Stock material or miscellaneous articles – Composite – Of metal
Reexamination Certificate
1999-02-02
2001-03-13
Speer, Timothy M. (Department: 1775)
Stock material or miscellaneous articles
Composite
Of metal
C148S317000, C148S421000, C420S421000
Reexamination Certificate
active
06200685
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates generally to a titanium alloy and, more particularly, to a titanium alloy suitable for use in the manufacture or fabrication of a variety of structures, products or devices, or components thereof
BACKGROUND OF THE INVENTION
Alloy titanium has been used for all types of structures, including aircraft, corrosion-resistant containers and medical implants. Titanium alloys are particularly useful for components used in corrosive environments due to their excellent corrosion resistance properties compared to alternative stainless steel, nickel-base alloys, aluminum and cobalt-chrome alloys. Titanium and its alloys are more prone to fretting and wear compared to harder (Rc42-44) Co—Cr—Mo alloys and age-hardened stainless steels. However, the lower elastic modulus, in combination with high strength allows titanium alloys to be useful for applications requiring shock absorption or high levels of strain. Thus, articles or devices formed from titanium alloys possess a useful combination of strength and flexibility, and tend to exhibit good wear resistance. Additionally, current titanium alloys, although more flexible (lower modulus) than steel, nickel, or cobalt, are not equivalent in flexibility to aluminum (modulus of 10 Msi) or magnesium (modulus of 7 Msi). It would be useful to have a corrosion-resistant titanium alloy that could possess a unique combination of high-strength, lower modulus (less than 10 Msi) and with the ability to develop a high, wear-resistant bulk hardness. Greater hardness can allow for less friction and improved abrasion resistance, in contrast to the poor wear resistance of softer stainless steels or flexible titanium, aluminum and magnesium alloys.
Examples of titanium alloys with a low-modulus (less than 130 GPa) include a room temperature beta titanium alloy for wire as described in U.S. Pat. No. 4,197,643. This patent describes the use of Mo, Nb, Ta and V to produce the beta alloy, and additionally, the use of Mn, Fe, Cr, Co, Ni, Cu, Al and Zr. There is no mention of the use of hafnium in the alloys. Alloy strength is achieved by aging to precipitate the alpha phase or by cold working. The preferred composition is Ti-11.5Mo-6Zi-4.5Sn, commonly called Beta III. However, the hardness is in the 30's on the Rockwell “C” scale. U.S. Pat. No. 5,312,247 describes a shape-memory or super elastic alloy having a predetermined activation temperature. This patent further describes the use of nickel-titanium based and titanium-molybdenum based alloys but as in the previous example, does not mention the use of hafnium (Hf) in the alloys. The use of nickel-containing metals is undesirable, as its presence reduces the corrosion resistance. Nitinol is another shape-memory alloy. However, this highly elastic alloy also has less than optimum corrosion resistance with respect to other alternative available titanium alloys because of the high concentrations of nickel. Nitinol also has a relatively low hardness in the Rc 30's. U.S. Pat. No. 5,232,361 describes another series of titanium alloys formulated of at least one of a group of alloys based on Ti, Zr, Si, B, Be, Cr, Nb and Co in a composition in which at least one of these elements exists in a range of between 40 weight percent and greater than 99 weight percent. A bracket containing at least 45 weight percent titanium is given as an example. Other examples include alloys with at least 80 weight percent Ti with the addition of Al, V, Fe and/or Nb, and even a 99 weight percent Ti alloy. Once again, the use of hafnium is not described, and strength, elastic modulus, hardness, and corrosion resistance are less than optimal.
Other examples of shape memory alloys include those described in U.S. Pat. Nos. 4,665,906 and 5,067,957 which describe devices and methods of installation using a non-specific shape memory alloy which displays stress induced martensitic behavior, versus an activation temperature. The present inventive Ti alloy does not exhibit shape memory behavior, and contains hafnium to improve corrosion resistance. Additionally, unlike prior art Ti alloys described above, the presence of hafnium allows the option of surface hardening of the alloy via a conversion surface oxide, nitride, carbide, or combination of these.
An early example of an improved titanium alloy for implants was discussed in U.S. Pat. No. 4,040,129 in which bone and dental implants having full tissue compatibility were described as being composed of a first component of about 3 to 30 weight percent selected from the group Nb, Ta, Cr, Mo and/or Al, and a second component of Ti and/or Zr; wherein the sum of the Cr, Mo and Al is less than 20 weight percent and the weights of Ti and/or Zr is less than 75 weight percent. This alloy was also free of Cu, Co, Ni, V and Sn. Examples described in the patent include Ti-9Nb-11Cr-3Al and Ti-4Mo-48Zr.
Additionally, in U.S. Pat. No. 4,040,129, the benefit and desirability of a lower elastic modulus of the described alloy was not discussed, nor was there any mention of the use of hafnium in the composition. A more recent patent, U.S. Pat. No. 4,857,269, also deals with the desirability of low elastic modulus in medical devices. This patent describes a titanium based alloy consisting of an amount of up to 24 weight percent of isomorphous beta stabilizers Mo, Ta, Nb and Zr, providing that molybdenum, when present, is at least 10 weight percent, and when present with zirconium, is between 10 and 13 weight percent with the zirconium being between 5 and 7 weight percent. Additionally, the same titanium based alloy also has up to 3 weight percent eutectoid beta stabilizers selected from Fe, Mn, Cr, Co and Ni, wherein the combined amount of isomorphous and eutectoid beta stabilizers is at least 1.2 weight percent. Optionally, up to 3 weight percent aluminum and lanthanum can be present in the alloy with the elastic modulus not exceeding 14.5 Msi. Examples include Ti-10-20Nb-1-4Zr-2Fe-0.5Al (TMZF)™. Once again, less than optimum elements (Mn, Co, Ni, Al), from a corrosion standpoint, are found in the alloy composition and there is no mention of hafnium or the ability to be surface hardened.
Hoars and Mears (1966) and Pourbaix (1984), based on electrochemical stability, suggested the use of Ti, Nb, Zr, and Ta as elemental constituents for improved corrosion resistance. However, it is important to note that Ti—Mo alloys were also included as acceptable materials and this was supported by comparative corrosion data between Ti and Ti-16Mo-3Nb-3Al in which the Ti—Mo alloy showed improved corrosion resistance. Thus, the presence of Mo in titanium alloys can actually be beneficial from the standpoint of corrosion. It has also been reported in the titanium literature (Titanium Alloys, E. W. Collings, ASM, 1986) that the addition of more than about 4 weight percent molybdenum improved the corrosion resistance of titanium, particularly in crevice-type environments. With many of device service applications requiring assembled components in corrosive environments, the presence of molybdenum can be beneficial in a titanium alloy.
In an effort to improve the corrosion resistance properties of the titanium alloy and to reduce its elastic modulus, Davidson and Kovacs (U.S. Pat. No. 5,169,597) developed a medical implant titanium alloy with 10-20 weight percent Nb, or 30-50 weight percent Nb and 13-20 weight percent Zr, or sufficient Nb and/or Zr to act as a beta stabilizer by slowing transformation of beta (U.S. Pat. No. 5,545,227). The preferred example is Ti-13Nb-13Zr (Ti1313™). Tantalum can also be used as a replacement for niobium where the sum of Nb and Ta is 10-20 weight percent of the alloy. Subsequent continuation-in-part patents and applications, describing this type of alloy for other medical device applications also exist and are considered herein with respect to prior art. All of these patents and applications describe the use of Ti, Nb, and/or Zr. However, the use of hafnium, molybdenum, the combination of Hf and Mo, or small quantities of selected strengthening
Fulbright & Jaworski L.L.P.
Speer Timothy M.
LandOfFree
Titanium molybdenum hafnium alloy does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Titanium molybdenum hafnium alloy, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Titanium molybdenum hafnium alloy will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2522160