The Creep and Fatigue Behavior of Haynes 282 at … · THE CREEP AND FATIGUE BEHAVIOR OF HAYNES 282...
Transcript of The Creep and Fatigue Behavior of Haynes 282 at … · THE CREEP AND FATIGUE BEHAVIOR OF HAYNES 282...
THE CREEP AND FATIGUE BEHAVIOR OF HAYNES 282 AT
ELEVATED TEMPERATURES
Sara C. Longanbach and Carl J. Boehlert
Michigan State University, Department of Chemical Engineering and Materials Science, East
Lansing, MI 48824
Haynes 282 is a wrought, gamma-prime strengthened nickel-based superalloy intended for use in
high temperature structural applications. In order to investigate processing-microstructure-
property relationships, the microstructure and elevated-temperature creep and fatigue behavior of
Haynes 282 were evaluated after it had been processed using strain-recystrallization
thermomechanical treatments. These treatments included a sequence of 20% cold rolling steps
followed by recrystallization annealing. Microstructural evaluation was performed using
scanning electron microscopy (SEM) and electron backscattered diffraction (EBSD). Figure 1(a)
illustrates the microstructure after the thermomechanical processing treatment. From the
collected EBSD data, the number fraction of certain boundary types was determined. General
high angle boundaries (GHAB) accounted for 38% of the boundaries, while low angle
boundaries (LAB) accounted for 4%. 58% of the boundaries were coincident site lattice
boundaries (CSLB) and it is noted that 47% of the overall boundaries were twins (Σ3). The
majority of the boundaries were categorized as CSLB+LAB, and these have been associated with
enhanced creep resistance for other superalloy systems. The creep and fatigue properties at
elevated temperatures (760°C – 815°C) of this alloy were examined and compared to the results
obtained for two solid solution-strengthened superalloys, nickel-based Haynes 230 and cobalt-
based Udimet 188. Figure 2 compares the creep behavior for the alloys and it is evident that the
Haynes 282 is the most creep resistant. The measured creep exponents (n) (Figure 2) for each of
the alloys suggest that similar creep deformation mechanisms may be active. Figure 3 (a)
illustrates a plot used to calculate the Qapp values for Haynes 282 at different stresses. It is
expected that the dominant secondary creep mechanism was dislocation climb and this will be
evaluated using TEM of the deformed samples. The strain-life history of the fatigue experiments
revealed that creep contributed to the total strain accumulated in the samples; see Figure 3 (b).
The Young’s modulus decreased during fatigue testing indicating that damage likely occurred
during these experiments. The creep-fatigue synergisms and deformation mechanisms will be
evaluated using electron microscopy.
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(a) (b)
Figure 2. (a) Creep strain versus time plot (T = 760°C and σ = 100 MPa) and (b) minimum creep rate
versus stress plot to determine the creep exponent value (n) at T = 760°C for Haynes 230, Haynes 282
and Udimet 188.
0
0.5
1
1.5
2
2.5
0 50 100 150 200 250 300 350
H230H282UD188
Cre
ep
Str
ain
[%
]
Time [hr]
T = 760ºC
σσσσ = 100 MPa
10-10
10-9
10-8
10-7
10-6
100 1000
H230 - n = 5.9H282 - n = 6.2UD 188 - n = 6.6
Min
imu
m C
reep
Rate
[s
-1]
Stress [MPa]
T = 760ºC
(a) (b)
Figure 1. (a) BSE SEM image of Haynes 282 microstructure before the age-hardening heat
treatment and (b) an EBSD image quality map highlighting the distribution of grain boundary
misorientations (red (2°-5°) and green (5°-15°) = LAB, blue = GHAB, purple = CSLB
(excluding Σ3) and yellow = Σ3).
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(a) (b)
Figure 3. (a) ln(minimum creep rate) versus 10000/T plot used to caluculate Qapp value for
Haynes 282 at three different creep stresses and (b) strain versus time plot during a load-
controlled fatigue experiment (R = 0.1) at a maximum applied stress of 175 MPa at T =
815°C. The strain/time behavior resembled that for the creep experiment at σ = 175 MPa and
T = 815°C which is overlaid on the plot.
0
1
2
3
4
5
6
7
8
0 50 100 150 200
H282 - Creep TestH282 - Fatigue Test
To
tal S
tra
in [
%]
Time [hr]
σσσσmax
= 175 MPa
T = 815ºC
-23
-22
-21
-20
-19
-18
-17
-16
-15
9.1 9.2 9.3 9.4 9.5 9.6 9.7
H282 - σσσσ = 100MPa - Qapp
= 701 kJ/mol
H282 - σ σ σ σ = 125MPa - Qapp
= 755 kJ/mol
H282 - σσσσ = 150MPa - Qapp
= 725 kJ/mol
ln(M
inim
um
Cre
ep
Ra
te)
10000/T [K-1
]
760ºC790ºC815ºC
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