Work hardening behavior in a steel with multiple TRIP mechanisms

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-

The redox transformations and nucleophilic replacements as possible metabolic reactions of the drug “Triazaverin”. The chemical modeling of the metabolic processes

As a model of metabolic transformations of antiviral drug “Triazaverin” and its analogues‑2-alkylthio‑6-nitro‑1,2,4-triazolo[5,1-c][1,2,4]triazine‑7-ones 1a-d examined the oxidation of alkylthio groups to the corresponding sulfoxides 2a-d and sulfones 3a-d, as well as the process of nucleophilic substitution sulfonyloxy group of cysteine and cysteamine with the formation of compounds 5 and 6

Effect of Phosphorus on Cleavage Fracture in Κ-Carbide

To understand the origin of cleavage fracture which dominates in Fe(Mn)-Al-C alloys at a high phosphorus concentration, we performed first-principles study of the phosphorus effect on ideal cleavage energy and critical stress in κ-carbide, Fe3 AlC, a precipitate in the austenitic alloys. We find that phosphorus has higher solubility in Fe3 AlC than in γ-Fe and sharply reduces the cleavage characteristics of κ-carbide. We show that strong anisotropy of the Fe-P bonds in Fe3 (Al,P) C under tensile stress, leads to the appearance of large structural voids and may facilitate crack nucleation

Role of direct exchange and Dzyaloshinskii-Moriya interactions in magnetic properties of graphene derivatives: C2_2F and C2_2H

According to the Lieb's theorem the ferromagnetic interaction in graphene-based materials with bipartite lattice is a result of disbalance between the number of sites available for $p_z$ electrons in different sublattices. Here, we report on another mechanism of the ferromagnetism in functionalized graphene that is the direct exchange interaction between spin orbitals. By the example of the single-side semihydrogenated (C$_2$H) and semifluorinated (C$_2$F) graphene we show that such a coupling can partially or even fully compensate antiferromagnetic character of indirect exchange interactions reported earlier [Phys. Rev. B {\bf 88}, 081405(R) (2013)]. As a result, C$_2$H is found to be a two-dimensional material with the isotropic ferromagnetic interaction and negligibly small magnetic anisotropy, which prevents the formation of the long-range magnetic order at finite temperature in accordance with the Mermin-Wagner theorem. This gives a rare example of a system where direct exchange interactions play a crucial role in determining a magnetic structure. In turn, C$_2$F is found to be at the threshold of the antiferromagnetic-ferromagnetic instability, which in combination with the Dzyaloshinskii-Moriya interaction can lead to a skyrmion state.Comment: 10 page

Role of Coulomb correlation on magnetic and transport properties of doped manganites: La0.5Sr0.5MnO3 and LaSr2Mn2O7

Results of LSDA and LSDA+U calculations of the electronic structure and magnetic configurations of the 50% hole-doped pseudocubic perovskite La0.5Sr0.5MnO3 and double layered LaSr2Mn2O7 are presented. We demonstrate that the on-site Coulomb correlation (U) of Mn d electrons has a very different influence on the (i) band formations, (ii) magnetic ground states, (iii) interlayer exchange interactions, and (iv) anisotropy of the electrical transport in these two manganites. A possible reason why the LSDA failures in predicting observed magnetic and transport properties of the double layered compound - in contrast to the doped perovskite manganite - is considered on the basis of a p-d hybridization analysis.Comment: 11 pages, 3 figure