Hardening Effect Research Articles

Comparison of analytical and numerical methods for estimating notch strains**

AbstractIn fatigue assessments, local strains and stresses can be easily evaluated using accurate finite element analysis in a case of an individual fatigue‐critical notch or structural detail. In practical design and analysis of global models, the consideration of local notch effects using suitable estimation rules in the combination with linear elastic analysis is reasonable. Various notch rules exist but the current knowledge lacks understanding how applicable different notch rules are for estimating notch strains from elastic stresses. This work studies the Neuber′s rules for sharp and mild notches, Glinka′s equivalent strain energy density method, the correction of Neuber′s rule proposed by Sonsino for mild notches, as well as the Seeger‐Beste method. The application of different estimation rules for notch strains, applied to the elastic‐perfectly plastic steel material and to Ramberg‐Osgood material model for the aluminum material, including work hardening effect, was studied in this work by comparing the estimations with the corresponding experimental data and finite element analysis results. The Neuber′s rule for mild notches and Sonsino′s averaging method gave best correlations with the experimental data and numerical (finite element analysis) results and can be thus recommended for such analyses in compatible cases studied in this work.

Effect of imine-containing phenolic hardeners with different chain lengths and epoxy functionalities on thermal, mechanical, and healing properties of bio-based epoxy vitrimers

Mixtures of polyglycerol polyglycidyl ether (PGPE) and poly(ethylene glycol) diglycidyl ether (PEGDGE) with different molar ratios were cured with imine-containing phenolic hardeners prepared by the reactions of vanillin with ethylene glycol bis(3-aminopropyl) ether, diethylene glycol bis(3-aminopropyl) ether, and a polyetheramine (JEFFAMINE® ED-600) to produce bio-based epoxy cured products. Fourier-transform infrared spectroscopy (FT-IR) of the cured products revealed that the curing reaction of the epoxy and phenolic hydroxy groups was almost complete. The cross-linking density, glass transition temperature, and mechanical strength of the cured products decreased with decreasing the PGPE/PEGDGE ratio and increasing the oligoalkyleneoxy chain length of the phenolic hardeners. All cured products were healed three times at 100 °C under 2 MPa for 2 h. The healing efficiency, in terms of tensile strength, increased with decreasing PGPE/PEGDGE ratio and increasing oligoalkyleneoxy chain length. The polyetheramine-based cured product with the lowest PGPE/PEGDGE ratio exhibited the highest healing efficiency (94–97%), which only slightly decreased following repeated healing treatments.

Designing the heterogeneous microstructure via a direct warm rolling process to synergistically enhance the strength-ductility in a medium Mn steel

This work introduced a facile method for fabricating heterostructures in a medium Mn steel via a direct warm rolling process. The heavy warm rolling promoted the transformation of metastable austenite (∼12.2 vol%) into hard domain α’ martensite, which formed a heterogeneous microstructure with the untransformed γ (soft domain). After 600 °C re-annealing, the hard domain α’ re-reversed to α + γ, and the heterostructure disappeared. Compared to the homogeneous structure, the heterostructure exhibited the synergistic enhancement of strength-ductility (yield strength (YS): 782 → 1113 MPa; ultimate tensile strength (UTS): 1099 → 1304 MPa; total elongation (TEL): 20.8 % → 21.7 %). Quantitative analysis showed that the heterogeneous deformation induced (HDI) strengthening (∼261 MPa) was the primary contributor to the increased ΔYS (782 → 1113 MPa) value, rather than the traditional strengthening mechanisms. Transformation induced plasticity (TRIP) and twinning induced plasticity (TWIP) effect were the main deformation mechanisms of both homogeneous/heterogeneous structures. However, compared to the homogeneous microstructure, the heterogeneous structure possessed the more pronounced TRIP and HDI hardening effects as well as L-C locks, the cooperative effect of these three factors further improved the strain hardening ability to break through the strength-ductility trade-off dilemma.

Microstructure and mechanical properties of Tip/GWZ723 composites adjusted by Tip/Mg laminate structure

In this work, the spherical Tip was introduced into Mg-7Gd-2Y–3Zn (GWZ723) alloy, the Tip/Mg laminar-like configuration was constructed by hot extrusion. The layers quantity and interlayer spacing were adjusted by Tip content. The effects of Tip/Mg laminar-like structure parameters on the microstructure, mechanical properties, work hardening and fracture behavior of Tip/GWZ723 composites were investigated. The results indicate that after extrusion, the Tip elongates along the extrusion direction (ED) and form Tip/Mg laminar-like configuration with the matrix. The Tip aspect ratio increases with the Tip content increases, resulting in a pronounced Tip/Mg laminar-like configuration. The addition of Tip promotes DRX, refines the grain size and promotes the precipitation of the lamellar 14H LPSO phase. The Tip/Mg laminar-like configuration induces the accumulation of high-density dislocations at the interface, thereby contributing to hetero-deformation induced (HDI) hardening, which improves the work hardening rate and dynamic recovery rate. With increasing of Tip content, the HDI hardening effect becomes more pronounced. The Tip/Mg laminar-like configuration facilitates strain redistribution, alleviates stress concentration, impacts crack initiation and inhibits crack propagation, enhancing the plasticity of the Tip/GWZ723 composites. At a Tip content of 15 vol%, the 15 vol%Tip/GWZ723 composite exhibits YS of 439 MPa, UTS of 477 MPa and EL of 3.3 %.

Hygrothermomechanical loading-induced vibration study of multilayer piezoelectric nanoplates with functionally graded porous cores resting on a variable viscoelastic substrate

Harnessing vibrations in multifunctional nanostructured plates is pivotal to next-gen microsystems but necessitates understanding scale effects under multifield loading. Investigated in this work are the forced and unforced vibrations of multilayered piezoelectric nanoplates supported on a variable viscoelastic medium and loaded hygrothermo-electromechanically with functionally graded porous (FGP) cores. The viscoelastic foundation is supposed to demonstrate non-linear changes in both stiffness and damping characteristics in the x-coordinate direction. The goal is to improve the accuracy of the results by using the nonlocal strain gradient theory (NSGT) and the third-order shear deformation assumption (TSDA), which include the effects of hardening and softening materials. The FGP core layer considers four states of porosity distribution patterns. These porosity distributions are expected to change in both the in-plane and thickness directions. The governing partial differential equations resulting from Hamilton's principle can be reduced to a system of algebraic equations by applying the Galerkin method. The parametric studies evaluate the effects of several factors, such as the initial electric voltage, viscoelastic medium parameters, moisture rise, temperature changes, porosity distributions, FG index, nonlocal and strain gradient features, and boundary conditions, on the vibration response. The novelty lies in the incorporation of advanced theories, such as the NSGT and TSDT, which capture size-dependent effects and material hardening/softening phenomena. Additionally, the consideration of four distinct porosity distribution patterns in the FGP core layer provides insights into the influence of porosity gradients on the dynamic response. The proposed model can guide the design and optimization of multifunctional nanostructured plates for applications in next-generation microsystems, energy harvesting devices, and smart structures.

Effects of differential hardening on energy absorption prediction of AA6061-T6 thin-walled rectangular tube

In this study, the energy absorption characteristics and deformation modes of AA6061-T6 thin-walled rectangular tube are investigated experimentally and numerically under different crushing conditions, including axial crushing, three-point bending and oblique crushing. Mechanical tests are carried out on four specimens of uniaxial tension, uniaxial compression, shear and plane strain tension along different loading directions for AA6061-T6. Besides, the effect of differential hardening behavior on the energy absorption prediction of AA6061-T6 rectangular tubes is illustrated by comparing Lou2022, von Mises and SY2009 functions. The mechanical experiment results indicate that AA6061-T6 shows obvious anisotropy, differential hardening behavior and tension-compression asymmetry, and its plastic evolution is accurately characterized by the Lou2022 model. The axial crushing properties show that the AA6061-T6 thin-walled rectangular tube undergoes the progressive symmetrical folding deformation mode. The introduction of geometric discontinuity can obviously reduce the peak force and improve the crashworthiness performances under the axial load. The main crushing mode is bending with a small amount of indentation for three-point bending. Moreover, the three-point bending simulation shows that the Lou2022 function considering differential hardening behavior has the highest simulation accuracy. Three different oblique crushing simulations of 10∘, 20∘ and 30∘ illustrate that the AA6061-T6 rectangular tube at 10∘ mainly occurs progressive folding deformation. while the other two oblique crushing angles undergo global buckling deformation. The total energy absorption at 10∘ is 1.87 and 2.43 times of that at 20∘ and 30∘, respectively. The crushing force efficiency of 20∘ and 30∘ is 41.28 % and 31.8 % lower than that of 10∘, respectively. A comprehensive understanding of the energy absorption performance of AA6061-T6 thin-walled rectangular tube under different crushing conditions is helpful to determine its position and shape as a vehicle safety structure, and to exert its optimal plastic deformation potential to dissipate the collision energy and ensure passenger safety.

Dynamic Mechanical Properties and Modified Material Constitutive Model for Hot Forged Ti2AlNb over Wide Ranges of Temperature and Strain Rate.

In this paper, the stress-strain curves of Ti2AlNb are established based on uniaxial impact tests over wide ranges of temperature and strain rate. The Ti2AlNb exhibited the work hardening effect but did not show an obvious yield stage during a quasi-static compression test. In the SHPB test, an obvious temperature softening effect was found, the strain rate strengthening effect was detected when the strain rate was 4000-8000 s-1, and the strain rate softening effect was detected in the range of 8000-12,000 s-1. A function describing the effect of strain rate on the strain rate strengthening parameters under various temperatures was proposed to modify the basic J-C constitutive model. The relative errors between the experimental measured value and predicted values in various experimental conditions with a modified J-C model were less than 5.0%. The results verified that the modified J-C model could accurately describe the dynamic mechanical properties of Ti2AlNb at high temperatures and strain rates. The research could help to illustrate the cutting mechanism and finite element simulation of Ti2AlNb alloy.

Time-varying compressive properties and constitutive model of EPDM rubber materials for tunnel gasketed joint

The stress relaxation of ethylene propylene diene monomer (EPDM) rubber material in a compressed state significantly increases the risk of water leakage at tunnel precast segmental joints. Additionally, EPDM rubber gaskets typically experience a complex precompression strain state, further complicating the prediction of long-term stress relaxation. Therefore, it is imperative to propose a novel constitutive model that realistically reflects the stress relaxation of rubber with arbitrary precompression strain, providing a reference for the long-term waterproof design of shield tunnels. In this study, the time-varying properties of EPDM rubber at material level were studied in detail. At first, a comprehensive set of accelerated aging tests were conducted on EPDM rubber samples with varying precompression strains. The hardening effect of rubber without precompression and the stress relaxation effect of rubber with precompression were explored. The time-varying law and mechanism governing rubber properties under these two effects were analyzed. Subsequently, a conversion relationship between the EPDM rubber test conditions and the actual service time was established. The predicted hardening coefficient for uncompressed EPDM after 100 years is 1.468, whereas the relaxation coefficient for compressed EPDM is 0.359. Comparative analysis revealed that the compression set index do not consider the beneficial effects of hardening, resulting in a 54.1% overestimation of the design water pressure. Finally, the analytical study on the constitutive model of EPDM rubber material was carried out. The error in compression curve for unaged sample obtained from empirical formulas exceeded three times that of the analytical model, underscoring the need to study time-varying constitutive models. An interpolation method was employed to extend the test curve, leading to the development of a new constitutive model that represents the stress relaxation characteristics of EPDM materials under arbitrary precompression strain states. By combining the proposed constitutive model with the timetemperature conversion relationship, the time-varying expressions of the constitutive parameters for relaxation and hardening effects during the service life were derived. In comparison with existing models, the proposed model demonstrates wider applicability, effectively captures the time-varying characteristics of EPDM materials under arbitrary precompression strains, offering an efficient approach for studying the long-term stress relaxation prediction of rubber gaskets in shield tunnels under complex precompression strain states.

Microstructural evolution and property evaluation of in‐situ Al‐MgAl2O4 nanocomposite prepared by ɣ‐Al2O3 and ultrasonication‐assisted impeller mixing

Synthesis of nanocomposites is challenging due to the difficulties in achieving homogeneous distribution of reinforcing particles in metal. In this paper, an in‐situ Al‐MgAl2O4 nanocomposite billet was prepared by the reaction of ɣ‐Al2O3 with molten Al and ultrasonication‐assisted impeller mixing. The microstructure of the composite showed homogeneously distributed MgAl2O4 crystals alongside their clusters in the Al matrix. Microstructural analysis revealed MgAl2O4 crystals distributed from 20 nm to 4 μm in size. The hardness was found to vary within the composite from 50 Hv for the matrix to 140 Hv for particle cluster regions. The grain size was reduced from 1000 μm in reference metal (CP Al) to 100 μm in the composite. The compression strength of the composite was increased substantially and higher strain hardening effect in comparison with Al was noticed in the compression test. The signatures of extensive plastic deformation such as dislocation pileups, deformed grains, grain boundary pinning etc. were observed in the composite via transmission electron microscopy. Damping properties of as‐cast composite were higher than those of CP Al in the temperature range from room temperature to 350 °C. After rolling the composite up to 40% reduction, the damping capacity (Tanδ) of the composite was found to increase marginally after 150 °C. Higher damping was found to reoccur after the annealing treatment of the composite. The improvement in damping capacity at RT was possibly influenced by the micron sized MgAl2O4 and at higher temperatures by the nano‐sized MgAl2O4 crystals. The reoccurrence of higher damping in the annealed composite underlined the stability of finer grains due to the grain boundary pinning by nano‐sized MgAl2O4 crystals. The studies on the damping property of the composite displayed the benefits of having dual size distribution of MgAl2O4 crystals (nm and μm) in the composite.This article is protected by copyright. All rights reserved.

Phase transformation behavior and shape memory effect of nickel-titanium shape memory alloy using the magnetic field assisted wire electrical discharge machining

Nickel-titanium shape memory alloy (NiTi-SMA) can restore its original shape after deformation, making it show great application in the fields of biomedicine, aerospace, etc. The wire electrical discharge machining (WEDM) has the advantage of machining micro and complex structures, which can greatly promote the application of NiTi-SMA. However, there are issues such as heat affected layer (HAL) on the surface of WEDM, which can affect the functionality of NiTi-SMA. Therefore, when using WEDM to NiTi-SMA, more attention should be paid to the functional changes after machining. This article primarily examine is the impact of peak current and pulse on time on the phase transformation behavior, shape memory effect, and mechanical properties of NiTi-SMA during WEDM, and introduces into the magnetic field assisted (MFA) process to improve the machining performance of NiTi-SMA. The results indicate that the HAL formed on the surface of NiTi-SMA is primarily composed of the irreversible phase transformation of B2 austenite. This layer induces a hardening effect, resulting in an increase in the phase transition temperature and a decrease in the phase transition energy (∆HM-A), as a result, the martensitic phase transformation behavior is suppressed. When the peak current and pulse on time increase, the surface quality of the NiTi-SMA processed decreases. The thickness of the HAL and microhardness increase, causing an increase in the phase transition temperature of the NiTi-SMA processed samples. Additionally, the transformation energy ∆HM-A, shape recovery rate, and mechanical properties decrease, and after recovery, more surface cracks appear and show larger extensions. MFA-WEDM can improve the surface quality of NiTi-SMA processing, reduce the thickness of the HAL, and effectively enhance the phase transformation temperature and energy ∆HM-A of the NiTi-SMA processed samples. With a magnetic field strength of 0.45 T, the tensile shape recovery rates of 98%, 94.4%, and 91.0% were achieved at 2%, 5%, and 8% strain, respectively. This represents an improvement of 8.9% compared to the maximum shape recovery rate with conventional WEDM. At the same time, it also inhibits the generation and propagation of surface cracks after deformation recovery. Additionally, MFA-WEDM improves the mechanical properties of NiTi-SMA, and reduces the thickness of the brittle fracture region by 49.7% compared to conventional WEDM. Therefore, MFA-WEDM can effectively enhance the shape memory effect of NiTi-SMA. However, it is important to avoid excessive peak currents and pulse on time to achieve optimal shape memory functionality.

Electric field response of ferroelectric domains near non-polar precipitates in BaTiO3-based ceramics

Precipitates have recently been found to significantly enhance the mechanical quality factor in piezoelectric ceramics. Such a piezoelectric hardening effect was attributed to strong interactions between ferroelectric domains and precipitates. In the present work, the response of domains to applied electric fields is observed in situ via transmission electron microscopy in aged (Ba, Ca)TiO3 ceramics with precipitates to reveal the underlying mechanism of this phenomenon. Ferroelectric domains in the Ba-rich matrix grain are observed to be more concentrated near non-polar Ca-rich precipitates. With increasing applied voltage, domains separate from precipitates merge together first, while those near precipitates persist to higher voltages. During ramping down, domains nucleate from precipitates. These direct observations confirm the strong interactions between ferroelectric domains and precipitates in piezoelectric ceramics.

A meshless computational framework for studying cold spray additive manufacturing including large numbers of powder particles with diverse characteristics

Cold spray (CS) has emerged as an appealing additive manufacturing (AM) technique for producing or repairing individual components or entire structures. Compared to fusion-based AM technologies, cold spray additive manufacturing (CSAM) offers distinct advantages in the fabrication of components, while avoiding some melting/solidification-related issues such as phase transformation and oxidation. It involves intricate processes that pose significant challenges for numerical modeling, particularly when simulating the entire process at a large scale. The smoothed particle hydrodynamics (SPH) method is highly suitable for handling large material deformations due to its Lagrangian and meshless nature. In this work, we develop an enhanced SPH method to conduct large-scale simulations of CSAM with different powder sizes, morphologies, and distributions. A modified material model has been incorporated to accurately capture the strain-rate hardening effects during the plastic stage. The computational scale is greatly improved by using a Message Passing Interface (MPI) based framework, enabling the simulation of approximately ten million SPH particles. To the authors’ knowledge, this study marks the first attempt to numerically reproduce the entire process of CSAM with real powder sizes and distributions. Experimental data measured for a wide range of powder velocities are used to validate the simulation results and assess the prediction accuracy. Subsequently, we comparatively study the bonding mechanisms of powders with the same or different sizes, while also identifying a four-stage coating process. The effects of powder morphology on the bonding process are thoroughly investigated. A large-scale CSAM process is finally reproduced to demonstrate the capability of the present meshless scheme, and mechanisms of pore formation are analyzed, providing valuable insights for practical engineering applications.

Novel compounds in the Sc-rich part of the systems Sc-{Co,Pd,Pt}-Ga: Structure and bonding

The present paper comprises a detailed structural analysis of two novel compounds in the Sc-Co-Ga system: τ3-Sc50Co13Ga3 (space group Fm-3; ε-Mg26-xAg7+x type), and τ4-Sc6Co1.73+x+yGa1-x (space group Immm; x=0.43; y=0.14; Ho6Co2Ga derivative type). Although alloys in the isothermal section are oxygen-free, the alloy of τ3, prepared for single crystal growth via partial melting in an alumina crucible, contained a minor amount of oxygen and can be considered as oxygen-stabilized Sc50Co13Ga3O1.1 (WDX-data). A search for homologous compounds in the systems Sc-{Pd,Pt}-Ga prompted the existence of two compounds Sc54{Pd,Pt,Ga}17, which from X-ray single crystal analyses proved both to be isotypic with the Hf54Os17-type structure (space group Immm). Whereas Sc54(Pd0.652Ga0.348)17 has a very limited homogeneity region at 850°C, Sc54(Pt1-xGax)17 exhibits at 850°C a large homogeneity region (0<x<0.28) extending from Ga-rich Sc76Pt17.2Ga6.8≡Sc54(Pt0.72Ga0.28)17 to novel binary Sc54Pt17. Interestingly, against the usual trend of solution hardening, hardness, Young's modulus and fracture toughness all decrease with increasing Ga-content: this effect is less pronounced for Sc54(Pd1-xGax)17 than for Sc54(Pt1-xGax)17 and is in line with DFT calculations indicating a weakening of bonding with increasing Ga content, thereby overcompensating the solution hardening effect. DFT modeling showed a common bonding feature for all the studied compounds – a strong electron localization inside the Sc6 octahedra, stacking of which leads to the formation of Mackay icosahedra in Sc54(Pd1-xGax)17, Sc54(Pt1-xGax)17, and Sc50Co13Ga3. The band structure of Sc6Co2.25Ga0.625 and Sc50Co13Ga3 indicates their metallic behavior, while Sc54(Pd1-xGax)17 and Sc54(Pt1-xGax)17 show distinct semimetal features. All investigated compounds in this work show similar trends in Bader charge distribution with a positively charged Sc-sublattice and a negatively charged sublattice formed by transition metals (Co, Pd, Pt) and Ga.

Analytical Study of Nonlinear Flexural Vibration of a Beam with Geometric, Material and Combined Nonlinearities

This article explores the nonlinear vibration of beams with different types of nonlinearities. The beam vibration was modeled using Hamilton’s principle, and the equation of motion was solved using method of multiple time scales. Three models were developed assuming (a) geometric nonlinearity, (b) material nonlinearity and (c) combined geometric and material nonlinearity. The material nonlinearity also included both third and fourth nonlinear elasticity terms. The frequency response equation of these models were further evaluated quantitatively and qualitatively. The models capture the hardening effect, i.e., increase in resonant frequency as a function of forcing amplitude for geometric nonlinearity, and the softening effect, i.e., decrease in resonant frequency for material nonlinearity. The model is applied on the first three bending modes of the cantilever beam. The effect of the fourth-order material nonlinearity was smaller compared to the third-order term in the first mode, whereas it is significantly larger in second and third mode. The combined nonlinearity models shows a discontinuous frequency shift, which was resolved by utilizing a set of transition assumptions. This results in a smooth transition between the material and geometric zones in amplitude. These parametric models allow us to fine tune the nonlinear response of the system by changing the physical properties such as geometry, linear and nonlinear elastic properties.

Nonlinear dynamics of cantilevered hyperelastic pipes conveying fluid: Comparative study of linearelasticity and hyperelasticity

In light of the softness and lightweight characteristics, hyperelastic pipes are prone to large deformation. Intending to provide accurate predictions of their large deformation vibrations, the present study aims to establish a rotation-angle-based geometrically exact model for cantilevered pipes conveying fluid composed of hyperelastic materials. Additionally, given the presence of nonlinear geometric relations, it is imperative to assess the role of hyperelasticity in the nonlinear dynamics of fluid-conveying pipes in comparison to linearelastic pipes. The modeling process integrates the Mooney-Rivlin hyperelastic model with a geometrically exact description of the pipe. And the final governing equation is developed through energy analysis and the extended Hamilton's principle. Subsequently, Galerkin's method and the finite difference method are employed to address the governing equation. Following the verification of the proposed model, parametric studies are conducted in the form of planar oscillation diagrams, time histories, phase trajectories, and bifurcation diagrams. The findings of the present study highlight three critical insights. Firstly, the hyperelastic model introduces numerous complicated nonlinear terms as function of the rotation angle with high-order nonlinearity. In the present study, at least fifth-order nonlinear terms should be preserved to adequately predict large deformation vibrations. Secondly, the Mooney-Rivlin hyperelastic model imparts a hardening effect in comparison to the linearelastic model, significantly reducing vibration amplitudes. Lastly, the third-order approximate model is demonstrated to be inadequate in predicting large deformation vibrations at high flow velocity, as it contains the approximation on not only the geometric description but the hyperelasticity-related terms.

PINN-based forward and inverse bending analysis of nanobeams on a three-parameter nonlinear elastic foundation including hardening and softening effect using nonlocal elasticity theory

PINN-based forward and inverse bending analysis of nanobeams on a three-parameter nonlinear elastic foundation including hardening and softening effect using nonlocal elasticity theory

Effect of Strain Hardening on Burr Control in Drilling of Austenitic Stainless Steel

Austenitic stainless steel has been widely used in various industries, such as aerospace, medical, and hydrogen energy, due to its high strength over a wide range of temperatures, corrosion resistance, and biocompatibility. However, stainless steel is a difficult-to-cut metal because its ductility and low thermal conductivity induce a strain hardening with significant plastic deformation at high temperatures. Burr formed at the back side of a plate is a critical issue which deteriorates the surface quality, especially in drilling. Burr removal operation, therefore, should be done in the machine shop. This study discusses the effect of strain hardening of austenitic stainless steel, SUS 316L, on burr formation. Hardness and cutting tests were conducted to compare the strain hardening effect for three types of workpieces: as-received, pre-machined, and tensile treated specimens. In the employed specimens, the tensile treated specimen is harder than the as-received specimen. Those specimens have uniform hardness in the depth direction from surfaces. Pre-machined specimen, in which the back side of the plate was finished by face milling, has a distribution of hardness in the depth direction from a surface. The highest hardness appears in the subsurface of the pre-machined specimen. The cutting forces in the steady processes, in which the entire edges remove material, were nearly the same as the tested specimens each other. However, remarkable differences were confirmed in the chip thickness and burr formation. The higher strain hardening of the tensile treated specimen is effective to suppress burr formation. The cutting characteristics are then identified to associate burr control with the shear plane model of orthogonal cutting using an energy-based force model. The shear stresses, shear angles, and friction angles of the tensile treated and as-received specimens are compared to discuss the effect of strain hardening on reduction of burr formation.

Dual-scale clusters enabling exceptional mechanical properties of a CoNiCr-based MP159 superalloy at 650 °C

Prior or early-stage precipitation products, e.g., GP zones and chemical short-range ordering, attract tons of interests recently due to their extremely small size and notable hardening effects. In this work in a commercial CoNiCr-based MP159 superalloy, we, for the first time, simultaneously introduced two kinds of these products, i.e., the atomic-scale L11 cluster, and the nano L12 cluster with 2.7 nm in size, by simply removing the standard annealing process and directly conducting the intermediate 650 °C tension. The ultra-dense co-existence of these dual-scale clusters generates over 200 MPa hardening effect at the specific 650 °C when compared to the standardly-annealed MP159 alloy that contains only larger (∼6.0 nm) L12 precipitates. High-angle annular dark field-transmission electron microscopy associated with atom probe tomography evidence that firstly, the atomic-scale cluster is of the L11 type, similar to the one observed in the NiCoV medium entropy alloy. And secondly, the composition of the nano L12 cluster is abnormally close to (Ni,Co)3Ti, whose equilibrium crystalline structure is otherwise D024. This likely leads to a high anti-phase boundary energy hence high shearing resistance for dislocations.

Study on Characteristics of Ultrasound-Assisted Fracture Splitting for AISI 1045 Quenched and Tempered Steel.

Ultrasonic vibration-assisted con-rod fracture splitting (UV-CFS) was used to carry out the fracture experiment of 1045 quenched and tempered steel. The effect of ultrasonic vibration on the fracture properties was studied, the fracture microstructure and the evolution of dislocations near the fracture were analyzed and the microscopic mechanism was analyzed. The results show that in the case of conventional fracture splitting without amplitude, the dimple and the fracture belong to ductile fracture. With the increase in ultrasonic amplitude, the plasticity and pore deformation of the con-rod samples decrease at first and then increase; when the amplitude reaches a certain point, the load required for cracking is reduced to a minimum and the ultrasonic hardening effect is dominant, resulting in a decrease in the plasticity of the sample, a cleavage fracture, a brittle fracture, the minimum pore deformation and high cracking quality. The research results also show that with the increase in ultrasonic amplitude, the fracture dislocation density decreases at first, then increases, and dislocation entanglement and grain breakage appear, then decrease, and multiple dislocation slip trajectories appear. The changes in the dislocation density and microstructure are consistent with the above results.

Investigation of microfriction properties of graphene/AlCoCrFeNi high entropy alloy

Applying graphene (Gr) coatings to high-entropy alloys (HEA) is anticipated to enhance their tribological characteristics. The current understanding of the mechanism by which the Gr/HEA is enhanced at the atomic level is still limited. Molecular dynamics simulations revealed the mechanical behavior and strengthening mechanism of the Gr/AlCoCrFeNi HEA during nanoindentation and nanoscratch. The results demonstrate a substantial increase in the indentation hardness of the Gr/AlCoCrFeNi HEA by about 2.4 times. When Gr changed from a single layer to three layers, it further improved (3.2 times for a double layer and 3.9 times for three layers). At the same time, the friction coefficient is effectively reduced. Furthermore, the elevated in-plane stiffness of the Gr coating leads to an expansion of the effective loading area, resulting in increased Shockley dislocation and stair-rod dislocation density within the Gr/AlCoCrFeNi HEA, thereby amplifying the strain hardening effect and reducing subsurface damage. Qualitative experiments confirmed the excellent wear resistance of the Gr/HEA, and coating Gr increased the width of scratches, effectively confirming our simulation results. These findings provide valuable insights for the development and design of Gr/HEA composite coatings with enhanced mechanical properties.