PSI - Issue 19

Yasuhiro Yamazaki et al. / Procedia Structural Integrity 19 (2019) 538–547 Author name / Structural Integrity Procedia 00 (2019) 000 – 000

544

7

RT Q

   

  

m   Bt

m

X

B

t

(1)

exp

0

Where, X is the thickness of the oxide layer [μm], t is the exposure time [s], T is the exposure temperature [K], Q is the activation energy [J/mol], R is the gas constant [J/(mol K)], B 0 is the growth rate constant, respectively. The m value obtained from Fig. 12(a) was 0.2176 which was closed to m = 0.25 obtained in a Ni-base superalloy, IN-100 (Remy et al. (1993)). The effect of the applied stress on the growth rate coefficient is shown in Fig. 13. For the results of Fig. 13, the thickness of the oxide layer was evaluated on the (100) specimen surface applied the compressive stress because the compressive stress was applied at elevated temperature in the crack propagation test. It was cleared from the comparison the oxide layer on both compression and tensile sides of the specimen that there was little difference in the growth rate of the oxide layer on both sides of the specimen.

Fig. 11. Typical oxide layer grown on the (100) surface of the specimen by thermal oxidation without the loading at 900°C for 100h.

a

b

Fig. 12. Results of the oxidation test without the loading, (a) the growth behavior, (b) temperature dependence of the reaction rate coefficient.

Fig. 13. Effect of the applied stress on the growth rate coefficient of the oxide layer on (100) specimen surface at 900°C for 10h.