JPH09209001A - Highly efficient alloy powder synthesis method in mechanical alloying method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To shorten the required time of milling and to synthesize an alloyed powder with high efficiency by adding a light element and performing mechanical alloying. SOLUTION: At the time of synthesizing an alloy powder by mechanical alloying, an element of atomic number 8 or below, preferably C or B, is added to raw material elements. The additive quantity of this element is regulated to a degree where this element does not act as a constituent element of the alloy, e.g. 0.01-10 mole %. This light element is mixed rapidly and finely into the alloy powder to form a homogeneous structure in a short time, increases hardness abruptly to improve powder effect, and further reduces the adhesion of the alloy powder to a vessel or balls due to electrostatic action or the coagulation of the alloy powder. By this method, the time needed to synthesize the alloy powder can be shortened, and increase of efficiency and reduction of cost can be attained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to improving the efficiency of alloy powder synthesis in a mechanical alloying (mechanical alloying, hereinafter referred to as "MA") method.

[0002]

2. Description of the Related Art The MA method applies mechanical energy to two or more kinds of raw material elements, repeats local fracture and pressure contact, causes mixing and pulverization on a microscopic scale, and produces a gas phase or a liquid phase. It is a solid-phase reaction method that obtains a non-equilibrium phase that cannot be obtained from the state. In the MA method, a hard ball serving as a grinding medium and two or more kinds of raw material powders are loaded into a hard closed container, and milling is performed by rotating, vibrating, or mechanically stirring the container. MA
Ball mills of rolling type, vibration type, stirring type, and planetary rotation type have been put into practical use as apparatuses for performing the method. Generally, the rolling type is a low energy mill, and the vibration type, the stirring type, and the planetary rotation type are high energy mills.

The MA method has been applied in the fields of alloys, composite materials, and compound synthesis. Among them, the application to alloy synthesis is most actively pursued. In alloy powder synthesis by the MA method, (1) alloying is not possible by the conventional melting method, alloying is possible even in a system having a large difference in melting point, boiling point, specific gravity, etc. (2) Normal Amorphous alloys and non-equilibrium alloys can be obtained with alloy compositions that cannot be obtained by the rapid solidification method.
There is a feature such as.

In order to execute the MA method, at present, there are bad conditions such as (1) small-scale equipment, (2) batch processing, and (3) long-time processing, so that the productivity is low and the manufacturing cost is high. That is the biggest problem in practical application. At present, since enormous cost is required to increase the size of the MA device, no cost advantage appears. Also, M
The method A generally requires atmosphere control and is often carried out in a closed container. Therefore, continuous treatment is difficult.
Therefore, it is difficult to improve the productivity by increasing the size of the device and making it continuous.

In the conventional MA method, in order to obtain a desired alloy phase in a short time, methods such as increasing the mechanical energy generated by the MA apparatus and keeping the MA container at a high temperature have been used. The mechanical energy can be increased by using a high energy mill such as a vibration type, a stirring type, or a planetary rotation type, and increasing the vibration speed or rotation speed or changing the weight ratio of the ball and the sample powder. However, if the mechanical energy applied is too high, contamination from the balls and the container may increase, and problems such as seizure of the alloy powder on the inner wall of the container may occur.

Keep the container temperature at 200-300 ° C.
However, there are problems such as the promotion of seizure on the inner wall of the container and the increase in reactivity of the sample powder, which limits the alloy systems that can be used. If you just want to mill for fine grinding, not for MA,
A surface active agent may be added to prevent the particles from adhering or aggregating. In general, the addition of surfactants
This is because the surface energy of the particles is reduced, the particles are less likely to adhere and condense, and the pulverization is promoted. However, in MA, the addition of a surface active agent or the like has the opposite effect because the new surfaces that have appeared due to rolling or wear during milling must be pressed against each other.

The alloys targeted by the MA method can be applied to most alloy systems provided there is a sufficient amount of ductile component. However, it is difficult to apply to alloy systems containing many brittle components such as B and Si, or alloy systems containing many components having high hardness and poor ductility such as W and Mo. Conventionally Fe-based, Ti
The MA method has been widely applied to alloys composed of ductile components such as Al and Al. Furthermore, the composition that does not form a solid solution in the phase diagram, the melting point, the boiling point, the system with a large difference in specific gravity, etc.
Even if it cannot be alloyed by the melting method, it can be alloyed by the MA method.

[0008]

Conventionally, since it takes a long time to synthesize an alloy by the MA method, the productivity is low,
There is a problem that the manufacturing cost is increased. The present invention
In the synthesis of alloy powder by the MA method, the purpose is to shorten the time required for synthesis of alloy powder.

[0009]

In order to solve the above problems, the present invention provides a method of synthesizing alloy powder by MA method,
This is a method for synthesizing an alloy powder in which light elements such as B and C are added in an amount that does not become an alloy constituent element.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION In the implementation of MA, the following three steps are taken. In the first stage, the raw material powder is microscopically forged and flattened. At this stage, the hardness of the particles rapidly increases due to cold work hardening. In the second stage,
The flattened raw material powder becomes a lamella (layered) structure by repeating pressure bonding and rolling. The sharply increased hardness and accumulated strain in the first stage is almost saturated at this stage. In the third stage, the particle size goes through the maximum value and gradually becomes an equiaxed shape, and the lamella structure is randomized and finally homogenized so as to be indistinguishable by an optical microscope. The crushing and the pressing are in equilibrium, and the powder particle size approaches a certain value. At this stage, alloying, amorphization, etc. are achieved.

Therefore, the progress of MA can be confirmed by observing the structure of the sample powder with an optical microscope or a scanning electron microscope. Moreover, the degree of progress of alloying and the state of generation of amorphous and intermetallic compounds can be confirmed by X-ray diffraction. Further, changes in the particle size and hardness of the powder are also indicators of the degree of progression of MA.

When B or C is added to the raw material powder, the following characteristics appear as compared with the sample without addition. (1) Transition from a lamella structure to a homogeneous structure at an early time. (2) Hardening of the sample powder in the early stage of MA occurs rapidly. (3) Adhesion of the sample powder to the container or the ball and generation of powder aggregates are reduced.

Corresponding to the above results, the mechanism of the effect achieved by the present invention is summarized in the following three points. (1) Since B and C having a high diffusion rate are finely mixed in the alloy powder, homogenization of the alloy is promoted, so that the time required for transition from the lamellar structure to the homogeneous structure is shortened. (2) By adding B or C, the increase in hardness that occurs from the flattening of the raw material powder to the formation of the lamella structure becomes sharp and becomes brittle, so that the pulverization efficiency is improved. (3) By adding B or C, the adhesion of the alloy powder to the container or the ball due to the electrostatic action and the agglomeration of the powder are reduced, and MA efficiently proceeds.

For the above reasons, B and C are used in MA.
The alloy powder can be synthesized with high efficiency by the method of the present invention of adding As the additional element, a light element having an atomic number of 8 or less with a small atomic radius is effective. However, it is difficult to control the addition amount of the elements H, He, N, and O, which are in a gaseous state at room temperature. In addition, a metal element that easily oxidizes,
Li and Be are difficult to handle in powder form. Therefore, B and C are preferable as the additional elements.

When the amount of B or C added is large, boride or carbide is formed due to the reaction with the raw material metal. Since borides and carbides have high hardness, they increase contamination from the container and balls. Therefore, it is necessary that the amount of B or C added is such that no compound is produced. The amount is preferably 10 mol% or less, more preferably 7.5 mol% or less. If the addition amount of B or C is too small, a sufficient effect cannot be obtained, so the lower limit of the addition amount is
It is preferably 0.01% or more, and more preferably 0.1 mol% or more.

Even when the MA powder produced by the present invention is heat-treated, a stable alloy phase can be deposited without depositing a compound consisting of the raw material metal and the additional element. Even if the MA powder produced according to the present invention is used for sintering, a sintered material can be produced without precipitating a compound consisting of a raw material metal and an additional element. INDUSTRIAL APPLICABILITY The present invention can be applied not only to alloys conventionally used for MA, but also to all alloys capable of MA.

[0017]

The present invention will be described in more detail with reference to the following examples. Example 1 Fe powder having a particle size of about 5 μm and Ti powder having a particle size of about 40 μm were mixed in a molar ratio of Fe: Ti = 40: 60, and 5 mol% of amorphous B powder was added to the mixture. Used as raw material. For comparison, a sample without B was also synthesized. MA
In order to confirm the process of alloy powder synthesis by and the change of characteristics by milling time, 1, 5, 10, 20, 50, 1
Samples for 00 and 200 hours were prepared. A vibration type mechanical alloying device was used for the synthesis of the samples, and 7 g of each sample was synthesized.

The change in grain size and structure of the alloy powder depending on the milling time will be described with reference to FIG. When B was not added, a clear lamella structure was confirmed up to 10 hours. Then, the lamella structure was enlarged as randomization progressed, and exceeded a maximum value of 500 μm in 20 hours. After that, the particles gradually became finer, and the particle size became stable at about 50 μm from about 50 hours.

On the other hand, when 5 mol% of B was added, a clear lamella structure was confirmed only for up to 5 hours. After that, randomization of lamella structure rapidly progressed,
The powder particle size reached the maximum value in excess of 500 μm in 10 hours. Next, miniaturization rapidly progressed, the particle size was cut to 100 μm in 20 hours, and the particle size was almost stabilized in about 30 hours. Therefore, the sample to which 5 mol% of B was added was
40 times for the particle size to stabilize rapidly
It was possible to shorten by ~ 50%.

Next, the change in hardness will be described with reference to FIG. The alloy powder obtained by MA was embedded in a resin and mirror-polished to obtain a cross section of the powder, and its hardness was measured by a micro Vickers hardness meter under a load of 10 g. When B was not added, the Vickers hardness (hereinafter referred to as Hv) reached 400 in 10 hours, then reached Hv450 in 20 hours, and exceeded 50 in 50 hours, and the hardness was saturated.

On the other hand, when B is added in an amount of 5 mol%, Hv rises more rapidly than in the case where B is not added.
Hv500 was reached during 20 hours and the hardness was saturated. Therefore, the sample to which 5 mol% of B was added was
The rate of increase in hardness at 0 hours was larger than that of the B-free sample, and it was found that a powder having high hardness can be obtained in a shorter time.

When a cross section of the B-free sample powder milled for 200 hours was observed with an optical microscope at 400 times, the structure near the surface of the powder particles was different from that inside, and a two-layer structure was formed. On the other hand, in the B-added sample powder,
Due to the effect of diffusion of B, homogenization of the alloy structure proceeded, and a completely uniform structure was obtained.

By heat treating the B-added sample powder milled for 200 hours at 630 ° C. for 30 minutes, a stable phase consisting of uniform crystals was obtained, but no boride was deposited. The B-added sample powder milled for 200 hours was compacted and heated at high frequency in an argon atmosphere to produce a sintered body. When the structure of the cross section of this sintered body was observed, no boride was deposited.

Example 2 In the same manner as in Example 1, Fe powder having a particle size of about 5 μm and Ti powder having a particle size of about 40 μm were used in a molar ratio of Fe: Ti = 40: 6.
MA was carried out using as a starting material a mixture of 0 and added with 0.5 mol% of C (graphite) powder. For comparison, MA was also performed on the sample without C addition. As a result, as in Example 1, by adding C, the time required for alloying could be shortened by 40 to 50%.

Example 3 In the same manner as in Example 1, Fe powder having a particle size of about 5 μm and Al powder having a particle size of about 100 μm were used in a molar ratio of Fe: Al = 20:
MA was carried out using as a starting material a mixture of 80 and 0.5 mol% of amorphous B powder. For comparison, MA was also performed on the sample without B addition.
As a result, similar to Example 1, by adding B, the time required for alloying could be shortened by 40 to 50%.

Example 4 To confirm the effect of the amount of B added, Fe having a particle size of about 5 μm was used.
Powder and Ti powder having a particle size of about 40 μm in a molar ratio of Fe: Ti =
It was blended at 40:60, and amorphous B powder was added to this,
0.1, 0.5, 1.0, 5.0, 8.0, and 15.0 mol% were added, and the progress of amorphization of each sample was examined at a milling time of 50 hours. A planetary rotation type MA device was used to synthesize the samples, and 40 g of each sample was synthesized.

The progress of amorphization was investigated by X-ray diffraction and differential scanning calorimetry. As a result, B is set to 0.
Amorphization was observed to be accelerated in the samples to which 1, 0.5, 1.0, 5.0, and 8.0 mol% were added, and the sample to which 5.0 mol% was added showed the highest amorphization. confirmed. In addition, in the material to which 15.0 mol% was added, some compounds were formed. From this, it was found that addition of an appropriate amount of B promotes amorphization.

[0028]

According to the present invention, the milling time of the MA method, which has been a problem that the conventional alloy synthesis takes too long, can be reduced to about half, and non-equilibrium powder such as amorphous alloy can be efficiently synthesized. It became so.

[Brief description of drawings]

FIG. 1 is a graph showing changes in average particle size of sample powder with respect to milling time in the present invention and a conventional method.

FIG. 2 is a graph showing changes in Vickers hardness of sample powder with respect to milling time for the present invention and a conventional method.

Front page continuation (72) Inventor, Ozaki, Hiroshi, Yatsushiro, 2-109, Yatsushiro-cho, Kita-ku, Nagoya, Aichi Prefecture (72) Inventor, Teruo Harahara, 1618, Ida, Nakahara-ku, Kawasaki-shi Nippon Steel Corporation Technology Development Division

Claims (3)

[Claims] 1. A method for synthesizing an alloy powder by a mechanical alloying method, wherein at least one of elements having an atomic number of 8 or less is used.
A highly efficient alloy powder synthesis method in a mechanical alloying method, characterized in that the milling time required for alloy powder synthesis is shortened by adding one or more elements. 2. C or B as an element having an atomic number of 8 or less
The method for synthesizing alloy powder with high efficiency in the mechanical alloying method according to claim 1, wherein the alloy powder is added. 3. A single or total amount of elements added is 0.01.
The high-efficiency alloy powder synthesizing method in the mechanical alloying method according to claim 1 or 2, wherein the content is in the range of mol% to 10 mol%.