JP2012132099A - Niobium-based alloy heat-resistant material - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a niobium-based alloy heat-resistant material having an alloy film formed thereon which exhibits excellent intercepting performance to oxygen and is less susceptible to modification owing to diffusion.SOLUTION: The niobium-based alloy heat-resistant material includes a first alloy film having a composition represented by general formula ReMR(M is one or more elements of Cr and Si; R is one or more elements among Nb, Mo, W, Hf, Zr, and C; a and b are atom ratio of M and R), on the surface of a substrate, and a second alloy film having a composition represented by general formula QSi(Q is one or more elements among Mo, W and Nb; c is atom ratio of Si), on the surface of the first alloy film.

Description

  The present invention relates to a heat-resistant material used for a gas turbine, a jet engine, and the like, and more particularly to a heat-resistant material of a niobium-based alloy in which a coating for suppressing high-temperature oxidation is formed on the surface of a niobium-based alloy substrate.

  In recent years, there has been a demand for a further increase in the operating temperature of a gas turbine for power generation, and a new heat-resistant material having a higher operating temperature limit is required than Ni-based alloys that have been widely used as turbine members. One of such materials is a niobium (Nb) -based heat-resistant material such as a solid solution strengthened or precipitation strengthened Nb alloy or Nb-Al intermetallic compound (in the present invention, these are called niobium-based alloys). ) Is attracting attention.

  Although these niobium-based alloys are excellent in high-temperature strength, they are all easily oxidized in a high-temperature range, for example, a temperature range of 800 ° C. or higher, and are difficult to use as they are in a high-temperature oxidizing atmosphere such as a gas turbine. Various studies have been made on coatings aimed at oxidation resistance.

Conventionally, a method of forming a diffusion layer of Cr or Al or a method of ceramic coating has been studied as a heat-resistant / oxidation-resistant coating for a metal member used in a high-temperature oxidizing atmosphere. In particular, in Ni-based alloys, a method called thermal barrier coating (TBC) has become mainstream. This is formed by laminating a metal bond layer on the substrate surface and a ceramic heat shield layer on the surface. The metal bond layer is MCrAlY alloy (M = Ni, Co, etc.), and the heat shield layer is ZrO. Ceramics mainly composed of ₂ are often used.

  As the oxidation-resistant coating of the niobium-based alloy, an Ir surface coating layer or an Ir surface coating layer and a diffusion prevention layer mainly composed of one or more of Ta, Re, and W are formed below the Ir surface coating layer. In addition, a heat-resistant Nb alloy member is disclosed (the following Patent Document 1). Also disclosed is a method for producing an oxidation-resistant coating layer in which Ir is vacuum-deposited on the surface of the substrate and simultaneously irradiated with Al ions to form a coating layer made of an Ir—Al alloy (Patent Document 2 below).

Japanese Patent Laid-Open No. 10-14333 Japanese Patent Laid-Open No. 10-140347

  In general, a ceramic film is insufficient in its toughness and adhesiveness to a base material, and thus often cracks or peels off due to thermal stress, leaving a problem in durability. Also in the above-described TBC, oxygen is blocked mainly in the metal bonding layer. Therefore, the coating for the purpose of oxidation resistance is an alloy coating with high adhesion to the substrate, and has the same ability to block non-metallic components such as oxygen and nitrogen as the above-mentioned metal bonding layer. Is desirable.

  Furthermore, the Nb-based alloy that is the subject of the present invention is intended to be used at a considerably higher operating temperature than that of the Ni-based alloy, for example, exceeding 1400 ° C. In such a high temperature range, the diffusion of elements between the film and the substrate is unavoidable, so the film is often altered in a relatively short time and loses its original function. Therefore, in order to ensure the durability of the oxidation-resistant film, it is necessary to suppress the diffusion as much as possible, and to form a coating structure with a slight alteration of the film even if there is some diffusion.

  The present invention has been made in view of the above circumstances, and is a niobium-based alloy in which an alloy film is formed on the surface of a base material of the niobium-based alloy that has excellent oxygen blocking performance and is unlikely to be altered by diffusion. An object is to provide a heat-resistant material.

The present invention for solving the above problems is as follows.
(1) on the substrate surface of the niobium-based alloy, substantially formula _{Re 1-ab M a R b} ( wherein, M represents Cr, 1 or more elements of Si, R is Nb, Mo, W , Hf, Zr, and C, wherein a and b are atomic ratios of M and R, respectively, and a first layer alloy film is formed. (wherein, Q is Mo, W, at least one element of Nb, c is a is atomic ratio of Si) substantially formula Q _1-c Si _c to a having a composition represented by It is a heat-resistant material of a niobium-based alloy formed by forming a two-layer alloy film.

  In the heat-resistant material of the niobium-based alloy, the atomic ratio a is 0.10 or more, the atomic ratio b is 0.01 to 0.50, a + b is 0.95 or less, and the atomic ratio c is 0.05 to 0. .95 is preferred.

  (2) The niobium-based alloy contains Nb as a base and contains at least one of Mo and W and Si, and optionally one or more of Cr, Hf, Zr, and C. The niobium-based alloy heat-resistant material according to item (1), wherein the element M in the alloy film of the first layer is Si.

  In the heat resistant material of the niobium-based alloy, the element Q in the alloy film of the second layer is preferably one or more of Mo and W.

  As described above, according to the present invention, it is possible to provide a niobium-based alloy heat-resistant material in which a coating having a large effect of suppressing high-temperature oxidation is formed on the surface of a niobium-based alloy substrate. This oxidation-resistant coating has a self-repairing function that maintains the action of regenerating the oxide by the oxidation of Si in the second layer film and blocking non-metallic elements such as oxygen and nitrogen in the atmosphere. In order to suppress the diffusion of elements by a single layer coating, the coating hardly changes even when kept in a high temperature range of 1200 ° C. or higher for a long time, and is extremely excellent in oxidation resistance and durability.

  FIG. 1 is a schematic cross-sectional view showing the structure of an oxidation-resistant coating of the niobium-based alloy heat-resistant material of the present invention. This oxidation resistant coating is composed of two layers of alloy film, and the second layer of alloy film 3 mainly blocks nonmetallic elements such as oxygen and nitrogen in the atmosphere by forming oxides on the surface thereof. With a purpose. At the same time, the alloy film 3 contains a metal element that becomes an oxide, and when the oxide generated on the surface falls off due to peeling or the like, the metal element is immediately oxidized to regenerate the oxide. Thus, it performs a self-repair function that maintains the action of blocking nonmetallic elements such as oxygen and nitrogen in the atmosphere. On the other hand, the first layer alloy film 2 is mainly intended to prevent diffusion between the base material 1 and the second layer alloy film 3.

First, the constituent materials and functions of the second layer coating 3 will be described. This coating has the general formula Q _1-c Si _c (here, Q is Mo, 1 or two or more elements selected from the group consisting of W and Nb, Si is silicon, c is the atomic ratio of Si It has a composition represented by.

Si is an element necessary for forming a dense oxide film when this heat-resistant material is oxidized in a high-temperature oxidizing atmosphere. Q is an element that forms a stable phase (alloy or intermetallic compound) with Si at high temperatures, and is an essential element for ensuring the heat resistance and durability of the second layer coating. That, Mo, W, silicides or mixtures or complex compounds of these Nb are both stable phase at a high temperature of at least 2,000 ° C. melting point, and this phase is oxidized SiO ₂ single dense An oxide film is formed.

Next, constituent materials and functions of the first layer coating 2 will be described. The coating by the formula _{Re 1-ab M a R b} ( where, Re is rhenium, M is at least one element selected from the group consisting of Cr and Si, R is Nb, Mo, W, Hf, 1 or 2 or more elements selected from the group consisting of Zr and C, wherein a and b are atomic ratios of M and R, respectively.

  Re is an element that plays a major role in preventing diffusion. The element M is mainly contained in the first layer coating and the second layer coating (some may be included in the base material), and between the first layer coating and the second layer coating (and the first layer coating and the base layer). This is effective in reducing the diffusion between materials. The element R is mainly contained in the first layer coating and the base material (some may be included in the second layer coating), and between the first layer coating and the base material (and the first layer coating and the first layer coating). This is effective in reducing the diffusion between the two-layer coatings.

  The elements M and R are elements that form a stable phase with Re at a high temperature. Since the phase itself has a high melting point, the first layer film itself is decomposed or diffused and lost. In addition, since the diffusion coefficient of other elements is small, the function of preventing diffusion is exhibited.

  The reason why the first layer film is composed of a ternary or higher composition is that not only the elements in the second layer film but also the elements in the base material are included in the first layer film in advance, and for each component. This is because by making the chemical potentials equal in each phase, diffusion is suppressed, and durability is improved by preventing decomposition and alteration of the oxidation-resistant coating.

  In addition, the alloy film of a 1st layer and a 2nd layer should just have said composition, and may contain an unavoidable impurity element.

FIG. 2 is a schematic cross-sectional view showing changes in the film after the heat-resistant material of the present invention is exposed to high-temperature air. As can be seen in the figure, a dense oxide layer 4a is formed on the surface of the alloy film 3 of the second layer. The oxide layer 4a is made of SiO ₂ alone, and has a high element blocking ability even if the layer thickness is small.

  When continuously used in this state, the first layer film 2 is a very stable phase at a high temperature containing Re and has a great effect of suppressing diffusion. Therefore, decomposition / degeneration of the second layer coating 3 can be prevented, and even if the outermost oxide layer 4a is cracked or separated, an oxide layer is formed again on the surface of the second layer coating 3. Has self-healing properties. Thus, the durability of the oxidation resistant coating is ensured.

  In the present invention, the atomic ratio a of the element M in the alloy film of the first layer is preferably 0.10 or more. If it is less than this, the diffusion of the element M from the second layer coating to the first layer coating increases. The atomic ratio b of the element R is preferably 0.01 to 0.50. If b is less than 0.01, the purpose of suppressing the diffusion of element R from the base material to the first layer film cannot be achieved. If b exceeds 0.50, the Re This is because the content of M and M is not preferable. Further, a + b is preferably 0.95 or less. If this value is exceeded, the amount of Re is too small, and the diffusion preventing function becomes insufficient.

  Moreover, it is preferable that the atomic ratio c of Si in the alloy film of the second layer is 0.05 to 0.95. If this is less than 0.05, the function of forming a dense oxide film becomes insufficient. If this exceeds 0.95, the amount of element Q is relatively small, and a stable phase is formed at high temperatures. It is because it becomes impossible.

  The present inventors have studied the mechanical properties of niobium-based alloys, and Nb—Mo or Nb—W binary alloys and Nb—Mo—W ternary alloys are excellent in high-temperature strength and toughness, and are turbine members. As a result, it was found that it is preferable. Appropriate ranges for the alloy element content are 1 to 30 at% for Mo and 1 to 15 at% for W.

  In addition, the present inventors have studied various oxidation-resistant coatings of these binary or ternary alloys, and when the niobium-based alloy further contains Si, the second layer film is made of Mo, W, or Nb. It has been found that the composition is composed of silicide and exhibits extremely excellent oxidation resistance.

  That is, in this heat-resistant material, the base material is an Nb- (one or more of Mo, W) -Si alloy, and the alloy film of the first layer is substantially composed of Re and Si (Mo, W, Nb). ) And the alloy film of the second layer substantially consists of Si and one or more of (Mo, W, Nb). Among these, it is preferable that the alloy film of the second layer is substantially composed of Si and one or more of (Mo, W). In addition, a base material may contain 1 or more types of Cr, Hf, Zr, and C as needed.

  The Re in the first layer film is preferably 10 to 60 at%, (Mo + W + Nb) is preferably 10 to 60 at%, and Si is preferably 1 to 50 at%. Further, (Mo + W + Nb) in the second layer film is preferably 20 to 60 at%.

  In the present invention, the method for forming the alloy film on the surface of the substrate is not particularly limited, and may be any of PVD, CVD, thermal spraying, electrolytic coating, and the like. It may be used. Further, the thickness of the alloy film of the first layer and the second layer is not particularly limited, but is usually about 1 to 100 μm. If the film thickness is too small, the functions of oxidation resistance and diffusion prevention are insufficient, and if the film thickness is excessive, the thermal stress increases. Therefore, an appropriate film thickness may be selected in consideration of these.

  An Nb-based alloy having a composition of Nb-5Mo-5W-5Cr-16Si (mol%) was melted in an Ar atmosphere by an arc melting method. As the raw material, 99.99% powder or granular material was used for Nb and 99.9% for Mo, W, Cr and Si. The melted alloy was heated at 1700 ° C. for 48 hours in an Ar stream of 1 atm to obtain a homogenization heat treatment. Thereafter, a test piece base material of 30 × 20 × 2 (thickness) mm was cut out and subjected to the next coating treatment.

First, metal Re having a thickness of 5 μm was electrodeposited on the surface of the base material from a molten chloride bath containing rhenium chloride. Subsequently, the substrate was dipped in a molten metal Si bath in an Ar atmosphere and then pulled up to perform Si plating. The amount of Si deposited at this time was about 60 g / m ² (corresponding to about 25 μm) from the weight change before and after plating. Subsequently, it is embedded in an alumina crucible together with alumina powder to perform diffusion treatment by holding at 1400 ° C. for 6 hours in a vacuum of 1 × 10 ⁻³ Pa, and further heating for 9 hours in a static atmosphere at 1100 ° C. It was.

  As a comparative material, a specimen base material prepared in the same manner was subjected to Si plating, diffusion treatment and oxidation treatment under the same conditions as those of the specimen of the present invention without performing metal Re electrodeposition. Prepared.

  As a result, in the test piece of the present invention (the material of the present invention), as shown in FIG. 2, the first layer film 2 and the second layer film 3 are laminated on the surface of the substrate 1, and the oxide layer ( A niobium-based alloy heat-resistant material in which (Si, O) 4a was formed was obtained. Table 1 shows the thickness and composition of each layer in the material of the present invention.

The Re electrodeposited layer is mainly formed by Si penetration into the Re electrodeposited layer formed on the surface of the base metal by the molten Si plating and subsequent diffusion treatment in vacuum, and further diffusion of Nb from the base material. It changed into the 1st layer membrane | film | coat 2 which consists of a ternary system of Re-Si-Nb. Further, the excess Si solid-dissolved Nb that passed through the Re electrodeposition layer to form a Si—Nb alloy layer, and the second layer film 3 was formed. Further, by the oxidation treatment, only the surface layer of the Si—Nb layer was oxidized, and an oxide layer (Si, O) 4a made of SiO ₂ was formed.

  On the other hand, in the comparative material after the diffusion / oxidation treatment, as shown in FIG. 3, in order from the surface, an oxide layer (Si, Nb, O) 4b having a thickness of about 1.5 μm and a thickness of about 45 μm on the inner side thereof. A layer mainly composed of Si and Nb (Si—Nb layer 5) was formed. Table 2 shows the thickness and composition of each layer in the comparative material.

  The oxidation resistance test was performed by isothermally heating the inventive material prepared in this way and the comparative material in a static atmosphere at 1200 ° C. to compare the oxidation resistance characteristics. For the inventive material, the heating time was 168 hours. Since the change in the appearance of the comparative material was remarkable, the time was 8 hours. The results are shown in Tables 3 and 4.

  In the material of the present invention, there was no significant change in the coating structure even after the oxidation resistance test, and the state shown in FIG. 2 was maintained. Table 3 shows the change in the thickness of the oxide layer 4a before and after the 168 hour oxidation resistance test of the material of the present invention and the change in the Si concentration in the second layer coating 3 under the oxide layer 4a. ing. Even after 168 hours of oxidation, the Si concentration of 69% is maintained in the second layer, and therefore, the first layer prevents inward diffusion of Si in the second layer, that is, the diffusion preventing layer It turns out that there is an effect.

The oxide layer 4a was SiO ₂ according to X-ray diffraction. Further, the fact that the oxide layer is maintained on the surface of the member without an extreme change in thickness indicates that the Si concentration of the second layer is higher than the concentration at which the SiO ₂ forming ability in the Si—Nb alloy can be expressed. ing.

  On the other hand, FIG. 4 shows the cross-sectional structure of the comparative material after the oxidation resistance test for 8 hours, and Table 4 shows the change in the thickness of the oxide layer before and after the oxidation resistance test. After the oxidation resistance test, the oxide layer (Si, Nb, O) 4b on the surface side and the oxide layer (Nb, O) 4c on the lower side were two layers, but the total thickness of the oxide layer was Most of (about 100 μm) is the layer 4c made of Nb and O, which indicates that the Nb-based alloy of the base material has been oxidized.

It is a cross-sectional schematic diagram which shows the structure of the oxidation resistant coating of the niobium-based alloy heat resistant material of the present invention. It is a cross-sectional schematic diagram which shows the change of the film | membrane after exposing the heat-resistant material of this invention to high temperature air | atmosphere. It is a cross-sectional schematic diagram which shows the coating | coated structure before the oxidation resistance test in the comparative material of a present Example. It is a schematic diagram which shows the cross-sectional structure after the oxidation resistance test in the comparative material of a present Example.

1 Base material 2 First layer coating 3 Second layer coating 4a Oxide layer (Si, O)
4b Oxide layer (Si, Nb, O)
4c Oxide layer (Nb, O)
5 Si-Nb layer

Claims (4)

The substrate surface of the niobium-based alloy, in substantially the general formula _{Re 1-ab M a R b} ( wherein, M represents Cr, 1 or more elements of Si, R is Nb, Mo, W, Hf, Zr and C are one or more elements, and a and b are atomic ratios of M and R, respectively. Of the second layer having a composition represented by the general formula Q _1-c Si _c (wherein Q is one or more elements of Mo, W, and Nb, and c is an atomic ratio of Si). Niobium-based alloy heat-resistant material formed with an alloy film. The atomic ratio a is 0.10 or more, the atomic ratio b is 0.01 to 0.50, a + b is 0.95 or less, and the atomic ratio c is 0.05 to 0.95. The heat-resistant material of the niobium-based alloy described. The niobium-based alloy is an alloy containing Nb as a base and containing at least one of Mo and W and Si, and optionally containing one or more of Cr, Hf, Zr, and C. The heat resistant material for a niobium-based alloy according to claim 1 or 2, wherein the element M in the alloy film of the first layer is Si. The heat resistant material for a niobium-based alloy according to claim 3, wherein the element Q in the alloy film of the second layer is one or more of Mo and W.

Images