Computational design of precipitation strengthened austenitic heat-resistant steels

A new genetic alloy design approach based on thermodynamic and kinetic principles is presented to calculate the optimal composition of MX carbonitrides precipitation strengthened austenitic heat-resistant steels. Taking the coarsening of the MX carbonitrides as the process controlling the life time for steels in high temperature use, the high temperature strength is calculated as a function of steel chemistry, service temperature and time. New steel compositions for different service conditions are found yielding optimal combinations of strength and stability of the strengthening precipitation for specific applications such as fire-resistant steels (short-time property guarantee) and creep-resistant steels (long-time property guarantee). Using the same modelling approach, the high temperature strength and lifetime of existing commercial austenitic creep-resistant steels were also calculated and a good qualitative agreement with reported experimental results was obtained. According to the evaluation parameter employed, the newly defined steel compositions may have higher and more stable precipitation strengthening factors than existing high-temperature precipitate-strengthened austenite steels.     

Computational design of UHS maraging stainless steels incorporating composition as well as austenitisation and ageing temperatures as optimisation parameters

An extended integral alloy design approach for the development of new ultra high strength maraging steels is presented, which incorporates not only chemical composition effects but also criteria accounting for the influence of the entire heat treatment. The approach considers the desired strengthening precipitates formed during the final ageing treatment as well as undesirable equilibrium phases present during the preceding high temperature homogenisation treatment. The results are compared with the predictions of a previous model, which considered the combination of composition and final precipitation tempering stage only.     

Fe40—45Cr30—35Co20—25Mo0—4Zr0—2合金微观结构对力学性能的影响

研究了高矫顽力型FeCrCo合金力学性能和微观结构间的关系.对抗弯强度和断裂韧性的测试 结果表明，高矫顽力型FeCrCo合金的力学性能远低于普通FeCrCo合金.透射电镜照片显示高 矫顽力合金的两相成分差较大；x射线衍射结果反映高矫顽力合金衍射峰强度较弱而半高宽 较大，说明高矫顽力合金中调幅分解进行彻底.合金中α₁，α₂两 相成分差的扩 大使晶格错配度增加，强度提高，韧性降低.这就是高矫顽力合金力学性能变差的原因. 关键词： 力学性能 调幅分解 抗弯强度 断裂韧性     

Laser ablation of alloys: Selective evaporation model

A mechanism of non-stoichiometric laser ablation is proposed and experimentally verified for multicomponent alloys. The analysis of four-component bronze samples in various excitation modes and the recorded laser plasma spectra revealed that disproportion of plasma elements during laser evaporation arises from selective evaporation of components at the heating-melting-evaporation stage. Correction coefficients proportional to the work function of the alloy component vapor in the heating-melting-evaporation cycle are calculated for the plasma spectrum. Correction procedure for the spectral lines leads to a good agreement of the measured sample composition with the tabulated data. To check that the proposed approach is universal, aluminum alloys and iron alloys (high-alloy stainless steels) are analyzed. It is found that selective evaporation for aluminum alloys is lower than for bronzes. Evaporation selectivity was insignificant for stainless steels. The proposed mechanism for selective evaporation during laser ablation and correction of the plasma spectrum make it unnecessary to use a standard in the quantitative elemental analysis of complex bronze and aluminum alloy samples.     

Ordering potential: the anomalous structure and properties of liquid KPb alloy

The anomalous structure and related properties of liquid KPb alloy are presented through an ab initio evaluated ordering potential as a function of concentration. It appears that considerable ordering occurs and it maximizes at the stoichiometric composition (c_k∼0.5). We then use the model to obtain the Bhatia-Thornton(BT) structure factors at different compositions (c_k=0.1,0.3,0.5 and 0.8). The calculations of concentration fluctuation and other related thermodynamic properties show that this ordering potential approach works reasonably for this compound forming liquid alloy.     

Crystal plasticity study on stress and strain partitioning in a measured 3D dual phase steel microstructure

Dual phase steels are advanced high strength alloys typically used for structural parts and reinforcements in car bodies. Their good combination of strength and ductility and their lean composition render them an economically competitive option for realizing multiple lightweight design options in automotive engineering. The mechanical response of dual phase steels is the result of the strain and stress partitioning among the ferritic and martensitic phases and the individual crystallographic grains and subgrains of these phases. Therefore, understanding how these microstructural features influence the global and local mechanical properties is of utmost importance for the design of improved dual phase steel grades. While multiple corresponding simulation studies have been dedicated to the investigation of dual phase steel micromechanics, numerical tools and experiment techniques for characterizing and simulating real 3D microstructures of such complex materials have been emerged only recently. Here we present a crystal plasticity simulation study based on a 3D dual phase microstructure which is obtained by EBSD tomography, also referred to as 3D EBSD (EBSD—electron backscatter diffraction). In the present case we utilized a 3D EBSD serial sectioning approach based on mechanical polishing. Moreover, sections of the 3D microstructure are used as 2D models to study the effect of this simplification on the stress and strain distribution. The simulations are conducted using a phenomenological crystal plasticity model and a spectral method approach implemented in the Düsseldorf Advanced Material Simulation Kit (DAMASK).     

Deformation and properties of heterophase metastable steels under high hydrostatic pressures

Abstract

This paper shows the possibility to control the strength and plasticity properties of heterophase metastable steels based on the Fe-Mn solid solution as a result of purposeful alteration of the phase composition and fault structure by varying the hydroextrusion process parameters. Practical means of realization of high-strength states (б_0.2 ? 1000… 1400 MPa) in 05G20S2 and I4G20K2F steels using the hydroextrusion are proposed.     

X荧光能谱法测定合金结构钢标样中五个元素

本文提出Ｘ荧光能谱法测定合金结构钢中５个元素含量的方法。本方法采用能说仪中定量分析软件，选择适当工作条件，测定合金结构钢中５个元素。其准确度精确度均能满足分析要求。     

Microstructure and mechanical properties of nano-Y2O3 dispersed ferritic steel synthesized by mechanical alloying and consolidated by pulse plasma sintering

Ferritic steel with compositions 83.0Fe–13.5Cr–2.0Al–0.5Ti (alloy A), 79.0Fe–17.5Cr–2.0Al–0.5Ti (alloy B), 75.0Fe–21.5Cr–2.0Al–0.5Ti (alloy C) and 71.0Fe–25.5Cr–2.0Al–0.5Ti (alloy D) (all in wt%) each with a 1.0?wt% nano-Y₂O₃ dispersion were synthesized by mechanical alloying and consolidated by pulse plasma sintering at 600, 800 and 1000°C using a 75-MPa uniaxial pressure applied for 5?min and a 70-kA pulse current at 3?Hz pulse frequency. X-ray diffraction, scanning and transmission electron microscopy and energy disperse spectroscopy techniques have been used to characterize the microstructural and phase evolution of all the alloys at different stages of mechano-chemical synthesis and consolidation. Mechanical properties in terms of hardness, compressive strength, yield strength and Young's modulus were determined using a micro/nano-indenter and universal testing machine. All ferritic alloys recorded very high levels of compressive strength (850–2850?MPa), yield strength (500–1556?MPa), Young's modulus (175–250?GPa) and nanoindentation hardness (9.5–15.5?GPa), with up to 1–1.5 times greater strength than other oxide dispersion-strengthened ferritic steels (<1200?MPa). These extraordinary levels of mechanical properties can be attributed to the typical microstructure of uniform dispersion of 10–20-nm Y₂Ti₂O₇ or Y₂O₃ particles in a high-alloy ferritic matrix.     

A Monte Carlo calculation of the voltage-current curves for GaxIn1−xSb solid solutions with allowance for scattering in the alloy

Monte Carlo calculations have been performed for the electron drift velocity in relation to electric field strength for certain Ga_xIn_1–xSb compositions with allowance for scattering in the alloy. A three-valley model for the band structure is used. A study has been made of the effects of scattering in the alloy and at ionized impurities on the V_dr(E) dependence. It is shown that scattering in the alloy in some cases can increase the ratio of the threshold and saturation drift velocities. An ionized impurity increases the saturation velocity. The reasons for these effects are discussed. The optimum composition from the viewpoint of using the Gunn effect is Ga_0.6In_0.4Sb, and the characteristics of these are substantially better than that of GaAs.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 9, pp. 10–15, September 1981.     

Mechanism of recovery of the mechanical properties of neutron-irradiated metals in the course of thermocycling

The mechanism of recovery of the strength and strain characteristics of neutron-irradiated metals and alloys (up to their initial values observed prior to irradiation) during periodic quenching in the temperature range below the irradiation temperature is considered. It is assumed that the removal of radiation-induced defects (interstitial and vacancy loops) from radiation-hardened metals is associated with the formation of defect-free channels along the slip planes (the phenomenon of dislocation channeling) under the thermal stresses arising in each cycle of quenching. The relationships describing both the kinetics of the decrease in the yield strength σ_Y and in the ultimate strength σ_U and the kinetics of the increase in the uniform strain ε_U of a preliminarily irradiated material with increasing number of quenching cycles are derived using the equations of dislocation kinetics. The theoretical results obtained are compared with experimental data on the kinetics of recovery of the mechanical properties of neutron-irradiated samples (the austenitic FeNiCr and ferritic FeCrMo structural steels and the titanium alloy TiAlZr) in the course of periodic quenching.     

Disorder-induced Anderson localization in GaAs1−xPx

We report on low-temperature photoluminescence studies of undoped GaAs_1?xP_x alloys. Arguments are presented for the identification of the strongly asymmetrically shaped peak, called M^X_O, with the recombination of electrons and holes bound to different regions of the alloy. It is proposed that at low temperatures, the carriers are subject to Anderson localization below a mobility edge in the potential wells which are induced by the fluctuating alloy potential. Variations in its properties with varying alloy composition suggest that the localization effects are primarily related to electrons with X-conduction band character.     

Mössbauer study of the structure of amorphous invar and a two-level model of the expansion anomaly

The methods of Mössbauer spectroscopy and dilatometry are used to study the local atomic structure and thermal expansion of amorphous invar alloy Fe₈₃B₁₇. It is assumed that the alloy contains regions in which the local order corresponds to metastable orthorhombic and tetragonal phases of the composition Fe₃B. The quantitative ratio of these regions is determined from Mössbauer spectra and is found to be 1:3. A quantitative two-level model of volumetric striction is presented. It is proposed in the model that heating is accompanied by reversible relaxation of orthorhombic configurations of the Fe₃B type to tetragonal configurations, which in turn shortens the distance between iron atoms.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 12, pp. 43–46, December, 1989.     

Atomistic simulation of the interaction between mobile edge dislocations and radiation-induced defects in Fe-Ni-Cr austenitic alloys

The classical molecular dynamics method is employed to simulate the interaction of edge dislocations with interstitial Frank loops (2 and 5 nm in diameter) in the Fe-Ni₁₀-Cr₂₀ model alloy at the temperatures T = 300–900 K. The examined Frank loops are typical extended radiation-induced defects in austenitic steels adapted to nuclear reactors, while the chosen triple alloy (Fe-Ni₁₀-Cr₂₀) has the alloying element concentration maximally resembling these steels. The dislocation-defect interaction mechanisms are ascertained and classified, and their comparison with the previously published data concerning screw dislocations is carried out. The detachment stress needed for a dislocation to overcome the defect acting as an obstacle is calculated depending on the material temperature, defect size, and interaction geometry. It is revealed that edge dislocations more efficiently absorb small loops than screw ones. It is demonstrated that, in the case of small loops, the number of reactions accompanied by loop absorption increases with temperature upon interaction with both edge and screw dislocations. It is established that Frank loops are stronger obstacles to the movement of screw dislocations than to the movement of edge ones.     

Dynamic cracking resistance of structural materials predicted from impact fracture of an aircraft alloy

A new approach to studying the dynamic strength properties of structural materials is demonstrated with fracture of 2024-T3 aircraft aluminum alloy. The central idea of this approach is the incubation time to failure. In [1], experimental data for dynamic fracture of this alloy were analyzed in terms of the classical fracture criterion, which is based on the principle of maximum critical stress intensity factor [2]. In [1], the dependence of the stress intensity factor limiting value (the dynamic fracture toughness K_Id, which was assumed to be a functional characteristic of the material) on the loading rate was also measured. The same experimental data were analyzed in terms of an alternative structure-time approach [3]. In this approach, the dynamic fracture toughness K_Id is considered as an estimable characteristic of the problem, so that determination of limiting loads does not require a priori knowledge of the loading-rate dependence of the dynamic fracture toughness. The incubation time to failure of the aircraft aluminum alloy is calculated. The difference in the loading-rate dependences of the dynamic fracture toughness, which is observed for various structural materials, is explained. The dynamic fracture toughness of the alloy under pulsed threshold loads is calculated.     

Theoretical analysis of reactivity on Pt(1 1 1) and Pt-Pd(1 1 1) alloys

The reactivity of Pt-Pd alloy surfaces towards the oxygen reduction reaction is studied as a function of the alloy overall composition and surface atomic distribution and compared to that on pure Pt surfaces. The systems include Pd and Pt monolayers on various substrates and Pt₃Pd, PtPd and PtPd₃ surfaces of ordered alloys. Reactivity is evaluated on the basis of the adsorption strength of oxygenated compounds which are intermediate species of the four-electron oxygen reduction reaction, separating the effect of the first electron-proton transfer from that of the three last electron-proton transfer steps. None of the alloys are found to provide better sites than those of pure Pt both for O₂ dissociation and for the reduction of O and OH to water; with the skin surfaces being the closest to pure Pt. The results are discussed in relation to those found in 10-atom clusters of similar compositions and to experiments.     

Optical properties of Hg1−xCdxTe

Optical properties of Hg_1−xCd_xTe are summarized in this study. Based on Penn-like models, the Moss relation and the Wemple and DiDomenico approach, calculations of energy gap, plasmon energy, Fermi energy, oscillator strength and electronic polarizability have been made. Comparisons are made with the data available in the literature. Details of the dependency of the properties on composition are presented.     

GaxAlyIn1-x-yN电子结构的第一原理虚晶近似计算

对Ga_xAl_yIn_1-x-yN四元合金材料进行了第一原理的虚晶近似计算.分别计算了在两种不同晶体结构，即纤锌矿结构和闪锌矿结构下的合金电子结构，特别是能隙随混晶比(x,y)的变化.得出了纤锌矿结构下能隙E_g和组分(x,y)的关系式. 关键词：     

Resonance Raman spectroscopy of Ga1−xAlxAs mediated via compositional variation

A specially prepared Ga_1−xAl_xAs sample with a laterally graded alloy composition has allowed a novel investigation of resonance Raman scattering from the optical phonons. Instead of varying the exciting light energy, the resonance is probed by changing the alloy composition at fixed incident energy. Both incoming and outgoing resonances are observed at the direct gap of the alloy, free of the usual overwhelming photoluminescence background.