Creep properties of an oxide dispersion strengthened nickel-base alloy: the effect of grain orientation and grain aspect ratio

A study of the high temperature tensile creep behaviour of the oxide dispersion strengthened (ODS) nickel-base alloy PM 1000 was conducted at 900°C in air. To investigate the effect of grain orientation and grain aspect ratio (GAR), three different heats of PM 1000 were tested: (i) a 〈100〉-fibre structured bar material with a grain aspect ratio of 10 along the longitudinal direction, (ii) a 〈111〉-fibre structured bar material with a GAR of 4 and (iii) a pancake structured sheet material with a GAR of 4 and 〈100〉{011} cube on edge texture deformed in the 〈110〉 axial direction. At high strain rates the creep resistance depends mainly on texture: the creep strength of the hard 〈111〉-orientation exceeds by far those of the 〈110〉- and the 〈100〉-orientations. At low creep rates, in the range of interest for practical applications, the situation is different: instead of the texture effect, tertiary creep processes, such as void formation and void growth on transverse grain boundaries and in fine grained ‘enclaves’, play the major role, creep life being controlled by creep ductility.