Specialized metallurgical processes – compositions for use therei – Processes – Producing or purifying free metal powder or producing or...
Utility Patent
1998-04-02
2001-01-02
Mai, Ngoclan (Department: 1742)
Specialized metallurgical processes, compositions for use therei
Processes
Producing or purifying free metal powder or producing or...
C075S352000, C075S354000, C075S363000, C423S645000
Utility Patent
active
06168644
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Technical Field
This invention relates to titanium hydride powders (including titanium hydride alloy powder, the same shall apply hereinafter), and titanium powders (including titanium alloy powder, the same shall apply hereinafter), and a process for production of the titanium powders.
2. Background Art
Recently, sintered titanium and sintered titanium alloys produced by powder metallurgy come to be widely used in various applications such as refractory metals. These sintered titanium metals and these alloys are usually applied to mechanical parts requiring high tensile strength and elongation. However, these mechanical properties are greatly affected by oxygen content in the metals and these alloys. When the oxygen content exceeds 0.3 wt %, the mechanical properties such as elongation are known to be significantly deteriorated. In consideration of inevitable oxygen contamination during powder metallurgy processes, the oxygen content of titanium powder as the raw material must be 0.15 wt % or less (Refer to R&D Review of TOYOTA CRDL, 26-1(1991)).
The sintered titanium and these alloys need titanium powder and titanium hydride powder with high purity, excellent flowability and compactibility, which powders can be produced by a hydride-dehydride (HDH) process. The HDH process are completed after hydrogenating titanium and its alloy, crushing hydrogenated metals to desired powder size and dehydrogenating its powder in vacuum-heating.
In detail, the HDH process comprises hydrogenating titanium metal or titanium alloy as a raw material at an elevated temperature in hydrogen gas, crushing the lumps of hydrogenated titanium metal or titanium alloy into a powder, with a prescribed particle size, dehydrogenating the powder at an elevated temperature in vacuum, breaking the sintered powders and sizing the powders into a desired range.
Thus obtained powders have an excellent purity and a highly uniform particle size. In addition, when high quality metals are employed as a raw material, high quality powders can be produced in the HDH process. For this reason, the HDH process is considered to be advantageous for producing titanium powders.
The smaller the particle size is, the higher becomes the specific surface area, resulting in higher oxygen content. In considering such characteristics of the titanium powders, a process for obtaining titanium powders with a low oxygen content has been proposed, in which after the particle size of the titanium hydride powder is preliminarily controlled by sieving and removing such that the ratio of the fine particles with a diameter of 63 &mgr;m or less, for example, is limited to a prescribed level in a particle size distribution of the powder, this powder is dehydrogenated to obtain a titanium powder (Japanese Patent Unexamined (KOKAI) Publication No. 247503/93). However, in this process, a large part of the fine particle powder is removed, causing a cost increase.
Flowability and compactibility are essential for the titanium powder and titanium hydride powder in using as a raw material for the powder metallurgy. Therefore, the titanium powder and the titanium hydride powder must satisfy the flowability and compactibility, too. As the titanium powder with both the fine particle size and excellent flowability, Japanese Patent Unexamined (KOKAI) Publication No. 278601/95 discloses a titanium powder with a particle diameter ranging from 5 &mgr;m to 74 &mgr;m and the average particle diameter of 20 &mgr;m or less. However, the titanium powder obtainable by this teaching has the oxygen content approximately in the range from 2000 to 3000 ppm.
The titanium sponge produced by the Kroll process usually contains chlorine of approximately 0.08% by weight because magnesium chloride remains as a by-product in the titanium sponge. Since this chlorine is not completely removed and remains as an impurity in the titanium powder even after the HDH process, pores are formed in the sintered titanium materials as a final product and the fatigue strength is degraded. Accordingly the titanium hydride powder and titanium powder are desired with low chlorine content. Japanese Patent Unexamined (KOKAI) Publication No. 139706/89) discloses a process for removing a residual chlorine by washing the titanium powder after the HDH process.
However, the washing water is essentially required to be an ion exchanged one substantially containing no chlorine and since oxygen contamination in washing is also inevitable, a drying step is essentially required to decrease an occurrence of the oxygen contamination. Thus, it brings a new problem that the drying cost is additionally required and the quality is degraded.
An object of the present invention is to provide titanium hydride powders, titanium powders, and a process for production of the same with maintaining the characteristics, in which the titanium hydride powders and titanium powders present an excellent flowability and compactibility, and in which an oxygen and chlorine content can be reduced simultaneously through this process with high yield.
SUMMARY OF THE INVENTION
A titanium hydride powder according to the present invention is characterized by having a maximum particle diameter of substantially 150 &mgr;m or less, the powder comprising a particle diameter of 10 &mgr;m or less being 8% or less by weight, which is produced via the step for embrittling a titanium or titanium alloy through hydrogenation. The titanium hydride powder thus obtained contains hydrogen of 3.5% to 4.5% by weight.
The expression “substantially 150 &mgr;m or less” herein used means that although there may remain some powders on a sieve of 150 &mgr;m in sieving, such powder is less than 1% by weight in the total powder and 99% or more by weight with a maximum particle diameter of 150 &mgr;m or less(the same shall apply hereinafter).
As previously mentioned, the higher the ratio of the fine powder contained in the titanium hydride powder is, the higher the oxygen content of the titanium powder becomes, which is ascribed to moisture and oxygen in the atmosphere. The study and investigation of the present inventors show that when the titanium hydride powder with particle diameters of 10 &mgr;m or less exceeds 8% by weight, the fine powder is overly increased and as a result, the oxygen content of this titanium hydride powder exceeds 0.15% by weight, resulting that the sintered titanium materials as a final product are deteriorated in mechanical properties. In addition, with the increase of the fine powder, the flowability of the powder is lowered and the compactibility thereof is also lowered under the adverse effect of the oxidized fine powders. Accordingly, it is essentially required for the titanium hydride powder of the present invention that the powder with particle diameters of 10 &mgr;m or less is 8% by weight or less.
It should be noted that the oxygen content of the titanium hydride powder must essentially be 0.15% or less by weight. When the oxygen content is in this range, the compactibility of the powders and the mechanical properties can be fully satisfied for a sintered titanium or sintered titanium alloy. The powder with particle diameters of 10 &mgr;m or less is approximately controlled within a range of 8% or less by weight and preferably 5% or less by weight, depending on the powder properties required for the target sintered product and an established cost thereof.
The chlorine content of the titanium hydride powder of the present invention is preferably 0.06% or less by weight. If the chlorine content exceeds 0.06% by weight, the titanium sintered products by the powder metallurgy has an increased number of enlarged pores and the mechanical properties thereof, such as fatigue strength, tend to be degraded.
Since the chlorine of the titanium hydride powder is localized in a fine powder with particle diameters of 10 &mgr;m or less, it is possible to control the initial chlorine content so that the powder with particle diameters of 10 &mgr;m or less occupies 8% or less by weight.
The titanium powder of the pres
Fukasawa Eiichi
Sugawara Satoshi
Mai Ngoclan
Oliff & Berridg,e PLC
Toho Titanium Co., Ltd.
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