JPS6343458B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention involves the addition of small, controlled amounts of manganese to nickel-based superalloys to improve corrosion resistance and creep strength at high temperatures. Thus, the addition of manganese greatly reduces high-temperature corrosion of nickel-based superalloys in the temperature range of 649-760°C. In the extensive material development research that has been conducted on nickel-based superalloys, almost all possible additive elements have been evaluated. However, manganese has not been observed to have positive effects on various properties of superalloys. Manganese is often mentioned in various patents relating to superalloys, but only as an impurity. Studies have been reported on using mixtures of lanthanum and manganese to improve oxidation performance at high temperatures. This study was based on General Electric Company's AFML-TR-69, published in February 1969.
-27, summarized in a report entitled ``Oxidation of Nickel-Based Superalloys'' by GEWasielewski et al. Lanthanum has been described as an element that promotes the formation of manganese-chromium spinel structures. "Impurities and trace elements in nickel-based superalloys" by RT Holt et al. published on pages 1 to 24 of Int. Metal Rev., March 1976.
In the article entitled, it is shown that manganese, although generally a harmful trace element, may be added to reduce the sulfur content of nickel alloys. In view of the fact that manganese is not used as an effective additive element in conventional nickel alloys, the present invention aims to improve corrosion resistance and creep strength at high temperatures by adding a small amount of manganese. The purpose of this research is to provide a nickel-based superalloy. All percentages herein are by weight unless otherwise specified. In accordance with the present invention, the intermediate temperature corrosion resistance of nickel-based superalloys is improved by adding about 0.2 wt% or more but less than 0.5 wt% manganese. It has also been found that such manganese additions, on the one hand, considerably improve the creep resistance of nickel-based superalloys. A wide range of alloy compositions improved by the addition of manganese include 12 to 20% chromium and 3 to 14% selected from the group consisting of tantalum, niobium, rhenium, tungsten, molybdenum, and mixtures thereof.
% refractory metal and 4% selected from the group consisting of aluminum, titanium, and mixtures thereof.
~10% metal, up to 20% cobalt, and the usual amounts of carbon, boron, zirconium, and hafnium traditionally added to superalloys (e.g. up to 0.2% carbon, up to 0.3% boron, up to 0.1% zirconium, up to 2% hafnium). These elements are often added to alloys used in polycrystalline form and are thought to strengthen grain boundaries. Additions of 0.2% or more but less than 0.5% manganese to alloys within the composition ranges described above have been found to be effective in improving corrosion resistance and creep properties. These alloys may be formed into various articles in various forms, such as equiaxed polycrystals, directionally solidified polycrystals, or single crystals. When the alloy is formed into single crystal form, the amounts of carbon, boron, and zirconium are preferably minimized. The present invention is directed to substantially improving the intermediate temperature corrosion resistance and creep properties of nickel-based superalloys. By adding a controlled amount of manganese of about 0.2 wt% or more but less than 0.5 wt%,
Corrosion resistance and creep strength are substantially improved. BACKGROUND ART Research and development of a wide variety of materials has been carried out in the development of alloys used in aircraft gas turbine engines. In the design of aircraft gas turbine engines, the main concerns are high thrust to weight ratio and efficiency (metal temperature
(obtained by operating the engine at high temperatures ranging from 982 to 1149 degrees Celsius). Accordingly, most gas turbine materials are tailored to be most suitable for use in such high temperature ranges. In recent years, research and development efforts have been directed toward commercially producing gas turbines for marine propulsion systems. In the application of marine propulsion systems, it is emphasized that long-term reliable operation is possible and there is little need for repair costs. This is accomplished by keeping operating temperatures as low as 649-760°C and limiting temperatures to 871°C under full thrust conditions. It has been observed that in lower temperature ranges, for example around 732°C, high temperature corrosion increases abnormally. To minimize hot corrosion at such low temperatures, attempts have been made to modify the various alloying elements added to superalloys, resulting in manganese additions of 0.2 wt% or more but less than 0.5 wt%. It has been found that it is effective to reduce hot corrosion at such low temperatures. The mechanism by which manganese reduces hot corrosion at such low concentrations is not well understood. Alloys in which hot corrosion has been observed to be reduced by manganese are those that form chromia and other chromium-rich oxides as the predominant surface oxide during use. Alloys that form chromia are those containing about 12% or more chromium, and the chromium content is substantially greater than (eg, at least twice) the aluminum content. A wide range of alloy compositions in which manganese provides the advantages described above are as follows. a 12-20% Cr b 3-14% refractory metal selected from the group consisting of Ta, Nb, Re, W, Mo, and mixtures thereof c selected from the group consisting of Al, Ti, and mixtures thereof 4-10% metals d up to 20% Co e up to 0.25% C, up to 0.3% B, up to 0.1% Zr, up to 2% Hf f 0.2% or more but less than 0.5% Mn Preferably, some kind of relationship exists within such composition ranges. i.e. low chromium content (approximately 15
%Cr) alloys, it is preferred that the total content of refractory metal elements be about 6% or more. Further, the ratio of titanium to aluminum is preferably 1 or more. This is because this ensures the formation of chromia surface oxides.
Also, if molybdenum is present, it should be less than half of the total refractory metal content, preferably 2wt%.
It is preferable that it is below. This is because molybdenum has been observed to exacerbate hot corrosion in some situations. As mentioned above, these alloys may be produced as equiaxed, directionally solidified, and single crystal articles. A method of making directionally solidified articles is described in US Pat. No. 3,260,505, and a method of making single crystal articles is described in US Pat. No. 3,494,709. If the alloy is produced in single crystal form, the elements carbon, boron and zirconium are preferably kept to a minimum. Thus, the reason for minimizing these elements in single crystal articles is explained in U.S. Pat.
Described in No. 4116723. Ti is a carbide forming material. If the Ti content is too high, the oxidation resistance of the alloy will decrease, and Ti
If the content is too low, the formation of the reinforcing layer will be impaired. Ti also has a reducing effect and, when carbon is not included, acts to form a gamma prime reinforcing layer expressed as Ni ₃ (Al+Ti). Al
provides oxidation resistance to the alloy and also aids in the formation of the gamma prime layer. If the Al content is too small, these effects cannot be obtained, and if the Al content is too large, it is wasteful. Ni forms an alloy with a face-centered cubic structure under all temperature conditions. but
If the amount of Ni is too large, the penetration of C will be inhibited and the volume fraction of the strong carbide layer will decrease. W acts as a solid solution reinforcement and carbide former.
If there is too much W, the amount of the carbide layer becomes too large, reducing the malleability of the alloy and worsening its workability. If the amount of W is too small, the amount of carbide formed will be insufficient and the strengthening by solid solution will decrease, resulting in a decrease in the strength of the alloy. Too much Mo will reduce the high temperature corrosion resistance of the alloy. Ta is a carbide forming material. If Ta is too high, the amount of carbide layer will be too large, which will reduce the hot workability and malleability of the alloy, and if Ta is too low, the strength of the alloy will be adversely affected. 3 to 14 regarding the above refractory metals
% and the contents of 5 to 10% for Al and Ti are determined as preferable ranges in consideration of the above-mentioned effects of each of these elements. The invention will now be explained in more detail by way of some examples with reference to the accompanying figures. Example 1 Eight test alloys were produced. They had three different nominal compositions to which manganese was added in varying amounts. Its nominal composition is shown in Table 1.
Shown below. Alloys having such nominal compositions were tested with no manganese added, with about 0.3% manganese added, and with about 0.9% manganese added. Testing was performed by exposing the specimen to combustion products formed by burning fuel oil in a duct ring to limit dilution of exhaust gases and pollutants by the surrounding air. . Sulfur dioxide was mixed with the combustion air and fuel to introduce sulfur content into the combustion products to the level that would occur if the fuel contained 2.6% sulfur. Additionally, 20 ppm of salt was added to promote high-temperature corrosion and mimic a ship's environment. Sample at approximately 732℃
A monitor/control system was used to maintain the metal temperature at . Specimens were removed periodically to examine corrosion depth. The results are shown in FIG. The graph in Figure 1 shows that the addition of about 0.3% manganese reduces hot corrosion by about 40% over a 500 hour test period compared to an alloy without manganese. Although based on limited data, the graph in Figure 1 shows that if manganese is added up to about 0.8%, 732
This shows that high-temperature corrosion at ℃ is reduced. Also, from this graph, 0.2% or more is 0.5
It can be seen that adding less than % manganese substantially reduces corrosion. Alloy-9, without the addition of manganese, is similar in composition to a commercial alloy known as IN-792 sold by the International Nickel Corporation, which is widely used in applications where hot corrosion is not an issue. . It can be seen that by adding a small amount of manganese as described above, corrosion is greatly improved compared to an alloy to which no manganese is added. Corrosion is similarly found to be reduced for the other two alloys containing up to 18% chromium. Since chromium is the element primarily thought to control hot corrosion behavior in superalloys, it is important that manganese is effective in reducing hot corrosion over a wide composition range of chromium; It has been shown that it is desirable to add manganese to a wide range of superalloys. Example 2 Figure 2 shows the same alloy tested in Example 1 under the same conditions as described for Example 1, except that the test temperature was increased to 899°C. shows the corrosion behavior of At such high temperatures, manganese is clearly detrimental to the high temperature corrosion resistance of the alloy. However, even at such high temperatures, the composition of manganese is approximately
The increase in corrosion depth due to the addition of manganese is relatively small until it reaches 0.5%. The alloy according to the invention is therefore suitable for use at temperatures of the order of 730°C, but may also be used in applications where it is occasionally exposed to temperatures of 899°C or higher. Example 3 Alloy - An alloy with a nominal composition of 17 mm (see Table 1) was prepared in single crystal form with manganese contents of 0, 0.5 and 1 wt% and subjected to a load of 2758 bar at 871°C. A creep test was conducted under the same conditions. The test results are shown in the table. From this table it can be seen that the addition of up to 0.5% manganese substantially and unexpectedly improves the creep properties. In the specific field in which these alloys are being developed, namely marine gas turbine engines, damage caused by creep occurs primarily on rare occasions when engine operating temperatures approach 816-927°C. In contrast, damage caused by high-temperature corrosion occurs in the low temperature range of 649-760°C. Therefore, the alloy according to the invention, which has improved high temperature corrosion resistance at 732°C and improved creep resistance at 871°C, has a variety of unique properties that are favorable for the special application of marine gas turbine engines. It has a combination.

【table】

[Table] Although the present invention has been described in detail with reference to several examples thereof, the present invention is not limited to such examples, and various modifications and omissions can be made within the scope of the present invention. It will be clear to those skilled in the art that

[Brief explanation of the drawing]

FIG. 1 is an illustrative graph showing the test results of Example 1. FIG. 2 is an illustrative graph similar to FIG. 1 showing the test results of Example 2.

Claims (1)

[Claims] 1. A nickel-based superalloy resistant to hot corrosion at a temperature of 732°C and improved in creep strength, containing 12-20% Cr and 3-14% Cr.
a refractory metal selected from the group consisting of Ta, Nb, Re, W, Mo and mixtures thereof;
A metal selected from the group consisting of Al, Ti and mixtures thereof, and in which the amount of Al is 1/2 or less of the amount of Cr;
Co up to 20%, C up to 0.25%, B up to 0.3%, Zr up to 0.1%, Hf up to 2%, 0.2
% or more but less than 0.5% Mn and the balance Ni. 2 12-20% Cr, 3-14% Ta, Nb, W,
A refractory metal selected from the group consisting of Mo and mixtures thereof, and a metal selected from the group consisting of 4 to 10% Al, Ti and mixtures thereof, and the amount of Al is 1/2 or less of the amount of Cr. , 5-20% Co, and 0.2
% or more, but less than 0.5% Mn, and the balance Ni, which forms a chromium-rich surface oxide layer when heated, and with the addition of manganese, the temperature ranges from 649 to 760 °C. Marine gas turbine components resistant to high temperature corrosion in the range.