Hardening Behavior Research Articles

On the anomalous strain rate dependence of working hardening and fracture behavior of an ultra-high strength 1470 MPa dual phase steel

On the anomalous strain rate dependence of working hardening and fracture behavior of an ultra-high strength 1470 MPa dual phase steel

Anisotropic Hardening of HC420 Steel Sheet: Experiments and Analytical Modeling

Choosing the appropriate yield function is essential to precisely predicting the anisotropic hardening behavior of steel metals considering general loading directions. This research investigates the anisotropic hardening behavior of HC420 steel sheet by combining experimental and analytical modeling. Experiments are conducted for uniaxial tensile tests according to the three different directions and bulging tests to obtain hardening data. The experimental findings show that the loading direction affects the anisotropic behavior of HC420 steel’s strength and plastic deformation. The Chen-coupled quadratic and non-quadratic (Chen-CQN) approach is used to ensure the convexity of the HC420 steel. By comparing the Chen-CQN approach with the Yld2000-2d and Stoughton-Yoon’2009 yield functions, the Chen-CQN approach shows superiority in predicting the hardening behavior of the HC420 sheet, exhibiting a more straightforward numerical implementation and enhanced accuracy in yield stress predictions under different loading directions. Results from experimental hardening tests reveal that the Chen-CQN function precisely and flexibly characterizes the yield surface of HC420 steel, with a constant variation of within 2% from its predictions.

Nanoindentation Crack Suppression and Hardness Increase in SrTiO3 by Dislocation Engineering

Abstract Dislocations in functional oxides have sparked interest in the potential they hold for harvesting both enhanced mechanical and functional properties for next-generation electronic devices. This has motivated the recent research endeavor to achieve tunable dislocation density and plastic zone size in functional oxides. However, the dislocation density-dependent micro-/nanomechanical properties in functional ceramics have yet to be assessed, which will be critical for the design of reliable electronic devices in the near future. In this work, we use a model material, single-crystal SrTiO3, as one of the most widely used substrates for oxide electronics, to assess the hardness and fracture behavior at micro-/nanoscale by pre-engineering the dislocation densities from ~ 1010 m-2 up to ~ 4.0 × 1014 m-2. We find crack suppression and enhanced hardness during nanoindentation in samples with pre-engineered dislocations. Post-indentation analysis using transmission electron microscopy revealed the critical role of pre-existing dislocations in regulating the crack suppression and increased hardness in SrTiO3. The results can help guide the design of mechanically reliable electronics via dislocation engineering.

Isothermal low-cycle fatigue and fatigue-creep of Alloy 709 using an unified viscoplasticity modelling

An improved unified viscoplastic model (UVM) is proposed to simulate the cyclic viscoplastic behaviors of Alloy 709 under low-cycle fatigue (LCF) and creep fatigue interaction (CFI) loadings. And the effects of strain amplitudes and hold times on the model parameters as well as the relationship between the static recovery parameter and the accumulated inelastic strain are considered to reflect the evolutionary behavior of strain-stress hysteresis loops, the varying stress relaxation and cyclic hardening behavior. Moreover, an efficient numerical implementation is proposed using Voigt notation and implicit radial return method with Newton-Raphson iteration, and the consistent tangent operator (CTO) for the improved UVM can be simply solved using matrix operations. The proposed model accurately depicts the mechanical behavior of Alloy 709 at 750°C.

Examining the Mechanical Properties of Al-SiC Metal Matrix Composites Produced Using the Stir Casting Method

Aluminum metal matrix composites have great corrosion resistance, light weight, and durability. Because of these characteristics, metal matrix composites made of aluminium can be used in a variety of automotive, marine, and aviation applications. The mechanical characteristics, microstructures, and wear properties of silicon carbide metal matrix composite aluminum are investigated in this study. In the current investigation, the matrix was aluminum and the material used for reinforcement was silicon carbide (30 microns). The various compositions in volume fraction—100% Al -0%Sic, 96.5% Al -3.5%Sic, and 93% Al -7.0%Sic—were selected. Stir casting was utilized in the fabrication process. Analysis was done on the produced composites microstructures, Vickers hardness, tensile strength, and wear behaviour. The hardness, tensile strength, and weight % of an aluminum (Al) matrix were all improved by the addition of silicon carbide (SiC) reinforcements, as indicated by the results. By observing the microstructure, silicon carbide (SiC) particle collection and The Al matrix's non-homogeneous distribution was verified. In aluminum matrix composites, porosities were seen in the microstructures and increased as the weight percentage of silicon carbide (SiC) reinforcements increased. A pin-on-disc wear test discovered that the Al matrix had been reinforced with silicon carbide (SiC) particles, improving wear rate.

Effect of Shot Peening-Induced Microstructure and Precipitate Evolutions on the Surface Residual Stresses, Hardness, and Wear Behavior of Al 6061 Alloy

Effect of Shot Peening-Induced Microstructure and Precipitate Evolutions on the Surface Residual Stresses, Hardness, and Wear Behavior of Al 6061 Alloy

Microstructure and Mechanical Behavior of Magnetron Co-Sputtering MoTaN Coatings

In recent years, there have been important developments in the refractory metal nitride coatings used for versatile applications, such as MoN, TaN, NbN, etc. Engineered approaches, including the deposition method, microstructure control, structural design, and the addition of functional elements, are put into practice for the promotion of coating characteristics. This study focuses on the microstructure and mechanical properties of ternary molybdenum tantalum nitride, MoTaN, coatings. MoTaN was deposited using a reactive radio frequency (r.f.) magnetron co-sputtering system with Mo/Ta target input power modulation control. The effects of composition and microstructure variations on its mechanical properties, including its hardness, elastic modulus, and wear behavior, were investigated. In general, the MoTaN coatings exhibited a columnar polycrystalline microstructure with MoN(111), Mo2N(111), Mo2N(200), TaN(200), and TaN(220) phases and orientations based on X-ray diffraction analysis. The addition of Ta triggered the transition of the primary orientation of Mo2N(111) into Mo2N(200). Transmission electron microscopy was utilized to analyze the transformation of the multiphase structure and changes in the grain size in terms of the Ta addition. According to nanoindentation and wear resistance analyses, superior hardness, elastic modulus, H/E, H3/E2, and wear-resistance values were identified for the MoTaN coatings with 6.8 to 10.4 at.% Ta, and a maximum hardness of 18.0 GPa was found for the MoTaN coating deposited at an input power of Mo/Ta = 150/100 W/W. An optimized hardness of 18.0 GPa and an elastic modulus of 220.7 GPa were obtained. The adjustment of the input power during deposition played a critical role in determining the overall performance of the MoTaN co-sputtering coatings. The MoTaN coating with optimized mechanical properties is attributed to its multiphase microstructure and fine columnar grain size of less than 30 nm.

Microstructure, Hardness, and Wear Behavior of Layers Obtained by Electric Arc Hardfacing Processes.

Hardfacing is a welding-related technique aimed at depositing a harder and tougher layer onto a softer, less wear-resistant substrate or base metal. This process enhances the abrasion resistance of the component, increasing its durability under working conditions. A key feature of hardfacing is dilution, which refers to the mixing of the hardfacing layer and the base metal. In this study, shielded metal arc welding (SMAW) was employed to hardface structural steel using chromium carbide vanadium consumables, with results compared to AISI D2 cold-work tool steel. Four different SMAW parameters were tested, and the abrasive test was conducted against SiC discs. Wear rate, represented by the wear loss rate, was correlated to microstructure, scanning electron microscopy, energy-dispersive X-ray spectroscopy, hardness, microhardness, and surface roughness. The results showed that key SMAW parameters, such as welding speed and current, significantly influence wear resistance. Specifically, slower welding speeds and higher currents, which result in greater heat input, led to the increased wear resistance of the deposited layer through the mechanism of the inoculation of larger and harder carbides.

Synthesis, hardness and tensile behavior of boron carbide reinforced Al6082 alloy composites for automotive applications

Synthesis, hardness and tensile behavior of boron carbide reinforced Al6082 alloy composites for automotive applications

Strain hardening and tensile deformation behaviour of two advanced high-strength steels with ferrite-bainite microstructure

Two advanced high-strength steels (AHSSs) with varying percentages of bainite present in the microstructure were examined for their deformation behaviour under tensile loading. Despite having comparable yield strength (680–700 MPa) and tensile strength (775–780 MPa), the two steels behaved differently in terms of deformation and damage during tensile loading. The strengthening mechanism was governed by the combined effect of precipitates and the harder bainite phase. Also, the two steels’ strain-hardening behaviour differed. At the early stages of the deformation, the amount of harder bainite phase determined the strain hardening rate, however, in the later stages, the strain hardening rate became sluggish and gradual due to restricted mobility of the dislocations caused by the nano-precipitates. This phenomenon was further confirmed by the EBSD and KAM maps, revealing differences in grain misorientation resulting from the deformation. Overall, steel with a reduced volume fraction of bainite phase demonstrated a ductile fracture behaviour in contrast to the steel with a predominantly bainitic microstructure. In this case, the quasi-cleavage kind of fracture was discovered.

Effect of Cu on precipitation hardening and clustering behavior of Al-Zn-Mg alloys in the early stage of aging

Effect of Cu on precipitation hardening and clustering behavior of Al-Zn-Mg alloys in the early stage of aging

Investigate the aluminium 1050-H4 microstructure, hardness, and wear characteristics when reinforced with maize cob particles

Abstract One of the effects of creating composite materials, which are classified as advanced materials, is a change to their mechanical properties. In this study, the effect of reinforcing aluminium 1050-H4 using corn-cob particles were investigated. Prior to being examined using scanning electron microscopy (SEM), the corn cob was crushed and milled in the experiment using a Aimil machine. The hardness, microstructure and wear behavior test were carried out. The aluminium alloy reinforced with corn cob particles of two distinct diameters, <0.425 mm and 0.425 mm, to create the composites. Casted samples were characterized by scanning Electron microscope (SEM). The findings indicate that adding maize cob particles larger than 0.425 mm in diameter improves the mechanical characteristics (hardness) of the aluminium matrix composite by 6.9% and raises its coefficient of friction and wear rate.

Molecular dynamics investigation of the elastic, mechanical, and anisotropic features of hexagonal (2H) diamond under extreme temperatures

2H diamond (lonsdaleite) is a promising material for contemporary science. However, there is still no well documented experimental or theoretical work for 2H diamond at high temperatures. Therefore, this work is the first theoretical contribution for the titled features of 2H diamond. The elastic constants decline with rising temperature and conform the Born stability. Both Pugh ratio and Poisson’s ratio results indicate the brittle character of 2H diamond. Both monotonic and non-monotonic hardness behavior with a notable elastic anisotropy were obtained and discussed. Presented results of this work for 2H diamond aligns well with available literature of other 2H materials.

Cryogenic Treatment Effect on the Wear Resistance of AM60 Magnesium Alloy

Magnesium alloys were used as structural materials due to their low density. However, the poor wear behavior of magnesium alloys limits their use. In this study, AM60 magnesium alloy was subjected to deep cryogenic heat treatment to enhance the wear properties in dry and wet conditions with different loads. For this purpose, a deep cryogenic treatment at –196°C was applied for 48 h to the AM60 magnesium alloy. On the other hand, the wear performance of the treated sample was compared to the untreated sample using the pin-on-disc method at loads of 1 N, 2 N, and 3 N. The microstructure and wear groove were investigated using imaging techniques, while the XRD method characterized the phase modification. The results showed that the microstructures of the untreated sample drastically changed; the eutectic phase around the β phase was dissolved in the matrix, and some twins were formed after heat treatment. The XRD analysis confirmed the formation of a new β phase belonging to twins and an increase of the current β phase. Regarding hardness behavior, it increased by ~17.5% compared to the untreated sample after cryogenic treatment. In dry conditions, abrasive wear was the primary mechanism, and the wear resistance was better for the treated sample for all loads applied due to probably new phase formation. The treated sample exhibited lower wear resistance against the untreated sample, apparently due to the oxidative wear mechanism.

Fabrication and Functional Behavior Studies of Polypropylene Composite Containing Hybrid Reinforcements

<div>Hybrid reinforcement-made polypropylene (PP) composites are beneficial over monolithic PP and utilized for various engineering and non-engineering applications. The present investigation of PP hybrid composites is developed with 10 percentages of weight (wt%) of E-glass fiber embedded with 0–6 wt% of silicon carbide via compression technique associated with hot press. E-glass fiber and SiC influencing wear rate, tensile strength, and microhardness behavior of PP and its composites are experimentally investigated. The peak loading of SiC as 6 wt% into PP/10 wt% E-glass fiber is recorded as better wear resistance (0.021 mm<sup>3</sup>/m), maximum tensile strength value (54.9 MPa), and highest hardness (68 HV). Moreover, the investigation results of hybrid PP composite are better resistance to wear and hiked tensile and hardness behavior compared to monolithic PP. This PP/10 wt% E-glass fiber/6 wt% of SiC hybrid composite is adopted for high-strength to lightweight sports goods applications.</div>

Nanoindentation behavior of the laser-repaired CoCrFeNiV high-entropy alloy

High-entropy alloys (HEAs) are solid-solution alloys composed of multiple elements, exhibiting excellent mechanical properties. The unique plastic deformation mechanism induced by their specific solid solution structures has attracted considerable attention but remains incompletely understood, particularly at the micro-scale. In this study, the surface morphology, chemical composition, and microstructures of CoCrFeNiV HEA before and after laser remelting repair were investigated. Nanoindentation testing was employed to characterize the surface hardness and creep behavior of the repaired surface. The distribution of surface hardness before and after laser remelting, as well as the indentation creep behavior under different loads, were studied. The mechanism of indentation creep on the repaired surface was discussed and analyzed. The effect of microstructures of HEAs, including precipitated phases and sub-grain boundaries, on dislocation-dominated micro-scale plastic deformation was elucidated by the transmission electron microscope (TEM). This study contributes to an in-depth understanding of the creep behavior and micro-scale deformation mechanisms in HEAs.

Insights into the anomalous hardness of the tantalum carbides from dislocation mobility

The tantalum carbides, TaCx, have been repeatedly shown to harden dramatically with some loss of carbon content, then soften with further decarburization. First observed in 1963, this anomalous hardness behavior has been reproduced for decades without satisfactory explanation. Prior attempts to characterize this phenomenon using elastic stiffnesses have failed to reproduce the anomalous hardness behavior. In this work, we demonstrate a change in slip system preference from {111}B1 to {110}B1 in TaCx as x decreases, while no such transition is observed in TiCx. We find this to be the primary mechanism of the anomalous hardness, arising from reduced energetic favorability of dissociation of dislocations on {111}B1 into Shockley partials at lower carbon contents. We also present experimental hardness measurements for bulk and thin-film TaCx at different carbon contents. An anomalous hardness peak is observed in the bulk samples, but not in the thin films, due to loss of dislocation plasticity in the nanocrystalline films.

A Method of Mortal Cement Hardening and Fracture Behaviors Tracking using the Graphite Paper Sensor

A Method of Mortal Cement Hardening and Fracture Behaviors Tracking using the Graphite Paper Sensor

Experimental study of flow-induced vibration in a two degrees-of-freedom flexibly mounted triangular prism in crossflow

This study experimentally investigates the flow-induced vibration (FIV) of a flexibly mounted triangular prism with two degrees of freedom (DoF), capable of oscillating in its first two vibrational modes in the crossflow direction. The experiments were conducted by varying the angle of attack (α) in the range of 0°–60° and eigenfrequency ratio (R), which is the ratio between the second and first eigenfrequency, from R = 1.5 to 3. For α = 0° and 15°, no significant oscillations were observed. At α=30°, both vortex-induced vibration (VIV) and galloping-type response were detected. For higher angles of attack, α = 45° and 60°, a pure galloping type response was identified. Hydrogen bubble flow visualization was employed to analyze the vortex-dominated wake and to discern the nature of the FIV response—whether it was VIV or galloping. Although the prism was free to oscillate in both its first and second modes, only the first mode contributed to the FIV response at α = 45° and 60°, where galloping was dominant. The FIV response remained primarily influenced by the first mode, except when mode two was externally excited, resulting in pronounced hard mode-two galloping behavior. Because mode one predominantly drives the system's overall FIV response, variations in the eigenfrequency ratio had minimal impact on the system's overall FIV behavior.

A strain rate-dependent distortional hardening model for nonlinear strain paths

In this paper, a strain rate-dependent distortional hardening model is firstly proposed to describe strain rate-dependent material behaviors under linear and nonlinear strain paths changes in 0≤θpathchange≤180∘. The proposed model is formulated based on the simplified strain rate-independent distortional hardening model (Choi and Yoon, 2023). Any yield function could be used for the strain rate-dependent isotropic and anisotropic yielding. For the linear strain path, the strain rate-dependent isotropic hardening behavior could be explained by two state variables representing rate-dependent yielding and convergence rate of flow stress under monotonically increasing loading condition, respectively. For the nonlinear strain paths, the strain rate-dependent material behaviors such as Bauschinger effect, yield surface contraction, permanent softening, and nonlinear transient behavior could be described by modifying the evolution equations of the simplified strain rate-independent distortional hardening model with a logarithmic term of strain rate. For the verification purpose, it was used the strain-rate dependent tension-compression experiments of TRIP980 and TWIP980 (Joo et al., 2019). In addition, a high speed U-draw bending test was conducted with original and pre-strained specimens. The springback prediction in high speed U-draw bending test was performed by using strain rate-independent isotropic, strain rate-dependent isotropic-kinematic and distortional hardening models. It is identified that the proposed model showed the most accurate prediction for the pre-strained specimen where the possible bilinear and trilinear path change in 0≤θpathchange≤180∘ is observed while it showed the same accuracy for the original specimen where main strain path change occur in forward-reverse manner (θpathchange=180∘).