Density functional theory calculations were performed to study the structure and magnetic properties of bcc (α) and fcc (γ) Fe with 3 at.% carbon and manganese impurities. We find that all bcc-based Fe, Fe-C and Fe-Mn-C phases exhibit a ferromagnetic (FM) ground state, while the antiferromagnetic double-layer (AFMD) state is lowest in energy within the collinear spin approach in fcc Fe, Fe-C and Fe-Mn-C phases. However, the carbon and manganese impurities affect the local magnetic interactions significantly. The states with opposite manganese magnetic moments are quasi-degenerate in bcc Fe-Mn alloy, whereas octa-site carbon stabilizes ferromagnetic coupling of the nearest manganese atom with the Fe host. We demonstrate that the antiferromagnetic (AFM) fcc Fe-C and Fe-Mn-C alloys are intrinsically inhomogeneous magnetic systems. Carbon frustrates the local magnetic order by reorientation of magnetic moments of the nearest Mn and Fe atoms, and favors their ferromagnetic coupling. The competition between ferromagnetic and antiferromagnetic Fe-Fe and Fe-Mn interactions and the local magnetovolume instability near carbon may give rise to the spin-glass-like regions observed in austenitic Fe-Mn-C alloys.

This paper reviews the physical metallurgy and damping characteristics of copper-manganese (Cu-Mn) alloys. Many of the examples given in this paper are based upon the authors' experimental investigations of an alloy with nominal composition (composition in weight percent) of 48Cu-48Mn-1.5Al-0.27 Si-0.072Sn-0.028C-0.05Er. The results for this material were obtained in a bending mode, and the reported strain amplitudes represent the maximum surface strain imposed. Damping in these materials is very sensitive to heat treatment and carbon content. Recent work has shown that carbon in solid solution is detrimental to the damping capacity and results in a strain aging behavior and subsequent loss of damping capacity when stored at room temperature. Copper-manganese alloys can lose more than 50% of their damping capacity during room temperature storage. The role of erbium in the stabilization of the damping capacity is explained in the context of the physical metallurgy of the Cu-Mn system.