Classifications

• • A—HUMAN NECESSITIES
  • A63—SPORTS; GAMES; AMUSEMENTS
  • A63B—APPARATUS FOR PHYSICAL TRAINING, GYMNASTICS, SWIMMING, CLIMBING, OR FENCING; BALL GAMES; TRAINING EQUIPMENT
  • A63B60/00—Details or accessories of golf clubs, bats, rackets or the like
• • A—HUMAN NECESSITIES
  • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
  • A61L—METHODS OR APPARATUS FOR STERILISING MATERIALS OR OBJECTS IN GENERAL; DISINFECTION, STERILISATION OR DEODORISATION OF AIR; CHEMICAL ASPECTS OF BANDAGES, DRESSINGS, ABSORBENT PADS OR SURGICAL ARTICLES; MATERIALS FOR BANDAGES, DRESSINGS, ABSORBENT PADS OR SURGICAL ARTICLES
  • A61L27/00—Materials for grafts or prostheses or for coating grafts or prostheses
  • A61L27/02—Inorganic materials
  • A61L27/04—Metals or alloys
• • A—HUMAN NECESSITIES
  • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
  • A61L—METHODS OR APPARATUS FOR STERILISING MATERIALS OR OBJECTS IN GENERAL; DISINFECTION, STERILISATION OR DEODORISATION OF AIR; CHEMICAL ASPECTS OF BANDAGES, DRESSINGS, ABSORBENT PADS OR SURGICAL ARTICLES; MATERIALS FOR BANDAGES, DRESSINGS, ABSORBENT PADS OR SURGICAL ARTICLES
  • A61L27/00—Materials for grafts or prostheses or for coating grafts or prostheses
  • A61L27/02—Inorganic materials
  • A61L27/04—Metals or alloys
  • A61L27/06—Titanium or titanium alloys
• • A—HUMAN NECESSITIES
  • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
  • A61L—METHODS OR APPARATUS FOR STERILISING MATERIALS OR OBJECTS IN GENERAL; DISINFECTION, STERILISATION OR DEODORISATION OF AIR; CHEMICAL ASPECTS OF BANDAGES, DRESSINGS, ABSORBENT PADS OR SURGICAL ARTICLES; MATERIALS FOR BANDAGES, DRESSINGS, ABSORBENT PADS OR SURGICAL ARTICLES
  • A61L27/00—Materials for grafts or prostheses or for coating grafts or prostheses
  • A61L27/28—Materials for coating prostheses
  • A61L27/34—Macromolecular materials
• • A—HUMAN NECESSITIES
  • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
  • A61L—METHODS OR APPARATUS FOR STERILISING MATERIALS OR OBJECTS IN GENERAL; DISINFECTION, STERILISATION OR DEODORISATION OF AIR; CHEMICAL ASPECTS OF BANDAGES, DRESSINGS, ABSORBENT PADS OR SURGICAL ARTICLES; MATERIALS FOR BANDAGES, DRESSINGS, ABSORBENT PADS OR SURGICAL ARTICLES
  • A61L31/00—Materials for other surgical articles, e.g. stents, stent-grafts, shunts, surgical drapes, guide wires, materials for adhesion prevention, occluding devices, surgical gloves, tissue fixation devices
  • A61L31/02—Inorganic materials
  • A61L31/022—Metals or alloys
• • A—HUMAN NECESSITIES
  • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
  • A61L—METHODS OR APPARATUS FOR STERILISING MATERIALS OR OBJECTS IN GENERAL; DISINFECTION, STERILISATION OR DEODORISATION OF AIR; CHEMICAL ASPECTS OF BANDAGES, DRESSINGS, ABSORBENT PADS OR SURGICAL ARTICLES; MATERIALS FOR BANDAGES, DRESSINGS, ABSORBENT PADS OR SURGICAL ARTICLES
  • A61L31/00—Materials for other surgical articles, e.g. stents, stent-grafts, shunts, surgical drapes, guide wires, materials for adhesion prevention, occluding devices, surgical gloves, tissue fixation devices
  • A61L31/08—Materials for coatings
  • A61L31/10—Macromolecular materials
• • A—HUMAN NECESSITIES
  • A63—SPORTS; GAMES; AMUSEMENTS
  • A63B—APPARATUS FOR PHYSICAL TRAINING, GYMNASTICS, SWIMMING, CLIMBING, OR FENCING; BALL GAMES; TRAINING EQUIPMENT
  • A63B53/00—Golf clubs
  • A63B53/04—Heads
  • A63B53/047—Heads iron-type
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C14/00—Alloys based on titanium
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22F—CHANGING THE PHYSICAL STRUCTURE OF NON-FERROUS METALS AND NON-FERROUS ALLOYS
  • C22F1/00—Changing the physical structure of non-ferrous metals or alloys by heat treatment or by hot or cold working
  • C22F1/16—Changing the physical structure of non-ferrous metals or alloys by heat treatment or by hot or cold working of other metals or alloys based thereon
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22F—CHANGING THE PHYSICAL STRUCTURE OF NON-FERROUS METALS AND NON-FERROUS ALLOYS
  • C22F1/00—Changing the physical structure of non-ferrous metals or alloys by heat treatment or by hot or cold working
  • C22F1/16—Changing the physical structure of non-ferrous metals or alloys by heat treatment or by hot or cold working of other metals or alloys based thereon
  • C22F1/18—High-melting or refractory metals or alloys based thereon
  • C22F1/183—High-melting or refractory metals or alloys based thereon of titanium or alloys based thereon
• • A—HUMAN NECESSITIES
  • A63—SPORTS; GAMES; AMUSEMENTS
  • A63B—APPARATUS FOR PHYSICAL TRAINING, GYMNASTICS, SWIMMING, CLIMBING, OR FENCING; BALL GAMES; TRAINING EQUIPMENT
  • A63B2209/00—Characteristics of used materials
• • A—HUMAN NECESSITIES
  • A63—SPORTS; GAMES; AMUSEMENTS
  • A63B—APPARATUS FOR PHYSICAL TRAINING, GYMNASTICS, SWIMMING, CLIMBING, OR FENCING; BALL GAMES; TRAINING EQUIPMENT
  • A63B2209/00—Characteristics of used materials
  • A63B2209/14—Characteristics of used materials with form or shape memory materials
• • A—HUMAN NECESSITIES
  • A63—SPORTS; GAMES; AMUSEMENTS
  • A63B—APPARATUS FOR PHYSICAL TRAINING, GYMNASTICS, SWIMMING, CLIMBING, OR FENCING; BALL GAMES; TRAINING EQUIPMENT
  • A63B53/00—Golf clubs
  • A63B53/04—Heads
• • A—HUMAN NECESSITIES
  • A63—SPORTS; GAMES; AMUSEMENTS
  • A63B—APPARATUS FOR PHYSICAL TRAINING, GYMNASTICS, SWIMMING, CLIMBING, OR FENCING; BALL GAMES; TRAINING EQUIPMENT
  • A63B53/00—Golf clubs
  • A63B53/04—Heads
  • A63B53/0416—Heads having an impact surface provided by a face insert
• • A—HUMAN NECESSITIES
  • A63—SPORTS; GAMES; AMUSEMENTS
  • A63B—APPARATUS FOR PHYSICAL TRAINING, GYMNASTICS, SWIMMING, CLIMBING, OR FENCING; BALL GAMES; TRAINING EQUIPMENT
  • A63B53/00—Golf clubs
  • A63B53/04—Heads
  • A63B53/0445—Details of grooves or the like on the impact surface

Definitions

• This disclosure relates to superelastic ⁇ titanium alloys, methods for manufacturing these alloys and articles derived therefrom.
• Alloys that undergo a martensitic transformation may exhibit a "shape memory effect".
• the high temperature phase known as "austenite” changes its crystalline structure through a diffusion-less shear process adopting a less symmetrical structure called 'martensite'.
• This process may be reversible as in shape memory alloys and therefore upon heating, the reverse transformation occurs.
• the starting temperature of the cooling or martensitic transformation is generally referred to as the M s temperature and the finishing temperature is referred to as the M f temperature.
• the starting and finishing temperatures of the reverse or austenitic transformation are referred to as A s and A f respectively.
• alloys undergoing a reversible martensitic phase transformation may be deformed in their high temperature austenitic phase through a stress-induced martensitic transformation as well as in their low temperature martensitic phase. These alloys generally recover their original shapes upon heating above the A f temperature and are therefore called "shape memory alloys".
• shape memory alloys At temperatures above the A f , the stress-induced martensite is not stable and will revert back to austenite upon the release of deformation.
• strain recovery associated with the reversion of stress-induced martensite back to austenite is generally referred to as "pseudoelasticity” or “superelasticity” as defined in ASTM F2005, Standard Terminology for Nickel-Titanium Shape Memory Alloys.
• the two terms are used interchangeably to describe the ability of shape memory alloys to elastically recover large deformations without a significant amount of plasticity due to the mechanically induced crystalline phase change.
• Nitinol is a shape memory alloy comprising a near-stoichiometric amount of nickel and titanium.
• pseudoelastic nitinol When deforming pseudoelastic nitinol, the formation of stress- induced-martensite allows the strain of the alloy to increase at a relatively constant stress. Upon unloading, the reversion of the martensite back to austenite occurs at a constant, but different, stress.
• a typical stress-strain curve of pseudoelastic nitinol therefore exhibits both loading and unloading stress plateaus. However, since the stresses are different, these plateaus are not identical, which is indicative of the development of mechanical hysteresis in the nitinol.
• Nitinol Deformations of about 8 to about 10% can thus be recovered in the pseudoelastic nitinol.
• Cold worked Nitinol also exhibits extended linear elasticity.
• Linear Superelasticity to differentiate from transformation induced “Pseudoelasticity” or “Superelasticity”.
• These properties generally make nitinol a widely used material in a number of applications, such as medical stents, guide wires, surgical devices, orthodontic appliances, cellular phone antenna wires as well as frames and other components for eye wear.
• nitinol is difficult to fabricate by forming and/or welding, which makes the manufacturing of articles from it expensive and time-consuming. Additionally, users of nickel containing products are sometimes allergic to nickel.
• a composition comprises about 8 to about 10 wt% molybdenum, about 2.8 to about 6 wt% aluminum, up to about 2 wt% vanadium, up to about 4 wt% niobium, with the balance being titanium, wherein the weight percents are based on the total weight of the alloy composition.
• a composition comprises about 8.9 wt% molybdenum, about 3.03 wt% aluminum, about 1.95 wt% vanadium, about 3.86 wt% niobium, with the balance being titanium.
• a composition comprises about 9.34 wt% molybdenum, about 3.01 wt% aluminum, about 1.95 wt% vanadium, about 3.79 wt% niobium, with the balance being titanium.
• a method for making an article comprises cold working a shape from a composition comprising about 8 to about 10 wt% molybdenum, about 2.8 to about 6 wt% aluminum, up to about 2 wt% vanadium, up to about 4 wt% niobium, with the balance being titanium, wherein the weight percents are based on the total weight of the alloy composition; forming the shape; solution heat treating the shape; and cooling the shape.
• a method comprises cold working a wire having a composition comprising about 8 to about 10 wt% molybdenum, about 2.8 to about 6 wt% aluminum, up to about 2 wt% vanadium, up to about 4 wt% niobium, with the balance being titanium, wherein the weight percents are based on the total weight of the alloy composition; cold working the shape; and heat treating the shape.
• Figure 1 is a graphical representation showing the effect of molybdenum content on elastic recovery
• Figure 2 is a graphical representation of the effect of aging at 350°C on the elastic recovery of Sample 4 from Table 1;
• Figure 3 is a graphical representation of the effect of aging at 350°C on the elastic recovery of Sample 5 from Table 1;
• Figure 4 is a graphical representation showing the effect of aging at 350°C on the elastic recovery of Sample 6 from Table 1;
• Figure 5 is a graphic representation showing the effect of aging at about 250 to about 550°C for 10 seconds on the elastic recovery of Sample 4 from Table 1;
• Figure 6 is a graphic representation showing the effect of aging at about 250 to about 550°C for 10 seconds on the elastic recovery of Sample 5 from Table 1;
• Figure 7 is a graphical representation showing the effect of cumulative cold drawing reduction on the UTS of Sample 11 from Table 2
• Figure 8 is a graphical representation showing the effect of cumulative cold drawing reduction on the Young's Modulus of Sample 11 from Table 2;
• Figure 9 is a graphical representation showing the effect of tensile stress-strain curve for a wire having the composition of Sample 11 from Table 2 with 19.4% drawing reduction, tested to 2% strain
• Figure 10 is a graphical representation showing the effect of tensile stress- strain curve for a wire having the composition of Sample 11 from Table 2 with 19.4% drawing reduction, tested to 4% strain
• Figure 11 is an optical micrograph showing the microstructure of a cold drawn wire having the composition of Sample 10 from Table 2 with a 14% reduction;
• Figure 12 is an optical micrograph showing partially recrystallized microstructure of a cold-drawn wire having the composition of Sample 10 from Table 2 having a 14% reduction after heat- treating at 816°C for 30 minutes;
• Figure 13 is an optical micrograph showing fully recrystallized microstructure of a cold-drawn wire having the composition of Sample 10 from Table 2 having a 14%o reduction after heat- treating at 871°C for 30 minutes;
• Figure 14 is an optical micrograph showing the microstructure of a betatized Sample 10 from Table 2 after aging at 816°C for 30 minutes;
• Figure 15 is an optical micrograph showing the microstructure of a betatized Sample 10 from Table 2 after aging at 788°C for 30 minutes;
• Figure 16 is a graphical representation showing the UTS of betatized Sample 10 from Table 2 after aging at 500-900°C for 30 minutes;
• Figure 17 is a graphical representation showing the ductility of betatized
• Figure 18 is a graphical representation showing a tensile stress-strain curve tested to 4% tensile strain of a wire having the composition of Sample 11 from Table 2 after strand annealing at 871°C; and Figure 19 is an optical micrograph showing the microstructure of a wire having the composition of Sample 11 from Table 2 after strand annealing at 871°C.
• a ⁇ titanium alloy composition having pseudoelastic properties and linear-superelastic properties that can be used for medical, dental, sporting good and eyewear frame applications.
• the ⁇ titanium alloy composition has linear elastic properties after solution treatment.
• the ⁇ titanium alloy composition has pseudoelastic properties that are improved with heat treatment.
• the ⁇ titanium alloy composition displays linear-superelastic properties after being cold worked.
• the composition advantageously can be welded to other metals and alloys.
• the articles manufactured from the ⁇ titanium alloy can also be deformed into various shapes at ambient temperature and generally retain the high spring back characteristics associated with superelasticity.
• Pure titanium has an isomorphous transformation temperature at 882°C.
• the body centered cubic (bcc) structure which is called /3-titanium, is stable above the isomorphous transformation temperature, and the hexagonal close packed (hep) structure, which is called a titanium is generally stable below this temperature.
• bcc body centered cubic
• hep hexagonal close packed
• the resulting alloys have an increased ⁇ phase stability at temperatures less than or equal to about 882°C ( ⁇ transus temperature).
• ⁇ transus temperature the temperature range of the stable phase is increased above the isomorphous transformation temperature.
• ⁇ stabilizers Elements which have the effect of increasing the ⁇ phase temperature range are called the ⁇ stabilizers, while those capable of extending the phase temperature range are called the a stabilizers.
• Titanium alloys having a high enough concentration of ⁇ stabilizers generally are sufficiently stable to have a meta-stable ⁇ phase structure at room temperature.
• the alloys showing such a property are called ⁇ titanium alloys.
• Martensite transformations are generally present in ⁇ titanium alloys.
• the martensitic transformation temperature in ⁇ titanium alloys generally decreases with an increasing amount of ⁇ stabilizer in the alloy, while increasing the amount of a stabilizer generally raises the martensitic transformation temperature. Therefore, depending on the extent of stabilization, ⁇ titanium alloys may exhibit a martensitic transformation when cooled rapidly from temperatures greater than those at which the ⁇ phase is the single phase at equilibrium.
• the ⁇ titanium alloy generally comprises an amount of about 8 to about 10 wt% of molybdenum, about 2.8 to about 6 wt% aluminum, up to about 2 wt% vanadium, up to about 4 wt% niobium, with the balance being titanium. All weight percents are based on the total weight of the alloy. Within the aforementioned range for molybdenum, it is generally desirable to have an amount of greater than or equal to about 8.5, preferably greater than or equal to about 9.0, and more preferably greater than or equal to about 9.2 wt% molybdenum. Also desirable within this range is an amount of less than or equal to about 9.75, preferably less than or equal to about 9.65, and more preferably less than or equal to about 9.5 wt% molybdenum, based on the total weight of the alloy.
• aluminum it is generally desirable to have an amount of greater than or equal to about 2.85, preferably greater than or equal to about 2.9, and more preferably greater than or equal to about 2.93 wt% aluminum. Also desirable within this range is an amount of less than or equal to about 5.0, preferably less than or equal to about 4.5, and more preferably less than or equal to about 4.0 wt% aluminum, based on the total weight of the alloy.
• niobium Within the aforementioned range for niobium, it is generally desirable to have an amount of greater than or equal to about 2, preferably greater than or equal to about 3, and more preferably greater than or equal to about 3.5 wt% niobium, based on the total weight of the alloy.
• the ⁇ titanium alloy it is generally desirable for the ⁇ titanium alloy to comprise 8.9 wt% molybdenum, 3.03 wt% aluminum, 1.95 wt% vanadium, 3.86 wt% niobium, with the balance being titanium.
• the ⁇ titanium alloy comprises 9.34 wt% molybdenum, 3.01 wt% aluminum, 1.95 wt% vanadium, 3.79 wt% niobium, with the balance being titanium.
• the ⁇ titanium alloy may be solution treated and/or thermally aged.
• solution treating the ⁇ titanium alloy the alloy is subjected to a temperature greater than or equal to about 850°C, the ⁇ transus temperature for the alloy.
• the solution treatment of the alloy is normally carried out in either vacuum or inert gas environment at a temperature of about 850 to about 1000°C, preferably about 850 to about 900°C, for about 1 minute or longer in duration depending on the mass of the part.
• the heating is followed by a rapid cooling at a rate greater than or equal to about 5°C/second, preferably greater than or equal to about 25°C/second, and more preferably greater than or equal to about 50°C/second, by using an inert gas quench or air cooling to retain a fully recrystallized single phase ⁇ grain structure.
• a rapid cooling at a rate greater than or equal to about 5°C/second, preferably greater than or equal to about 25°C/second, and more preferably greater than or equal to about 50°C/second, by using an inert gas quench or air cooling to retain a fully recrystallized single phase ⁇ grain structure.
• an inert gas quench or air cooling to retain a fully recrystallized single phase ⁇ grain structure.
• it is preferred that the quenched alloy is subsequently subjected to an ageing treatment at about 350 to about 550°C for about 10 seconds to about 30 minutes to adjust the amount of a fine precipitate of the ⁇ phase.
• the ⁇ titanium alloy may be solution treated at a temperature below the ⁇ transus temperature of about 750 to about 850°C, preferably about 800 to about 850°C, for about 1 to about 30 minutes to induce a small amount of ⁇ precipitates in the recrystallized ⁇ matrix.
• the amount of the ⁇ precipitates is preferably less than or equal to about 15 volume percent and more preferably less than or equal to about 10 volume percent, based on the total volume of the composition. This improves the tensile strength to an amount of greater than or equal to about 140,000 pounds per square inch (9,846 kilogram/square centimeter).
• the ⁇ titanium alloy in the solution treated condition may exhibit pseudoelasticity.
• the solution treated ⁇ titanium alloy generally exhibits a pseudoelastic recovery of greater than or equal to about 75% of the initial strain when elastically deformed to a 2% initial strain, and greater than or equal to about 50% of the initial strain when elastically deformed to a 4% initial strain.
• the initial strain is the ratio of the change in length to the original length of the alloy composition.
• the ⁇ titanium alloy in the solution treated condition may exhibit linear elasticity.
• the solution treated ⁇ titanium alloy generally exhibits a linear elastic recovery of greater than or equal to about 75% of the initial strain when elastically deformed to a 2% initial strain, and greater than or equal to about 50% of the initial strain when elastically deformed to a 4% initial strain.
• the initial strain is the ratio of the change in length to the original length of the alloy composition.
• the ⁇ titanium alloy may be cold worked by processes such as cold rolling, drawing, swaging, pressing, and the like, at ambient temperatures.
• the ⁇ titanium alloy may preferably be cold worked to an amount of about 5 to about 85% as measured by the reduction in cross-sectional area based upon the original cross sectional area.
• ⁇ titanium alloy in the cold worked state exhibits linear superelasticity where greater than or equal to about 75 % of the initial strain is elastically recoverable after deforming to a 2% initial strain, and greater than or equal to about 50% of the initial strain is elastically recoverable after deforming to a 4% initial strain.
• the elastic modulus of the ⁇ titanium alloy is reduced through cold working by an amount of greater than or equal to about 10, preferably greater than or equal to about 20 and more preferably greater than or equal to about 25% based upon the elastic modulus, after the alloy is heat treated.
• the ⁇ titanium alloy having linear elastic, linearly superelastic, pseudoelastic or superelastic properties may be used in the manufacturing of various articles of commerce. Suitable examples of such articles are eyewear frames, face inserts or heads for golf clubs, medical devices such as orthopedic prostheses, spinal correction devices, fixation devices for fracture management, vascular and non-vascular stents, minimally invasive surgical instruments, filters, baskets, forceps, graspers, orthodontic appliances such as dental implants, arch wires, drills and files, and a catheter introducer (guide wire).
• medical devices such as orthopedic prostheses, spinal correction devices, fixation devices for fracture management, vascular and non-vascular stents, minimally invasive surgical instruments, filters, baskets, forceps, graspers, orthodontic appliances such as dental implants, arch wires, drills and files, and a catheter introducer (guide wire).
• the superelastic ⁇ titanium alloy generally provides an adequate spring-back for eyewear applications. It is generally desired to use superelastic ⁇ titanium alloy having a minimum recovery of about 50% of the initial strain, when the alloy is deformed to an outer fiber initial strain of about 4% in a bend test. It is preferable to have a minimum recovery of greater than or equal to about 75% of the initial strain when the alloy composition is deformed to about 4% of the outer fiber initial length in a bend test. It is also generally desirable for the superelastic ⁇ titanium alloy to have a minimum recoverable strain of about 50% of the initial strain, when the alloy composition is strained to about 4% initial tensile strain.
• the strain recovery is measured as a function of the initial bending strain and the initial bending strain is expressed as a percentage of the ratio of the change in length to the original length.
• All of the sample alloys discussed below were prepared by a double vacuum arc melting technique.
• the ingots were hot rolled and flattened to sheets having a thickness of 1.5 millimeter (mm).
• the sheets were then heat treated at 870°C for 30 minutes in air and air cooled to ambient temperature. Oxides on the sheets were removed by double-disc grinding and lapping to a thickness of 1.3 mm.
• Heat aging experiments were conducted at 350°C using a nitride/nitrate salt bath. Permanent deformation and pseudo-elastic recovery strains were determined using bend tests. Specimens having dimensions 0.51 mm x 1.27 mm x 51 mm were cut from the sheets.
• Tensile strain recovery was measured by tensile elongation to a strain of 4% followed by unloading to zero stress. Tensile specimens with a cross sectional dimension of 0.90 mm x 2.0 mm were used and the strain was monitored using an extensometer. An environmental chamber with electrical heating and CO 2 cooling capabilities provided a testing capability from -30°C to 180°C. Nine ⁇ titanium alloys having the compositions listed in Table 1 were examined. The percentage of the elastic recovery strain with respect to the total bend strain was measured for comparison.
• Sample 1 and Samples 6 - 9 are comparative examples.
• the results of elastic recovery after bending to approximately 4% outer fiber strain is graphically demonstrated in Figure 1.
• the figure shows a maximum elastic strain recovery at about 9 wt% molybdenum, where the alloy after solution heat treatment and subsequent air cooling, exhibits an elastic recovery strain of approximately 80% of the applied 4%> deformation strain.
• Increasing or decreasing the molybdenum content from 9 wt%> generally results in decreasing elastic recovery.
• an aging treatment at 350°C for a short duration of 10 seconds results in an improved elastic recovery, for titanium alloys having a molybdenum content between 8.4 and 11 wt%.
• the optimal elastic strain recovery after heat aging at 350°C for 10 seconds for the alloy having about 9 wt% molybdenum is approximately 90% of the applied 4% bend strain. Alloys with a molybdenum content less than 8.4 wt% exhibit a different aging characteristic. Aging at 350°C may degrade elastic strain recovery as for alloy 2 having about 8.03 wt% molybdenum, or has no significant effect as for alloy 1 having about 7.63 wt% molybdenum.
• the percents of the elastic recovery to the total deformation during thermal aging at about 250 to about 550°C for 10 seconds for Samples 4 and 5 respectively are plotted in the Figures 5 and 6, respectively.
• An optimal for Sample 4 appears at 350°C, which improves the elastic recovery to a percentage close to 90% while aging at temperatures equal to or higher than 400°C degrade elastic recovery to about 40%.
• aging in this temperature range generally improves the elastic recovery.
• the maximum improvement occurs at about 450°C where the elastic recovery is improved to 90%.
• the alloys shown in Table I also exhibit linear superelasticity after cold working with a reduction of greater than or equal to about 30% in the cross-sectional area.
• a wire fabricated from an ingot having a composition of 11.06 wt% molybdenum, 3.80 wt% niobium, 1.97 wt% vanadium, 3.07 wt% aluminum with the remainder being titanium exhibited an elastic recovery strain of 3.5% after bending to a total deformation of 4% outer fiber strain, when the reduction in the cross sectional area after cold working was 84%.
• the ⁇ titanium alloys were manufactured by double vacuum arc melting. Chemistries of the alloys were analyzed using inductively coupled plasma optical emission spectrometry (ICP-OE). The results are tabulated in Table 2.
• the ingot was hot-forged, hot-rolled and finally cold-drawn to wire of various diameters in the range of about 0.4 to about 5 mm.
• Inter-pass annealing between cold reductions was carried out at 870°C in a vacuum furnace for wires having a diameter of larger than 2.5 mm or by strand annealing under inert atmosphere for the smaller diameters.
• Tensile properties were determined using an Instron model 5565 material testing machine equipped with an extensometer of 12.5 mm gage length. Microstructures were studies by optical metallography using a Nikon Epiphot inverted metallurgical microscope. Table 2
• the strand-annealed wires generally have a higher ultimate tensile strength (UTS) around 1055 mega Pascals (MPa) than vacuum annealed wires and sheets, the typical UTS of which is about 830 MPa.
• UTS ultimate tensile strength
• Figure 7 plots the UTS of wires drawn from an annealed 1.0 mm diameter Sample 11 wire stock as a function of reduction in cross-section area. After a 49% reduction, the UTS was elevated from 1055 MPa to only 1172 MPa indicating a fairly weak strain hardening effect. Young's Modulus was determined by tensile testing the wire to 1% strain and measuring the linear slope of the stress-strain curve. As shown in Figure 8, cold-drawn wires generally have a lower modulus than does annealed wire.
• the modulus of approximately 65.9 gigapascals (GPa) for the annealed wire, decreases with increasing accumulative amount of reduction and stabilizes at approximately 50 GPa after cold drawing with a cumulative reduction greater than 20%.
• Samples 10 and 11 exhibit linear superelasticity after cold working. Loading and unloading stress-strain curves tested to 2% and 4% tensile strains of a cold drawn, 0.91 mm diameter wire of Sample 11 with a 19.4% reduction are plotted in Figures 9 and 10, respectively. As may be seen in Figure 7, after unloading, following a 2% tensile elongation, the wire recovers the majority of the deformation leaving only a small plastic deformation of 0.1 %> strain.
• a micrograph in Figure 11 reveals the cold- worked microstructure of the
• Sample 10 wires hot-rolled to 8.6 mm in diameter were further drawn down to 6.0 mm diameter. After being fully betatized at 871°C for 30 minutes the 6.0 mm diameter wires were again aged at temperatures of about 500 to about 850°C for 30 minutes. As can be seen in Figure 14, the ⁇ structure was preserved after aging at 816°C. When the aging temperature was lowered to 788°C, intragranular ⁇ -phase precipitates began to appear in the microstructure as may be seen in Figure 15. The amount of intragranular ⁇ -phase precipitate increased with decreasing aging temperature, ⁇ -phase precipitates eventually appeared along the grain boundary when aged at 649°C and below.
• a transverse cross-sectional view of the wire microstructure is shown in a micrograph of Figure 19.
• the microstructure consists of equiaxial ⁇ precipitates in ⁇ matrix. It appears that the short duration of strand annealing did not allow the wire to fully recrystallize into the ⁇ grain structure. Without being limited by theory, it is believed that this may explain why strand- annealed wire generally has a higher UTS when compared to that of a fully betatized material.
• the ⁇ titanium alloys can display an elastic strain recovery of 88.5%, when subjected to an initial bending strain of 4%.
• the strain recovery is measured as a function of the initial bending strain and the initial bending strain is expressed as a percentage of the ratio of the change in length to the original length.
• These alloys may be advantageously used in a number of commercial applications such as eyewear frames, face insert and heads for golf clubs, orthodontic arch wires, orthopedic prostheses and fracture fixation devices, spinal fusion and scoliosis correction instruments, stents, a catheter introducer (guide wire) and the like. While the invention has been described with reference to exemplary embodiments, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the invention.

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• 2003
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