Excellent Strengthening Effect Research Articles

In-situ TiC/Ti composites based on Ti2AlC–Ti system: Reaction process, microstructure, and mechanical properties

Based on the improvement of the phase transition temperature of Ti by Al element and the excellent strengthening effect of TiC particles, this paper selects Ti2AlC as the precursor, striving to improve the high-temperature performance of the Ti matrix. The composites with 1–10 vol% Ti2AlC addition were fabricated by hot-pressing sintering. And a detailed study was conducted on the reaction process, microstructure, room and high temperature compression properties of the composites. The experimental results show that the separation of Al elements at the A-position occurs at around 700 °C in Ti2AlC, and the Al element is homogenized in the matrix during the subsequent sintering process. Micron sized TiC particles are mainly distributed at the Ti grain boundaries, while the content of sub-micron sized TiC particles entering the crystal increases with the increasing Ti2AlC addition. The interface mismatch between TiC and Ti is small, and the bonding is well. These microstructures enable composite materials to exhibit excellent mechanical properties, with 10 vol% Ti2AlC/Ti composite having a yield strength of 1858 MPa and an ultimate strength of 2200 MPa at room temperature, and maintaining a yield strength of 602 MPa and an ultimate strength of 1264 MPa at 500 °C.

Influence of Bamboo Fibers Weight Fraction on the Quasi-Static and Dynamic Compressive Responses of Epoxy Matrix Composites

ABSTRACT The influences of natural bamboo fibers (BFs) weight fraction on the microstructure, quasi-static and dynamic compressive responses of the epoxy resin matrix composites were investigated with the aid of scanning electron microscope, electronic universal testing machine and the modified Split Hopkinson pressure bar (SHPB) setup. The quasi-static compressive properties of the BFs/epoxy resin matrix composites suggested that the compressive strength were strongly improved with the addition of the natural BFs, which was attributed to the excellent strengthening effect. When the BFs content increased up to 15 wt.%, the compression ratio of the BFs/epoxy resin matrix composites showed 11% reduction than that of the unmodified epoxy resin. Moreover, the stress and strain were linear at the initial part but nonlinear when stress exceeds a certain value. SHPB impact tests results indicated that, compared with the pristine epoxy resin, the natural BFs reinforced epoxy matrix composite with 15 wt.% BFs exhibited the highest dynamic compressive strength, compression modulus and the best strengthening effect. Epoxy resin matrix composites also showed an obvious effect rate effective under impact load. Similar to that in the quasi-static compressive test, the addition of natural BFs has a positive effect in improving the compressive strength of the epoxy matrix.

Substitution solid solution hardening effect of vanadium in Ni–Co–V medium entropy alloys

The single-phase polycrystalline NiCoV medium-entropy alloy (MEA) has shown ∼1 GPa yield strength, surpassing most single face centered cubic alloys. This excellent strength has been theoretically devoted to the special solid solution hardening effect of V. However, the intrinsic reasons for this excellent strengthening effect of V in high-/medium-entropy alloys are still less experimentally explored. To this end, we here investigated the solid solution hardening effect of V in the NiCoV system. The results showed that the solid hardening mechanism changes from lattice distortion to atomic volume mismatch when the V content exceeds 6 at. %. Particularly, the increase in V content increases the Hall–Petch coefficient of NiCoV MEAs significantly. The combination of efficient grain boundary hardening and atomic volume mismatch hardening leads to the excellent yield strength of concentrated NiCoV.

Influence of Ti addition on the precipitation behavior and mechanical properties of Ni-7.9Cr-5.9W-22.2Mo superalloy

The Ni-7.9Cr-5.9W-22.2Mo-1.4Ti superalloy based on Ni-8Cr-6W-22.5Mo (the Haynes 244 alloy) was prepared to investigate the effect of Ti addition on the precipitation behavior and mechanical properties. The results indicate that the addition of Ti can facilitate the formation of C11b and D022 superlattice phases simultaneously after age-treated at 650 °C for 240 h. The yield strength is significantly improved to 1645 MPa compared with Ni-8Cr-6 W-22.5Mo with only the formation of C11b and a yield strength of 1297 MPa. The excellent strengthening effect of C11b and D022 superlattice phases are attributed to both order strengthening and coherency strengthening, and their calculated contributions to strengthening are 148 MPa and 439 MPa for D022 and 83 MPa and 208 MPa for and C11b, respectively. Together with solid-solution strengthening and grain refinement strengthening, the theoretically calculated yield strength matches well with the experimental results. In addition, the deformation mode changes from deformation slip to strain-induced twinning after the Ti addition.

Oxygen-assisted spinodal structure achieves 1.5 GPa yield strength in a ductile refractory high-entropy alloy

Refractory high-entropy alloys (RHEAs) with room-temperature ductility are drawing growing attention for potential high-temperature applications. However, the most widely used metallurgical mechanisms appear weak in optimizing their strength and ductility. Here, we report that the nanoscale spinodal structure in Ti41V27Hf15Nb15O2 leads to the highest tensile yield strength (∼1.5 GPa) among the existing RHEAs and good elongation of ∼12%. With the aid of thermodynamic calculations, we show that oxygen plays a dominant role in controlling the formation of the spinodal structure by influencing the spinodal gap of the Ti-V-Hf-Nb system. Exploring the atomic structure of the spinodal structure (β + β*), we showed that the large lattice misfit of the spinodal phases is mainly responsible for the excellent strengthening effect while the planar to wavy dislocation glide mode transition accounts for the retained ductility. This work provides a novel strategy to improve the mechanical properties of the RHEAs and deepens the understanding of their phase stabilities.

Matrix effect on strengthening behavior of carbon nanotubes in aluminum matrix composites

Many studies have shown that carbon nanotubes (CNTs) have excellent strengthening effect as a reinforcement in pure aluminum (Al). However, it is unknown that whether such merit can be also achieved in strong Al alloys for achieving higher-strength Al matrix composites. In this study, CNTs were incorporated into pure Al and a high-strength Al alloy (AA5083) via the same powder metallurgy route. Results showed that during the dispersion stage, the high energy ball milling process caused different amounts of deformation to pure Al and AA5083, which led to a better dispersion state of CNTs in powders and composites of pure Al. Although the two composites had the same tensile strength coincidentally, the reinforcing effect of CNTs in pure Al composite was more than five folds larger than that in AA5083, suggesting a strong matrix effect on strengthening behavior of CNTs in Al matrix composites. The present finding may show significant guidance for the optimization of fabrication processes and development of high-performance CNTs/Al composites. • Strengthening behavior of CNTs/pure Al and CNTs/AA5083 composites were compared. • The dispersion states of CNTs in the CNTs/pure Al and CNTs/AA5083 composites were compared especially. • The reinforcing efficiency of CNTs under poor dispersion state and fine dispersion state in two different matrices were discussed.

Effect of Volume Fraction of Reinforcement on Microstructure and Mechanical Properties of In Situ (Ti, Nb)B/Ti2AlNb Composites with Tailored Three-Dimensional Network Architecture.

The mechanical properties of (Ti, Nb)B/Ti2AlNb composites were expected to improve further by utilizing spark plasma sintering (SPS) and inducing the novel three-dimensional network architecture. In this study, (Ti, Nb)B/Ti2AlNb composites with the novel architecture were successfully fabricated by ball milling the LaB6 and Ti2AlNb mixed powders and subsequent SPS consolidation. The influence of the (Ti, Nb)B content on the microstructure and mechanical properties of the composites was revealed by using the scanning electron microscope (SEM), transmission electron microscopy (TEM) and electronic universal testing machine. The microstructural characterization demonstrated that the boride crystallized into a B27 structure and the α2-precipitated amount increased with the (Ti, Nb)B increasing. When the (Ti, Nb)B content reached 4.9 vol%, both the α2 and reinforcement exhibited a continuous distribution along the prior particle boundaries (PPBs). The tensile test displayed that the tensile strength of the composites presented an increasing trend with the increasing (Ti, Nb)B content followed by a decreasing trend. The composite with a 3.2 vol% reinforcement had the optimal mechanical properties; the yield strengths of the composite at 25 and 650 °C were 998.3 and 774.9 MPa, showing an 11.8% and 9.2% improvement when compared with the Ti2AlNb-based alloy. Overall, (Ti, Nb)B possessed an excellent strengthening effect and inhibited the strength weakening of the PPBs area at high temperatures; the reinforcement content mainly affected the mechanical properties of the (Ti, Nb)B/Ti2AlNb composites by altering the α2-precipitated amount and the morphology of (Ti, Nb)B in the PPBs area. Both the continuous precipitation of the brittle α2 phase and the agglomeration of the (Ti, Nb)B reinforcement dramatically deteriorated the mechanical properties.

Microstructures and mechanical properties of a precipitation hardened refractory multi-principal element alloy

Precipitation hardening is used as a powerful strengthening pathway to tailor the mechanical properties of traditional alloys. However, in refractory multi-principal element alloys (RMPEAs), the precipitates with remarkable strengthening effect are relatively less explored. Here, we report novel precipitation hardened body-centered-cubic (BCC) TiVNb RMPEAs through doping surplus boron. 2000 ppm (0.2 wt%) boron doping leads to TiB precipitates, which can enhance the yield strength of TiVNb by ∼350 MPa. Orowan strengthening caused by TiB precipitates serves as the primary strengthening mechanism compared to non-boron alloys. Due to boron doping, the dislocation-mediated deformation transfers from planar-slip to cross-slip and thus avoids stress concentration caused by high-density geometrically necessary dislocation. The excellent strengthening effect and tuned deformation mechanisms led to an optimal RMPEA with a yield tensile strength of ∼972 MPa and an elongation of ∼12%. This work demonstrates that TiB is an efficient precipitate in BCC RMPEAs, which is constructive for the development of precipitation hardened RMPEAs.

Improving tensile strength and impact toughness of plasticized poly(lactic acid) biocomposites by incorporating nanofibrillated cellulose

Abstract Poly(lactic acid) (PLA) biocomposites are usually plasticized to overcome the problem of poor ductility, which decreases the valuable tensile strength. In this study, novel nanofibrillated cellulose (NFC) was extracted to enhance the acetyl tributyl citrate (ATBC) plasticized PLA biocomposites. Interestingly, NFC not only exhibited an excellent strengthening effect but also showed a further toughening effect in the biocomposites. When 4 wt% NFC was added, the tensile strength, elongation at break, and impact strength of the biocomposites with 15 wt% ATBC and 20 wt% ATBC reached 52.6 MPa, 28.4%, 34.9 J/m and 35.8 MPa, 300.1%, 40 J/m, respectively. This is at least 1.1 folds higher in strength and 2.3 folds higher in impact toughness than the biocomposites without NFC. Glass transition and melting temperature slightly increased with NFC addition. More importantly, the mechanism of the strengthening and toughening effect was definitely elucidated, and the comprehensive performance of the application was evaluated. The findings of the study provide significant guidance for PLA application, such as in food packaging, medical engineering materials, and household products.

Splitting tensile strength and microstructure of xanthan gum-treated loess

The tensile strength of loess is closely related to geological disasters. As eco-friendly materials, biopolymers have an excellent strengthening effect on the mechanical properties of soil. The effect of different initial dry densities and xanthan gum (XG) contents on the microstructure and mechanical behavior of XG-treated loess was studied with a series of microscopic tests and splitting tensile tests based on the particle image velocimetry technique. The results show that the XG became concentrated and agglomerated during dehydration, forming bridge links between soil particles and covering their surfaces. The XG-treated loess had a significant concentration of micropores and mesopores, with greater peak pore size distribution values than untreated loess. The specimens’ load–displacement curves with different XG contents and initial dry densities showed strain-softening. The displacement vector field indicated that specimens’ primary cracks were radial–vertical, and the secondary cracks were well-developed. The strain-softening phenomenon was more significant with increased XG content and initial dry density, and the specimens’ splitting tensile strength and brittleness increased. XG treatment gave the soils stronger cementation and a denser structure, helping to increase strength and brittleness. This research provides a scientific basis and practical experience for applying XG in geotechnical engineering.

Nanoscale precipitates with quasicrystal domains enhanced strength-ductility synergy in a Mg–6Zn–4Al–1Sn–0.5Mn alloy

Precipitation strengthening is one of the significant strengthening mechanisms for metallic alloys owing to its excellent strengthening effect. Here, we effectively introduce homogenous nanosized precipitates into a Mg–6Zn–4Al–1Sn-0.5Mn (wt.%) alloy via extrusion and double aging to enhance strength-ductility synergy. The yield strength, ultimate tensile strength, and total elongation of the Mg alloy are 303.1 ± 15.8 MPa, 392.5 ± 3.9 MPa, and 21.1 ± 2.4%, respectively. Using transmission electron microscopy and atomic level high angle annual dark field-scanning TEM, in addition to the icosahedral quasicrystalline (IQC) particles at the grain boundary, we find that there are two kinds of nanoprecipitates in the matrix. The majority of nanoprecipitates are cuboid IQC phases with nanodomains parallel to the basal plane of the Mg matrix, while the minority of nanoprecipitates are rod-like β1′ phases containing IQC clusters vertical to the basal plane. These homogenous nanoscale precipitates and grain refinement contribute 50.5% and 30.2% of the yield strength. This work sheds new light on understanding the nanoscale IQC precipitate strengthening mechanisms of magnesium alloys and provides a novel method to fabricate alloys with superior mechanical properties.

Prefabricated prestressed variable truss to strengthen RC beams based on the concept of geometrically unstable system

A new prefabricated prestressed variable truss (PPVT) system based on the concept of geometrically unstable system is proposed for the strengthening of reinforced concrete (RC) beams. The advantages of truss and external prestressing can be combined in this system. The novelty of the system lies in that the external prestressing is applied through a variable truss during the assembly process rather than the final stability truss, which improves both the utilization of prestressing and the cooperativity between truss and beam. An experimental test is performed in the present study to investigate the strengthening efficiency of the proposed PPVT system. The effects of the anchorage strength of external prestressing and the pre-damage of structure on the strengthening efficiency of the system are also discussed. Results show that the structural behaviors of RC beams after strengthened by PPVT system are significantly improved. In the present test, the crack resistance and bearing capacity of the beams after strengthening increased by 210% and 125%, respectively. The anchorage strength has a slight effect on the strengthening efficiency of the PPVT system, but can affect the deformation of beams. The PPVT system has an excellent strengthening effect on the pre-damaged members, and even can increase the bearing capacity of the completely damaged beam by 108%.

Improving mechanical, thermal, and erosive wear performance of natural bamboo fibers modified epoxy resin matrix composites

Natural bamboo fibers (BFs), which were treated by silane coupling agents, reinforced epoxy resin (EP)–based composite were synthesized. Effects of the coupling agents on the chemical structures of the BFs were characterized by Fourier Transform Infrared Spectroscopy. The mechanical properties, such as tensile strength, flexural strength, impact strength, and hardness of the BFs/EP-based composites were improved significantly, which could be attributed to the excellent strengthening effect of the BFs. Simultaneously, experimental investigations on the thermal behaviors of the BFs/epoxy composites were also presented, indicating that the thermal decomposition temperature of the polymer materials was lowered but the flame retardancy was improved. The bamboo fiber breakage and fiber split were also observed on the impact fracture surface of the composites, which indicate energy dissipation during fiber debonding and pullout process. Moreover, the erosive wear tests have also been carried out to analyze the erosive wear properties of the natural bamboo fibers which modified the epoxy matrix composites. The results indicate that the erosive wear resistance of the EP-based composite was improved greatly when the natural bamboo fibers content was 15 wt.%.

Excellent strengthening effect of L12 precipitates on the selective laser melting Al0.3CoCrFeNiCu high entropy alloy via annealing treatment

The influence of annealing treatment on the microstructure and mechanical properties of single phase structural Al0.3CoCrFeNiCu high entropy alloy (HEA) fabricated by selective laser melting (SLM) were investigated. The results indicated that the L12 precipitates were dispersed in matrix and also enriched at sub-grain boundaries of the SLM specimens annealed at 600 °C for 10 h. Besides, wetting transition was observed at the sub-grain boundary. Meanwhile, the microhardness and room compressive yield strength of this as-built HEA were dramatically enhanced from 255 HV and 419 MPa to 357 HV and 647 MPa after annealing treatment, respectively. Besides, the as-annealed HEA still possessed considerable ductility. Based on the microstructure analysis, the strength mechanism of as-annealed alloy was ascribed to the nano-sized L12 precipitates in sub-grains and also their enrichment at the sub-grain boundaries.

The Influence of Graphene Oxide and Cristobalite Phase of Silica Precipitate on Chitosan – Based Nanocomposites

Nanocomposites are commonly used as fillers with size at the nanoscale and have low loading, have the potential to match or significantly improve performance to supply conventional composites. Graphene oxide (GO), an oxidative exfoliating product of natural graphite, has attracted much attention due to its excellent strengthening effect on polymers. Young modifications of the GO sheet and the strong interaction interface between GO and the matrix polymer. Therefore, graphene oxide is expected to offer a promising nanoscale for the next generation of nanocomposite materials. Besides that, silica precipitate a critical materials used in many applications worlwide. Silica Precipitates have become key fillers in nanocomposites due to their properties which can improve mechanical properties. In this study, Chitosan-based Nanocomposite Films have been made by casting methods. The effect of graphene oxide and silica precipitates on the chitosan film and their properties were investigated. Graphene oxide used in this study was synthesized with chemicals from pure graphite using the Hummer Method. Graphene oxide produced from the hummer method was characterized by X-Ray Diffraction and Scanning Electron Microscope. Silica precipitates in this study uses cristobalite phase of silica. The measurement results of the mechanical properties of nanocomposite films show that adding christobalite phase of silica precipitate content in composites increases the tensile strengh of 21.3 Mpa and higher than addition of GO in the chitosan films. Meanwile, addition of GO in chitosan film increases the young modulus up to 2.73 Gpa.

Exploration of D022-Type Al3TM(TM = Sc, Ti, V, Zr, Nb, Hf, Ta): Elastic Anisotropy, Electronic Structures, Work Function and Experimental Design.

The structural properties, elastic anisotropy, electronic structures and work function of D022-type Al3TM (TM = Sc, Ti, V, Y, Zr, Nb, La, Hf, Ta) are studied using the first-principles calculations. The results indicate that the obtained formation enthalpy and cohesive energy of these compounds are in accordance with the other calculated values. It is found that the Al3Zr is the most thermodynamic stable compound. The mechanical property indexes, such as elastic constants, bulk modulus, shear modulus, Young’s modulus, Poisson’s ratio, and Vickers hardness are systematically explored. Moreover, the calculated universal anisotropic index, percent anisotropy and shear anisotropic factors of D022-type Al3TM are analyzed carefully. It demonstrates that the shear modulus anisotropy of Al3La is the strongest, while that of Al3Ta is the weakest. In particular, the density of states at Fermi level is not zero, suggesting that these phases have metal properties and electrical conductivity. More importantly, the mechanisms of correlation between hardness and Young’s modulus are further explained by the work function. Finally, the experimental design proves that D022-Al3Ta has an excellent strengthening effect.

Thickness effect of graphene film on optimizing the interface and mechanical properties of Cu/Ni multilayer composites

In the present work, laminated Cu/Ni samples reinforced by graphene film with various thicknesses were produced via electrophoretic depositing graphene oxide (GO) on Cu foil by controlling deposition voltage, and the effect of thickness of graphene film on strengthening Cu/Ni multilayer composites were investigated in detail. Microstructural examination revealed that the fragments of graphene film were dispersed at the interface between Cu and Ni layer after hot rolling, with a range of thickness from 0.76 to 5.13 μm. The graphene film showed an excellent strengthening effect in the composites regardless of their thickness according to the tensile testing. However, the toughing effect achieved optimal as the thickness of 4.12 μm. The role of deposited graphene film played in determining the load transfer and optimizing the interface was discussed. Graphene film with appropriate thickness can effectively inhibit the severe asymmetric diffusion behavior of Cu and Ni elements, which plays an important role in strengthening and toughening clad interfaces by inhibiting the formation of Kirkendall voids. This study provides novel insights into understanding the strengthening and toughing behaviors of graphene reinforced multilayer composites, which can be developed into a technical strategy for fabricating high performance laminated metal matrix composites.

A precipitation-strengthened high-entropy alloy for additive manufacturing

As newly developed metallic materials, several high-entropy alloys (HEAs) have been fabricated via additive manufacturing (AM) and have been found to exhibit more uniform microstructures and better mechanical properties than their as-cast counterparts. However, current additive-manufactured HEAs are relatively unsatisfactory in terms of strength owing to the inevitable micropores or microcracks that occur during their processing. A significant challenge is to further increase the mechanical properties of single-solid-solution HEAs for AM. In light of this, in the present study, a precipitation-strengthened Ni2.1CoCrFeNb0.2 HEA was designed that is particularly easy to print for use in AM. Bulk samples without observed defects were successfully produced by direct laser deposition. The as-deposited Ni2.1CoCrFeNb0.2 HEA showed an excellent strength-ductility combination. After proper heat-treatments, the tensile strength increased dramatically to ∼ 1127 MPa with a tensile elongation of ∼ 17 %, which is the best performance in the reported AM-fabricated HEAs. The precipitation of the γ″ phase was quantitatively analyzed to reveal the excellent strengthening effect in this new AM-fabricated HEA. In the present study, a superior precipitation-reinforced HEA with fully dense microstructures was successfully developed for AM. These results open up new possibilities for the further development of AM-fabricated HEAs.

Optimization of design variables for carbon/glass hybrid composites laminates using the Taguchi Technique

Purpose The purpose of this paper is to analyze the significance of disparate design variables on the mechanical properties of the composite laminate. Four design variables such as stacking sequence, stacking angle, types of resins and thickness of laminate have been chosen to analyze the impact on mechanical properties of the composite laminate. The detailed investigation is carried out to analyze the effect of a carbon layer in stacking sequence and investigate the impact of various resins on the fastening strength of fibers, stacking angles of the fibers and the thickness of the laminate. Design/methodology/approach The Taguchi approach has been adopted to detect the most significant design variable for optimum mechanical properties of the hybrid composite laminate. For this intend, L16 orthogonal array has been composed in statistical software Minitab 17. To investigate an effect of design variables on mechanical properties, signal to noise ratio plots were developed in Minitab. The numerical analysis was done by using the analysis of variance. Findings The single parameter optimization gives the optimal combination A1B1C4D2 (i.e. stacking sequence C/G/G/G, stacking angle is 00, the type of resin is newly developed resin [NDR] and laminate thickness is 0.3 cm) for tensile strength; A4B2C4D2 (i.e. stacking sequence G/G/G/C, stacking angle is 450, the type of resin is NDR and laminate thickness is 0.3 cm) for shear strength; and A2B3C4D2 (i.e. stacking sequence G/C/G/G, stacking angle is 900, the type of resin is NDR and thickness is 0.3 cm) for flexural strength. The types of resins and stacking angles are the most significant design variables on the mechanical properties of the composite laminate. Originality/value The novelty in this study is the development of new resin called NDR from polyethylene and polyurea group. The comparative study was carried out between NDR and three conventional resins (i.e. polyester, vinyl ester and epoxy). The NDR gives higher fastening strength to the fibers. Field emission scanning electron microscope images illustrate the better fastening ability of NDR compared with epoxy. The NDR provides an excellent strengthening effect on the RCC beam structure along with carbon fiber (Figure 2).

Influence of pulse reverse current on mechanical and corrosion resistance properties of Ni-MoSe2 nanocomposite coatings

The Ni-MoSe2 nanocomposite coating was successfully prepared on mild steel specimen using pulse reverse current technique by varying its duty cycle and frequency at the fixed concentration of 2.5 g/ L of MoSe2 nanoparticles in Watt's nickel plating bath. The surface morphology and crystal orientation of nanocomposite coatings were investigated by FE-SEM and XRD, respectively. The influence of duty cycles on the co-deposition and microhardness of Ni-MoSe2 nanocomposite coatings have been evaluated. The 60% duty cycle exhibited better crystal orientation with excellent strengthening effect due to the refinement of Ni. The Tafel polarization and electrochemical impedance studies were performed for Ni-MoSe2 nanocomposite coatings in 3.5 wt% of NaCl solution. These results revealed that the incorporation of MoSe2 in nickel matrix has improved mechanical and corrosion resistance properties.