Hardness Enhancement Research Articles

Enhancement of Strength and Hardness in Copper–Chromium–Zirconium Alloy Using Single‐Pass Multi‐Angular Twist Channel Extrusion: A Microstructural and Deformation Study

Herein, the strength and hardness of copper–chromium–zirconium alloy are enhanced in a single pass by a severe plastic deformation (SPD) technique called the multiangular twist channel extrusion (MATE) process. In equal channel angular pressing (ECAP) and twist extrusion (TE), requisite strain and uniformity are achieved through several extrusion passes. MATE is a single‐pass novel SPD technique developed by integrating TE with the ECAP followed by a direct channel zone. The deformation behavior of metal in the MATE process is elucidated through experimental and microstructural studies conducted in each zone. The MATE‐processed Cu–Cr–Zr alloy achieves a hardness of 184.4 Hv and a tensile strength of 645.2 MPa, reflecting an increase of 80.43% and 69.7%, respectively, relative to the annealed condition. The electrical conductivity of the MATE‐processed Cu–Cr–Zr alloy decreases to 74.29% International Annealed Copper Standard. The electron backscatter diffraction investigation reveals an average grain size of 2.8 μm, with 61% comprising low‐angle grain boundaries, while the calculated dislocation density, from X‐ray diffraction analysis, is 3.93 × 1014 m−2. The transmission electron microscopy image verifies the existence of dislocations and precipitates in the Cu–Cr–Zr alloy. The experimental and microstructural findings in each zone have aligned effectively.

Microstructural evolution and hardening mechanisms in A286 superalloy thin-walled tubes subjected to cold forging

This paper aims to elucidate the microstructural evolution and hardening mechanisms in the thin-walled tube of A286 rivet sleeves subjected to cold forging. The strain distribution, microstructure, and hardness changes within the thin-walled tube were analyzed using Optical Metallography, Electron Backscatter Diffraction, a microhardness tester, and numerical simulations. The results indicate that cold forging leads to a 54% increase in the tube’s maximum hardness compared to the initial billet. Notable hardness gradients are observed along both the axial (329–356 HV) and radial (343–370 HV) directions. This hardness enhancement primarily originates from grain boundary strengthening and dislocation strengthening. The non-uniform strain distribution in the tube causes varying degrees of hardening effect, contributing to the observed hardness gradient. Additionally, Cold forging promotes the development of {111} fiber textures oriented parallel to the normal direction within the tube. These findings provide valuable insights for optimizing cold forging process parameters and enhancing the quality of aerospace blind rivets.

Analysis of microstructure and hardness of a double-layered AA7075 build developed by friction stir additive manufacturing

In this work, a double-layered AA7075 build was formed using the friction stir additive manufacturing technique, and the microstructural evolution along the build and hardness were investigated. Build cross-section and microstructural evolution were conducted using optical macroscopy, electron backscattered diffraction, and transmission electron microscopy, while hardness measurement was conducted using a Vickers hardness tester. Solid-state deformation resulted in a defect-free build with a basin-shaped cross-section. Recrystallized microstructures were observed along the build due to dynamic recrystallization, with grain sizes measuring 2.32, 2.70, and 2.82 μm at the top, center, and bottom, respectively. Maximum hardness of 146.3 HV was observed at the top of the build, and the values dropped at the overlapped and bottom zones due to grain growth caused by excess thermal cycle. Enhancement in hardness is attributed to strain hardening, grain boundary strengthening, and Orowan strengthening mechanisms.

Significant enhancement of hardness and stability in the Sc Ta1-B2 transition-metal diborides system

Significant enhancement of hardness and stability in the Sc Ta1-B2 transition-metal diborides system

Effect of Carbon Black Dispersion on Hardness Properties of Polyurethane Elastomer for Wheel Dolly

This study investigates the enhancement of hardness and mechanical properties of PPG-based polyurethane elastomers for wheel dolly applications through the incorporationof carbon black and the use of Plast 002 as a dispersing agent. The challenge addressed is the inherent lower mechanical performance of cost-effective PPG-based polyurethane compared to traditional polyester-based alternatives. Three dispersion methods were explored: the impactof Plast 002 on carbon black distribution, varying carbon black content (1, 3 and 5 phr), and comparing high-speed agitation with ultrasonic dispersion. The results indicate that without Plast 002, carbon black tends to agglomerate, leading to significant differences in hardness between the top and bottom of samples, particularly at higher carbon black contents. The addition of Plast 002 significantly improved dispersion, resulting in uniform hardness. Ultrasonic dispersion had more effective than high-speed agitation, delivering higher and consistent hardness values across the sample. Optimal mechanical performance was observed at 1 and 2 phr of carbon black, where tensile strength and modulus improved. The optimized carbon black content and ultrasonic dispersion can significantly enhance the performance of PPG-based polyurethane, offering a more economical alternative to polyester-based polyurethanes for wheel dolly applications.

Microstructure and Mechanical Properties of 28 % High Chromium White Cast Iron

The chemical composition of the metal and carbide phase, hardness, and common mechanical properties of cast iron, ICH28H2 cast iron, a type of high-chromium white cast iron, and the dependence of hardening, annealing, and tempering process types were studied. Therefore, annealing and hardening heat treatments were employed, and the results were compared to measurements in the as-cast state. The metal matrix exhibited content within the range of 16.8% to 19.7% Cr and 71.9% to 76% Fe, while the carbide phase showed 63.4% to 64.7% Cr and 23% to 24.8% Fe. The Cr carbide in high Cr white iron primarily appeared as (Fe, Cr)7C3 type, leading to the calculated chemical formula of the eutectic carbide as (Fe2Cr5)C3. The as-cast white iron displayed a hardness of 53 HRC, which increased marginally to 56.2 HRC after hardening. This suggests that the 28% Cr white iron alloy does not exhibit a significant hardness enhancement compared to the cast state, attributed to its high Cr content. The hardness of the metal phase directly influences the overall hardness change of the alloy, while the carbide hardness is dependent on its Cr content. Abrasive wear studies revealed that 28% Cr white cast iron exhibited superior wear resistance in the as-cast state compared to the hardened state, aligning with research indicating that cast iron demonstrates optimal wear resistance in its cast state.

Optimisation of LPBF process parameters and residual stress analyses of Invar-10wt% TiC and Invar-10wt% TiN metal matrix composites

AbstractTo enhance the mechanical properties of Invar (Fe–36Ni) for a broader range of applications, reinforcement with Titanium Carbide (TiC) and Titanium Nitride (TiN) was investigated. Laser powder bed fusion was used to manufacture the Invar metal matrix composites with TiC and TiN respective additions. Optimization of the process parameters was conducted using response surface methodology. The optimal parameters for Invar-TiC are 180 W laser power with a scanning speed of 450 mm/s, while for Invar-TiN, the optimal parameters are 190 W laser power with a scanning speed of 400 mm/s. High densities (> 99%) and significant improvements in hardness were achieved. X-ray diffraction and scanning electron microscopy analyses confirmed the uptake of TiC and TiN into the Invar matrix, leading to the enhanced properties. Residual stress evaluation through non-destructive neutron diffraction (ND) measurements and inherent strain modelling (ISM) simulations was done. The addition of TiC and TiN to the Invar matrix influenced the stress distribution, with Invar-TiC showing higher tensile stresses due to its thermal conductivity properties, and higher compressive stresses due to grain refinement. Close agreement was found between the ISM simulation and ND-measured results, indicating predominantly compressive stresses in the interior and tensile stresses on the sample surfaces. These findings demonstrate the potential for developing Invar-based MMCs with enhanced mechanical properties through LPBF. Due to the enhancement in hardness and, thus, wear resistance, the investigated compositions offer applications in parts and tools used in rough and demanding conditions, such as mouthpieces for extrusion or turbine blades in water turbines.

Plasma sprayed Titanium- Nanodiamond composite coatings with enhanced mechanical properties

This research aims to investigate the mechanical properties of plasma-sprayed Ti-nanodiamond (Ti-NDs) composite coatings, leveraging the zero-dimensional structure, outstanding mechanical properties, and remarkable chemical and thermal stability of nanodiamonds (NDs) as a prudent choice for enhancing the mechanical properties of Ti coatings. The deposited coatings were tested for their mechanical properties, including Ultimate Tensile Strength (UTS), Yield Strength (YS), Hardness, and Elastic Modulus. The relative density of the coatings experienced a substantial increase with the addition of NDs, from 82.31% to 94.79% for 1wt%. This improved relative density was attributed to the effective melting of powders under the plasma plume facilitated by the presence of NDs having higher thermal conductivity. Consequently, a remarkable improvement of 22.7% in UTS and 20.5% in YS, accompanied by a considerable enhancement in hardness (20%) and elastic modulus (26.7%). These enhancements in the coating properties are credited to the excellent mechanical properties and higher thermal conductivity of NDs, facilitating the uniform melting of the Ti matrix and, consequently, leading to improved density and the formation of TiC within the coatings.

Microstructure Evolution and Wear Behavior of Stellite12 Coating Prepared by Laser-Directed Energy Deposition on H13 Steel

Laser-directed energy deposition (LDED) was employed to apply a Stellite12 coating onto an H13 steel substrate. This study explored the effects of processing parameters on the dimensions of the deposited tracks. Comprehensive examinations were conducted on the coatings to assess their phase composition, microstructure, and wear resistance properties. The relationship between microstructural characteristics and thermal field was investigated through a synergy of numerical simulations and experimental analyses. The findings revealed that the Stellite12 coating displayed a heterogeneous microstructure with epitaxial growth and a slight texture across successive layers. The primary phase comprised a γ-Co solid solution and M23C6 carbides, contributing to a significant enhancement in hardness, which was observed to be 2.2 times higher than that of the substrate. The coating demonstrated superior performance in terms of lower friction coefficients and reduced wear rates at both room and elevated temperatures. The predominant wear mechanisms identified were oxidative wear. These results underscore the promising applications of Stellite12 coatings in industrial contexts facilitated by LDED technology.

Evolution of microstructure and properties of nanocrystalline NiCo alloy under high-energy laser shock

In this study, nanocrystalline NiCo alloy was prepared through electrodeposition and subjected to high-energy laser shock (HELS) treatment to investigate the influence of laser shock on the microstructures and properties. An analysis of phase composition, microstructural evolution, texture evolution, and hardness was conducted. The results indicated that under HELS, there was no change in phase composition, while there was a slight reduction in grain size, as well as in the quantities of Low-angle grain boundaries (LAGBs) and twin boundaries (TBs). The texture evolution revealed that HELS led to a more uniform overall texture due to grain boundary (GB) mediate deformation mechanisms, along with the generation of a significant amount of 9R phases, causing a shift in texture orientation from (110) to (100). The internal structure of nanocrystalline NiCo showed an accumulation of numerous dislocations post-laser shock, with randomly oriented dislocations interacting to form Lomer-Cottrell Locks (L-C Locks) and 9R phases. Additionally, interactions with large stacking faults (SFs) also resulted in their dissociation into multiple 9R phases. The hardness enhancement was mainly attributed to the accumulation of dislocations within the grain and the generation of a significant quantity of 9R phases.

Effect of ultrasonic surface rolling extrusion on microstructural evolution and wear resistance of laser-clad CoCrFeMnNi high-entropy alloy with low stacking fault energy

Ultrasonic surface rolling extrusion (USRE) was employed to strengthen face-centered cubic (FCC) phase CoCrFeMnNi high-entropy alloy (HEA) coatings prepared by laser cladding. The influence of USRE's static load on the microstructure, mechanical properties, and wear resistance of the coatings was examined to elucidate the grain refinement mechanism. The findings indicate that USRE preserves the phase composition of the CoCrFeMnNi HEA coatings. After USRE at loads of 100 N, 200 N, and 300 N, the measured thicknesses of the severe plastic deformation layers are 2.51 μm, 3.03 μm, and 3.45 μm, respectively. The process triggers dislocation multiplication, which accumulates at the boundaries of Mn-rich regions, forming dislocation cells and evolving into subgrains, thereby refining the grain structure under severe plastic deformation. Statistical analysis reveals that the dislocation density within the grains is 7 × 1014 m−2, while at the grain boundaries, the dislocation density is 4 × 1015 m−2. The average grain size has been refined from 97.7 μm to 34.7 μm. Both microhardness and wear resistance escalate with increased static load, with the maximum microhardness of 347 HV and the minimum wear rate of 2.6 × 10−5 mm3·N−1·m−1 achieved at a 300 N static load. This hardness enhancement is due to the combined effects of grain refinement, dislocation strengthening, and sub-grain formation. The wear mechanisms for the USRE-treated CoCrFeMnNi HEA coatings include adhesive wear, abrasive wear, and oxidative wear. While adhesion and abrasion diminish with higher static pressures, oxidative wear intensifies.

Magnetic response and hardness enhancement by spontaneous directional coarsening of Fe2AlB2 in quasicrystal-rich matrix

This study investigates the Al55Cu20Fe15B10 alloy system to understand the characteristics of the Fe2AlB2 (Cmmm) phase and its interactions with a quasicrystal-rich matrix. The alloy’s composition was chosen for its boron content, which promotes the formation of well-defined Fe2AlB2 crystals. We examined how different heat treatments affect the alloy’s microstructure, magnetic properties and hardness. Microstructural and Electron Backscatter Diffraction analyses revealed the stable icosahedral Al59Cu27Fe12B2 quasicrystalline phase and a metastable Al70Fe20Cu10 approximant that is isostructural with C2/m Fe4Al13. Additionally, the alloy contained Al-Cu phases known from meteorites, such as AlCu stolperite and Al2Cu khatyrkite. Heat treatments at 706∘C and 828∘C yielded favorable microstructure for ballistic armor, characterized by Fe2AlB2 lamellae embedded within the quasicrystalline matrix, reinforced by AlB2 precipitation on the grain boundaries. Vickers hardness improvements were attributed to Hall-Petch strengthening and grain orientation effects. Notably, annealing at 943∘C nearly tripled the magnetic entropy change. Quantum Diamond Microscopy confirmed that Fe2AlB2 significantly contributed to magnetization. The improvement of magnetic properties was found to be due to preferential orientation of Fe2AlB2 grains along the [010] zone axis, as a consequence of directional coarsening induced by annealing. The enhanced magnetocaloric properties observed at 943∘C are primarily due to intrinsic changes in the Fe2AlB2 phase rather than strain relaxation or phase contributions from the quasicrystalline matrix.

Effect of tea polyphenols on the quality of frozen cooked noodles

AbstractBackground and ObjectivesThe growing consumer demand for natural, healthy, and convenient food options has led to the rising popularity of frozen cooked noodles (FCN). Tea polyphenols (TPs), known for their diverse biological activities, are increasingly being utilized as a natural food additive in research and development. Therefore, this study aims to investigate the effects of TPs on the thermal and pasting properties of wheat flour as well as their influence on the quality of FCN.FindingsThe results from differential scanning calorimeter and RVA analyses showed that TPs did not significantly affect the thermal and pasting properties of wheat flour. However, the addition of low‐dose TPs (<1.5%) improved the quality of FCN during storage. Texture and tensile analyses demonstrated an enhancement in hardness, chewiness, resistance, and an increase in resistant starch content in the noodles. Low‐field nuclear magnetic resonance findings revealed an increase in the proportion of strongly bound water, accompanied by a decrease in free water content. Scanning electron microscopy observations illustrated a well‐developed gluten network structure. In contrast, the incorporation of 1.5% TPs adversely affected the quality of FCN.ConclusionsThe appropriate integration of TPs plays a significant role in alleviating the quality degradation of FCN during storage.Significance and NoveltyThis study provides a theoretical basis for the development of polyphenol‐enriched flour products and functional foods.

Microstructure evolution and properties of (Nb,M)C (M=Ti,V and Zr) reinforced Ni-WC coatings by laser cladding

To enhance the surface properties of AISI 1045 steel, high-performance composite carbide-reinforced coatings were prepared using laser cladding technology. Specifically, (Nb,M)C (M = Ti, V, and Zr) reinforced Ni-WC coatings were developed. The effects of various composite carbides on the microstructure and properties of the coatings were examined through a combination of first-principles calculations and experimental methods. Initially, the microstructures of (Nb,M)C (M = Ti, V, and Zr) were constructed using first-principles calculations, and the microscopic mechanical and electronic properties of these composite carbides were determined. The impact of different doping elements on the properties of the composite carbides was investigated. Subsequently, an in-situ synthesis system was designed to fabricate the composite coatings. The feasibility of synthesizing the composite carbides (Nb,M)C (M = Ti, V, and Zr) within the laser cladding coatings was confirmed using XRD, SEM, and EDS techniques. Additionally, the formation mechanism of the composite carbides was analyzed. Under different element doping conditions, the reinforcement phase in the composite coating exhibited various grain morphologies, with (Nb0.5Ti0.5)C grains showing the best particle size and density. Microalloyed interfaces were observed at the WC interfaces in each coating, indicating strong bonding between WC and the FCC matrix. The presence of WC also improved the fineness of the surrounding phase structure. Due to differences in kinetics and thermodynamics, a core-shell structure of (Nb0.5Ti0.5)C-core and WpC-shell was observed in the (Nb0.5Ti0.5)C coating. Friction-wear tests revealed that this core-shell structure helps alleviate crack sensitivity between the reinforcing phase and the matrix. Hardness analysis showed that the average hardness of the (Nb0.5Ti0.5)C, (Nb0.5V0.5)C, and (Nb0.5Zr0.5)C coatings was 62.89 HRC, 60.91 HRC, and 58.27 HRC, respectively. Among these, (Nb0.5Ti0.5)C demonstrated the most significant hardness enhancement for AISI 1045 steel, achieving a 3.51-fold increase. In the friction and wear tests, the (Nb0.5Ti0.5)C coating exhibited the best wear resistance. The primary friction-wear mechanisms of the coatings were found to be adhesive wear, oxidative wear, and minor abrasive wear. These research findings provide a theoretical basis for the preparation of high-performance composite carbide-reinforced coatings using laser cladding.

Enhanced mechanical hardness of mixed-phase BiFeO3 films through quenching

Due to epitaxial strain, BiFeO3 (BFO) thin films exhibit a morphotropic phase boundary with coexisting rhombohedral-like (R-like) and tetragonal-like (T-like) phases. The T-like phase, distinguished by its large c/a ratio and giant polarization, has garnered extensive interest. In this work, by quenching an epitaxial mixed-phase BFO thin film grown on a LaAlO3 substrate, a pronounced transition from the R-like to the T-like phase is observed. This transition is concomitant with improved phase structure stability under the force field induced by an atomic force microscope tip. PeakForce Quantitative NanoMechanics mapping reveals that the T-like phase exhibits a higher Young's modulus than the R-like phase, signifying an overall enhancement in the mechanical hardness of the BFO film. This work introduces a simple but powerful approach to manipulating the fraction of the T-like phase in the mixed-phase BFO films, presenting prospects for enhancing their performance and expanding their application range in advanced techniques.

Characterisation of AZ31/TiC composites fabricated via ultrasonic vibration assisted friction stir processing

In this study, the effect of ultrasonic vibration during Friction Stir Vibration Processing (FSVP) on the microstructure and mechanical behaviour of AZ31/TiC surface composites was investigated. Specifically, Titanium Carbide (TiC) particles were introduced as a reinforcement (15 vol%) into the magnesium alloy AZ31 using both Friction Stir Processing (FSP) and FSVP. Comprehensive examinations were carried out to analyse the microstructure, hardness, and tensile behaviour of the resulting composites. The study revealed significant improvements in mechanical properties due to the application of ultrasonic vibration during FSP. Firstly, the stir zone region was found to be free from voids, enhancing material flow and promoting even dispersion of TiC powders within the matrix. Secondly, refinement of grains was observed due to dynamic recrystallization and the pinning effect imposed by TiC particles, leading to the formation of more dislocations in the composite and indicating a considerable alteration in the material’s structure. Importantly, the vibration during FSP introduced an auxiliary energy source, resulting in a remarkable enhancement in both hardness and tensile strength. Compared to the AZ31/15 vol% TiC FSP composite, the composites produced via FSVP exhibited a grain size reduction of about 64% and improvements in hardness and ultimate tensile strength (UTS) of about 55% and 21%, respectively. Notably, these improvements were achieved without compromising the ductility of the composite, which remained at appreciable levels.

Effect of ZrB2 addition on microstructure and mechanical properties of 95W-HEA alloys

In tungsten heavy alloys, the substitution of conventional binders with novel high entropy alloys and the addition of rare metal borides have demonstrated considerable promise in enhancing comprehensive performance. In this study, 95W-5CoCrFeNiMn -x ZrB2 (x = 0.1, 0.2, 0.4, 0.6, 0.8) was synthesized by powder metallurgy method and characterized. The results show that: the spherical tungsten grains are distributed in binder network, and the added ZrB2 reacts with oxygen to generate ZrO2 and B2O3, which will affect the microstructure and properties of the alloys. An increase of ZrB₂ content results in a reduction in alloy density, accompanied by an enhancement in hardness; the changes in grain size, contiguity, and solid volume fraction present a trend of first falling and then rising, and the minimum value is obtained when the addition is 0.4 wt%. At this time, 95WHEAs-0.4 ZrB2 presents the best comprehensive performance, exhibiting an average grain size of 16.80 μm, a relative density of 96.10 %, a hardness of 411.68 HV1, and a compressive strength of 2457.64 MPa. The primary fracture mode observed in the alloys is W-binder interfacial separation, with a minor occurrence of tungsten cleavage when the ZrB2 addition is within an optimal range.

Mechanisms of hardness enhancement in CrB2 thin films with varying VB2 concentrations

Transition metal borides are well-known for their high hardness, excellent wear resistance, chemical inertness, and electrical conductivity, making them promising for a wide range of applications. Understanding the interconnections between material structure, composition, and mechanical properties is essential for designing and synthesizing effective coatings. This study systematically investigates the structural and mechanical properties of CrB₂ thin films with varying concentrations of VB₂ (0–10 wt%), focusing on structure, hardness, elastic behavior and deformation characteristics mechanisms through atomic force microscopy and nanoindentation measurements. The results show that increasing VB₂ content leads to the formation of island cluster structures, which significantly strengthens atomic bonds and, in turn, enhances the hardness of the thin films. As particle size decreases, the higher proportion of surface atoms and increased surface energy have a more pronounced effect on the mechanical properties. In particular, the addition of VB₂ up to 10 wt% in CrB₂ thin films results in a marked improvement in superhard properties. 26 % increase in hardness value is also influenced directly by the changes in Young's modulus and Poisson's ratio that depend on the VB₂ concentration.

Effects of non-isothermal aging and microalloying on precipitation strengthening for Al-Mg-Si alloys

The impacts of non-isothermal aging (NIA) and microalloying (Ag and/or Cu) on precipitation strengthening and mechanical properties in Al-Mg-Si alloys are investigated using advanced microscopic analysis techniques combined with tensile testing. The NIA treatment exhibits different age hardening for this alloy with different compositions. The Ag-Cu-added A3 alloy exhibits the most significant enhancement in peak hardness under NIA treatment than that of the isothermal aging (IA), while only marginal increases are observed for the other alloys (the base A1 alloy and the Cu/Ag-added alloys). The optimal NIA treatment for the Ag-Cu-added A3 alloy is identified as follows: 200 °C × 1 h + cooling down to 180 °C at 20 °C/h. This specific treatment leads to a peak hardness of 139.0 HV and an ultimate tensile strength of 384.0 MPa for this alloy, which is 16.0 HV higher than that of the base Al-Mg-Si alloy when subjected to IA at 180 °C. These findings provide valuable insights for the advancement of novel aluminum alloys and heat treatment methodologies.

Investigation into graphene nano-platelet reinforced aluminum coating on mild steel substrate

Pure Aluminum (Al) and composite coating of Al with the reinforcement of carboxyl functionalized graphene nano-platelet (fGNP) were successfully electrodeposited on mild steel. The chloroaluminate ionic liquid melt was used for electrodeposition under ambient conditions. Electron probe microanalyzer analysis and Raman spectroscopy revealed the existence of fGNP in the composite coating. 3D optical profilometry of both coatings depicted the changes in the surface because of the presence of fGNP in the composite coatings. The micro-hardness test demonstrated enhancement in hardness, which can be ascribed to the existence of fGNP in the composite coating.