Deformation Process Research Articles

Micromechanical response of graphene coating on nt-TiAl under nanoindentation

The nanoindentation response of graphene (Gr) coating on nanotwin titanium-aluminum (nt-TiAl) matrix composites was studied using molecular dynamics (MD) simulation. The indentation velocity, twin boundary spacing, and parallel and vertical Z-axes are studied. The results show that the bearing capacity and hardness of Gr coating is significantly higher than that after coating failure, and the load-displacement curve shows the same phenomenon. Damage to the substrate material at varying speeds is indicated by atomic aggregation near the Gr coating, with the center of aggregation showing a negative correlation with indentation velocity. The matrix's damaged area is larger when the twin layer is perpendicular to the Z-axis and deeper when parallel, showing that the twin structure limits material damage by hindering dislocation expansion. Moreover, the presence of Gr coating delayed the matrix's plastic deformation process. This delay effect significantly improves the mechanical properties of composites, which have potential applications in aerospace.

Synthesis of Nd-lean (Nd,Ce,La)-Fe-B magnets via hot deformation and rolling

In this work, we have used bulk combinatorial synthesis to rapidly identify a (Nd,Ce,La)-Fe-B composition that is both Nd-lean (<50 % of total rare earth content) and exhibits good thermal stability (TC∼269 °C). Bulk anisotropic magnets of the corresponding composition [i.e. (Nd0.47Ce0.28La0.25)2.2Fe14B1 (at%) + (1.5 wt% TiC)] were synthesized by hot deformation and hot-roll processes. To enhance the energy product of the hot deformed alloys, feedstock powder with 2.5–7.5 wt% Ce-Al-Cu grain boundary modifier was blended together prior to deformation processing. Moreover, hot deformation processing parameters, temperature (T), and processing time (t), were examined over a wide range to enhance the energy product of the resultant magnet alloys. We found that adding just 2.5 wt% Ce-Al-Cu increased the maximum energy product from ∼12 MGOe for the monolithic alloy to ∼20 MGOe for the alloy with added grain bounder modifier. The processing parameters (e.g., temperature and time) identified for hot deformation were applied to the hot-rolling process to synthesize samples with larger dimensions that exhibit an energy product of 17.7 MGOe with 5 wt% Ce-Al-Cu added.

Fabrication of Medium Mn Advanced High-Strength Steel with Excellent Mechanical Properties by Friction Stir Processing.

Friction stir processing (FSP) manufacturing technology was used to fabricate medium Mn advanced high-strength steel in this study. The mechanical properties and microstructure of the steel fabricated using FSP were investigated. The steel obtained a total elongation of 35.1% and a tensile strength of 1034.6 MPa, which is about 59% higher than that of the steel without FSP. After FSP, a gradient structure occurs along the thickness direction. Specifically, across the thickness direction from the base material zone to the transition zone and finally to the stirring zone, both the grain size and austenite fraction decrease while the dislocation density increases, which results from the simultaneous effect of severe plastic deformation and recrystallization during FSP. Due to the gradient structure, an obvious difference in the strain across the thickness direction of the steel occurs during the deformation process, resulting in significant hetero-deformation-induced (HDI) strengthening. The deformation mechanism analysis reveals that HDI strengthening and dislocation strengthening are the main factors in the improvement in the strength-ductility balance. The obtained knowledge sheds light on the process of fabricating medium Mn steels with excellent properties using FSP manufacturing technology.

Microstructure and mechanical properties of Mg/Al laminated composite: The effect of transition layer thickness

This study successfully prepared Mg/Al laminated composites with various thicknesses of pure Cu transition layer via extrusion, overcoming the challenge of forming of Mg/Al composite plates through stacked extrusion technology. The effects of varying Cu layer thicknesses on the microstructure, mechanical properties, and fracture behaviors were systematically investigated. Microstructure analysis showed an uneven Cu layer distribution at the interface of the composite plate, characterized by alternating thicker and thinner layers, which stemmed from the low fluidity of pure Cu during extrusion. Although the thicker Cu layer significantly inhibited the diffusion of Mg and Al elements, there was still a significant enrichment of Mg-Al intermetallic compounds (IMCs) in the thinner Cu layer. There hard and brittle IMCs caused cracking during the deformation process. Increasing Cu layer thickness did not significantly affect the microstructure but contributed to the decrease of strength owing to increased stress concentration. Moreover, the thicker Cu layer exacerbated its uneven distribution and Mg-Al IMCs enrichment at the interface, resulting in a pattern of first decreasing and then increasing elongation and shear strength of the laminated composite.

Fragmentation /spheroidization of constituent phases and correlated flow softening during thermomechanical processing of AlCoCrFeNi2.1 eutectic high entropy alloy

The present study explores the morphological evolutions of constituent phases during the hot deformation process of a promising as-cast AlCoCrFeNi2.1 eutectic high-entropy alloy. Through which, a quasi-in-situ approach was employed using the Poliak-Jonas technique to carefully select interruption strains for conducting hot compression tests at 1000 °C. This approach allowed for tracking the sequence of microstructural evolutions. Furthermore, to understand the dominancy of shearing or thermally activated fragmentation mechanisms responsible for these evolutions, hot compression tests were conducted at different strain rates. Encountering an unexpected sharp softening behavior in the hot compression flow curve, its underlying micro-mechanisms were investigated using electron backscatter diffraction (EBSD) characterization and scanning electron microscopy (SEM) micrographs combined with detailed image processing and numerical calculations. It is shown that lamellar B2 eutectic regions underwent significant spheroidization with an increase in strain rate (from 12.6% ± 3.3%–64.5% ± 9%), while dendrites fragmentation was more pronounced in lower strain rates. These findings indicate that dynamic spheroidization and dendritic fragmentation mechanisms predominantly contribute to the aforementioned softening behavior observed in the alloy at high temperature.

High-temperature dependence of yield strength and microstructure in Ni54Fe19Ga27 and (Ni54Fe19Ga27)99.7B0.3 alloys

The deformation behavior, yield strength temperature dependence, and plasticity of the high-temperature L21(B2)-phase during compression in the temperature range 773–1173 K for Ni54Fe19Ga27 and (Ni54Fe19Ga27)99.7B0.3 shape memory alloys was determined for the first time. The studied alloys were characterized by high plasticity (over 70 %) and minimum yield strength level (13–65 MPa) at temperatures from 973 to 1173 K. Possible mechanisms of yield strength decrease, plasticity increase, and microstructure formation during the deformation process depending on test temperature and chemical composition are discussed. The possibility of hot rolling of Ni54Fe19Ga27 alloys at elevated temperatures was demonstrated.

Experimental study of poromechanical behavior of Callovo-Oxfordian claystone in undrained triaxial compression and extension tests

The Callovo-Oxfordian (COx) claystone is selected as the host rock in the French project for geological disposal of radioactive waste. In its initial state, the host rock is fully saturated. Due to the low permeability, the pore fluid pressure can locally evolve in a quasi undrained condition due to subsequent mechanical and thermal loading, and then significantly affects deformation and cracking process of geological barrier. Most previous studies were carried out in quasi drained conditions or with constant pore pressure. Poromechanical behavior of COx claystone in undrained condition has been so far rarely investigated. In the present work, we carry out a new series of laboratory tests. Two representative loading paths are considered: triaxial compression with constant confining pressure and triaxial extension with constant mean stress. The variations of strain and pore pressure are measured during the tests. It is found that the poromechanical behavior of the claystone is clearly affected by loading path. The failure strength is higher in triaxial compression than in extension. The evolution of pore fluid pressure is correlated with volumetric strain. Compared with the results obtained in drained tests, it seems that the Terzaghi effective stress can be used for the description of pore fluid pressure effect on failure strength.

Dynamic mechanical properties and energy dissipation analysis of rubber-modified aggregate concrete based on SHPB tests

The fluctuation of the waveform curves in the Split Hopkinson Pressure Bar (SHPB) test can provide a more intuitive reflection of the material's dynamic deformation process, with different strain rates resulting in varying damage states and σ-ε curves. A Φ120×100 mm size SHPB experiment was conducted to study the dynamic mechanical properties of new rubber-modified aggregate concrete (RAC). Based on the different characteristics of waveform and σ-ε curves, combined with high-speed photography technology, the typical failure modes and dynamic compressive strength of rubber-modified aggregate concrete under different loading rates were analyzed. Furthermore, the energy dissipation capacity and mechanism of rubber-modified aggregate concrete at different stages was discussed. The reflected wave of RAC shows a "double-peak" trend of "first high and then low" instead of "first low and then high" of normal concrete due to its exceptional capacity of energy absorption and dissipation. As strain rate increases, a plateau period appears in the reflected wave before first peak. The evolution process is dominated by the energy storage mechanism until it hits the limit, then by the energy dissipation mechanism. These findings can help us design and use RAC materials under dynamic stress.

Molecular Dynamics Investigation of Metastable Structure and Hybridization Bond Evolution in High-Entropy CoCrFeNi Heterostructured Amorphous Carbon Films.

Heterogeneous element doping in amorphous carbon films can reduce residual stresses and improve plastic deformation. Nevertheless, the effects of dopant content and size on the metastable transition mechanism between sp2-C and sp3-C atoms during the deformation process are unclear and difficult to be in situ observed and researched, experimentally. In this work, the mechanical properties and the structural evolution during the nanoindentation of amorphous CoCrFeNi sphere-doped carbon heterostructured films with different radii were simulated. The results indicate that the hardness H and elastic modulus E of the films decreased with the increase of the dopant addition. H decreases from 50.69 to 28.94 GPa, and E decreases from 664.39 to 448.62 GPa. The decrease in the elastic recovery and the enlargement of the shear transition zones indicate that the presence of the amorphous CoCrFeNi dopant can significantly improve the plastic deformation capacity of the films. During the nanoindentation process, the spherical dopants reduce the stress and shear strain of the regions under the indenter in a-C films. The reduction of compressive and shear stresses in the film can inhibit the C atom metastable transition from sp2-C to sp3-C. This can provide a theoretical basis for the development and design of heavy-load and high-deformation-rate a-C films.

Study on interface toughening mechanism based on modified PBO fiber for CFRP/ plastic honeycomb sandwich structure

CFRP (carbon fiber reinforced composites)/honeycomb sandwich structures are widely used in aerospace, automotive, and high-speed rail industries due to their excellent mechanical properties and lightweight characteristics. This study investigates the impact of three designed toughened interfaces on the three-point bending performance of honeycomb structures. The results show that introducing a multiscale toughened interface made of poly(p-phenylene benzobisoxazole) (PBO) fibers grafted with polydopamine (PDA) and multi-walled carbon nanotubes (CNT) increases the peak load and post-peak load of the sandwich structure by 49.7 % and 51.9 %, respectively, and the absorbed energy by 92.4 %. This toughened interface adjusts the stress relationship between the panel, interface, and honeycomb, altering the deformation process and crack propagation mode of the sandwich structure. The micro-nano fibers form fiber bridging at the interface, changing the crack extension mode between the interfaces, transforming the delamination from a single debonding to the combined action of plate core debonding and honeycomb core buckling. Additionally, experimental results show that PBO fibers treated with PDA and CNT exhibit significantly improved surface roughness, Surface area per unit mass, wettability, and tensile strength, which delay and prevent crack propagation at the interface, effectively reducing panel debonding at the bonded joints.

Microstructural characteristics with process-microstructure-property relations during high-frequency ultrasonic vibration-assisted cutting of metallic material

Microstructural characteristics of chips and machined surfaces are influenced by the multiphysics fields distribution. This study investigates the multiphysics-induced microstructural deformation behaviors of CuZn37 metallic alloy during high-frequency ultrasonic vibration-assisted cutting (HFUVAC) and conventional cutting (CC). One the one hand, the multiphysics field distribution was established to clarify the chip formation of cutting characteristics and transient deformation process. The multiphysics field distribution of HFUVAC exhibited periodic changes due to tool intermittent movement, resulting in reduced cutting temperature and force. This intermittent movement also enhanced the sharpening shear effect due to instantaneous impact stress, transitioning from fragmented quasi-shear strain to continual multiple-shear strain during chip formation. One the other hand, the microstructural changes were examined to explain material removal mechanisms. The microstructure of CC demonstrated grain refinement and dislocation slip induced by friction and significant shear deformation. The microstructure of HFUVAC revealed the formations of dynamic recrystallization, twinning structures, and stacking faults, which were associated with enhanced plastic activity and limited slipping due to high-frequency impacts. The work reveals the response of the workpiece microstructure under the composite effects of high-frequency impacts and cutting process, which provides theoretical basis for the microstructure modification design through cutting technology.

Effect of Temperature and Strain on Bonding of Similar AA3105 Aluminum Alloys by the Roll Bonding Process

Accumulative roll bonding (ARB) is a severe plastic deformation process that enables the production of materials with ultrafine microstructures and enhances the characteristics of the base material, particularly in metal matrix composites. The primary objective of this study is to experimentally investigate the bonding strength in AA3105 strips that underwent the roll bonding process, with a specific focus on examining the influence of temperature and reduction rate on bonding. Three temperature levels (200 °C, 300 °C, and 400 °C) and three thickness reduction levels (35%, 50%, and 65%) were considered. The T-peel test was carried out to assess the bonding quality. It was employed to determine the peak force required to separate the two bonded strips. Additionally, ANOVA analysis was performed to develop a regression equation for analyzing peak force. Optical microscopy was used to evaluate the interface bonding quality in the longitudinal section. The results indicate that the bonding strength increases with both temperature and percentage reduction.

Microstructural evolution and mechanical behavior of pearlitic steel under multi-directional forging

The mechanical behavior and the microstructural evolution of a pearlitic SAE 1080 steel were analyzed along 12 Multi-Directional Forging (MDF) cycles at room temperature and strain amplitude Δε ≈ 0.30 (MDF0.30). The resulting cumulative strain flow curve is typical of metals undergoing extensive dynamic recovery, displaying appreciable work hardening up to a strain εt ≈ 0.9, followed by a very low work hardening, where flow stress rises from ≈1400 MPa to ≈1510 MPa. Similarly, the microhardness raises up to a total cumulative strain εt ≈ 1.8 and seems to stabilize for further straining, reaching ∼3626 MPa after εt ≈ 10.8. Conversely, yield strength initially rises and then falls remarkably after εt > 5.4. This behavior is related with directional cross effects that favor dynamic recovery as the total applied strain increases. These results differ remarkably from those connected to a monotonic deformation process such as axisymmetric drawing. In addition, directional cross effects decrease the material yield stress as the total applied strain increases. Microstructural results revealed that MDF0.30 leads to increasing shearing, bending and fragmentation of the cementite lamellae into particles <50 nm in diameter dispersed in the ferritic matrix as the total imposed strain rises. As a consequence, only limited alignment and changes in the cementite interlamellar spacing are observed, up to a total applied strain ≈10.8. It is considered that the work hardening of pearlitic steel deformed through MDF0.30 is dominated by the dynamic recovery of the interlamellar ferrite and a limited contribution from the cementite. Such results have never been reported in the literature and are of practical importance, since extensive cold working of eutectoid steel through MDF can be performed with standard presses and large specimens.

Application of deep learning for technological parameter optimization of laser shock peening of Ti-6Al-4V alloy

The paper is devoted to the development of the method of laser shock peening (LSP) of metals. To optimize the mode of LSP for Ti-6Al-4V specimens a deep learning model for predicting residual stresses by laser shock peening was developed. A numerical-experimental method was used to carry out the model training, in which an experimental study of the effect of different processing mode on the depth and distribution of residual stresses was carried out. The Johnson-Cook model was used as the governing relationship for modeling the dynamic deformation process. At the second stage, the problem of static equilibrium of a body with a plastically deformed area was numerically solved to determine residual stresses. The results of research on determination of the optimal configuration of the deep learning model showed that when using sinusoidal activation function of the neural network with 4 hidden layers and the number of neurons 10, the best level of accuracy in solving the problem is achieved. The obtained model allows us to optimally determine the LSP mode according to the given limitations of values and depth of residual stresses.

Capric-lauric & capric-palmitic/modified bentonite composite as phase change materials for thermal energy storage

This paper proposes a new double layer structure shape-stabilized thermal energy storage wallboard (TESW), by employing microwave radiation modified bentonite (Bm) to stabilize capric acid-lauric acid (CA-LA) and capric acid-palmitic acid (CA-PA) as major components of internal and external wallboard. Leakage test showed that CA-LA/Bm and CA-PA/Bm had good morphological stability. The chemical compatibility, phase change behaviors, and microstructure of CA-LA/Bm and CA-PA/Bm were analyzed. The maximal loading capacities of CA-LA/Bm and CA-PA/Bm can be reached 45 % and 50 %, respectively. In addition, the mechanical and thermal performance of CA-LA/Bm and CA-PA/Bm-based thermal energy storage concrete (CL&CP/Bm-TESC) was systematically studied. The Digital Image Correlation (DIC) technology was used to collect and analyze the speckle images of CL&CP/Bm-TESC20 before and after 100 cycles of phase change, determining the evolution of principal strains during the deformation and failure processes. It is worth noting that the numerical simulation results of the designed double layer structure shape-stabilized CA-LA&CA-PA/Bm-based thermal energy storage wallboard (CL&CP/Bm-TESW) show better temperature adjusting performance. These results demonstrate that the prepared composite of CA-LA/Bm and CA-PA/Bm has potential application in the field of thermal energy storage.

Experimental investigation on the mechanical properties and failure mechanism of key joints in a new-type prefabricated pile-wall composite structure for the open-cut tunnel

To improve the failure resistance of the lining and make use of the retaining structure, this paper proposed a novel method of adding the key joints to connect the lining with the retaining structure. Usually, the joint is the weak point of the whole structure. The failure mechanism of key joints significantly influences the design and safety of the prefabricated structure. In this study, full-scale loading tests were conducted on three types of key joints: sleeve joint, spiral stirrup joint, and U-shaped rebar joint. The joint deformation, failure mechanism, concrete strain, and reinforcement strain are investigated. The results demonstrated that the deformation and failure process of the key joints can be divided into four stages. The flexural-shear failure caused by the joint opening and the sliding of lining is considered as the main failure mode of the key joints. The U-shaped rebar joint exhibited the best mechanical performance. Furthermore, the finite element modes were created to analyze the influence of axial force and the reinforcement diameter. Combining the test and numerical analysis results, the failure mechanism was revealed. In addition, the joints’ loading-carrying capacity was increased with the increase of axial force due to the axial force limiting the joint opening. The research results provide a theoretical basis and reference for the new-type prefabricated pile-wall composite structure (PPCS).

Gap bridging in laser welding of EN AW 5083 with different joint configurations via beam oscillation and filler wire

The extended use of laser welding in the industry requires a less sensitive process in terms of geometrical tolerances of the joint edges. As the industrial availability of laser systems increases, the demand to use laser welding technology possibly with parts coming from less precise production steps is increasing. Gap formation is often caused by the edge quality of the parts coming from previous manufacturing steps such as sheet forming. Al alloy sheets deformed to box-shaped 3D forms often require welded joints on the edges in lap, but, and corner joint configurations. These joints are hard to carry out by laser welding due to the large gap formation caused by the tolerances of the deformation processes involved. Laser welding of Al alloys is already challenging in the absence of gap formation, while these joint configurations have been not feasible with a stationary beam due to incomplete fusion and defect formation. Laser welding with beam oscillation and wire feeding can improve the weldability of these joints. The oscillating motion of the high-intensity beam can achieve a deep weld together with a wider seam. Combined with wire feeding, the process can close gaps in the butt, lap, and corner joint configurations. On the other hand, the added oscillation and wire-related parameters require extending the experimental space, which requires a methodological study to identify feasible conditions. Accordingly, this work proposes a methodological approach to identify and set laser welding process parameters with beam oscillation and wire feeding for an EN AW 5083. Process parameters were initially studied using a simple analytical model that depicts the beam trajectory. Bead-on-plate tests were conducted to assess beam size, power, and weld speed ranges. Lap, butt, and corner joint conditions with a 0.5-mm gap were welded with high quality by manipulating the laser power, oscillation amplitude, and wire feed rate. The results show that welding speeds could be maintained as high as 55 mm/s with complete filling of gaps of up to 0.5 mm, eliminating the surface undercuts and achieving weld widths in the order of 2.5 mm. Moreover the results show the possibility control the depth of the welds from 3 mm to full-penetration conditions.

Hot Deformation Characteristics and Dynamic Recrystallization Mechanisms of a Semi-Solid Forged AZ91D Magnesium Alloy.

Magnesium alloys show great promise in high-speed transport, aerospace, and military technology; however, their widespread adoption encounters challenges attributed to limitations such as poor plasticity and strength. This study examines the high-temperature deformation of semi-solid forged AZ91D magnesium alloy through a combination of experiments and simulations, with a focus on comprehending the influence of deformation conditions on dynamic recrystallization (DRX). The findings disclose that conspicuous signs of DRX manifest in the yield stress curve as strain increases. Additionally, decreasing the strain rate and temperature correlates with a reduction in both yield stress and peak strain, and the activation energy is 156.814 kJ/mol, while the critical strain and peak strain remain relatively consistent (εc=0.66208εp). Microstructural changes during high-temperature deformation and the onset of DRX are thoroughly examined through experimental methods. Moreover, a critical strain model for DRX and a predictive model for the volume fraction of DRX were formulated. These equations and models, validated through a combination of experiments and simulations, serve as invaluable tools for predicting the mechanical behavior and microstructural evolution, which also establishes a foundation for accurately predicting the deformation behavior of this alloy. By analyzing the hot deformation characteristics and dynamic compression mechanism of the newly developed semi-solid forging AZ91D magnesium alloy, a numerical simulation model can be effectively established. This model objectively reflects the changes and distributions of stress, strain, and rheological velocity, providing a scientific basis for selecting subsequent plastic deformation process parameters and designing mold structures.

Effects of swift heavy ions on metal nanoparticles embedded in silica: Using linearly polarized light to monitor the elongation kinetics.

The elongation of metallic nanoparticles (NPs) embedded in a dielectric matrix after irradiation with swift heavy ions is a phenomenon that has been known for several years. However, the precise mechanism behind this deformation process is still not fully understood, primarily due to the dearth of information during intermediate stages of deformation. In this study, we report the continuation of our previous work [Peña-Rodríguez et al., Sci. Rep. 7(1), 922 (2017)], exploiting the strong dependence of the localized surface plasmon resonance on the aspect ratio of elongated metal NPs to study the elongation kinetics in situ. In situ optical absorption spectra were measured using a polarizing beam splitter to separate the longitudinal and transverse plasmon modes of the anisotropic NPs. Then, the detailed geometrical and compositional parameters were determined from a fit of these spectra. The use of linearly polarized light allowed for a more accurate analysis of the elongation kinetics, particularly useful in the first stages, where longitudinal and transverse modes overlap.

Experimental Study on Shear Creep Characteristics of Residual Soil with Different Stone Content

The residual soil on a slope can slowly move downward under the influence of gravity, forming a creep landslide. These types of landslides are known for their extensive coverage, significant magnitude, and prolonged duration of hazard. A systematic study of the creep properties of creep landslide geotechnical bodies is essential for the analysis of the deformation process and long-term safety evaluation of landslides. This paper focuses on studying a creep landslide involving residual soil in western Henan Province. The creep characteristics of residual soil with different stone content are investigated through direct shear creep experiments. The findings reveal that stone content has a profound impact on the creep behavior of residual soil. As the stone content of the soil increased, the structure of the test soil changed significantly, resulting in a gradual decrease in its shear creep. The Burgers model can effectively fit the deceleration creep and steady-state creep stages of the residual soil. With the increase in stone content, the four parameters of the Burgers model show a significant increase, with the instantaneous elasticity coefficient G1 and the viscosity coefficient η1 experiencing more noticeable changes. The average long-term strength of specimens with different stone content is only 54% of their instantaneous strength. Additionally, as the stone content increases, the ratio of long-term strength to instantaneous strength also increases. Notably, the long-term strength of specimens with 10–30% stone content is significantly lower than that of specimens with 50–70% stone content.