Metal treatment – Process of modifying or maintaining internal physical... – Carburizing or nitriding using externally supplied carbon or...
Reexamination Certificate
1998-09-24
2001-04-24
Yee, Deborah (Department: 1742)
Metal treatment
Process of modifying or maintaining internal physical...
Carburizing or nitriding using externally supplied carbon or...
C148S238000, C148S421000, C148S671000, C148S317000
Reexamination Certificate
active
06221173
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a titanium or titanium alloy for use in decorative articles such as a wristwatch case, wristwatch band, pierced earrings, earrings, a ring, the frame of eyeglasses, and a method of surface treatment thereof.
BACKGROUND TECHNOLOGY
A titanium or titanium alloy has recently attracted much attention as a metallic member hardly causing metallic allergy and friendly to human bodies, and consequently, has been utilized for such decorative articles as represented by a wristwatch, eyeglasses, accessories, and the like.
It has been pointed out, however, that the titanium or titanium alloy has a problem of susceptibility to scratches due to its low surface hardness, and a tendency of degradation in the quality of appearance after use for long duration.
Many attempts have so far been made to apply various surface hardening treatments to the titanium or titanium alloy in order to overcome such problems.
Conventional methods of applying a surface hardening treatment to the titanium or titanium alloy can be broken down into a method of coating the surface of a metal with a hard film, and a method of hardening the metal itself.
Among methods of coating the surface of the metal with the hard film, there are known a wet process as represented by electroplating, and a dry process as represented by vacuum deposition, ion plating, sputtering, plasma CVD, and the like.
Any of these methods, however, has had a problem with adhesion between the titanium or titanium alloy and the hard film, and a drawback of the hard film being prone to peeling off.
On the other hand, ion implantation, ion nitriding, gas nitriding, carburizing, and the like are well known among methods of applying a hardening treatment to the titanium or titanium alloy itself. There is no risk of a hard layer, formed at the surface of the titanium or titanium alloy by means of such surface hardening methods, peeling, as in the case of the hard film described above.
However, conventional surface hardening methods have had shortcomings of low productivity due to long processing time, and also a drawback of degradation in the quality of appearance because the surface of the titanium or titanium alloy becomes coarse due to growth of crystal grains taking place in the surface owing to high processing temperatures. It has further been pointed out that since it is difficult to form a hard layer in regions deep down from the surface, there is a tendency for the quality of appearance to deteriorate due to scratches and the like incurred during use, presenting a major problem.
The invention has been developed in light of the circumstances described above. That is, it is an object of the invention to provide a titanium or titanium alloy superior in the quality of appearance, and having hardness sufficient to withstand large impact.
Another object of the invention is to provide a surface treatment method whereby a titanium or titanium alloy is provided with such properties as described in the foregoing.
DISCLOSURE OF THE INVENTION
To this end, a titanium or titanium alloy according to the invention is of a structure wherein a hard surface layer is formed up to an optional depth from the surface, and the hard surface layer comprises a first hard layer, formed in a region up to an optional depth from the surface and containing nitrogen and oxygen in solid solution therein, and a second hard layer, formed in a region at an optional depth deeper than the first hard layer and containing oxygen in solid solution therein.
That is, in order not to cause the surface roughness but yet to enhance surface hardness thereof, there is a need of forming the first hard layer in the vicinity of the surface of the titanium or titanium alloy, containing nitrogen as well as oxygen in solid solution therein.
Further, in order to obtain the hard surface layer extended up to greater depths, there is a need of forming the second hard layer containing oxygen in solid solution at depths of the member, deeper than the first hard layer.
It has been made possible to obtain the titanium or titanium alloy having not only excellent quality of appearance without the surface roughness thereof but also sufficient hardness by forming the hard surface layer comprising the first hard layer with nitrogen and oxygen residing in solid solution therein, and the second hard layer with oxygen residing in solid solution therein.
In this connection, in the first hard layer, nitrogen and oxygen in solid solution can be contained in the range of 0.6 to 8.0 wt % for nitrogen, and in the range of 1.0 to 14.0 wt % for oxygen. In the second hard layer, oxygen in solid solution can be contained in the range of 0.5 to 14.0 wt %. Accordingly, it is desirable to contain as much nitrogen or oxygen in solid solution as possible within the aforesaid ranges wherein these elements can reside in solid solution.
However, from the standpoint of maintaining excellent quality of appearance, there is need for selecting the concentration of nitrogen or oxygen in solid solution within ranges so as not to cause the surface roughness.
Further, the first hard layer with nitrogen and oxygen in solid solution residing therein may preferably be formed substantially up to a depth of 1.0 &mgr;m from the surface. By forming the first hard layer at such a depth, formation of the coarse surface due to growth of crystal grains can be inhibited while sufficient surface hardness can be obtained.
On the other hand, the second hard layer with oxygen in solid solution residing therein may preferably be formed in a region deeper than the first hard layer and substantially up to 20 &mgr;m from the surface. By forming the second hard layer at such a depth, surface hardness can be further enhanced.
In this description of the invention, the titanium is a metal composed primarily of high purity titanium, and refers to titanium class 1, class 2, class 3, and the like as described in the JIS (Japan Industrial Standards). The titanium alloy is a metal composed primarily of a high purity titanium with aluminum, vanadium, iron, and the like added thereto, and refers to titanium 60, 60E, and the like as described in the JIS. Besides the elements described, various titanium alloys and intermetallic compounds of various titanium radicals may be included in the titanium alloy.
The titanium or titanium alloy according to the invention has major applications for decorative articles such as a wristwatch case, wristwatch band, pierced earrings, earrings, a ring, the frame of eyeglasses, and the like. It is important for these decorative articles to have high quality in appearance and maintain a property impervious to scratches for a long duration. The titanium or titanium alloy according to the invention can meet such requirements.
A first method (first method of the invention) of surface treating a titanium or titanium alloy, according to the invention, comprises the following processes:
(1) a heating process comprising steps of disposing a titanium or titanium alloy in a vacuum vessel, and applying annealing treatment thereto by heating;
(2) a hardening treatment process comprising steps of feeding a mixed gas consisting primarily of nitrogen with a trace of oxygen component into the vacuum vessel, and heating inside the vacuum vessel at temperatures in the range of 700 to 800° C. in a predetermined reduced pressure condition for a predetermined length of time such that nitrogen and oxygen are diffused into the interior of the titanium or titanium alloy from the surface thereof so as to pass into solid solution therein; and
(3) a cooling process whereby the titanium or titanium alloy is cooled to room temperature after the hardening treatment process.
For example, at the surface of the titanium or titanium alloy formed into a desired shape by hot forging and polishing thereafter, there exists a working strain layer. Accordingly, in the method of surface treatment of the titanium or titanium alloy according to the invention, a heating process whereby an annealing treatment is applied thereto by heati
Hanai Kenji
Nanya Takanori
Sato Junji
Sato Masahiro
Shibuya Yoshitsugu
Armstrong, Westerman Hattori, McLeland & Naughton, L.L.P.
Citizen Watch Co. Ltd.
Yee Deborah
LandOfFree
Titanium or titanium alloy member and surface treatment... 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 or titanium alloy member and surface treatment..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Titanium or titanium alloy member and surface treatment... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2519616