Abstract
The deformation behaviour of the wrought nickel base superalloy EI698 VD has been investigated in condition of low cycle fatigue. The tensile hold periods, imposing a constant stress into fatigue loading, have been introduced at the maximum stress value. The individual hold periods were in the range of 1 minute to 10 hours. The fatigue tests were of tension-tension type defined by stress ratio R = 0.027 and were conducted at a temperature of 650°C. The tests were performed up to fracture. The time to failure, corresponding to total load at amplitude peak, and number of cycles to failure have been the criteria for evaluation of the deformation behaviour of the alloy subjected to complex cyclic creep loading. In order to predict the lifetime of the alloy, regarding type of cyclic tests, the Kitagawa’s modified linear cumulative damage criterion has been considered. Two regression functions for applied hold period interval were proposed to calculate the time to failure. The formulae can be used to predict the life of nickel base superalloy considering the specific conditions of low cycle fatigue without and with tensile holds period.

Key words
nickel base superalloy, fatigue, creep, hold time, lifetime prediction

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