No abstract

No abstract

The creep and fatigue properties of the directionally solidified nickel base superalloy CM247LC DS have been investigated. Constant creep tests have been carried out on specimens with different orientations in the temperature range of 700-1OOO'C at different loads to obtain times to rupture up to 35000 h. The comparison of the creep properties with the IN738LC conventionally cast alloy and with the oxide dispersion strengthened MA6000 alloy has shown the better creep performance of the alloy CM247LC DS in the temperature range of interest for application in land based gas turbines. A series of cyclic load creep tests has allowed to study the effect of load variations on the creep. The effect of cycling stress is to increase the strain rate, compared with the constant load creep tests and then to reduce the rupture life of the alloy. The LCF tests, performed at the temperatures of 85O'C and 950°C in longitudinal strain controlled conditions, have evidenced a fairly stable cyclic response. Basquin and Coffin-Manson relationships can adequately predict the fatigue life of the alloy. The CM247LC DS alloy exhibits a better fatigue life than IN738LC and MA6000 alloys.

No abstract

No abstract

No abstract

The high temperature low cycle fatigue behaviour of a directionally solidified Ni-base superalloy hardened by about 65% volume fraction of y'-precipitates was investigated in order to determine the fatigue life parameters for longitudinal (L) and longitudinal transverse (LT) grain orientations. The fatigue resistance was compared with that of two oxide dispersion strengthened (ODS) Ni-base superalloys with a similar elongated grain structure.The fatigue life of the alloy can be adequately predicted by Basquin and Cof6n-Manson empirical relationships and the fatigue ductility parameters in these relationships show a similar trend with the tensile ductility properties.The studied alloy exhibits a fairly stable cyclic stress response, with only a slight stress softening. Fatigue crack initiation occurs mainly at shrinkage pores on the surface or sub-surface of the specimens. The crack growth direction is predominantly perpendicular to the applied load. The fracture mode in the LTdirection is transgranular and fatigue life is shorter by a factor of about six compared to the L-direction. The fatigue life of the alloy is longer than that of the ODS Ni-base superalloys with which it is compared. NOMENCLATURE N = number of cycles to failure n = progressive number of cycles E = Young's modulus A% = total strain range L\E, = elastic strain component A E~ = plastic strain component Au, = stress amplitude Q = failure ductility coefficient by= fatigue strength coefficient

No abstract