JPH07242960A - Production of oxide dispersion strengthened alloy - Google Patents

Abstract

PURPOSE:To increase the performance of the characteristics of an oxide dispersion strengthened alloy by subjecting NiO-MgO solid solution or FeO-MgO solid solution as full ratio solid solution to selective reducing treatment by a reducing gas and uniformly dispersing the fine grains of MgO into a mother phase of Ni or Fe metal. CONSTITUTION:Powdery NiO and powdery Mg (OH)2 are mixed, and after that, Mg (OH)2 is thermally decomposed to form into MgO. Next, it is subjected to compression molding to allow NiO and MgO to enter into solid solution. After that, this solid solution is subjected to reducing treatment by using a reducing gas, preferably, gaseous CO and, more preferably, gaseous H2, and NiO is subjected to selective reduction. At this time, MgO is formed into fine crystals, which are uniformly precipitated into the Ni mother phase. Moreover, since pores are generally present in the sintered body in this stage, densifying treatment is furthermore executed by compressing treatment, heat treatment or the like. Even in the case FeO is used, treatment is executed by the method similar to the case in NiO.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing an oxide dispersion strengthened alloy.

[0002]

2. Description of the Related Art An oxide dispersion strengthened alloy obtained by dispersing fine oxide particles in a matrix metal such as Ni is an excellent heat resistant material for jet engines because the oxide particles are stable up to high temperatures. It is used as a material for wings.

A mechanical alloying method (MA method: mechanical alloying method) is conventionally known as a method for producing the oxide dispersion strengthened alloy. This mechanical alloying method was developed by INCO (The International Nickel Company Incorporated), in which a base metal powder and oxide powder were charged into a mixer such as a ball mill. Then, pulverization, mixing, plastic deformation, etc. of the powder are repeatedly caused by a mixer, and the oxide particles are uniformly dispersed inside the matrix.

[0004]

However, in the case of this method, the milling treatment with the mixer must be performed for an extremely long time (for example, one week), and the time required for producing the oxide dispersion strengthened alloy is long. However, there is a limit to the miniaturization and uniform dispersion of oxide particles, and there is naturally a limit to improving the performance of oxide dispersion strengthened alloys by dispersing finer oxide particles more uniformly. There is.

[0005]

Under the circumstances described above, the invention of the present application is an oxide dispersion strengthened alloy capable of dispersing oxide particles more finely and uniformly by a novel method completely different from the conventional method. The present invention has been made to provide a manufacturing method of a Ni or Fe metal matrix in which a NiO-MgO solid solution or a FeO-MgO solid solution, which is a solid solution, is selectively reduced by a reducing gas. To M
It is to uniformly disperse fine particles of gO.

The present inventors have found that NiO or FeO and MgO
Paying attention to the fact that and form a solid solution, and when these solid solutions are formed and then only NiO or FeO is selectively reduced with a reducing gas, MgO in the solid solution is crystallized to form Ni. Alternatively, it was confirmed that the MgO particles were precipitated in the mother phase, and the MgO particles became extremely fine precipitates and were uniformly dispersed in the mother phase.

For example, a raw material MgO for producing a solid solution
When powder having a particle size of about 1 μm is used, MgO crystal particles precipitated by reduction are precipitated as extremely fine particles of about 50 to 70 nm.

That is, according to the present invention, the oxide can be precipitated and dispersed in the mother phase as extremely fine particles which have not been obtained in the past and can be uniformly dispersed. High performance can be achieved.

In the present invention, first, NiO or FeO is used.
(Hereinafter, NiO will be described as a representative example) and a solid solution of MgO is produced. As a specific method, for example, Ni
After mixing O powder and Mg (OH) ₂ powder, Mg (O)
H) ₂ is thermally decomposed into MgO. Next, this is compression-molded and sintered to make NiO and MgO a solid solution.

Thereafter, this solid solution is subjected to reduction treatment with a reducing gas, preferably CO gas, more preferably H ₂ gas to obtain Ni.
Selective reduction of O is performed. At this time, MgO becomes fine crystals and is uniformly precipitated in the Ni matrix. Since pores generally exist in the sintered body at this stage, it is preferable to carry out a densification treatment by compression treatment, heat treatment or the like after that.

[0011]

EXAMPLES Examples of the present invention will be described in detail below. A commercially available primary reagent NiO and Mg (OH) ₂ powder were mixed with an aqueous solution adjusted to pH 10 with NH ₃ by a ball mill to form 3
Mix for 6ks, air dry, and then heat at 973K for 3.6 hours.
Thermal decomposition treatment of Mg (OH) ₂ was performed in the atmosphere of × ks.
The average particle diameters of the NiO powder and the MgO powder particles were 1 μm and 0.75 μm, respectively, as measured by a light transmission type sedimentation method.
It was m.

Next, 1 to 3 of the mixed powder after the thermal decomposition treatment is added.
Compression molded into a cylinder with a diameter of about mmφ, then 1473K ×
Sintering was performed in the air for 3.6 ks to obtain a NiO-MgO total solid solution.

Next, this solid solution was subjected to reduction treatment with H ₂ gas at 1273 K using a packed bed composed of a reaction tube having an inner diameter of 50 mm to selectively reduce NiO to Ni. The gas flow rate was kept constant at 4 Nl / min, and reduction treatment was performed for 5.4 ks. Subsequently, the reduction-treated Ni—MgO compacted sintered body was compression-molded again, and then heat-treated in a 1273K, H ₂ atmosphere. This treatment is a treatment for increasing the density of the Ni-MgO compacted sintered body.

Regarding the sintered body thus obtained, X
The dispersed state of MgO was observed using a line diffractometer and an electron microscope. In addition, hardness measurement was also performed using a micro Vickers hardness meter. The results are shown in FIGS.

FIG. 1 shows Ni containing 20 mol% MgO.
An O-MgO solid solution ((a) in the figure) and an X-ray diffraction measurement result ((b) in the figure) of the reduction treatment product are shown. In (a) of the figure, only the peak of NiO appears, and since it is slightly shifted to the lower angle side, it can be determined that MgO is solid-dissolved in NiO in all proportion.

On the other hand, both Ni and MgO peaks were observed in the product subjected to the reduction treatment as shown in (b),
Moreover, there is no shift of the Ni peak to the lower angle side, and MgO
Is present as crystals in Ni.
The peak intensity of this MgO increased linearly with the increase of the content of MgO when the content of MgO was changed.

The TEM (transmission electron microscope) observation of the reduced material confirmed that MgO was present in Ni in a granular form. As a result of surface analysis by SEM (scanning electron microscope), Mg and oxygen were uniformly observed in Ni, and segregation did not occur.

These results show that MgO in a state of solid solution with NiO forms NiO as MgO crystals as the reduction proceeds.
It shows that it is uniformly dispersed in the medium. The size of the MgO crystal particles precipitated in Ni was measured to be 5
It was extremely fine as 0 to 70 nm.

On the other hand, when the above-mentioned reduced material was compressed under a constant pressure, the porosity of the compressed body increased with an increase in the content of MgO.
The phenomenon that the compression resistance increases due to the presence of the is observed.

FIG. 2 shows the MgO content and hardness (load: 50 gf) of the sample treated so that the porosities are almost equal.
Shows the relationship with. In addition, in order to remove the influence on hardness of each sample due to the difference in compression pressure, 1273K, 99k
Hardness was measured after heat treatment in s, H ₂ atmosphere.

As shown in FIG. 2, the hardness increases linearly with the increase of the MgO content, and it is clear that the hardness is improved by the dispersion of MgO particles.

Although the embodiment of the present invention has been described in detail above, this is merely an example. For example, in the present invention, it is possible to perform a selective reduction treatment of the total solid solution of FeO and MgO to uniformly disperse MgO in Fe, and use C as a reducing gas.
O 2 gas can be used, and various modifications can be made without departing from the spirit of the invention.

[0023]

INDUSTRIAL APPLICABILITY As described above, the present invention provides a novel method for producing an oxide particle-dispersed alloy which is completely different from the conventional one, and in which extremely fine MgO particles are uniformly dispersed in the matrix phase. The obtained effect is that the performance of the oxide dispersion strengthened alloy can be further improved. Also M
Since gO forms a solid solution with the metal oxide serving as the parent phase, there is an advantage that the MgO content (precipitation amount in the parent phase) can be freely controlled.

[Brief description of drawings]

FIG. 1 shows the result of X-ray diffraction measurement of a reduced sintered body obtained in an example of the present invention, which shows that NiO not subjected to reduction treatment.
FIG. 6 is a diagram showing a comparison with a MgO solid solution.

FIG. 2 is a diagram showing a relationship between the content of MgO and hardness in the reduced sintered body.

Claims (1)

[Claims] 1. A MgO in a parent phase of Ni or Fe metal by selectively reducing a NiO-MgO solid solution or a FeO-MgO solid solution, which is a solid solution, with a reducing gas.
A method for producing an oxide dispersion strengthened alloy, characterized in that fine particles of O are uniformly dispersed.