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Transformation induced plasticity (TRIP) behavior was studied in steel with composition Fe-0.07C-2.85Si-15.3Mn-2.4Al-0.017N that exhibited two TRIP mechanisms. The initial microstructure consisted of both {\epsilon}- and {\alpha}-martensites with 27% retained austenite. TRIP behavior in the first 5% strain was predominately austenite transforming to {\epsilon}-martensite (Stage I), but upon saturation of Stage I, the {\epsilon}-martensite transformed to {\alpha}-martensite (Stage II). Alloy segregation also affected the TRIP behavior with alloy rich regions producing TRIP just prior to necking. This behavior was explained by first principle calculations that revealed aluminum significantly affected the stacking fault energy in Fe-Mn-Al-C steels by decreasing the unstable stacking fault energy and promoting easy nucleation of {\epsilon}-martensite. The addition of aluminum also raised the intrinsic stacking fault energy and caused the {\epsilon}-martensite to be unstable and transform to {\alpha}-martensite under further deformation. The two stage TRIP behavior produced a high strain hardening exponent of 1.4 and led to ultimate tensile strength of 1165 MPa and elongation to failure of 35%., Comment: submitted to Met. Mater. Trans. A manuscript E-TP-12-953-A

We present ab-initio simulation of manganese, aluminum and carbon impurities in austenite and demonstrate their inhomogeneous distribution, which involves the repulsion of interstitial carbon atoms, the formation of bonded Mn-C pairs as well as a short range Al-ordering of D03-type. The mechanisms for the formation of stacking faults in Fe-Mn-Al-C are considered, and we find that the impurities have influence on the stacking fault energies only when located within a few interatomic layers near stacking fault. As a result, the stacking fault energy does not depend on the average concentration of impurities in matrix, but is highly sensitive to the concentration of the impurities in the vicinity of stacking fault defect. We predict that manganese shows a slight tendency for segregation near SF, while carbon prefers to be located far from the stacking fault region. Both aluminum and carbon impurities linearly increase the SFE, while the formation of Mn-C pairs and short range Al-ordering restrain the SFE growth. Short range order in Fe-Al-C alloys strongly affects the energy barrier for nucleation of dislocations and may lead to softening phenomenon.

Electronic structure and cohesive properties of metastable hexagonal AgB_{2} and silver-deficient borides Ag_{0.875}B_{2} and Ag_{0.750}B_{2} were investigated by means of the projected augmented wave method in the framework of the density functional theory (VASP package). We found that the density of states at the Fermi level for nonstoichiometric diborides is almost constant within a range of vacancy content up to 25%. The formation energy of metal vacancies in silver diboride is the least among all 4d metal diborides, i.e. for AgB_{2} is possible to expect the wide homogeneity region., Comment: 6 pages, 3 figures

Energy band structure of the discovered ternary perovskite-like compound ZnCNi3 reported by Park et al (2004) as a non-superconducting paramagnetic metal was investigated using the FLMTO-GGA method. The electronic bands, density of states, Fermi surface, charge density and electron localization function distributions for ZnCNi3 are obtained and analyzed in comparison with the isoelectronic and isostructural 8K superconductor MgCNi3. The effect of external pressure on the electronic states of ZnCNi3 and MgCNi3 is studied., Comment: 6 pages, 4 figures

Atomic models of zigzag (n, 0)- and armchair (n,n)-like NiCl2 nanotubes (n = 4 - 29) formed by rolling (100) single layers of the bulk NiCl2 which crystallizes in the CdCl2-type structure, are constructed and their electronic properties and bond indices are investigated using the tight-binding band theory. The calculations performed show that all the considered nanotubes in non-magnetic state are uniformly metallic-like. The density of states at the Fermi level contains a considerable contribution from Ni3d states, its value depends on the atomic configuration and diameter of the tubes. The Ni-Cl covalent bonds were found in NiCl2 tubes, whereas Ni-Ni and Cl-Cl covalent interactions are almost absent. According our estimations, the zigzag (n, 0)-like NiCl2 nanotubes are more energetically favorable., Comment: 6 pages, 3 figures, 2 tables