Temperature Effect on Deformation Mechanisms and Mechanical Properties of Welded High-Mn Steels for Cryogenic Applications.

High-manganese steel (high-Mn) is valuable for its excellent mechanical properties in cryogenic environments, making it essential to understand its deformation behavior at extremely low temperatures. The deformation behavior of high-Mn steels at extremely low temperatures depends on the stacking fault energy (SFE) that can lead to the formation of deformation twins or transform to ε-martensite or α'-martensite as the temperature decreases. In this study, submerged arc welding (SAW) was applied to fabricate thick pipes for cryogenic industry applications, but it may cause problems such as an uneven distribution of manganese (Mn) and a large weldment. To address these issues, post-weld heat treatment (PWHT) is performed to achieve a homogeneous microstructure, enhance mechanical properties, and reduce residual stress. It was found that the difference in Mn content between the dendrite and interdendritic regions was reduced after PWHT, and the SFE was calculated. At cryogenic temperatures, the SFE decreased below 20 mJ/m2, indicating the martensitic transformation region. Furthermore, an examination of the deformation behavior of welded high-Mn steels was conducted. This study revealed that the tensile deformed, as-welded specimens exhibited ε and α'-martensite transformations at cryogenic temperatures. However, the heat-treated specimens did not undergo α'-martensite transformations. Moreover, regardless of whether the specimens were subjected to Charpy impact deformation before or after heat treatment, ε and α'-martensite transformations did not occur.

Reversible crystal-to-amorphous structural conversion in the single end-on azide-bridged Co(II) complex: concomitant color and magnetic modulations.

Crystal clear: An end-on (EO) azide-bridged Co(II) layer (see scheme; 1) with coordinated water molecules, long spacer p-XBP4 ligands, and unbound azide anions was evacuated to generate a dehydrated sample of 2. A reversible crystal-to-amorphous structural transformation accompanied by color and magnetic changes takes place between 1 and 2 by using a desolvation-solvation protocol.

A growth mechanism of porous film formed on Al in 0.6 M oxalic acid electrolyte.

Understanding of mechanism of porous film formation is of fundamental importance for anodizing in general because, the onset of pore initiation terminates the barrier film growth process over the macroscopic metal surface. Several mechanisms have been proposed to explain pore formation. They include direct injection of aluminum ions into electrolyte and a field-assisted dissolution mechanism. High-resolution scanning electron microscopy of anodized surfaces and direct TEM of ion beam thinned films and ultrarmicrotomed film sections have been employed to gain further insight into the mechanism of initial porous film growth in 0.6 M oxalic acid. From detailed examination of the behavior of the xenon-tagged layer in the film during pore initiation and development in oxalic acid, the film structure of the barrier layer is found to be unstable during pore initiation and the instability of the film structure is possibly related to the field-assisted structure modification process.

Strain-Rate Dependence of Tensile Behavior in Commercial-Grade Tungsten-Effect of Recrystallization Condition.

The tensile deformation behavior of double-forged (DF-W) and recrystallized (RX-W) commercial-grade tungsten was investigated at 700 °C. With increasing strain rate, the dominant dynamic recrystallization (DRX) mechanism changes from continuous dynamic recrystallization (CDRX) to discontinuous dynamic recrystallization (DDRX). For DF-W, pre-existing sub-grains promote CDRX and associated a high-DRX fraction, resulting in reduced post-necking strain under a static condition. With increasing strain rate, a shift in the restoration mechanism from CDRX to DDRX contributes to the enhanced ductility in DF-W, while RX-W shows enhanced flow hardening without a loss of ductility. These results suggest that the strain-rate dependence of mechanical behavior depends on the initial microstructure.

One-dimensional end-to-end azide-bridged Mn(III) complexes incorporating alkali metal ions: slow magnetic relaxations and metamagnetism.

Three azide-bridged Mn(III) chains [Mn(3-MeOsalpn)(N(3))]⋅0.5 AClO(4) (A = Na (1), K (2), Rb (3); 3-MeOsalpn = N,N'-propylenebis(3-methoxysalicylideneiminato) dianion) incorporating alkali metal ions and perchlorate anions were systematically synthesized. The overall structure can be described as a one-dimensional chain bridged by end-to-end azide ligands, although spatial arrangements of Jahn-Teller axes of Mn in 1 and 2 are different from that in 3. Relying on the alkali metal ions, magnetic properties are varied from a two-step phase transition (1) to metamagnetic transitions (2 and 3). In this system, spin canting definitely plays a central role in giving rise to the apparent slow magnetic relaxations in 1 and 2 because application of a high external magnetic field tends to destroy single-chain magnet (SCM) properties. Despite the existence of a long-range antiferromagnetic order at T(N) , slow magnetic relaxation is notably observed in 2, which likely emanates from the operative spin canting below T(N) .

Cyanide-bridged W(V)Mn(III) single-chain magnet with isolated Mn(III) moieties exhibiting two types of relaxation dynamics.

A 5d-3d bimetallic compound was prepared by self-assembling [W(CN)(8)](3-) and the Mn(III) Schiff bases. This neutral complex consists of cyanide-linked W(V)Mn(III) anionic chains and isolated Mn(III) Schiff base cations. We demonstrate that two types of relaxation processes are involved in the system; the low-T dynamics may come from magnetic domain dynamics and the high-T relaxation stems from the anionic chain, revealing single-chain magnet character.

End-to-end azide-bridged manganese(III) chain compounds: field-induced magnetic phase transitions and variation of T(C) to 38 K depending on the side groups of the Schiff bases.

Three one-dimensional coordination polymers [Mn(L)(N(3))](n) [L = L1 (1), L2 (2), L3 (3); L1H(2) = N,N'-bis(5-chlorosalicylideneiminato)-1,3-diaminopentane, L2H(2) = N,N'-bis(5-bromosalicylideneiminato)-1,3-diaminopentane, L3H(2) = N,N'-bis(5-bromosalicylideneiminato)-1,3-diamino-2-dimethylpropane] bridged by end-to-end azides were prepared. The crystal systems differ according to the Schiff bases used. Each Mn atom adopts a typical Jahn-Teller distortion. The helicity of the chains occurs in a racemic manner only for 2. No noncovalent forces are relevant in 2, while π-π contacts are visible in 1 and 3. Magnetic measurements show the presence of apparent spin canting. Complexes 1 and 3 exhibit a field-induced metamagnetic transition from an antiferromagnetic state to a weak ferromagnetic phase, whereas 2 embraces a field-induced two-step magnetic phase transition. The critical temperature is observed at 38 K for 2, which is relatively higher than those for 1 (11 K) and 3 (10 K). The pronounced long-range order may contribute from intrachain exchange couplings and through-space dipolar interactions between adjacent chains.

Cyanide-bridged Fe(III)-Mn(III) bimetallic systems assembled from the fac-Fe tricyanide and Mn Schiff bases: structures, magnetic properties, and density functional theory calculations.

Reaction of [(Tp)Fe(CN)(3)](-) [Tp = hydrotris(pyrazolyl)borate] with respective Mn(III) Schiff bases led to the formation of four dimeric molecules, [(Tp)Fe(CN)(3)][Mn(1-napen)(H(2)O)].MeCN.4H(2)O [1; 1-napen = N,N'-ethylenebis(2-hydroxy-1-naphthylideneiminato) dianion], [(Tp)Fe(CN)(3)][Mn(5-Clsalen)(H(2)O)] [2; 5-Clsalcy = N,N'-(trans-1,2-cyclohexanediylethylene)bis(5-chlorosalicylideneiminato) dianion], [(Tp)Fe(CN)(3)][Mn(2-acnapen)(MeOH)].MeOH [3; 2-acnapen = N,N'-ethylenebis(1-hydroxy-2-acetonaphthylideneiminato) dianion], [(Tp)Fe(CN)(3)][Mn(3-MeOsalen)(H(2)O)] [4; 3-MeOsalen = N,N'-ethylenebis(3-methoxysalicylideneiminato) dianion], and a one-dimensional (1D) zigzag chain [(Tp)Fe(CN)(3)][Mn(2-acnapen)].H(2)O (5). The dimers contain multiple intermolecular interactions such as hydrogen bonds, face-to-face pi-pi contacts, and edge-to-face CH-pi forces, raising molecular dimensions from one-dimensional (1D) up to three-dimensional (3D) arrays, whereas there are no pi-pi stacking interactions in the 1D chain compound. Magnetic measurements reveal that ferromagnetic couplings are obviously operative between Mn(III) and Fe(III) spin centers transmitted by CN bridges for 1-3 and 5, and antiferromagnetic interactions are however unexpectedly present in 4. On the basis of the proper spin Hamiltonians, magnetic exchange couplings are estimated to be in the span from 1.79 to 7.48 cm(-1) for the ferromagnetically coupled systems and -1.40 cm (-1) for the antiferromagnetic dimer. A slow magnetic relaxation is tangible in 5, which is in connection with isolated chains devoid of any intermolecular noncovalent interactions. Density Functional Theory (DFT) calculations and comparison of structural parameters suggest that the observed magnetic behaviors are mainly associated with the bending of the Mn-N[triple bond]C angle in the bridging pathway.

Measurement of Fracture Toughness of Pure Tungsten Using a Small-Sized Compact Tension Specimen.

The evaluation of fracture toughness of pure tungsten is essential for the structural integrity analysis in a fusion reactor. Therefore, the accurate quantification of fracture toughness of tungsten alloys is needed. However, due to the inherent brittleness of tungsten, it is difficult to introduce a sharp fatigue pre-crack needed for the fracture toughness test. In this study, a novel fatigue pre-cracking method was developed and applied to the small-sized disc-type compact tension (DCT) specimens of double-forged pure tungsten. To overcome the brittleness and poor oxidation resistance, a low-frequency tensile fatigue pre-cracking was performed at 600 °C in Ar environment, which resulted in the introduction of a sharp pre-crack to DCT specimens. Then, fracture toughness tests were conducted at room temperature (RT), 400 °C, and 700 °C in air and Ar gas environments using as-machined and pre-cracked DCT specimens. At RT and 400 °C, the test environment and crack tip radius did not affect the fracture toughness measurement. However, at 700 °C, the Ar gas environment and the presence of a sharp fatigue pre-crack resulted in a decrease in the measured fracture toughness. Thus, it was suggested that, for the conservative fracture toughness measurement of pure tungsten, fatigue pre-cracking and fracture toughness test should be performed in an inert environment, especially for high-temperature tests.

An end-on azide-bridged antiferromagnetic single-chain magnet involving spin canting and field-induced two-step magnetic transitions.

Two-step magnetic transitions: An azide-bridged 1D Mn(III) coordination polymer with a unique single end-on mode was prepared; it displayed atypical antiferromagnetic couplings and field-induced two-step magnetic transitions (see figure). The spin-canted phenomenon in the antiferromagnetic chain complex plays a pivotal role in establishing the slow magnetic relaxation.

Cyanide-bridged one-dimensional ferromagnetic Ru(III)Mn(III) coordination polymer exhibiting a field-induced magnetic phase transition.

A cyanide-linked Ru(III)(4d)-Mn(III)(3d) bimetallic chain complex (1) was prepared by the self-assembly of a ruthenium(III) bicyanide and a Mn(III) Schiff base. Ferromagnetic couplings between the magnetic centers are present within a chain, while antiferromagnetic interactions between chains (T(N) = 2.5 K) transmit. Complex 1 also shows a field-induced magnetic phase transition.

One-dimensional cyanide-bridged Mn(III)W(V) bimetallic complexes: metamagnetism, spontaneous resolution, and slow magnetic relaxation.

The reaction of [W(CN)(6)(bpy)](-) with the corresponding Mn Schiff bases led to the formation of two antiferromagnetic (1) and ferromagnetic (2) chains. The formation of the conglomerate (2) is associated with chiral induction by the enantiomeric chelate-ring conformation of the Mn Schiff base. Modulation of the linking groups in the Mn Schiff bases affects the interchain contacts, causing alteration of the magnetic behaviors from metamagnetism (1) to slow magnetic relaxation (2).

Octacyanometalate-based ferrimagnetic M(V)Mn(III) (M = Mo, W) bimetallic chain racemates with slow magnetic relaxations.

Cyanide-bridged M(V)-Mn(III) (M = Mo, W) bimetallic chain complexes with racemic spatial dispositions were constructed by self-assembling [M(CN)(8)](3-) precursors and Mn(III) Schiff bases. Antiferromagnetic couplings between spin centers within a chain result in a ferrimagnetic nature, and slow magnetic relaxations are observed as well.

Intermolecular contact-tuned magnetic nature in one-dimensional 3d-5d bimetallic systems: from a metamagnet to a single-chain magnet.

Assembling [W(CN) 6(bpy)] (-) and magnetic anisotropic Mn Schiff bases produced two Mn (III)(3d)-W (V)(5d) bimetallic chains. Modulation of the types and degrees of interchain pi-pi interactions in the one-dimensional coordination polymers leads to the variation of the magnetic behavior from a metamagnetic character to a single-chain magnet property.

Chiral azide-bridged two-dimensional Cu(II) compounds showing a field-induced spin-flop transition.

Two azide-bridged chiral Cu(II) compounds, [Cu(R,R-dacy)(N3)2]n (R,R-dacy = trans-(1R,2R)-diaminocyclohexane) and [Cu(S,S-dacy)(N3)2]n (S,S-dacy = trans-(1S,2S)-diaminocyclohexane), with two-dimensional layer structures exhibiting end-to-end and end-on azide bridging patterns, were prepared and among them was examined to show a field-induced spin-flop transition.

Spin crossover in the cyanide-bridged Mo(V)Mn(III) single-chain magnet containing Fe(II) cations.

A 1D Mo(V)Mn(III) chain compound balanced by {Fe[HC(3,5-Me(2)pz)(3)](2)}(2+) dications was prepared. This complex displays a typical single-chain magnet character associated with the Mo(V)Mn(III) chain and a spin crossover phenomenon arising from cationic Fe(II) subunits. The spin crossover behavior tends to slightly affect single-chain magnetic properties at low temperature.

Magnetic metal-organic framework constructed from a paramagnetic metalloligand exhibiting a significant sorption and reversible magnetic conversions.

A Co(II)-Cu(II) framework based on a paramagnetic metalloligand [Co(Tt)(2)] shows a permanent porosity with a record high surface area for magnetic MOFs as well as a reversible magnetic transformation between a paramagnetic-like state and a short-range magnetic order in the low-temperature regime upon solvation-desolvation cyclings.

Syntheses, crystal structures and magnetic properties of cyano- and phenoxide-bridged Fe(iii)Mn(iii) tetramers containing fac-Fe(iii) tricyanides and Mn(iii) Schiff bases.

Three cyanide-linked Fe(iii)Mn(iii) bimetallic clusters, [(Tp)Fe(CN)(3)](2)[Mn(acphen)](2) [; acphen = N,N'-ethylenebis(2-hydroxyacetophenylideneiminato) dianion], [(Tp)Fe(CN)(3)](2)[Mn(5-Bracphen)](2) [; 5-Bracphen = N,N'-ethylenebis(5-bromo-2-hydroxyacetophenylideneiminato) dianion], and [(Tp)Fe(CN)(3)](2)[Mn(salen)](2).6H(2)O [; salen = N,N'-ethylenebis(salicylidineiminato) dianion], were prepared by self-assembling a facial [(Tp)Fe(CN)(3)](-) [Tp = hydrotris(pyrazolyl)borate] precursor and respective Mn(iii) Schiff bases. X-Ray crystal structure analyses revealed that each complex is composed of a central Mn(iii) dimer doubly linked by phenoxides of the tetradentate N(2)O(2) Schiff bases and the terminal [(Tp)Fe(CN)(3)](-) groups connecting to the center through cyanides. Using the spin Hamiltonian H = -2J(1)(S(Fe1).S(Mn1) + S(Mn1a).S(Fe1a)) - 2J(2)(S(Mn1).S(Mn1a)), where J(1) stands for the exchange coupling constant between Fe(iii) (S(Fe) = 1/2) and Mn(iii) (S(Mn) = 2) through cyanides and J(2) between Mn(iii) ions via phenoxides, the best fits corresponded to J(1) = 2.61 cm(-1) and J(2) = 0.85 cm(-1) for , J(1) = 2.50 cm(-1) and J(2) = 1.30 cm(-1) for , and J(1) = -2.15 cm(-1) and J(2) = 0.55 cm(-1) for . The phenoxide routes transmit ferromagnetic interactions in all cases, while ferromagnetic or antiferromagnetic couplings occur through the cyanide linkage. Although the geometric parameters relevant to the magnetic Fe-C[triple bond, length as m-dash]N-Mn pathways are analogous to each other their magnetic natures are varied across the compounds, which supports that a degree of orbital overlap is quite sensitive to a subtle structural change in the present system.

Ferrimagnetic FeIII-MnIII zigzag chain formed by a new mer-positioned ironIII cyanide precursor.

A new cyanide-bearing molecular precursor, mer-[Fe(pzcq)(CN)(3)]- (1), and a zigzag chain, [Fe(pzcq)(CN)(3)][Mn(salen)].4H(2)O (2), were prepared and characterized in terms of structure and magnetism. Magnetic data reveal that intrachain antiferromagnetic couplings via cyanide ligands in 2 are clearly operating, resulting in a ferrimagnetic nature.