Abstract
The invention relates to the use of a ternary Titanium-Zirconium-Oxygen (Ti—Zr—O) alloy, characterized in that it comprises from 83% to 95.15 mass % of titanium, from 4.5% to 15 mass % of zirconium and from 0.35% to 2 mass % of oxygen, with said alloy being capable of forming a single-phase material consisting of a stable and homogeneous α solid solution of Hexagonal Close Packed (HCP) structure at room temperature in the medical, transport or energy fields.
Claims
1. A product comprising a ternary Titanium-Zirconium-Oxygen (Ti—Zr—O) alloy comprising from 83% to 95.15 mass % of titanium, from 4.5% to 15 mass % of zirconium and from 0.35% to 2 mass % of oxygen, with the alloy being a single-phase material consisting of a stable and homogeneous α solid solution with a Hexagonal Close Packed (HCP) structure at room temperature.
2. The product according to claim 1 wherein the product is a medical device.
3. The product according to claim 1 wherein the product is a medical device, said medical device being an orthopedic implant.
4. The product according to claim 1 wherein the product is a component for medical applications or dental applications.
5. The product according to claim 1 wherein the product is a component for aerospace applications, nuclear applications, energy applications, chemical processing applications or transportation applications.
6. A ternary Titanium-Zirconium-Oxygen (Ti—Zr—O) alloy comprising from 83% to 95.15 mass % of titanium, from 4.5% to 15 mass % of zirconium and from 0.35% to 2 mass % of oxygen, with the alloy being capable of forming a single-phase material consisting of a stable and homogeneous a solid solution with a Hexagonal Close Packed (HCP) structure at room temperature, said alloy being in the form of a powder.
7. A product comprising a ternary Titanium-Zirconium-Oxygen (Ti—Zr—O) alloy comprising from 83% to 95.15 mass % of titanium, from 4.5% to 15 mass % of zirconium and from 0.35% to 2 mass % of oxygen, with the alloy being capable of forming a single-phase material consisting of a stable and homogeneous α solid solution with a Hexagonal Close Packed (HCP) structure at room temperature, wherein the product is a medical device, the medical device being a dental implant.
Description
BRIEF DESCRIPTION OF THE DRAWINGS
(1) Further characteristics and advantages of the invention will be clear from reading the following description, made in reference to the appended figures, which show:
(2) FIG. 1 shows schematically the basic structure of a Ti—Zr—O ternary alloy according to a first embodiment of the invention;
(3) FIG. 2 shows the thermomechanical processing route used to modify the properties of a ternary alloy according to another embodiment of the invention;
(4) FIG. 3 shows curves illustrating the effect of oxygen on the mechanical properties of recrystallized alloys according to the invention;
(5) FIG. 4 shows curves illustrating the effect of zirconium on the mechanical properties of recrystallized alloys according to the invention;
(6) FIG. 5 illustrates the effect of thermomechanical treatments (including a 85% reduction of thickness) on the mechanical properties of an alloy according to the invention;
(7) FIG. 6 illustrates the effect of thermomechanical treatments (including a 40% reduction of thickness) on the mechanical properties of an alloy according to the invention; and
(8) FIG. 7 compares the mechanical properties of Ti—Zr—O ternary alloys obtained according to the invention with the properties of reference alloys.
(9) For greater clarity, identical or similar features are identified by identical reference signs in all the figures.
DETAILED DESCRIPTION
(10) FIG. 1 shows schematically the basic structure of a ternary alloy according to the invention obtained by solid solution hardening. The hardening of the alloy according to the invention, in a recrystallized condition, results from the substitutional (Zr) and interstitial (O) solid solution hardenings. Regarding the occupied sites, it can be seen that, in such a solid solution, zirconium atoms occupy Ti lattice positions (substitutional positions) and the oxygen atoms occupy interstitial positions (between the atoms of the hexagonal lattice). According to this schema, oxygen is a hardening element with an interstitial nature, and zirconium is a hardening element with a substitutional nature.
(11) The invention relies on the desired and exclusive addition of fully biocompatible alloying elements having a high solid solution strengthening capacity. Selecting zirconium results from the capacity thereof to form a homogeneous solid solution with titanium at any temperature. The composition range (from 4.5 mass % to 15 mass % of zirconium) has been chosen in order to keep a titanium-rich alloy with the objective to optimize the cost of alloys. Selecting oxygen as a full alloying element is based on the very high capacity thereof to harden the material. It is usually present in commercial materials in quantities not exceeding 0.35% (mass %) only.
(12) Differently and against a prejudice, in the family of alloys according to the invention, oxygen is added in a high quantity (from 0.35% to 2%) and in a controlled manner, as a solid-state addition of a chosen quantity of TiO.sub.2 or of ZrO.sub.2, so as to obtain, upon completion of the melting, a homogeneous solid solution as regards its composition, and rich in oxygen. The material obtained is single-phase, with the alpha phase, at any temperature (up to temperatures close to the beta transus temperature).
(13) Besides, as shown in FIG. 2, a thermomechanical treatment can be used to reach an optimized microstructural condition. An innovative sequence or a succession of thermomechanical treatments of the alloys according to the invention is provided, in order to obtain a more significant strengthening. The method comprises several steps, one of which is a heat treatment which must be short (from 1 min to 10 min) so as to obtain a recovered and not recrystallized condition. According to such treatment, the starting material is in a recrystallized condition (step 1), then a cold-working (e.g. cold-rolling) is carried out, at room temperature (step 2). Reduction rate can range from 40% to 90%, depending on the considered alloy; such step of the method makes it possible to increase the mechanical strength of the material. Then, a short—so called flash—(3) heat treatment is preferably executed, which consists in heating to a temperature ranging from 500° C. to 650° C., for a period ranging from one to ten minutes. The so-called flash heat treatment makes it possible to partially restore ductility while preserving the mechanical strength above that of the starting recrystallized condition. The material thus keeps a high mechanical strength and recovers the ductility lost when the metal has been cold-worked.
(14) The invention thus provides a solution with a ternary alloy exclusively containing a single-phase, with the alpha phase, and completely homogeneous solid solution, i.e. with no precipitates from another additional phase.
(15) Various hardening modes have been considered to reach all such characteristics, by varying the quantities of zirconium and oxygen respectively.
(16) As shown in FIGS. 3 and 4 respectively, the effect of solute strengthening, i.e. using a solid solution, could be noted by carrying out mechanical tensile tests on the new alloys, in the recrystallized condition. The increase in the mechanical strength of the alloy can be noted, both after adding oxygen (FIG. 3) and after adding zirconium (FIG. 4).
(17) The four curves of FIG. 3, which show the stress versus the relative elongation (or strain) of the considered alloy, are obtained for alloys with 4.5% of zirconium and for oxygen rates of, respectively 0.35% in curve A, 0.40% in curve B, 0.60% in curve C and 0.80% in curve D.
(18) The three curves of FIG. 4, which show the stress versus the relative elongation (or strain) of the considered alloy, are obtained for alloys with 0.40% of oxygen and for a zirconium content of, respectively 4.5% in curve B and 9% in curve C. The alloy corresponding to curve A contains no zirconium.
(19) Ductility with a recrystallized condition remains very high in the composition range considered, when compared to ductility of commercially pure titanium, for instance (of about 20%).
(20) FIG. 5 shows the additional effect of the various steps in the sequence of thermomechanical treatments on a 0.4% O-4.5% Zr alloy. More precisely, the starting condition is a recrystallized alloy, as shown in curve A. This alloy then has a high ductility, above 25%, but a relatively low mechanical strength of approximately 700 MPa. The execution of cold-working (e.g. cold-rolling), at room temperature, with 85% of reduction in thickness (TR), for instance, makes it possible to significantly increase the mechanical strength, but in return, significantly reduces ductility. Curve B shows such characteristic condition. Curve C shows the condition of the alloy after the subsequent application of a flash heat treatment to such deformed condition. Such heat treatment makes it possible to partially restore ductility while keeping a high mechanical strength. The combined final properties obtained on the 0.4% 0 and 4.5% Zr (mass %) alloy after the cold-rolling and a flash treatment for 1 minute and 30 seconds at 500° C. are higher than those of the known TA6V alloy. As regards the results corresponding to curve C, according to the invention a mechanical strength of approximately 1,100 MPa and ductility of the order of 15% can be noted. As previously known, the mechanical strength of TA6V alloy amounts to about 900 MPa and the associated ductility is about 10%.
(21) FIG. 6 illustrates the effects of several thermomechanical treatments on a 0.4% O-9% Zr alloy. Curve A shows the mechanical properties of the recrystallized alloy obtained after a heat treatment operated at 750° C. during 10 minutes. A reduction of thickness (TR) of 40% is then carried out, on said alloy. Curve B relates to the cold-rolled state. “Flash” heat treatments are applied to this cold-worked state. Curve C deals with the material heat-treated at 500° C. during 150 seconds; curve D shows the material heat-treated at 550° C. during 60 seconds; and curve E concerns the material heat-treated at 600° C. lasting 90 seconds. Both recrystallized and heat-treated alloys show interesting mechanical properties, comparable to or higher than the properties of the known TA6V alloy.
(22) FIG. 7 shows the superiority of several alloys according to the invention with respect to two known alloys: TA6V and TA6V ELI. TA6V ELI is currently used in medical field. ELI means Extra Low Interstitial. Characteristics of TA6V are illustrated through the upper rectangle whereas characteristics of TA6V ELI correspond to the lower rectangle. For each rectangle, the high level is the typical mechanical strength and the low level is the typical yield strength. The wide of each rectangle, equal to about 10%, corresponds to the ductility of the associated alloy. The four curves of FIG. 7 correspond to alloys according to the invention. They show higher properties than both TA6V-Ti grade 5- and TA6V ELI-Ti grade 23. To confirm the caption of the FIG. 7, curve A corresponds to a ternary alloy with 4.5% of zirconium and 0.4% oxygen to which a heat treatment at 500° C. for 90 seconds is applied after a reduction of thickness (TR) of 85%. Curve B deals with the properties of an alloy comprising 0.4% Oxygen and 9% of zirconium and heat-treated at 500° C. during 150 seconds after a reduction of thickness of 40%; curve C shows the properties of an alloy comprising 0.4% Oxygen and 9% of zirconium and heat-treated at 550° C. during 60 seconds after a reduction of thickness of 40%. Curve D is obtained with a recrystallized alloy comprising 0.4% oxygen and 9% zirconium, this recrystallized state is obtained with a heat treatment at 750° C. for 10 minutes after a 40% reduction of thickness (TR). Curve A of the FIG. 7 is thus the one referenced C on FIG. 5. Curves B, C and D of the FIG. 7 are thus respectively the ones referenced C, D and A on FIG. 6.
(23) As regards preferred method of the invention, a step of cold-working with a reduction rate (or reduction of thickness TR) of 40% or more, is executed on a ternary alloy as described above, and is followed by a step of heat treatment at a temperature ranging from 500° C. to 650° C. for a period ranging from one minute to ten minutes.
(24) The desired and voluntary presence of a controlled, and high, quantity of oxygen in such ternary alloy makes such alloy new. Besides, this goes against a prejudice since, so far, the presence of oxygen was limited or not controlled, mainly because of the impurities existing in the raw materials. In other words, the quantity of oxygen present in the known titanium alloys is generally limited to contents of less than 0.35 mass %, and generally results from the relative impurity of the raw materials used.
(25) Besides, the alloys according to the invention can be in massive or powder forms. Under massive form, the alloys according to the invention can be in a wide range of products such as ingots, bars, wires, tubes, sheets and plates, and so on.
(26) Further, the alloys according to the invention can be easily cold-worked: for example, tubes can easily be formed with such alloys. This results from the ductility level of the alloys according to the invention.
