Thermal expansion and P-V-T equation of state of cubic silicon nitride

We performed in-situ X-ray diffraction measurements of polycrystalline cubic silicon nitride samples at high temperatures under atmospheric pressure and at simultaneous high-pressure-temperature conditions. In air, cubic silicon nitride survives metastably up to 1733 K without oxidation. The temperature dependence of the thermal expansion coefficient was determined to be α(T) = a₁ + a₂T – a₃T⁻² where a₁ = 1.34(6) × 10⁻⁵ K⁻¹, a₂ = 5.06(44) × 10⁻⁹ K⁻², and a₃ = 0.20(10) K. Using all the experimental data obtained under atmospheric and high pressures, a complete set of parameters of the high-temperature third-order Birch Murnaghan equation of state was obtained: K₃₀₀,₀ = 303(5) GPa, K′_300,0 = 5.1(8), and (∂K_T,0/∂T)_P = –0.017(1) GPa K⁻¹, where K₀, K′₀, and (∂K_T,0/∂T)_P are the isothermal bulk modulus, its pressure derivative, and its temperature derivative, respectively. These parameters are necessary to calculate the equilibrium phase boundary between the β and cubic phases in silicon nitride.     

Feasibility of laser surface treatment of pearlitic and bainitic ductile irons for hot rolls

The effects of laser surface treatment on the microstructure, crackability and stresses generated on laser hardened layers produced in several ductile cast iron materials were investigated. Two kinds of alloys having pearlitic (SGP) and acicular (SGA) matrix microstructures were selected. Hardened layers with thicknesses ranging from 1.5 to 2.5 mm were obtained by means of laser remelting (LSRm) or laser hardening (LSH). Thermal stresses generated upon laser processing have been estimated by a simple thermal model. For energy densities delivered onto the material at above 40 J/mm², extensive cracking was developed in SGA and SGP irons due to the contribution of thermal stresses. By lowering the energy density, crack formation was avoided in SGP irons only. At low energy densities, crack formation is controlled by the generation of transformational stresses due to excessive austenite retention. An increase of the surface temperature or the alloying content gave rise to an increase of the retained austenite and the formation of lower bainite at the remelted zone and the heat affected zones, respectively. K_C fracture toughness of Fe₃C carbides embedded in pearlitic and acicular matrixes was measured by means of the nano-indentation technique. Fracture toughness of cementite in SGP irons was slightly higher than in SGA irons, which can help to reduce the crackability of LSH layers.     

Correlation and path coefficient analysis between thermal extraction yield and coal properties

Thermal extraction yields were obtained for 13 coals in supercritical ethanol at 250°C. The direct and indirect relationships between extraction yield and coal properties were determined using correlation and path analyses. Both nitrogen content and hydrogen content have significant and positive correlations with thermal extraction yield. However, moisture content, sulfur content, and oxygen content exhibited negative correlations with extraction yield. Path analysis demonstrated that nitrogen and carbon contents had significant direct and indirect influences on extraction yield, respectively. Nitrogen content is the preferential factor for a high extraction yield, followed by carbon and hydrogen contents.     

Distribution system feeder re-phasing considering voltage-dependency of loads

Phase-balancing creates voltage changes in the network which calls for incorporating voltage-dependency of loads in the process of phase-balancing. Hence, inclusion of voltage-dependency in current-injection based three-phase load flow is investigated and the results are compared with constant-power load model in terms of phase-balancing. The problem being combinatorial, application of particle swarm optimization is investigated for phase-balancing problem of radial distribution network. The effects of phase unbalance and load representation are studied in terms of various parameters. It is observed that there are situations that lead to increase in losses despite improvement in phase-balancing.     

Structure and magnetic properties of a multi-principal element Ni–Fe–Cr–Co–Zn–Mn alloy

A nanocrystalline alloy with a nominal composition of Ni₂₀Fe₂₀Cr₂₀Co₂₀Zn₁₅Mn₅ was produced by mechanical alloying and processed using annealing treatments between 450 and 600 °C for lengths from 0.5 to 4 h. Analysis was conducted using x-ray diffraction, transmission electron microscopy, magnetometry, and first-principles calculations. Despite designing the alloy using empirical high-entropy alloy guidelines, it was found to precipitate numerous phases after annealing. These precipitates included a magnetic phase, α-FeCo, which, after the optimal heat treatment conditions of 1 h at 500 °C, resulted in an alloy with reasonably good hard magnetic properties. The effect of annealing temperature and time on the microstructure and magnetic properties are discussed, as well as the likely mechanisms that cause the microstructure development.     

Phase formations in low density high entropy alloys

Phase formations in high entropy alloys (HEAs) with at least two light elements in literature are predicted by CALPHAD (CALculation of PHAse Diagrams) thermodynamic calculations and the results are compared with experimental observations. The comparison suggests that the applicability of traditional CALPHAD calculations depends on the manufacturing processes of HEAs. Factors such as solute trapping, energies of defects need to be considered while predicting phases in HEAs prepared by non-equilibrium processes. The effects of light elements (Al, Ti, Si, alkali and alkaline earth metals) on the phase formations in HEAs are discussed. Especially, intermetallics predicted for Si-containing HEAs by traditional CALPHAD calculation can be suppressed in rapid solidification process, due to the solute trapping effect. Mg or other alkali and alkaline earth metals can lead to the formations of various intermetallics in HEAs prepared by conventional casting, but could be dissolved into solid solutions by non-equilibrium processes such as mechanical alloying. It is proposed that non-equilibrium processes may be an effective way to introduce light elements Si, alkali and alkaline earth metals into HEAs.     

Phase equilibria and mechanical properties of the Ir–W–Al system

Phase equilibria in the Ir–W, Ir–Al and Ir–W–Al systems at temperatures between 1100 °C and 1600 °C were experimentally investigated using diffusion couples and two- or three-phase alloys, and the mechanical properties of γ′ (L1₂) strengthened Ir–W–Al alloys were examined by hardness and compression tests at room and elevated temperatures. The phase boundaries between the γ(A1)/ε′(D0₁₉), ε′/ε(A3) and ε/ε″(B19) in the Ir–W system at 1400 °C–1600 °C and those between the γ/β(B2) and β/Al_2.7Ir in the Ir–Al system at 1100 °C–1400 °C were determined. The phase diagrams in the Ir-rich corner of the Ir–W–Al ternary system at 1300 °C and 1400 °C were also determined. The existence of the γ′ phase of the Ir₃(W,Al) ternary compound was confirmed, and this system was found to consist of the γ, γ′, ε, ε′ and β phases in the Ir-rich portion. It was also found from hardness and compression tests up to 1200 °C that Ir–Al–W alloys having the γ + γ′ structure with a small lattice misfit show high hardness and strength at room and high temperatures.     

Deformation-induced austenite grain rotation and transformation in TRIP-assisted steel

Uniaxial straining experiments were performed on a rolled and annealed Si-alloyed TRIP (transformation-induced plasticity) steel sheet in order to assess the role of its microstructure on the mechanical stability of austenite grains with respect to martensitic transformation. The transformation behavior of individual metastable austenite grains was studied both at the surface and inside the bulk of the material using electron back-scattered diffraction (EBSD) and X-ray diffraction (XRD) by deforming the samples to different strain levels up to about 20%. A comparison of the XRD and EBSD results revealed that the retained austenite grains at the surface have a stronger tendency to transform than the austenite grains in the bulk of the material. The deformation-induced changes of individual austenite grains before and after straining were monitored with EBSD. Three different types of austenite grains can be distinguished that have different transformation behaviors: austenite grains at the grain boundaries between ferrite grains, twinned austenite grains, and embedded austenite grains that are completely surrounded by a single ferrite grain. It was found that twinned austenite grains and the austenite grains present at the grain boundaries between larger ferrite grains typically transform first, i.e. are less stable, in contrast to austenite grains that are completely embedded in a larger ferrite grain. In the latter case, straining leads to rotations of the harder austenite grain within the softer ferrite matrix before the austenite transforms into martensite. The analysis suggests that austenite grain rotation behavior is also a significant factor contributing to enhancement of the ductility.