followed, these defects can be eliminated. This rep-
resents an important accomplishment in improving
materials reliability for jet engines and other com-
parably demanding applications.
Jet engine rotors are manufactured from forgings
or rolled rings. The fan disk is typically a large,
single-piece forging. An example of a fan disk
after
fi
nal machining is shown in
Fig. 24
. From a
weight standpoint, it is bene
fi
cial to use a higher
strength alloy for the fan disk and the two most
common alloys (in addition to Ti-6-4) are Ti-5Al-
2Zr-2Sn-4Cr-4Mo (Ti-17) or Ti-6Al-2Sn-4Zr-6Mo
(Ti-6-2-4-6). The limiting properties for the fan
disk (at a given strength) are low cycle fatigue
(LCF) and fatigue crack growth. Attention to pro-
cessing can optimize these particular properties and
b
forging is now commonly used to create a Wid-
manstatten microstructure. This structure reduces
crack growth without an unacceptable penalty in
LCF life. Ten years ago it was not possible to do
this because the control of the forging process was
not adequate to provide reproducible structures. In
contrast, the compressor rotor, also called a spool,
is a multi-stage component frequently made from
several forgings or rolled rings and joined together
before machining. The compressor spool can incor-
porate as many as 7 compressor stages into a single
followed, these defects can be eliminated. This rep-resents an important accomplishment in improvingmaterials reliability for jet engines and other com-parably demanding applications.Jet engine rotors are manufactured from forgingsor rolled rings. The fan disk is typically a large,single-piece forging. An example of a fan diskafterfinal machining is shown inFig. 24. From aweight standpoint, it is beneficial to use a higherstrength alloy for the fan disk and the two mostcommon alloys (in addition to Ti-6-4) are Ti-5Al-2Zr-2Sn-4Cr-4Mo (Ti-17) or Ti-6Al-2Sn-4Zr-6Mo(Ti-6-2-4-6). The limiting properties for the fandisk (at a given strength) are low cycle fatigue(LCF) and fatigue crack growth. Attention to pro-cessing can optimize these particular properties andbforging is now commonly used to create a Wid-manstatten microstructure. This structure reducescrack growth without an unacceptable penalty inLCF life. Ten years ago it was not possible to dothis because the control of the forging process wasnot adequate to provide reproducible structures. Incontrast, the compressor rotor, also called a spool,is a multi-stage component frequently made fromseveral forgings or rolled rings and joined togetherbefore machining. The compressor spool can incor-porate as many as 7 compressor stages into a single
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