Thermal-mechanical Processing Research Articles

In-situ EBSD investigation of excellent strength-ductility synergy mechanism achieved by thermal-mechanical processing of Al0·25FeCoNiV high-entropy alloy

The development of high-entropy alloys (HEAs) is plagued by a trade-off between strength and ductility. In this study, we investigated the effects of different cold rolling ratios and subsequent heat treatments on the microstructures and mechanical properties of the Al0·25FeCoNiV HEA. An efficient and economical thermal-mechanical processing route was successfully explored to prepare multiscale, multiphase heterogeneous structures consisting of heterogeneous grain structures and duplex structures. Yield strength, ultimate tensile strength, and fracture elongation of 1277.3 MPa, 1633.6 MPa, and 26.4 %, respectively, could be achieved. The strength-ductility trade-off was avoided. Detailed information on the evolution of grain boundary distribution, grain orientation changes, and grain rotation under stress and strain fields were obtained with in-situ electron backscatter diffraction (EBSD) tensile tests. The mechanism of coordinated plastic deformation and the intrinsic mechanism of excellent strength and ductility were investigated by quantitatively calculating the activation of the slip system, slip transfer at the phase boundaries, and grain rotation paths. It was found that the excellent mechanical properties can be attributed to multistage hetero-deformation-induced (HDI) strengthening and strain-hardening coupling mechanisms. In this study, an effective method for designing novel HEAs with excellent strength-ductility combinations and an analytical method based on in-situ tests are proposed.

Refined microstructure to improve the mechanical properties of the as-cast NiCoCr multi principal element alloy via mechanical vibration

The NiCoCr multi principal element alloy (MPEA) show excellent ductility at cryogenic temperatures and corrosion-resistance properties under the condition that it prepared by thermal–mechanical processing. However, the coarse as-cast grains negatively impact mechanical properties significantly and grain refinement is necessary for forming complex castings. Most grain refining methods need extra alloying elements, which may result in loss of ductility by brittle second phases. In this work, a significant microstructure refinement of the as-cast NiCoCr MPEA was achieved by pollution-free vacuum mechanical vibration, with the average grain size refined from the initial value of 620 μm to 140 μm. As a result, the room-temperature yield strength was increased by 54 % (from 255 MPa to 392 MPa) without loss of elongation compared to the as-cast condition without vibration.

Dynamic Recrystallization Constitutive Model and Texture Evolution of Metastable β Titanium Alloy TB8 during Thermal Deformation.

The mechanical properties of metastable β-titanium alloys are highly susceptible during the thermal mechanical processing (TMP). In this process, the recrystallization process plays an important role in determining the microstructure and texture evolution. The implementation of dynamic recrystallization (DRX), a process for achieving β-grain refinement, is considered of great significance for the improvement of the properties of metastable β-titanium alloys and their industrial production. Along these lines, in this work, an isothermal compression test of TB8 titanium alloy was carried out by using a Gleeble-3500 thermal simulator. As a result, the rheological stress behavior was analyzed, the thermal processing map was accurately established based on the stress-strain curve, and the optimal processing interval was determined. The DRX kinetic and the DRX grain size models were developed, on the basis of which a new DRX intrinsic model was established to improve the material parameters. Therefore, the actual situation in the working process could be better predicted. The microstructural evolution of TB8 titanium alloy during thermal deformation was comprehensively investigated using the electron backscatter diffraction (EBSD) technique. The obtained results demonstrate a close correlation between the diversity of DRX mechanisms in TB8 alloy and the distribution of dislocation density. Four microstructural textures during thermal deformation were identified, in which the cube texture of (001) <010> and the R-Gorss Nd texture of (110) <110> dominate. Due to the random orientation of the dynamically recrystallized grains, the strength of the R-Gorss Nd texture of (110) <110> increases with the increase in the volume fraction of DRX. On the contrary, it was verified that the dynamic recrystallization behavior has a significant weakening impact on the cube texture of (001) <010>.

Development of magnesium alloys: Advanced characterization using synchrotron radiation techniques

Magnesium alloys are the lightest metal structural materials owing to their excellent physical and chemical properties. Microstructural evolution in magnesium alloys under the conditions of casting, thermal-mechanical processing, and in-service environment, play an important role in governing their mechanical properties and reliability/sustainability. A synchrotron light source produces high flux, tunable X-ray energy, high resolution, and high coherence X-ray beams, which can realize in-situ dynamic observation of microstructural evolution in a wide range of alloys during the entire processing chain and in simulated service environments. This article reviews the fundamentals of synchrotron radiation characterization techniques (imaging, diffraction, scattering, and fluorescence holography) and state-of-the-art advanced synchrotron characterization techniques on the microstructure evolution mechanism of magnesium alloys. Case studies span a broad range of solidification, deformation, precipitation, fracture and damage, corrosion, and energy storage. Research opportunities and challenges of physical metallurgy studies of magnesium alloys are highlighted for future studies.

A novel (CoFeNi)82Ti5Al5V8 medium entropy alloy showing an ultra yield strength and a good ductility by L12 nanoparticles strengthening and dislocation strengthening

This paper designed a novel (CoFeNi)82Ti5Al5V8 medium entropy alloy (MEA) with “fcc + L12” typical structure using JMatPro. The microstructure of the alloy, like recrystallization/non-recrystallization and L12 nanoparticle size, can be well controlled by thermal-mechanical processing. The result shows that the (CoFeNi)82Ti5Al5V8 MEA exhibits a good combination of ultra high yield strength of ∼1500 MPa and ultimate tensile strength of ∼1747 MPa with total ductility of ∼10.8 % when the volume fraction of non-recrystallized region with high-density L12 nanoparticles (∼46 nm) is up to ∼91 %. Here, the high volume fraction non-recrystallization region is along with the high-density dislocations (∼6.29 × 1014 m−2). Thus, the high strength of present MEA is mainly attributed to L12 nanoparticle precipitation strengthening and dislocation strengthening, which contributes ∼686 MPa and ∼305 MPa to the total yield strength (accounting for ∼66 %), respectively. Therefore, the idea of combining precipitation strengthening with dislocation strengthening offers a paradigm to develop advanced structural materials for modern industrial applications.

The influence of microalloying and preparation process on phase transformation, mechanical properties, and friction/corrosion behavior of Cu–Ni–Sn alloys: A review

This review provides an overview of Cu–Ni–Sn alloys, which have great advantages as a potential substitute for beryllium bronze. The characteristics of spinodal decomposition in Cu–Ni–Sn alloys are thoroughly discussed by conducting a comprehensive analysis of thermodynamics and the phase diagram. The traditional casting process for Cu–Ni–Sn alloys is subject to several limitations, including segregation during solidification as a primary constraint. Another significant limitation is the occurrence of discontinuous precipitation during aging. Thus, the strategies to overcome these limitations are further elaborated. Commonly used methods include thermal-mechanical processing and composition design. Finally, the application of Cu–Ni–Sn alloys in friction and corrosion is discussed. The purpose of this review is to provide a comprehensive summary of the research progress and significant limitations encountered in Cu–Ni–Sn spinodal alloys. This includes a discussion of traditional casting methods as well as novel preparation techniques. The aim is to serve as a valuable reference for the development of new manufacturing methods and the future advancement of Cu–Ni–Sn spinodal alloys.

How Does the Thermal Environment Affect the Exosphere/Surface Interface at Mercury?

The fate of Mercury’s exospheric volatiles and, in a lesser way, of the refractory particles absorbed in the first few centimeters of the surface both depend highly on the temperature profile with depth and its diurnal variation. In this paper, we review several mechanisms by which the surface temperature might control the surface/exosphere interface. The day/night cycle of the surface temperature and its orbital variation, the temperature in the permanent shadow regions, and the subsurface temperature profiles are key thermal properties that control the fate of the exospheric volatiles through the volatile ejection mechanisms, the thermal accommodation, and the subsurface diffusion. Such properties depend on the solar illumination from large to small scales but also on the regolith structure. The regolith is also space-weathered by the thermal forcing and by the thermal-mechanical processing. Its composition is changed by the thermal conditions. We conclude by discussing key characteristics that need to be investigated theoretically and/or in the laboratory: the dependency of the surface spectra with respect to temperature, the typical diffusion timescale of the volatile species, and the thermal dependency of their ejection mechanisms.

Abnormal annealing-induced strengthening in Ni39.3Al15.7Fe45 eutectic medium entropy alloy

Cold-working combined with annealing is frequently used to enhance strength of traditional alloy materials. However, this thermal-mechanical processing is not adapted to the preparation for some near net shape parts. In this paper, a dual-phase Ni39.3Al15.7Fe45 eutectic medium entropy alloy (EMEA) was prepared by vacuum arc melting and abnormal annealing-induced strengthening is demonstrated and analyzed via XRD, SEM, EDS, TEM and room temperature tensile testing. It is found that the Ni39.3Al15.7Fe45 EMEA is composed of FCC solid solution phase and BCC phase. After annealing, ordered L12 phase precipitated from FCC solid solution, which induces a significant increment of tensile strength and a weak decrease of tensile plasticity. The tensile strength and elongation are 991 MPa and 24.1 % at as-cast state, the tensile strength and elongation are 1279 MPa and 22.4 % after annealing at 700 °C for 1 h.

Possibility of using natural cheeses for pizza production

The paper presents the results of studying sensory, physico-chemical, structural-mechanical (rheological) and biochemical indicators as well as functional properties of natural cheeses of various type groups for a possibility of using as a main raw material to produce pizza. Cheeses were produced in the research-and-development shop of the All-Russian Scientific Research Institute of Butter- and Cheesemaking (VNIIMS) and purchased in the retail chain. Sensory indicators (taste and odor, consistency, appearance) and functional properties (shreddability, meltability, blistering, free oil release, browning, stretchability) of cheeses from various groups were assessed by 100-point scale for assessing cheeses for pizza developed in VNIIMS. Shreddability was determined before baking by grinding a cheese sample chilled to a temperature of 4 ± 2 °C using a kitchen food grinder. Cheeses were baked at a temperature of 200 ± 5 °C for 12 min. Meltability was determined by changes in the cheese diameter after high-temperature treatment and stretchability by the “fork test”. It has been found that physico-chemical, structural-mechanical and biochemical indicators of cheeses used as a raw material affected sensory characteristics and functional properties of the final product after baking. The correlation between the fat content, protein mass fraction and active acidity of cheeses and functional properties such as meltability, free oil release, stretchability and shreddability was confirmed with statistical significance. The highest correlation was noted between shreddability, mass fraction of total protein and consistency (correlation coefficients were 0.74 and 0.76, respectively). However, none of the studied cheese types corresponded to the full extent to the targeted functional properties. To produce pizza, it is preferable to use cheeses with cheddaring and thermal-mechanical processing of cheese mass as well as unripened semihard cheeses with low temperature of the second heating that are molded from a layer, and semihard cheeses with high temperature of the second heating.

Interaction of dynamic precipitation and dynamic recrystallization of a Mg-4Sn-3Al-1Zn alloy during hot compression

The intrinsic correlation between dynamic precipitation and Dynamic Recrystallization (DRX) in a rare earth (RE)-free engineering Mg-4Sn-3Al-1Zn (TAZ431, wt.%) magnesium alloy has been systematically investigated. Hot compression tests were performed on the TAZ431 alloy, in comparison to Mg-3Al-1Zn (AZ31, wt.%) as a reference alloy, with varying temperatures, strain rates, and strain levels (T = 300 ‐ 460 °C; ε̇ = 0.001 - 1 s‐1; ε = 0 to -0.9). Correlative microstructural characterizations including Scanning Electron Microscopy (SEM), Transmission Electron Microscopy (TEM), and Electron Backscatter Diffraction (EBSD), were employed to explore the behaviors of precipitation, DRX and intragranular deformation as subjected to hot compression. The results indicate a significant interaction between Mg2Sn dynamic precipitation and the formation of DRXed grains. The TAZ431 alloy with Sn alloying exhibits profuse precipitation and larger DRX fraction within the microstructure, resulting in the increase of modulus and hardness. Nucleation of DRXed grains in the TAZ431 alloy was stimulated by relatively large (over 1 micrometer) undissolved Mg2Sn intermetallic particles. Meanwhile, the precipitation of nano-sized Mg2Sn occurred within DRXed grains and was facilitated by DRX process, consequently hindering the further growth of DRXed grains. The findings here may have implications for alloy design and thermal-mechanical processing of magnesium alloy structural components.

Influences of Fe Content and Cold Drawing Strain on the Microstructure and Properties of Powder Metallurgy Cu-Fe Alloy Wire.

To study the effects of Fe content and cold drawing strain on the microstructure and properties, Cu-Fe alloys were prepared via powder metallurgy and hot extrusion. Scanning electron microscopy was applied to observe the Fe phase, and the ultimate tensile strength was investigated using a universal material testing machine. Alloying with an Fe content below 10 wt.% formed a spherically dispersed Fe phase via the conventional nucleation and growth mechanism, whereas a higher Fe content formed a water-droplet-like Fe phase via the spinodal decomposition mechanism in the as-extruded Cu-Fe alloy. Further cold drawing induced the fiber structure of the Fe phase (fiber strengthening), which could not be destroyed by subsequent annealing. As the Fe content increased, the strength increased but the electrical conductivity decreased; as the cold drawing strain increased, both the strength and the electrical conductivity roughly increased, but the elongation roughly decreased. After thermal-mechanical processing, the electrical conductivity and strength of the Cu-40Fe alloy could reach 51% IACS and 1.14 GPa, respectively. This study can provide insight into the design of high-performance Cu-Fe alloys by tailoring the size and morphology of the Fe phase.

Исследование свойств сплавов на основе кремниевой бронзы, напечатанных с применением технологии электронно-лучевого аддитивного производства

Introduction. Additive technologies make it possible to curb material expenses by reducing allowances for the final dimensional machining of workpieces. For such expensive materials as copper and copper alloys, this method is considerably attractive from a perspective of increasing resource efficiency in production. The operational properties of the C65500 alloy manufactured using additive technologies have not been fully studied and require additional research. The aim of the work is to study the structural and phase state, mechanical and operational properties of C65500 bronze specimens printed using electron beam additive manufacturing technology. In the work, specimens made of C65500 wire with different heat input values are studied, some of which were subjected to thermal treatment and mechanical processing, as well as specimens, manufactured using multi-wire technology. The work uses such research methods as the study of corrosion resistance of bronze specimens using a potentiostat, confocal laser scanning microscopy, friction tests and X-ray phase analysis. Results and discussion. Processing of specimens by plastic deformation (compression) and subsequent annealing leads to the most serious structural changes. Based on X-ray phase analysis, it is found that higher silicon content is observed in the case of the addition of silumins to bronze. The study of mechanical properties shows that the specimens, printed using multi-wire technology, have the highest strength properties. During tribological testing, fluctuations in the value of the friction coefficient are revealed, due to the scheme of the experiment and the combined adhesive-oxidative mechanism of specimens’ wear. The addition of 10 wt.% aluminum filament to bronze in the additive manufacturing process is an effective means for increasing the resistance of the material to electrochemical corrosion and increasing its wear resistance.

Hydrogen storage performance and phase transformations in as-cast and extruded Mg-Ni-Gd-Y-Zn-Cu alloys

Thermal-mechanical processing of magnesium-based materials is an effective method to tailor the hydrogen storage performance. In this study, Mg-Ni-Gd-Y-Zn-Cu alloys were prepared by Direct Chill (DC) casting, with and without extrusion process. The influences of microstructure evolution, introduced by DC casting and thermal-mechanical processing, on the hydrogen storage performance of Mg-Ni-Gd-Y-Zn-Cu alloys were comprehensively explored, using analytical electron microscopy and in-situ synchrotron powder X-ray diffraction. The result shows that the extruded alloy yields higher hydrogen absorption capacity and faster hydrogen ab/desorption kinetics. As subjected to extrusion processing, the α-Mg grains in the microstructure were significantly refined and a large number of 14H type long-period stacking ordered (LPSO) phases appeared on the α-Mg matrix. After activation, there were more nanosized Gd hydride/Mg2Ni intermetallics and finer chips. These modifications synergistically enhance the hydrogen storage properties. The findings have implications for the alloy design and manufacturing of magnesium-based hydrogen storage materials with the advantages of rapid mass production and anti-oxidation.

A Novel Thermal–Mechanical Processing Route for Improving the Microstructural Homogeneity of High-Speed Steel

A Novel Thermal–Mechanical Processing Route for Improving the Microstructural Homogeneity of High-Speed Steel

Influence of Phase Composition on Stress-Corrosion Cracking of Ti-6Mo-5V-3Al-2Fe-2Zr Alloy in 3.5% NaCl Solution

The metastable β titanium alloys used in marine engineering applications suffered from stress-corrosion cracking in seawater. The different phase composition leads to the distinct stress-corrosion cracking behaviors of the alloy. In this work, the influence of the phase composition on the stress-corrosion cracking of a novel metastable β titanium alloy Ti-6Mo-5V-3Al-2Fe-2Zr was investigated. The alloys with different phase compositions were prepared by three types of thermal-mechanical processing, i.e., the single β phase (assigned as M(β)), the β phase plus fine α phase (assigned as M(β+fα)), and the β phase plus coarsened α phase (assigned as M(β+cα)). The electrochemical tests and constant-stress loading tests were performed, and the phase composition and microstructure were analyzed by XRD and SEM. The M(β) alloy exhibits the best corrosion resistance as well as the compact properties of oxide films, followed by the M(β+fα) alloy and the M(β+cα) alloy. Tear ridges and a flat facet with an undulating surface were observed on the stress-corrosion cracking fracture surface, which indicated the occurrence of high-degree dislocations movement and localized plastic deformation. Absorption-induced dislocation emission (AIDE) and hydrogen-enhanced localized plasticity (HELP) are the primary mechanisms for the stress-corrosion cracking of the alloy. The increased amount of β phase has a beneficial effect on stress-corrosion cracking resistance. For the alloy with β and α phases, the α phase with wider spacing has an adverse effect on stress corrosion performance.

Dynamic mechanical behavior, microstructure evolution, and restoration mechanism of a β‐Ti alloy during hot compression deformation

AbstractMetastable β titanium alloys are promising materials for lightweight and energy‐efficient applications due to their high strength and low density. Thermal–mechanical processing (TMP) is one of the most effective ways to improve the mechanical properties of such alloys. This paper describes a systematic TMP investigation on a new metastable β titanium alloy, including its dynamic mechanical behavior, and microstructure evolution, via isothermal compression tests and electron back‐scattered diffraction characterizations. The results show that the compression stress increases with an increase in the strain rate and a decrease in the temperature. After yielding, the compression stress–strain pattern shows flow‐softening behavior at a low temperature and a high strain rate, while sustaining a steady flow state at a high temperature and a low strain rate. The temperature‐rise effect contributes to a large degree of flow softening at high strain rates. After the correction for temperature rise, the stress–strain constitutive relationships are established, showing that the compression behavior varies in different phase regions. Based on the microstructure characterizations, it is found that the dynamic recovery and dynamic recrystallization dominate the hot deformations in β phase region and at low strain rates, while the deformation band as an additional product is found in α + β phase region and at high strain rates. The results contribute to a better understanding of the TMP for the considered alloy and may also represent a useful database for β‐Ti alloy applications in lightweight mechanical systems.

The application of in situ TEM on the grain boundary brittleness of precipitation-strengthened Ni-based superalloys: Recent progress and perspective

Due to their superior strength and oxidation resistance at high temperatures, precipitation-strengthened Ni-based superalloys are widely used in load-bearing hot components in energy generation systems, such as gas/steam engines in aircraft or power plants. However, brittleness originating from a grain boundary (GB) in a certain temperature range is one of the greatest deadlocks, which desperately restricts their thermal-mechanical processing capabilities and also industrial applications. Experimental and theoretical investigations of the origin of GB brittleness with aims to overcome it still attract many research efforts in the high-temperature material field. It is desirable to understand the GB embrittlement mechanism by dynamically investigating the entire GB cracking process in real time under stress/temperature combination, which might be hardly revealed by a traditional experiment on precipitation strength/theoretical technologies. Current advances in high-temperature mechanical testing systems, which can be operated in a transmission electron microscope (TEM), provide unique opportunities for in situ exploration of the mechanistic origins of GB brittleness of superalloys with the resolution up to an atomic scale. Here, we first briefly give an overview of the phenomenon and current understanding on GB brittleness, followed by introducing the state-of-art techniques in an in situ TEM/mechanical testing system (MTS). In the end, we will also discuss the potential application of the in situ TEM/MTS on GB brittleness and a perspective overlook.

Evolving asymmetric and anisotropic hardening of CP-Ti sheets under monotonic and reverse loading: Characterization and modeling

Commercially pure titanium (CP-Ti) sheets are promising to manufacture high-performance and lightweight components in many fields such as aerospace, marine, energy, electrics and healthcare. However, due to its low symmetric hexagonal close-packed (HCP) structure and complex thermal-mechanical processing history, CP-Ti sheets may exhibit significant asymmetry and anisotropy under monotonic and reverse loading. Therefore, the coupling effect of loading-path dependent asymmetric and anisotropic hardening behaviors of CP-Ti sheets need to be systemically characterized and accurately described under monotonic and reverse loading paths. In this study, firstly, the rheological tests were performed to systemically explore the evolving asymmetric and anisotropic hardening behavior of CP-Ti sheet under monotonic and reverse loading modes. With the help of anti-buckling support fixture and DIC system in tension and compression tests, the coupling effect of asymmetric and anisotropic hardening under monotonic and reverse loading of CP-Ti sheet was identified. Secondly, a loading-path dependent constitutive modeling framework was constructed in which the stress invariants-based model (SIM) integrated with distorted hardening (DH) under reverse loading (RL) conditions (SIM+DH+RL) were considered. Within the proposed modeling framework, a judging criterion of stress reversal for explicit solution method and an activation criterion of different reverse loading modes were introduced. Finally, the proposed SIM+DH+RL model was implemented, calibrated and further applied to simulate typical V-/U-bending of CP-Ti sheets. The results show that the proposed SIM+DH+RL model can significantly improve the prediction accuracy of V-/U-bending springback with the relative errors less than 7.8% and 2.1%, compared with 15.2% and 12% relative errors of Mises+IH, 19.5% and 7.3% relative errors of SIM+DH, 15.1% and 8.4% relative errors of Yoon2014+IH, 14.5% and 5.2% relative errors of CPB06+IH, and 17.3% and 11.5% relative errors of Hill48+IH. It is noted that for the thickness distributions after V-/U-bending springback, the above used models have similar prediction accuracies with the relative errors less than 1.8%.

Comparative study on mechanical and corrosion fatigue properties of high-strength bridge steels produced by TMCP and intercritical quenching & tempering process

The mechanical and corrosion fatigue properties of Q690 bridge steels produced by two different process were comparatively investigated. The steel produced by thermal-mechanical controlled processing (TMCP) and tempering had a slightly superior corrosion fatigue property to that produced by intercritical quenching & tempering (IQT). However, the TMCP + T prepared steel had a poor ductility and corrosion fatigue microcracks were prone to initiate due to high density of dislocations and M/A constituents. On the contrary, the steel produced by IQT had a good combination of mechanical and corrosion fatigue property. The corrosion fatigue initiation and propagation mechanism for both steels was proposed.

On the critical strain of thermal-mechanical processing to tailor grain boundary character distribution in INCOLOY 925 alloy

Through a series of thermal-mechanical processing (TMP) routes with various ratios of cold rolling and subsequent high-temperature annealing, the samples with different critical strain states were prepared to explore the evolution of grain boundary character distribution (GBCD) in INCOLOY 925 during grain boundary engineering (GBE). The GBE microstructure was characterized using the electron backscatter diffraction to study the influence of TMP parameters on the evolution of GBCD and the penetration of random high angle grain boundaries. The results show that the different states of pre-strain correspond to the variational formation mechanism of grain boundary network (GBN). The strain induced boundary migration is the predominant mechanism with the rolling reduction lower than critical strain. With the slight increase of strain, the recrystallization nucleation can be initiated to generate the strain-free grains at a certain annealing temperature. Moderate strain is needed to ensure adequate growth for twin related domains (TRDs). Besides, with the increase of strain and temperature, the dominant mechanism of GBCD gradually transfers from the new twinning mechanism to the Σ3 regeneration mechanism. Specifically, the TMP sample with 10% rolling reduction followed by annealing at 1075 °C for 10min shows relatively higher grain size difference ratio and average grains numbers in the TRDs, indicating that a larger initial grain size can increase critical strain and delay the nucleation of strain-free grains during TMP treatment. The moderately higher grain size shows an opposite effect on the formation of GBN. Finally, an estimation model of critical strain, as a function of initial grain size and annealing temperature, was constructed based on the artificial neural network, and the predicted results show a high consistency with the actual microstructure evolution.