Improvement Of Mechanical Properties Research Articles

Enhancing concrete durability and strength: An innovative approach integrating abrasion and cement slurry treatment for recycled coarse aggregates

AbstractThis study introduces a novel approach to enhance the durability and strength of concrete by integrating abrasion and cement slurry treatments on surface‐treated recycled coarse aggregates (STRCA). Initial abrasion treatment removes aged mortar from the recycled coarse aggregate (RCA) surface, while subsequent cement slurry modification provides a fresh surface, reinforcing the bond with the concrete matrix. Through detailed material analyses including x‐ray diffraction, scanning electron microscopy, and energy‐dispersive x‐ray, microstructural changes are evaluated alongside compressive strength, drying shrinkage, electrical resistivity, and chloride ion penetration of STRCA‐based concrete. Results indicate significant improvements in mechanical properties and durability as the treatments eliminate mortar and enhance the interfacial connection with cement paste. Notably, a substantial 29.37% strength enhancement is observed at 25% replacement (STRCA 25), demonstrating treatment efficacy. While a reduction of 11.58% occurs at 100% replacement (STRCA 100), up to 75% replacement shows minimal strength loss, with optimal enhancements at 50% replacement. Additionally, STRCA concrete exhibits lower drying shrinkage (11%–20% reduction) and increased electrical resistivity (28%–36% rise), indicating improved durability at 100% replacement. Enhanced resistance to chloride ion penetration is also evident, with a 22%–28% increase at 100% replacement compared to conventional RCA. Overall, this study highlights the effectiveness of dual treatments for enhancing concrete properties using STRCA.

Synergistic improvement of erosion-corrosion resistance and mechanical properties of nickel aluminium bronze alloy by the addition of Cr

Synergistic improvement of erosion-corrosion resistance and mechanical properties of nickel aluminium bronze alloy by the addition of Cr

Strengthening mechanism of sub-nano Ni3P and Cu3P phases particles on the Pb–Sn bronze alloy

The influence of the sub-nano Ni3P and Cu3P phases on the microstructure, mechanical properties, and strengthening mechanism of Cu–20Pb–5Sn-xP (x = 0,0.05,0.1,0.3,0.5) alloy were discussed under the addition of P to obtain a new Pb–Sn bronze alloy applying for bimetallic cylinder block. The results showed that the tensile strength and hardness of the Pb–Sn bronze alloy increase with the P contents, while the elongation increased first and then decreased. The main strengthen mechanism was that sub-nano Ni3P and Cu3P phases dispersed in the matrix, hindering the movement of dislocations during deformation. Additionally, the grain refinement also contributed to the improvement of mechanical properties. The Ni3P phase is easier to form than the Cu3P phase. And it is easier to combine with the matrix and more stable. The Ni3P and Cu3P phases were studied by using different characterization techniques, such as OM, SEM, EDS, XRD, TEM and First-principles, Phase diagram calculation method. When P is added to the alloy, the Ni3P phase first appears in the alloy, and when the P content increases to more than 0.3 wt%, the Cu3P phase begins to appear. This is because the Ni3P phase is easier to form than the Cu3P phase and is more stable. Only after part of P reacts with Ni dissolved in copper to form Ni3P, the remaining P and Cu can form Cu3P.

Enhancing fusion welding in die-cast Mg alloys: A combined ultrasonic vibration and hot rolling approach for porosity reduction, microstructure refinement, and mechanical property improvement

Severe weld porosity has led the industry to believe that die-cast magnesium alloys cannot be fusion welded. To address this challenge, a new process of ultrasonic vibration coupled with hot rolling was employed to eliminate porosity, and the mechanism associated with weld porosity in die-cast magnesium alloys was analyzed in detail. Unlike conventional welding processes, ultrasonic vibration coupled with hot rolling is effective and efficient. In this study, a roller with ultrasonic vibrations is synchronized with the molten pool to apply pressure to the weld, which is in a semi-solid state on the upper surface. The results showed that hot rolling and ultrasonic vibration coupled with hot rolling could eliminate 78.12 % and 85.5 % of the porosity, respectively. Compared to hot rolling, the ultrasonic vibration coupled with the hot rolling process resulted in smaller and fewer porosities and finer β-Mg17Al12. This is attributed to the cavitation effect of ultrasonic vibration that promotes bubble overflow and breaks the β-Mg17Al12 dendrites in the melt pool, as well as the thermal effect that improves the plasticity of the weld. Furthermore, after closing the porosity under pressure, recrystallized grains will be produced around it. Tensile test results indicated that hot rolling was able to increase the ultimate tensile strength by 84.21 % and elongation by 44.03, whereas ultrasonic vibration coupled with hot rolling was able to increase the ultimate tensile strength by 244.46 % and elongation by 71.70 %. Combining the micron-scale industrial computed tomography results with theoretical calculations, it is found that the porosity of die-cast magnesium alloys is mainly caused by nitrogen, and they originate from gas entrapment during the die-casting process; further, the formation mechanism of die-cast magnesium alloys' fusion-welding porosity is revealed in detail. A physical model of the formation process of welded porosity morphology was established, and the analysis suggested that the pattern of the inner wall of the porosity was related to the Kelvin–Helmholtz instability. This research is expected to improve the weld quality of alloys manufactured by the die-casting process.

Effect of morphology and structure of MXene Ti3C2Tx on mechanical, thermal properties of PEEK nanocomposite

As a new type of 2D nanomaterials, MXene can improve the thermal, mechanical, and tribological performance of polymers as a reinforcing additive. However, there is a lack of systematic research on the impact of the morphology and structure of MXene on the performance of nanocomposite. In this study, MXene Ti3C2Tx with different morphologies was prepared and the effect of morphologies on the mechanical, thermal and creep properties was explored. Mechanical test results illustrate that the addition of MXene Ti3C2Tx fillers contributes to the improvement of mechanical properties. Among the three fillers, d-Ti3C2Tx exhibit a better reinforcement effect in PEEK than m-Ti3C2Tx and f-Ti3C2Tx, which are greatly related to the morphology of the MXene Ti3C2Tx, the interface and defects between the PEEK and the MXene Ti3C2Tx. After adding MXene to the PEEK matrix, the internal friction of PEEK molecule segment motion would aggrandize and the composites would deform and take longer relaxation times. Due to the larger interface between d-Ti3C2Tx and the matrix, the composite material exhibits the smallest creep strain magnitude and permanent deformation behavior after recovery. However, the high activity of 2D MXene nanomaterials resulted in a decrease in the thermal stability of PEEK.

Tribological and mechanical properties improvement of G20CrNiMo alloy via fabricating gradient composite layer through ultrasonic strengthening grinding process

Fretting wear is one of the main causes of damage failure at the contact interface, which significantly limits the reliable application of mechanical parts. To address this issue, a composite microstructure comprising a gradient structure, α-Al2O3 particles, and micro-dimples was fabricated on the G20CrNiMo alloy by an improved method of ultrasonic strengthening grinding process (USGP). Subsequently, the fretting resistance and mechanical properties of the treated G20CrNiMo alloy were investigated. The results indicated that USGP could significantly enhance mechanical strength and wear resistance properties. The USGP-treated sample demonstrated an increment of approximately 25.32 % in tensile strength compared to the untreated sample. It also exhibited reductions of about 19.61 % and 49.56 % in friction coefficient and wear volume, respectively. After USGP treatment, the gradient structure incorporating dense dislocation and high-angle grain boundaries (HAGBs) limited the shear motion of the G20CrNiMo alloy, thereby enhancing its mechanical properties. Furthermore, the synergistic effect of gradient structure, Al2O3 particles, and micro-dimples effectively restricted shear deformation and formed a supplementary glaze to further improve its fretting wear resistance.

Multi-material structures of Ti6Al4V and Ti6Al4V-B4C through directed energy deposition-based additive manufacturing

The demand for advanced materials has driven innovation in titanium alloy design, particularly in the aerospace, automotive, and biomedical sectors. Additive manufacturing (AM) enables the construction of multi-material structures, offering potential improvements in mechanical properties such as wear resistance and high-temperature capabilities, thus extending the service life of components such as Ti6Al4V. Directed energy deposition (DED)-based metal AM was used to manufacture radial multi-material structures with a Ti6Al4V (Ti64) core and a Ti6Al4V-5 wt.% B4C composite outer layer. X-ray diffraction analysis and microstructural observation suggest that distinct B4C particles are strongly attached to the Ti6Al4V matrix. The addition of B4C increased the average hardness from 313 HV for Ti6Al4V to 538 HV for the composites. The addition of 5 wt.% B4C in Ti6Al4V increased the average compressive yield strength (YS) to 1440 MPa from 972 MPa for the control Ti6Al4V, i.e., >48% increase without any significant change in the elastic modulus. The radial multi-material structures did not exhibit any changes in the compressive modulus compared to Ti6Al4V but displayed an increase in the average compressive YS to 1422 MPa, i.e., >45% higher compared to Ti6Al4V. Microstructural characterization revealed a smooth transition from the pure Ti6Al4V at the core to the Ti64-B4C composite outer layer. No interfacial failure was observed during compressive deformation, indicating a strong metallurgical bonding during multi-material radial composite processing. Our results demonstrated that a significant improvement in mechanical properties can be achieved in one AM build operation through designing innovative multi-material structures using DED-based AM.

Advancing sintering and matrix-reinforcement interaction in Al/AlN metal matrix composites through use of novel AlN reinforcement

Demand for energy-efficient transportation has led to increased use of lightweight aluminium alloys due to their exceptional strength-to-weight. Meanwhile, aluminium-based metal matrix composites (MMCs) are being developed to enhance wear resistance and strength. However, traditional ceramic reinforcements often have poor bonding with the matrix, compromising performance. Here, we demonstrate the use of a novel ex-situ AlN reinforcement powder to enhance sintering and interfacial bonding for powder metallurgy preparation of Al/AlN MMCs. We compared two series of Al/AlN MMCs featuring 10 vol.% ex-situ AlN reinforcement, one prepared using commercial AlN powder, and the other using our novel AlN reinforcement prepared by low temperature direct nitridation of Al powder. Metallic Al contained in the synthesized reinforcement significantly improved interfacial adhesion between matrix and reinforcement and enhanced densification during sintering. This resulted in a substantial improvement in tensile mechanical properties, with an 11.5% increase in ultimate tensile strength and almost five-fold improvement in ductility compared to composites prepared using the conventional ceramic AlN reinforcement. This study provides a strategy for powder metallurgy production of advanced Al/AlN MMCs with superior physical and mechanical properties.

Effect of heat treatment on microstructure and mechanical properties of 18Ni-350 maraging steel fabricated by Wire and Arc Additive Manufacturing

An 18Ni-350 maraging steel single wall structure was fabricated using Wire Arc Additive Manufacturing (WAAM). Due to the rapid cooling and cyclic heating, elements such as Ni, Ti, and Mo were segregated within the single wall, resulting in a microstructure characterized by coarse primary dendrites and secondary dendrites. Various heat treatment were devised for the samples, encompassing Solution Treatment (ST), Solution + Aging Treatment (SAT), and Direct Aging Treatment (DAT). The findings revealed that elemental segregation persisted when the ST temperature was below 1050 °C, but disappeared when it exceeded 1150 °C, withthe microstructure transitioning from dendritic to equiaxed grains. ST resulted in the decrease of microhardness and tensile strength, but an enhancement in elongation. The effect of DAT was unsatisfactory for the improvement of mechanical properties while SAT could significantly improve them. Transmission Electron Microscope (TEM) analysis showed that a uniform distribution of Ni3Ti and Ni3Mo strengthening phases was formed in the martensitic matrix after SAT. The ultimate tensile strength of the sample reached 2163 ± 42 MPa under the optimal heat treatment condition (SAT 1150 °C-1 h + 480 °C-6 h).

Microstructures, mechanical properties, and strengthening mechanisms of the (NbMoTa)100−xCx refractory medium-entropy alloys

Refractory high/medium-entropy alloys (RH/MEAs) are known for their outstanding performance at elevated temperatures; however, they usually exhibit poor room-temperature plasticity, which can be attributed to the non-uniform deformation that occurs at room temperature. Once cracks nucleate, they will rapidly propagate into vertical splitting cracks. Here, we introduce multiple phases including FCC and HCP phases into the NbMoTa RMEA via appropriate addition of carbon. The results show that multiple-phase synergy effectively suppresses non-uniform deformation, thereby delaying the onset of vertical splitting cracks. An optimal combination of compressive strength-plasticity is achieved by the (NbMoTa)92.5C7.5 alloy. The significant improvement in room-temperature mechanical properties can be attributed to its hierarchical microstructure: in the mesoscale, the BCC matrix is divided by eutectic structures; while at the microscale, the BCC matrix is further refined by abundant lath-like FCC precipitates. The FCC precipitates contain high-density stacking faults, acting as a dislocation source under compressive loading. The HCP phase in the eutectic microstructures, in turn, acts as a strong barrier to dislocation movement and simultaneously increases the dislocation storage capacity. These findings open a new route to tailor the microstructure and mechanical properties of RH/MEAs.

Improvement of Mechanical and Wear Properties of Tungsten Heavy Alloy Using Two-Stage Sintering and Carburizing Processes

Improvement of Mechanical and Wear Properties of Tungsten Heavy Alloy Using Two-Stage Sintering and Carburizing Processes

Mechanical and thermal property analysis and optimization design of hybrid lattice structure based on triply periodic minimal surfaces

Hybrid lattice structures have significant potential in engineering applications owing to their outstanding mechanical and thermal properties. In this paper, an innovative design strategy for hybrid lattice structures is proposed involving the integration of primitive surfaces with truss lattice configurations. This approach allows for the full exploitation of the mechanical and thermal properties inherent in each component, leading to the development of new hybrid lattice structures. Firstly, the quasi-static compression and fluid-solid coupling heat conduction analysis of the hybrid lattice structure is carried out by numerical simulation. Then the effects of surface wall thickness, and truss diameter on the mechanical and thermal properties of the lattice structure are discussed. Additionally, the mechanical performance of the array hybrid lattice structure is evaluated through quasi-static compression experiments. These experimental results are compared with those from the numerical simulations, validating the accuracy of the simulation model. Finally, a multi-objective optimization model targeting specific elastic modulus and heat dissipation performance (indicated by Nusselt number) is established, in response to the demand of aviation and aerospace industries for lightweight, load-bearing, and heat-dissipating multi-functional integrated lattice design. The non-dominated sorting genetic algorithm is utilized to solve the optimal model, and the distribution of feasible solutions and Pareto front are obtained. The results show that the interpenetrating hybrid lattice structure has a greater improvement in mechanical and thermal properties than the primitive surfaces. This research holds significant implications for the design of multi-performance hybrid lattice structures.

3-Pentadecylphenol (PDP) as a Novel Compatibilizer for Simultaneous Toughened and Reinforced PA10,12 Composites.

The utilization of polyamide 10,12 (PA10,12) composites in various industries has been limited constrained by their inherent low toughness, making it a challenge to achieve a balance between toughness and structural integrity through conventional elastomer addition strategies. Herein, we introduce a straightforward method for the concurrent toughening and reinforcement of PA10,12 composites. This is accomplished by blending polyolefin elastomer (POE) and 3-pentadecylphenol (PDP) with the PA10,12 matrix. The incorporation of 5 wt% PDP effectively blurred the PA10,12/POE interface due to PDP's role as a compatibilizer. This phenomenon is attributed to the formation of intermolecular hydrogen bonds, as evidenced by Fourier Transform Infrared Spectroscopy (FTIR) analysis. Further investigation, using differential scanning calorimetry (DSC), elucidated the crystallization thermodynamics and kinetics of the resulting binary PA10,12/POE and ternary PA10,12/POE/PDP composites. Notably, the crystallization temperature (Tc) was observed to decrease from 163.1 °C in the binary composite to 161.5 °C upon the addition of PDP. Increasing the PDP content to 10% led to a further reduction in Tc to 159.5 °C due to PDP's capacity to slow down crystallization. Consequently, the ternary composite of PA10,12/POE/PDP (92/3/5 wt%) demonstrated a synergistic improvement in mechanical properties, with an elongation at break of 579% and a notch impact strength of 61.54 kJ/m2. This represents an approximately eightfold increase over the impact strength of unmodified PA10,12. Therefore, our work provides the potential of PDP as a compatibilizer to develop nylon composites with enhanced stiffness and toughness.

Enhanced mechanical and interfacial performances of carbon fiber reinforced composites with low percentage of amine functionalized graphene

AbstractThis paper reports improvement in the tensile, flexural and interlaminar shear strength (ILSS) properties of ADG‐NH2/Epoxy/CFRP composites at low filler content. Five symmetrical CFRP composite laminates were prepared through wet layup process assisted by vacuum bagging technique with varying wt% proportions (0.25, 0.5, 0.75 and 1) of ADG‐NH2/Epoxy. Tensile tests, short beam shear test and flexural tests were carried out as per ASTM D3039, ASTM D2344 and ASTM 790‐10 respectively to assess the effect of the ADG‐NH2 functionalized nano additives on their mechanical properties. The variation in ILSS were studied for varying temperatures (room temperature, 35, 50, 75, 85, & 100°C for each type of ADG‐NH2/Epoxy wt% (neat, 0.25, 0.5, 0.75 & 1)) of ADG‐NH2/Epoxy/CFRP composites. The ILSS was enhanced up to ∼27% for 0.5 wt% of ADG‐NH2 reinforced CFRP at room temperature but reduced with the higher concentrations (0.75 wt% & 1 wt%). It was observed that ILSS reduced with gradual temperature variations up to 100°C w.r.t room temperature. But an increment was observed up to 0.5 wt% for ADG‐NH2 for all temperature. Form the test results, it has been recorded an improvement in mechanical properties that is, the elastic modulus by ∼18%, ultimate tensile strength by ∼21%, % elongation at break by∼19% and toughness by∼28% for the 0.5 wt% of ADG‐NH2 graphene nano additive reinforced CFRP composite laminates as compared to neat epoxy CFRP laminates. Results also show the augmentation in the Max load by ∼24%, flexural strength by ∼33%, flexural modulus by ∼43%, and flexural strain by ∼26% were observed for the 0.5 wt% of ADG‐NH2 graphene nano additive reinforced CFRP composite laminates as compared to neat epoxy CFRP composite laminates. Fractographic studies of fractured surface using SEM analyses shows better adhesion mechanisms which supports the augmentation in mechanical properties with addition of amine functionalized graphene to CFRP laminate.Highlights Reinforcement of amine functionalized (ADG‐NH2) graphene in the epoxy matrix and incorporation with carbon fibers to enhance the interfacial and flexural properties. Evaluation of temperature effects on interlaminar shear strength properties of amine functionalized CFRP composites Improvements in tensile, ILSS and flexural properties observed for a low percentage (0.5 wt%) of ADG‐NH2 graphene reinforced CFRP composite laminates. Use of aerospace grade epoxy and resin with amine functionalized graphene for further use in aerospace industry applications.

Effects of chain extender types and contents on the properties of modified recycled polyethylene terephthalate

AbstractRecycling polyethylene terephthalate (PET) bottles post‐consumption is highly desirable but remains challenging because of their poor properties after recycling. Using a chain extender to rejoin the cleaved polymer chains is considered a reasonable solution to this issue. However, the functionality of the chain extenders affects the cross‐linking and properties of the resulting products. Therefore, this study focuses on the effects of functional groups and number of chain extenders on the properties of recycled polyethylene terephthalate (rPET). Three commercial chain extenders—methylene diphenyl diisocyanate (MDI), triphenyl phosphite (TPP), and Joncryl (JC), represented as di‐, tri‐, and multi‐functional chain extenders, respectively—are introduced into rPET by reactive blending. The intrinsic viscosity, rheological properties, thermal properties, and mechanical properties of the chain‐extended rPET are investigated. The results indicate that all the chain extenders increase the molecular weight of rPET. Di‐ and multi‐functional chain extenders (MDI and JC) induce branching and cross‐linking owing to the highly reactive functional groups, whereas a tri‐functional chain extender (TPP) showed the lowest improvement in mechanical properties, owing to chain scission from by‐products occurring during chain extension. Furthermore, increasing the content of all chain extenders significantly increased their intrinsic viscosity, cross‐linking, and mechanical properties.

Analysing the Impact of Severe Shot Peening on the Fatigue Strength of Wire Arc Additively Manufactured Carbon Steel

The study investigates the impact of severe shot peening on the fatigue strength of wire arc additively manufactured carbon steel. Initial characterization revealed a material with prominent equiaxed grains and large grain sizes. However, the application of SSP induced a considerable reduction in grain size, particularly on the surface, consequently enhancing the surface's strength and hardness, yet leading to an inhomogeneous structure within the WAAM CS SSP part. Hardness measurements demonstrated a substantial impact on surface hardness, reaching a depth of approximately 0.4 mm, with a 64% increase observed due to SSP, elevating it from an average of 165 HV to a maximum of 270 HV near the surface. Tensile tests on WAAM CS and WAAM CS SSP displayed notable improvements in mechanical properties following SSP treatment. Yield strength increased by approximately 5%, and ultimate tensile strength rose by 2.5%, resulting in a peak tensile strength of 513 MPa. However, this enhancement was accompanied by reduced ductility, evidenced by decreased elongation from 44% in WAAM CS to 35% in WAAM CS SSP. Bending fatigue tests highlighted a significant enhancement in fatigue resistance due to SSP treatment. The fatigue limit increased by 21% from 190 MPa for WAAM CS to 230 MPa for WAAM CS SSP, indicating improved resistance in both low-cycle and high-cycle fatigue regimes. This enhancement in fatigue resistance is attributed to the heightened mechanical strength post-SSP treatment, suggesting a trade-off between increased strength and reduced ductility. The results demonstrate that SSP significantly enhances surface attributes, strength, and fatigue resistance of WAAM CS. This advancement bears implications for engineering applications where enhanced mechanical properties and fatigue resistance are vital, despite the induced trade-offs in material characteristics.

Chondroitin Sulfate Derivative Cross-Linking of Decellularized Heart Valve for the Improvement of Mechanical Properties, Hemocompatibility, and Endothelialization.

Tissue-engineered heart valve (TEHV) has emerged as a prospective alternative to conventional valve prostheses. The decellularized heart valve (DHV) represents a promising TEHV scaffold that preserves the natural three-dimensional structure and retains essential biological activity. However, the limited mechanical strength, fast degradation, poor hemocompatibility, and lack of endothelialization of DHV restrict its clinical use, which is necessary for ensuring its long-term durability. Herein, we used oxidized chondroitin sulfate (ChS), one of the main components of the extracellular matrix with various biological activities, to cross-link DHV to overcome the above problems. In addition, the ChS-adipic dihydrazide was used to react with residual aldehyde groups, thus preventing potential calcification. The results indicated notable enhancements in mechanical properties and resilience against elastase and collagenase degradation in vitro as well as the ability to withstand extended periods of storage without compromising the structural integrity of valve scaffolds. Additionally, the newly cross-linked valves exhibited favorable hemocompatibility in vitro and in vivo, thereby demonstrating exceptional biocompatibility. Furthermore, the scaffolds exhibited traits of gradual degradation and resistance to calcification through a rat subcutaneous implantation model. In the rat abdominal aorta implantation model, the scaffolds demonstrated favorable endothelialization, commendable patency, and a diminished pro-inflammatory response. As a result, the newly constructed DHV scaffold offers a compelling alternative to traditional valve prostheses, which potentially advances the field of TEHV.

Innovative insights into the preparation of tamarind gum base film loaded with pomelo essential oil via a low-energy emulsion method combined with melatonin: Maximizing the dual functions of tamarind gum

Pomelo essential oil has good antioxidant and antimicrobial properties. The objective of this study was to modify the active packaging loaded with essential oil through low-energy emulsification, in order to achieve both film-forming and emulsifying properties of tamarind gum, and to investigate the surface activity of melatonin in the emulsion. When α:β mixing ratio of 60:40, the resulting film solution exhibited favorable apparent viscosity and reduced emulsion flocculation and precipitation phenomena. Particle size distribution analysis and optical microscopy results demonstrated that the obtained emulsion was uniformly dispersed at an α:β mixing ratio of 60:40, with droplet diameters mainly concentrated within the range of 1–100 μm. After undergoing film-forming treatment, E-3-F (α:β mixing ratio of 60:40) exhibited a smoother and more compact microstructure, leading to significant improvements in mechanical properties and barrier performance. Laser confocal microscopy imaging revealed that the addition of melatonin further reduced interfacial tension between oil and water, while simultaneously weakening hydrophobic interaction forces among oil droplets, thereby effectively inhibiting droplet aggregation behavior. Moreover, incorporation of melatonin also enhanced material compactness and imparted excellent antioxidant effects to the packaging material. Consequently, this study ultimately unveils potential for low-energy emulsification combined with melatonin application in bio-based packaging field while providing novel insights into developing multifunctional bio-based packaging.

Effect of the TiB2 content on the mechanical and tribological properties of TiB2/AZ91 composites fabricated by vacuum hot-press sintering process incorporating vacuum ball milling

Magnesium alloys have poor strength and wear resistance, restricting their application greatly, while Mg matrix composites can improve these deficiencies. TiB2/AZ91 composites with high TiB2 content were prepared by vacuum hot-press sintering process incorporating vacuum ball milling. The effects of TiB2 content on the microstructure, mechanical properties and tribological properties of the composites were investigated in detail. The results suggested that the TiB2 particle exhibited good bonding with the Mg matrix. With the increasing TiB2 content, the ultimate tensile strength, yield strength and elongation of TiB2/AZ91 composites firstly increased and then decreased, while the wear rate and wear surface roughness presented an opposite trend, and the hardness and coefficient of friction gradually increased. The composites with 5 wt% TiB2 obtained the maximum tensile properties (UTS: 234 MPa YS: 91 MPa EL: 7.3 %). This improvement in mechanical properties was attributed to the uniform distribution of TiB2 particles and the well bonding at the interface. The strengthening mechanisms were found to be the load transfer strengthening and the thermal mismatch strengthening. Furthermore, the composites with 15 wt% TiB2 demonstrated the lowest wear rate of 1.06×10−6 mm3/Nm and lowest wear surface roughness of 2.971 μm. This wear resistance was enhanced because of the significant increasing in hardness. The dominant wear mechanisms observed in TiB2/AZ91 composites were abrasive wear and oxidation wear.

Enhanced mechanical properties of dispersed carbide-strengthened CrFeNi-based medium entropy alloys prepared via powder metallurgy

In this study, a set of CrFeNi -based medium-entropy alloys (MEAs) with varying carbon contents were prepared by spark plasm sintering (SPS) using atomized alloy powders as raw material. The microstructures of powders and as-sintered alloys were characterized using ECCI and EBSD. The mechanical properties of as-sintered alloys were tested and the strengthening mechanical were discussed. The results showed that the microstructures of the CrFeNi gas atomized powder and sintered alloy were both single FCC phase in an equiaxed state. However, the matrix grains of powder with carbon addition were mostly dendritic, and few eutectic carbides could be observed between matrix grains. Compared with the CrFeNi MEA, the addition of 8 at. % C led to an increase in the yield strength and tensile strength from 395 MPa to 630 MPa–590 MPa and 990 MPa, respectively. Orowan strengthening and grain refinement resulting micro/nano carbides are responsible for the improvement in mechanical properties.