Investigation of structural, elastic and magnetic properties of Fe70Mn30 alloys doped with interstitial elements

In this thesis, the structural, elastic and magnetic properties of Fe70Mn30 Invar alloys with added carbon interstitial element were investigated. In the experimental part, (Fe70Mn30)100-xCx (x=0.02, 0.11, 0.55, and 0.81 at %) alloys were produced by vacuum arc melting method. The crystal structures of these alloys were examined with x-ray diffractometry. Elastic modulus measurements were performed with a resonance frequency damping analyzer. The temperature dependent magnetization measurements were obtained with a superconducting quantum interference device by applying 1 Tesla external magnetic field. Crystal structure, temperature dependent modulus of elasticity and magnetization results of C-doped Fe70Mn30 alloys were evaluated in terms of the Invar property. As a result of the experiments, hcp phase was detected together with fcc in alloys with 0.02 and 0.11 at% carbon additives in x-ray diffractometry, while only fcc formation was observed in alloys with 0.55 and 0.81 at% carbon additions. It was determined that the elastic modulus increased from room temperature to Neel temperature, unlike the normal metallic behavior. However, after the Neel temperature, the elastic modulus decreased with the increase in temperature in the paramagnetic region. In addition, it was observed that the transition in elastic properties shifted to lower temperatures with the addition of carbon interstitial element. It was determined that the magnetic properties increased up to the Neel temperature and the magnetic properties of the 0.02% and 0.11% carbon added alloys decreased after the Neel temperature. It was observed that the magnetic properties remained constant after the Neel temperature for 0.55% and 0.81% carbon added alloys. With the magnetization results, it was determined that the Neel temperature decreases as the carbon addition increased and these temperatures corresponded to the softening temperature observed in the elastic properties. Thus, the temperature region in which the Invar feature is observed with the carbon addition has been pulled down to room temperatures, which makes the material usable for application areas where thermal expansion at room temperature is not desired.