HIGH FATIGUE RESISTANT WIRE

Abstract

A high fatigue resistant nickel-titanium alloy wire, the wire having a transition temperature A.sub.F from 15 C. to +10 C. after annealing at a temperature in the range of 700 C. to 900 C., the wire being characterized by a Full-Width at Half-Maximum (FWHM) of austenite nickel-titanium diffraction peak in the range of 0.6 2 to 0.7 2 in a X-ray diffraction pattern using a Cu Ka radiation source.

Claims

1-15. (canceled)

16. A high fatigue resistant nickel-titanium alloy wire, said wire having a transition temperature from 15 C. to +10 C. after annealing at a temperature in the range of 700 C. to 900 C., said wire being characterized by a Full-Width at Half-Maximum (FWHM) of austenite nickel-titanium diffraction peak in the range of 0.6 2 to 0.7 2 in a X-ray diffraction pattern using a Cu K radiation source, wherein the X-ray diffraction pattern is measured by a continuous -2 measurement from 25 to 80 under the following conditions: Radiation source voltage: 40 kV Radiation source amplitude: 40 mA Monochromator: graphite Detector: Scintillation Variable divergence slit: 6 mm Primary and secondary soller slit Antiscatter slit: 2 mm Receiving slit: 0.2 mm Detector slit: 0.6 mm Step size: 0.02 Scan speed: 0.02/min Background correction: linear subtraction between 38 to 48 2.

17. The high fatigue resistant nickel-titanium alloy wire according to claim 16, wherein the peak intensity ratio of the peak of Ni.sub.3Ti to the sum of the peak of austenite NiTi and the peak of Ni.sub.3Ti is in the range of 5% to 20% after a background correction of linear subtraction between 25 to 80 2.

18. The high fatigue resistant nickel-titanium alloy wire according to claim 16, wherein the total number of cycles before the breaking of the high fatigue resistant nickel-titanium alloy wire is above 10000 under 1% strain at constant rotation speed 3600 rpm at 20 C. to 23 C.

19. The high fatigue resistant nickel-titanium alloy wire according to claim 16, wherein the austenite finish temperature A.sub.F is greater than 40 C.

20. The high fatigue resistant nickel-titanium alloy wire according to claim 16, wherein said wire having a transition temperature from 15 C. to +10 C. after annealing at a temperature in the range of 700 C. to 900 C. for 5 to 30 minutes.

21. The high fatigue resistant nickel-titanium alloy wire according to claim 16, wherein the transition temperature of said wire is about 7 C. after annealing at a temperature of 850 C. for 20 minutes.

22. The high fatigue resistant nickel-titanium alloy wire according to claim 16, wherein the diameter of the wire is in the range of 0.1 mm to 3 mm.

23. A method for manufacturing a high fatigue resistant nickel-titanium alloy wire according to claim 16, comprising the steps of: (a) provide a nickel-titanium alloy wire rod or wire having a composition of about 5010 wt % nickel with a balance of titanium and trace elements, (b) anneal said nickel-titanium alloy wire rod or wire at a temperature in the range of 700 C. to 900 C., (c) draw said nickel-titanium alloy wire rod or wire through one or more passes to achieve a nickel-titanium alloy wire with desired diameter, (d) anneal said nickel-titanium alloy wire at a temperature in the range of 500 C. to 600 C., (e) heat treat said annealed nickel-titanium alloy wire at a temperature in the range of 350 C. to 380 C.

24. The method for manufacturing a high fatigue resistant nickel-titanium alloy wire according to claim 23, wherein in step (b) said nickel-titanium alloy wire rod or wire is annealed for a time period of 5 to 30 minutes.

25. The method for manufacturing a high fatigue resistant nickel-titanium alloy wire according to claim 23, wherein in step (c) said nickel-titanium alloy wire rod or wire is drawn through two or more passes, and the nickel-titanium alloy wire undergoes annealing at 600 C. to 850 C. after one or more passes.

26. The method for manufacturing a high fatigue resistant nickel-titanium alloy wire according to claim 23, wherein in step (c) said nickel-titanium alloy wire rod or wire is drawn through two or more passes to achieve a cross-section area reduction of about 40%, subsequently undergoes annealing, and is further drawn to achieve a cross-section area reduction of about 40%.

27. The method for manufacturing a high fatigue resistant nickel-titanium alloy wire according to claim 23, wherein in step (e) heat treatment, the time period varies from about 5 to about 60 minutes.

28. A device for endodontic, said device comprising a working portion made from the wire according to claim 16.

29. The device for endodontic according to claim 28, wherein said device is a dental file.

30. A method for manufacturing devices for endodontic according to claim 28, said method comprising the steps of: (i) providing a nickel-titanium alloy wire, (ii) forming devices for endodontic from said nickel-titanium alloy wire by performing cutting and machining operations.

Description

BRIEF DESCRIPTION OF FIGURES IN THE DRAWINGS

[0041] The invention will be better understood with reference to the detailed description when considered in conjunction with the non-limiting examples and the accompanying drawings, in which:

[0042] FIG. 1 schematically shows the configuration of the diffractometer used to characterize the NiTi alloy wire according to the present invention.

[0043] FIG. 2 schematically shows the diagram of production process of the NiTi alloy wire according to the present invention.

[0044] FIG. 3 compares the fatigue resistance of the NiTi alloy wire according to the present invention with a reference NiTi alloy wire.

[0045] FIG. 4 illustrates the DSC curve of the NiTi alloy wire after full annealing according to an embodiment of the present invention.

[0046] FIG. 5 illustrates the DSC curve of the NiTi alloy wire as produced according to an embodiment of the present invention.

[0047] FIG. 6 shows the XRD spectrum of the NiTi alloy wire according to an embodiment of the present invention.

MODE(S) FOR CARRYING OUT THE INVENTION

[0048] A nickel-titanium alloy wire rod or wire having the composition as shown in table 1 is taken as the starting material.

TABLE-US-00001 TABLE 1 nickel-titanium alloy composition. Chemical compostion Min (wt %) Max (wt %) Tolerances (wt %) Nickel 54.500 57.000 0.2000 Carbon 0.050 0.0020 Cobalt 0.050 0.0010 Copper 0.010 0.0010 Chromium 0.010 0.0010 Hydrogen 0.005 0.0005 Iron 0.050 0.0100 Niobium 0.025 0.0040 Nitrogen plus oxygen 0.050 0.0040 Titanium 43.000 45.500 0.0040

[0049] The material was eventually processed into a wire end product having a diameter in the range of 0.1 mm to 1.5 mm. The process was schematically shown in FIG. 2. The process started with a wire rod or wire having a diameter of about 2.35 mm. The wire rod or wire was first paid off from a coil (A of FIG. 2). The wire rod or wire was then fully annealled at a temperature of about 750 C. to release stresses (B). Then the wire rod or wire was drawn by passing several dies (C). The cross-section area reduction of the wire per pass was in the range of 10% to 15%. After a cross-section area reduction of about 40%, a full annealing at about 650 C. to 800 C. was applied to the drawn wire to release stresses (D). Depending on the desired reduction of the wire, steps (C) and (D) can be repeated. Then the wire was finally drawn to achieve a cross-section area reduction of about 40% (E) and followed by a straight annealing at about 500 C. to 600 C. (F). Thereafter, a post heat treatment (G) in the range of 350 C. to 380 C. for about 5 to 600 minutes was carried out on the processed wire while the wire was still on the coninuous line. Optionally, one or multiple heat treatments (G) in the range of 380 C. to 600 C. may be applied between straight annealing (F) and post heat treatment (G). Finally, the wire was cooled down and taken off from the continuous line.

[0050] The fatigue resistance of the processed wire is measured by rotating-beam fatigue testing method. The measurements were done respectively under 1%, 1.5% and 2% strain at constant rotation speed 3600 rpm at about 20 C. to 23 C. The Chuck-bushing distance under 1%, 1.5% and 2% strain are respectively 120 mm, 80 mm and 60 mm, and the sample Length under 1%, 1.5% and 2% strain are respectively 290 mm, 200 mm and 160 mm. Reference wires processed in similar steps as the invention wire but without a post heat treatment (G and/or G) are taken for comparison. The average number (of 3 tests) of cycles before the wires were broken in the fatigue test are shown in FIG. 3. The number of cycles before the breaking of the inventon wire (column A in FIG. 3) is about 11000 under 1% strain, is about 1650 under 1.5% strain, and is about 450 under 2% strain while the refence wires (column B in FIG. 3) are broken after about 4800 cycles under 1% strain, after about 800 cycles under 1.5% strain and after about 310 cycles under 2% strain. The invention wire (column A in FIG. 3) has high fatigue resistance and behaves significantly better than the reference wire (column B in FIG. 3) over all the investigated strain rates.

[0051] The produced wire according to the present invention can be used to make endodontic devices and in particular dental files.

[0052] The wire or the file was characterized by DSC method. The measure

[0053] Instrument was DSC Q2000 V24.10 Build 122. The heat flow was measured under the following conditions:

[0054] Module DSC Standard Cell RC

[0055] Data storage Off

[0056] Equilibrate at 120.00 C.

[0057] Isothermal for 2.00 min

[0058] Data storage On

[0059] Ramp 5.00 C./min to 80.00 C.

[0060] Isothermal for 2.00 min

[0061] Ramp 15.00 C./min to 120.00 C.

[0062] Isothermal for 2.00 min

[0063] Ramp 5.00 C./min to 80.00 C.

[0064] Isothermal for 2.00 min

[0065] 1) The transition temperature of the processed wire after a full annealling was measured. The processed wire was heated at about 850 C. for 15 to 30 minutes and followed by water quenching. The measured heat flow as a function of temperature was shown in FIG. 4. During heating, the As is about 20 C. and the A.sub.F is about 7 C.

[0066] 2) The A.sub.F of the wire as produced was measured. The DSC result was shown in FIG. 5. During heating, the As is about 10 C. and the A.sub.F is about 46 C.

[0067] The processed wire or file according to the present invention was measured by XRD. The measure conditions were the same as described above (see paragraph [0015]). The measured spectrum was shown in FIG. 6. The FWHM of the (110) peak of austenite NiTi (indicated by .square-solid. in FIG. 6) after a background correction of linear subtraction between 38 to 48 2 is about 0.63. In this spectrum, it is also observed the peaks or the existence of Ni.sub.3Ti. The (202) peak of Ni.sub.3Ti is indicated by a in the spectrum. The peak intensity ratio of the (202) peak of Ni.sub.3Ti to the sum of the (110) peak of austenite NiTi and the (202) peak of Ni.sub.3Ti is about 12% after a background correction of linear subtraction between 25 to 80 2.

[0068] Two commercially available products are taken as references. The properties or characterizations of the invention wire or file are compared with referenced products in table 2. As shown in table 2, both the A.sub.F of the wire after full annealling and A.sub.F of the wire as produced are different with referenced products indicating different properties. The peak intensity ratios of the (202) peak of Ni.sub.3Ti to the sum of the (110) peak of austenite NiTi and the (202) peak of Ni.sub.3Ti of the referenced products are much less than that of the invention wire. The specific FWHM of (110) peak of austenite NiTi and the presence of certain amount of Ni.sub.3Ti illustrate an exclusive microstructure. The composition together with the microstructure of the invention wire or file makes it unique over the available products.

TABLE-US-00002 TABLE 2 the properties or characterizations of the invention wire compared with two referenced products. A.sub.F after A.sub.F of FWHM of Peak intensity ratio full wire as (110) peak (%) Ni.sub.3Ti(202)/ annealing produced of austenite [NiTi (110) + Sample ( C.) ( C.) NiTi (2) Ni.sub.3Ti(202)] Invention ~7 ~45 0.627 12 Reference 1 ~1 ~57 0.541 3 Reference 2 ~10 ~60 0.746 <1