus, the outer surface of the polished ceramic coating may be non-homogeneous, with portions comprising alumina and adjacent portions comprising TiN, TiCN or mixtures of TiN and TiCN. These TiN and TiCN defects appear gold in color on an otherwise brown or black polished coating surface. In such instances, the outer surface of the polished ceramic coating is defined by materials that have different properties, which may lead to sub-optimal scratch, corrosion and wear resistance of the coating.
To reduce the occurrence of TiN and TiCN defects in the outer alumina layer of the ceramic coating on the CoCrMo substrate surface, the substrate surface is preferably treated to dissolve the interdendritic (Co, Cr, Mo) carbides into the solid solution matrix phase prior to coating the substrate. In accordance with one aspect of the present invention, this substrate surface treatment comprises a combination of hot isostatic pressing (HIP) and homogenization. The HIP'd and homogenized substrate surface is more uniform than the as-cast surface, so that the topography of the layers of ceramic coating is more even, with fewer peaks and consequently with fewer defects in the polished surface of the outer ceramic layer.
Hot isostatic pressing of the as-cast substrate may comprise, for example, placing the component in a high pressure containment vessel and pressurizing the vessel with an inert gas such as argon. The chamber is heated, resulting in pressure being applied to the component. Common pressures of the inert gas pre-heating may be, for example, between 15,000 psi and 25,000 psi for an as-cast Co-28Cr-6Mo substrate. Common temperatures range between 2165 degrees and 2200 degrees for an as-cast Co-28Cr-6Mo substrate. Common process times range between 4 and 4½ hours for an as-cast Co-28Cr-6Mo substrate.
A specific example of HIP process parameters useful for treating an as-cast Co-28-8Mo substrate include the following: heat to 2200° F., at a pressure of 15,000 psi and hold at that temperature and pressure for a period of at least 4 hours.
For each of the above processes, thermocouples are used and the hold time starts when the coldest thermocouple and the minimum pressure have been obtained. In each of the above processes, the atmosphere comprises argon gas. It should be understood that the process parameters identified above are provided as examples only; the claimed invention is not limited to any particular process parameter unless expressly called for in the claims.
Homogenization of the HIP'd substrate may comprise, for example, heating the HIP'd component to a temperature of 2220° F. for at least four (4) hours in an atmosphere of 500-700 microns partial pressure of Argon, and cooling from 2220° F. to 1400° F. in 8 minutes maximum (that is, a minimum cooling rate of from 2220° F. to 1400° F. in 8 minutes). It should be understood that “homogenization” as used herein includes heat treatment processes such as surface annealing that result in the CoCr product being austenitic with a fine distribution of carbides, with no continuous blocky carbides in the grain boundaries and without widespread thermally induced porosity. It should also be understood that “homogenization” as used herein includes processes such as solution treatment or solutionizing; generally, “homogenization” includes any process that dissolves carbide precipitates into solid solution in the metal substrate.
It should be understood that the process parameters described above for the HIP and post-HIP homogenization processes are provided as examples only; the invention is not limited to any particular HIP or homogenization parameter unless expressly called for in the claims.
Although the HIP'd and homogenized metal substrate may then be coated with ceramic material (including multiple layers of ceramic material), if the metal substrate has been mechanically worked prior to HIP'ing and homogenizing, the inventors of the present invention have discovered that when a mechanically-worked HIP'd and homogenized Co-28Cr-6Mo metal substrate is subsequently coated with layers of TiN, TiCN, combinations of TiN and TiCN and Al2O3, adhesion of some of the layers of the coating to the metal substrate may be less than optimal. The inventors discovered that the HIP'd and homogenized Co-28Cr-6Mo that had been rough ground and CNC (computer numerical control) ground prior to the HIP and homogenization treatments had recrystallized grains present on the surface of the metal substrate (such grains are illustrated in
In general, if about ½ to 1 mm of the outer surface of the HIP'd and homogenized substrate is removed through a grinding, machining, polishing or other mechanical process, recrystallized grains should be removed, leaving the parent phase of the metal on the substrate surface, providing a better surface to receive and bond with the ceramic coating. Any available machining, grinding or polishing technique and equipment that removes this amount of material from the outer surface of the substrate should suffice for the purposes of this process. The ground/machined surface is preferably polished to a mirror smooth finish (for example, having a surface roughness Ra of 0.03 or 0.04 microns prior to coating; see ISO 4287 (1997)).
The presence of recrystallized grains in the metal substrate appears to decrease the growth rate of the ceramic coating on the metal substrate. For a fixed process time for forming the coating, the thickness of at least the initial layers of the ceramic coating may thus be reduced, seeming to lead to a weaker bond with the outer alumina layer. Accordingly, instead of removing a portion of the outer surface of the HIP'd and homogenized metal substrate, it is expected that the adverse effect of recrystallized grains could be reduced by adjusting the process parameters for forming the initial layers of the ceramic coating, such as by increasing the process time for forming the initial layer or layers.
The above HIP'ing processes may also advantageously close internal porosity of the as-cast metal substrate.
The HIP'd, homogenized and ground/machined/polished substrate may then be coated with ceramic material. The ceramic coating and technique may produce a dual layer coating, as described in U.S. Pub. No. 2007/0078521A1. Alternatively, the HIP'd, homogenized and ground/machined/polished substrate may then be coated with multiple thin layers of ceramic as described in U.S. Pub. No. 2010/0129626A1. The ceramic coating may comprise three stacked bands (shown diagrammatically in cross-section in
Preferably, the first band 3 or first layer comprises TiN, TiCN, or both TiN and TiCN is deposited upon the HIP'd, homogenized and ground/machined/polished metal substrate 1, followed by the middle band 5, comprising multiple thin layers (e.g. 7a-7i) of TiN, TiCN or both TiN and TiCN deposited on the first band or layer 3 and followed by the thicker outer band 9 comprising a single layer of ceramic material deposited on the outermost layer of the middle band 5.
The layers defining the first 3 and middle 5 ceramic bands may comprise TiN, TiCN, or both TiN and TiCN. Where the first band/layer 3 comprises one of TiN, TiCN or both TiN and TiCN, the initial layer 7a of the middle band 5 preferably comprises a different one of TiN, TiCN or both TiN and TiCN. The subsequent layers 7b et seq. of the middle band 5 may comprise one or more repetitions of the first band/layer 3 and layers 7a et seq. of the middle band 5. As used herein, a layer that is a “repetition” of a different layer is generally of the same chemical composition as the different layer, of the same thickness as the different layer, or both. For example, if the first band/layer 3 includes only TiN and the adjacent layer 7a includes only TiCN, two subsequent layers 7b, 7c that are repetitions of these layers 3, 7a will include only TiN and TiCN, respectively. The entirety of the complement of subsequent layers 7b et seq. may comprise one or more repetitions of the first and second layers 3, 7a, or only some of the subsequent layers 7b et seq. may comprise one or more repetitions of the first and second layers 3, 7a. In one embodiment, the second layer 7a is different than the first layer 3, and all of the subsequent layers 7b et seq. comprise repetitions of the first and second layers 3, 7a; the resulting structure will therefore comprise layers that alternate between the material of the first layer 3 and the material of the second layer 7a. In a preferred version of this embodiment, the first layer 3 is TiN, the second layer 7a is TiCN, and the subsequent layers 7b et seq. comprise alternating layers of TiN and TiCN. Among the first layer 3, the second layer 7a, and the at least one subsequent layer 7b et seq., it is preferred that at least one of the layers comprises TiN and at least one adjacent layer comprises TiCN. The top or final layer of the middle band 5, i.e., the last of the at least one subsequent layers, may comprise TiCN, TiN or a mixture TiN and TiCN.
The material used for the top or outer ceramic band or layer 9 may vary depending on the anticipated bearing environment. For example, if the implant component is expected to bear against a polymer such as ultrahigh molecular weight polyethylene, then the top or outer ceramic band or layer 9 may preferably comprise alumina. If the component is expected to bear against a different material, such as another ceramic-coated metal substrate or a harder material like metal or another ceramic, and to thus be placed in high contact stress applications, the top or outer ceramic band or layer 9 may comprise TiN, TiCN or a mixture of TiN and TiCN instead of alumina.
It should be understood that it is anticipated that other ceramic materials may be useful in the present invention. For example, it is anticipated that titanium carbide TiC could be used as part of the ceramic coating. Accordingly, the present invention is not limited to any particular ceramic material unless expressly called for in the claims.
The thickness of the first band or layer 3 may be less than about 10 microns, less than about 8 microns, less than about 6 microns, less than about 5 microns, 2-3 microns or about 2.5 microns. Preferably, the thickness of the first band or layer 3 is about 2-3 microns, and most preferably, about 2.5 microns. Generally, the first ceramic band 3 comprises a ceramic layer that is thicker than the individual ceramic layers 7 of the second ceramic band 5.
The middle ceramic band 5 may comprise multiple thin ceramic layers 7 deposited upon the first ceramic band or layer 3. The initial layer 7a of the middle ceramic band 5 may have a thickness that is less than about 1 micron, less than about 0.75 microns, less than about 0.5 microns, less than about 0.3 microns, less than about 0.2 microns, or less than about 0.1 micron. In some embodiments, the initial layer 7a of the second band 5 may have a thickness that is about 0.1 microns, about 0.2 microns, about 0.3 microns, about 0.5 microns, about 0.7 microns, about 0.8 microns, about 0.9 microns, about 1 micron, about 2 microns, about 3 microns, about 4 microns and about 5 microns. The initial layer 7a of the middle band 5 preferably has a thickness that is less than that of the first band/layer 3. The middle ceramic band preferably includes multiple thin layers of ceramic, and may include, for example, 2-100 thin layers of ceramic, 2-50 thin layers of ceramic, 5-50 layers of ceramic, 10-50 layers of ceramic, 20-50 layers of ceramic, or 30-50 layers of ceramic. As illustrated below, improved scratch resistance can be achieved with about 30 layers of ceramic as well as with about 50 layers of ceramic in the middle band 5.
Alternatively, the second band 5 may comprise a single ceramic layer deposited upon the first ceramic band or layer 3. For example, the second band 5 may comprise a single layer of TiN, TiCN or a mixture of TiN and TiCN having a thickness of about 2.5 microns, although it is believed that optimum results are achieved when the second band comprises multiple thinner layers of ceramic.
The top or outer ceramic band 9 preferably comprises a single thicker layer of ceramic material. The top or outer ceramic band may, for example, be alumina having a thickness of about 2 microns to 15 microns, for example, about 3 microns to 15 microns, about 4 microns to about 15 microns, about 5 microns to 15 microns. In a particular embodiment, the top or outer ceramic band 9 is about 4-7 microns thick. The top or outer ceramic band may comprise, for example, alumina, TiN, TiCN or both TiN and TiCN and have a thickness of about 1 micron, about 2 microns, about 3 microns, about 4 microns, about 5 microns, about 6 microns, about 7 microns, about 8 microns, about 9 microns, about 10 microns, about 12 microns, about 15 microns, about 17 microns or about 20 microns. In some embodiments, the top or outer ceramic band is the thickest of the all the layers defining the ceramic coating. The thickness of the outermost layer may be dictated by any of a number of considerations readily understood among those skilled in the art, such as production cost, implant type, environment of use, layer adhesion, inherent layer durability, the roughness of the as-deposited outermost layer and the need to polish the coating, and the like.
Preferably, the entire ceramic coating 13 (including the first, second and third bands 3, 5, 9 and any bonding band 11) has a thickness of between about 8.5 microns and 20 microns, and more particularly, between about 8.5 microns and about 15-16 microns. It has been found that if the ceramic coating is too thick, then the coating may fail mechanically.
Examples of thicknesses for the ceramic coating are set forth in the table below:
It should be understood that although the above thicknesses are expected to provide advantageous results, the present invention is not limited to any particular thickness, number of bands or layers or thickness of a particular band or layer unless expressly called for in the claims. As used herein, the “thickness” of a given layer or of the entire ceramic coating refers to the average thickness of that layer or coating over its entire area; accordingly, if the “thickness” of a layer is about 1 micron, there may be portions of that layer that are less than 1 micron thick, and/or portions of that layer that are thicker than one micron, but the average thickness over the entire area of the layer may be calculated as about 1 micron.
The metal substrate preparation processes of the present invention are expected to be most advantageous when used in conjunction with a chemical vapor deposition (CVD) process for forming the bands and layers of ceramic on the metal substrate. It is expected that once provided with the desired number, constituency and thickness of the layers defining the coating, those in the coating art (such as Ionbond AG Olten, of Olten, Switzerland, Seco Tools AB, of Fagerstra, Sweden, and Sandvik AB of Sandvik, Sweden) will readily set CVD process parameters (such as temperature, pressure, reactive concentrations and heating and cooling rates) to deposit the layers as desired.
It should be understood, however, that the present invention is not limited to a CVD process for depositing the bands or layers unless expressly called for in the claims. Various techniques (such as physical vapor deposition, chemical vapor deposition, and thermal spraying deposition, for example, plasma spraying) are available for forming bands and layers of ceramic coatings, although it may be difficult to form some of the thinner layers using plasma spraying. The deposition of any of the layers of the present invention may be performed in accordance with any acceptable technique that provides layers having the characteristics, e.g., thickness profile, as provided herein. Although the respective bands and layers may all be deposited using a single technique, it is anticipated that different bands and layers may be deposited using different techniques; for example, thicker layers may be deposited by a technique that is suitable for “thick” layer deposition, whereas thinner layers may be deposited by a technique that may achieve deposition of thinner layers. The advantages of the metal substrate preparation processes of the present invention may be expected to vary somewhat with the technique used to deposit the ceramic coating, particularly with the technique used to deposit the initial band 3 adjacent to the substrate.
The process or method of the present invention may also include depositing a bonding band or layer (band 11 in
Available techniques for depositing a bonding layer will be appreciated by those skilled in the art, such as any of the techniques describe above with respect to the deposition of the first, second, and at least one subsequent layers. For example, chemical vapor deposition may be used to deposit a bonding layer in accordance with the present invention. Bonding layers may have a thickness that is less than 2 microns, and may have a thickness less than 1 micron, less than 500 nanometers, less than 250 nanometers, less than 100 nanometers, less than 50 nanometers, less than 30 nanometers, less than 20 nanometers, or less than 10 nanometers. Various companies (for example, Ionbond AG Olten, of Olten, Switzerland, Seco Tools AB, of Fagerstra, Sweden, and Sandvik AB of Sandvik, Sweden) provide the service of applying bonding layers and can be contacted for this purpose.
It is expected that the constituency and thicknesses of the layers defining the coating of a finished component may be analyzed using known techniques, such as TEM (transmission electron microscopy, no less than 10,000 magnification), EDX Energy-dispersive X-ray spectroscopy or EELS (Electron energy loss spectroscopy).
Orthopaedic implants such as those illustrated in
It should be understood that knee, hip, shoulder and ankle orthopaedic implant components may be provided in the form of kits. For example, a knee implant kit may include all of the elements illustrated in
Particular processes used in preparing samples and particular tests run on at least some of these samples are described below. Unless otherwise indicated, the samples were prepared from flat discs, rather than from implant components.
Metal Substrate Preparation
Samples of as-cast Co-28Cr-6Mo cobalt chromium alloy were obtained as well as a sample of a Zr—Nb alloy and a sample of a titanium alloy. The following table summarizes the material and initial preparation parameters for the metal substrates.
The following tables summarizes any the further processes used in preparing the metal substrates prior to coating.
Coating
Coatings were applied by an outside vendor, Ionbond Ag Olten of Olten, Switzerland.
The table below summarizes the characteristics of the coatings applied to the samples.
Most of the ceramic-coated samples were polished prior to testing; samples 14, 16, 18 and 20 were not polished before testing.
Scratch Testing
To compare the resistance of conventional coatings and the present coatings to surface damage by scratching, 10 mm-long scratches were formed along the surface of coated samples 6, 7, 8 and 9 using a 200 micron radius diamond indenter tip on a CSM Revetest® scratch tester under a constant load of 40 N (a relatively high load compared to scratching loads that would be expected to act on an implant that has been implanted in a patient) using. See Smith, B., Schlachter, A., Ross, M., and Ernsberger, C., “Pin on Disc Wear Testing of a Scratched Engineered Surface,” Transactions 55th ORS, No. 2292, 2009.
As depicted in
With respect to the structure of Sample 6 (a single, 2.5 μm thick inner band of TiN, a second band comprising a single, 2.5 μm thick layer of TiCN, and an outer band comprising 5 μm thick alumina overlayer; such structures are generally referred to as “dual layered” herein in reference to the total number of layers of TiN and TiCN), it was observed that cracks and alumina spalls (Lc2-type cracking per ASTM C1624-05 specification, incorporated by reference herein in its entirety) occurred at regular intervals along the scratch length (
Scratching of the oxidized Zr—Nb alloy of Sample 8 (5 μm oxide layer) at such relatively high loads (Zr is relatively soft) resulted in exposure of the base substrate material within the scratch trough along the entire length of the test damage (
The images of the monolayer TiN coating of Sample 7 (thickness 10 μm, deposited by arc evaporation PVD) on a Ti-6Al-4V substrate show that large chips of the coating material were removed along the scratch line, exposing the substrate material (
The diamond-like carbon (DLC) coating (Richter Precision Inc., Medikote™ C11 material, thickness 6 μm, deposited by PVD on HIP'd/homogenized F75 CoCrMo substrate; not shown in the above tables) underwent considerable chipping under 40 N applied loads (
In addition to the optical analysis of the scratches, scratches were also analyzed acoustically to determine the number of acoustic emission peaks characteristic of Lc2 chipping or buckling spallation type cracking events per ASTM C1624-05 that occur under various load conditions. The polished samples where polished using Buehler Metadi diamond suspensions together with Texmet papers; polishing was undertaken starting with a 9 micron diamond suspension, through a 6 micron diamond suspension and ending with a 1 micron diamond suspension. Polished samples were polished to an optically flat finish. Five (5) scratches were placed 0.25 mm apart, each scratch 10 microns in length, and performed at a speed of 1 mm per second, using a 200 micron radius diamond indenter tip on a CSM Revetest® scratch tester. Results are as follows:
Progressive load scratch testing of various samples was also performed per ASTM C1624-05 using a 200 micron radius diamond indenter tip on a CSM Revetest® scratch tester. The dual layer samples comprised an inner band and a middle band; these two bands comprised a layer of TiN and a layer of TiCN; these two layers were covered with an outer band comprising an Al2O3 overcoat. The multilayer coating samples all had a middle band comprising 50 (fifty) layers of TiN and TiCN coated onto a single layer inner band TiN and an Al2O3 overcoat as the outer band. The results are presented in the table below:
These results demonstrate that HIP'd/homogenized/ground/polished multilayer coatings of the present invention minimize scratch-induced damage and are more effective in preventing the generation of microcracks as compared with conventional coatings.
Samples 1-13 were aggressively scratched in preparation for corrosion testing. For these samples, networks of five repeating groups of five parallel diamond indenter scratches were made on the corrosion test samples using a 200 micron radius diamond indenter on a CSM Revetest® scratch tester. The scratches were spaced 0.25 mm between centers. Each group of five parallel scratches was made with scratch loads of 6, 9, 12, 15, and 18 N as shown in
Corrosion Testing
All samples subjected to corrosion testing (Samples 1-13) first had scratch networks put onto the outer surface of the ceramic coating as described above.
Cyclic potentiodynamic polarization testing of some samples was performed. The testing was similar to the method described in ASTM F2129. A BioLogic VMP3 potentiostat/galvanostat with a flat cell and a saturated Ag/AgCl/KCl reference electrode was used. Some of the samples were scratched and cyclic scanned in Hanks solution with 25 vol. % bovine calf serum at 37° C. to simulate the presence of biological macromolecules and increased viscosity conditions in-vivo. The rationale for performing cyclic polarization testing on polished and scratched samples was to measure the corrosion resistance of the coating/substrate system in the presence of simulated excessive in-vivo abrasive scratch damage.
The test area of each sample was immersed in electrolyte for 1 hour prior to each scan to allow open circuit potential stabilization. Cyclic polarization scans were performed at a scan rate of 0.166 mV/sec (10 mV/min).
The solution used was HyClone HyQ Hanks solution (Part no. SH30030) with a composition given in the table below, mixed with 25 volume % HyClone bovine calf serum (Part no. SH30073.03). No deaeration was performed to the Hanks solution, which had a pH of 7.4, prior to or during any of the scans. In the cyclic potentiodynamic scans, the test area of each sample was immersed for 1 hour prior to each scan to allow open circuit potential stabilization.
The results of the cyclic potentiodynamic polarization testing are illustrated in
From
Rockwell C Indentation
Rockwell C indentation was performed on polished areas of coated samples as prescribed by the VDI 3198 norm. Hardness was measured and deformation patterns in the samples were optically analyzed to detect any spalling/cracking around the indentation marks. Hardness values were consistently between about 36 and 40 RHC, the measured value for the substrate material. A comparison of
TEM Imaging
As the above tests indicate, aggressively scratched ceramic coatings that include a band of multiple thin layers formed on CoCrMo substrates display consistently greater corrosion and scratch resistance when the CoCrMo substrate has been HIP'd, homogenized, ground (rough and CNC) and polished prior to being coated with the ceramic material. It is anticipated that use of such coatings on orthopaedic implant components will demonstrate improved wear resistance in vivo as well. In addition,
This is a continuation-in-part of U.S. patent application Ser. No. 12/782,315, entitled “Multilayer Coatings,” filed on May 18, 2010 and of U.S. patent application Ser. No. 12/605,756, U.S. Pub. No. 2010/012926A1, entitled “Multilayer Coatings,” filed on Oct. 26, 2009 by Jason B. Langhorn, and which claims priority to U.S. provisional application Ser. No. 61/117,468, filed on Nov. 24, 2008.
Number | Date | Country | |
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61117468 | Nov 2008 | US |
Number | Date | Country | |
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Parent | 12782315 | May 2010 | US |
Child | 12950073 | US | |
Parent | 12605756 | Oct 2009 | US |
Child | 12782315 | US |