Relating the mechanical properties of a pseudo-binary a L12 alloy to the deformation induced microstructure

Compressive tests at a constant strain rate conducted on a pseudo-binary L12 Ni55Fe20Ge25 intermetallic in a wide range of temperatures (from room temperature to 823 K) show the occurrence of a positive flow stress anomaly behaviour with a peak of flow stress occurring around 600 K. The induced dislocation substructures (morphology and core) were investigated by means of transmission electron microscopy (TEM) in weak beam conditions. In the domain of the increase of the flow stress, the dislocation substructure consists of screw dislocations locked in a Kear-Wilsdorf (KW) configurations as commonly observed in L12 alloys. With increasing temperature, gliding superdislocations are found to interact strongly with dislocations, in complete KW configurations. This interaction leads to a non-negligible quantity of dislocation dipoles. In the domain of the decrease of the flow stress, the most striking feature was the presence of a relatively high density of superlattice stacking faults. A close observation shows that the faulted defects exhibit in fact two linked faulted ribbons of unequal widths bounded by three superpartials having the same 1/3〈112〉 Burgers vector and lying in the same plane. The observed mechanical behaviour is discussed in relation with the TEM investigations.