Phonon dispersion and elastic constants in Fe-Cr-Mn-Ni austenitic steel

The lattice dynamics of Fe-18Cr-10Mn-16Ni austenitic steel was studied by inelastic neutron scattering techniques. Phonon dispersion curves were measured in the [100], [011] and [111] directions at low wavevectors. The measured dispersion curves are similar to those of the -Fe and the Fe_0.75Ni_0.25 alloy, but do not show the anomalous concave curvature of the T ₁ [001] branch at lower wave vectors as characteristic for -Fe. All available data were used for the evaluation of the atomic force constants, elastic constants and engineering elastic moduli of Fe-18Cr-10Mn-16Ni steel.     

Evolution of the microstructure and mechanical properties of eutectic Fe<Subscript>30</Subscript>Ni<Subscript>20</Subscript>Mn<Subscript>35</Subscript>Al<Subscript>15</Subscript>

The microstructure of the eutectic alloy Fe₃₀Ni₂₀Mn₃₅Al₁₅ (in at.%) was modified by cooling at different rates from 1623 K, i.e., above the eutectic temperature. The lamellar spacing decreased with increasing cooling rate, and in water-quenched specimens lamellae widths of ~100 nm were obtained. The orientation relationship between the fcc and B2 lamellae was found to be sensitive to the cooling rate. In a drop-cast alloy the Kurdjumov–Sachs orientation relationship dominated, whereas the orientation relationship in an arc-melted alloy with a faster cooling rate was \textfcc( [`1]12 )//\textB2( 0 1 1 );  \textfcc[ 1[`1]1 ]//\textB2 [ 1[`1]1 ]  \textand \textfcc( 0[`1]1 )//\textB2( 00 1 );\text fcc[ 0 1 1 ]//\textB2[ [`1][`1]0 ] {\text{fcc}}\left( {\bar{1}12} \right)//{\text{B2}}\left( {0 1 1} \right);\;{\text{fcc}}\left[ {1\bar{1}1} \right]//{\text{B2 }}\left[ {1\bar{1}1} \right] \,{\text{and}}\,{\text{fcc}}\left( {0\bar{1}1} \right)//{\text{B2}}\left( {00 1} \right);{\text{ fcc}}\left[ {0 1 1} \right]//{\text{B2}}\left[ {\bar{1}\bar{1}0} \right] . The hardness increased with microstructural refinement, obeying a Hall–Petch-type relationship. The strength of the alloy decreased significantly above 600 K due to softening of the B2 phase.     

Thermodynamic study of the Cu-As-S system by EMF measurements with Cu<Subscript>4</Subscript>RbCl<Subscript>3</Subscript>I<Subscript>2</Subscript> as a solid electrolyte

The Cu-As-S system has been studied at temperatures from 300 to 370 K using emf measurements with Cu₄RbCl₃I₂ as a Cu⁺ ion conducting solid electrolyte, and its subsolidus phase diagram has been mapped out, including the ternary compounds Cu₃AsS₄, Cu₆As₄S₉, Cu₄As₂S₅, Cu₃AsS₃, and CuAsS. From the emf data, we have calculated the partial molar thermodynamic functions (D[`(G)]\Delta \bar G, D[`(H)]\Delta \bar H, and D[`(S)]\Delta \bar S) of the copper in the alloys and the standard thermodynamic functions of formation and standard entropies of the ternary compounds.     

Solid-state phase equilibria and thermodynamic properties of ternary compounds in the Tl-Sb-S system

The Tl-Sb-S system has been studied in the composition region Tl₂S-Sb₂S₃-S using differential thermal analysis, X-ray diffraction, and emf measurements on thallium concentration cells at temperatures from 300 to 390 K, and the 300-K isothermal section of its phase diagram has been mapped out. The existence of the ternary compounds TlSb₅S₈, TlSb₃S₅, TlSbS₃, TlSbS₂, Tl₃SbS₄, and Tl₃SbS₃ has been confirmed, and the position of the phase fields involving these compounds has been accurately determined. Using emf data, we have evaluated the partial molar functions (D[`(G)]\Delta \bar G , D[`(H)]\Delta \bar H , D[`(S)]\Delta \bar S ) of the thallium in the alloys studied, the standard thermodynamic functions of formation of the ternary compounds, and their standard entropies.     

Indium adsorption and incorporation mechanisms in AlN

Density functional theory calculations are implemented in order to scrutinize indium adsorption and incorporation mechanisms in polar AlN. Indium adsorption is promoted on both polarity surfaces and adatom kinetics calculations indicate lower diffusion barriers of indium along the prismatic 〈11[`2]0 11\bar{2}0 〉 directions on (0001) as well as (000[`1] 000\bar{1} ) AlN. The latter is correlated to experimental observations of In_0.24Al_0.76N grown by metal organic vapour phase epitaxy, demonstrating indium concentration along the facet junctions of V-defects. This can be attributed to In surface diffusion along the 〈11[`2]0 11\bar{2}0 〉 directions of the pyramidal facets. Surface thermodynamics reveal a manifold behaviour of indium in polar AlN surfaces, significantly affected by polarity, growth stoichiometry as well as surface termination. In particular, N-rich growth conditions enhance indium incorporation on Al-terminated surfaces of both polarities, leading up to full monolayer coverage. Incorporation on N-terminated (0001) and (000[`1] 000\bar{1} ) surfaces is hindered independent of growth stoichiometry.     

Nanostructured InSiAs solid solution grown by molecular beam epitaxy on the Si(001) surface

The possibility of obtaining a new nanostructured material, an InSiAs solid solution, by molecular beam epitaxy on the Si(001) surface is reported. It is demonstrated that, during simultaneous deposition of indium, silicon, and arsenic, nanometer-size islands with a rectangular base and the sides oriented along the {110} directions can form when the layer thickness exceeds 35 nm. After depositing a 100 nm thick layer of the solid solution, islands with the side ratio d₁₁₀ /d_{1[`1]0</sub> = 1.35d_{110} /d_{1\bar 10} = 1.35 and a typical lateral size of d<sub>1[`1]0} ~ 35 ±10d_{1\bar 10} \sim 35 \pm 10 nm are obtained.     

A Proposed New Measurement of the Superconducting Gap Around $\bar{M}$ -point in Bi2Sr2CaCu2O8

In previous publications, Zhao et al. have presented first-principle calculations of the electronic structure, T _c, and the superconducting energy gaps on the Fermi surfaces of YBa₂Cu₃O₇ (YBCO). However, experimental measurements of the superconducting gaps on the Fermi surfaces of YBCO still face some challenges due to surface problems for YBCO samples. Considering the similarities between the crystal structure, electronic properties, and features of the Fermi surfaces of YBCO and those of Bi₂Sr₂CaCu₂O₈ (BSCCO), we discuss the need to measure the superconducting gap on the small sheet of the Fermi surface around the [`(M)]\bar{M} -point in BSCCO. This gap may be similar to the one of YBCO around the S-point. The superconducting gap on this small sheet of the Fermi surface around the [`(M)]\bar{M} -point in BSCCO is expected to show minor variations from about 18 to 25 meV, as we found on the small sheet of the Fermi surface around the S-point of YBCO. There is no node on the superconducting gap on this small sheet of the Fermi surface around the [`(M)]\bar{M} -point of BSCCO.     

Controlled growth of quasibicrystal zinc oxide structures

The first results on the controlled growth of quasibicrystal structures containing interblock boundaries in epitaxial zinc oxide layers on sapphire (α-Al₂O₃) are reported. The structures with boundaries oriented in a preset direction can be used as a base for submicron microelectronic devices. Using the method of buffer layers, it is possible to obtain highly oriented layers of (11[`2]0)ZnO(11\bar 20)ZnO and (0001)ZnO with clear boundaries between blocks on the same (10[`1]2)Al₂ O₃(10\bar 12)Al_2 O_3 substrate surface. Data on the features of structure and morphology of these layers are presented.     

Properties of austenitic Fe-25Mn-1Al-0.3C alloy for automotive structural applications

Austenitic Fe-25Mn-1Al-0.3C steel, cold-rolled and annealed at about 800 °C, exhibited 2.5 times higher tensile strength than current automotive ferritic sheet steel, while possessing comparable formability. The formation of strain-induced deformation twinning gave rise to an optimum combination of high strength and good formability.     

Combustion synthesis/quasi-isostatic pressing of TiC<Subscript>0.7</Subscript>–NiTi cermets: microstructure and transformation characteristics

TiC_0.7–NiTi cermets were produced by combustion synthesis followed by quasi-isostatic consolidation while the reaction products were still hot and ductile. The TiC_0.7–NiTi cermets were characterized by differential scanning calorimetry, room temperature transmission electron microscopy (TEM), and in-situ TEM (temperature varied during observation). The matrix of the as-synthesized 20NiTi, 40NiTi, and 60NiTi composites contains both R and B19′ martensites at room temperature. No distinct R-phase morphology could be imaged. In the B19′ martensite, [011] Type II twinning, Type I twinning and (001) compound twinning modes were observed as the lattice invariant shear (LIS) of the R-B19′ transformation. The [011] Type II twinning is often reported as the LIS of the B2-B19′ transformation, but this is the first experimental confirmation of its predicted presence as a qualified LIS of the R-B19′ transformation. The (001) compound twinning mode is responsible for the fine structure of the martensite with a wavy morphology. Nanoscale structures with a thickness of 5 nm were obtained inside the twins. Twinning was also observed at the interface with carbide particles, which confirms that some stress relaxation of the elastic mismatch occurs. At room temperature, the matrix of the 80NiTi composite had the R-phase structure, which appeared with a needle-like morphology. Thermal cycling resulted in the suppression of the R-phase transformation. This is the opposite of the behavior observed in un-reinforced NiTi alloys.     

Barrier characteristics of Pt/Ru Schottky contacts on <Emphasis Type="Italic">n</Emphasis>-type GaN based on <Emphasis Type="Italic">I–V–T</Emphasis> and <Emphasis Type="Italic">C–V–T</Emphasis> measurements

We have investigated the current–voltage (I–V) and capacitance–voltage (C–V) characteristics of Ru/Pt/n-GaN Schottky diodes in the temperature range 100–420 K. The calculated values of barrier height and ideality factor for the Ru/Pt/n-GaN Schottky diode are 0·73 eV and 1·4 at 420 K, 0·18 eV and 4·2 at 100 K, respectively. The zero-bias barrier height (Φ_b0) calculated from I–V characteristics is found to be increased and the ideality factor (n) decreased with increasing temperature. Such a behaviour of Φ_b0 and n is attributed to Schottky barrier (SB) inhomogeneities by assuming a Gaussian distribution (GD) of barrier heights (BHs) at the metal/semiconductor interface. The current–voltage–temperature (I–V–T) characteristics of the Ru/Pt/n-GaN Schottky diode have shown a double Gaussian distribution having mean barrier heights ( [`(F)]<sub>\textb0</sub> {\bar{{\Phi}}_{\text{b}0}} ) of 1·001 eV and 0·4701 eV and standard deviations (σ <sub>0</sub>) of 0·1491 V and 0·0708 V, respectively. The modified ln (J<sub>0</sub> /T<sup>2</sup> )-( q<sup>2</sup>s <sub>0</sub><sup>2</sup>/2k<sup>2</sup>T<sup>2</sup> ){ln} ({{J}_{0} /{T}^{2}} )-( {{q}^{2}{\sigma} _{0}^{2}/{2}{k}^{2}{T}^{2}} ) vs 10<sup>3</sup>/T plot gives [`(F)]_\textb0 \bar{{\Phi}}_{\text{b}0} and Richardson constant values as 0·99 eV and 0·47 eV, and 27·83 and 10·29 A/cm²K², respectively without using the temperature coefficient of the barrier height. The difference between the apparent barrier heights (BHs) evaluated from the I–V and C–V methods has been attributed to the existence of Schottky barrier height inhomogeneities.     

Phase and morphology evolution of calcium carbonate precipitated by carbonation of hydrated lime

Phase and morphology evolution of CaCO₃ precipitated during carbonation of lime pastes via the reaction Ca(OH)₂ + CO₂ → CaCO₃ + H₂O has been investigated under different conditions (pCO₂ ≈ 10^−3.5 atm at 60 % RH and 93 % RH; pCO₂ = 1 atm at 93 % RH) using XRD, FTIR, TGA, and SEM. Simulations of the pore solution chemistry for different stages and conditions of carbonation were performed using the PHREEQC code to investigate the evolution of the chemistry of the system. Results indicate initial precipitation of amorphous calcium carbonate (ACC) which in turn transforms into scalenohedral calcite under excess Ca²⁺ ions. Because of their polar character, { 21[`3]4 } \left\{ {21\bar{3}4} \right\} scalenohedral faces (type S) interact more strongly with excess Ca<sup>2+</sup> than non-polar { 10[`1]4 } \left\{ {10\bar{1}4} \right\} rhombohedral faces (type F), an effect that ultimately favors the stabilization of { 21[`3]4 } \left\{ {21\bar{3}4} \right\} faces. Following the full consumption of Ca<sup>2+</sup> ions and further dissolution of CO<sub>2</sub> leading to a pH drop of the pore solution, { 21[`3]4 } \left\{ {21\bar{3}4} \right\} scalenohedra are subjected to dissolution. This eventually results in re-precipitation of { 10[`1]4 } \left\{ {10\bar{1}4} \right\} rhombohedra at close-to-neutral pH. This crystallization sequence progresses through the carbonated depth with a strong dependence on the degree of exposure to CO₂, which is controlled by the carbonated pore structure governing the diffusion of CO₂. Both the carbonation process and the scalenohedral-to-rhombohedral transformation are kinetically favored under high RH and high pCO₂. Supersaturation plays a critical role on the nucleation density and size of CaCO₃ crystals. These results have important implications in understanding the behavior of ancient and modern lime mortars for applications in architectural heritage conservation.     

Kinetics of flow stress in ultra-pure tantalum single crystals in stress/temperature regime III

The temperature dependence of the critical resolved shear stress (CRSS), τ, of ultra-pure tantalum single crystals (RRR ≥ 14000) observed below 250 K for a range of shear-strain rates [(g)\dot] = 2×10 ^{- 5} - 6×10 ^{- 3}  \texts ^{- 1} \dot{\gamma } = 2\times 10^{ - 5} - 6\times 10^{ - 3} \,{\text{s}}^{ - 1} was analyzed within the framework of a kink-pair nucleation model of flow stress. The CRSS/strain-rate data follow the model formulation t ^{1/ 2} = C + D  ln[(g)\dot] \tau^{ 1/ 2} = C + D\,{ \ln }\dot{\gamma } , where C and D are positive constants, for each deformation temperature T in the range 78–250 K. Evaluation of the various slip-parameters of flow stress points to (211)[[`1]11] [\bar{1}11] slip system responsible for the yielding of ultra-pure tantalum single crystals in the so-called stress/temperature regime III (T < 250 K). The value of the pre-exponential factor [(g)\dot]_\texto \dot{\gamma }_{\text{o}} in the Arrhenius-type equation for the shear-strain rate [(g)\dot] \dot{\gamma } is found to be of the order of 10⁵ s⁻¹, which is substantially lower than that ( [(g)\dot]_\texto ~ 10⁷  \texts ^{- 1} ) \left( {\dot{\gamma }_{\text{o}} \sim 10^{7} \,{\text{s}}^{ - 1} } \right) determined in the stress/temperature regime II (250–400 K) and contradicts the assumption invariably made in most of the theoretical models of flow stress that [(g)\dot]_\texto \dot{\gamma }_{\text{o}} is a constant over a wide temperature range.     

Application of extended Mohr–Coulomb criterion to ductile fracture

The Mohr–Coulomb (M–C) fracture criterion is revisited with an objective of describing ductile fracture of isotropic crack-free solids. This criterion has been extensively used in rock and soil mechanics as it correctly accounts for the effects of hydrostatic pressure as well as the Lode angle parameter. It turns out that these two parameters, which are critical for characterizing fracture of geo-materials, also control fracture of ductile metals (Bai and Wierzbicki 2008; Xue 2007; Barsoum 2006; Wilkins et al. 1980). The local form of the M–C criterion is transformed/extended to the spherical coordinate system, where the axes are the equivalent strain to fracture [`(e)]<sub>f</sub>{\bar \varepsilon_f} , the stress triaxiality η, and the normalized Lode angle parameter [`(q)]{\bar \theta} . For a proportional loading, the fracture surface is shown to be an asymmetric function of [`(q)]{\bar \theta}. A detailed parametric study is performed to demonstrate the effect of model parameters on the fracture locus. It was found that the M–C fracture locus predicts almost exactly the exponential decay of the material ductility with stress triaxiality, which is in accord with theoretical analysis of Rice and Tracey (1969) and the empirical equation of Hancock and Mackenzie (1976), Johnson and Cook (1985). The M–C criterion also predicts a form of Lode angle dependence which is close to parabolic. Test results of two materials, 2024-T351 aluminum alloy and TRIP RA-K40/70 (TRIP690) high strength steel sheets, are used to calibrate and validate the proposed M–C fracture model. Another advantage of the M–C fracture model is that it predicts uniquely the orientation of the fracture surface. It is shown that the direction cosines of the unit normal vector to the fracture surface are functions of the “friction” coefficient in the M–C criterion. The phenomenological and physical sound M–C criterion has a great potential to be used as an engineering tool for predicting ductile fracture.     

TEM observation of liquid-phase bonded aluminum–silicon/aluminum nitride hetero interface

Liquid-phase bonded aluminum–silicon/aluminum nitride interface structure was investigated using high-resolution transmission electron microscopy. A textured layer of aluminum formed a stable orientation relationship with aluminum nitride, which showed Al(111) to be tilted by about 4° with respect to the AlN(0001) interface plane. The unique orientation relationship between Al and AlN was predicted as one of the stable orientation relationships using coincidence of reciprocal lattice point method, which surveys the degree of geometrical coherency between two crystals in three-dimensional space. A stable orientation relationship was found to be (001)[1_boxclose \bar{1} 0]Al//(2[`2] \bar{2} 03)[11[`2] \bar{2} 0]AlN.     

Identification of referencing and citation processes of scientific journals based on the citation distribution model

In this article, we firstly analyze the referencing process and the citation process of a scientific journal in theory, and find that the observed referencing or citation process includes the diffusing process and the aging process of cited literature and the publishing process of citing literature, thereby it is illuminated why the identified average publication delay ( [`(T)] = T_s + t ) \left( {\bar{T} = T_{s} + \tau } \right) was longer than the observed value. Secondly, we compare the transfer function model of the observed citing process with other classical citation distribution models and find that the model is superior to others. Finally, using the model, we identify parameters of actual referencing and citation processes from data of age distributions of references and citations of 38 journals of neurology and applied mathematics in JCR, respectively; and then compare differences of identified parameters and obtain some interesting conclusions.     

热轧变形对高碳TWIP钢组织缺陷和力学性能的影响

为解决高碳Fe-20Mn-3Cu-1.3C TWIP钢凝固组织中易形成显微疏松、损害合金的力学性能的问题,研究了在相同热轧温度下,改变轧制变形总量对合金微孔缺陷的消除及拉伸力学性能的影响.研究表明:通过热轧变形可以有效地减少Fe-20Mn-3Cu-1.3C TWIP钢的微孔缺陷,提高组织致密度;随着热轧变形量的增加,合金的综合力学性能显著提高,当热轧变形量达到91%时,该合金中的微孔面密度由固溶态的1.67%降低至0.71%,抗拉强度达到1223.7 MPa,延伸率达到86.8%,强塑积高达106217.2 MPa.%,比未热轧变形处理提高了78.3%,显示出优异的综合力学性能,表明消除微孔缺陷是充分发挥其高强韧性的关键.     

Cavitation erosion resistance of Fe-26Mn-6Si-7Cr-1Cu shape memory alloy

Abstract

The cavitation erosion of low stacking fault energy Fe-26Mn-6Si-7Cr-1Cu shape memory alloy has been investigated in water using an ultrasonic vibratory apparatus, and compared with the behaviour of 0Cr13Ni5Mo stainless steel. It is shown that Fe-26Mn-6Si-7Cr-1Cu alloy has higher cavitation erosion resistance than 0Cr13Ni5Mo stainless steel. The cavitation erosion mechanism of Fe-26Mn-6Si-7Cr-1Cu was studied by examining the eroded surface using X-ray diffraction (XRD) and scanning electron microscopy (SEM). During early stages of cavitation erosion, Fe-26Mn-6Si-7Cr-1Cu alloy undergoes strain induced martensitic transformation. Exposure to further cavitation results in the deformation of ? martensite. The boundaries of ? martensite impede plastic deformation, leading to strain accumulation and subsequent material removal. On the basis of an XRD study and indentation tests, the better cavitaton erosion resistance of Fe-26Mn-6Si-7Cr-1Cu alloy is mainly ascribed to strain induced martensitic transformation, which can absorb impact energy without damage.     

An engineering methodology to assess effects of weld strength mismatch on cleavage fracture toughness using the Weibull stress approach

This work describes the development of an engineering approach based upon a toughness scaling methodology incorporating the effects of weld strength mismatch on crack-tip driving forces. The approach adopts a nondimensional Weibull stress, [`(s)]_w{\bar{{\sigma}}_w}, as a the near-tip driving force to correlate cleavage fracture across cracked weld configurations with different mismatch conditions even though the loading parameter (measured by J) may vary widely due to mismatch and constraint variations. Application of the procedure to predict the failure strain for an overmatch girth weld made of an API X80 pipeline steel demonstrates the effectiveness of the micromechanics approach. Overall, the results lend strong support to use a Weibull stress based procedure in defect assessments of structural welds.