PSI - Issue 43

A. Shanyavskiy et al. / Procedia Structural Integrity 43 (2023) 215–220 Author ame / Structural Integr ty P o edi 00 (2022) 000 – 00

217 3

2

3

4

   

   

2

a w

w a

w a

w a

w a

+

  

 

 +  

  

 −  

  

  +  0.866 4.64

13.32

14.72

  −   5.6

f

=

(2)

1

(

)

1.5

1

a w

−

where a is the crack length, w is the length of the working area of the specimen, b is the specimen thickness, and P is the applied load. 3. Material The material used in the tests is heat-resistant XH73M nickel-based alloy, which is used for a GTE turbine disk and operates at elevated temperatures with the occurrence of creep conditions. The chemical composition and the main mechanical characteristics of analyzed material at both the ambient and elevated temperatures are summarized in Table 1 and Table 2, respectively. In Table 2, E is Young's modulus, σ 0.2 is yield stress, σ u is tensile strength, δ is elongation, ψ is reduction of area, B and n are the Norton creep constant and exponent. The material structure is typical for Ni- based superalloys with hardening γ’ -phase of spherical shape.

Table 1. Chemical composition for XH73M alloy.

C

Cr

Mo

Al

Ti

Nb

Ni

0.03-0.07

13.0-16.0

2.8-3.2

1.45-1.8

2.35-2.75

1.9-2.2

balance

B [1/(MPa*n ⋅ hr)] n - -

Table 2. Main mechanical static characteristics for XH73M alloy.

T [ ° C]

σ u [MPa]

σ 0.2 [MPa]

E [GPa]

δ [%]

ψ [%]

1298 1230 1206 1079

904 831 836 866 705

216 193 206 193 161

34.9 32.3 27.7 10.7

54.2 50.9 30.1 18.4 17.9

23

2.5*10 -11 4.0*10 -12 2.1*10 -16 4.0*10 -26

2.50 3.53 4.80 8.85

400 550 650 750

840

8.3

4. Test results Typically, the fatigue fracture diagram is represented by CGR coordinates da/dN versus K 1 , where N is the number of loading cycles. The present study focuses on the couple effects of temperature and different type of cyclic loading, therefore it would be useful to compare the fatigue fracture diagrams for the classic harmonic cycle (with constant loading frequency and loading waveform) and trapezoidal cycle with the holding time at a maximum load, and all other factors being equal. To this end, Fig. 1a shows the fatigue fracture diagrams of C(T) specimens, which were tested at a frequency of 10 Hz and temperatures of 23 ° C, 150 ° C, 650 ° C and 750 ° C. For simplicity, the CGR, da/dN , was set to be dependent on the elastic SIF, K 1 . A comparison of these diagrams shows that as the elastic SIF increased, the CGR during the harmonic loading conditions at high temperatures 650°C and 750°C sharp increased with respect to the ambient ( 23°C ) and moderately elevated ( 150°C ) temperatures. Fig. 1b illustrates the creep-fatigue interaction CGR, da/dN , versus the elastic SIF for the C(T) specimen as a function of the test temperature ranging between 450 ° C and 750 ° C, which consists of the dwell time during 120 sec and 5 sec loading/unloading time, for each loading cycle. Note that the each separate experimental CGR diagram falls within a relatively narrow scatter band. A fairly sharp increase in the crack growth rate is observed during the transition from temperature 650 ° C to temperature 750 ° C.