Thermal Mechanical Deformation Research Articles

High-temperature hot deformation behavior and processing map of Ti-22Al-25Nb alloy

The high-temperature deformation behavior of the Ti-22Al-25Nb alloy was investigated by conducting hot compression experiments. A constitutive equation predicting the flow behavior of the Ti-22Al-25Nb alloy was established by analyzing its stress–strain curves. The strain-compensated constitutive equation effectively predicted the flow stress of the alloy with a correlation coefficient of 0.992 between the measured and predicted values and an average absolute relative error of 6.548 %. A hot processing map was obtained based on a dynamic material model. It demonstrated that the optimal processing region corresponded to the deformation temperatures of 1273–1353 K and strain rates of 0.001–0.01 s−1. Using electron backscatter diffraction data, thermal deformation mechanisms were elucidated under different deformation conditions within the safe region. The obtained results revealed that under the low temperature (T ≤ 1323 K) and low strain rate (ε̇ ≤ 1 s−1) conditions, continuous dynamic recrystallization and dynamic recovery (DRV) were the main thermal deformation mechanisms. Under the medium-to-high temperature (T ≥ 1323 K) and low strain rate (ε̇ ≤ 1 s−1) conditions, the main thermal deformation mechanisms were discontinuous dynamic recrystallization and DRV. At high strain rates (ε̇ ≥ 1 s−1), the primary thermaldeformation mechanism was DRV. The occurrence of discontinuous yielding in the alloy at high strain rates was related to the proliferation of mobile dislocations at grain boundaries.

A comparative study of hot tensile deformation behavior of 6016 aluminum alloy under LSTM neural network and Arrhenius model

Abstract The isothermal tensile test of 6016-T6 aluminum alloy was carried out on Gleeble-3500 at the temperature range of 400 °C–550 °C and the strain rate range of 0.01–10 s−1. The results show that the thermal deformation mechanism of 6016-T6 is dynamic recovery and dynamic recrystallization. In this paper, the phenomenological Arrhenius constitutive model and the data-driven WOA-LSTM constitutive model for predicting the hot tensile deformation behavior of 6016-T6 aluminum alloy were studied in contrast. The whale optimization algorithm was used to optimize the hyperparameters of LSTM neural network to improve the prediction accuracy of flow stress. The optimization results show that the optimal hidden layer node, maximum training period, initial learning rate and mini batch size of WOA-LSTM are 46, 260, 0.0248 and 16, respectively. In addition, the influence of the number of hidden layers on the results of the network was discussed. The appropriate hidden layer of the network was determined to be 2. The result show that the prediction accuracy of WOA-LSTM constitutive model is better than the Arrhenius constitutive model. The mean absolute error and correlation coefficient are 0.9348% and 0.99952, respectively. Among them, in this study, the Arrhenius constitutive model has low precision and only has high precision within a single temperature range.

Coupled field modelling of thermomechanical response in materials using peridynamic heat transport model and non-ordinary state-based peridynamics

Predicting the mechanical response of materials subjected to transient heat processes is crucial in various engineering applications. This paper introduces a novel peridynamic (PD) coupled field model formulated within the framework of Non-Ordinary State-Based Peridynamics (NOSBPD). This model offers the capability to simulate the coupled thermo-mechanical behavior of materials by incorporating both thermal transport and mechanical deformation analyses. To verify the model’s accuracy, a benchmark problem involving a steel plate undergoing transient thermal expansion is investigated. This model presents a valuable tool for various engineering applications involving coupled thermo-mechanical processes.

The thermal-mechanical deformations of CO2 mixture gases dry gas seal based on two-way thermal-fluid-solid coupling model

PurposeThis study aims to investigate the influence mechanism of thermal-mechanical deformations on the CO2 mixture gases dry gas seal (DGS) flow field and compare the deformation characteristics and sealing performance between two-way and one-way thermal-fluid-solid coupling models.Design/methodology/approachThe authors established a two-way thermal-fluid-solid coupling model by using gas film thickness as the transfer parameter between the fluid and solid domain, and the model was solved using the finite difference method and finite element method. The thermal-mechanical deformations of the sealing rings, the influence of face deformation on the flow field and sealing performance were obtained.FindingsThermal-mechanical deformations cause a convergent gap between the two sealing end faces, resulting in an increase in the gas film thickness, but a decrease in the gas film temperature and sealing ring temperature. The axial relative deformations of rotating and stationary ring end faces caused by mechanical and thermal loads in the two-way coupling model are less than those in the one-way coupling (OWC) model, and the gas film thickness and leakage rate are larger than those in the OWC model, whereas the gas film stiffness is the opposite.Originality/valueThis paper provides a theoretical support and reference for the operational stability and structural optimization design of CO2 mixture gases DGS under high-pressure and high-speed operation conditions.

Processing correlations of laser direct energy deposited Inconel718 based on multi-field numerical simulation

Laser direct energy deposited (LDED) Inconel718 always have problems of non-uniform temperature distribution because of the complex flow of molten pool and layer-by-layer fabrication characterization which directly affected the microstructure and mechanical properties of materials. In this work, Inconel718 revealed a refined grains and a weave structure exhibiting excellent mechanical properties which were superior to those of the conventional casting process were successfully fabricated by adopt a high-precision and intelligent coaxial powder feeding system during the LDED processing. Moreover, based on multi-field numerical simulation method, a two-phase flow model and a transient thermal mechanical deformation model were established to simulate the LDED processing, while takes into account the evaporated mass loss of the inconel718 alloy. The morphology prediction of laser directed energy deposition by multi-physics numerical simulation, the relationship among the laser process parameters, i.e., the laser power, scanning speed and the amount of powder feeding, the temperature filed and the microstructure and mechanical properties of Inconel718 alloy during LDED were investigated and established. The simulated results consistent well with the experimental results. Results shown that the relative density of sample was sensitive to the laser power, the precision and stability of the powder feeding rate. With increasing laser power, the grain size of Inconel718 is refined, and the microhardness and tensile properties of the materials increased. The optimized LDED processing parameters were determined. Evaluating the mechanical properties of the materials LDEDed at a laser power of 600W and a scanning speed of 8.5mms-1 exhibited a high tensile strength of 944±5 MPa and a good elongation of 29 ± 0.5 %. This work suggests that the processing parameters can be optimized to prepare densified materials with excellent mechanical properties.

Microstructural Evolution and Deformation Mechanisms of In Situ TiC Reinforced Ti‐6Al‐4V Composites during High‐Temperature Hot Compression

Deformation processing is a key strategy to improve the strength‐ductility of metal matrixcomposites. Herein, TiC/TC4 composites are spark plasma sintered usingreinforcement precursors of reduced graphene oxide to reinforce TC4 matrix. Inorder to investigate the hot deformation behaviors and mechanisms of TiC/TC4 composites, the composites are hot compressed over temperature range of 870–1070 °C and strain range of 0.001–10 s−1. The results indicate that the optimal processing window of hot deformation ismainly within the temperature range of 890–970 °C and the strain rate range of 0.01–0.1 s−1. The flow instability of TiC/TC4 composites occurs in the temperature range of 890–930 and 1000–1060 °C at the strain rate range from 0.1 to 10 s−1. The thermal deformation mechanism of TiC/TC4 composites in the processingwindow region involves continuous dynamic recrystallization and discontinuous dynamic recrystallization. TiC can effectively hinder thedislocation motion, leading to the generation of high‐density dislocationsaround TiC. Consequently, this promotes sub‐grains formation and rotation,facilitating CDRX. Meanwhile, TiC particle induces high‐angle grain boundarymigration and provides more nucleation sites for recrystallized grains. These findings enhance understanding the role of hot deformation behaviors of Ti compositesand provide insights into their deformation processing.

Machine Learning Assisted Electronic/Ionic Skin Recognition of Thermal Stimuli and Mechanical Deformation for Soft Robots.

Soft robots have the advantage of adaptability and flexibility in various scenarios and tasks due to their inherent flexibility and mouldability, which makes them highly promising for real-world applications. The development of electronic skin (E-skin) perception systems is crucial for the advancement of soft robots. However, achieving both exteroceptive and proprioceptive capabilities in E-skins, particularly in terms of decoupling and classifying sensing signals, remains a challenge. This study presents an E-skin with mixed electronic and ionic conductivity that can simultaneously achieve exteroceptive and proprioceptive, based on the resistance response of conductive hydrogels. It is integrated with soft robots to enable state perception, with the sensed signals further decoded using the machine learning model of decision trees and random forest algorithms. The results demonstrate that the newly developed hydrogel sensing system can accurately predict attitude changes in soft robots when subjected to varying degrees of pressing, hot pressing, bending, twisting, and stretching. These findings that multifunctional hydrogels combine with machine learning to decode signals may serve as a basis for improving the sensing capabilities of intelligent soft robots in future advancements.

A study on the collaborative deformation mechanisms of continuous and discontinuous dynamic recrystallization under low strain rates for the Ti6455x alloy with a low activation energy

To reveal the collaborative dynamic recrystallization mechanisms occurring only at low strain rates, the Ti6455x titanium alloy was designed and prepared by hot deformation. The microstructure, activation energy, and the dynamic recrystallization (DRX) process under different strain rates and temperatures were investigated, with a corresponding mechanism revealed for the first time. Results show that at low strain rates of 0.01 and 0.001 s-1, as temperature from 1173 to 1223 K, the grain size decreases, jagged bumps appear at the grain boundaries and new small grains are produced. The activation energy of Ti6455x titanium alloy is 128.63 kJ/mol. Quantitative calculations revealed that the thermal deformation mechanisms depend on the dissipation efficiency factor, η. With an increasing value of η, the dynamic softening mechanism changes from dynamic reversion (DRV) to DRV and continuous dynamic recrystallization (CDRX). While with a high η value, CDRX and discontinuous dynamic recrystallization (DDRX) occur at a temperature of 1223 K, and a strain rate of 0.001 s-1. The collaborative deformation process proceeds because: low activation energy titanium alloys facilitate the rotation of sub-grain boundaries, while dislocations can easily migrate. This condition enables CDRX to occur, leading to the refinement of grains and producing jagged grain boundaries. Then, CDRX provides nucleation sites for DDRX, promoting grain boundary migration and breaking down grains. This mechanism can significantly refine the grain size and improve mechanical properties. It is shown that both the design of low activation energy alloys and controlling hot processing conditions are effective in the development of high-strength titanium alloys.

Modeling and improvement for the thermal stability of ring-shaped workpieces with shape boundary constraints

Ring-shaped workpieces are commonly utilized in high-precision measuring instruments, and their thermal deformation affects the instruments’ measuring accuracy. A novel method for establishing the thermal deformation model of ring-shaped workpieces is proposed in this article. The mechanism of thermal deformation caused by shape boundaries is investigated using the principle of molecular dynamics. A mathematical model between deformation degree and height, diameter ratio, or temperature is created using a large-scale atomic/molecular massively parallel simulator. The established model is verified by measuring the thermal deformation of ring-shaped workpieces. The model is used to optimize laser collimation systems, and stability experiments for laser collimation systems in different sizes are performed. The stability of optimized systems can be improved by 50%, 50%, and 48% with temperature increases of 10 °C, 20 °C, and 30 °C, respectively. The experimental results indicate the obtained model can be utilized to improve the stability of instruments.

Martensitic phase transformation in short-range ordered Fe50Rh50 system induced by thermal stress and mechanical deformation

Metallic/intermetallic materials with BCC structures hold an intrinsic instability due to phonon softening along [110] direction, causing BCC to lower-symmetry phases transformation when the BCC structures are thermally or mechanically stressed. Fe50Rh50 binary system is one of the exceptional BCC structures (ordered-B2) that has not been yet showing such transformation upon application of thermal stress, although mechanical deformation results in B2 to disordered FCC (γ) and L10 phases transformation. Here, a comprehensive transmission electron microscopy (TEM) study is conducted on thermally-stressed samples of Fe50Rh50 induced by quenching in water and liquid nitrogen from 1150 °C and 1250 °C. We demonstrated that samples quenched from 1150 °C into water and liquid nitrogen show the presence of 1/4{110} and 1/2{110} satellite reflections, the latter of which is expected from phonon dispersion curves obtained by density functional theory calculation. Therefore, it is proposed that Fe50Rh50 maintains the B2 structure that is in premartensite state. Once Fe50Rh50 is quenched from 1250 °C into liquid nitrogen, formation of two short-range ordered tetragonal phases with various c/a ratios (∼1.15 and 1.4) is observed in line with phases formed from mechanically deformed (30 %) sample. According to our observations, an accurate atomistic shear model ({110}〈11¯0〉) is presented that describes the martensitic transformation of B2 to these tetragonal phases.

Application of end-face fiber optic sensor for thermooptical research

The principles of operation and implementation features of the developed fiber-optic device for pulsed thermoreflectometry based on an external Fabry-Perot interferometer are discussed. The possibility of studying local thermal processes in the near-surface layers of samples by changing the thermal reflection of probing radiation during pulsed laser heating is shown. Comparison of experimental data with modeling calculations showed the predominant influence of the thermal deformation mechanism in the case of metal samples.

Quasi-in-situ observation and analysis of grain boundary evolution of GH4169 nickel-based superalloy during the micro-strain stage of thermal deformation

A systematic study was conducted to analyze the grain boundary microstructure evolution of GH4169 nickel-based superalloy during the micro-strain stage of thermal deformation. A quasi-in-situ EBSD (electron backscatter diffraction) approach was used for observation. Moreover, at a temperature of 1100 °C and a strain rate of 0.1 s−1, a continuous strain uniaxial compression experiment was carried out. We observed the development of the grain boundary structure and the grain boundary deformation. The experimental findings revealed that GH4169 underwent locally inhomogeneous thermal deformation during the micro-strain stage, and the simultaneous occurrences of grain boundary slip, grain rotation, and grain boundary migration, exhibiting microstructural diversity. The grain boundary structure changed continuously as a result of the random movement of high-angle grain boundaries. Twin grains displayed a stable structure during the migration of grain boundaries, and their content indicated a considerable decrease as the strain increased. This provides a basis for directing the design of grain boundary engineering since it suggests that twin boundaries are easier to migrate during thermal deformation. In addition, no evidence of dynamic recrystallization was found throughout the entire micro-strain stage and a <101>/<111> micro-texture was observed, which is compatible with common dislocation slips in face-centered cubic crystals. Then, on the basis of the transmission electron microscope images of the microstructure, the numerous forms of grain boundary deformation were rationally explained from the standpoint of the relation mechanisms among grain boundaries and dislocations. Finally, the synergistic mechanism of grain boundary slip and migration is established as the primary mechanism of thermal deformation in the micro-strain stage.

Three-dimensional bi-metallic lattice with multi-directional zero thermal expansion

Metamaterials with zero coefficient of thermal expansion (CTE) are of increasing interest with the rapid development in aerospace applications. Despite numerous two-dimensional (2D) metamaterials with high thermal stability have been investigated, studies on three-dimensional (3D) zero CTE structures are still limited by the complexity of fabrication and geometric connections. In this study, novel 3D bi-metallic lattices with multi-directional zero CTEs are designed, fabricated and experimentally validated. A theoretical method has been developed to predict the effective CTE of the lattice with different materials and geometric parameters and illustrated by comparison with experimental results and numerical simulation results. The 3D lattice had identical effective CTEs along three orthogonal directions and the CTE results were extreme close to zero (0.62 ppm/°C), which is the first time to achieve nearly zero CTE over a wide temperature range in 3D metallic lattice. In addition, the mechanical performance and the effect of geometric parameters of the lattice has been investigated using finite element analysis (FEA). Different thermal deformation mechanisms in the lattice are revealed by different selections of materials for connection bar. The proposed design method and thermal mechanisms are promising for the design of the bearing platform with zero CTE in aerospace engineering.

Compressibility and microstructure of kaolin in varying thermo-hydro-mechanical states imposed by energy geostructures

The thermal volumetric behaviour of soils plays a critical role in designing energy geostructures, withstanding temperature fluctuations. This study examined, for the first time, the thermal deformation of the partially saturated kaolin clay (matric suction of 0–300 kPa) within the operating temperature range of energy geostructures (8 °C to 45 °C), subjected to varying most recent stress histories (normal stress of 0–400 kPa). The thermal cycle has been applied to samples with identical hydro-mechanical stress histories initiated by heating or cooling from room temperature. Scanning electron microscopy (SEM) tests have been performed to investigate the impact of temperature on soil microstructure as a potential determining mechanism of thermal deformation. The volumetric deformation associated with thermal cycles is analysed, considering the concurrent role of the overconsolidation ratio and the most recent stress. Secondary thermal consolidation (i.e., particle rearrangement) mainly depends on the most recent stress history, occurring only in samples heated beyond the yield limit, with cooling preventing secondary thermal consolidation. A clear relationship between thermal volume change and matric suction was observed, with higher matric suction resulting in less pronounced particle rearrangement. Further SEM analysis revealed that heating beyond the yield limit alters the soil microstructure permanently, with cooling showing no impact.

Physical metallurgy guided machine learning to predict hot deformation mechanism of stainless steel

This study proposes a novel approach to address the limitations of traditional experimental and mathematical statistical methods in predicting the deformation mechanism of materials. Specifically, a physical metallurgy-guided machine learning method is proposed to achieve fast and accurate prediction of the thermal deformation mechanisms of antibacterial stainless steels with varying Cu contents. First, the Arrhenius and the dynamic recrystallization model were developed utilizing experimental data for the preliminary prediction of the effect of Cu content on the thermal deformation behavior of antibacterial stainless steel. Then, the calculated intermediate parameters were incorporated into the original data set as additional input features to construct a physical metallurgy (PM) guided least squares support vector machine (LSSVM) prediction model, and the optimization of the prediction model is performed through utilization of a particle swarm optimization (PSO) algorithm. The results indicate that the addition of Cu content influences the rheological stress of antibacterial stainless steel at low temperatures and high strain rates. Furthermore, the increase of Cu content reduces the thermal deformation activation energy, inhibiting the dynamic recrystallization of antibacterial stainless steel, while an increase in deformation temperature or a decrease in strain rate promotes recrystallization. The proposed PM-PSO-LSSVM model is in good agreement with experiments, providing theoretical guidance for optimizing the composition and process parameters of antibacterial stainless steel.

Effects of Ag on High-Temperature Creep Behaviors of Peak-Aged Al-5Cu-0.8Mg-0.15Zr-0.2Sc(-0.5Ag)

The tensile creep of Al-5Cu-0.8Mg-0.15Zr-0.2Sc(-0.5Ag) was tested at 150–250 °C and 125–350 MPa, and the effect of Ag on the high-temperature creep of Al-Cu-Mg alloys was discussed. After the addition of Ag, the high-temperature creep performances of the alloy were significantly improved at 150 °C/300 MPa and 200 °C/(150 MPa, 175 MPa). Then, constitutive relational models of the alloy during high-temperature creep were built, and the activation energy was calculated to be 136.65 and 104.06 KJ/mol. Based on the thermal deformation mechanism maps, the high-temperature creep mechanism of the alloy was predicted. After the addition of Ag, the creep mechanism of the alloy at 150 °C transitioned from lattice diffusion control to grain boundary diffusion control. At 250 °C, the mechanism was still controlled by grain boundary slip, but as the stress index increased and after Ag was added, the alloy fractures lead to the formation of dimples, thus improving the high-temperature creep performance.

Thermal Behavior of Saturated Sand at Different Relative Densities

Abstract With the proposal of a dual carbon goal in China, shallow geothermal energy as a kind of clean energy has been gradually promoted and applied. At the same time, more and more geotechnical workers have gradually paid attention to the influence of temperature on the mechanical characteristics of rock and soil mass. Existing experimental research has shown that the thermodynamic behavior for cohesive soil such as clay and silt is relatively mature but is relatively less mature for noncohesive soil, especially for sand. Based on the hollow cylinder triaxial specimen, a series of temperature-controlled triaxial tests have been carried out on saturated Fujian sand under different initial relative density and temperature conditions to capture the change of axial and volumetric strains for saturated sand specimen with increasing temperature. In addition, a bulk volumetric coefficient of thermal expansion of the sand specimen has been put forward, and the relationship between this coefficient and initial relative density also has been established. Then, the thermal deformation mechanism of saturated sand specimen has been revealed. After that, based on the test data during undrained shearing, the stress–strain relationship, deviatoric stress, and pore water pressure at peak state for loose and medium-dense saturated sand specimens have been explored, which can be used to provide some theoretical guidance for shallow geothermal energy and other temperature-related engineering applications.

Phase transformation and deformation of the high-frequency induction brazed grinding wheel based on multi-field coupling

With the characteristic of the high bonding strength to matrix, good sharpness, and large chip-storage spaces, the brazed super abrasive grinding wheels have superiorities in the machining of difficult-to-machine materials. However, thermal deformation is caused by the high temperature during the brazing process, leading to the accuracy of the brazed grinding wheel being degraded greatly. By means of local heating, high-frequency induction brazing can reduce the thermal deformation of the wheel. Aiming at the thermal deformation mechanism of the induction brazed wheel, a numerical simulation model of thermal-stress-phase multi-field coupling was established considering the temperature-dependent physical properties of the material. The simulation result indicated that the phase transformation occurred near the work surface of the wheel substrate. The depth of phase transformation layer decreased from 6.0 mm to 2.9 mm with the scanning speed increasing from 0.5 mm/s to 2.0 mm/s. The microstructure of the phase transformation layer mainly consisted of ferrite, pearlite, and bainite after brazing. An appropriate scanning speed was more important for the high accuracy of the wheel substrate during the induction brazing, since it had remarkable influence on the stress and deformation than brazing temperature. The experimental results of the microstructure morphology and deformation proved that the numerical simulation model was correct with 10.4% error.

Tunable thermal expansion and bandgap properties of the bi-material-directional honeycomb metamaterial

The excellent shape stability of thermally expanded metamaterials and the good bandgap properties of acoustic metamaterials have a wide range of promising applications in aerospace and sensors. Here, a bi-material-directional honeycomb metamaterial (BHM) with tunable coefficient of thermal expansion (CTE) and bandgap properties is proposed. The theoretical analysis and numerical simulations are employed to reveal the thermal deformation mechanism of the BHM. In addition, the analytical expression of the effective Young’s modulus is established by considering both tensile and bending deformation. Based on the Bloch theorem, the band structures of the BHM are calculated by the finite element method. Parameter analysis confirms that the CTE and bandgap of the BHM can be simultaneously regulated and drastically adjusted by changing the geometric parameters and material combinations. Meanwhile, the coupling relationship of the effective CTE, Young’s modulus, and total effective bandgap width are investigated. The results show that the BHM can have tunable CTE function and large total effective bandgap width by selecting suitable parameters while satisfying stiffness requirements. This study achieves a dual objective of specific CTE properties and bandgap design through rational material selection and shape design, which makes the metamaterials have better tunability and multifunctionality.

Mechanism of flash boiling bubble breakup based on rim-like structure

Flash boiling is an important phenomenon in internal multiphase flow and could lead to unique spray structures. Many researchers have investigated this phenomenon using optical diagnostic methods, and progress has been made in spray morphology studies as well as bubble dynamics inside the nozzle. However, the detailed transition mechanism from in-nozzle bubble to out-nozzle spray droplets has not been experimentally observed, and present theories could not elaborate the morphology change in the micro-scale droplets with high velocities. To illustrate the transition procedure from bubble to droplets of flash boiling bubbles, high-speed imaging technique is adopted on a specially designed optical nozzle with a two-dimensional ambient cavity to investigate the transition from in-nozzle flash boiling bubbles to out-nozzle spray droplets. A unique rim-like structure has been observed, and quantitative and qualitative analyses are made to figure out the nature of this rim. Based on the study, the driving force, as well as the transition process of flash boiling bubbles, has been demonstrated in detail, it is found that under high superheated degrees, the bubble burst process is governed by joint effort of thermal phase change and mechanical deformation. Based on the observed phenomena and theoretical analysis, a new flash boiling spray breakup theory that coincides with the actual physical process has been established.