JP4947690B2 - Method for producing titanium-based alloy spherical powder - Google Patents

Description

  The present invention relates to a method for producing a spherical powder made of a titanium-based alloy such as a Ti—Al alloy (Ti: Al = 64: 36) or a Ti-6Al-4V alloy (Ti: Al: V = 90: 6: 4). More specifically, the present invention relates to a method for producing a titanium-based alloy spherical powder capable of reducing an alloy composition difference due to a product particle size.

  One of the methods for producing a titanium-based alloy spherical powder used for powder metallurgy raw materials is by a gas atomizing method. In this method, after mixing titanium powder and additive alloy element powder, the mixed powder is compressed into a melting raw material (compact), and the molten metal obtained by melting this is scattered into fine droplets with high-pressure gas. The spherical powder of the titanium alloy is produced by solidification. The process of scattering and solidifying the molten metal obtained by melting the compact with high-pressure gas is gas atomization, and particles having high sphericity can be stably produced.

  This spherical powder manufacturing method is described in, for example, Patent Documents 1 to 3, and in these methods, induction heating is used to dissolve the compact, and the rod-shaped compact is gradually dissolved in a non-contact manner from the bottom. By continuously forming and flowing down the molten metal and directly gas atomizing the molten metal, it is possible to eliminate the crucible and greatly reduce contamination due to contact with foreign matter. And in patent document 1, the spherical powder of Ti-6Al-4V alloy (Ti: Al: V = 90: 6: 4) is manufactured by this method, and in patent document 2 and 3, Ti-Al alloy (Ti: A spherical powder of Al = 64: 36) is produced.

JP-A-5-93213 JP-A-6-116609 JP 2002-241807 A

  It is known that such a method for producing a titanium-based alloy spherical powder by the gas atomization method has a problem in that the alloy composition varies depending on the product particle size. Specifically, in the method for producing a Ti-6Al-4V alloy powder described in Patent Document 1, when classification is performed after gas atomization, the concentration of added metal elements in the powder having a small particle size (in the case of Ti-6Al-4V alloy) Al) is higher than the ratio (mixing ratio) in the mixed raw material, which is a raw material powder, and conversely, this is lower for a powder having a large particle size.

  Regarding the non-uniformity of the alloy composition depending on the product particle size of the gas atomized alloy spherical powder, the case of a Ti—Al alloy is regarded as a problem. And in the same literature, in order to eliminate this non-uniformity, from the viewpoint that uniform composition of the molten metal is indispensable, fine spherical particles having a particle size of 250 μm or less manufactured by gas atomization method are used as raw material powder. It is presented as a problem solving means. Such spherical fine particles are excellent in fluidity and high in apparent packing density, so that it is possible to produce a compact in which raw material powders are homogeneously mixed. ing.

  As a specific example, when sponge titanium particles having a particle size of 0.75 to 12.7 mm and granular aluminum having a particle size of 4 to 10 mm are used as the raw material powder, the difference in Al concentration for each product particle size is 2 at the maximum. %, And when titanium sponge particles having a particle size of 0.75 to 12.7 mm and aluminum powder having a particle size of 250 μm or less are used, the difference in Al concentration for each product particle size is 2.6% at maximum. (Comparative Examples 3 and 4). On the other hand, when gas atomized Ti powder having a particle size of 250 μm or less and Al powder having a particle size of 250 μm or less are used, the difference in Al concentration is 0.4% at maximum (Example 1). In addition, when a gas atomized Ti powder having a particle size of 150 μm or less and an Al powder having a particle size of 150 μm or less are used, the difference in Al concentration is 0.3% at maximum (Example 2).

  However, gas atomized Ti powder is very expensive compared to sponge titanium powder, and measures using this as a raw material are not economical and result in an increase in the price of the product powder.

  In addition, when the product is Ti-6Al-4V alloy powder, the additive metal element ratio is as small as 10%. For this reason, the Ti-6Al-4V alloy powder may not be allowed in the Ti-6Al-4V alloy powder, even if the Ti-6Al-4V alloy powder has an allowable difference in particle size between the Ti-Al alloy powder (additional metal element ratio 36%). In the production of the above, uniform composition between the product particle sizes is a particularly important technical issue.

The object of the present invention is to significantly and economically reduce the difference in alloy composition when the ratio of the additive alloy in which the problem of the alloy composition difference due to the product particle size becomes significant is small , and the product is made of Ti-6Al-4V alloy powder. Also in the case, it is providing the manufacturing method of the titanium type alloy spherical powder which can reduce the alloy composition difference by a product particle size effectively.

  In order to achieve the above object, the present inventors paid attention to the type of raw material titanium particles and the method of mixing with additive metal element particles. That is, in order to reduce the raw material cost, the use of gas atomized titanium powder must be avoided, and the use of sponge titanium powder is indispensable. Therefore, the present inventors planned to produce a titanium sponge powder as fine as possible. This is because, in the case of the sponge titanium powder, if it is fine, it is considered that the mixing property with the alloy element powder is improved and the difference in the alloy composition due to the product particle size can be eliminated. However, it is difficult to produce a fine sponge titanium powder having a gas atomization level (250 μm or less). For example, in the process of refining the sponge titanium for wrought material, generally, large and small sponge titanium lumps are crushed by a jaw crusher, and classified (sieving), the particle diameter becomes 0.75-12. 7 mm fine-grained products are manufactured.

  In such a general-purpose method, it is impossible to produce a fine sponge titanium powder with a gas atomization level (250 μm or less), and the particle size is 0.3 mm or more even for a low-class sieve product in a classification process. It is. In other words, in the case of sponge titanium powder, it is very difficult to manufacture a fine sponge titanium powder with a gas atomization level (250 μm or less), but a powder of 0.3 mm or more can be easily manufactured. .

  Next, as a mixing method of raw material particles, in the manufacture of a titanium alloy by a gas atomization method, simple mixing using a V-type mixer is used for mixing raw material titanium particles and additive metal element particles. Therefore, the present inventors obtained three types of sponge titanium particles having an average particle size of 0.3 mm, 1 mm, and 3 mm from the sieved product and the product powder particles in the sponge titanium refinement and classification process by sieving classification. These, Al particles, and V particles were simply mixed with a V-type mixer, compressed, and gas atomized as a compact for dissolution. However, the nonuniformity of Al concentration due to the product particle size was not solved.

  Further, instead of using Al particles and V particles individually, a gas atomized Ti alloy powder was produced in the same manner by simply mixing Al and V mother alloy particles with the Ti particles using a V-type mixer. Although the nonuniformity of the Al concentration due to the product particle size was slightly eliminated, it was not a satisfactory level. Incidentally, since the nonuniformity of the Al concentration is generally proportional to the nonuniformity of the V concentration, the nonuniformity of the additive metal element concentration can be represented by the nonuniformity of the Al concentration.

  Based on such a result, the present inventors reconsidered a method for eliminating the unevenness of the additive metal element concentration, and finally came to a mixing method of sponge titanium particles and additive metal element particles. And the simple mixing by the V type mixer until now was changed into the pulverization mixing by a ball mill. As a result, despite the use of the above-mentioned three types of sponge titanium particles having an average particle size of 0.3 mm, 1 mm, and 3 mm as the Ti particles, the deviation from the mixing ratio of the Al concentration depending on the product particle size is dramatic. Decreased.

  That is, with regard to the mixing of raw material grains, it has been considered first to improve the uniformity, and the mixing time and the like have been thought-and-errored. However, there was no idea of changing the type of the mixer. Under such circumstances, the present inventors paid attention to a mixer having a crushing function such as a ball mill, and as a result of considering from various angles, if a mixer having a crushing function is used, particle mixing is performed. In the process, fine particles by grinding, especially grinding of added metal element particles, grinding, and further application of titanium particles by grinding, etc., progresses as if fine particles were uniformly mixed. I found out. As a result, the prior dissolution of the additive metal element particles is effectively suppressed, and even if relatively large diameter raw material particles such as 0.3 mm or more are used, the result is equivalent to using fine spherical particles in the end. It was confirmed that the uniform mixing effect was excellent and the non-uniformity of the alloy composition due to the product grain size was dramatically eliminated.

The method for producing a titanium-based alloy spherical powder of the present invention has been completed on the basis of such knowledge, and in the method for producing a spherical powder made of a titanium-based alloy having an additive metal element ratio of 20% or less, A step of mixing the additive metal element particles with a ball mill, an attritor or a vibration mill, which is a mixer having a pulverizing function, and a step of forming the mixed particles obtained by mixing with the mixer into a rod-shaped molten raw material by compression; It includes a step of inductively heating the formed rod-shaped melting raw material in an insoluble atmosphere to perform non-contact melting, and a step of pulverizing a molten alloy formed by non-contact melting by a gas atomization method.

  In the method for producing a titanium-based alloy spherical powder of the present invention, by using a mixer having a pulverizing function for mixing titanium particles and additive metal element particles, it is possible to obtain amorphous sponge titanium particles and 0.3 mm. Despite the use of large-diameter titanium particles as described above, the additive metal element particles are fixed to the titanium particles by grinding (or grinding) of the additive metal element particles in the mixing process, and the additive metal element particles having a low melting point are preceded. Suppresses the phenomenon of melting, resulting in an excellent uniform mixing action similar to that when using fine gas atomized Ti grains, resulting in a remarkable and economical solution to non-uniform alloy composition due to product grain size. Is done.

  More specifically, when the additive metal element particle is a soft Al particle, rubbing to the sponge titanium particle is caused exclusively by grinding, and when it is a brittle Al-V particle, the titanium sponge is finely pulverized into fine particles. In any case, the titanium particles and the additive metal element particles are mixed well, and the titanium particles are not fine spherical particles. An equivalent non-uniformity elimination effect can be obtained. This is the first feature of the present invention.

  Furthermore, in the mixing of titanium grains and additive metal element grains using a mixer having a grinding function, alloying by mechanical alloying, which is a solid-phase reaction, partially proceeds and may contribute to the elimination of compositional non-uniformity. There is also sex.

  The coating action by grinding of the additive metal element particles and the filling and fixing to the titanium particle surface by fine pulverization cannot be expected much when the raw material titanium particles are spherical gas atomized particles with a smooth surface, rather the surface unevenness is severe More inexpensive amorphous titanium sponge particles can be expected. That is, the sponge titanium particles have a large number of irregularities on the surface, and the additive metal element particles are more effectively fixed in a mixer having a grinding function. Thus, in the present invention, it is important to combine inexpensive sponge titanium particles with a mixer having a pulverizing function, and this is the second feature.

  Specifically, the mixer having a pulverizing function is a ball mill, an attritor, a vibration mill, or the like, and a particularly preferable mixer is a ball mill having a remarkable pulverizing action and a grinding action by rubbing.

  The average particle size of the sponge titanium particles used as the raw material titanium particles is preferably 0.3 to 5 mm, more preferably 0.4 to 3 mm, and particularly preferably 0.6 to 3 mm. This is because it is difficult to produce sponge titanium particles having a particle size of less than 0.3 mm, and when the particle size of the sponge titanium particles becomes small, the concentration of impurities such as impurity metal elements and oxygen in the product powder tends to increase. Because it becomes. This is due to an increase in the surface area of the titanium sponge particles and an increase in contamination in the manufacturing process of the titanium sponge particles.

  As the sponge titanium particles having a diameter of 0.3 mm or more, it is possible to use a sieving material derived from a fine particle classification process of sponge titanium for wrought material, and its use is economical and preferable. In other words, it is also one of the features of the present invention that a particularly inexpensive sieving material can be used among the sponge titanium particles.

  As a raw material for producing the gas atomized alloy spherical powder, finely divided Ti particles are preferable. However, as described above, Ti particles are difficult to be fined because of high ductility. For this reason, Ti grains refined by the gas atomization method or HDH method are used, but the production cost increases and the product price increases. In the present invention, a low-grade product called a sieve product can be used effectively, so that the cost for fine granulation can be reduced. This is the third feature of the present invention.

  Regarding the upper limit of the particle size of the sponge titanium particles, the feature of the present invention is that the composition of the product powder can be made uniform even if the particle size of the sponge titanium particles is large, but if the particle size is too large, the effect of uniforming the composition is obtained. From this viewpoint, it is preferably 5 mm or less, and particularly preferably 3 mm or less.

  The kind of the additive metal element particles is appropriately selected according to the product composition. For example, when the product is a Ti—Al alloy powder, it is Al particles, and when the product is a Ti-6Al-4V alloy powder, V grains or Al-V master alloy grains obtained by melting Al and V. The use of Al-V master alloy grains is more advantageous in terms of uniform composition than the use of Al grains and V grains mixed. Since the melting points of Al grains and V grains are greatly different, the prior dissolution of Al grains proceeds also due to the application action to the titanium sponge grains, which is disadvantageous in terms of uniform composition.

  The average particle size of the additive metal element particles is desirably 0.2 to 50 mm, and particularly desirably 0.5 to 30 mm. If this particle size is too small, the effect of the present invention is ineffective because the characteristic action of the present invention, that is, the application of the additive metal element particles to the titanium sponge particles accompanying the pulverization or grinding is not sufficient. It will be enough. On the other hand, when it is too large, the pulverization efficiency in the initial stage of mixing and pulverization deteriorates.

  As described above, the problem of the difference in the alloy composition due to the product particle size becomes more prominent in the manufacture of an alloy having a small additive metal element ratio. The present invention that can effectively solve this problem is effective in manufacturing an alloy having a small additive metal element ratio, specifically, an alloy having an additive metal element ratio of 20% or less. In particular, this ratio is 10%. Therefore, it is effective in the production of Ti-6Al-4V alloy.

The titanium alloy spherical powder production method of the present invention is a mixture of sponge titanium particles and additive metal element particles, and when the titanium alloy spherical powder is produced by the gas atomization method as a rod-shaped melting raw material, the particle mixing function is pulverized. By using a ball mill, an attritor, or a vibration mill, which is a mixer having the following, the problem of the alloy composition difference due to the product particle size becomes prominent. In producing an alloy powder having an additive metal element ratio of 20% or less, the gas atomization method is used. Without using expensive fine spherical titanium particles, it is possible to impart a high alloy composition uniformity equivalent to that used to the product alloy powder. Therefore, high-quality alloy spherical powder can be manufactured much more economically than before. In addition, a particularly inexpensive unsieved product can be used as the sponge titanium particles, and the economy can be improved from this point.

Embodiments of the present invention will be described below. First, as a reference example, a case where a Ti—Al alloy spherical powder having an additive metal element ratio of 36% will be described.

  As raw material powder, relatively coarse sponge titanium particles having an average particle size of 0.3 mm or more are prepared. As the sponge titanium particles, a sieve material and a product (sieved product) generated in a fine particle classification process by a jaw crusher of sponge titanium for wrought material are classified and used. Also, as the additive metal element particles, relatively large Al particles having an average particle diameter of 0.2 mm or more, desirably 0.5 mm or more are prepared.

  When the raw material powder is prepared, as a first step, sponge titanium particles and Al particles are mixed at a weight ratio of 64:36 using a ball mill. The ball mill has not only a mixing function but also a pulverizing function. In the mixing process, the Al particles are particularly pulverized to a small size, and the comparatively soft Al particles are crushed and pressed against the surface of the sponge titanium particles by pressing the particles together. As a result, the Al particles are firmly fixed to the uneven surface of the sponge titanium particles, and it is as if the fine particles are uniformly mixed.

  When the mixing of the sponge titanium particles and the Al particles is completed, the mixed particles are compressed into a rod-shaped melting raw material as the second step. As the compression molding method, a known method such as a die press or a cold isostatic press can be used.

  When the rod-shaped melting raw material is formed, a Ti—Al alloy spherical powder is produced by a gas atomization method as a third step. Specifically, a rod-shaped melted raw material stands vertically in an inert gas chamber, and is supplied from the top to the bottom inside an annular induction heating coil that is also arranged vertically. As a result, the melted raw materials are sequentially melted in a non-contact manner from the bottom, and a Ti—Al alloy melt is continuously formed and flows downward. And an inert gas is sprayed from the circumference | surroundings to this molten metal flow, and it scatters finely and solidifies, A Ti-Al alloy spherical powder is manufactured.

  When simple mixing using a V-type mixer is used in the first step, the low melting point Al particles are first dissolved in the third step, causing the alloy composition to vary, but in this embodiment, as described above, In the first step, Al particles are half-coated on the surface of the sponge titanium particles and firmly fixed, so that the prior dissolution of Al is prevented and the alloy composition difference is eliminated. As the induction heating coil, a spiral coil whose diameter gradually decreases from top to bottom as shown in Patent Document 3 is preferable.

Next, as an example of the present invention, a case of manufacturing a Ti-6Al-4V alloy spherical powder having an additive metal element ratio of 10% will be described.

  As raw material powder, relatively coarse sponge titanium particles having an average particle size of 0.3 mm or more are prepared. As the sponge titanium particles, a sieve material and a product (sieved product) generated in a fine particle classification process by a jaw crusher of sponge titanium for wrought material are classified and used. Further, as the additive metal element particles, Al-V alloy particles having a relatively large diameter (Al: V = 6: 4 mother alloy particles) having an average particle diameter of 0.2 mm or more, desirably 0.5 mm or more are prepared. .

  When the raw material powder is prepared, as a first step, sponge titanium particles and Al—V alloy particles are mixed at a weight ratio of 9: 1 using a ball mill. The ball mill has not only a mixing function but also a grinding function. Since the Al-V master alloy grains are more brittle than Ti, they are pulverized particularly small during the mixing process, and are tightly packed and fixed in the recesses on the rough surface of the sponge titanium grains, as if the fine spherical particles were uniformly mixed. It becomes such a state.

  When the mixing of the sponge titanium particles and the Al-V alloy particles is completed, the mixed particles are compressed into a rod-shaped melting raw material as a second step. As the compression molding method, a known method such as a die press or a cold isostatic press can be used.

  When the rod-shaped melting raw material is formed, a Ti-6Al-4V alloy spherical powder is produced by a gas atomization method as a third step. Specifically, a rod-shaped melted raw material stands vertically in an inert gas chamber, and is supplied from the top to the bottom inside an annular induction heating coil that is also arranged vertically. As a result, the melted raw material is gradually non-contact melted from below, and a Ti-6Al-4V alloy melt is continuously formed and flows downward. And an inert gas is sprayed from the circumference | surroundings to this molten metal flow, and it disperses finely and solidifies, A Ti-6Al-4V alloy spherical powder is manufactured.

  Also in this embodiment, since the Al-V alloy particles, which are additive metal element particles, are finely pulverized into fine particles and firmly fixed to the surface of the sponge titanium particles by mechanical fitting in the first step as described above, the additive metal Pre-dissolution of elements is prevented and the alloy composition difference is eliminated. As the induction heating coil, a spiral coil whose diameter gradually decreases from top to bottom as shown in Patent Document 3 is preferable.

  When the Ti-6Al-4V alloy spherical powder was produced by the above-described method, the average particle diameters of the sponge titanium grains and the Al-V alloy grains were variously changed. As the sponge titanium particles, sieved materials and products (sieved products) generated in the refinement and classification process of the expanded titanium sponge titanium jaw crusher were used. A ball mill was used as the mixer. The Al concentration, Fe concentration, and O concentration of the produced Ti-6Al-4V alloy spherical powder were investigated. The product particle size is 45 μm or less. For comparison purposes, the same investigation was performed for the case where a V-type mixer was used as the mixer. The results are shown in Table 1.

  When the average particle diameter of the sponge titanium particles is 0.3 mm, the deviation from the Al concentration blending ratio (6.0%) is 0.05% (the deviation rate is 0.05 / 6 = about 1/100). Small (Example 4). This is because a ball mill was used for the mixer. This is because when the V-type mixer is used as the mixer, the deviation from the Al concentration blending ratio (6.0%) is 0.5% (the deviation rate is 0) even though the other conditions are the same. .5 / 6 = about 1/10) and very large (Comparative Example 2). However, since the surface of the titanium grains is rough, the grain size is small and the surface area is large, the impurity concentration is somewhat higher.

  Even when the average particle diameter of the sponge titanium particles is as large as 3 mm, the deviation from the blending ratio of Al concentration (6.0%) is 0.2% (the deviation rate is 0.2 / 6 = 1/30). Small (Example 3). The impurity concentration is suppressed to a low level because the particle size of the sponge titanium particles is large and the surface area is small.

  When the average particle diameter of the sponge titanium particles is 1 mm, the results are shown for the case where the average particle diameter of the Al-V alloy particles is 10 mm, which is the same as described above, and 0.5 mm, which is smaller than the above. When the average particle diameter of the Al-V alloy particles is 10 mm as described above, the deviation from the Al concentration blending ratio (6.0%) is the same as when the average particle diameter of the sponge titanium particles is 0.3 mm. 0.05% (the deviation rate is 0.05 / 6 = about 1/100), which is very small (Example 2). The impurity concentration is suppressed to a low level close to that when the average particle size of the sponge titanium particles is 3 mm because the particle size is larger and the surface area is smaller than when the average particle size of the sponge titanium particles is 0.3 mm.

  When the average particle diameter of the Al—V alloy grains is 0.5 mm, the deviation from the Al concentration blending ratio (6.0%) is 0.1% (the deviation rate is 0.1 / 6 = 1/60). ) And increase slightly (Example 1). This is because the pulverization of the Al-V alloy grains did not proceed sufficiently by mixing with the ball mill. Since the impurity concentration is governed by the average particle diameter of the sponge titanium particles, it is the same as in Example 2.

  In the above example, the product Ti-6Al-4V alloy spherical powder has a fine particle size of 45 μm or less. In this case, the additive metal element concentration (represented here by the Al concentration) is higher than the mixing ratio in the raw material mixed powder, and the present invention contributes to the elimination of the concentration deviation. When it is larger, the concentration of the added metal element (here, the Al concentration) is lower than the mixing ratio in the raw material mixed powder, contrary to the case of fine particles. It goes without saying that the present invention is effective in eliminating the concentration deviation in this case.

  That is, the present invention can greatly and economically reduce the alloy composition difference due to the product particle size.

Claims (4)

In a method for producing a spherical powder composed of a titanium-based alloy having an additive metal element ratio of 20% or less, sponge titanium particles and additive metal element particles are mixed by a ball mill, an attritor or a vibration mill which is a mixer having a pulverizing function. A step of forming mixed particles obtained by mixing with a mixer into a rod-shaped melting raw material by compression, a step of non-contact melting of the molded rod-shaped melting raw material by induction heating in an inert atmosphere, and non-contact melting And a step of pulverizing the molten alloy formed by the gas atomization method. The additive metal element powder, Al and V master alloy (Al: V = 6: 4 ) a and, titanium-based alloy spherical claim 1 you produce Ti-6Al-4V spherical powder using this Powder manufacturing method. The method of manufacturing a spherical powder comprising Ti-6Al-4V, sponge titanium particles and, of Al and V master alloy and an additive metal element particles made of (Al:: V = 6 4 ), a mixer having a pulverizing function A step of mixing by a ball mill, an attritor or a vibration mill, a step of forming mixed grains obtained by mixing by a mixer into a rod-shaped molten raw material by compression, and induction heating of the formed rod-shaped molten raw material in an inert atmosphere A method for producing a titanium-based alloy spherical powder, which includes a step of non-contact melting by a gas and a step of pulverizing a molten alloy formed by non-contact melting by a gas atomizing method. The titanium sponge particles have an average particle diameter of Ri 0.3~5mm der method of manufacturing a titanium-based alloy spherical powder according to the additive metal element powder according to claim 3 mean particle size of Ru 0.2~50mm der .