Microstructure and mechanical properties of directionally solidified γ/γ-α eutectic composites

The microstructure and mechanical properties of four directionally solidified γ/γ-α eutectic composites with chemical composition Ni-20.1Mo-13.6Al, Ni-20.2Mo-14.1Al-3.5Cr, Ni-20.4Mo-14.7Al-1.8V and Ni-18.4Mo-13.9Al-2.0V-0.5Re (at.%) are characterised. The crystallographic relationships between the coexisting phases, the effect of the growth rate of eutectic composite on the microstructural parameters and experimentally determined critical values for the stability of planar solid-liquid interface are outlined and discussed. An analytical model for prediction of the tensile offset yield stress based on the concept of Orowan stress is proposed. The fracture micromechanisms identified during tensile in-situ straining in SEM and fracture mode are described. High-temperature creep characteristics including stress exponents and activation energies for creep are calculated and compared to those of other intermetallic Ni3Al-based alloys. An analytical model for steady-state creep behaviour is presented. Creep fracture mode and effect of coexisting phases on initiation and crack propagation are discussed.