INTERNAL FRICTION STUDY OF THE γ PEAK IN COLD-WORKED NIOBIUM

The γ peak due to the double kink generation (DKG) along screw dislocations has been observed in high purity niobium. This peak appears at 270K (1Hz) and is unstable. Some special thermomechanical treatments have been realized in order to develop and stabilize this peak. The evolution of the internal friction spectra has been studied as a function of these treatments. The screw dislocations network created by low temperature deformation is unstable and rearranges in two stages : a W stage (180K-240K) and a X stage (280K-350K). The transformation accomplished in the W stage and the effect of the γ peak stabilization treatment have been observed by transmission electron microscopy