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

Abstract

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 Δσ σ of the applied stress amplitude to the mean applied stress at low Δσ σ , but certainly decreases at high values of this ratio and depends significantly on the period of superimposed loading Δt c; and (iii) the strain to fracture increases with increasing ratio Δσ σ approximately independently of the period Δt c.