Fatigue damage resistant wire and method of production thereof
AssigneeFort Wayne Metals Research Products Corporation
InventorJeremy E. Schaffer
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Abstract
Fatigue damage resistant metal or metal alloy wires have a submicron-scale or nanograin microstructure that demonstrates improved fatigue damage resistance properties, and methods for manufacturing such wires. The present method may be used to form a wire having a nanograin microstructure characterized by a mean grain size that is 500 nm or less, in which the wire demonstrates improved fatigue damage resistance. Wire manufactured in accordance with the present process may show improvement in one or more other material properties, such as ultimate strength, unloading plateau strength, permanent set, ductility, and recoverable strain, for example. Wire manufactured in accordance with the present process is suitable for use in a medical device, or other high end application.
Claims24
A metallic wire comprising an implant grade, metal or non-shape memory metal alloy having one of a diameter and a thickness less than 1.0 mm, and a mean grain size of less than 500 nanometers.
A method of forming a wire made of an implant grade, metal or non-shape memory metal alloy, comprising the steps of:
- providing a wire having a relatively larger diameter D1;
- subjecting the wire to cold work conditioning to impart one of:
- i) 50% and 99.9% cold work and ii) 0.69 and 6.91 units of true strain by drawing the wire to a relatively smaller diameter D2, wherein % cold work is determined by the following formula:
- c
-
-
- w
- =
- 1
- -
- (
- D
- 2
- D
- 1
- )
- 2
- and true strain is determined by the following formula:
- t
-
-
- s
- =
- ln
-
- (
- (
- D
- 1
- D
- 2
- )
- 2
- )
- ;
- and
- annealing the wire to create a crystal structure having a mean grain size of less than 500 nanometers.
A wire made of nickel-titanium shape memory material, having an average grain size of less than 300 nm, and being substantially free of TixNiy precipitates that exceed 5 nanometers in size.
A method of forming a wire made of nickel-titanium shape memory material, comprising the steps of:
- providing a wire having a relatively larger diameter D1;
- subjecting the wire to cold work conditioning to impart between 15% and 45% cold work by drawing the wire to a relatively smaller diameter D2, wherein the percent cold work is determined by the following formula:
- c
-
-
- w
- =
- 1
- -
- (
- D
- 2
- D
- 1
- )
- 2
- ;
- and
- annealing the wire at a temperature of between 300° C. and 600° C. for a dwell time of between 0.2 and 900 seconds, wherein said annealing creates a crystal structure having an average grain size of less than 500 nanometers.
Dependencies are inferred from the claim text.