Patent Description:
Shape memory or superelastic NiTi alloys have been known for a considerable period of time and have garnered widespread use in a variety of applications, including, for example, medical devices, electronics, micro-electromechanical systems, and mechanical devices and systems. NiTi alloys may be binary, ternary or quaternary alloys and each alloy will exhibit different physical, mechanical, electrical, and chemical properties depending upon a number of factors, including, for example, the elements present in the alloy, the stoichiometry of the elements in the alloy, the physical state of the material, e.g., crystalline, polycrystalline, or amorphous, the grain morphology and grain density, and/or the nature, number and/or size of inclusions in the material.

Conventionally, precursor materials fabricated from NiTi ternary and quaternary alloys are made by melting elemental metals into ingots and then working the ingot into the precursor material form, such as a hypotube, as disclosed by <CIT> which discloses forming an ingot by melting nickel with titanium and tungsten, then cooling to form an ingot, hot rolling the alloy ingot and then cold-forming the alloy into a cylinder and drilling the cylinder to form tubing, then cold drawing the tubing and annealing the tubing. Similarly, <CIT> discloses providing an ingot fabricated form NiTi with a ternary alloying element of either tantalum, hafnium, vanadium, zirconium or combinations thereof, with the ternary element present at about <NUM> atomic percent (at %) to about <NUM> at %, with the alloy being a two-phase alloy having a first NiTi-rich phase and a second phase rich in the ternary element. The ingot is then processed by cold working the material which forms dendrites and a eutectic mixture that elongates in the working direction.

By using PVD processing, ternary and quaternary NiTi alloy, bulk materials may be made in in the as-deposited state such that the configuration and conformation of a desired precursor material, e.g., wires, tubes, planar materials, curvilinear, or as the near finished end product, e.g., hypotube for stent manufacture, semilunar for cardiac valves or conical for embolic or caval filters, is formed on a removable deposition substrate in the configuration and conformation of the precursor material or near-finished end product. In this manner, either precursor materials or near-finished end product, only post-processing steps such as passivation, electropolishing, laser machining features in the material, and assembly, if required, are needed.

Methods of making NiTi ternary shape-memory alloys materials by PVD are known from <CIT> or <CIT>.

It is an object of the present disclosure to provide a method of PVD deposition in which a NiTi ternary or quaternary alloy is deposited from one or more targets onto a removable substrate having the configuration and conformation of a desired precursor and/or near-finished as disclosed in claims <NUM>-<NUM>.

<FIG> is a is a graph depicting the tensile property comparison between wrought nitinol material after heat treatment in curve A, the inventive multi-layer PVD deposited nitinol engineered material in curve B, and the inventive multi-layer PVD deposited PVD deposited nickel-titanium-cobalt alloy in curve C.

For purposes of clarity, the following terms used in this patent application will have the following meanings:.

The terminology used herein is for the purpose of describing example embodiments only and is not intended to be limiting. The method steps, processes, and operations described herein are not to be construed as necessarily requiring their performance in the order discussed or illustrated, unless specifically identified as an order of performance.

When an element or layer is referred to as being "on," "engaged," "connected," or "coupled" to or with another element, it may be directly on, engaged, connected or coupled to the other element or layer, or intervening elements or layers may be present. In contrast, when an element is referred to as being "directly on," "directly engaged to," "directly connected to," or "directly coupled to" or with another element or layer, there may be no intervening elements or layers present. Other words used to describe the relationship between elements should be interpreted in a like fashion (e.g., "between" versus "directly between," "adjacent" versus "directly adjacent," etc).

For example, if the device in the figures is turned over, elements described as "below", or "beneath" other elements or features would then be oriented "above" the other elements or features.

"Substantially" is intended to mean a quantity, property, or value that is present to a great or significant extent and less than, more than or equal to total. For example, "substantially vertical" may be less than, greater than, or equal to completely vertical.

"About" is intended to mean a quantity, property, or value that is present at +<NUM>%. Throughout this disclosure, the numerical values represent approximate measures or limits to ranges to encompass minor deviations from the given values and embodiments having about the value mentioned as well as those having exactly the value mentioned. Other than in the working examples provided at the end of the detailed description, all numerical values of parameters (e.g., of quantities or conditions) in this specification, including the appended claims, are to be understood as being modified in all instances by the term "about" whether or not "about" actually appears before the numerical value. In addition, disclosure of ranges includes disclosure of all values and further divided ranges within the entire range, including endpoints given for the ranges.

Recitation of ranges of values herein are merely intended to serve as a shorthand method of referring individually to each separate value falling within the recited range, unless otherwise indicated herein, and each separate value is incorporated into the specification as if it were individually recited herein.

Unless otherwise expressly stated, it is in no way intended that any method or aspect set forth herein be construed as requiring that its steps be performed in a specific order. Accordingly, where a method claim does not specifically state in the claims or descriptions that the steps are to be limited to a specific order, it is in no way intended that an order be inferred, in any respect. This holds for any possible non-express basis for interpretation, including matters of logic with respect to arrangement of steps or operational flow, plain meaning derived from grammatical organization or punctuation, or the number or type of aspects described in the specification.

The term "material" is intended to refer to elemental metals, alloyed metals or pseudometals.

For purposes of this application, the terms "pseudometal" and "pseudometallic" are intended to mean materials which exhibit material characteristics substantially the same as metals. Examples of pseudometallic materials include, without limitation, composite materials, polymers, and ceramics. Composite materials are composed of a matrix material reinforced with any of a variety of fibers made from ceramics, metals, carbon, or polymers.

As used in this application the term "layer" is intended to mean a substantially uniform material limited by interfaces between it and adjacent other layers, substrate, or environment. The interface region between adjacent layers is an inhomogeneous region in which extensive thermodynamic parameters may change. Different layers are not necessarily characterized by different values of the extensive thermodynamic parameters but at the interface, there is a local change at least in some parameters. For example, the interface between two steel layers that are identical in composition and microstructure may be characterized by a high local concentration of grain boundaries due to an interruption of the film growth process. Thus, the interface between layers is not necessarily different in chemical composition if it is different in structure.

The term "build axis" or "build direction" is intended to refer to the deposition axis in the material. For example, as a material is being deposited onto a substrate, the thickness or Z-axis of the material being deposited will increase, this is the build axis of the material.

The terms "circumferential" or "circumferential axis" is intended to refer to the radial direction of a tubular, cylindrical or annular material or to the Y-axis of a polygonal material.

The terms "longitudinal," "longitudinal axis," or "tube axis" are intended to refer to an elongate aspect or axis of a material or to the X-axis of the material.

The term "bulk material" is intended to refer to the entirety of the material between its surfaces.

The term "film" is intended to encompass both thick and thin films and includes material layers, coatings and/or discrete materials regardless of the geometric configuration of the material.

The term "thick film" is intended to mean a film or a layer of a film having a thickness greater than <NUM> micrometers.

The term "thin film" is intended to mean a film or a layer of a film having a thickness less than or equal to <NUM> micrometers. The terms "physical vapor deposition" and/or is acronym "PVD" is intended to encompass sputtering, electron-beam deposition, hot-boat evaporation, reactive evaporation, ion platting, plasma sputtering and/or ion beam sputtering.

The following examples are provided in order to illustrate the invention, and are not intended to limit the scope of the invention. In each of the following examples, the described general PVD equipment and process steps and parameters were employed. PVD was performed using a hollow cathode magnetron with the target material lining the inside of the process chamber. Interior to the targets was a carousel loaded with substrates. In the case of tubing, this is a planetary carousel. A suitable PVD reactor with a planetary carousel is described in <CIT>. Substrates were typically constructed of polished metal with a diffusion barrier layer on it outer (deposition) surface. Substrates used were tubular, wire, profiled, and three-dimensional. After pumping down to a high vacuum pressure, e.g., <1E-6Torr, an inert gas was introduced into the chamber at a controlled rate and the chamber pressure was controlled to a fixed level. Magnetic field and electrical potential was applied sufficient to ignite the plasma and generate process temperatures into a range that results in Zone <NUM> (columnar and most typical) or Zone <NUM> process temperatures in the Thomton diagram. The charged atoms (ions) from the plasma bombarded the target surface and ejected atoms of target material into the vacuum chamber. Using a DC electric field, the sputtered atoms from the targets were transported to the substrates where they organized into a crystalline structure. Electromagnets on the exterior of the chamber were used to shape the plasma profile to control the uniformity of deposition onto the substrates inside the chamber. Layers were created by interrupting the deposition process enough to initiate a new layer of deposited material or a "plane" of grains. Plasma or pseudo-plasma etching, synonymously faux etching, was used at the start of a new layer to increase interlayer bond strength. This bond can also be intentionally weakened, if desired. PVD process parameters were driven by a table of values that were input to a PLC program which executed the process and recorded its outputs. Material properties, total deposition thickness, layer profile, property gradients, and final temper were all controlled by the PLC program and its input parameters. The material produced in this fashion was crystalline with final properties in the as-deposited configuration.

The disclosed PVD method of forming ternary or quaternary NiTi materials is capable of forming coherent single layer bulk materials or bulk materials made of multiple layers in which Individual layers or groupings of layers may be deposited to have different mechanical, electrical, chemical or physical properties by controlling the process parameters for each layer during the deposition.

It will be understood by those skilled the PVD arts, that deposition of films with different chemistries can also be achieved by manipulation of the sputter yields, in-situ doping, or by sequential depositions in different process chambers (or a multi-chamber system). Further material property manipulation can also be achieved post-deposition, if desired, by employing traditional heat treatment and/or working processes.

A cylindrical substrate was introduced into a deposition chamber with capabilities of glow discharge substrate cleaning and sputter deposition of nickel-titanium (NiTi) alloy. The deposition chamber was evacuated to a pressure less than or equal to <NUM> x <NUM>-<NUM> Torr. The substrate temperature was controlled to achieve a temperature between about <NUM> and <NUM> degrees Centigrade. A bias voltage between -<NUM> and +<NUM> volts, preferably between -<NUM> and +<NUM> volts, was applied to the substrate. Power was applied to the cathode to form a plasma within the deposition chamber. Power wattage may be varied to control the applied power and will vary depending upon the plasma conductance, inert gas flow, magnetron power settings, chamber cooling, and deposition chamber configuration, in such a manner to achieve a process temperature to deposit crystalline material. During deposition, the deposition pressure was maintained between <NUM> and <NUM> mTorr. A sacrificial or barrier layer of substantially uniform thickness may, optionally, be deposited circumferentially on the substrate, alternatively the substrate, itself, may be sacrificial. A NiTi alloy target with cobalt wires welded to it was employed. NiTiCo alloy was deposited from the NiTiCo target onto the cylindrical substrate at a deposition rate between about <NUM> to <NUM> microns/hour until a <NUM> micron layer of NiTiCo was deposited onto the cylindrical substrate.

The same process parameters are employed as in Example <NUM>, except that a Ni target, a titanium target, and a tantalum target are employed in the cylindrical magnetron, and a plurality of semilunar removable substrates are employed. NiTiTa is deposited onto the semilunar substrates at a deposition rate between about <NUM> to <NUM> microns/hour until a <NUM>-micron layer of NiTiTa was deposited onto the semilunar substrates.

<FIG> is a tensile property comparison between wrought NiTi, binary NiTi, and ternary NiTiCo showing that ternary NiTiCo has a far higher tensile stress plateau of about <NUM> MPa to about <NUM> MPa when compared to both binary NiTi and wrought NiTi and recovery energy of about <NUM> MPa.

The NiTiCo ternary alloy of the Example <NUM> was created in two compositions as per Table <NUM> below:.

Binary shape memory or superelastic NiTi typically has a Nickel:Titanium ratio of about <NUM>, whereas the Nickel:Titanium ratio in the ternary NiTiCo alloy of Example <NUM> was about <NUM>.

Claim 1:
A method of making a nickel-titanium ternary or quaternary shape memory alloy, comprising the steps of:
a. Selecting a target made of at least three metals consisting of nickel, titanium, cobalt, or consisting of nickel, titanium, cobalt and a metal selected from the group consisting of hafnium, tantalum, tungsten, rhenium, iridium, platinum, gold, silver, vanadium, iron, chromium, bismuth, palladium, combinations or alloys thereof, wherein nickel and titanium are present in a nickel to titanium ratio of about <NUM>;
b. Physical vapor depositing the at least three metals in a vacuum chamber from the target onto a removable cylindrical substrate and forming a coherent cylindrical bulk material ternary or quaternary alloy layer on the removable cylindrical substrate;
c. Removing the removable cylindrical substrate and cylindrical coherent bulk material ternary or quaternary alloy layer thereupon from the vacuum chamber; and
d. Removing the removable cylindrical substrate from the cylindrical coherent bulk material ternary or quaternary alloy layer.