Classifications

• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B22—CASTING; POWDER METALLURGY
  • B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
  • B22F3/00—Manufacture of workpieces or articles from metallic powder characterised by the manner of compacting or sintering; Apparatus specially adapted therefor ; Presses and furnaces
  • B22F3/22—Manufacture of workpieces or articles from metallic powder characterised by the manner of compacting or sintering; Apparatus specially adapted therefor ; Presses and furnaces for producing castings from a slip
  • B22F3/225—Manufacture of workpieces or articles from metallic powder characterised by the manner of compacting or sintering; Apparatus specially adapted therefor ; Presses and furnaces for producing castings from a slip by injection molding
• • 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
  • A61L27/042—Iron or iron 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
  • A61L27/045—Cobalt or cobalt 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
  • A61L27/047—Other specific metals or alloys not covered by A61L27/042 - A61L27/045 or A61L27/06
• • 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
  • 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
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B22—CASTING; POWDER METALLURGY
  • B22D—CASTING OF METALS; CASTING OF OTHER SUBSTANCES BY THE SAME PROCESSES OR DEVICES
  • B22D15/00—Casting using a mould or core of which a part significant to the process is of high thermal conductivity, e.g. chill casting; Moulds or accessories specially adapted therefor
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B22—CASTING; POWDER METALLURGY
  • B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
  • B22F3/00—Manufacture of workpieces or articles from metallic powder characterised by the manner of compacting or sintering; Apparatus specially adapted therefor ; Presses and furnaces
  • B22F3/17—Manufacture of workpieces or articles from metallic powder characterised by the manner of compacting or sintering; Apparatus specially adapted therefor ; Presses and furnaces by forging
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C1/00—Making non-ferrous alloys
  • C22C1/12—Making non-ferrous alloys by processing in a semi-solid state, e.g. holding the alloy in the solid-liquid phase
• • 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
• • 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
  • C22F1/10—Changing the physical structure of non-ferrous metals or alloys by heat treatment or by hot or cold working of nickel or cobalt 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
• • 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
  • C22F1/186—High-melting or refractory metals or alloys based thereon of zirconium or alloys based thereon
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B22—CASTING; POWDER METALLURGY
  • B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
  • B22F2998/00—Supplementary information concerning processes or compositions relating to powder metallurgy
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
  • Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
  • Y02P10/00—Technologies related to metal processing
  • Y02P10/25—Process efficiency

Definitions

• the present invention relates to metal objects which may be formed using casting, incremental forming, or consolidation processes followed by wrought processes. Such objects exhibit favorable properties, including ductility and strength, with reduced cost and lead-time.
• the present invention combines pre-wrought processes with conventional wrought processes to produce wrought orthopaedic components at reduced cost and lead-time, but comparable to conventional forgings in ductility and strength.
• any orthopaedic alloy such as Co-28Cr-6Mo, stainless steel, Ti-alloys or Zr-alloys, may be manufactured using the combined processes according to this invention.
• These combined processes may also apply to several orthopaedic components, such as hip stems, knee femorals, tibial trays, or skeletal fixation plates.
• this invention could easily be applied to forged hip stems and tibial trays made of either Co-28Cr-6Mo or Ti-6AI-4V.
• the wrought barstock used conventionally for forging feedstock is replaced with a bar or preform cast in metal molds and exhibiting the required ductile strength and refined grain structure to be forgeable.
• Other methods for producing a bar or preform with sufficient forgeability may be used such as metal powder consolidation forming, metal injection molding, solid free form fabrication, metal rapid prototyping, laser and electron beam forming, spray forming, and semi- solid forming processes, so long as the process produces the fine grain structure and ductility, and if desired, low-notch brittleness and other properties according to the present invention as discussed herein.
• pre- wrought processes in addition to forming the pre- wrought material using a metal mold, there are at least two other categories of pre- wrought processes according to the present invention: (1 ) processes that achieve the necessary ductility and refined grain structure for wrought processing through rapid heat removal through the component or a quenching atmosphere; and (2) pre-wrought processes that achieve the necessary ductility and refined grain structure through consolidation of powder or semi-solid material under conditions which restrict coarsening of the grain structure.
• This material, bar or preform may then be forged using one or more forging or wrought processes to produce grain size refinement and increase in material integrity.
• Appropriate forging or wrought methods that give the final shape and properties to the material, bar or preform include: presses (screw, mechanical, hydraulic), hammering, rolling, extruding or upsetting, cold forging, any thermal / mechanical forming process, or any other suitable process for producing wrought metal objects.
• the term "forging” as used in this document means any or all of such processes.
• material for the wrought process is produced using metal mold casting or another forming process which produces requisite ductility and grain size, and then preshaped.
• One option is to produce an oversized bar in the shape of wrought barstock which would be subsequently swaged, upset, extruded, or bent to distribute the material closer to the shape of the final product.
• a second option is to utilize an oversized preform shape resembling the final product.
• the preshaped bar or preform is subsequently forged to produce an orthopaedic product that meets the minimum requirements specified in appropriate industry standards for conventionally forged products.
• Materials suitable for processes according to the present invention include CoCr alloys. Alloys similar to CoCr alloys can also be appropriate, for example Ni-alloys. In these systems, the maximum forging temperature is limited by dissolution or precipitation of second phases.
• the material to be forged must have a refined grain structure in order to prevent cracking or non-uniform flow during the forging operation.
• Other alloy systems which would require a refined grain size to be made forgeable may also be processed according to the present invention.
• high forging temperatures are required to break down a coarse cast grain structure; an intermediate step is often required to refine the original cast structure. Starting with a refined grain structure in accordance with the present invention may eliminate this additional step and reduce cost.
• the present invention can also be used to produce original alloy compositions that are not commercially available in barstock form.
• Pre-wrought processes according to the invention allow for the production of new alloys not currently available, such as new or custom alloy compositions. These alloys can then be wrought to produce high quality products which could not be produced by the conventional barstock/forging method cost-effectively.
• a refined grain size is again required to make these new alloys forgeable. For example, new titanium, zirconium or stainless steel alloy compositions may fall into this category.
• the combined processes according to the present invention may be used to produce a variety of orthopaedic components, including but not limited to: total hip systems: stems, femoral heads, unipolar heads, distal sleeves, trial necks, bipolar shells, stem endoprosthesis; acetabular systems: shells, rings; total knee systems: femoral components, femoral lugs, tibial components, conversion modules, wedges, stems; total shoulder systems: stem humeral components, glenoid metal-backed components, skeletal fixation systems: hip screw nails, hip screw plates, screws, pins, rings, posts, cubes; instrumentation: possibly all metallic instruments including broaches, reamers, collets, guides, handles, trials, osteotomes, impactors, and cutting blocks.
• Advantages of processes according to the invention over conventional use of wrought barstock as forging feedstock include a reduction in product cost through reduction in material cost (less material used and less scrap), reduction of the number of operations involved in making the final product, and reduction in delivery and manufacturing lead time.
• Advantages of the permanent mold casting processes of the invention over using disposable ceramic shells in investment casting for bar or preform production include reduction in processing cost through reduction in the number of operations involved in the casting process, reduction in manufacturing lead time, enhanced casting process repeatability, improved dimensional accuracy and stability of the castings, and reduction of impurities in the casting.
• Figure 1 is a schematic process flow diagram for a conventional casting process.
• Figure 2 is a schematic process flow diagram for a first set of pre-wrought processes according to the present invention.
• Figure 3 is a schematic process flow diagram for a second set of pre-wrought processes according to the present invention.
• Figure 4 is an optical micrograph of metal mold cast Co-28Cr-6Mo from Example 1 , as discussed below.
• Figures 5-1 , 5-2, 5-3, 5-4, 5-6 and 5-7 are optical micrographs of compression tested metal mold cast Co-28Cr-6Mo with respective specimen numbers from Example 1 , as discussed below.
• Figures 6a and 6b, left and right respectively, are optical micrographs of conventional wrought Co-28Cr-6Mo.
• Figures 7a and 7b, left and right respectively, are optical micrographs of metal mold cast Co-28Cr-6Mo from Example 2, as discussed below.
• Figures 8a and 8b, left and right respectively, are optical micrographs of conventional investment cast Co-28Cr-6Mo.
• Figure 9 is an optical micrograph of MIM Co-28Cr-6Mo.
• wrought barstock used conventionally for forging feedstock is replaced with a metal mold cast bar, perform or other material exhibiting the required ductile strength and refined grain structure to be forgeable.
• Other methods for producing a bar or preform with a sufficient forgeability may be used such as metal powder consolidation forming, metal injection molding, solid free form fabrication, metal rapid prototyping, laser and electron beam forming, spray forming, and semi-solid forming processes, so long as the process provides sufficient heat transfer to impart a sufficiently rapid cooling rate in order to produce the fine grain structure and ductility, and, if desired, low-notch brittleness and other properties according to the present invention as discussed herein.
• This bar or preform may then be forged using a wrought process to produce grain size refinement and increase in material integrity.
• pre- wrought processes there are at least two other categories of pre- wrought processes according to the present invention: (1) processes that achieve the necessary ductility and refined grain structure for wrought processing through rapid heat removal through the component or a quenching atmosphere; and (2) processes that achieve the necessary ductility and refined grain structure through consolidation of powder or semi-solid material under conditions which restrict coarsening of the grain structure.
• Figure 1 show steps in a conventional casting process.
• any of the pre-wrought processes of the present invention mentioned in the paragraph above may be succeeded by a preshaping step before forging (and if necessary or desired, finishing).
• forging may occur without preshaping.
• Appropriate forging methods which give the final shape and properties to the bar/preform include: presses (screw, mechanical, hydraulic), hammering, rolling, extruding or upsetting, cold forging, any thermal / mechanical forming process, or any other suitable process for producing wrought metal objects.
• Objects of the pre-wrought process include to produce the bar or preform having at least sufficient ductility and refined grain size for the subsequent wrought process.
• Metal mold casting is the first category of such pre-wrought processes according to the present invention.
• Metal mold casting processes suitable for the present invention are disclosed in G. N. Colvin, "Permanent mold casting of titanium aerospace and automotive hardware", Titanium '95: Science and Technology, P. A. Blemkishop, W. J. Evans, and H. M.
• Examples of the second category of pre-wrought processes according to the present invention in which the necessary ductility and refined grain structure are obtained through rapid heat removal through the material, bar or preform already formed or accreted, or through a quenching medium or atmosphere, include laser and electron beam forming and spray forming, where the material accretes incrementally while heat flows into the material already formed and/or the medium or atmosphere, or both, during or after application of the material.
• the third category of pre-wrought processes according to the present invention includes processes that achieve the necessary ductility and refined grain structure through consolidation of powder or semi-solid material under conditions which restrict coarsening of the grain structure.
• MIM Metal Injection Molding
• PMM Powder Metal Molding
• PIM Powder Injection Molding
• the MIM process involves combining metal powder with a polymer binder and injection molding the part. Once the part has been molded, the binder is removed, and the part is then sintered to increase the density of the part. These debinding and sintering operations must be conducted at temperatures and other conditions that prevent excessive grain coarsening of the metal. Suitable forms of MIM in accordance with the present invention are disclosed in the following reference which is incorporated herein by this reference: R.M. German, Powder Metallurgy Science 2 nd ed., Metal Powder Industries Federation, Princeton, NJ (1994).
• fine grain specimens were produced for high temperature compression testing that simulates wrought processing.
• Metal mold casting was used to produce Co-28Cr-6Mo bars, about 1.5 cm (0.6 in) in diameter and 46 cm (18 in) in length. Specimens were machined from these bars to a diameter of 1.3 cm (0.5 in) and cut to length with a height to diameter aspect ratio of 1.2. Concentric grooves were machined on the top and bottom of the specimens and boron nitride spray was used at the specimen/die interface to minimize frictional effects. A small hole was drilled into the center of the specimen to place a thermocouple to monitor the temperature during testing. These specimens were tested on a high temperature, controlled atmosphere (argon) compression system.
• argon controlled atmosphere
• a matrix of process parameters included two temperatures (1125 and 1175°C), two strain rates (1 and 10 sec “1 ), and three strains (0.10, 0.25, and 0.50) that were selected to be representative of practical forging parameters for CoCr alloys [See “Forging of heat-resist alloys, Forming and Forging, Volume 14, Metals Handbook Ninth Edition, ASM International, Ohio 231-36 (1998) which is incorporated herein by this reference.].
• the selected strain was produced, the specimens were gas-quenched using a high rate argon flow.
• the engineering stress/strain data were corrected for frictional effect and adiabatic heating. [See M. Long and H. J. Rack: "Thermo-mechanical stability of forged Ti-26AI-10Nb-3V-1 Mo (at.%)", Materials Science & Engineering, A194, 99-111 (1995) incorporated herein by this reference.]
• the original metal mold cast microstructure is shown in Figure 4. All of the compression tests produced a reduction in grain size, as shown in Figure 5 (note the increase in magnification relative to Figure 4), although grain size refinement was not uniform across some specimens (specimen #2 for example). This indicated that recrystallization did not occur fully throughout the specimen. However, the parent grains from the original cast microstructure appeared always to be reduced. It appeared that higher temperature, faster strain rate, and large strain produced more uniform refined microstructure.
• Table 1 A summary of the grain size measurements is given in Table 1.
• the original grain size of the metal mold cast material was 293 ⁇ m. After deformation, average grain size values ranged from 10.8 to 17.1 ⁇ m. This represented approximately 95% reduction in grain size.
• the grain size of a typical conventional wrought component (produced in accordance with ASTM F-799-96, which is incorporated by this reference) is 8.0 ⁇ m, as illustrated in Figure 6. Based on grain size measurements, the cast-forge material approaches grain sizes comparable to conventional wrought microstructures. It can then be expected that material processed in accordance with the present invention can have wrought-like properties acceptable for forged products. Table 1. Summary of grain size measurements.
• Example 1 greater reduction in grain size than demonstrated in Example 1 may be desired to achieve higher strength values after wrought processing. This may be achieved by reducing the grain size of the original pre- wrought material or by optimizing the wrought process.
• a critical aspect of this invention is that the fine grain structure of the bar or preform provides improved ductile strength and sufficient forgeability to the material. It is believed that an elongation greater than 18% and an average grain size finer than 300 ⁇ m, and more preferably below 150 ⁇ m, are required for a Co-28Cr-6Mo bar/preform, such as produced by metal mold casting, to be wrought processed to produce a product with favorable properties. Average grain size values for conventional investment castings range from about 300 to 1400 ⁇ m, typical examples being shown in Figure 8.
• Castings that exhibit this range of grain size are considered to be not forgeable by the forging industry. Furthermore, refined carbides may also improve forgeability; large blocky carbides are typically observed in conventional investment castings.
• Metal mold casting of Co-28Cr-6Mo such as for example the gravity metal mold casting process, can produce an average grain size of about 100 to 150 ⁇ m, as shown in Figure 7.
• Other metal mold casting processes with faster heat removal, such as for example vacuum die casting have the potential to produce even finer grain size.
• Table 3 shows the results for both materials.
• the MIM CoCr material exhibited 47% greater tensile strength, 6% greater yield strength, 145% greater ductility, and 4 to 20 times smaller grains compared to conventional investment cast CoCr.
• Figure 9 shows that both the grain size for the MIM material is more refined than for the conventional investment cast material shown in Figure 8.
• the MIM material also has more finely dispersed carbides than conventional investment cast material which are effective in impeding grain growth during the HIP and ST processes.
• the improved mechanical properties for MIM CoCr are attributed to its refined grain structure and fine carbide size.

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