Dislocation densities have been measured in Ni3Al(Hf) single crystals after deformation at various temperatures and strains. In addition, effective and athermal stresses have been determined by strain dip tests. A model is proposed for the strength anomaly domain which correlates the athermal part of the stress with the operation of dislocation sources, to compensate for the strong dislocation exhaustion. Dislocation density data, which evidence an anomaly in the density with temperature over the stress anomaly domain, are shown to support this model predictions between 373K and 683K for plastic strains larger than 3x102 but not at yield. In addition, the presence of Hf atoms (3.3 at. %) induces a friction stress close to 63MPa.