Yield Strength Of Composites Research Articles

The Effect of Solution Aging on the Microstructure and Mechanical Properties of a Laser Powder Bed Fusion-Formed WC-Reinforced 18Ni300 Composite

The addition of WC particles has the potential to improve the properties of 18Ni300 alloy, but the effect of heat treatment on the microstructure and mechanical properties of 18Ni300 matrix composites needs to be further investigated. In this work, WC-reinforced 18Ni300 composites were fabricated using laser powder bed fusion (LPBF). The composites were made into solutions at 846 °C for 51 min, followed by aging at 388 °C for 300 min. The microstructural evolution and compressive properties of the composites before and after heat treatment were systematically studied. The results indicate that the microstructures of the composites consist of heterogeneous cellular and fine columnar grains. As the WC content increases, the primary phase in the LPBF-formed samples gradually shifts from α-Fe martensite to γ-Fe austenite. After heat treatment, the primary phase transforms to α-Fe with only a small residual amount of γ-Fe. The microstructure becomes more uniform, featuring a significant reduction in grain size. Many precipitated phases can be found in the intergranular, accompanied by an increase in the thickness of diffusion layers. The WC content in the composite material is positively correlated with its hardness and compressive strength. As the WC reinforcement content increases from 5% to 20%, the yield strength and compressive strength of the LPBF-formed composites increase to 1042.5 MPa and 2900.7 MPa, respectively, while the compressive elongation decreases from 64% to 43%. After heat treatment, the yield strength of the composites significantly increases to 2356.8 MPa, with a slight increase in the compressive strength to 2939.7 MPa. However, the elongation decreases from 32.5% to 22%.

A novel prediction method for nanoplatelets content dependent yield strength of graphene nanoplatelets reinforced metal matrix composites at different temperatures

Especially, the quantitative relationship between the thickness and volume fraction of graphene and the grain size of graphene nanoplatelets reinforced metal matrix composites was revealed, based on which the influence of grain refinement, load transfer and dislocation strengthening on the yield strength of composites and their evolution with temperature was quantitatively characterized. Furthermore, by introducing the weakening effect of graphene agglomeration on associated control mechanism of yield strength, a prediction model of temperature dependent yield strength of graphene nanoplatelets reinforced metal matrix composites was established. The proposed prediction approach is verified by comparing the predictions with the experimental data in other literature. Moreover, using the established model, the quantitative effects of length and thickness of nanoplatelets on the yield strength of composites and their evolution with temperature were carried out. This research also provides an effective method for investigating the optimal volume fraction and failure volume fraction of added graphene.

Theoretical prediction method of Young's modulus and yield strength of micron particle reinforced metal matrix composites at different temperatures

To begin with, a theoretical characterization model of temperature and porosity dependent Young's modulus for micron particle reinforced metal matrix composites is established by considering the evolution of properties of reinforced particles and metal matrix with temperature. Additionally, combining the existing strengthening mechanism theory and incorporating the influence of grain boundary slip on the related strengthening mechanism and the yield strength of metal matrix, a temperature dependent yield strength analysis model of micron particle reinforced metal matrix composites is proposed. These models only require material parameters at room temperature and temperature dependent specific heat capacity at constant pressure for application. In addition, the predicted results from these models are reasonable and consistent with measured results. Moreover, based on the established models, the effects of key material parameters and main mechanisms on Young's modulus and yield strength of composites and their variation with temperature are explored. Furthermore, the variation of various control mechanisms with the particle size and temperature is clarified. It lays a theoretical foundation for the development of micron particle reinforced metal matrix composites that are suitable for high-temperature environments and for the optimization of their key parameters.

Hardening mechanisms in stainless steel/aluminum bronze composite fabricated using electron beam additive manufacturing

The authors investigated the features of structural-phase state of a composite based on stainless austenitic steel with addition of 25 % (vol.) aluminum bronze. The composite was obtained by electron beam additive technology with simultaneous feeding of two wires. The paper considers analysis of the structural-phase state and mechanical characteristics. The contributions of various mechanisms to the composite hardening were evaluated. It was established that a multiphase structure is formed in the steel – 25 % bronze composite, which consists of 43.9 % austenite, 32.0 % ferrite and 24.2 % bronze. Dispersion-hardened copper particles are isolated in austenite grains, volume fraction of which counts 47 %. Dispersion-hardened NiAl particles with a volume fraction of 20 % are isolated in ferrite grains. Transmission electron microscopy data indicate a coherent conjugation of arrays of dispersion-hardened particles with the matrix. Such a composite structure provides an increase in the tensile strength by an average of 50 % compared to austenitic steel obtained by electron beam additive technology without the addition of aluminum bronze. It was found that the contributions of various hardening mechanisms to yield strength of austenite, ferrite and bronze amounted to 959.3, 972.7 and 408.7 MPa, respectively. Bronze grains do not make a significant contribution to increase in yield strength of the composite, except for its increase due to dislocation hardening. The main contributions to increase in the composite yield strength are made by austenite grains due to grain-boundary, dispersion and dislocation hardening and by ferrite grains due to grain-boundary, solid-solution and dislocation hardening.

Hardening Mechanisms in Stainless Steel/Aluminum Bronze Composite Fabricated Using Electron Beam Additive Manufacturing

The authors investigated the features of structural-phase state of a composite based on stainless austenitic steel with addition of 25% (vol.) aluminum bronze. The composite was obtained by electron beam additive technology with simultaneous feeding of two wires. The paper considers analysis of the structural-phase state and mechanical characteristics. The contributions of various mechanisms to the composite hardening were evaluated. It was established that a multiphase structure is formed in the steel–25% bronze composite, which consists of 43.9% austenite, 32.0% ferrite and 24.2% bronze. Dispersion-hardened copper particles with 47 vol % content precipitated inside the austenite grains while only 20 vol % of the dispersion-hardening NiAl particles precipitated in the ferrite grains. Transmission electron microscopy data indicate a coherent conjugation between crystalline lattices of these dispersion hardening particles and matrix. Such a composite structure provides 50%, on average, improvement of the tensile strength compared to that of austenitic steel obtained by electron beam additive technology without the addition of aluminum bronze. It was found that the contributions of various hardening mechanisms to yield strength of austenite, ferrite and bronze amounted to 959.3, 972.7 and 408.7 MPa, respectively. Bronze grains do not make a significant contribution to increase of the yield strength of the composite, except for its increase due to dislocation hardening. The main contributions to the increase of the composite yield strength are made by austenite grains due to grain-boundary, dispersion and dislocation hardening, and by ferrite grains due to grain-boundary, solid-solution and dislocation hardening.

Zinc Matrix Composites Reinforced with Partially Unzipped Carbon Nanotubes as Biodegradable Implant Materials

The activity of zinc is between that of magnesium and iron, and it has a suitable degradation rate and good biocompatibility. It has been regarded as a very promising biodegradable metal material for biomedicine. However, the insufficient mechanical properties of pure Zn limit its practical application in the field of orthopedic implants. In this paper, partially unzipped carbon nanotubes (PUCNTs) obtained by meridionally cutting multi-walled carbon nanotubes (MWCNTs) were used as reinforcements and combined with spark plasma sintering to prepare partially unzipped carbon nanotube reinforced Zn matrix composites. The effects of PUCNT addition on the microstructure and the mechanical properties of Zn matrix composites were investigated. The microstructure analysis showed the good interface bonding between PUCNTs and the Zn matrix. Additionally, the strength of PUCNTs/Zn composites showed a trend of increasing first and then decreasing with the PUCNT content increases. When the PUCNT content was 0.2 wt%, the tensile strength and yield strength of composites were about 78.4% and 64.4% higher than that of pure Zn, respectively, while maintaining a high elongation (62.6%).

Effect of CNT Content on Microstructure and Properties of CNTs/Refined-AZ61 Magnesium Matrix Composites.

Carbon nanotubes (CNTs) reinforced magnesium matrix composites have great application potential in the transportation industry, but the low absolute strength is the main obstacle to its application. In this paper, copper-coated CNTs and AZ61 powder were used as raw materials to prepare CNTs/refined-AZ61 composites with good interfacial bonding, uniformly dispersed CNTs and fine grains by the process of ball milling refinement of AZ61 powder, ball milling dispersion and hot-pressing sintering. When the volume fraction of CNTs is less than or equal to 1 vol.%, CNTs can be uniformly dispersed and the yield strength and compressive strength of composites increase with higher CNT content. When the volume fraction of CNTs is 1 vol.%, the compressive strength and yield strength of composites reach 439 MPa and 361 MPa, respectively, which are 14% and 9% higher than those of matrix composites with nearly the same value of fracture strain. When the volume fraction of CNTs is greater than 1 vol.%, with the increase in CNT content, CNT clustering becomes more and more serious, resulting in a decrease in the strength and fracture strain of composites.

Study on tensile properties of carbon fiber reinforced AA7075 composite at high temperatures

The short carbon fiber reinforced AA7075 composites were fabricated through powder metallurgy and extrusion. The effects on the tensile strength of composites were investigated by the volume fraction of short carbon fiber and temperature. The results showed that the carbon fiber was aligned to the extrusion direction in the composites. The yield strength of composites with 8 and 12 vol % short carbon fibers tested at 150 °C were approaching that of AA7075 tested at 100 °C produced by the same methods. The hardness of composites with 12 vol % short carbon fibers increased to over 200 HV0.1. The interface is mainly composed of Al4C3 and segregated by Mg, resulting in an efficient coupling between fiber and matrix. The enhancement in high-temperature strength is dependent on the load transfer mechanism and the contribution of residual thermal stress. The tensile strength of composites corresponded to the prediction model.

Effects of ultrasound assisted solidificaiton on the microstructure and mechanical properties of nano-sized TiB2/Al-4.5Cu composites

Ultrasound assisted solidification (UAS) was applied in the fabrication of nano-sized TiB2p/Al-4.5Cu composites with the aim of decreasing the aggregation of TiB2 particles at α-Al grain boundaries (GBs) and inducing more TiB2 particles to distribute within grains. Experimental results showed that UAS could remarkably refine microstructure of Al-4.5Cu matrix and induced more TiB2 particles to distribute within α-Al grains, leading to the further improvement in both strength and ductility of composites. This research indicated that ultrasound was able to promote the nucleation of α-Al on more TiB2 particles and made TiB2 particles more susceptible to engulfment by moving solid/liquid interface during the solidification. Curve regression fitting method was conducted based on the strengthening model considering yield strength of composites, by which it was found that the ratio of TiB2 particles playing strengthening effects was increased from 0.035 to 0.06 with UAS treatment, indicating that the improvement in mechanical properties of composites treated with UAS was mainly attributed to the distribution of more nano-sized TiB2 particles within α-Al grains.

Effect of rare metal element interfacial modulation in graphene/Cu composite with high strength, high ductility and good electrical conductivity

We investigated the atomic and electronic structures and interface interaction of graphene/copper interface with rare earth elements (REEs) modified using density functional theory. The effect of interface interaction enhancement induced by interfacial modification is revealed, which results in significant improvement of the mechanical properties of graphene/copper. Thereby, we applied a novel strategy to incorporate Y element at the interface of graphene nanoplatelets/copper (GNPs/Cu) to improve mechanical properties of composites. Tensile tests demonstrated that the yield strength of composites increases by 95.4% via very low fraction (0.2 wt%) of Y modification with elongation comparable to Cu, which exhibits excellent matched relationship between strength and ductility. Simultaneously, the composite equips with improved electrical conductivity compared with that of the matrix. We illustrated the strengthening effects of REEs modification at the interface that give rise to the effective load transfer, in consistence with the theoretical predication. Furthermore, the GNPs/Cu composites with the interface Ce/Sc elements modified were also fabricated, both of which showed excellent strength-ductility combination. Therefore, the universality of the present method is verified for the preparation of metal matrix composites with excellent mechanical properties through interface modification with REEs.

Experimental study and optimization of fracture properties of epoxy-based nano-composites: Effect of using nano-silica by GEP, RSM, DTM and PSO

The main purpose of this study was to examine, modelling and optimization the fracture toughness and the fracture energy of bisphenol-A epoxy resin reinforced by silica nano-particles. Three different approaches including Gene Expression Programming (GEP), Response Surface Method (RSM) and, Decision Tree Method (DTM) have been employed to predict the effects of particle size and the weight fraction of nano-particles on the mentioned parameters. Three sizes of the nano-particles with the mean diameters of 17 nm, 25 nm and 65 nm up to 6 wt% have been used. The two general series of the nano-composites consisting of unimodal and bimodal particle size systems have been investigated. Experimental and modelling results showed that the Young’s modulus, the fracture toughness and the fracture energy increased in all composites by the addition of the silica nano-particles and also by increasing the silica weight percent. In addition, it was observed that the particle size had no considerable effect on the properties. Mixed use of particles with different sizes in a composite also showed a negligible synergy effect on the Young’s modulus and the fracture characteristics. The addition of these nano-particles did not have a significant effect on the yield strength of composites. Moreover, the best modelling approach is selected and optimized values resulted by Particle Swarm Optimization (PSO). The fracture surface was examined to understand the role of nanoparticles on toughening mechanisms by SEM.

Investigation of Microstructural, Mechanical and Corrosion Properties of AA7010-TiB2 in-situ Metal Matrix Composite

Abstract Aluminum alloys with ceramic reinforced particulates are made prospective in aerospace, transportation, and industrial applications ampler to their low mass density, stiffness, and high specific strength. In this work, Aluminium Alloy(AA) 7010 - TiB2 (Titanium Diboride) composites with different amounts of reinforcement (5, 7.5 and 10 wt.%) were produced by the exothermic reaction of halide salts K2TiF6 and KBF4 added in 120% excess to the stoichiometric ratio with molten AA7010.The effect and dispersion of TiB2 particulates in AA7010 were analyzed by microstructural, mechanical and corrosion behavior. The dispersion of reinforcement in the matrix alloy was analyzed by optical microscope and field emission scanning electron microscope (FESEM) images. X-ray diffraction patterns of the prepared composites reveal the formation of TiB2 particles in the matrix alloy. Indeed samples are tested according to ASTM G34 standard for ex- foliation corrosion rate by weight loss method. The result shows improved hardness, tensile strength and yield strength of composites to about 35%, 260%, and 240% respectively. The mechanical and corrosion resistance of 10% TiB2 shows better results compared with matrix alloy and other concentrations of reinforcements.

Temperature dependent strengthening mechanisms and yield strength for CNT/metal composites

Strengthening mechanisms in CNT/metal composites are significant guidelines on composites design. However, the strengthening mechanisms at high temperatures have few been reported. In this work, the evolution of four common strengthening mechanisms in CNT/metal composites, including load transfer strengthening, grain refinement strengthening, enhanced dislocation density strengthening and Orowan strengthening, with temperature was investigated by our developed theoretical models. Then by considering those temperature dependent strengthening mechanisms, a temperature dependent yield strength model for CNT/metal composites was established. Further, the effects of residual thermal stress and quicker softening of matrix on the temperature dependent yield strength of composites were also taken into account. Good agreement is obtained between the model predictions and available experimental results. This study contributes a simple method to predict the yield strength for CNT/metal composites over a wide range of temperatures. In addition, the contribution of each strengthening mechanism to the yield strength of composites at different temperatures was extensively discussed. Some useful suggestions for the design of new CNT/metal composites with high yield strength at elevated temperatures were provided.

Magnesium alloy-silicon carbide composite fabrication using chips waste

Interest in Mg-based composites has grown with their potential use as engineering materials due to having a high strength-to-weight ratio, wear resistance, and creep behavior. While magnesium chips are typically considered as waste on production shop floors, there can be a promising way to fabricate Mg-based composites with carefully distributed reinforcements. This research is concerned with the reuse of AZ91 magnesium-alloy chips to fabricate Mg-based composites. The fabrication process requires to collect and clean magnesium chips and then mix them with SiC particles as reinforcements. Finally, this composition is melted and stirred by a stir casting method to fabricate the AZ91/SiC composites. The results clearly show that not only magnesium chips waste can be reused in a sustainable way, but also that they improve the reinforcement distribution substantially, leading to enhanced mechanical properties so that the composite yield strength increases by 62.7% when adding 5% SiC particles, volume percentage. Moreover, the composites with 5% reinforcements, demonstrate a hardness increase of about 46%.

Investigations on mechanical and wear behavior of nano Al2O3 particulates reinforced AA7475 alloy composites

In the present investigation synthesis, microstructure, mechanical and wear behavior of 5 weight percentage of nano Al2O3 particulate reinforced AA7475 alloy composites has been reported. AA7475 matrix composite containing nano Al2O3 were fabricated by conventional stir casting method. The microstructures of the composites were examined by scanning electron microscopy. Further, mechanical and wear behavior of as cast AA7475 alloy and AA7475 - 5 wt. % nano Al2O3 composites were studied. Mechanical properties like hardness, ultimate, yield strength and percentage elongation were evaluated as per ASTM standards. Pin on disc apparatus was used to conduct the dry sliding wear tests. The experiments were conducted by varying loads and constant sliding speed of 300rpm for sliding distance of 4000m. Microstructural observation revealed the uniform distribution of particles in the AA7475 alloy matrix. From the analysis, it was found that the hardness, ultimate tensile strength and yield strength of composites were increased due to addition of nano Al2O3 particle in the AA7475 alloy matrix. Percentage elongation of the composite decreased in 5 wt. % nano Al2O3 reinforced composites. Further, the volumetric wear loss was found to increase with the load and sliding distance for all materials. Worn surface analysis made by using scanning electron micrographs to know the various mechanisms involved in the wear process.

The improved mechanical properties of Al matrix composites reinforced with oriented β-Si3N4 whisker

The β-Si3N4 whiskers (β-Si3N4w) reinforced Al matrix composites were first fabricated by hot pressing, then treated through hot extrusion. The microstructure characterization demonstrated the preferred orientations of both β-Si3N4w and Al grains in the as-extruded composites. It indicated that β-Si3N4w were aligned along the extrusion direction and Al grains exhibited a distinct <111>Al texture. The interface between β-Si3N4w and Al was in a good bonding status without voids and reaction products. Effects of extrusion process on the mechanical properties of composites were also investigated. The results indicated the extrusion process had a prominent strengthening effect on the mechanical properties of composites. The maximum yield strength and ultimate tensile strength of composites reached up to 170 and 289 MPa, respectively, accompanied by a 12.3% elongation at fracture when the whisker fraction was 15 vol.%. This improvement was collectively attributed to the densification of composites, the strong interface, and the preferred orientation inside composites. The yield strength of the composites reinforced with 5 vol.% β-Si3N4w corresponded well with the theoretical value from different strengthening mechanisms.

Microstructure and Mechanical Properties of Powder Thixoforged Amorphous Ni55Nb35Si10-Reinforced Al Matrix Composites

Powder thixoforging was used to produce amorphous Ni55Nb35Si10-reinforced Al matrix composites from recycled Al powders obtained from ball-milled Al520 end-milled billets. The amorphous reinforcing material was uniformly dispersed in the Al matrix and bonded adequately with it without undesired interfacial reactions. The compressive yield strength of composites with 45% reinforcement content increased 248% to 794 MPa over as-cast samples. The maximum elongation and hardness of samples were 15%, and 60.4 HRA, respectively. The relative density of the unreinforced thixoforged sample was 99.8%, indicating near-perfect compaction of Al powders. The maximum elongation, hardness, and compressive yield strength of thixoforged monolithic matrix alloys were, respectively, 40%, 56.9 HRA, and 747 MPa (a 228% increase in CYS over the cast alloy). In contrast, cold-forged samples showed only 82% increase in compressive yield strength over the as-cast alloy. Powder thixoforging introduced in this study—even without reinforcement—delivers better mechanical properties compared to cold forging most likely due to the refinement and modification of the microstructure during powder ball milling.

Formation of transition layer and its effect on mechanical properties of AlCoCrFeNi high-entropy alloy/Al composites

The 5 vol% AlCoCrFeNi high-entropy alloy (HEA) reinforced Al matrix composites were fabricated successfully by spark plasma sintering at the temperatures ranging from 540 °C to 600 °C. At 540 °C, there is a smooth interface between HEA reinforcement and Al matrix. At the sintering temperature above 560 °C, the melting of particle-contacting zone between HEA reinforcement and Al matrix leads to the formation of a transition layer with a single FCC phase. Furthermore, its thickness increases with increasing sintering temperature. This is favorable for the transformation of the stress state from the iso-stress condition to the iso-strain condition for the composites during deformation process. Therefore, both yield strength and ductility are significantly improved. The yield strength and compressive strain of composites without transition layer are 96 MPa and 36%, respectively. In contrast, the yield strength of composites containing the transition layer with an average thickness of 7.6 μm is about 137 MPa and no macroscopic fracture can be observed in the Al matrix composite after 50% compression strain. This work can provide guidance for fabrication of HEA/Al composites with high strength and good plasticity.

Multiscale graphene/carbon fiber reinforced copper matrix hybrid composites: Microstructure and properties

Multiscale graphene/carbon fiber (G/CF) reinforcements were developed for copper matrix hybrid composites. The homegenious G/CF/Cu mixture powders were firstly prepared by the simple wet-mixing process, and then densified by hot-pressed sintering to obtain bulk composites. Microstructure, electrical conductivity and mechanical properties of such composites were investigated. In the sintered compacts, the hybrid G and CF reinforcements distributed randomly in Cu matrix. CF presented the various space orientations, and G nanosheets exhibited the interconnected network distribution. Hardness and tensile yield strength of composites were improved evidently by hybrid G/CF addition, which increased with G increasing. However, the ultimate tensile strength were firstly enhanced and then deteriorated by increasing G content. The lower electrical conductivity showed in the more G-added composite, but still reached more than 80.0% IACS. These performance change could be sought in the spatially geometrical distribution and characteristic of hybrid CF/G additions, and the relevant mechanisms were discussed.

Contact elasto-plasticity of inhomogeneous materials and a numerical method for estimating matrix yield strength of composites

Abstract For inhomogeneous materials such as case carburized steels, the localized micro-plasticity is induced at the scale of the inhomogeneity even if the stress field is elastic at the global scale. The matrix yield strength is a critical measure of integrity of such materials but is largely unknown and difficult to be directly measured due to the disturbances from distributed inhomogeneities. A numerical method is proposed to estimate the matrix yield strength of an inhomogeneous material. This allows for extracting matrix yield strength of the carburized bearing steel M50-NiL. The results show that, the difference between the macroscopic yield strength and matrix yield strength is small, suggesting that the direct strengthening from carbides as particle reinforcement is limited.