INFLUENCES OF ADDITIONS OF Nb, Ti AND Cu ON DAMPING CAPACITY AND CORROSION RESISTANCE OF Fe--13Cr--2.5Mo ALLOY

Fe--Cr base high damping alloys (HDA), as the typical ferromagnetic type HDA, have been well investigated in a long history due to their merits in low cost and superior workability like steels, and are widely applied for suppression of noise or vibration in many industrial fields. The agnetoelastic coupling in ferromagnetic materials is well known to be an important source of internal friction, which could produce a high damping capacity. The damping mechanism has been mainly attributed to the stress--induced irreversible movements of magnetic domain walls. Fe--(12%---16%)Cr--(2%---4%)Mo (mass fraction) base alloys were found to possess higher damping capacity and better corrosion resistance. As well known Nb, Ti and Cu can improve corrosion resistance of stainless steel. In the present work, dynamic mechanical analyzer (DMA) and field--emission scanning electron microscope (FESEM) were used to investigate the influences of additions of 1.0%Nb, 1.0%Ti and 0.5%Cu on the damping capacity and corrosion resistance of Fe--13Cr--2.5Mo alloy. The results show that addition of 1.0%Nb causes abundant precipitations of (Nb, Mo)C, which can obstruct the movement of domain walls, and significantly deteriorate the damping capacity at low strain amplitude. At strain amplitudes higher than 3.5×10-5, the amplitude--dependent dislocation damping Qdis-1 is generated due to dislocations interaction with (Nb, Mo)C, so the damping capacity of Nb--containing alloy becomes higher than other alloys. Addition of Ti or Cu inhibits the precipitation of grain--boundary carbides, while promotes the intragranular precipitations in the alloy distinctly. As a result, the damping capacity of the alloy with Ti or Cu is slightly lower than that of Fe--13Cr--2.5Mo alloy. Pitting corrosion test indicates that the three alloying elements can all improve the corrosion resistance of Fe--13Cr--2.5Mo damping alloy. The 1.0%Ti--containing alloy possesses not only high damping capacity but also good corrosion resistance.