JP2005281736A - Method for producing titanium alloy sintered compact by metal powder injection molding method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method capable of producing a titanium alloy sintered compact combining high strength and ductility at a low cost by jointly using low-cost hydrogenated titanium powder with hydrogenated-dehydrogenated titanium powder or gas atomized titanium powder, or substitutively using the same therefor as raw material powder in an injection molding method. <P>SOLUTION: In the method for producing a titanium alloy sintered compact by a metal powder injection molding method, a kneaded material of a powdery mixture in which the mixing ratio of hydrogenated titanium powder to hydrogenated-dehydrogenated titanium powder or gas atomized titanium powder is 10 to 100 wt.%, and the other kind of metal powder and an organic binder is injection-molded, is degreased, and is sintered. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a method for producing a titanium alloy sintered body produced by a metal powder injection molding method.

  In the metal powder injection molding method, a compound, which is a mixture of metal powder and an organic binder, is injected into a mold to produce a molded product, and then the organic binder component is degreased and removed from the molded product. This is a technique for producing a metal part having a large degree of freedom in a three-dimensional shape by sintering. At present, the metal powder injection molding method is used for manufacturing precision parts in various metal materials such as stainless steel, magnetic material and tool steel.

  Titanium and titanium alloys are expensive metal raw materials, and machining such as cutting is difficult, so there is no chip loss without machining, and the metal powder injection molding method that yields products with good raw material yields is the focus Has been.

  Until now, the raw material titanium powder of the titanium powder injection molding method has been either a powder produced by hydrodehydrogenation (referred to as hydrodehydrogenated titanium powder) or a powder produced by gas atomization (referred to as gas atomized titanium powder). One or a mixture is used as a raw material powder, and in the case of a titanium alloy, another kind of alloyed metal powder has been mixed and used.

  A technique for producing a Ti-6Al-4V alloy sintered body by metal powder injection molding using a gas atomized titanium powder as a titanium raw material powder and adding a predetermined amount of 60Al-40V alloy powder to this as a mixed powder is described in the literature "Powder and Powder". Metallurgy ”, Vol. 46, No. 10 (issued in October 1999), pp. 1053-1057,“ Effects of MIM process conditions on microstructure and mechanical properties of Ti-6Al-4V alloy sintered body ” Yes.

  However, these titanium raw material powders are very expensive, and this has increased the product cost, and has spread the use of titanium and titanium alloy parts by metal powder injection molding.

  By the way, besides these, titanium hydride powder can be used as the titanium raw material powder. This powder is expected to be used because it is cheaper than both (hydrodehydrogenated titanium powder and gas atomized titanium powder). The titanium hydride powder contains two hydrogen atoms in the powder for one titanium atom, and when this is sintered, a large amount of hydrogen contained in the sintering temperature rising process is released as a gas. Therefore, defects such as deformation of the molded body and a decrease in the density of the sintered body are likely to occur.

  So far, in metal powder injection molding, titanium hydride powder is mixed with titanium powder such as hydrodehydrogenated titanium powder or gas atomized titanium powder in a mixing ratio of 35 to 95% by weight, and this is used as a raw material powder. A method for producing a high-density titanium sintered body is disclosed in “Method for producing a high-density titanium sintered body” in Patent Document 1.

  However, this Patent Document 1 is limited to a pure titanium sintered body and does not describe manufacturing a titanium alloy sintered body.

  Further, Patent Document 1 describes conditions for obtaining a density of 95% or more for the sintered body to be produced, but does not describe the strength and ductility characteristics of the sintered body at all. When considering application of titanium and titanium alloy sintered bodies to mechanical parts, high strength and ductility characteristics are important. However, in the method described in Patent Document 1, high strength and ductility are obtained even if a sufficient density is obtained. Characteristics are not always obtained.

  By the way, titanium absorbs interstitial impurity elements such as oxygen and carbon during the sintering process, and thus becomes brittle. Therefore, titanium and titanium alloy sintered bodies are not limited to the compacting method and the metal powder injection molding method. There is a drawback that it is difficult to obtain a good ductility. For this reason, in the metal injection molding method of titanium and titanium alloy, it is important to prevent oxygen and carbon from entering particularly in each process and to keep the amount of oxygen and carbon in the sintered body as low as possible.

  Titanium is not only used as pure titanium, but is often used as a titanium alloy depending on the application, and development of its production method is extremely important.

  Therefore, in order to produce a titanium alloy sintered body using titanium hydride powder, another kind of alloyed metal powder is added to hydrodehydrogenated titanium powder or gas atomized titanium powder and titanium hydride powder. Thus, it is necessary to use a titanium alloy raw material mixed powder.

  In this regard, a method for producing a titanium alloy sintered body by adding another type of alloyed metal powder to hydrodehydrogenated titanium powder or gas atomized titanium powder and titanium hydride powder is described in “High Density” A method for producing a sintered titanium alloy has been proposed.

  However, this production method is not metal powder injection molding, but is a method of compacting a mixed powder. After compacting, the compact is placed in a temperature range of 600 ° C. or more and less than 800 ° C. for a long time of 10 to 30 hours. After holding and dehydrogenating, the temperature is further raised to a predetermined sintering temperature and sintered. At this time, if the dehydrogenation holding time is shortened, the vaporized hydrogen gas stays inside the compact, and the shrinkage of the voids of the compact due to sintering is hindered, so that a high-density sintered compact cannot be obtained. In addition, this manufacturing method cannot directly produce a complicated shape as much as metal powder injection molding without machining, and requires a long time for dehydrogenation, which is disadvantageous in terms of cost.

Thus, in the titanium alloy sintered body, the characteristics of the sintered body greatly vary depending on the kind of alloying powder to be added, the addition method, the sintering conditions, the molding method, and the like.
The present inventor is the type of titanium hydride powder, particle size, oxygen content difference, mixing ratio, mixing method, type of alloyed metal powder, degreasing conditions, dehydrogenating conditions, sintering temperature, time, atmosphere, sintering A setter and the like were examined in detail, and a production method of a titanium alloy sintered body having good characteristics by a metal powder injection molding method was found.
JP 2000-17301 A JP 7-278609 A

The problem to be solved is that the titanium alloy sintered body produced by conventional metal powder injection molding has a high price of hydrodehydrogenated titanium powder or gas atomized titanium powder, which is the raw material powder, which has increased the product cost There is to solve the point.
In the metal powder injection molding method, the present invention uses a low-cost titanium hydride powder as a raw material powder and is used in combination with or in place of a hydrodehydrogenated titanium powder or a gas atomized titanium powder, and has both high strength and ductility at a low cost. It is providing the method which can manufacture a titanium alloy sintered compact.

In order to achieve the above-mentioned problems, the present invention is characterized by the following configuration.
1. In the method for producing a titanium alloy sintered body by the metal powder injection molding method, a mixed powder in which the mixing ratio of the titanium hydride powder to the hydrogenated dehydrogenated titanium powder or the gas atomized titanium powder is 10 wt% to 100 wt%, and another type A kneaded product of the metal powder and organic binder is injection-molded, degreased and sintered.
2. In the above 1, the mixing ratio of the mixed powder is 10 wt% to 60 wt% of the titanium hydride powder with respect to the hydrodehydrogenated titanium powder or the gas atomized titanium powder, and another type of metal powder is a 60Al-40V alloy. The mixing ratio of the mixed powder: 60Al-40V alloy powder is 9: 1 in weight ratio.

In the conventional metal powder injection molding of titanium alloy, expensive hydrodehydrogenated titanium powder or gas atomized titanium powder has been used as raw material titanium powder. However, in the present invention, low-cost titanium hydride powder is hydrodehydrogenated titanium. By using a powder or gas atomized titanium powder in combination or instead, and developing an optimum manufacturing process, a sintered body having both high strength and ductility is obtained, thereby solving the two problems of cost and ductility.
The mixing ratio of the hydrogenated dehydrogenated powder or the titanium hydride powder mixed with the gas atomized titanium powder is 10 to 100% by weight, and another mixed metal powder such as 60Al-40V alloy powder or other alloyed powder is added to both mixed powders. A predetermined amount of the added powder is added and mixed with a V-type mixer or a ball mill.
If the mixing ratio of the titanium hydride powder was less than 10% by weight, it was excluded because the merit of cost reduction was small. The mixing ratio is desirably 10 to 60% by weight, and a sintered body having both high strength and ductility is obtained at a mixing ratio of 10 to 60% by weight. On the other hand, when the amount is 60% by weight or more, high density and strength can be obtained, but sufficient ductility cannot be obtained.
The mixing ratio of the mixed powder and another type of metal powder, such as 60Al-40V alloy powder, is 9: 1 by weight, and when the powder of this mixing ratio is sintered, structural titanium has a good balance between strength and ductility. It becomes a Ti-6Al-4V alloy which is an alloy.

An organic binder made of polypropylene, wax or the like is added to the mixed powder or the like in a volume ratio of 30 to 50% by weight, and kneaded with a pressure kneader to make a kneaded material called a compound. This kneaded product is injection-molded to form a molded body.
After removing the organic binder component from the molded body by a method such as solvent extraction degreasing or heat degreasing with an electric furnace, etc., the remaining organic binder component and hydrogen in titanium are vaporized and removed by heating in an electric furnace. Then, the temperature is further raised, held at a predetermined sintering temperature for a predetermined time, and sintered. When degreasing the organic binder component in the electric furnace and removing the hydrogen in the titanium by vaporization, the temperature is gradually raised in order to avoid blistering, deformation and a decrease in the density of the sintered body. However, degreasing and dehydrogenation are carried out continuously, and the vaporized hydrogen smoothly escapes to the outside through the voids between the powder particles generated by the degreasing, so it is not necessary to hold for a long time for dehydrogenation. During sintering, it is necessary to increase the vacuum in the furnace and appropriately select the materials for the sintering tools such as the sintering box and the floor plate in order to suppress the absorption of interstitial elements such as oxygen and carbon into the sintered body. is there. By this method, a titanium alloy sintered body having both high strength and ductility can be obtained.

A. According to claim 1, in the metal powder injection molding method, by using titanium hydride powder instead of or in combination with gas atomized powder or hydrodehydrogenated titanium powder as raw material powder of titanium alloy, low cost can be obtained. Thus, a titanium alloy sintered body having both high strength and ductility can be produced.
B. According to claim 2, a Ti-6Al-4V alloy sintered body can be manufactured.

Next, an example of manufacturing a Ti-6Al-4V alloy sintered body according to claim 2 will be described as an embodiment of the method for manufacturing a titanium alloy sintered body according to the metal powder injection molding method of the present invention.
As the titanium raw material powder, the weight ratio of the titanium hydride powder having a particle size of 45 μm or less to the gas atomized titanium powder having a particle size of 45 μm or less is set to 25, 50, 75, or 100% by weight. (Al: V weight ratio 3: 2) was added at a mixing ratio of 9: 1 by weight and mixed by a ball mill.
An organic binder made of polypropylene, acrylic resin, paraffin wax or the like was added to the mixed powder at a volume ratio of 35 to 45%, and kneaded by a pressure kneader to prepare a compound.

The compound was pulverized and adjusted to a particle size of 2 to 8 mm, and injection molded in a mold to produce a flat dumbbell-shaped molded article for tensile test as shown in FIG. About this molded object, it heated at 70 degreeC with hexane vapor | steam for 6 hours, and organic binder components other than a polypropylene were substantially extracted and degreased.
Thereafter, the molded body is placed on a zirconia plate, placed in a zirconia box or a molybdenum box, and charged in an electric furnace, slowly heated to 430 ° C. over 16 hours in a reduced pressure argon flow of several hundred Pa, and the rest After vaporizing and removing hydrogen in polypropylene and titanium as a binder component, the temperature was further raised to a sintering temperature of 1000 to 1350 ° C. in a high vacuum atmosphere of 10 ⁻² Pa or less, held for 1 to 8 hours, and baked. I concluded. After sintering, it was cooled in the furnace to room temperature.

Among the Ti-6Al-4V alloy sintered bodies 1 produced by the above method, Sample No. 1 having a sintering temperature of 1100 ° C. and a sintering holding time of 8 hours was used. The numerical values of relative density, tensile strength, elongation, and oxygen content in the sintered body are shown in FIG.
Sample No. The relative densities of 1-6 Ti-6Al-4V alloy sintered bodies 1 all showed a high density of 96% or more. However, as the titanium hydride powder content increases, the amount of oxygen increases and the elongation decreases. In addition, when the sintered box material type is zirconia, the amount of oxygen in the sintered body increases as compared with the molybdenum sintered box.

As a result, when the sintered box material type is made of titanium, the Ti-6Al-4V alloy sintered body 1 (sample No. 1) having a titanium hydride powder content of 25% has a relative density of 97.0% and a tensile strength. It showed 910 MPa, elongation 14%, oxygen amount 3106 PPM.
Ti-6Al-4V alloy sintered body 1 (sample No. 3) having a titanium hydride powder content of 50% exhibited a relative density of 97.5%, a tensile strength of 955 MPa, an elongation of 12%, and an oxygen content of 3682 PPM.
Further, Ti-6Al-4V alloy sintered body 1 (sample No. 5) having a titanium hydride powder content of 75% has a relative density of 97.5%, a tensile strength of 957 MPa, an elongation of 1.9%, and an oxygen amount of 4380 PPM. Indicated.
Further, Ti-6Al-4V alloy sintered body 1 (sample No. 7) of titanium hydride powder 100% showed a relative density of 97.4%, a tensile strength of 943 MPa, an elongation of 0.9%, and an oxygen content of 4992 PPM. It was.

  As described above, the Ti-6Al-4V alloy sintered body 1 having a titanium hydride powder content of 25% and 50% exhibits a high density of 97% or more, a tensile strength of 900 MPa or more, and an elongation of 10%. The above good ductility is shown. These values satisfy the JIS standard value of the Ti-6Al-4V alloy defined by the melted material. However, when the content of titanium hydride powder further increased to 75% and 100%, the elongation decreased and became below the JIS standard value. From these results, it is desirable that the titanium hydride powder content is 60%.

The Ti-6Al-4V alloy sintered compact produced by the metal powder injection molding method of this invention is shown, (a) is a top view, (b) is a front view. The table | surface which shows the characteristic of the Ti-6Al-4V alloy sintered compact of this invention.

Explanation of symbols

  1 Ti-6Al-4V alloy sintered body

Claims (2)

  In the method for producing a titanium alloy sintered body by the metal powder injection molding method, a mixed powder in which the mixing ratio of the titanium hydride powder to the hydrogenated dehydrogenated titanium powder or the gas atomized titanium powder is 10 wt% to 100 wt%, and another type A method for producing a sintered titanium alloy, comprising: injection molding, degreasing, and sintering a kneaded product of a metal powder and an organic binder.   The mixing ratio of the mixed powder is 10% to 60% by weight of titanium hydride powder with respect to hydrodehydrogenated titanium powder or gas atomized titanium powder, and another kind of metal powder is mixed with 60Al-40V alloy powder. The method for producing a titanium alloy sintered body according to claim 1, wherein the mixing ratio of the powder: 60Al-40V alloy powder is 9: 1 by weight.

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