JPS60262928A - Manufacture of heat resistant alloy containing dispersed oxide - Google Patents

Abstract

PURPOSE:To improve the strength of a heat resistant alloy contg. dispersed oxide at very high temp. by evaporating an alloy contg. an element having a specified oxide forming capacity in an inert gas to produce hyperfine powder of the alloy, forming stable oxide on the surface of the powder, compression-molding the powder, and hot extruding it. CONSTITUTION:An Ni, Co or Fe alloy contg. one or more kinds of elements each having >=100kcal/mol oxide forming free energy at room temp. such as Al and Be are evaporated with plasma arc in an inert gaseous atmosphere to produce hyperfine powder of the alloy. Oxygen is then introduced to form an oxide film on the surface of the hyperfine powder, and the oxidized hyperfine powder is compression-molded and hot extruded. The heat resistant alloy contg. dispersed oxide is obtd. The alloy has satisfactory strength even at such a very high temp. as about 1,000 deg.C.

Description

Detailed Description of the Invention (Field of Application of the Invention) The present invention is an oxidized material that is used as a material for moving blades or stationary blades of gas turbines, jet engines, etc., and has sufficient strength even at extremely high temperatures of around 1000°C. The present invention relates to a method for manufacturing a material-dispersed heat-resistant alloy.

[Background of the invention]

Oxide-dispersed alloys are alloys with a structure in which stable oxide fine particles are finely and uniformly distributed in a metal (or alloy) matrix, and compared to precipitation-strengthened alloys, they can be used at particularly high temperatures (more than 70% of the melting point). ) is characterized by extremely high strength. For this reason, it is mainly used as a heat-resistant alloy, and its application to moving blades, stationary blades, combustors, etc. of gas turbines is desired.

This is because the Ni-based and Co-based superalloys that have been put into practical use so far have a γ′ phase (Ni, (An, Ti) ordered lattice set).
, is strengthened by precipitation of carbide phases, etc., but 900
This is because if the temperature exceeds about 0.degree.

Oxide dispersed alloys (hereinafter abbreviated as ODS alloys) have a relatively long history.At the beginning of this century, it was discovered that W in which fine T h Oz particles were dispersed was extremely stable at high temperatures. It is considered to be the dawn of the dawn. ODS began to attract worldwide attention in 1950 when Switzerland's Ir.
S A P (Si
It is probably from Ntared Aluminum Product). Later, in 1962, TD-Ni, developed by 0DnPont in the United States, became the first commercially available ODS.
Around this time, ODS research became active in alloys. However, although TD-Ni and improved TD-NiCr also have good strength at high temperatures, their low strength at medium and low temperatures makes them unsatisfactory for application to actual structural members.

The mechanical alloying method announced by Inco in 1971 is a very innovative ODS alloy manufacturing method.
h*'T! N i M OD S alloy MA75
4. MA6000 etc. have been industrialized to this day. Theoretical research is active, and it is predicted that ODS alloy will play an extremely important role as a high-temperature material for turbines in the future. However, the reason why M A 6000, which is still the most powerful, has not been commercialized as a turbine component is due to the process. This is because high-quality materials cannot be supplied at a commensurate cost due to the complexity, large amount of time and effort, etc. Below are the ODs proposed so far.
Among the S alloy manufacturing methods, we will discuss the contents and shortcomings of a few highly practical methods.

AQ20. in the AΩ matrix. The method for manufacturing SAP alloy in which . That is, the AQ alloy powder is pulverized in a controlled oxidizing atmosphere to form a film of AQ, O, on the powder surface. When this is solidified by pressing, sintered, and molded by extrusion, the AQ, O, and films on the powder surface are dispersed as particles. It has higher strength than ultra-super duralumin at high temperatures, but the dispersed particle size is 0. The size is on the order of several μm, and there are many flaky particles that adversely affect mechanical properties, and the particle spacing, which determines strength, is far from ideal. No examples have been found for other alloy systems.

The method for producing TD-Ni is called a coprecipitation method.

A colloidal aqueous sol of N i (N O,), 6H, O solution and diluted thorium oxide was stirred and mixed with ammonium carbonate-ammonium hydroxide solution, and the pH was adjusted to 7.5.
Keep it. Then, a nickel hydroxide-nickel carbonate precipitate is deposited uniformly around the thorium oxide particles. This is filtered, washed, and then dried at 300°C. The resulting product is ground and reduced with hydrogen. Then press, sinter,
When extruded, the product becomes a product with a structure in which fine particles are dispersed in Ni. This is an extremely complicated method and has severe restrictions. For example, in hydrogen reduction, temperature,
It is necessary to strictly control the hydrogen flow rate for 1 hour and the temperature.

Chemical treatment also requires careful attention.

Furthermore, as mentioned above, although it has high high temperature strength, it is insufficient in strength at medium and low temperatures, so its use is limited. Oxidation resistance is also not good. TD NiC:r, which has improved oxidation resistance by adding Cr, has also been released, but it is fundamentally difficult to achieve medium- and low-temperature strength that can compete with general Ni-based superalloys. .

An alloy powder is created in which an element with a greater tendency to form oxides than the matrix is dissolved in the matrix, and this alloy powder is kept in an oxidizing atmosphere to selectively oxidize the solute elements to form oxides in the powder. There are ways to disperse particles. Thereafter, this is compression molded and given the final shape by extrusion processing or the like. This method, called the internal oxidation method, uses Cu groups, Ni
Fundamental studies have been carried out on this method, but it cannot be applied to practical alloys with complex compositions.

A method of simply mixing alloy powder and oxide fine particles has been attempted, but in order to narrow the distance between dispersed particles and increase strength, the particle size of the starting alloy powder must be fine.

Until now, it has not been possible to easily obtain particles as fine as this, so there has been no successful example of this method.

Inco is the ODS alloy manufacturing method that is currently promising.
This is the company's mechanical alloying method. Each elemental powder (or alloy powder) constituting the alloy composition of the matrix and the ultrafine oxide powder are intensively mixed in a high-energy ball mill (attritor). At this time, the powder is compressed and compressed in the gap between the colliding balls.
After repeated fracture and cold joining, a powder with oxide particles dispersed in the matrix alloy is produced. The resulting powder is canned, vacuum degassed and then hot extruded to produce the product. The strongest alloy produced using this method is called MA 6000. This is an alloy in which approximately 2voQ% of Y20□ fine particles are dispersed in the Ni-based superalloy.

The matrix contains γ′ as well as ordinary cast Ni-based superalloys
The phase (Ni, (AQ, Ti) standard lattice set) is precipitated to provide strength at medium and low temperatures. However, as mentioned above, there are many drawbacks: it takes a considerable amount of time to achieve sufficiently uniform alloying, and what is even more fatal is that there are always areas where insufficient alloying remains, which is the final product. This can become a weakness.

[Purpose of the invention]

The object of the present invention is to provide an ODS alloy that can be applied to alloy matrices of various compositions and that the obtained ODS alloy has very excellent properties.
An object of the present invention is to provide a method for manufacturing a DS heat-resistant alloy.

[Summary of the invention]

The key point of the present invention is to evaporate the alloy in an inert gas to produce ultrafine particles of the same alloy with a size of 0.5 μm or less, and then introduce a controlled amount of oxygen into the atmosphere to coat the surface of the ultrafine particles. An oxide film is formed, and the obtained ultrafine grains are compression molded and extruded to produce an ODS heat-resistant alloy. The composition of the ultrafine particles produced at this time is Ni, Co
, Fe as a base, and is characterized by containing at least a specific amount of at least one of the elements with high oxide-forming ability, such as AQ and Bet rare earth elements.

When a metal is melted in an inert gas, the evaporated atoms repeatedly collide with inert gas molecules and other evaporated atoms and are cooled, resulting in fusion growth of the metal atoms. This is thought to be the principle of ultrafine particle generation. Further, in the case of an alloy, even if there is a difference in vapor pressure between the -5 constituent acids, ultrafine particles of the desired components can be basically produced. In this case, it is not clear whether each element evaporates individually, as an alloy, or somewhere in between, but if the evaporation conditions are kept constant, each element will always be evaporated into ultrafine particles at a constant rate. go inside. It is easy to adjust the alloy composition of the ultrafine particles to the target composition range by investigating the trends among the elements through preliminary experiments. In addition, there is also a method of forming the desired alloy in an inert gas space by separately evaporating each of the component elements or by dividing them into several types of alloys, that is, by providing multiple evaporation sources. It is possible. This allows for more precise alloy composition control.

The surface of the produced ultrafine alloy particles is very active.

Therefore, when this ultrafine powder is taken out into the atmosphere, it is necessary to gradually introduce pure oxygen and allow it to come into contact with it. It should be noted that since the oxide film formed on the surface is used as a dispersed phase, if air is introduced, nitrides may be formed depending on the element, which is not a good idea.

The dispersed phase must be stable even at high temperatures. Therefore,
The ultrafine alloy particles must contain at least one element that produces this stable oxide in a specified amount6.
The standard of stability is given by the standard free energy of formation of the oxide. The free energy of formation at room temperature per oxygen atom is, for example, -126 kcan at Aμ. 1000
In order to not coarsen or decompose at high temperatures of ~1100°C, it should be at least larger (negatively) than this value, that is, about -100 kcaΩ, and these elements include yttrium, thorium, and rare earth elements. . Even if the ease of bonding with oxygen is high, if the content of that component is low, the oxide will not be sufficient to cover the surface of the fine particles, and will form a mixed film with the oxides of other components. Put it away. What kind of oxide is generated depends on the content (activity) of each component, ease of bonding with oxygen (free energy of oxide formation), and oxygen pressure. Once unstable oxides are formed, they can be removed in a subsequent reduction treatment step, but the treatment time will be longer and, in some cases, special steps will have to be taken.

Although there have been various discussions about the mechanism of high-temperature deformation of metals, that is, creep, there is currently no theory that can explain all phenomena in a unified manner.

However, regardless of the theories such as dislocation creep, diffusion creep, and creep due to grain boundary slip, for ODS alloys, the smaller the diameter of the dispersed particles and the narrower the interval between the dispersed particles, the higher the strength. is explained. For example, if grain boundary slip is considered to be dominant, the grain boundary slip velocity will be , 9 are given by the following equation.

9, □=(8τΩλ2・δD,)/(kTR')...
・(1) Here, τ: shear stress (external force), Ω: atomic volume, δ: thickness between the dispersed particles and the matrix.

D is the diffusion constant of the two-plane boundary, where: Borckmann's constant T: temperature, and λ: the distance between particles R: the radius of the dispersed particles From equation (1), in order to reduce the creep rate, λ → small, It is clear that R must be made small.

It is thought that the oxide film on the surface of the ultrafine particles is torn off and aggregated into fine particles by the large shear force applied during hot extrusion. Therefore, the distance between these dispersed particles cannot be made as fine as the diameter of the ultrafine metal particles. This is where the value of ultrafine powder produced by evaporation in gas lies. That is, the particle size is 1/100 to 1/
This is because fine particles on the order of 10 μm can be generated with a relatively sharp distribution. At this time, the particle size changes depending on the atmospheric gas pressure, evaporation temperature, etc. If it is too fine, it may be difficult to handle (difficult to degas or compact), so 0.03 μm or more is convenient for handling. As the particle size increases, the distance between the oxide particles increases when solidified, which tends not to contribute to strengthening, and the ratio of the volume of the oxide film formed to the volume of the metal also decreases. , these phenomena are observed at a limit of about 0.5μ intestine, which has many disadvantages such as the need for additional oxidation treatment to generate the desired VOQ% oxide.

As mentioned above, if unstable oxides are generated in the slow oxidation step, a reduction treatment is performed after the powder compaction step. Usually, the treatment is carried out at a temperature of 400 to toooC in a stream of dry hydrogen. Since the green compact is porous, the inside of the green compact is sufficiently reduced.

When the particle size of the ultrafine powder is small, sintering progresses during the reduction process, and it may take time for the reduction to reach the inside. In this case, it is best to add a ball mill process before the reduction treatment and powder compaction process to agglomerate the ultrafine powder in advance.The agglomerated ultrafine powder can be used as it is, or it can be lightly compacted and then subjected to the reduction treatment. If so, the reduction will proceed easily. After this treatment, the gas is replaced with an inert gas and the next step is carried out.

The iIk final process for producing ODS alloys is a hot extrusion process. In this case, the obtained ultrafine powder is packed into cans.

As for the material, mild steel, SUS, etc. are sufficient.

Evacuate the inside of the can and seal the exhaust hole. The extrusion temperature depends on the material, but ranges from 950 to 1200°C for superalloys. The produced extruded product is subjected to appropriate heat treatment to become a test material.

As described above, the feature of the present invention is to form stable oxides on the surface of ultrafine alloy powder produced by in-gas evaporation method,
This is actively utilized to produce dispersion reinforced materials.

In addition, as a method to supplement the control of the amount of oxide to be dispersed,
Additionally, ultrafine oxide powder may be mixed and added. If added during the ball milling process, uniform dispersion can be obtained. In addition, after the gradual oxidation process, a predetermined amount of ultrafine oxide particles are mixed with ultrafine metal powder in an organic solvent (polar solvent such as methanol is good), and after stirring and mixing with a V-type mixer, the solvent If the is removed by drying, a very homogeneous mixture is obtained.

In the process of compacting ultrafine powder, only hot extrusion was described, but HI P (Hot 1 Sostatic Pres
After s), a similar material may be obtained by hot rolling or hot swaging. What should be noted is that the cross-sectional area should be reduced to about 115 or less by plastic deformation.

If it is more than this, densification is insufficient.

[Embodiments of the invention]

The present invention will be explained in detail below.

Example I NlNi-8(%)AQ gold alloy was evaporated by plasma arc in a reduced pressure Ar atmosphere. Air was gradually introduced into this ultrafine powder to form an oxide film on the surface. Analysis of the ultrafine powder after this oxidation treatment revealed that AQ was 7.3 wt% and oxygen was 0.8 wt%. Moreover, the results of spectroscopic analysis showed that the surface oxide was almost 100% A Q t O3. The obtained ultrafine powder was pressurized at 2 t/aJ and filled into a 5US304 cylindrical container. 400℃ inside the container
The vacuum was evacuated to 2 x 10-" Torr. This was heated to 1150°C and extrusion molded. The cross-section reduction ratio was 20:1. The obtained rod-shaped specimen was then crystallized. An attempt was made to improve the creep strength by adding grain coarsening heat treatment.This is a process in which the sample is gradually passed through a furnace maintained at a temperature above the recrystallization temperature, and the grains elongate in the length direction. A thin film for transmission electron microscopy and a creep test piece were cut out from this test piece, and the microstructure was examined and a high temperature strength test was conducted.

As a result of transmission electron microscopy, it was found that the oxide (AQzO,) fine particles were dispersed in a fairly good condition.

The average particle diameter was 0.035 μm. Calculated from the oxygen analysis results, the contained AQ20. The amount is approximately 3.
It is 5%. Therefore, the distance between dispersed particles is approximately 0.17 from the calculation.
It becomes μm.

Creep rupture test was performed at 871°C and 982°C.

Tests were conducted at three temperatures of 1093° C. and with three types of stress applied. The data after the test was organized, and the creep rupture stress for 100 hours was calculated and plotted in FIG. The value of 1N-100, which is the strongest among the ODS alloy TD-Ni (Ni-ThOs) and the cast Ni-based superalloy, is shown for comparison. Compared to TD-Ni, the production method of the present invention
The i-8AQ alloy has excellent strength over the entire temperature range because not only AQ and O are finely dispersed, but also the γ' phase (Ni3AM) is precipitated in the matrix.

1N-100 is a material for moving blades in practical use, and since it contains a large amount of alloy components, it has higher strength than the above two materials at temperatures below 1050°C. However, the γ′ phase, which contributes to strengthening, becomes coarser and re-dissolves at high temperatures, resulting in a significant decrease in strength.
At temperatures above 1050°C, the strength will be lower than that of ODS alloy.In future gas turbines, the rotor blades or stationary blades will be 11
It is expected that it will be placed in an environment of around 00℃, and here
DS alloy has an advantage. In addition, in the present invention, Ni-
The 8AQ alloy also has better oxidation resistance than TD-Ni.

Example 2 Ni-24Cr-5AQ-2Y alloy was evaporated by plasma arc in a reduced pressure Ar atmosphere. After the oxidation treatment in the same manner as in Example 1, it was taken out into the atmosphere and compacted into a pellet shape. This was reduced in an electric furnace at 700° C. for 5 hours while flowing hydrogen. The hydrogen flow was switched to an Ar flow, and pure 02 was added to the Ar to stabilize the surface oxide at 700° C. for 2 hours. After that, as in Example 1, it was packed into a SUS can and hot extruded. A thin section is cut from the extruded material, electrolytically polished, and subjected to a transmission electron microscope 4IItlItll! I submitted it to the police. Electron beam diffraction and EDX analysis were also performed at the same time, and the first dispersed phase was mostly Y and O.
, particles or a mixed oxide of Y,03 and AQ,o□. The average particle size is approximately 0.55 μ-
1 distribution rate was approximately avo %. These values are ODS
This alloy can be expected to produce very effective results. A low oxidation test and a corrosion resistance test of the extruded material were also conducted.

For the former, 10
The test was carried out for 0 hours, and the weight increase due to oxidation was 0.1% or less, which was excellent. Regarding the latter, a burner rig test (simulating the atmosphere of a gas turbine) was conducted at 800°C for 100 hours.
It has become clear that internal deterioration due to corrosion is approximately 0.1+m or less from the surface, which is excellent.

Example 3 Ni-based superalloy decompression A with the trade name Rena' 80
Ultrafine powder was produced by melting and evaporating by plasma arc in r. The composition of Rane'80 is as follows.

Ni: 60.5. Cr: 13.9. Co: 9
．． 5°Mo: 3.9. w: 4.0. AQ: 3
．． 0. Ti:5.0. Ci: 0.15. B:0.01
．． Zr: 0.04 The average particle size of the produced ultrafine powder was 0.1 μm, and it was confirmed by EDX analysis that it contained almost the entire composition.

After oxidation treatment as in the example, 1.0voQ% Y, 03
The powder was mixed with ultrafine powder (average particle size of 0.03 μm) in a ball mill, and the resulting mass was subjected to reduction treatment at 900° C. for 5 hours in a hydrogen stream.

After that, the process was the same as in Example 1, and it was packed in SUS cans.

After evacuation, the container was sealed and hot extrusion was performed at 1150°C. The extrusion ratio was 1/20. Thereafter, it was introduced into a high frequency furnace maintained at 1250° C. at a rate of about 1 cn/hr to coarsen the crystal grains and elongate them in the length direction.

The structure of the material obtained by the above treatment was confirmed by optical microscopic observation and SEM* observation. As a result, it was found that the ultrafine oxide particles were uniformly dispersed at intervals of about 0.2 μm. The length of crystal grains is 3~
It had grown to about 10m long and 1m wide.

Heat treatment was performed at 1120°C for 2 hours and at 850°C for 16 hours. As a result, the tensile strength at room temperature is 125 kg.
/m'', and the elongation was 2.5%.

Creep rupture tests were conducted at 982°C and 1150°C. Stresses are 26 and 24 kgf/m", respectively, 14.
12 kgf/m" at two points each. The results are shown in Figure 2. For comparison, M A by mechanical alloying method
6000 data were shown. +iy A 6 at 982℃
Slightly better than 000. Although there is some difference at 1150° C., this is thought to be because the matrix composition is not specially adjusted for ODS. If the alloy composition is further improved, it is possible to achieve performance exceeding M A 6000.

C. Effects of the Invention As described above, the oxide-dispersed heat-resistant alloy produced by the method of the present invention exhibits extremely excellent properties.

[Brief explanation of drawings]

Figure 1 is a diagram showing 100 hour creep rupture strength, Figure 2 is a diagram showing 100 hour creep rupture strength.
The figure is a diagram showing creep rupture test results. 2...TD-Ni, 5...MA6000.6...
982℃. 7...1150℃. Agent Patent Attorney Akio Takahashi

Claims (1)

[Claims] 1. Using either Ni or Fee Co as a substrate, the free energy of oxide formation at room temperature is 100 kcoQ/
An alloy containing at least one element with moQ or higher,
evaporating in an inert gas atmosphere to produce ultrafine powder of the alloy; oxidizing the ultrafine powder placed in the inert gas;
A method for producing an oxide-dispersed heat-resistant alloy, comprising the steps of coating the surface of the ultrafine powder with an oxide, and applying sufficient heat and plastic deformation to the oxidized ultrafine powder to make it dense.