M. Khadhraoui et al., EXPERIMENTAL INVESTIGATIONS AND MODELING OF RELAXATION BEHAVIOR OF SHOT PEENING RESIDUAL-STRESSES AT HIGH-TEMPERATURE FOR NICKEL-BASE SUPERALLOYS, Materials science and technology, 13(4), 1997, pp. 360-367
Residual stresses induced by two shot peening conditions in nickel bas
e superalloy Inconel 718 and their relaxation after different exposure
times (10 and 100 h) at 600 and 650 degrees C were evaluated by an X-
ray diffraction technique. The behaviour of stress relaxation (effects
of exposure time and applied temperature) is particularly analysed an
d discussed. A significant decrease of the initial stress values was o
bserved in the first period of exposure time, followed by slowing down
and then stabilisation. Experimental results showed that the maximum
relaxation always occurred at the surface. It was also observed that a
higher applied temperature produced greater relaxation, but had no si
gnificant effect on the pattern of the depth profile of stress. The re
laxation mechanism is essentially interpreted by thermal recovery char
acterised by a rapid annihilation of the unstable crystalline defects
in highly deformed materials. Complex changes of various microscopic m
agnitudes under high temperature are described by macroscopic magnitud
es related to the plastic strains and associated residual stresses. An
existing model is developed and actualised by integrating the limitin
g state of recovery and the integrated width of X-ray diffraction peak
s in order to predict relaxation of the residual stresses. The relaxat
ion predicted by the model agrees satisfactorily with the experimental
results in the studied cases.