Saturated Solid Solution Research Articles

A STUDY OF PROPERTIES OF AUSTENITIC STEEL IN THE INITIAL STATE

High-manganese steel is used in the rocket, space, and defense industries due to its low specific gravity, stable austenitic structure over a wide temperature range, and ability to strengthen under mechanical deformation. However, the wider application of this steel is hindered by such factors as: instability of mechanical properties in the initial state, tendency to thermal embrittlement and very poor machinability. Therefore, the work is aimed at solving the problems of eliminating the above-mentioned negative factors. Conducted studies of the effect of temperature-time parameters on the structure and properties of steel made it possible to establish the mechanism of thermal embrittlement of 9Г28Ю9МВБ steel. During slow cooling from hot deformation temperatures with speeds of the order of 0.03 º/s in steel, a large number of gray-blue coarse phase particles are released, which are located on the grain boundaries, which causes a sharp decrease in impact viscosity. It was established that in the temperature range of 500-800 ºС, the solid solution disintegrates with the release of particles of the strengthening K-phase - (Fe, Mn)3 AL, Cx. It was determined that the simultaneous decrease in hardness and impact strength in the temperature range of 750-950ºС provides a significant improvement in machinability. The lowest values of mechanical properties are achieved during aging at 700 ºС, the improvement of machinability in this case is maximal compared to exposure to other temperatures. So, for example, with an increase in the temperature of isothermal holding at 650ºС for 35 hours. machinability improves by almost 1.7 times, and for the same time at 700 ºС – by 2.4 times. When the holding temperature is increased to 950ºС for 35 hours. the machinability of steel increases only 1.6 times, which is due to the less intense decomposition of the saturated solid solution. Significant anisotropy of mechanical properties is formed as a result of the development of liquid chemical heterogeneity and its imitation during further thermomechanical processing. The value of the coefficient of anisotropy in sample bars of different grades of initial steel reaches values from 1.5 for a bar with a cross section of 105x105 mm to 3.9 units for a bar with a diameter of 120 mm. The study of the influence of the annealing temperature on the homogeneity of austenitic steel made it possible to develop a mode of heat treatment of austenitic steel 9Г28Ю9МВБ, which consists of heating to 1250°С, holding for 2 hours. at this temperature and subsequent cooling in water, in order to fix a homogeneous supersaturated solid solution. After such heat treatment, the striated microchemical heterogeneity is significantly reduced, the anisotropy coefficient does not exceed 1.1 units for all types of steel assortment.

Ageing evolution process of the [formula omitted]-phase in Al-Si-Cu-Mg alloys: Atomic-scale observations and first-principles calculations

This work characterizes the high temperature (above 200 °C) ageing process of the θ′ phase in Al-Si-Cu-Mg alloys by using atomic-resolution HAADF-STEM and first-principles calculations. By characterizing the morphology and coarsening growth process of the θP′ and θP1′ precursor, experimental observations suggest that the θP′ phase is based on GPI (Guinier-Preston I) growth expansion. With the ageing time increases and the atomic concentration changes, the Cu atoms on the outside of the θP′ phase rearrange to form the θP1′ phase. Subsequently, the θP2′ precursor phase is formed locally in the θP1′ phase as the Cu atoms gradually enter the θP1′ phase. Besides, it has been observed experimentally that the θP2′ precursor phase can be directly transformed into the θ′ phase without changing the morphology, structure and orientation relationships of the phase. Based on the experimental characterization and theoretical calculations of this work, we have proposed a novel ageing precipitation sequence: SSSS (Super Saturated Solid Solution)→GPI→θP′→θP1′→θP2′→θ′.

Evaluation of hole expansion formability of high strength AA7075 alloy under varying temper conditions

There has been a widespread increase in the use of aluminum alloys in automotive industries for meeting ever-growing light-weighting requirements. However, edge formability is a critical manufacturing challenge that restricts their widespread use. Edge formability of sheet metal is determined using a hole expansion test (HET) and is evaluated by the hole expansion ratio (HER). The present study investigates the effect of temper conditions on the edge formability of AA7075 alloy sheets. Hole expansion tests were conducted in different temper such as W-temper (super saturated solid solution followed by water quenching), under aged (UA), and peak aged (PA) conditions. Two different hole preparation techniques, a punching and a drilling process, were used to prepare samples with varying edge conditions. The results demonstrate that the W-temper has the highest edge formability irrespective of hole edge conditions. Researchers have reported that uniaxial stress state prevails at the hole edge during the HET. Consequently, uniaxial tensile tests were conducted on for each temper condition and various tensile properties such as yield stress (YS), ultimate tensile strength (UTS), ratio of yield stress to ultimate tensile strength (YS/UTS) were determined to evaluate edge formability. Furthermore, microstructural and failure analysis of the failed specimens were performed to explain the deformation behavior during the HET.

Stability of hydrogenated silica glass and desorption kinetics of molecular hydrogen

The stability of saturated solid solutions of molecular hydrogen in silica glass was examined in the temperature range 85 ÷ 175 K by Raman spectroscopy. The kinetics of hydrogen desorption was studied in-situ by tracking time-dependent changes in the intensities of hydrogen rotational modes at an elevated temperature. The heating results in an exponential decrease in the hydrogen content with a temperature dependent time constant. The data at different temperatures are well described by the Arrhenius formula showing the activation character of desorption with the activation energy EA = (0.16 ± 0.01) eV and time constant A = (0.027 ± 0.003) sec.

Combinatorial aspects of the Löwenstein avoidance rule. Part II: local and global constraints.

The determination of the independence ratio of a periodic net requires finding a subgroup of the translation group of the net for which the quotient graph and a fundamental transversal have the same independence ratio; the respective motif defines a periodic factor of the net. This article deals with practical issues regarding the calculation of the independence ratio of mainly 2-periodic nets, with an application to the 200 2-periodic nets listed on the RCSR (Reticular Chemistry Structure Resource) site. A companion paper described a calculation technique of independence ratios of finite graphs based on propositional calculus. This paper focuses on criteria for the choice of the translation subgroup and of the transversal. The translation subgroup should be chosen in such a way as to eliminate every cycle in the quotient graph that is shorter than structural cycles, or rings, of the net. Topological constraints provide an upper bound to the independence ratio of 2-periodic nets and mostly enable the determination of the associated factor, thus giving a description of a periodic distribution in saturated solid solutions obeying some avoidance rule.

Development of hard and tough tool steel through precipitation of ultrafine carbides from super saturated solid solution

This study was inspired by the short life of the pins used in cotton seed separating machines in textile industries. The tip has been flame hardened to increase its hardness, and multiple heat treatment processes have been performed to distribute the hard carbide particles uniformly in the slightly soft ferrite matrix. The high carbon steel chosen as a base metal contains enough carbide-forming elements to supply the matrix with fine carbides. When the as-received sample was examined, needle-like martensitic structures with previous austenite grain boundaries were apparent. A carbide deposit forms both at the main and sub-boundary grain boundaries during grain boundary formation. A few spots of retained austenite are visible as white spots at some locations. The percentage of retained austenite is around 1%. With increased tempering time, the carbide was observed to shrink in size until it achieved its smallest size. Within the ferrite/martensitic phase, carbide grew in a specific direction after eight hours of tempering. The XRD results confirmed that these are Fe3C (cementite). SEM study at high magnification reveals the size and distribution of carbides. The existence of Fe3C is confirmed by EDS analysis of white spots, which exhibits iron and carbon peaks. There is also evidence of chromium, silicon, and magnesium in other locations. The Vickers hardness of the sample as obtained was 416 HV however it was reduced to 240 HV after precipitation. Following with flame hardening, the material's surface hardness is increased to 600 HV. Consequently, the material has a hard surface and a tough core. As a result, the material has a ductile fracture rather than brittle fracture.

Effects of Sc alloying on the evolution of solidification microstructure and formation of W phase in as-cast 2519 aluminum alloys

In this study, the effect of Sc content on the phase transformation of the 2519 alloy during solidification is investigated through microstructure characterization and thermodynamic calculations. The results show that the grain size of the 0.3–0.4Sc alloy is reduced by 70% (approximately 28.9 µm) to achieve maximum refinement in the as-cast 2519(Sc) Al alloy. The phase diagram calculation shows that the sequence of intermetallic formation during the solidification of 2519(Sc) Al alloy is as follows: Al3Sc, W phase, θ. The primary Al3Sc particles appear at the center of the α–Al grains and evidently acted as heterogeneous nucleating agents. Transmission electron microscopy shows that the nano-sized bean-like Al3Sc phase precipitated from the saturated solid solution. Moreover, the phase transition analysis of the 0.3–0.4Sc alloy during solidification shows that the formation of the W phase underwent two different types of reactions: the peritectic-eutectic reaction (L + Al3Sc → αAl + W) and eutectic reaction (L → αAl + W, L → αAl + θ + W). The W phase formation mechanism of these two reactions is revealed through experiments. Simultaneously, W phases with different morphologies are observed in the 0.3–0.4Sc alloy, i.e., the W phase of the spherical-shell structure is formed by the peritectic-eutectic reaction, and the long strip W phase (~6 µm in size) is precipitated by the eutectic reaction.

Modeling of interstitials diffusion during debinding/sintering of 3D printed metallic filaments: Application to titanium alloy and its embrittlement

Parts made by metal additive manufacturing processes assisted by sintering suffer from embrittlement due to binder/powders interactions. Using a core-shell approach, we modelled the diffusion of carbon and oxygen from the binder into the metallic powders. The model was assessed by measuring the interstitials content upon various debinding/sintering steps. The diffusion/precipitation phenomena during these non-isothermal treatments lead to either a saturated solid solution or the precipitation of titanium carbides. The consequences on the mechanical behavior of single 3D printed filaments were quantified by bending tests, highlighting a transition from brittle to ductile fracture depending on the debinding parameters. This approach can be applied to understand the role of fast diffusing interstitial elements into various powders systems in order to optimise the chemical composition and the mechanical properties of 3D printed metallic parts.

Effect of basicity on the reduction swelling properties of iron ore briquettes

Abstract The influence mechanism of basicity on the reduction swelling index (RSI) of iron ore briquettes was investigated using the SEM analysis and Factsage 7.3 thermodynamic calculations based on the addition of pure CaO to Bayan Obo iron concentrate. The results revealed that the solid solution of Ca2+ in the FeO lattice increased with the basicity of the briquettes, whereas the diffusion channels of Fe2+ ions increased during the reduction process from FeO to Fe and resulted in the formation of a great number of slender and anisotropic iron whiskers, which consequently increased the RSI. Furthermore, the melting point of the slag phase decreased as the CaO content increased; this reduced its ability to resist the reduction swelling of iron oxides. When the basicity was increased from 0.3 to 0.8, the RSI reached a maximum of 69.85%. However, due to the saturated solid solution of Ca2+ in FeO lattice, as the basicity further increased from 0.8 to 1.2, excess CaO melting into the slag phase promoted the precipitation of spinel minerals with high melting points and difficult reduction properties. Thus, the diffusion of Fe2+ and the growth of the iron whiskers were hindered, and the RSI was reduced.

Raman study of hydrogen-saturated silica glass

The Raman spectra of saturated solid solutions of hydrogen and deuterium in silica glass, SiO2-0.6H2 and SiO2-0.63D2, have been measured for the first time at liquid nitrogen temperature. The comparative analysis of H2 phonon modes in solid solution of hydrogen in silica glass and those of hydrogen gas shows a decrease in the frequency of rotational modes contrary to an increase in the H–H stretching vibration mode frequency. Hydrogen rotational modes, overlapped with the phonon modes of silica glass, strengthen at an elevated temperature, while the phonon modes of silica glass soften. The isotopic substitution of hydrogen by deuterium leads to a decrease in the stretching vibration mode frequency proportionally to the square root of D2/H2 mass ratio, whereas rotational mode frequencies decrease as a ratio of D2 to H2 inertia moments. The intensity of H2 phonon modes gradually decreases upon the heating of hydrogen-saturated silica glass along with the evolving of dissolved hydrogen.

Microstructure and constitutive model for flow behavior of AlSi10Mg by Selective Laser Melting

This work is devoted to investigate the flow behavior and microstructure evolution of AlSi10Mg by additive manufacturing in hot deformation. Tensile test is carried out under different temperatures, i.e. 200 ∘ C, 250 ∘ C, 300 ∘ C, 350 ∘ C and 400 ∘ C, with various strain rates of 0.004/s, 0.002/s and 0.0004/s. Theoretically, the modified Arrhenius-type model of additive manufacturing materials at high temperature is established. Experimentally, scanning electron microscope and optical microscope are used to analyze the mechanism of hot deformation. It is found that at 200 ∘ C both the dendritic eutectic Si and acicular eutectic Si precipitate, forming cellular structure and strengthening phases. And then, the acicular eutectic Si is partially dissolved into Al matrix, but there is no obvious growth of dendritic Si at 300 ∘ C. With the temperature increasing, the cellular structure and melt pool boundary gradually disappear. For 400 ∘ C temperature, like homogenization process, the precipitation of saturated solid solution forms the dispersed phase, and the stress-strain curve shows a weak hardening. Meanwhile, the statistical result shows that that the constitutive model agrees well with the experimental results at high temperature. This study may provide guidance for the improvement of additive manufacturing material properties by post-treatment. • The modified Arrhenius-type equation of AlSi10Mg is theoretically established. • Microscope images show that the micropores may decrease as the temperature rises. • The melt pool, heat affected zone and remelt zone are weakened under hot deformation. • The precipitates are spheroidized under hot deformation at 400 ∘ C. • Evolution of AlSi10Mg: saturation precipitate and dispersion strengthened stage.

Complex interactions between precipitation, grain growth and recrystallization in a severely deformed Al-Zn-Mg-Cu alloy and consequences on the mechanical behavior

Combining submicrometer grain size with nanoscaled precipitation is an attractive approach to achieve high yield stress with reasonable ductility in aluminum alloys. The control of super saturated solid solutions decomposition in ultrafine grain structure during precipitation annealing treatments is however a huge challenge. It raises indeed the general question of competition between precipitation, grain growth and recrystallization. All these microstructure changes are driven by the minimization of the free energy of the system but connected to three different factors, the thermodynamic driving force, the grain boundary energy and the dislocation density, respectively. In this work, we have systematically investigated the interconnection of these mechanisms in an Al-Zn-Mg-Cu alloy processed by high pressure torsion at room temperature to achieve a submicrometer grain size from the solutionized state. Ageing heat treatments were carried out to study the precipitation kinetics using complementary characterization techniques such as in-situ small-angle X-ray scattering, differential scanning calorimetry, transmission electron microscopy and atom probe tomography. Experimental data clearly demonstrate that precipitation starts at much lower temperature in the deformed state and that the precipitation sequence is modified as compared to the classical coarse grain alloy. Beyond the detailed understanding of precipitation mechanisms and the competition with recrystallization and recovery processes, the systematic relationship between microstructural features and the mechanical behavior was also studied. A special emphasis was given on the specific contribution of precipitates nucleated heterogeneously along grain boundaries.

Post Solutionising Rolling Sway on the Precipitation Behaviour of Eutectoid Steel Powder Reinforced Al7075 Ternary Alloy Composites

The solitary distinguished thermal treatment to aluminium alloy matrix of nonferrous group with uniformly dispersed reinforcement particles is precipitation or age hardening with or without mechanical working. Al7075 ternary alloy composites belongs to Al-Zn-Mg group and bulk properties can be enhanced by the formation of the immensely small consistently spread out precipitates of solute rich second phase within the matrix phase. The treatment comprises solutionising (550°C) supported by controlled aging (100 and 180°C) below the solvus temperature of the given alloy. Aging expedites the diffusion of solute atoms to form secondary particles (intermetallics) from the room temperature super saturated solid solution. This process is supported by deformation known as rolling as post activity, develops strain hardening in matrix and reinforcement. The present work shows the distinction in the aging phenomenon on alloy and alloy matrix composites (reinforced with 3 and 6 wt% of eutectoid steel powder, 10-30 micron size) upon undergoing cold rolling prior to aging i.e., after solution treatment. The variation in the hardness distribution with aging kinetics for both aging temperatures with and without cold deformation (10 and 20%) in between the consecutive stages like, solution treatment and aging were investigated and peak hardness values were noted in each aging temperatures and results were analysed. In every hardness test 10 trials were performed and the average of 6 consistent readings are taken as the outcome. 20 to 40% improvement in peak hardness is observed with intentional deformation over without deformation. The composite may be used for light duty cold working dies where bulk hardness and frictional characteristics are very important.

On the S-phase precipitates in 2024 aluminum alloy: An atomic-scale investigation using high-angle annular dark-field scanning transmission electron microscopy

Abstract

In-situ synthesized novel eyeball-like Al2O3/TiC composite ceramics reinforced Fe-based alloy coating produced by laser cladding

In this study, the precursor mixtures of Fe-Cr-C-B alloy powders and 0, 10 and 20 wt% Ti3SiC2 is successfully cladded on 16Mn steel substrate by laser cladding (LC). Microstructure and properties of composite coatings are explored by using X-ray diffractometer (XRD), scanning electron microscopy (SEM), energy dispersive spectrometer (EDS), X-ray photoelectron spectra (XPS), electrochemical workstation, Vickers hardness tester and UMT-2 tribo-meter. Results show that the phases in the composite coating with Ti3SiC2 addition mainly are super saturated solid solution α-Fe, hard phases such as eyeball-like Al2O3/TiC composite ceramics, Ti(B,C)2, TiC, Fe3C, γ-(Fe, Ni)/(Cr, Fe)23C6 laminar eutectics and Ti3SiC2 etc. The microhardness, wear and corrosion resistance of composite coatings increase with the weight percent of Ti3SiC2 increasing from 0 to 20%. The existence of super saturated solid solution α-Fe, hard phases such as Al2O3/TiC composite ceramics, Ti(B,C)2, TiC and Fe3C etc. and the Ti3SiC2 solid lubricant contribute to the higher microhardness and wear resistance. The increased corrosion resistance of coatings is attributed to the fact that Cr is the important element which increases the corrosion resistance of the composite coating. With Ti3SiC2 addition increasing, more Ti atoms are easy to interact with C atoms to form TiC carbides, which remain higher content of free Cr atoms in composite coatings.

Structure Modification of a Rheocast Aluminum–Zinc Alloy by Friction Stir Butt Welding: Microstructural Evolution

In this study, friction stir butt welding was applied to weld an aluminum–zinc alloy produced by semi-solid method (rheocasting). For this aim, the effect of tool rotational and traverse speeds on the microstructure was investigated. The microstructures of the processed materials were studied using optical microscopy, scanning electron microscopy equipped with energy dispersive spectroscopy, and X-ray diffraction. The Vickers hardness test was used to evaluate the hardness of the joints. The results showed that the friction stir welding using optimum parameters improved the structure of the rheocast alloy. The porosities were eliminated due to severe plastic deformation induced to the material, which caused filling the voids. Friction stir welding lead to replacement of the semi-solid structure by finer equiaxed grains, which are formed by continuous dynamic recrystallization mechanism. High rotational speeds and low traverse speeds (high heat inputs) caused formation of larger grains, due to grain growth at higher temperatures. On the other hand, at high heat inputs the eutectic phases were more scattered throughout the microstructure, and super saturated solid solution was formed. Because of this behavior, the relationship between the hardness and grain size of the joints did not follow the classical Hall–Petch equation.

Mechanochemical processing of IrO2–Ta2O5: An alternative route for synthesizing Ir and Ir(Ta)O2 solid solution

This paper describes a study exploring milling and subsequent heat treatments of pure IrO2 and Ta2O5 powders. Reactants were milled under Ar atmosphere in a SPEX 8000D mill, with structural, morphological, and compositional characterizations (during milling and after subsequent heat treatments) by X-ray diffraction, energy-dispersive spectroscopy, and transmission electron microscopy. Electrochemical stability of powders was evaluated by open circuit potential (OCP). Results showed that the mechanical energy transferred during this process induces a reaction between IrO2 and Ta2O5, forming metallic Ir and Ir(Ta)O2 saturated solid solution. The study additionally shows that this reaction can be thermally induced with previous mechanical activation of reactants. Electrochemical evaluations of milled powders immersed in H2SO4 solution revealed that OCP shifts negatively with increasing milling time, approaching that of pure Ir at 15h milling.

SOC-dependent high-rate dischargeability of AB5-type metal hydride anode: Mechanism linking phase transition to electrochemical H-desorption kinetics

The current application of nickel-metal hydride (Ni-MH) batteries places a particular emphasis on the high-rate dischargeability (HRD) at varying state-of-charges (SOCs). However, most research on the HRD of AB5-type MH anodes only considers the fully charged case but overlooks the significant impact of SOC. In this work, at first, the great SOC effect on the HRD or pulse power of AB5-type MH anode is presented. Then, by crosschecking the SOC dependence of both ‘in situ’ polarization and ‘ex situ’ kinetic parameters, a definite SOC-dependent H-desorption kinetics for AB5-type MH anode is acquired. Finally, a novel mechanism linking phase transition to H-desorption kinetics for AB5-type MH anode is proposed. The HRD or pulse power of AB5-type MH anode significantly improves when SOC decreases from 100% to an appropriate range (90-60%) and suddenly deteriorates when SOC drops below ∼20%. The former improvement relates to the formation of saturated solid solution that simultaneously facilitates both charge-transfer reaction and hydrogen diffusion. The latter deterioration is due to the complete depletion of hydride causing an insufficient supply of hydrogen atoms.

Structure and mechanical behavior of ultrafine-grained aluminum-iron alloy stabilized by nanoscaled intermetallic particles

Ultrafine-grained aluminum alloys offer interesting multifunctional properties with a combination of high strength, low electrical resistivity, and low density. However, due to thermally induced grain coarsening, they typically suffer from an intrinsic poor thermal stability. To overcome this drawback, an Al-2%Fe alloy has been selected because of the low solubility of Fe in Al and their highly positive enthalpy of mixing leading to the formation of stable intermetallic particles. The two-phase alloy has been processed by severe plastic deformation to achieve simultaneously submicrometer Al grains and a uniform distribution of nanoscaled intermetallic particles. The influence of the level of deformation on the microstructure has been investigated thanks to transmission electron microscopy and atom probe tomography and it is shown that for the highest strain a partial dissolution of the metastable Al6Fe particle occurred leading to the formation of a Fe super saturated solid solution. The thermal stability, and especially the precipitation of particles from the ultrafine-grained solid solution and the way they pin grain boundaries has been investigated both from static annealing and in-situ transmission electron microscopy experiments. The correlation between microstructural features and microhardness has been established to identify the various strengthening contributions. Finally, it is shown that ultrafine grained high purity Al with less than 0.01 at. % Fe in solid solution could preserve a grain size only 300 nm after 1 h at 250 °C.

The Influence of Rapidly Solidified Ribbons Pre-treatment on Structure of Bulk AlFeMm Alloys Prepared by Powder Metallurgy

Rapidly solidified AlFe7Mm4 ribbons were prepared by melt spinning process. The ribbons were composed from super saturated solid solution of alloying elements in Al matrix, stable intermetallic phases and metastable quasicrystalline phases. Both metastable phases can potentially provide self-healing properties to the material - super saturated solid solituon by precititation and quasicrystals by decomposition to stable phases. Key problem of processing such materials is to preserve the microstructure of rapidly solidified material during its compaction. Spark plasma sintering enables powder solidification in very short time - in range of few minutes. This article describes the best way of raidly solidified ribbons before SPS compaction to obtain bulk material. The ribbons were solidified in the initial state and after cryo-milling. Ball-milling before of rapidly solidified ribbons was also tested. Vickers hardnes HV0.01 was also evaluated. Cryo-milling was chosen as an optimal pre-treatment before compaction by SPS.