JPH10218700A - Alloy-based nanocrystal assembly and its production - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enable a highly tough material to be produced at low cost by the presence of such a crystal assembly that nanocrystals are oriented in the identical azimuth in the crystals of an alloy system capable of forming noncrystalline state. SOLUTION: In an alloy system capable of forming noncrystalline state, such an alloy being in noncrystalline state that the composition is deviated from the stoichiometric composition pref. to the extent so as to be easier to form deposits by about 1-5% is treated under heating at a temperature not higher than the crystallization temperature to obtain such an alloy-based nanocrystal assembly that nanocrystals each about 10-60nm in size are oriented in the identical azimuth in crystal grains each 1-10μm in size. A material afforded by the above nanocrystal assembly has a yield strength about 10 times that of a material with crystal grains each 1-2μm in size, and about 30 times that of a material with ordinary crystal grains each 20-40μm in size. This material with nanocrystal assembly is high in stretchability, and is hard to be broken.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a nanocrystal aggregate and a method for producing the same. More specifically, the invention of this application relates to a nanocrystal aggregate useful for realizing a so-called supermetal by strengthening a material, and a method for producing the same.

[0002]

2. Description of the Related Art Conventionally, various attempts have been made to reduce the size of crystal grains as a method for toughening alloy-based materials. By such a method, a considerably high-strength material has been realized until now. However, despite the ingenuity of the composition and the heat treatment method in the conventional technology, there is a limit to further increasing the strength level up to now, for example, to dramatically improve the strength up to 10 times or more. The current technology is difficult, and new knowledge that is fundamentally different from conventional technical knowledge is required.

Accordingly, the invention of this application is to overcome the conventional technical limitations as described above, and to provide a new practical material capable of making a breakthrough breakthrough and a simple manufacturing method therefor. The purpose is.

[0004]

Means for Solving the Problems The present invention solves the above-mentioned problems by providing an alloy system in which an amorphous state can be formed, in which a nano-scale crystal in a crystal grain has the same crystal. Disclosed is an alloy-based nanocrystal aggregate that exists as a crystal aggregate that is oriented in an azimuthal direction.

[0005] Further, the invention of the present application is directed to a method of forming a nano-scale crystal in an alloy system in which an amorphous state can be formed, wherein the alloy in the amorphous state is heated at a temperature lower than a crystallization temperature. Provided is a method for producing an alloy-based nanocrystal aggregate existing as a crystal aggregate oriented in the same crystal orientation.

[0006]

BEST MODE FOR CARRYING OUT THE INVENTION The embodiments of the present invention will be described in more detail. First, the nanocrystal aggregate of the invention of this application has a nanoscale, that is, 100 nanometers (n).
m) Nanocrystals having an ultra-fine crystal size expressed in the following units are oriented in the same crystal direction in ordinary meaning crystal grains, for example, micro-meter (μm) scale fine crystal grains. In this state, for example, tens of thousands exist.

[0007] Such a nanocrystal aggregate is characterized in that its composition deviates from the stoichiometric composition, and that it is an alloy system capable of forming an amorphous state. If the composition is shifted to the side where precipitates are easily formed, it becomes extremely difficult to include extra atoms as a uniform solid solution when the composition changes from amorphous to crystalline. Therefore, at the same time as the crystallization, the crystallized portion becomes an ordered alloy having a stoichiometric composition, and the excess atoms of the element on the excess component side are exposed to the amorphous phase. When this amount exceeds a certain amount, plate-like matched precipitates are precipitated to form a boundary, and as a result, nanocrystals are produced. This process is repeated to create a nanocrystal aggregate having the same crystal orientation.

[0008] More specifically, in the alloy-based nanocrystal aggregate of the present invention, the composition thereof is preferably shifted by about 1 to 5% from the stoichiometric composition in a direction in which a precipitate is easily formed. That is. For example, in the case of a Ti—Ni alloy, it is conceivable that it is shifted to the Ti side (Ti excess side). Such a shift is appropriately determined from the phase diagram of the alloy system. As the alloy system, for example, a Ti-Ni-based alloy, a Ti-Co-based alloy, a Ti-Al-based alloy, an Fe-Al-based alloy and the like are exemplified. And, for example, the diameter of a nanoscale crystal is about 10-6.
A crystal grain having a diameter of 0 nm and a diameter of about 1 to 10 μm is exemplified.

[0009] The nanocrystal aggregate of the present invention is generated in the process of crystallization from amorphous from the viewpoint of its formation, and therefore must be an alloy belonging to an alloy system that realizes an amorphous state. That is, for example, Ti-Ni, Ti-A
It is possible to manufacture the nanocrystal aggregate of the present invention in an alloy system of 1, Ti—Co, and Fe—Al, and an alloy system showing a phase diagram similar to these alloys.

In the production of the nanocrystal aggregate according to the present invention, an ordered lattice having a stoichiometric composition is formed simultaneously with the crystallization, and the excess alloy element is used as a precipitate to form the nanocrystals and the amorphous phase. Since it is based on the mechanism of release to the interface, it is necessary that the alloy system be slightly deviated from the stoichiometric composition in a direction in which precipitates are easily generated. The formation can be achieved by heating the alloy in an amorphous state at a temperature lower than the crystallization temperature.

The yield strength of the material provided by the present invention is about ten times as high as that of a material having a particle size of 1 to 2 μm, which is said to be extremely fine, and ordinary crystal grains of 20 to 40 μm It is about 30 times as large as. Moreover, since they are composed of nanocrystals having the same crystal orientation, they have high elasticity and are not easily broken. Further, in the present invention, in the crystallization from an amorphous state, it is possible to practically use the method very easily as long as there is an appropriate alloy system by a method that skillfully combines the tendency of ordering and the direction of precipitation. Yes, it can also realize what is called super metal.

The present invention will be described in more detail with reference to the following Examples.

[0013]

EXAMPLE An amorphous material of a Ti-48.2 at% Ni alloy in which the Ti-Ni alloy is shifted from the iso-composition to the Ti side (excess Ti) is about 50K higher than the crystallization temperature (737K).
Heat treatment at low temperature produced nanocrystals with a diameter of 20-40 μm. It was confirmed that these aggregates formed so-called crystal grains having a diameter of about 1 to 2 μm. FIG. 1 is a photograph of a crystal grain formed by annealing at a temperature of 687 K for 2 hours by a normal electron microscope. FIG. 2 shows that one crystal grain in FIG. 5 is an electron micrograph showing that the sample is composed of nanoscale crystals of the present invention.

More specifically, FIG. 3 of the accompanying drawings illustrates the [111] bc of the resulting nanocrystal assembly.
FIG. 4 is a high-resolution electron microscope photograph when an electron beam is incident from the c direction, and FIG. 4 is an enlarged photograph of a white frame portion in FIG. From the images of the atomic row and lattice plane, it can be seen that adjacent nanocrystals have exactly the same crystal orientation. Further, it can be seen that an amorphous portion also exists between adjacent nanocrystal grains.

FIG. 5 shows the resulting nanocrystal aggregate,
FIG. 6 is a high-resolution electron microscope photograph when an electron beam is incident from the [001] bcc direction, and FIG. 6 is an enlarged photograph of a white frame portion in FIG. Plate-like precipitates are observed at the interface between adjacent nanocrystals. Then, as shown in FIG. 6, a portion that looks white and shining is a precipitate, has a (bct) structure, and an amorphous portion is also observed at this boundary surface.

FIG. 7 of the accompanying drawings shows the atomic arrangement of precipitates (bct) generated at the interface between adjacent nanocrystals. 8 to 10 are schematic diagrams showing the process of forming nanocrystals in the same direction. FIG.
01] bcc direction, and FIG. 9 shows [1]
11] A diagram observed from the bcc direction. The hatched portions indicate precipitates. FIG. 10 shows the whole image in three dimensions.

The process of forming nanocrystals will be described first with reference to FIG. 8 having a [001] orientation. Although the crystallized portion (1) grows spherically, its diameter is 20 to 40 nmφ.
When the surface becomes amorphous, plate-like matched precipitates are formed at the interface with the amorphous phase (shaded area). Next, nuclei are generated at the interface from the interface, and new crystal grains that maintain the consistency with the precipitates are grown to become crystal grains (2). Thereafter, this process is repeated. The high-temperature phase of the Ti-Ni alloy is a body-centered cubic lattice (bcc), and the plate-like precipitate is # 1.
Since it is generated on the 00｝ plane, there are three variants,
In FIG. 8, the crystal grains can grow from (2) to (3). In this way, the nanocrystal grains are multiplied three-dimensionally. FIG. 8 is a diagram projected from the [001] direction, and FIG. 9 is a diagram projected from the [111] direction.

FIG. 10 shows such a nanocrystal aggregate three-dimensionally, and large circles indicate individual nanocrystal grains. However, for the sake of clarity, each nanocrystal grain is drawn away from adjacent nanocrystal grains. Although plate-like matched precipitates are not drawn in this figure, they exist where adjacent nanocrystal grains are in contact. Of course, the present invention is not limited by the above examples. Various nanocrystal aggregates will be provided.

[0019]

As described in detail above, the present invention provides a nanocrystal aggregate composed of nanocrystals having the same crystal orientation, which could not be expected at all with the prior art. This makes it possible to produce extremely tough materials at a low production cost, and it is also possible to realize characteristics called a so-called supermetal.

[Brief description of the drawings]

FIG. 1 is a photograph of a crystal grain formed when annealed at 687K for 2 hours, taken by a normal electron microscope instead of a drawing.

FIG. 2 is an electron micrograph instead of a drawing, showing that one crystal grain of FIG. 1 is composed of 20 to 40 μm nanocrystals.

FIG. 3 is a high-resolution electron micrograph instead of a drawing when an electron beam is incident from a [111] bcc direction on a nanocrystal aggregate as an example of the present invention.

FIG. 4 is an enlarged electron micrograph of a white frame portion in FIG. 3;

FIG. 5 is a high-resolution electron micrograph instead of a drawing when an electron beam is incident on the nanocrystal aggregate from the [001] bcc direction.

FIG. 6 is an electron microscope enlarged photograph of a white frame portion in FIG. 5;

FIG. 7 is a diagram showing an atomic arrangement of a precipitate formed on an interface between adjacent nanocrystals.

FIG. 8 is a schematic diagram showing a process of forming a nanocrystal aggregate having the same orientation, and is a diagram observed from the [001] bcc orientation.

FIG. 9 is a schematic view showing a process of forming a nanocrystal aggregate having the same orientation, as viewed from the [111] bcc orientation.

FIG. 10 is a schematic diagram showing a process of forming nanocrystal aggregates having the same orientation, and is a diagram showing a three-dimensional overall image.

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁶ Identification symbol FI C22F 1/00 630 C22F 1/00 630A 682 682 691 691B (72) Inventor Shuichi Miyazaki 1-1-1, Tennodai, Tsukuba-shi, Ibaraki Pref. University of Tsukuba, Department of Materials Engineering (72) Inventor Ken Matsunaga 1-1-1, Tennodai, Tsukuba, Ibaraki Prefecture, Department of Materials Engineering, University of Tsukuba

Claims (6)

[Claims] 1. An alloy system capable of forming an amorphous state, wherein nanoscale crystals are present in a crystal grain as a crystal aggregate oriented in the same crystal orientation. Crystal aggregate. 2. The composition according to claim 1, wherein said composition is from about 1 to 5 from the stoichiometric composition.
% In a direction in which precipitates are easily formed.
Alloy-based nanocrystal aggregates. 3. A nano-scale crystal having a diameter of about 10 to 60.
The alloy-based nanocrystal aggregate according to claim 1 or 2, wherein the crystal grains have a diameter of about 1 to 10 µm in nm. 4. A Ti—Ni-based alloy, a Ti—Co-based alloy,
The alloy-based nanocrystal aggregate according to any one of claims 1 to 3, which is a Ti-Al-based alloy or an Fe-Al-based alloy. 5. An alloy system capable of forming an amorphous state, wherein a nano-scale crystal is heat-treated at a temperature equal to or lower than a crystallization temperature in an amorphous state alloy, and the nano-scale crystals are oriented in the same crystal orientation. A method for producing an alloy-based nanocrystal aggregate present as a crystal aggregate in a state of being separated. 6. The composition according to claim 1, wherein the composition is 1 to 5% from the stoichiometric composition.
The method for producing an alloy-based nanocrystal aggregate according to claim 5, wherein the nanocrystal aggregate is shifted only in a direction in which a precipitate is easily generated.