Classifications

• • 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
  • 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

Definitions

• the invention relates to a nanostructured material and, more particularly, a
• nanostructured titanium alloy having a developed a-titanium structure with enhanced material properties.
• microstructure plays a key role in the establishment of mechanical properties.
• a material's structure can be developed to enhance material properties. For instance, it is possible to modify the grain or crystalline structure of the material using mechanical, or thermo-mechanical processing techniques.
• United States Patent Application 2011/0179848 discloses a commercially pure titanium product having enhanced properties for biomedical applications.
• the titanium product has a nanostructure, which provides enhanced properties in relation to the original mechanical properties, including mechanical strength, resistance to fatigue failure, and biomedical properties.
• the known titaniu m product is first subject to severe plastic deformation (SPD) using an equal channel angular pressing (ECAP) technique at a temperature no more than 450° C with the total true accumulated strain e ⁇ 4, and then subsequently developed using thermomechanical treatment with a strain degree from 40 to 80%.
• an object of the invention is to increase the level of strength and fatigue resistance of a titaniu m alloy.
• the nanostructu red alloy includes a developed titanium structure having at least 80% of grains of a size ⁇ 1.0 microns.
• Figure 1 is a micrograph of a known commercially pure titanium alloy taken using electron back scatter diffraction
• Figure 2 is a micrograph of a nanostructured commercially pure titanium alloy accord ing to the invention taken using electron back scatter diffraction;
• Figure 3 is a graphical representation, obtained using electron back scatter diffraction, showing the grain size distribution of the known commercially pure titanium alloy
• Figure 4 is a graphical representation, obtained using electron back scatter diffraction, showing the grain size distribution of the nanostructured commercially pure titanium alloy according to the invention.
• Figure 5 is a graphical representation, obtained using electron back scatter diffraction, showing the misorientation angle distribution of the known commercially pure titanium alloy
• Figure 6 is a graphical representation, obtained using electron back scatter diffraction, showing the misorientation angle distribution of the nanostructured commercially pure titanium alloy according to the invention.
• Figure 7 is a graphical representation, obtained using electron back scatter diffraction, showing the grain shape aspect ratio distribution in the longitudinal plane of the nanostructu red commercially pure titanium alloy accord ing to the invention.
• Figure 8 is a graphical representation, obtained using electron back scatter diffraction, showing the grain shape aspect ratio distribution in the transverse plane of the nanostructured commercially pure titanium alloy accord ing to the invention.
• Figure 9 is a micrograph of the commercially pure nanostructured titanium alloy according to the invention having a plurality of equiaxed grains, obtained using transmission electron microscopy;
• Figure 10 is a micrograph of the commercially pure nanostructured titanium alloy according to the invention having a plurality of grains with high dislocation density, obtained using transmission electron microscopy;
• Figure 11 is a micrograph of the commercially pure nanostructured titanium alloy according to the invention showing a plurality of sub-grains, obtained using transmission electron microscopy;
• Figure 12 is a micrograph of a known titanium alloy Ti6AI4V taken using electron back scatter diffraction
• Figure 13 is a micrograph of a nanostructured titanium alloy Ti6AI4V according to the invention taken using electron back scatter diffraction;
• Figure 14 is a graphical representation, obtained using electron back scatter diffraction, showing the grain size distribution of the nanostructured titanium alloy Ti6AI4V according to the invention.
• Figure 15 is a graphical representation, obtained using electron back scatter diffraction, showing the misorientation angle distribution of a known titanium alloy Ti6AI4V;
• Figure 16 is a graphical representation, obtained using electron back scatter diffraction, showing the misorientation angle distribution of the nanostructured titanium alloy Ti6AI4V according to the invention.
• Figure 17 is a micrograph of a known titanium alloy Ti6AI4V ELI taken using electron back scatter diffraction
• Figure 18 is a micrograph of a nanostructured titanium alloy Ti6AI4V ELI according to the invention taken using electron back scatter diffraction;
• Figure 19 is a graphical representation, obtained using electron back scatter diffraction, showing the grain size distribution of the nanostructured titanium alloy Ti6AI4V ELI according to the invention.
• Figure 20 is a graphical representation, obtained using electron back scatter diffraction, showing the misorientation angle distribution of a known titanium alloy Ti6AI4V ELI.
• Figure 21 is a graphical representation, obtained using electron back scatter diffraction, showing the misorientation angle distribution of the nanostructured titanium alloy Ti6AI4V ELI according to the invention.
• the invention is a nanostructu red titanium alloy that can be used in different industries for production of various useful articles, such as orthopedic implants, medical and aerospace fasteners, aerospace structural components, and high performance sporting goods.
• a composition of commercially pure titanium having an a-titaniu m matrix that may contain retained ⁇ -titanium particles, is processed to develop the structure to achieve a nanostructure with at least 80% of the grains being ⁇ 1 micron.
• the nanostructured titanium alloy exhibits various material property changes such as an increase in tensile strength and/or shear strength and/or fatigue endurance limit.
• the nanostructured titanium alloy structure is developed using a combination of thermomechanical processing steps according to the invention. This process provides a developed microstructure having a preponderance of ultrafine grain and/or nanocrystalline structures.
• Figures 1, 12, and 17 show the starting commercially pure titanium alloy, Ti6AI4V, and Ti6AI4V ELI microstructure, respectively.
• Figures 2, 13, and 18 show the resulting structure of the nanostructured commercially pure titanium alloy, Ti6AI4V, and Ti6AI4V ELI according to the invention, respectively. Examination of the figures clearly shows the d ifference between the starting and nanostructured titanium alloys.
• the workpiece can be comprised of various commercially available titanium alloys known in the art, such as commercially pure titanium alloys (Gradesl-4), Ti-6AI-4V, Ti-6A1-4V ELI, ⁇ -6 ⁇ - 7N b, Ti-Zr, or other known alpha, near alpha, and alpha-beta phase titanium alloys.
• an alpha-beta phase titanium alloy is processed from a combination of a severe plastic deformation process type and non-severe plastic deformation type thermomechanical processing steps to develop a nanostructure with at least 80% of the grains being ⁇ 1 micron.
• a coarse grain commercially pu re titaniu m alloy is used for the workpiece, which has the following composition by weight percent: nitrogen (N ) 0.07% maximum, carbon (C) 0.1% maximu m, hydrogen (H) 0.015% maximum, iron (Fe) 0.50% maximu m, oxygen (O) 0.40% maximum, total of other trace impurities is 0.4% maximu m, and titanium (Ti) as the balance.
• titanium alloys may be used, including but not limited to other commercially pure titanium alloys, Ti-6AI-4V, Ti-6A1-4V ELI, Ti-6AI-7Nb, and Ti-Zr. Standard chemical compositions of these titanium alloys can be fou nd in Tables 1-3, which identify the standard chemical compositions by wt% max.
• the workpiece for instance a rod or bar, is subjected to severe plastic deformation ("SPD") and thermomechanical processing.
• SPD severe plastic deformation
• the combined processing steps induce a large amount of shear deformation that significantly refines the initial structure by creating a large number of high angle grain boundaries (misorientation angle > 15°) and high dislocation density.
• the workpiece is processed using an equal channel angular pressing - conform (ECAP-C) machine, which consists of a revolving wheel having a circumferential groove and two stationary dies that form a channel that intersect at a defined angle.
• ECAP-C equal channel angular pressing - conform
• the workpiece is pressed into the wheel groove and is driven through the channel by frictional forces generated between the workpiece and the wheel.
• a commercially pure titanium alloy workpiece is processed through the ECAP-C machine at temperatures below 500°C, preferably 100-300°C.
• Other titanium alloys: Ti6AI4V, Ti6AI4V ELI, and Ti6Al7N b are processed through the ECAP-C machine at a temperature below 650°C, preferably 400- 600°C.
• the workpiece passes through the ECAP-C machine between 1 and 12 times, preferably 4 to 8 times.
• ECAP route B c This method of rotation is known as ECAP route B c .
• the ECAP route may be changed, including but not limited to known routes A, C, B A , E, or some combination thereof.
• thermomechanical processing further evolves the structu re of the workpiece, more than the ECAP-C alone.
• one or more thermomechanical processing steps may be carried out, including but not limited to drawing, rolling, extrusion, forging, swaging, or some combination thereof.
• the thermomechanical processing for commercially pure titanium alloy is carried out at temperatures T ⁇ 500°C, preferably room temperatu re to 250°C.
• Thermomechanical processing of titanium alloys Ti6AI4V, Ti6AI4V ELI, and Ti6Al7N b is carried out at temperatures not greater than 550°C, preferably 400-500°C.
• Thermomechanical processing provides a cross-sectional area reduction of > 35%, preferably > 65%.
• the combination of severe plastic deformation and thermomechanical processing substantially refines the initial structure, which consists of an a-titaniu m matrix that may contain retained ⁇ -titanium particles, to a predominantly submicron grain size.
• the ECAP-C process fragments the starting grain structure by introducing large numbers of twins and dislocations that organize to form dislocation cells with walls having a low misorientation angle ⁇ 15°.
• the resulting nanostructured titanium alloy includes an a- titanium matrix that may contain retained ⁇ -titanium particles.
• Figure 3 is a histogram showing the grain size distribution in the starting commercially pure titanium alloy.
• Figures 4, 14, and 19 are histograms showing the grain size distribution in the nanostructured commercially pure titanium alloy, nanostructu red Ti6AI4V, and nanostructured Ti6AI4V ELI, respectively, according to the invention.
• the average grain size of the nanostructured titanium alloys is red uced from the starting titanium alloys.
• Figure 5 shows that the starting commercially pure titanium alloy has 90%-95% of the grain boundaries with misorientation angle > 15°
• Figure 6 shows that the nanostructured commercially pure titanium alloy retains 20%- 40% of the grain boundaries with misorientation angle > 15°.
• Figures 15 and 20 show that the starting titanium alloys: Ti6AI4V and Ti6AI4V ELI has 40-55% of the grain boundaries with misorientation angle > 15°
• Figures 16 and 21 show that the nanostructured Ti6AI4V and Ti6AI4V ELI retains 20-40% of the grain boundaries with misorientation angle > 15°. These distributions contribute to the retention of useful ductility levels.
• Figures 7 and 8 show the grain aspect ratio distribution in the longitudinal and transverse planes of the nanostructured commercially pure titanium alloy, which demonstrates an increased proportion of lower grain shape aspect ratio grains in the longitudinal plane compared to the transverse plane. The similar aspect ratio is observed in nanostructured Ti6AI4V and Ti6AI4V ELI alloys.
• FIGS. 9-11 are TEM micrographs showing equiaxed grains, high dislocation density, and a high number of sub-grains in the nanostructured commercially pure titanium alloy, according to the invention.
• the eq uiaxed grains are highlighted by continuous lines
• Figure 10 the high dislocation density regions are highlighted with continuous lines.
• the grains are highlighted with continuous lines and the sub-grains are highlighted with dotted lines.
• Table 4 shows typical room temperature mechanical property levels of the starting titanium alloys and the nanostructured titanium alloys accord ing to the invention that can be achieved because of structure development.
• Nanostructured 1200 1050 10 25 650 700 650 Commercially
• the resulting nanostructured titanium alloys exhibit various material property changes, such as increased tensile strength and/or shear strength and/or fatigue endu rance limit.
• the nanostructured titanium alloys according to the exemplary embodiment of the invention have a total tensile elongation greater than 10% and a reduction of area greater than 25%.
• the nanostructured titanium alloys have at least 80% of the grains with a size ⁇ 1.0 microns, with approximately 20-40% of all grains having high angle grain boundaries, and > 80% of all grains have a grain shape aspect ratio in the range 0.3 to 0.7.
• the nanostructured titanium alloy articles have grains with an average crystallite size below 100 nanometers and a dislocation density of > 10 15 m "2 .
• the invention provides a nanocrystalline structure having enhanced properties from the starting workpiece, as a result of severe plastic deformation and thermomechanical processing.
• Titaniu m alloys that may be used in accordance with the present invention include commercially pure titanium alloys (Grades 1-4), Ti-6AI-4V, Ti-6A1-4V ELI, Ti-Zr, or Ti-6AI-7Nb.
• the nanostructured titanium alloy in accordance with the present invention can be used to produce useful articles with enhanced material properties, includ ing aerospace fasteners, aerospace structural components, high performance sporting goods, as well as articles for medical applications, such as spinal rods, screws, intramedullary nails, bone plates and other orthopedic implants.
• the invention may provide aerospace fasteners comprised of nanostructured Ti alloy having increased ultimate tensile strength, such as above 1200 M Pa, and increased shear strength, such as above 650 M Pa.

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• Chemical & Material Sciences (AREA)
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• Organic Chemistry (AREA)
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• Crystallography & Structural Chemistry (AREA)
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• Powder Metallurgy (AREA)
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• Manufacture Of Metal Powder And Suspensions Thereof (AREA)
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• Extrusion Of Metal (AREA)

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• 2014
  • 2014-03-14 US US14/212,344 patent/US20160108499A1/en not_active Abandoned
• 2015
  • 2015-03-13 WO PCT/US2015/020389 patent/WO2015199769A2/en not_active Ceased
  • 2015-03-13 CN CN201580022326.7A patent/CN106460101A/zh active Pending
  • 2015-03-13 EP EP15811866.1A patent/EP3117016A4/de not_active Withdrawn
  • 2015-03-13 JP JP2016557304A patent/JP2017512901A/ja active Pending

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