Metal treatment – Process of modifying or maintaining internal physical... – Heating or cooling of solid metal
Reexamination Certificate
2002-04-11
2004-10-05
Oltmans, Andrew L. (Department: 1742)
Metal treatment
Process of modifying or maintaining internal physical...
Heating or cooling of solid metal
C148S670000, C148S687000, C148S269000, C148S281000, C148S284000
Reexamination Certificate
active
06800153
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to &bgr;-titanium alloy wire which is suitable for metallic wires, such as various kinds of precision springs, various kinds of ropes or cables, tension member for communication cable, probe card pin for inspection of conduction, metallic fishing line and the like. The present invention also relates to a method for producing said &bgr;-titanium alloy wire and medical instruments made by said &bgr;-titanium alloy wire.
DESCRIPTION OF PRIOR ART
Titanium is hexagonal close-packed structure (hcp, &agr;-structure) at a room temperature. Titanium is converted into body-centered cubic structure (bcc, &bgr;-structure) by allotropic transformation at a temperature of 1158 K or more. A density of titanium is about 60% of that of Fe. Titanium's specific strength (proof stress divided by density) is the maximum of all metals. Young's modulus and thermal expansion coefficient of titanium are about a half of stainless steel's value respectively. A specific heat, an electrical conductivity and a thermal conductivity of titanium are much lower than those values of aluminum alloy or magnesium alloy respectively. Titanium has a perfect corrosion-proofness under the oxidation environment. Titanium is corrosion-resistant to chlorine ion. As described above in detail, titanium has many good properties. Accordingly, titanium is widely utilized for heat-conducting pipes of heat exchanger of fossil power station or nuclear power station in which sea water is used for cooling, sea water desalination apparatus, various electrodes for electrolysis, petroleum refining plant and the like.
The equilibrium phase diagrams of two elements containing mainly titanium are classified into &agr;-stabilized type, &bgr;-stabilized type, &bgr;-eutectoid type, and &agr;−&bgr; homogeneous solid solution type. Titanium alloy is obtained by combination of &agr;-stabilized elements which raise &agr;−&bgr; transformation point by extending &agr;-phase region to a high temperature part, &bgr;-stabilized elements which lower &agr;−&bgr; transformation point by extending &bgr;-phase region to a lower, temperature part and neutral elements which have no effects on phase-stabilization. For example, there are aluminum and tin as &agr;-stabilized elements, vanadium and chromium as &bgr;-stabilized elements, zirconium and hafnium as neutral elements. Titanium alloys are classified into a &agr;-titanium alloy (hcp), &agr;+&bgr; type titanium alloy (hcp+bcc), &bgr;-titanium alloy (bcc) according to crystal structure of phase constituting micro structure under a normal temperature.
&agr;-titanium alloy is a single phase alloy obtained by solid solution hardening as a result of addition of &agr;-stabilized elements to titanium. Aluminum, which has a large solubility limit to titanium and a high solid solution hardening capacity, is mainly used as the addition element. So, &agr;-titanium alloy is a good oxidation-resistant under a high temperature but a little poor in workability. &agr;+&bgr; type titanium alloy is two phase alloy under coexistence of &agr;-phase and &bgr;-phase at a normal temperature by addition of &agr;-stabilized elements and &bgr;-stabilized elements. Titanium-6aluminum-4vanadium, which is a representative &agr;+&bgr; type titanium alloy, has a high specific strength and a high ductility, but shows a brittleness if working conditions would not be enough controlled at hot working.
On the other hand, &bgr;-titanium alloy is a single phase alloy obtained by retaining at a normal temperature &bgr;-phase which have been formed under a high temperature. &bgr;-titanium alloy is good in cold workability and has a high strength and a good ductility due to the heat treatment. Recently a research on &bgr;-titanium alloy has been actively conducted. For example, in case of titanium-15 vanadium-3-chromium-3 tin-3 aluminum, when the conditions of cold rolling and solid solution treatment have been optimized, it is reported that a tensile strength of nearly 1900 N/mm
2
and an elongation of 10% have been obtained. Patent unexamined publication No. 11-71621 discloses an invention on a method for producing &bgr;-phase titanium alloy bar wire which states that it is possible to improve the strength and the ductility by forming working texture of &bgr;-phase prior to aging treatment and controlling &agr;-phase transformation texture precipitated by aging treatment. The details of this invention is as follows:
&bgr;-phase titanium alloy bar wire is subjected to solution treatment or hot rolling at a temperature of more than transformation temperature, followed by cold working of reduction ratio of area of 30% or more and then annealing at a range between a temperature of 100° C. lower than &bgr;-transformation point and a temperature of 10° C. lower than &bgr;-transformation point. After that, &bgr;-phase titanium alloy bar wire is shaped into a fixed form and subjected to an aging treatment, resulting in obtaining a high strength and a high ductility. This invention is hereinafter referred to as the prior method for producing &bgr;-titanium alloy bar wire.
Recently, it has been increasing to perform a diagnosis or a therapy by inserting a catheter into a blood vessel or a digestive tract. As to medical instruments which make use of the catheter, there are a guide wire which is manipulated through the inside of the catheter or a stent which is placed in the aim portion after passing through the inside of catheter.
The explanation of guide wire for medical treatment will be given below. The guide wire for medical treatment is used as a guide for introducing the catheter to perform a minimally invasive treatment. Generally, the guide wire for medical treatment is pushed out from the tip of the catheter and inserted into the blood vessel. For the reason, it is necessary for the guide wire for medical treatment to pass through a serpentine: blood vessel or a stenosis portion (crossability) and selectively go into a requested direction at a junction (selectivity or pushability). Also, it is preferable that the tip of the guide wire for medical treatment would, be a little bent to insert into the catheter and then slightly twisted at the base of wire to select the direction toward which said tip should go by rotating the bent portion of the tip. To give a little bend is referred to as reshaping. Accordingly, the guide wire for medical treatment should have the function that the tip would move correspondingly to the twist motion of the base (torque transmittability).
The guide wire for medical treatment may be roughly divided into two categories. One is such that its center core would be a stainless steel wire and a stainless steel coil would be wound around the distal portion of the stainless steel wire. The other is such that its center core would be a super-elastic alloy and a synthetic resin would cover the center core.
But stainless steel has a high yield strength and a good pushability. Furthermore, stainless steel is easy to make plastic deformation. As a result, when stainless steel is used as center core, it is supposed that the center core would injure the blood vessel wall at its serpentine portion or its stenosis portion. Furthermore, when the plastic deformed guide wire is pulled out, it is feared that the guide wire would injure the blood vessel wall. In addition, it is a large matter that the guide wire made of stainless steel has a very low transmittability of twisting in the serpentine blood vessel and a poor selectivity or operationality at a junction.
On the other hand, the guide wire made of super-elastic alloy has a high torque transmittability in the serpentine blood vessel but it is impossible to make re-shaping at the tip thereof. And the guide wire made of super-elastic alloy has little resistance to bending at a bend portion. For solving the above problems, the guide wire comprising the following features has been demanded. The guide wire should be easily and safely manipulated by a person in attendance on the
Ishii Naoki
Kaneko Takashi
Nagao Ichiro
Sumimoto Shin
Yamamoto Hideki
Marshall & Gerstein & Borun LLP
Oltmans Andrew L.
Terumo Corporation
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