EFFECT OF CYCLIC LOADING SUPERPOSITION IN THE PRIMARY CREEP STAGE ON THE STRAIN AND FRACTURE-BEHAVIOR 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 fra cture behaviour of a commercial heat-resistant nickel-base 16Cr-1OW-4M o-TiAl alloy are presented. It is shown that such a superposition affe cts the strain rate as well as the fracture behaviour of the alloy in a rather complicated way. Thus, (i) measurements of the strain rates i mmediately before and immediately after any applied stress change clea rly suggest that the strain rate behaviour cannot be described by a si mple constitutive equation; (ii) the time to fracture seems to increas e with increasing ratio Delta sigma/sigma of the applied stress amplit ude to the mean applied stress at low Delta sigma/sigma, but certainly decreases at high values of this ratio and depends significantly on t he period of superimposed loading Delta t(c); and (iii) the strain to fracture increases with increasing ratio Delta sigma/sigma approximate ly independently of the period Delta t(c).