Effect of cyclic loading superposition in the primary creep stage on the strain and fracture behaviour of 16Cr10W4MoTiAl nickel-base alloy

Results of an investigation of the low frequency cyclic applied stress superposition effect in the primary creep stage on the strain and fracture behaviour of a commercial heat-resistant nickel-base 16Cr10W4MoTiAl alloy are presented. It is shown that such a superposition affects the strain rate as well as the fracture behaviour of the alloy in a rather complicated way. Thus, (i) measurements of the strain rates immediately before and immediately after any applied stress change clearly suggest that the strain rate behaviour cannot be described by a simple constitutive equation; (ii) the time to fracture seems to increase with increasing ratio Δσσ of the applied stress amplitude to the mean applied stress at low Δσσ, but certainly decreases at high values of this ratio and depends significantly on the period of superimposed loading Δtc; and (iii) the strain to fracture increases with increasing ratio Δσσ approximately independently of the period Δtc.