Patent Application
20140356150
The present disclosure relates to dampers for gas turbine engines, and more particularly to grain microstructure in the damper material.
Gas turbine engines typically include dampers to dampen vibrations transferred from rotating components. During operation, these dampers are subject to high temperatures and flexural loading that may affect the flexural strength of the damper over time. Although various methods such as structurally redesigning and forming the dampers are known to contribute in improving the flexural strength of the damper, dampers of any form and shape possess flexural strength by virtue of a grain microstructure present therein. Therefore, studies undertaken in the field of grain microstructures may be believed to hold a key to improving flexural strength of the dampers.
U.S Published Application No. 2012/0282086 ('086 application) relates to a class of nickel-base alloys for gas turbine applications. The '086 application discloses compositions of the nickel-base alloys such that the nickel-base alloys can be used to form useful articles of manufacture possessing a unique combination of mechanical properties, microstructural stability, resistance to localized pitting and hot corrosion in high temperature corrosive environments, and high yields during the initial forming process, post-forming manufacturing, and repair processes. Although, the '086 application discloses various constituents in the nickel-based alloys for imparting certain mechanical properties, the '086 application does not disclose any methods of arranging a microstructure of grains at specified zones of the damper to improve the flexural strength of the damper.
In one aspect, the present disclosure provides a damper for a gas turbine engine. The damper comprises a first portion, a second portion, and a surface. The second portion angularly extends from the first portion to define an interior corner therebetween. The surface bounds the first portion, the second portion, and the interior corner. The damper further comprises a grain composition containing columnar grains and equiaxed grains. The equiaxed grains are disposed adjacent to the surface such that a volume of the columnar grains is less than a volume of the equiaxed grains in the grain composition.
In another aspect, the present disclosure provides an angled component for a gas turbine engine. The angled component comprises a first portion, a second portion, and a surface. The second portion angularly extends from the first portion to define an interior corner therebetween. The surface bounds the first portion, the second portion, and the interior corner. The angled component further comprises a grain composition containing columnar grains and equiaxed grains. The equiaxed grains are disposed adjacent to the surface such that a volume of the columnar grains is less than a volume of the equiaxed grains in the grain composition.
In another aspect, the present disclosure provides a method of producing a damper for a gas turbine engine. The method comprises casting the damper including a first portion, a second portion, and an interior corner therebetween such that the cast damper has a surface bounding the first portion, the second portion, and the interior corner. The method further comprises imparting a grain composition containing columnar grains and equiaxed grains to the damper. The equiaxed grains are disposed adjacent to the surface such that a volume of the columnar grains is less than a volume of the equiaxed grains in the grain composition.
Other features and aspects of this disclosure will be apparent from the following description and the accompanying drawings.
The present disclosure relates to grain microstructure in a damper for a gas turbine engine. Although the present disclosure discloses dampers configured for use in gas turbine engines, it can be appreciated that the methods disclosed herein can be similarly applied to other angled components manufactured to handle flexural loads in gas turbine engines during operation.
As shown in
As shown in
A volume fraction of metal grains in a given cross-sectional specimen is defined as a ratio of a volume of the columnar grains 126 to a volume of equiaxed grains 122 in the thickness 118 of the given cross-sectional specimen. The respective volumes are taken from a central axis 132 of the cross-sectional specimen up to any one outer surface 128, 130 of the cross-sectional specimen. Thus, volume fraction may be given by the following equation:
Volume fraction=a/b eq. 1;
wherein a=volume of columnar grains 126 in the cross-sectional specimen taken from the central axis 132 up to any one outer surface 128, 130; and b=volume of equiaxed grains 122 in the cross-sectional specimen taken from the central axis 132 up to the same outer surface 128, 130.
Further, creep rate factor for any given damper under a bending load applied transversely across the thickness 118 thereof may be given by the following equation:
E
average
/E
equiaxed=[1+{m*(a/b)*(2+(a/b))n}]/[1+(a/b)] eq. 2;
wherein:
Eaverage/Eequiaxed=overall creep rate factor.
Eaverage=average creep rate in the thickness under bending loads when metal grains include a combination of equiaxed and columnar grains 122, 126. A damper containing zones of columnar and equiaxed grains may locally creep according to their respective creep laws. However, the average creep rate across a cross-sectional specimen of the damper may be the average of their individual creep rates based on their respective volume fractions.
Eequiaxed=creep rate across the thickness under bending loads when metal grains consist purely of equiaxed grains 122.
n=power law stress exponent for the damper material which is considered to be a constant for a given material. This value of ‘n’ is based on the creep behaviour of the material, whereby the creep rate in the material is related to the stress applied to the material raised to the power of ‘n’.
m=columnar-to-equiaxed creep rate ratio. The columnar-to-equiaxed creep rate ratio may be defined as a ratio of creep rate in a specimen purely of columnar grains 126 to a creep rate in a specimen purely of equiaxed grains 122. Thus, columnar-to-equiaxed creep rate ratio may be obtained from the following equation:
m=E
columnar
/E
equiaxed eq. 3.
Under the same assumptions for ‘m’ and ‘n’ as disclosed above, eq. 2 may be used to compute the overall creep rate factor for other volume fractions of columnar grains 126 to equiaxed grains 122 in the conventional damper. Assuming that the volume fraction in the thickness 118 of the conventional damper is 25%. Using eq. 2, the overall creep rate factor (Eaverage/Eequiaxed) may be computed as 24. This may imply that with inclusion of 25% columnar grains 126 in the thickness 118 of the conventional damper, the creep resistance of the conventional damper may reduce by approximately a factor of 24.
Similarly, while keeping ‘m’ and ‘n’ constant as disclosed above, various volume fractions and the corresponding overall creep rate factors are plotted in the graph of
It may be observed that as the volume fraction of columnar grains 126 increases in the thickness 118 of the conventional damper, the overall creep rate factor increases linearly by a factor of ‘m’ and exponentially by a factor of ‘n’. This increase in overall creep rate factor affects creep resistance of the conventional damper. As shown in one exemplary embodiment of Table 1, when volume fraction in the thickness 118 of the conventional damper is 50%, the overall creep factor of the given conventional damper is 66. This may imply that the creep resistance of the conventional damper having 50% columnar grains 126 decreases approximately 66 times in comparison to a specimen consisting purely of equiaxed grains 122. Therefore, an increase in the overall creep rate factor of the conventional damper implies a proportional reduction in creep resistance of the conventional damper.
Dampers employed in gas turbine engines typically experience flexural loading and hence, may be formed from materials that exhibit lower creep during such flexural loading. Studies show that factors affecting creep in a damper during operation may be but not limited to, stress in the damper, time under loading, and temperature. However, keeping temperature and the stress in the damper constant, the time under loading or a life of the damper before failure may reduce with increase in columnar grains 126 adjacent to the outer surfaces 128, 130 in the thickness 118 of the conventional damper. Therefore, a conventional damper having columnar grains 126 adjacent to the outer surfaces 128, 130 in the thickness 118 may be prone to developing cracks easily under repeated cycles of bending.
As shown in
A person of ordinary skill in the art may appreciate that by replacing columnar grains 126 with equiaxed grains 122, the volume of equiaxed grains 122 in the total volume of metal grains increases in relation to the volume of the columnar grains 126. An increase in volume of equiaxed grains 122 may decrease an effective volume fraction (a/b) of the damper 106. In another exemplary embodiment, the volume fraction (a/b) may be 0% which implies an absence of columnar grains 126 in the grain composition of the damper 106, and that the damper 106 is composed purely of equiaxed grains 122.
In an embodiment, the creep resistance of the damper 106 at the interior corner 114 under bending loads is a function of the volume fraction (a/b) of the columnar grains 126 to the equiaxed grains 122. In one embodiment, the creep resistance of the damper 106 at the interior corner 114 increases for bending loads with a decrease in volume of the columnar grains 126 in the grain composition. Therefore, the equiaxed grains 122 located adjacent to the surface of the damper 106 may increase the creep resistance of the damper 106 when subjected to repeated bending loads.
In an embodiment, a thickness of the damper 106 may be in a range of approximately 1 millimetre to 100 millimetres. In an embodiment, the damper 106 is made from nickel-based super alloys. In one embodiment, the nickel-based super alloy may be Mar-M-421 alloy. In an alternative embodiment, the nickel-based super alloy may be IN792 alloy.
In an embodiment, imparting the grain composition may include agitating a molten alloy during solidification to initiate formation of equiaxed grains 122 adjacent to the surface 116. In one exemplary embodiment, the molten alloy may be mechanically agitated. In another exemplary embodiment, the molten alloy may be electromagnetically agitated. In an alternative embodiment, imparting the grain composition may include insulating the molten alloy during solidification to initiate formation of equiaxed grains 122 adjacent to the surface 116.
In another embodiment, casting the damper 106 may include casting an oversized damper 106 to include columnar grains 126 adjacent to the surface 116. In this embodiment, the method further includes machining off the columnar grains 126 to impart a grain composition containing equiaxed grains 122 disposed adjacent to the surface 116.
The equiaxed grains adjacent to the surface 116 increases the creep resistance of the damper 106 and configures the damper 106 to absorb vibrations from rotating blades 104 mounted on the rotor disk 102. The vibrations from the rotating blades 104 manifest themselves as repeated flexural loading on the first portion 111, the second portion 112, and the interior corner 114 of the damper 106. Equiaxed grains 122 located adjacent to the surface 116 of the damper 106 may serve to add an amount of creep resistance to the damper 106 such that the damper 106 may be prevented from forming cracks when subjected to the repeated flexural loading.
By imparting the equiaxed grains 122 adjacent to the surface 116 of the damper 106, disintegration of the damper 106 may be reduced. Therefore, a risk of a disintegrated damper falling out of the rotor disk onto other rotating components of the gas turbine engine may be reduced. Thus, the equiaxed grains 122 at the surface 116 of the damper 106 may prolong a service life of the damper 106 and reduce costs associated with repair and replacement of the damper 106.
Although the present disclosure discloses equiaxed grains 122 imparted adjacent to the surface 116 of the damper 106, a person having ordinary skill in the art may appreciate that the equiaxed grains 122 may also be imparted at other pre-determined locations of the damper 106 to increase the creep resistance of the damper 106 under bending at the pre-determined locations. Further, the present disclosure may also be applied to other structures or angled components that are typically manufactured by casting to absorb vibrations, and to components that require improved creep resistance to withstand repeated flexural loading during operation.
While aspects of the present disclosure have been particularly shown and described with reference to the embodiments above, it will be understood by those skilled in the art that various additional embodiments may be contemplated by the modification of the disclosed machines, systems and methods without departing from the spirit and scope of what is disclosed. Such embodiments should be understood to fall within the scope of the present disclosure as determined based upon the claims and any equivalents thereof.
