Metallic material with an elasticity gradient

Abstract

A monolithic titanium alloy having, in a temperature range (T) and at atmospheric pressure: an outer peripheral zone of a microstructure having a modulus of elasticity (E.sub.1) and possessing superelastic properties in the range (T), and a core of a microstructure having a modulus of elasticity (E.sub.2), and possessing elastic properties in the range (T); the microstructures and being different from one another, and the modulus of elasticity (E.sub.1) being lower than said modulus of elasticity (E.sub.2).

Claims

1. A monolithic titanium alloy comprising, in a temperature range (T) and at atmospheric pressure: at least 70 atomic % of titanium based on the total atomic % of titanium alloy, the alloy also comprising niobium; a one and only outer peripheral zone consisting of a microstructure (m.sub.1) having a modulus of elasticity (E.sub.1) and possessing superelastic properties in said temperature range of 35 to 40 C., and a core consisting of a microstructure (m.sub.2) having a modulus of elasticity (E.sub.2), and possessing elastic properties in said range of temperature of 35 to 40 C.; said microstructures (m.sub.1) and (m.sub.2) being different from one another, and the difference between said modulus of elasticity (E.sub.1) and said modulus of elasticity (E.sub.2) being greater or equal to 20 GPa.

2. The titanium alloy as claimed in claim 1, wherein E.sub.1 is between 20 and 50 GPa.

3. The titanium alloy as claimed in claim 1, wherein E.sub.2 is between 70 and 90 GPa.

4. An implant comprising the titanium alloy as claimed in claim 1.

5. A dental implant comprising the titanium alloy as claimed in claim 1.

6. A dental implant consisting of the titanium alloy as defined in claim 1.

7. The dental implant as claimed in claim 5, comprising an implant body consisting of a metallic material.

8. The titanium alloy as claimed in claim 1, wherein the alloy is in the form of a bar, a cylinder, an ingot, an implant body or a dental implant.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

Figures

(1) FIG. 1: representation of a dental implant (1) installed in the maxillary bone (2) and surmounted by a prosthesis (4) level with the gum (3).

(2) FIG. 2: representation of a dental implant comprising an implant body (5) intended to receive a pillar (6) that makes it possible to attach the prosthesis.

(3) FIG. 3: diffraction spectra for three samples: drawn (cold drawn), surface (flash annealed T1) and core (flash annealed T2).

(4) FIG. 4: Young's modulus measured by instrumented microindentation along a radius for three samples: cold drawn, flash annealed T1 and flash annealed T2.

DETAILED DESCRIPTION

Examples

(5) The alloy of composition Ti-24Nb (at. %) is obtained by arc melting of the two pure metals. The composition of this 20 g ingot is homogenized by a heat treatment at 950 C. for 20 hours, under a high vacuum of 10.sup.6 Pa. The sample is then quenched after an annealing at 850 C. for 360 s, for the purpose of retaining the high-temperature beta phase, which is more ductile than the stable phase at low temperature: the alpha phase. Drawing at ambient temperature then makes it possible to pass from an ingot having a diameter of around 11 mm to a rod having a diameter of 4 mm. A 2 mm slice is cut in order to characterize the material in the cold drawn state. Another piece which is 1 cm long is also cut from the drawn rod, then annealed for 360 s at 600 C. in a silica tube filled with helium and submerged in salt baths. At the end of this time, the tube is cooled rapidly in water.

(6) Two cross sections of the cylinder are cut, after annealing, with a thickness of 2 mm. One originates from the end of the cylinder (flash annealed T1) and will make it possible to analyze the microstructure and the mechanical behavior at the surface, the other is extracted from the middle (flash annealed T2) and will make it possible to visualize whether the temperature gradient during the annealing creates a visible gradient for the microstructure and the mechanical behavior.

(7) The X-ray diffraction equipment is a Philips PW1710 machine with a copper tube (.sub.K1=1.542 ) operating at 40 kV and 25 mA. The instrumented microindenter is a CSM indenter. The tip used is made of diamond and is of Vickers type. The force F and the displacement h of the tip are recorded during a cycle in which the maximum force is 3000 mN (achieved in 30 s). The unloading portion is purely elastic, it is therefore directly linked to the Young's modulus. The calculation follows the conventional models of Sneddon, who links the slope at the start of unloading and the Young's modulus, and of Oliver and Pharr, who link the measured depth h to the actual depth h.sub.c [ref].

(8) The projected contact area, necessary for the estimation of E, was calibrated by being based on the measurement of fused silica. The result is the following:
A.sub.c=24.5h.sub.c.sup.2+1190h.sub.c

(9) The area function for an ideal Vickers indenter is 24.5 h.sub.c.sup.2, the additional term takes into account the geometry defects. 20 tests were carried out every 100 m along a radius.

(10) The microstructure of the cold drawn, flash annealed Ti and flash annealed T2 samples is estimated by X-ray diffraction (FIG. 3). The idea is to compare the diffraction diagrams in order to estimate the effect of the temperature gradient on the microstructure. The cold drawn sample has broad peaks and a large proportion of phase. These two aspects are the result of the defects induced by the plastic deformation: a large dislocation density and martensitic phase induced under residual strain. The flash annealed T2 sample is textured since the main peak is (211) and not (110). It is also possible to identify the and phases. The result is relatively close to the cold drawn sample, but two significant differences can be indicated: the peaks are narrower and the proportion of phase is smaller. The flash annealed T1 sample is composed of the phase mainly and of a few percent of . This means that the phase disappears and the phase recrystallizes. The energy is even sufficient to form a few crystals.

(11) These results represent an average microstructure of the various cross sections: cold drawn, flash annealed T1 and flash annealed T2. The first two are, a priori, homogeneous but the third is seemingly heterogeneous. Indeed, the peripheral zone for T2 is identical to T1 since it is a question of surface.

(12) However, the diffraction spectrum of T2 principally shows a textured phase in the presence of . The conclusion is, consequently, that the sample T2 has a microstructure gradient and that the proportion of is probably greater at the center of the sample than that which it is possible to estimate by X-ray diffraction.

(13) The mechanical behavior was then studied locally by instrumented microindentation. FIG. 4 presents the Young's modulus values for the three samples. E is constant along the radius for the cold drawn sample (75 GPa) and the flash annealed T1 sample (40 GPa). For the flash annealed T2 sample, the modulus increases gradually from 40 GPa to 75 GPa over a zone around 400 m, and then remains constant. This demonstrates that the microstructure gradient may have an effect on the elastic behavior, for this composition and under these production conditions.