JPS6221859B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to high-temperature cobalt-base superalloys (superalloys), and more particularly to high-temperature cobalt-base superalloys comprising a superalloy matrix reinforced with aligned embedded carbide fibers. Performance demands on gas turbine engines, such as those used to power aircraft, are constantly increasing as their designs advance. Accordingly, there is a continuing need for improved materials, such as, for example, for turbine components that operate and are used under harsh, high temperature environmental conditions. The materials used in these components are extremely important in influencing the overall performance of the engine, and the development of such materials allows designers to improve power generation, operating temperatures, and component life. Alternatively, a combination of these can be increased. The development of superalloys, which have been based on nickel or cobalt and have been used extensively in the gas turbine engine industry for many years, is now based not only on the superalloy itself, but also on the orientation of the superalloy phases or reinforcement materials such as fibers. It has reached the point where progress is being made based on the inclusion of These latter can be formed in situ during solidification of the alloy. One form of such coagulation that has been used and widely reported is what is commonly referred to as unidirectional coagulation. Applying such unidirectional solidification to a eutectic alloy is
It has been recognized that this is one viable method for producing metallic composites containing fibers arranged as reinforcement in a matrix. Such eutectic composites offered the possibility of achieving high strength in at least one of the aligned eutectic phases and also the possibility of achieving strong cohesion between the phases. Briefly stated, the present invention provides a high temperature cobalt-based superalloy having a directionally solidified anisotropic metallic composite comprising a solid solution matrix and an aligned carbide reinforcing fibrous phase embedded therein. The matrix is comprised of a Co-based superalloy and includes at least about 2% by weight Re to strengthen the matrix. Further, it is preferable that the carbide reinforcing fiber phase is mainly TaC. In a preferred form of the alloy of the invention based on Co, the alloy composition, expressed in weight percent, is 20%
Cr up to 5~20% Ni, W up to 8%, 7~
It consists of 20% Ta, 0.5-1.3% C, 2-9% Re, and the remainder essentially Co and impurities that are inevitably mixed. An example of a preferred form within this range is substantially 10-16% Cr, 7-15% by weight.
%Ni, 1~6%W, 10~15%Ta, 0.5~1%C,
It consists of 2 to 6% Re, the balance Co, and unavoidably mixed impurities. Thus, the alloys of the present invention, which are capable of developing an improved combination of stability and high temperature properties through unidirectional solidification, have at least 2% by weight
Contains Re, 0.5-1.3% C and 7-20% Ta
Made of Co-based superalloy. Although cobalt-based superalloy composites embedded with aligned carbide fibers have great potential to provide improved properties, it is important to strengthen the matrix and at the same time avoid harmful interactions between the matrix and the fibers. For this purpose, a careful compositional balance must be achieved between the matrix and the fibers. If such an alloy system is to be fabricated into articles for use in the turbine section of advanced jet engines, it will require stability and good high temperature properties, especially factors that limit the service temperature and stress of the airfoil metal. It must have one of the stress rupture properties. An important feature of the present invention is that the superalloy matrix in which the aligned carbide reinforcing fiber phase is formed and embedded contains at least about 2% Re. As previously mentioned, the composition of the alloy that is directionally solidified to form the alloy of the present invention requires careful homogenization of the elements to strengthen the matrix and provide the ability to produce high solubility fraction carbide fibers. requires a match. One of the important matrix strengthening elements included in the alloy of the present invention is Re. This greatly increases the stress rupture properties, as will be shown below. Unlike element W, Re is not a carbide-forming element. Similarly, through research, Os, Ru, Hf,
It has been found that elements such as Mo and W, some of which are included in the alloys of the present invention, are not equivalent to Re in that they do not have the same effect as Re. It has been found that less than about 2% Re does not appreciably improve stress rupture strength. Thus, the present invention includes at least the element Re in an amount of about 2% by weight. From a practical point of view, it is impractical to include more than about 9% Re, based on the high cost of Re and the diminishing effectiveness in too large a quantity. The main carbide fiber forming element in the present invention is
It is Ta. Less than about 7% Ta in Co-based form
The amount is insufficient to react with carbon in the formation of TaC. Above 20%, in combination with the % W level, matrix solubility is exceeded, leading to undesirable phase and carbide morphology. In the composition of the present invention, element C is required to combine with Ta to produce carbide fibers that reinforce the matrix. The amount of C included in the compositions of the present invention is primarily a function of the amount of Ta and is sufficient to form a monocarbide of this element. W is an optional component and mainly functions as a solid solution strengthening element. Above 8%, W prevents the formation of carbide fibers. The favorable contribution of W occurs in Co-based alloys up to about 6%, preferably in the range 1-6%. Cr is an optional component and can be tolerated up to 20%, but no beneficial effects will be produced if it exceeds 20%. Cr acts primarily as a solid solution strengthening element, but also as a carbide fiber forming element, helping to resist oxidation and sulfidation. Ni is used at least 5% to replace some of the Co, while 20% is used to avoid deleterious interactions between the solid solution matrix and the eutectic carbide fiber phase and to ensure matrix stability. Must not be exceeded. As previously mentioned, to produce the alloys of the present invention, an alloy with the careful elemental balance described above is combined with eutectic carbide fibers formed integrally in and bonded to a reinforced solid solution matrix. It must be unidirectionally solidified to allow it to be solidified. This unidirectional solidification can be performed in one or more of a number of ways using equipment well known in the art. A number of alloy compositions were considered in evaluating the present invention. In the tables and the following description, all percentages are by weight unless otherwise specified. Alloy coupons were melted in an alumina crucible under an argon atmosphere and chill cast in copper bar molds. The cast specimens were solidified with a planar solidification front to provide unidirectional article specimens used for subsequent testing. Mechanical specimen materials for examining longitudinal properties were cut from the ingot parallel to the growth direction. To investigate the properties in the transverse direction, the specimen material was electrical discharge machined perpendicular to the growth direction. These materials were then assembled into specimen holders and the entire assembly was ground into the shape of a mechanical specimen. One of the essential features of the present invention is the inclusion of the element Re, primarily to strengthen the alloy matrix. This strength improvement is particularly evident in the stress rupture properties of the directionally solidified coupons. In the table, "ksi" represents psi×10 ³ , and "P _LM " means the stress rupture relationship in metallurgy, which is well known and widely used as the Larson-Miller parameter. P _LM =T(C
+Logt)×10 ⁻³ (here C=20). For more information on this, please refer to the American Society
American Society of Engineers Transactions
Transactions) 1952, Vol. 74, pp. 765-771. Use of this parameter allows a wide variety of comparisons between stress rupture lives at different temperatures and at selected stress levels. In evaluating the present invention, Co-based alloys were evaluated. The following table shows that in the Co group up to 20% Cr, 5 to 20% Ni, up to 8% W, 7 to 20
The composition and stress rupture properties of two of the alloys evaluated within a wide range of % Ta, 0.5-1.3% C and 2-9% Re are shown. The coupons were prepared by unidirectional solidification.

【table】

Table: Co-based alloys of the type to which this invention relates are not gamma prime strengthened, so they rely solely on solid solution strengthening within the matrix. In the present invention, high strength properties are achieved from a combination of improved matrix strength through the presence of Re and reinforcing reinforcement by aligned carbide fibers, primarily TaC. Composition of Co-based alloy, especially 10-16% Cr, 7-15
The preferred composition of %Ni, 1-6%W, 10-15%Ta, 0.7-1%C and 2-6%Re is so as to avoid deleterious interactions between the matrix and the aligned fibers. They are chosen to ensure matrix stability, for example to avoid allotropic transformations. A more preferable composition of the Co-based alloy is 14 to 16%
Cr, 9-10% Ni, 2-4% W, 11-12% Ta, 0.7
It consists of ~0.8% C, 2-6% Re and the balance Co. The invention has been described in connection with specific embodiments and forms. However, in the superalloy matrix
It will be appreciated by those skilled in the art that the present invention, including the inclusion of Re and reinforcement through aligned carbide fibers of the matrix, is susceptible to various modifications within its scope.

Claims (1)

[Claims] 1. 5-20% Ni, 7-20% by weight
Ta, 0.5-1.3% C, 2-9% Re and balance cobalt, in a solid solution matrix, Ta,
Forming a unidirectionally solidified anisotropic metallic composite embedded with an aligned reinforcing fiber phase of eutectic carbides of components selected from the group consisting of W and alloys and mixtures thereof; A heat-resistant cobalt-based superalloy characterized by: 2 Expressed by weight, 20% or less Cr, 5 to 20%
Ni, 8% or less W, 7-20% Ta, 0.5-1.3% C, 2
Embedded in a solid solution matrix, an aligned reinforcing fiber phase of eutectic carbides of components selected from the group consisting of Ta, W, and alloys and mixtures thereof, containing ~9% Re and balance cobalt;
A heat-resistant cobalt-based superalloy characterized by forming an anisotropic metallic composite solidified in one direction.