What can be learnt on the yield stress anomaly of Ni3Al using AFM observations

• Observations obtained using a unique and recently developed equipment.
• Examination by AFM of slip traces of Ni3Al deformed at various temperatures.
• At the nanometer scale slip traces are related to single superdislocation.
• Dislocation mean free path decreases with increasing temperature.
• A striking result with observation of long cube cross-slip traces.

We examined by in situ scanning probe microscopy the slip traces at the free surface of Ni3(Al,Ta) single crystals deformed in ultra high vacuum environment at various temperatures. It is evidenced that the mean free path of superdislocations in the primary octahedral planes strongly decreases with increasing temperatures. This is quantified by the decrease in the number of dislocations along slip traces corresponding to the primary (111) slip planes. Correlatively the number of cross-slip events increases with increasing temperature, together with a drastic increase of the distance travelled by the dislocations on the cube cross-slip plane. The experimental results are discussed in the frame of previous theoretical models that have been proposed to predict the yield stress anomaly of L12 intermetallic compounds.