High-temperature strength member

Details High-temperature strength member High-temperature strength member

2002-10-25

2004-11-16

McNeil, Jennifer (Department: 1775)

Stock material or miscellaneous articles

All metal or with adjacent metals

Composite; i.e., plural, adjacent, spatially distinct metal...

C428S650000, C428S678000, C428S679000, C428S680000, C428S655000, C428S687000, C428S660000, C416S24100B

Reexamination Certificate

active

06818321

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a high-temperature strength member used in a high-temperature exposed portion of a gas turbine, a jet engine or the like, and more particularly to a high-temperature strength member constructed by forming a film for preventing the lowering of high-temperature strength due to plastic work strain on a surface of a dynamic-static blade substrate made of Ni-based single crystal alloy or Ni-based unidirectional solidified alloy.
2. Description of Related Art
Recently, studies on the gas turbine are made for raising a working gas temperature in order to improve a heat efficiency, and hence a temperature of an inlet port in the turbine becomes higher than 1500° C. at the present time, and it is demanded to develop a further temperature raising technique.
Such a temperature raising technique of the gas turbine is largely dependent upon the advance of a material for a turbine blade member directly exposed to a high-temperature combustion gas (including development of coatings for resistance to high-temperature oxidation and heat shielding) and the development of a technique of cooling the blade, and is also an important studying matter up to the present.
Particularly, the turbine blade is a central matter on the study of the blade member because it is subjected to creep through centrifugal force under an operating environment, thermal fatigue through start and stop of the turbine, high cycle fatigue through mechanical vibrations, and further corrosion action through impurities included in combustion gas such as sea salt particles, sulfur, vanadium and the like.
The outline of the state studying and developing the conventional turbine blade member is summarized as follows.
(1) Strengthening of alloys through precipitation-dispersion of a great amount of an intermetallic compound [Ni
3
(Al, Ti)] called as &ggr;′-phase;
(2) Development of alloying process considering solid-solution strengthening of matrix phase &ggr; and &ggr;′-phase and atomic arrangement of crystal boundary bade on a delicate balance of compositions in both phases, and development of alloys utilizing the success;
(3) Establishment of production method of high quality alloys by removing influence of slight impurities, gas and the like through adoption of vacuum melting technique;
(4) Development of high performance blade member through conversion from cast shaping to precision casting technique (enlargement of freedom degree in the field of cooling mechanism);
(5) Production of columnar crystal blade member from equiaxed crystal through development of unidirectional solidifying process of alloy;
(6) Development of a single crystal blade member solving the deterioration of material strength resulted from crystal grain boundary of polycrystalline alloy;
(7) A chemical composition of the single crystal blade member comprises Ni: 55-70 mass % as a main component and further contains other elements of Cr: 2-15 mass %, Co: 3-13 mass %, Mo: 0.4-8 mass %, W: 4.5-8 mass %, Ta: 2-12 mass %, Re: 3-6 mass %, Al: 3.4-6 mass %, Ti: 0.2-4.7 mass %, Hf: 0.04-0.2 mass %, C: 0.06-0.15 mass %, B: 0.001-0.02 mass %, Zr: 0.01-0.1 mass %, Nb: 0.1-1.5 mass % and the like. In these alloys, Cr and Al contents effective for resistance to high-temperature oxidation is relatively small, so that an excellent high-temperature strength is first developed by applying a surface-treated coating having a resistance to high-temperature oxidation and resistance to high-temperature corrosion (hereinafter referred to as resistance to high-temperature environment).
(8) To a high-temperature exposed member such as a gas turbine, a jet engine or the like is further applied an alloy coating having an excellent resistance to high-temperature oxidation called as “MCrAlX alloy”. In this case, M is Ni, Co or Fe alone, or an alloy consisting of these plural elements and X is an element of Y, Hf, Sc, Ce, La, Th, B or the like.
Even in such MCrAlX alloy, there are many proposals having various chemical compositions in accordance with use purposes. Prior techniques as to these alloys are mentioned as follows:
JP-A-58-37145, JP-A-58-37146, JP-A-59-6352, JP-A-59-89745, JP-A-50-29436, JP-A-51-30530, JP-A-50-158531, JP-A-51-10131, JP-A-52-33842, JP-A-55-115941, JP-A-53-112234, JP-A-52-66836, JP-A-52-88226, JP-A-53-33931, JP-A-58-141355, JP-A-56-108850, JP-A-54-16325, JP-A-57-155338, JP-A-52-3522, JP-A-54-66342, JP-A-59-118847, JP-A-56-62956, JP-A-51-33717, JP-A-54-65718, JP-A-56-93847, JP-A-51-94413, JP-A-56-119766, JP-A-55-161041, JP-A-55-113871, JP-A-53-85829, JP-A-57-185955, JP-A-52-117826, JP-A-60-141842, JP-A-57-177952, JP-A-59-1654.
These alloys have been mainly developed as a coating for polycrystalline alloy blade member having a resistance to high-temperature environment, but they are effective for a single crystal alloy or a unidirectional solidified alloy and are widely adopted.
On the other hand, Ni-based single crystal alloy and Ni-based unidirectional solidified alloy (hereinafter abbreviated as single crystal alloy, unidirectional solidified alloy simply) have a characteristic that when it is heated to a higher temperature at a state of subjecting to fatigue or thermal fatigue damage by plastic working or impact or further under an actual operating environment as a turbine blade, a portion of residual strain based on working or impact is modified to form a modified layer (see FIG.
4
(
a
)-FIG.
4
(
d
)). This modified layer portion is considered to be an aggregate of fine crystals, which can not be determined by the observation with an optical microscope, or a preparatory state thereof, but is confirmed by the inventors' experiment that it is very brittle and simply forms many small cracks under a slight stress as a start point of breakage (see FIG.
5
(
a
)-FIG.
5
(
b
)).
Heretofore, there has been studied no technique that the decrease of the high-temperature strength resulted from the modified layer appearing on the surface of the substrate is prevented by surface coating. It is well-known that the aforementioned MCrAlX alloy coating is only applied to the improvement of the resistance to high-temperature environment targeting corrosion damage resulted from the high-temperature combustion gas.
SUMMARY OF THE INVENTION
The invention is to solve the following subject matters inherent to the blade member made of the single crystal alloy or unidirectional solidified alloy by the formation of sprayed coating or vapor deposition coating.
(i) The blade member of the single crystal alloy or unidirectional solidified alloy has a characteristic that when it is subjected to slight machining strain, roughening through blast treatment and the like at the production step, in the operation as the turbine blade, at the formation step of the protection coating and the like and then heated to a higher temperature, many fine crystal are produced on an affected portion to form a modified layer. This modified layer is brittle and produces many fine cracks under an application of small stress, which considerably deteriorate the high-temperature strength.
(ii) When only the conventional MCrAlX alloy sprayed coating is formed on the surface of the blade member made of the single crystal alloy or unidirectional solidified alloy at a state of subjecting to strain or machining, there can not be prevented the deterioration of the high-temperature strength accompanied with the formation of the above modified layer.
(iii) As a result, even in the dynamic and static blade members made of the single crystal alloy or unidirectional solidified alloy having an excellent high-temperature strength in a material technology, there is a state that the significance can not be sufficiently developed in the present technique.
The invention is to prevent the above problem inherent to the single crystal alloy or unidirectional solidified alloy as a high-temperature strength member, i.e. the deterioration of the high-temperature strength resulted from the breakage of crystal control (recrystall

Affiliated with

Also associated with

Rating

High-temperature strength member does not yet have a rating. At this time, there are no reviews or comments for this patent.

If you have personal experience with High-temperature strength member, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and High-temperature strength member will most certainly appreciate the feedback.

Rate now

Comments { 0 }

Profile ID: LFUS-PAI-O-3325235