JPH02294458A - Method for forming oxidation-resistant film on the surface of ti-al intermetallic compound or alloy - Google Patents

Abstract

PURPOSE:To form an oxidation-resistant Al2O3 film on the Ti-Al intermetallic compound or alloy and to improve the oxidation resistance on the surface by holding a Ti-Al intermetallic compound or alloy in the oxygen atmosphere under specified conditions and selectively oxidizing Al only. CONSTITUTION:A Ti-Al intermetallic compound or a Ti-Al base alloy is held in the oxygen atmosphere of 1X10<-2> to 1X10<-5> Pa oxygen partial pressure at 900 to 1050 deg.C for 30min to 100hr. By this treatment, Al only is selectively oxidized without oxidizing Ti to form an oxidation-resistant Al2O3 film on the surface of the intermetallic compound or alloy. In this way, the oxidation resistance of the above intermetallic compound or alloy used at a high temp. can be improved.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention provides T on the surface of an intermetallic compound or alloy of TiAL.
By selectively oxidizing only Al without oxidizing 1, Al2
It is an object of the present invention to provide a material that forms an oxidation-resistant film of 0.0, is inexpensive, lightweight, and has high temperature and oxidation resistance equivalent to or higher than that of the Ni-based superalloy Inconel 713C. Mainly 9 of internal combustion engines used in ships, spacecraft materials, structural materials such as steam turbines or gas turbines for power generation, jet engine materials, and materials for automobile turbochargers, etc.
Intermetallic compound T as a device member that reaches a temperature of 00°C or higher
When iAL or TiAL-based alloys are used, an oxidation-resistant film is formed by surface treatment to improve their oxidation resistance.

(Prior Art) Conventionally, N1-based superalloys such as Inconel 713C have been widely used as such high-temperature, heat-resistant, oxidation-resistant device components, but in order to increase thermal efficiency and output, the operating temperatures of the various engines mentioned above have increased. As the temperature rises, materials that can withstand even higher temperatures are needed. In addition, in engines that rotate at high speeds such as jet engines or gas turbines, materials with lower specific gravity are desired in order to reduce the centrifugal force caused by rotation, which acts as an external force that causes the creep phenomenon. There is. Under these circumstances, considering the metal compound TiAL or its alloy, its melting point is approximately 1460°C, which is higher than that of ordinary Ni.
Due to its properties such as being 100°C higher than the base superalloy and having a specific gravity of approximately 3.8, which is less than 172 compared to normal superalloys, it can be used as an alternative material to conventional Ni-based superalloys. Furthermore, it is currently attracting a lot of attention and expectations as one of the most promising candidates for next-generation materials to be used in harsher environments than before.

However, several problems have been pointed out with this intermetallic compound TiAL, and the two most important obstacles to its practical application are its lack of ductility at room temperature and its lack of oxidation resistance at high temperatures of 800°C or higher. This has become a major obstacle. As seen in many research publications both domestically and internationally, the problem of lack of ductility at room temperature is being resolved, but so far there have been no reports of particularly effective means of improving oxidation resistance at high temperatures. Not talked about.

(Problems to be Solved by the Invention) Generally, methods for improving the oxidation resistance of metals include alloying metal elements such as Cr that are effective in improving oxidation resistance,
Methods of forming a surface layer with good oxidation properties through surface treatments such as plating or diffusion treatment are known, but their greatest advantage lies in alloying the intermetallic compound TiAL with a third element. Since a certain low density is lost, it is considered that a surface treatment method with a relatively small increase in density is promising here.

However, for the surface treatment of the intermetallic compound TiAL, diffusion infiltration treatment or vacuum evaporation treatment of Cr, Si or Al has been considered;
Vacuum deposition treatment has no particular effect, and diffusion infiltration treatment has not shown any particular improvement in high-temperature oxidation resistance, except for ^l. Furthermore, regarding the diffusion treatment of A1, some problems have been pointed out in the properties of the diffusion film, and there is a desire to develop a more effective surface treatment method.

? Means for Solving the Problems) The present invention provides an intermetallic compound or alloy of TiAL in an oxygen atmosphere with an oxygen partial pressure of 1 x 10-2 to 1 x 10-'Pa at a temperature of 900°C to 1050°C for 30 minutes to 1000°C. 100
A TiAl intermetallic compound characterized by selectively oxidizing only A1 without oxidizing Ti by holding for a time to form an oxidation-resistant film on the surface of the intermetallic compound or alloy in advance. Another method is to form an oxidation-resistant film on the alloy surface.

(Function) When untreated intermetallic compound TiAL or T1^L-based alloy is oxidized in the atmosphere at a temperature of 900°C or higher, 3
Oxide film with layered structure, i.e. Ti02 layer from the outermost layer, ^
It is known that an oxide film having a structure consisting of a 1, 0 layer and a mixture of both layers is formed.

Among these, it is thought that the preferential growth of the TiO layer as the oxidation time progresses is the cause of the deterioration of the oxidation resistance of TiAL.
After oxidation for about 50 hours, this oxide film becomes about 2cm thick.
It grows until it reaches 00 μm.

? Intermetallic compound Ti subjected to heat treatment under low oxygen partial pressure
AL or TiAL-based alloys have a very thin Al. 0. It was confirmed by X-ray diffraction and an X-ray microanalyzer that only a film was formed, and no Ti layer was observed.

Furthermore, when the treated test piece was subjected to repeated oxidation tests at 900°C in a static atmosphere, an Al203 film was observed at T! It has been found that it has the function of suppressing the progress of oxidation that accompanies the growth of the 0■ layer. In this heat treatment, only the Al20 film became Tin. Regarding the fact that Al is formed preferentially to Ti, the value of the heat of oxidation formation of Al is negatively larger than that of Ti, and
Due to reasons such as the fact that the amount of oxygen that can be solidly dissolved in Ti is smaller than that of Ti, Al preferentially bonds to the deficient oxygen atoms in an atmosphere of low oxygen partial pressure, and only A1■0 is produced. It can be explained that it is a thing.

Among metal oxides, ^l20 is known to be chemically extremely stable and one of the slowest self-diffusing metal elements, and is similar to the intermetallic compound TiAL or T.
It is believed that by forming a dense film with few defects on the surface of iAL-based alloys, their oxidation resistance can be significantly improved.

Furthermore, it is already well known that the diffusion of Al, O, and other elements that grow the film mainly takes place via the grain boundaries. Therefore, Al. 0. It can be said that the growth rate of the film depends on the area of grain boundaries serving as diffusion paths, or in other words, the grain size.

By the way, Al. 03 When the film is formed and grows, the oxide crystal grains become coarser than in the case of oxidation at atmospheric pressure.
Felten studied the growth of Al, O, and films on alloys.
It has been revealed by Mr. The reason for this is that when oxidation begins under low oxygen partial pressure, there are fewer nucleation positions for oxides than at atmospheric pressure, resulting in the formation of an oxide film with relatively coarse grains. It is thought that there is.

It is thought that the Al, O, film formed on the surface of the substrate by the heat treatment under low oxygen partial pressure of the present invention also becomes coarse grained, and the effect of this treatment on improving oxidation resistance is as follows.
It is thought that this effect also plays a role, but if the heating temperature is low, the heating time should be selected to be long, and if the heating temperature is high, the heating time should be selected to be short. Moreover, if the oxygen partial pressure is small, the heating time must be increased.

Moreover, if the oxygen partial pressure is large, the heating time may be short. From the above viewpoint, the heating time was set to 30 minutes to 100 hours.

(Example) Examples of heat treatment under low oxygen partial pressure of the present invention will be described below.

Example 1 The sample used in this example had a purity of 99. 99% A1 and 99.6% sponge Ti are blended into the stoichiometric composition of the intermetallic compound TiAL, and approximately 28% is mixed by argon arc melting.
It was melted into a 0g rod-shaped ingot. After applying homogenization annealing treatment at 1000℃ for 168 hours, 10X5
Cut out a test piece with dimensions of x2mm, and mark the surface of the test piece with #
Polished with emery paper up to 1000.

Table 1 shows intermetallic compounds T subjected to heat treatment under low oxygen partial pressure.
The compositions of iAL and TiAL-based alloys are shown.

This test piece was subjected to heat treatment under low oxygen partial pressure under various conditions as shown in Table 2, and then an oxidation test was conducted to examine the heat treatment conditions that showed the best oxidation resistance.

The pressures in the table indicate air pressure.

Table 2 Oxidation test under heat treatment conditions in a low oxygen partial pressure atmosphere:
Each specimen was inserted into a horizontal tubular electric furnace previously maintained at 900°C and oxidized in a still atmosphere. After a predetermined period of time, it was taken out of the furnace to measure changes in mass and observe the surface, and then returned to the furnace. It was carried out in an intermittent manner by returning it and continuing oxidation. In addition, the oxidation layer was analyzed using a scanning microscope (SEI), X-ray microanalyzer (XMA), and X-ray diffractomer as necessary.As a comparison material, Ni-based superalloy Inconel 713C was oxidized at the same time. The composition of this comparative material is shown in Table 3.

Table 3 and FIG. 1 show the mass changes of the untreated intermetallic compound T1^, the N1-based superalloy Inconel 713C used as a comparison material, and the pure Ti plate due to the oxidation test. This figure shows that untreated intermetallic compound TiAL has better oxidation resistance than pure T1, but Inconel 713
It can be seen that it is several steps inferior to C.

Next, FIG. 2 shows the results of an oxidation test on samples in which the intermetallic compound TiAL was subjected to the heat treatment under the low oxygen partial pressure shown in Table 2. Both the Nα1 and Nα3 specimens have considerably improved oxidation resistance compared to the TiAL specimen (TA) without heat treatment, but the Nα2AJ and Nα2B have much less mass increase due to oxidation compared to them. , which is two orders of magnitude smaller than that of the untreated TiAL specimen (TA). Their oxidation resistance exceeds Inconel 713C.

The film on the untreated TiAL test piece (TA) after oxidation for 150 hours was white in appearance and had a thickness of about 100 μm. From XM^ and X-ray diffractometer analysis, this oxide film consists of a Ti02 layer, an Al,03 layer, and a third layer containing both from the outside.
Is there a T13AL layer several μm thick between the iAL? It was recognized that this was achieved. In general, TEAL has poor oxidation resistance due to the growth of the TiO2 layer, which is caused by the growth of the second Al layer.
O. Since the layer is non-uniform and discontinuous, the outward diffusion of T1 cannot be prevented, and as the oxidation progresses, the outer T1
I think that in2 has grown. Among the test pieces subjected to the heat treatment of the present invention, No. 1 and No. 1 had relatively large oxidation weight increases. 3 partially formed a white oxide film (TI02> similar to the untreated TiAL specimen (TA), but N
Even when 12B was tested for up to 250 hours, it remained a dense gray-black oxide film (Al203) and no change was observed.

FIG. 3 shows an optical micrograph and the results of XMA analysis of the cross section of Nα2A as it was heat-treated under low oxygen partial pressure. Although it is very thin, about a few μm, on the surface of the base material,
A uniform film is produced.

It was identified as ^1■03 by X-ray analysis.

The dramatic improvement in oxidation resistance caused by heat treatment under low oxygen partial pressure is thought to be due to this ^1■0, film. That is, this A1203 film was denser than the oxide film produced by normal oxidation of TiAL, so it is presumed that it prevented outward diffusion of Ti during the oxidation test and suppressed the growth of the oxide film. No. It is thought that under treatment conditions such as No. 1, the continuity of this Al203 film was still insufficient, so the growth of the Ti02 layer progressed from the incomplete parts of the film. Especially for Nα3, which has a moderately large oxidation weight gain, the entire surface has a diameter of 1
It was found that hemispherical white oxides of about mm size were sparsely dispersed. This can be thought of as the oxide film starting to grow from the incomplete portion of the Al203 film.

As described above, when TiAL is heat-treated at 1000°C under low oxygen partial pressure, a thin Al203 film that looks gray-black in appearance is produced, and the formation and growth of an oxide film (T+0=) in normal oxidation is dramatically inhibited. It was found that there is a suppressive effect on This phenomenon was maintained even after intermittent oxidation at 900° C. for up to 250 hours.

(Comparative example) After homogenizing and annealing the two types of samples shown in Table 1 above at 1000°C in a vacuum of 10-3 Pa for 168 hours, a plate with dimensions of 10 x 5 x 2 mm was cut out to make a test piece, and the surface was After polishing with #1000 emery paper, various surface treatments were performed.

The surface treatments tested in this experiment were conventional diffusion infiltration treatment and vacuum evaporation treatment, and were compared with the low oxygen partial pressure heat treatment of the present invention. Among them, test specimens with relatively good surface conditions or with improved oxidation resistance were subjected to an oxidation test at 900° C. in a static atmosphere for 25 to 150 hours. Further, as comparison materials, Ni-based superalloy Inconel 713C and SOS 430 stainless steel were also subjected to oxidation tests at the same time. The composition of Inconel 713C used is the same as shown in Table 3. Also SOS 43
The composition of the 0 stainless steel is shown in Table 4.

The results of this oxidation test do not indicate an increase in oxidation due to continuous oxidation, but are due to intermittent oxidation in which the oxidation process is continued by taking the product out of the furnace after a predetermined period of time, measuring the change in mass, and then returning it to the furnace. It is. The mass of the peeled film was also measured.

The effects of each treatment on oxidation resistance are determined after the oxidation test.
This is done by observing the test piece and measuring the oxidation weight increase per unit surface area, and by using an X-ray diffractometer, XMA, etc.
etc. were also used for evaluation.

First, untreated TiAL (TA), 1.5% Mn
-TiAl (TAM), nickel-based superalloy (Inconel 713C) and stainless steel (SOS 430)
The results of the oxidation test conducted on the sample are shown in Figure 4. As is already known, TiAL with Mn added has a higher degree of oxidation than TiAL without Mn. T iAL
The oxide film of (TA) is white, and the Mn-added TiAL (TA)
M) was black.

Furthermore, at this temperature, peeling of both TA and TAM films was observed, and the oxidation enhancement was considerably greater than that of Inconel 713C, which maintains a stable film.

Next, each surface treatment will be explained together with the results of an oxidation test.

First, we decided to use the powder bag method for the diffusion and penetration treatment. For this purpose, a test piece is filled in a stainless steel tube together with a powder packing material having a particle size of 200 mesh or less, and then treated in a Kanthal wire furnace under the conditions shown in Table 5.

Table 5 Diffusion and Penetration Treatment Conditions These methods have already been established for superalloys, and are expected to be effective for TiAl as well. Three types of diffusion materials were tried: Cr, Si, and Al, but within the scope of the inventor's work, Cr, Si, and Al were used.
It was difficult to obtain a sufficient diffusion film for Si.

Regarding the diffusion and penetration treatment of Al, we varied the treatment temperature and treatment time within the range shown in Table 5, and tried two types of backing material formulations to find the optimal conditions.
It has been found that the best diffusion film can be obtained with the longest time. At this time, the thickness of the diffusion film was approximately 100 μm, dense, and had a good appearance. The composition of this film was identified as TiAL3 based on the results of an X-ray diffractometer. When the treatment conditions were changed, in general, many cracks were observed in the structure of the film at high temperatures for a short period of time, while a dense film with good adhesion was obtained at low temperatures and for a long period of time.

Table 6 Heat treatment conditions after diffusion and penetration Also, after Al diffusion and penetration, vacuum heat treatment as shown in Table 6 was prepared, and oxidation tests were also conducted. The results of the oxidation test are shown in FIG. Compared to untreated TiAl^
It was found that the material subjected to the spreading penetration treatment of No. 1 has excellent oxidation resistance and is comparable to Inconel 713C. It was also found that the material subjected to vacuum heat treatment had even better oxidation resistance, surpassing Inconel 713C.

However, there is a problem that occurs under any processing conditions. As shown in FIG. 6(a), large cracks occur in the spreading film near the edge of the test piece. The specimen in this test had a rectangular parallelepiped shape with sharp edges, so
As a trial, a test piece with rounded edges was prepared and subjected to diffusion infiltration treatment, and as shown in Figure 6, etc.), the cracks became clearly smaller. Therefore, it is assumed that this problem can be solved by further finding an optimal shape, and it is considered that this problem can be dealt with industrially as well.

Now, the inventor of the present invention has investigated the vacuum deposition process for Cr, Si, and N.
Four types were tried: i and A1. Vapor deposition itself is difficult for Cr and Si, but on the other hand, Ni and Al can be vapor-deposited.
After heat treatment at 1000 to 1050°C for 4 hours in a vacuum of Pa, an oxidation test was conducted. The results are shown in FIG. As shown in FIG. 7, no significant improvement in oxidation resistance was observed with Ni vapor deposition. Also, Al
Although a slight effect was observed, the effect was lost in a relatively short period of time, and observation with an optical microscope revealed that sufficient diffusion had not occurred, as shown in Figure 8 below. We believe that it is necessary to further consider appropriate vapor deposition and diffusion conditions.

Example 2 The same intermetallic compounds TiAL and Mn as shown in Table 1
The added TiAL was subjected to heat treatment under low oxygen partial pressure under a wide range of conditions, and repeated oxidation tests were conducted at 900° C. in still air.

Table 7 shows the treatment conditions of the low oxygen partial pressure heat treatment applied to the intermetallic compound TiAL or TiAL-based alloy. The parameters that were changed as processing conditions in this heat treatment were processing air pressure (degree of vacuum), processing temperature, and processing time, and the actual heat treatment was performed by heating the sample in an atmosphere with the conditions shown in Table 7. It is held for a predetermined period of time.

Table 7 Intermetallic compound Ti subjected to heat treatment under the conditions shown in Table 7
Repeated oxidation tests were conducted on AL or TiAL-based alloy test pieces at 900° C. in a static atmosphere to examine the relationship between each treatment condition and oxidation resistance. Figure 9 to 1
The graphs up to Figure 1 represent the increase in mass of each test piece when an oxidation test was conducted. The horizontal axis of these graphs shows the cumulative oxidation time, and the vertical axis shows the change in mass of the test piece as a value per unit surface area.

According to the present invention, the treatment air pressure and treatment time when heat treating the intermetallic compound TiAL under low oxygen partial pressure are 6.7X, respectively.
FIG. 9 shows the oxidation weight gain of each test piece when the treatment temperature was changed while keeping the 10-' Pa and lO time constant. It is clear that the oxidation resistance is improved by the heat treatment under low oxygen partial pressure compared to the untreated case shown in FIG. 1 shown above. Regarding this effect, it is recognized that the oxidation weight gain decreases as the temperature approaches 1000°C from 900°C within the treatment temperature range of 900°C to 1000°C, and the effect of improving oxidation resistance is particularly greatest at around 1000°C.

Figure 10 shows the oxidation resistance of an intermetallic compound TiAL test piece that was heat-treated under low oxygen partial pressure at a treatment air pressure of 6.7 x 1o-3Pa, a treatment temperature of 1000℃, and a treatment time of 10 hours. 71
This is a comparison with that of 3C. Cumulative oxidation time 500
It is found that the oxidation resistance exceeds that of Inconel 713C in the range of up to 100 minutes.

FIG. 11 shows the oxidation curve (J) of a sample of a T1^L-based alloy to which 1.5% Mn was added, which was subjected to the heat treatment under low oxygen partial pressure according to the present invention. The oxidation curve (K) of the same sample without the same treatment is also shown.

It is recognized that the heat treatment under low oxygen partial pressure according to the present invention is effective in improving the oxidation resistance of this Mn-containing sample TiAL alloy as well.

Table 8 summarizes the evaluation of oxidation resistance improvement by repeated oxidation tests according to treatment conditions as described above. The symbol O in the table indicates that oxidation resistance equivalent to or higher than that of Inconel 713C was obtained, the symbol △ indicates that the oxidation resistance was increased several times that of Inconel 713C, and the symbol × indicates that the same level of oxidation resistance was obtained. This indicates that the amount increased by oxidation as described above.

Table 8 A1. OPa B 6.7 xto-3Pa C I. 3xto-3Pa As described above, in the present invention, it has been confirmed that heat treatment under low oxygen partial pressure has a remarkable effect as a surface treatment method for improving the oxidation resistance of intermetallic compounds TiAL and TiAL-based alloys. . By applying the treatment of the present invention, the oxidation resistance of the intermetallic compound TiAL (TA) and the TiAL-based alloy (TAM) added with 1.5% Mn is improved, and the most excellent among them is the N1-based alloy. superalloy inconel 7
It was confirmed that the oxidation resistance exceeded that of 13C.

(Effect of the invention) By applying the treatment of the present invention, the intermetallic compound TiAL (
The oxidation resistance of TA) and TiAL alloy (TAM) with 1.5% Mn added is improved, and the best of them is above 900°C, which exceeds the oxidation resistance of the N1-base superalloy Inconel 713C. It has great industrial effects in that it can provide heat-resistant, lightweight, and inexpensive oxidation-resistant materials at high temperatures, and is useful for internal combustion engines used in aircraft, ships, etc.
It is extremely useful as a spacecraft material, a structural material for steam turbines or gas turbines for power generation, a jet engine material, or a material for automobile turbochargers.

[Brief explanation of the drawing]

Figure 1 is a characteristic diagram showing the results of a comparative oxidation test on the untreated intermetallic compound TiAL and comparative materials (pure Tl material and Inconel 713C), and Figure 2 is a test piece NαLNα2ASNα2B treated with the present invention. ,Nα
Figure 3 (A) is a comparative test characteristic diagram showing the results of an oxidation test comparing 3 and untreated material (TA) with Inconel 713C. (B) is a micrograph and an XMA diagram of a cross section of a TiAL specimen heat-treated in a low oxygen partial pressure atmosphere according to the present invention. Figure 5 shows the oxidation resistance characteristics of Inconel 71, which shows the results of an oxidation test compared with stainless steel SUS430.
Oxidation resistance characteristic diagram showing oxidation test results compared with 3C, Figure 6(a). (b) is a micrograph showing the state of coating cracks at the steep corners and gentle corners of the test specimen (TiAl) with the Al diffusion treatment film. Figure 8 is a microscopic photograph of a film obtained by depositing Al on TiAl, Figures 9 and 10. are intermetallic compounds TiAL (D, E, F
Figure 11 shows the results of an oxidation test comparing Inconel 713C (G, H curves) with Inconel 713C (G, H curves). It is a comparative test characteristic diagram showing the results of an oxidation test comparing the treated material with the untreated material. Figure 2! Figure 1 Cumulative oxidation time A Fig. 1 Cumulative oxidation time/h Fig. 4 50 l〃 1# Presentation examination A Fig. 5 gt Yoigao Ibi σ Konkaku/λ Fig. 6 Fig. 7 50 f00 ] [Oki Acid-i Otsui Ki^i/Inf50 Acid-i L increase th-m-2 - Thailand and JtiF/t-O2 Procedural master book (method) Figure 11 September 27, 1989

Claims (1)

[Claims] 1. TiAL intermetallic compound or alloy at oxygen partial pressure 1×
At a temperature of 900°C to 1050°C in an oxygen atmosphere of 10^-^2 to 1 x 10^-^5 Pa for 30 minutes to 10
A TiAl intermetallic compound or an intermetallic compound of TiAl, which is held for 0 hours to selectively oxidize only Al without oxidizing Ti, thereby forming an oxidation-resistant Al_2O_3 film on the surface of the intermetallic compound or alloy in advance. A method of forming an oxidation-resistant film on the surface of an alloy.