Hardening Behavior Research Articles

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.

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

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

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∘).

Tribological, Compressibility and Micro Hardness Behaviour of Al7075/SiC Composites

Tribological, Compressibility and Micro Hardness Behaviour of Al7075/SiC Composites

A Comparison Study of High-Temperature Low-Cycle Fatigue Behaviour and Deformation Mechanisms Between Incoloy 800H and Its Weldments

The high-temperature low-cycle fatigue (LCF) behaviour of Incoloy 800H and its weldments with Haynes 230 and Inconel 82 filler metals, which were fabricated with the gas tungsten arc welding (GTAW) technique, was investigated and compared at 760 °C. The results revealed that the Incoloy 800H weldments showed lower fatigue lifetimes compared to the base metal. However, the weldments with the Haynes 230 filler metal demonstrated an improved fatigue life at the low strain amplitude compared to both Incoloy 800H and the weldment with the Inconel 82 filler metal. The Incoloy 800H base metal showed pronounced initial cyclic hardening with hardening factors increasing with strain amplitudes. In contrast, the weldments with Haynes 230 and Inconel 82 filler metals displayed short initial cyclic hardening and saturation stages, followed by long continuous cyclic softening. The fractography and microstructure after LCF the tests were characterized with scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Transgranular fracture with multiple crack initiations was the predominant failure mode on the fracture surfaces of both Incoloy 800 base metal and the weldments. TEM examination revealed that planar dislocation slips at the low strain amplitude evolved to wavy slips, eventually forming a cell structure at high strain amplitudes in the Incoloy 800H material as the strain amplitudes increased. However, the weld metal exhibited a planar slip mode deformation mechanism regardless of cyclic strain amplitude in the weldment specimens. The differing cyclic hardening and softening behaviours between Incoloy 800H and its weldments are attributed to the higher strength of the weldment specimens compared to the base metal. In the Incoloy 800H base material specimens, the reverse strains during LCF created wavy dislocation structures, which could not fully recover due to the non-reversible nature of the microstructure. As a result, cells or subgrains formed within the microstructure once created. In contrast, the higher strength of the weld metal in the weldment specimens significantly suppressed the formation of wavy dislocation structures, and deformation primarily manifested as planar arrays of dislocations.

(Invited) Nanostructured Silicon Loaded with FePt Nanoparticles – a Composite with High Energy Product

In this work silicon nanotubes (SiNTs) and porous silicon (PSi) are loaded with Co nanoparticles (NPs) and hard magnetic FePt nanoparticles. These composite systems are used as platform to create nanomagnet-arrays. The magnetic response of FePt-loaded composite materials is investigated, which have potential in high-performance magnets and as rare earth magnet alternatives. These results are compared with the PSi/SiNTs-Co composites. PSi/FePt demonstrates superior hard magnetic behavior with a higher coercivity and remanence compared to SiNTs/FePt. Varying the Fe molar ratio in deposits results in a small variation of the coercivity of about 5%. FePt-loaded samples consistently show increased coercivity and remanence compared to Co-loaded samples, with PSi exhibiting a stronger effect compared to SiNTs. The dependence of the magnetization on the temperature between 4.2 K and 300 K shows a decrease of the coercivity with increasing temperature, which is common for a ferromagnetic behavior. High temperature magnetization measurements allow to determine the Curie Temperature (TC) of PSi and SiNTs loaded with FePt NPs. The PSi templated system offers a lower TC compared to the SiNTs composite system.

Impact of laser shock peening on microstructure hardness and corrosion properties of AA6061 alloy

In recent times, laser shock peening (LSP) has emerged as a pioneering technique to modify the surface properties of various aluminium-based alloys. In this study, AA6061 was treated by single and multi-pass LSP, and its microstructure, hardness, and corrosion behaviour were investigated. Microstructural studies were performed using X-ray diffraction, electron back-scattered diffraction, and transmission electron microscopy methods. Texture studies were conducted using the neutron diffraction method, while hardness measurements were carried out using a Vickers hardness tester. Corrosion studies were conducted using the potentiodynamic method, and surface examination was performed using scanning electron microscopy. The results indicate that laser peening led to the dissolution of strengthening precipitates, resulting in a microstructure characterized by a greater volume of low-angle grain boundaries and dense dislocations. The texture index of laser-peened specimens decreased drastically to 1.1952 and 1.0970, with a significant rise in the volume fraction of Goss, S, and brass components. Specimens subjected to a single LSP pass exhibited a maximum hardness of 132.4 HV and better resistance to pitting, with Ecorr and Icorr values of −0.6721 V and 0.0043 A/cm2, respectively, while multiple LSP passes resulted in reduced hardness and pitting resistance due to excess heat.

Nanocrystalline/Amorphous Tuning of Al-Fe-Nb (Mn) Alloy Powders Produced via High-Energy Ball Milling.

The demand for advanced Al-based alloys with tailored structural and magnetic properties has intensified for applications requiring a high thermal stability and performance under challenging conditions. This study investigated the phase evolution, magnetic properties, thermal stability, and microstructural changes in the Al-based alloys Al82Fe16Nb2 and Al82Fe14Nb2Mn2, synthesized via mechanical alloying (MA), using stearic acid as a process control agent. The X-ray diffraction results indicated that Al82Fe16Nb2 achieved a β-phase solid solution with 13-14 nm crystallite sizes after 5 h of milling, reaching an amorphous state after 10 h. In contrast, Al82Fe14Nb2Mn2 formed a partially amorphous structure within 10 h, with enhanced stability with additional milling. Magnetic measurements indicated that both alloys possessed soft magnetic behavior under shorter milling times (1-5 h) and transitioned to hard magnetic behavior as amorphization progressed. This phenomenon was associated with a decrease in saturation magnetization (Ms) and an increase in coercivity (Hc) due to structural disorder and residual stresses. Thermal stability analyses on 10 h milled samples conducted via differential scanning calorimetry showed exothermic peaks between 300 and 800 °C, corresponding to phase transformations upon heating. Post-annealing analyses at 550 °C demonstrated the presence of phases including Al, β-phase solid solutions, Al₁3Fe₄, and residual amorphous regions. At 600 °C, the Al3Nb phase emerged as the β-phase, and the amorphous content decreased, while annealing at 700 °C fully decomposed the amorphous phases into stable crystalline forms. Microstructural analyses demonstrated a consistent reduction in and homogenization of particle sizes, with particles decreasing to 1-3 μm in diameter after 10 h. Altogether, these findings highlight MA's effectiveness in tuning the microstructure and magnetic properties of Al-Fe-Nb (Mn) alloys, making these materials suitable for applications requiring a high thermal stability and tailored magnetic responses.