Effect of alloying with Mn and Co on the temperature dependence of internal friction in Fe-Ni-C invar alloys

Abstract

Temperature dependences of internal friction (TDIF) have been studied by the method of resonance bending vibrations in a kilohertz frequency range in the temperature range from 100 to 900 K in fcc Fe-Ni-X and Fe-Ni-X-C (X = Mn, Co) alloys with a Ni content of about 30 wt %. To produce a single-phase austenitic structure, the alloys were homogenized at 1373 K in vacuum and rapidly cooled in oil. At temperatures of 550–587 K, above the Curie temperature of the alloys, in the TDIF curves there is observed a carbon relaxation peak of internal friction. It has been demonstrated that in the alloys studied the temperature of the peak Tmax at vibration frequencies of 1.5–2 kHz is more than 100 K higher than the Curie point TC and that the alloying elements Mn and Co increase the difference between Tmax and TC. The activation energy calculated within the framework of the Wert-Marx model is equal to 1.1 eV. It has been found out that the alloying of Fe-Ni-C with Mn induces a certain decrease in the temperature and intensity of the carbon peak, while addition of Co, on the contrary, leads to an increase in the peak temperature and intensity of damhing of elastic vibrations. The causes of such effect have been considered.