Thermodynamic calculations and experiments on inclusions to be nucleation sites for intragranular ferrite in Si-Mn-Ti deoxidized steel

Microstructures and inclusions in the Si-Mn-Ti deoxidized steels after cooling in the furnace were investigated. The composition and morphology of the inclusions were analyzed using a field emission scanning electron microscope （FE-SEM） with energy dispersive X-ray spectrometry （EDS）. The kind and composition of the inclusions calculated from the thermodynamic database were in good agreement with the experimental results. There were two main kinds of inclusions formed in the Si-Mn-Ti deoxidized steels. One kind of inclusion was the manganese titanium oxide （Mn-Ti oxide）. Another kind of inclusion was the MnS inclusion with segregation points containing Ti and N. According to the thermodynamic calculation, those segregation points were TiN precipitates. The formation of intragranular ferrite （IGF） microstructures refined the grain size during the austenite-ferrite transformation. The mechanisms of IGF formation were discussed. Mn-Ti oxide inclusions with Mn-depleted zone （MDZ） were effective to be nucleation sites for IGF formation, because the MDZ increased the austenite-ferrite transformation temperature. TiN had the low misfit ratio with IGF, so the TiN precipitated on the MnS surface also promoted the formation of IGF because of decreasing interfacial energies.

First-principles calculations of structural and thermodynamic properties of β-PbO

We employed ab-initio calculations to investigate the structural and thermodynamic properties of Massicot or orthorhombic phase of PbO named β-PbO using the projector augmented-wave（PAW） method within the generalized gradient approximation（GGA）. The temperature and pressure dependence of bulk modulus, heat capacity at constant pressure and constant volume, entropy, thermal expansion coefficient and Grüneisen parameter were discussed. Accuracy of two different models, the Debye and Debye-Grüneisen which are based on the quasi-harmonic approximation（QHA） for producing thermodynamic properties of material were compared. According to calculation results, these two models can be used to designate thermodynamic properties for β-PbO with sensible accuracy over a wide range of temperatures and pressures, and our work on the properties of this structure will be useful for more deeply understanding various properties of this structure.

Thermodynamic Calculations of Melt in Melt Pool During Laser Cladding High Silicon Coatings

Based on the Miedema＇s formation heat model for binary alloys and the Toop＇s asymmetric model for ternary alloys, the formation heat, excess entropy, and activity coefficients of silicon ranging from 1 900 K to 4 100 K in the Fe-Si-C melt formed during the laser cladding high silicon coatings process were calculated. The results indicated that all values of lnγ^0Si, ε^CSi,ρ^SiSi and ρ^CSi are negative in the temperature range and these values increase as the temperature increases. And all values of ε^SiSi and ρ^Si-CSi are positive and these values decrease with increasing temperature. The iso-activity lines of silicon are distributed axisymmetrically to the incident laser beam in the melt pool vertical to the laser scanning direction. And the iso-activity lines of silicon in the front of the melt pool along the laser scanning direction are more intensive than those in the back of the melt pool. The activity of silicon on the bottom of the melt pool is lower than that in the effecting center of laser beam on the top surface of the melt pool and it may be the important reason for the formation of the silicides and excellent metallurgical bonding between the laser cladding coating and the substrate.

Prediction of the thermal conductivity of Mg–Al–La alloys by CALPHAD method

Mg-Al alloys have excellent strength and ductility but relatively low thermal conductivity due to Al addition.The accurate prediction of thermal conductivity is a prerequisite for designing Mg-Al alloys with high thermal conductivity.Thus,databases for predicting temperature-and composition-dependent thermal conductivities must be established.In this study,Mg-Al-La alloys with different contents of Al2La,Al3La,and Al11La3phases and solid solubility of Al in the α-Mg phase were designed.The influence of the second phase(s) and Al solid solubility on thermal conductivity was investigated.Experimental results revealed a second phase transformation from Al_(2)La to Al_(3)La and further to Al_(11)La_(3)with the increasing Al content at a constant La amount.The degree of the negative effect of the second phase(s) on thermal diffusivity followed the sequence of Al2La>Al3La>Al_(11)La_(3).Compared with the second phase,an increase in the solid solubility of Al in α-Mg remarkably reduced the thermal conductivity.On the basis of the experimental data,a database of the reciprocal thermal diffusivity of the Mg-Al-La system was established by calculation of the phase diagram (CALPHAD)method.With a standard error of±1.2 W/(m·K),the predicted results were in good agreement with the experimental data.The established database can be used to design Mg-Al alloys with high thermal conductivity and provide valuable guidance for expanding their application prospects.

Thermodynamic calculation of high zinc-containing Al-Zn-Mg-Cu alloy

Phase fraction and solidification path of high Zn-containing Al-Zn-Mg-Cu series aluminum alloy were calculated by calculation of phase diagram （CALPHAD） method. Microstructure and phases of Al-9.2Zn-1.7Mg-2.3Cu alloy were studied by X-ray diffraction （XRD）, differential scanning calorimetry （DSC） and scanning electron microscopy （SEM）. The calculation results show that η（MgZn2） phase is influenced by Zn and Mg. Mass fractions of η（MgZn2） in Al-xZn-1.7Mg-2.3Cu are 10.0%, 9.8% and 9.2% for x=9.6, 9.4, 8.8 （mass fraction, %）, respectively. The intervals of Mg composition were achieved for θ（Al2Cu）＋η（MgZn2）, S（Al2CuMg）＋η（MgZn2） and θ（Al2Cu）＋S（Al2CuMg）＋η（MgZn2） phase regions. Al3Zr, α（Al）, Al13Fe4, η（MgZn2）, α-AlFeSi, Al7Cu2Fe, θ（Al2Cu）, Al5Cu2MgsSi6 precipitate in sequence by no-equilibrium calculation. The SEM and XRD analyses reveal that α（Al）, η（MgZn2）, Mg（Al,Cu,Zn）2, θ（Al2Cu） and Al7Cu2Fe phases are discovered in Al-9.2Zn-1.7Mg-2.3Cu alloy. The thermodynamic calculation can be used to predict the major phases present in experiment.

Thermodynamic analysis of the compositional control of inclusions in cutting-wire steel

Data from a thermodynamic database and the calculation software FactSage were used to investigate the phase diagrams of the MnO？CaO？SiO2？Al2O3 system in cutting-wire steel and the effects of oxide components on the low-melting-point （LMP） zone in the cor-responding phase diagrams. Furthermore, the activities of oxide components in the quaternary system at an Al2O3 content of 25wt%were calculated. The contents of dissolved [Al] and [O] in liquid steel in equilibrium with LMP inclusions in the MnO-CaO-SiO2-Al2O3 system were optimized. The results show that the MnO-CaO-SiO2-Al2O3 system possesses the largest LMP zone （below 1400℃） at an Al2O3 content of 25wt%and that the CaO content should be simultaneously controlled in the range of 40wt%to 45wt%. The activities of the oxide components CaO, MnO, and SiO2 should be restricted in the ranges of 0 to 0.05, 0.01 to 0.6, and 0.001 to 0.8, respectively. To obtain LMP inclusions, the [Al] and [O] contents in cutting-wire steel must be controlled within the ranges of 0.5 ×10^-6 to 1.0 ×10^-5 and 3.0 ×10^-6 to 5.0 × 10^-5, respectively.

EXPERIMENTAL INVESTIGATION AND THERMODYNAMIC CALCULATION ON PHASE PRECIPITATION OF INCONEL 740

A novel nickel-based superalloy INCONEL 740 was under development for application in ultra-supercritical superheater tubers above 750℃. The precipitation behaviors of η phase and γ' particles of the alloy were investigated through experimental study and phase computation. Experimental results showed that η phase formed a Widmanst?tten pattern structure following long-term exposure at elevated temperatures and that the coarsening of γ' particle follows a cube rate law:r-3 ∝ t. Thermodynamic calculation results showed that Al and Ti had an important effect on the precipitation behavior of γ' andη phases. Two suggested novel modified alloys, wherein the Al and Ti contents were modified, were designed and melted for the experimental study. The preliminary results indicated that the modified alloys exhibited higher structural stability following long-term exposure at 750℃ till 5000h.

Influence of alloying elements on hot tearing susceptibility of Mg-Zn alloys based on thermodynamic calculation and experimental

Based on the hot tearing index|△T/△(fs)^(0.5)|recently proposed by Kou and the thermodynamic calculations of Pandat software,Al,Cu,and Mn elements were picked up and their influence on hot tearing susceptibility of Mg-x Zn(x=6,8,10,wt%)alloys was studied by experiments.The results indicate that Al addition can significantly reduce the hot tearing susceptibility of Mg-Zn alloys.Either 0.5Cu or 0.3Mn addition individually can reduce the HTS of the Mg-6Zn-(1,4)Al alloys,while adding together increases the susceptibility.The addition of 0.5Cu and 0.3Mn both individually and together increases the HTS of Mg-8/10Zn-1Al alloys.Based on the experimental and calculation results,the index can be modified to|△T/△(fs)^(0.5)|(d)^(2)for more accurate prediction on the hot tearing resistance of Mg-Zn based alloys.Grain refinement significantly improves the hot tearing resistance of Mg-Zn based alloys.

Thermodynamics calculation on the oxidation and sulfur removal abilities of slag in EAF dust pellet reduction process

The valuable metals in the dust can be recycled by mixing it with reducing agent carbon and lignosulfonate as the binder to make pellets, then returning the pellets to electric arc furnace (EAF) and adding ferro silicon. Part of valuable metals in the dust is reduced by carbon and part of them reduced by ferro silicon for the economical consideration. The reduced metals get into the steel in the stainless steel or special steel production. But the sulfur in the lignosulfonate may affect the quality of produced steel, which is dependent on the status of the smelting slag. The experiments were conducted in the way of changing the ratio of start iron, pellets, ferro silicon and lime. The content of the slag was checked by XRF for the calculation thermodynamics study. The active concentrations of materials in the slag, the slag abilities of oxidation and sulfur removal in EAF dust reduction process were determined by thermodynamics calculation study on CaO MgO FeO Fe 2O 3 SiO 2 S slag at 1 550 ℃. The oxidation ability of slag can be expressed as N (FetO)= N (FeO)+6 N (Fe 2O 3)+8 N (Fe 3O 4). The sulfur removal ability is dependent on the amount of added ferro silicon and the basicity of the slag. The calculation thermodynamics model was set up and it could be applied to the practical production.

Thermodynamic study of direct amination of isobutylene to tert-butylamine

On basis of thermodynamic empirical equations, the thermodynamic parameters for the direct amination of isobutylene to tert‐butylamine, an atomically economic and green chemical reaction,were calculated. In particular, the equilibrium conversion of isobutylene under various reactionconditions close to those used in industry was calculated and discussed. Isobutylene amination is atemperature sensitive reaction due to its exothermic nature and isobutylene equilibrium conversiondecreases with temperature. However, kinetically, the amination reaction will be faster at ahigher temperature. Thus, there must be an optimum temperature for the reaction. A high pressureand n(NH3)/n(i‐C4H8) molar ratio promote the transformation of isobutylene to tert‐butylamine.Developing a highly efficient catalyst under mild reaction conditions is preferred for the aminationprocess. The reaction was investigated over a series of acidic zeolites. ZSM‐11 zeolite exhibited thebest performance with 14.2% isobutylene conversion (52.2% of the equilibrium conversion) and >99.0% tert‐butylamine selectivity. The effect of reaction conditions on the performance of the ZSM‐11 catalyst agreed with the thermodynamic results, which provides guidance for further catalyst development and reaction condition optimization.

Thermodynamic evaluation and hydrothermal preparation of K_xNa_(1-x)NbO_3

The Gibbs free energies of reaction △rGτ of KNbO3 and NaNbO3 were calculated and then that of KxNa1-xNbO3 was estimated. On the basis of the thermodynamic calculation results, the hydrothermal temperatures were designed at 100, 160, and 230℃ respectively. However, NaNbO3 was prepared when the heating temperature was higher than 160℃, and KNbO3 and KxNa1-xNbO3 were obtained at 230℃, suggesting that only at a higher temperature the kinetic requirement is satisfied. According to the X-ray diffraction results, both the solid solutions, NaNbO3-based solid solution, Na1-xKxNbO3, and KNbO3-based solid solution, K1-xNaxNbO3, were hydrothermally synthesized in 6 mol/L alkali （NaOH and KOH） solution at 230℃.

Thermodynamic Calculation of A_(r3) Temperature inLow Alloy Steels

On the basis of superelement model, Cahn's transformation kinetics theory and Scheil's additivity rule, actual γ/α transformation start temperature, A.3 in Fe-Σ Xi-C (Xi=Mn, Si, Ni, Mo etc.)multi-component low alloy Steels during continuous cooling process was calculated. Influences of chemical composition, hot deformation of γ and cooling rate on Ar3 temperature were analyzed. Calculated Ar3 temperatures are in reasonable agreement with measured ones.

Effect of Atmosphere on Sintering of High Cr_2O_3 Bearing Refractories Considered from Thermodynamic Calculation

Pure Cr2O3 refractories and high Cr2O3 bearing refractories are difficult to sinter in oxidizing atmosphere, but they can be sintered easily in carbon embedded conditions. In the latter case it is attributed to the formation of liquid CrO in reducing atmosphere. The thermodynamic calculation shows that the Cr2O3 is reduced by CO at 1 550 ℃ to chromium carbides, which disproves the existence of liquid CrO. This is confirmed by further sintering experiment of the Cr2O3 refractories. Effect of atmosphere on sintering of high Cr2O3 bearing refractories and measures to accelerate the sintering process are discussed based on the experiment and thermodynamic calculation.

Thermodynamic optimization of the DyCl_3-KCl and DyCl_3-CaCl_2 systems

From the measured phase diagram data and experimental thermochemical properties, the DyCl3-KCl and DyCl3-CaCl2 phase diagrams were optimized and calculated by the CALPHAD technique. The Gibbs energies of liquid phase in the two systems has been optimized and calculated by new modified quasi-chemical model in the pair-approximation for short-range ordering, and a series of thermodynamic functions has also been optimized based on an interactive computer-assisted analysis. The results showed that the calculated phase diagrams and thermodynamic data were serf-consistent.

Thermodynamic Calculation on the Formation of Titanium Hydride

A modified Miedema model, using interrelationship among the basic properties of elements Ti and H, is employed to calculate the standard enthalpy of formation of titanium hydride TiHx （1≤x≤2）. Based on Debye theories of solid thermal capacity, the vibrational entropy, as well as electronic entropy, is acquired by quantum mechanics and statistic thermodynamics methods, and a new approach is presented to calculate the standard entropy of formation of TiH2. The values of standard enthalpy of formation of TiHx decrease linearly with increase of x. The calculated results of standard enthalpy, entropy, and free energy of formation of TiH2 at 298.16 K are -142.39 kJ/mol, -143.0 J/（mol·K） and -99.75 kJ/mol, respectively, which is consistent with the previously-reported data obtained by either experimental or theoretical calculation methods. The results show that the thermodynamic model for titanium hydride is reasonable.

Thermodynamic Calculation of Carbide Precipitate in Niobium Microalloyed Steels

On the basis of regular solution sublattice model, thermodynamic equilibrium of austenite/carbide in Fe-Nb-C ternary system was investigated. The equilibrium volume fraction, chemical driving force of carbide precipitates and molar fraction of niobium and carbon in solution at different temperatures were evaluated respectively. The volume fraction of precipitates increases, molar fraction of niobium dissolved in austenite decreases and molar fraction of carbon increases with decreasing the niobium content. The driving force increases with the decrease of temperature, and then comes to be stable at relatively low temperatures. The predicted ratio of carbon in precipitates is in good agreement with the measured one.

Calculating detonation performance of explosives by VLWR thermodynamics code introduced with universal VINET equation of state

Thermodynamic calculation is the theoretical basis for the study of initiation and detonation,as well as the prerequisite for forecasting the detonation performance of unknown explosives.Based on the VLWR(Virial-Wu)thermodynamic code,this paper introduced the universal solid equation of state(EOS)VINET.In order to truly reflect the compressibility of nanocarbon under the extremely high-temperature and high-pressure environment in detonation,an SVM(support vector machine)was utilized to optimize the input parameters of carbon.The detonation performance of several explosives with different densities was calculated by the optimized universal EOS,and the results show that the thermodynamic code coupled with the universal solid EOS VINET can predict the detonation performance parameters of explosives well.To investigate the application of the thermodynamic code with the improved VINET EOS in the working capacity of explosives,the interrelationship between pressure P-particle velocity u and pressure P-volume V were computed for the detonation products of TNT and HMX-based PBX(HMX:binder:insensitive agent=95:4.3:0.7)in the CJ isentropic state.A universal curve proposed by Cooper was used to compared the computed isentropic state,where the ratio of pressure to CJ state were plotted against the ratio of velocity to CJ state.The parameters of the JWL(Jones-Wilkins-Lee)EOS for detonation products were obtained by fitting the P-V curve.The cylinder tests of TNT and HMX-based PBX were numerically simulated using the LS-DYNA,it is verified that,within a certain range,the improved algorithm has superiority in describing the working capacity of explosives.

Thermodynamic prediction of the composition of Fe-based amorphous alloys

The liquidus univariant lines of the Fe-Nb-B ternary system have been thermodynamically calculated by means of CALPHAD method and Fe-based thermodynamic data. It is found that there are two eutectic reactions in the Fe-rich corner,that is,（1） L（Fe-3Nb-15B） →α＋γ＋ M2B （1430 K）,and （2） L（Fe-10Nb-27B） → FeB ＋ Lc14 ＋ M2B （1575 K）. Moreover,the eutectic points are very close to the compositions with high glass forming ability determined experimentally. This means that it is feasible to design the compositions of multicomponent bulk metallic glasses by looking for the eutectic points in the Fe-Nb-B system by means of thermodynamic calculation.

Thermodynamic Analysis of the Fracture Inheritance in Overheated Steels

Based on the experimental result that Cr and C segregated on the prior grain boundaries of austenite in overheated steels,causing the inheritance of fracture mode after re-austeni- tization,a thermodynamic analysis is conducted through the calculation of equilibrium segregation amount of Cr and C in grain boundary at 860 and 1050℃ and the segregation kinetics of Cr is also calculated.Thermodynamic calculation gives an evidence that the segregation of Cr and C at grain boundaries may be regarded as one of the mechanisms of the fracture inheritance in overheated steels.

VARIATIONAL CALCULATION OF THERMODYNAMIC PROPERTIES OF SUPERCOOLED LIQUID METALS

By means of Gibbs-Bogoliubov (GB) thermodynamic variational calculation,the thermodynamic properties of the supercooled liquid metals,such as the 3rd family elements Al,Ga and Tl and transition metal Ti were calculated using the hard-sphere (HS) system as reference.The values of mean atomic volume,Helmholtz free energy,internal energy and entropy as well as specific heat at constant volume,isothermal bulk modulus,thermal expan- sion coefficient and specfic heat under constant pressure were evaluated.The glass transition temperature,T_g,is easily obtained from the C_p-T plot.The glass forming ability for metal can be predicted from T_g/T_m,which is in agreement with the experimental results.