Effect of the SiC particle size on the dry sliding wear behavior of SiC and SiC–Gr-reinforced Al6061 composites

The effect of size of silicon carbide particles on the dry sliding wear properties of composites with three different sized SiC particles (19, 93, and 146 μm) has been studied. Wear behavior of Al6061/10 vol% SiC and Al6061/10 vol% SiC/5 vol% graphite composites processed by in situ powder metallurgy technique has been investigated using a pin-on-disk wear tester. The debris and wear surfaces of samples were identified using SEM. It was found that the porosity content and hardness of Al/10SiC composites decreased by 5 vol% graphite addition. The increased SiC particle size reduced the porosity, hardness, volume loss, and coefficient of friction of both types of composites. Moreover, the hybrid composites exhibited lower coefficient of friction and wear rates. The wear mechanism changed from mostly adhesive and micro-cutting in the Al/10SiC composite containing fine SiC particles to the prominently abrasive and delamination wear by increasing of SiC particle size. While the main wear mechanism for the unreinforced alloy was adhesive wear, all the hybrid composites were worn mainly by abrasion and delamination mechanisms.     

Evaluation of non-linear behavior of timber–concrete composite structures using FE model

This article describes a numerical model that was developed for the analysis of composite timber–concrete beams. This model presents a simplified methodology for determining the effective bending stiffness of the timber–concrete composite structure. It is based on previous work done usually referred to in some non-normative literature by γ-method. The implemented methodology assumes some simplifications, as for instance, linear elastic behavior of all components, constant stiffness of the connection and sinusoidal loading. For comparison purposes, the work benefits from an experimental program in which full-scale beams were tested in bending and timber–concrete connections were tested in shear. The FE model has shown the ability to overcome the simplifications of the Eurocode, namely the variation of shear force along the beam axis. The numerical model is capable of detecting and quantifying the influence of the non-linear behavior of the connections on the composite structure. Different parameters are analyzed and, for instance, the ductility behavior of the timber–concrete connection could be more important than the maximum strength, which is an interesting result. By comparing theoretical predictions with test results, it is clear that the numerical model used in this work is a very interesting method when compared with the usual design models, such as that of Annex B of Eurocode 5 (EN 1995-1-1). The influence of the connections behavior on the ultimate load of the composite structure is very important and the described approach proved to give good predictions.     

Evaluation of subgrain formation in Al2O3–SiC nanocomposites

Both theoretical analysis and transmission electron microscopy (TEM) complementary studies have been conducted to evaluate the possible role of subgrain formation as a strengthening mechanism in a nanocomposite consisting of Al2O3 and 5 vol % 0.15 m SiC particles. The theoretical calculation predicted that the residual stresses due to thermal expansion mismatch between Al2O3 and SiC are insufficient to induce the extensive plastic deformation required for subgrain formation upon annealing. This prediction was consistent with TEM observations that the bulk of the material was completely free from subgrains, and that only a low density of dislocations was present in isolated areas. The results suggest, therefore, that microstructure refinement through subgrain formation cannot account for the superior mechanical behaviour of the nanocomposite reported in previous studies.TEM examination of the ground surfaces revealed significant plastic deformation in both single phase Al2O3 and the nanocomposite. Upon annealing at 1300°C for 2 h, dislocation-free subgrains were formed in Al2O3, whereas a high density of tangled dislocations were present in the nanocomposite. These observed differences are consistent with the fact that during annealing, residual stress relaxation is more difficult in the nanocomposite than in Al2O3.     

High and low cycle fatigue behavior of linear friction welded Ti–6Al–4V

Linear friction welded Ti–6Al–4V was investigated in fatigue at various stress amplitudes ranging from the high cycle fatigue (HCF) to the low cycle fatigue (LCF) regime. The base material was composed of hot-rolled Ti–6Al–4V plate that presented a strong crystallographic texture. The welds were characterized in terms of microstructure using electron backscatter diffraction and hardness measurements. The microstructural gradients across the weld zone and thermomechanically affected zone of the linear friction welds are discussed in terms of the crystallographic texture, grain shape and hardness levels, relative to the parent material. The location of crack nucleation under fatigue loading was analyzed relative to the local microstructural features and hardness gradients. Though crack nucleation was not observed within the weld or thermomechanically affected zones, its occurrence within the base material in LCF appears to be affected by the welding process. In particular, by performing high resolution digital image correlation during LCF, the crack nucleation site was related to the local accumulation of plastic deformation in the vicinity of the linear friction weld.     

Deformation behavior of Al–Si alloy based nanocomposites reinforced with carbon nanotubes

Nanocrystalline Al–Si alloy-based composites containing carbon nanotubes (CNTs) were produced by hot rolling ball-milled powders. During the milling process, the grain size was effectively reduced and the Si element was dissolved in the Al matrix. Furthermore, CNTs were gradually dispersed into the aluminum powders, providing an easy consolidation route using a thermo-mechanical process. The composite sheet containing 3 vol.% of CNTs shows ～520 MPa of yield strength with a 5% plastic elongation to failure.     

Fabrication and mechanical evaluation of SiC–TiC nanocomposites by SPS

In the present study, the composites of SiC–TiC are prepared by spark plasma sintering (SPS) in vacuum without additive. The relationship of density and temperature of SiC–TiC composites with different content of TiC is studied. The maximum relative density reached was 98%. The mechanical properties of SiC–TiC composites with different content of TiC, which were sintered at 1800 °C, have been evaluated. From the fracture surface observation, two models of fracture mechanisms of the composites existed: transgranular and intergranular.     

Low-temperature microwave sintering of TiN–SiC nanocomposites

Densification kinetics study during microwave sintering of titanium nitride-based nanocomposite has been conducted. A series of TiN–SiC compositions with 1, 3, 5 wt% of silicon carbide were microwave sintered at relatively low sintering temperatures (900–1,300 °C) for 0–30 min. The SiC content influenced on heating uniformity and final density and grain-size achieved. Densification process during microwave sintering obeyed the mechanism of grain-boundary diffusion with activation energy of 235 kJ mol⁻¹. Microwave sintering resulted in fine microstructure (~300 nm) and hence high values of micro hardness (~20 GPa).     

A comparative study on the capability of Johnson–Cook and Arrhenius-type constitutive equations to describe the flow behavior of Mg–6Al–1Zn alloy

In the current study, the predictability of two phenomenological constitutive equations, Johnson–Cook (JC) and Arrhenius-type ones, for describing the flow behavior of a magnesium alloy (Mg–6Al–1Zn) under hot deformation conditions has been evaluated. Towards this end, a series of hot compression tests were performed over a temperature range of 250–450 °C, under strain rates of 0.001, 0.01 and 0.1 s⁻¹. Using the experimental results obtained through implementing the predetermined compression tests, the related parameters and material constants in the constitutive equations were calculated. In order to compare the performance of the models, the statistical parameters of correlation coefficient and absolute mean error were employed. The results imply that the predictability of the Arrhenius-type equations is much stronger in estimating the flow behavior compared to that of the JC model; although more constants are needed to be calculated when using the former equation. It is concluded that the JC model, in contrast to the Arrhenius-type equations, is not reliable for the materials possessing tangible softening stage in their stress–strain curves such as magnesium AZ series.     

Study of linear and non-linear optical properties of In–Se doped chalcogenide semiconducting glasses

Journal of Materials Science: Materials in Electronics - The present work focuses on the various linear and non-linear optical properties of antimony (Sb) and gallium (Ga) (both 0.1 at.%) doped...     

New exact solutions of the Tzitzéica-type equations in non-linear optics using the expa function method

One specific class of non-linear evolution equations, known as the Tzitzéica-type equations, has received great attention from a group of researchers involved in non-linear science. In this article, new exact solutions of the Tzitzéica-type equations arising in non-linear optics, including the Tzitzéica, Dodd–Bullough–Mikhailov and Tzitzéica–Dodd–Bullough equations, are obtained using the exp_a function method. The integration technique actually suggests a useful and reliable method to extract new exact solutions of a wide range of non-linear evolution equations.     

Study on the machining of Al–SiC functionally graded metal matrix composite using die-sinking EDM

Functionally graded aluminum matrix composites (FGAMCs) are new materials with excellent capabilities for design and development of complex engineering works. In this work, FGAMCs are machined using electrical discharge machining (EDM) with the process input parameters such as pulse current, pulse on time, and zone position in brake disk. Design of experiments is used for the experimental planning with full factorial method. The selected input process parameters are optimized using gray relational analysis to minimize the electrode wear ratio, overcut, power consumption, and surface roughness. The influential studies of input process parameters on the output responses are also conducted. The optimal EDM parameter setting for achieving better output parameters is pulse current at 5 A, pulse on time at 50?µs and 45?mm zone position distance in the brake disk. The pulse current (39.40%) contributed the maximum in minimizing the output responses. Further, the surface morphology is also analyzed on the material to observe the crater formation and the erosion mechanism.     

Wetting behavior and interfacial microstructure of palladium- and silver-based braze alloys with C–C and SiC–SiC composites

High-temperature sessile-drop wettability tests were conducted on unpolished C–C and SiC–SiC composite substrates using commercial braze alloys Palco (Pd-35Co), Palni (Pd-40Ni), Cusil-ABA (63Ag–35.3Cu–1.75Ti), and Ticusil (68.8Ag–26.7Cu–4.5Ti). Observations revealed non-uniform, anisotropic spreading, copious braze infiltration of the composite substrates, particularly C–C composite, and Ti enrichment at the composite/braze interface together with dissolution of Si (from SiC–SiC composite) in braze and diffusion of Co (from Palco) in the composite. The droplet/composite contact region near the droplet center revealed intimate and microstructurally sound bonding. However, inter-laminar shear cracking within the SiC–SiC composite in contact with Ticusil, Palco, and Palni, and partial substrate/droplet de-cohesion near the edge of the droplet were also observed. In Palco and Palni droplets, fiber tows in the contact region de-laminated from the main body of the composite via inter-laminar shear cracking resulting in fiber flotation, segregation, and surface degradation. The study is one of the first empirical enquiries into the complex wetting and spreading behavior of brazes on commercial C–C and SiC–SiC composites.     

Effects of post-annealing on the microstructure and mechanical properties of friction stir processed Al–Mg–TiO2 nanocomposites

Aluminum matrix nanocomposites were fabricated via friction stir processing of an Al–Mg alloy with pre-inserted TiO₂ nanoparticles at different volume fractions of 3%, 5% and 6%. The nanocomposites were annealed at 300–500 °C for 1–5 h in air to study the effect of annealing on the microstructural changes and mechanical properties. Microstructural studies by scanning and transmission electron microscopy showed that new phases were formed during friction stir processing due to chemical reactions at the interface of TiO₂ with the aluminum matrix alloy. Reactive annealing completed the solid-state reactions, which led to a significant improvement in the ductility of the nanocomposites (more than three times) without deteriorating their tensile strength and hardness. Evaluation of the grain structure revealed that the presence of TiO₂ nanoparticles refined the grains during friction stir processing while the in situ formed nanoparticles hindered the grain growth upon the post-annealing treatment. Abnormal grain growth was observed after a prolonged annealing at 500 °C. The highest strength and ductility were obtained for the nanocomposites annealed at 400 °C for 3 h.     

Mechanical behavior and wear prediction of stir cast Al–TiB2 composites using response surface methodology

Al6061 was reinforced with various percentages of TiB₂ particles by using high energy stir casting method. The characterization was performed through X-ray Diffraction, Energy Dispersive Spectrum and Scanning Electron Microscope. The mechanical behaviors such as hardness, tensile strength and tribological behavior were investigated. Wear experiments were conducted by using a pin-on-disc wear tester at varying load. The curve fitting technique was used to develop the respective polynomial and power law equations. The wear mechanism of the specimen was studied through SEM. Response Surface Methodology was used to minimize the number of experimental conditions and develop the mathematical models between the key process parameters namely weight percentage of TiB₂, load and sliding distance. Analysis of Variance technique was applied to check the validity of the developed model. The mathematical model developed for the specific wear rate was predicted at 99.5% confidence level and some useful conclusions were made.     

Microstructure and thermal expansion behavior of spray-deposited Al–50Si

The evolution of microstructure and coefficient of thermal expansion (CTE) of the Al–50Si (wt.%) alloy manufactured by spray deposition followed by hot isostatic pressing (HIP) are systematically investigated. The results indicate that the microstructure of the deposited alloy is composed of primary Si with average size of 12.5 ± 0.1 μm and α-Al. The CTE of the deposited alloy is higher than the corresponding alloy produced by casting due to the high solid solubility of Al in Si. After HIP, the CTE is lower than the parent as-deposited alloy owing to the high solid solubility of Si in Al. The residual thermal stress results in a higher CTE during the second heating as a result of the CTE mismatch between the Al matrix and the primary Si particles. Furthermore, the measured CTE value is in good agreement with the Turner model after complete densification by HIP at 843 K.     

Influence of notch radius and microstructure on the fracture behavior of Al–Zn–Mg–Cu alloys of different purity

The influence of notch radius on the fracture behavior of two high-strength Al–Zn–Mg–Cu alloys with different Fe content in the T73 condition was investigated. The fracture toughness tests were performed on non-fatigue-precracked notched bending specimens with different notch radii ranged from 0.15 mm to 1.0 mm. The obtained data were interpreted using the concept of Notch Fracture Mechanics combined with finite-element method (FEM) calculations. It was found that both alloys are very sensitive to the notch radius. The fracture toughness increases with increasing notch radius. For a given notch radii, the increase in fracture toughness is more significant for the more pure alloy. The fracture behavior of investigated alloys with respect to microstructural features and their relation with the fracture micromechanisms were analyzed.     

Investigation of corrosion and mechanical properties of Al–Cu–SiC–xNi composite alloys

In this study, dry sliding wear behavior and corrosion resistance of Al–Cu–SiC–xNi (x: 0, 0.5, 1, 1.5 wt.%) composites were investigated. Effect of nickel content on the microstructure and hardness of the alloys was also studied. Wear tests were conducted using a ball on disc wear test device. Corrosion behavior of Al–Cu–SiC–xNi composite alloys in 3.5% NaCl solution was investigated by using potentiodynamic polarization, impedance spectroscopy and cronoamperometric methods. The results showed that the hardness of the composite alloy increases with increasing nickel content. Maximum wear resistance is reported with the addition of 1 wt.%Ni. It was determined that corrosion resistance of Al–Cu–SiC composite alloys improved with increasing nickel content in the alloy.     

Effect of sliding distance on the wear and friction behavior of as cast and heat-treated Al–SiCp composites

The present investigation aims to evaluate the effect of sliding distance on the wear and friction behavior of as cast and heat-treated Al–SiCp composites using pin-on-disc wear testing machine, giving emphasis on the parameters such as wear rate and coefficient of friction as a function of sliding distance (0–5000 m) at different applied pressures of 0.2, 0.6, 1.0 and 1.4 MPa, and at a fixed sliding speed of 3.35 m/s. Characterizing the alloy and composites in terms of microstructure, X-ray diffraction analysis, microhardness and wear surface analysis. The results revealed that the heat-treated composite exhibited superior wear properties than the base alloy, while the coefficient of friction followed an opposite trend. Moreover, the wear rate of the composite is noted to be invariant to the sliding distance and increased with applied pressures. Microstructure of composite shows fairly uniform distribution of SiC particles in the metallic matrix. The hardness value of heat-treated composite increased 20–30% by addition of SiC particles to the alloy, intermetallic phases like Al₂Mg₃ and Al₂CuMg, etc., were obtained from X-ray analysis. The wear mechanism of the investigated materials was studied through worn surfaces examination of the developed wear tracks.     

The role of thermal residual stress on the yielding behavior of carbon nanotube–aluminum nanocomposites

The initial yield envelopes of aluminum (Al) nanocomposites reinforced with carbon nanotubes (CNTs) subjected to biaxial loading are predicted in the presence of thermal residual stress (TRS) arising from the manufacturing process. Micromechanical model based on the unit cell method is presented to generate the yielding surfaces. The formation of the interphase caused by the interfacial reaction between the CNT and Al matrix is taken into account in the analysis. The effects of several important parameters, i.e. the change of temperature, CNT volume fraction, interphase thickness and Al material properties on the yielding onset of the CNT/Al nanocomposite are explored extensively. The results clearly reveal that the initial yield surfaces of nanocomposite are dependent on the TRS. Also, the interphase has a significant influence on the yielding behavior of Al nanocomposite in the presence of TRS. The results demonstrate that the size of initial yield surfaces become minimum with considering the coupled effects of TRS and interphase. With increasing the temperature variation, interphase thickness, elastic modulus and coefficient of thermal expansion of Al matrix, the size of initial yield surfaces reduces. The present study is consequential for understanding the key role of TRS on the initial damage of CNT/Al nanocomposites.     

Fatigue fracture of friction-stir processed Al–Al3Ti–MgO hybrid nanocomposites

This paper presents experimental results on the fatigue properties of Al-matrix nanocomposites prepared by the friction stir processing (FSP) technique. An Al–Mg alloy (AA5052) with different amounts (∼2 and 3.5 vol%) of pre-placed TiO₂ nanoparticles were FSPed up to 6 passes to attain homogenous dispersion of nano-metric inclusions. Microstructural studies by electron microscopic and electron back scattering diffraction (EBSD) techniques showed that nano-metric Al₃Ti (50 nm), TiO₂ (30 nm), and MgO (50 nm) particles were distributed throughout a fine-grained Al matrix (<2 μm). Consequently, a significant improvement in the tensile strength and hardness was attained. Uniaxial stress-controlled tension–tension fatigue testing (R = 0.1) were utilized to evaluate the fatigue behavior of the prepared nanocomposites. The results were compared with the un-processed (annealed) and FSPed alloy without pre-placing TiO₂ particles. It was found that FSP of the aluminum alloy increased the fatigue strength (at 10⁷ cycles) for about 28% and 32% compared with the annealed specimen when the concentration of the reinforcing particles was 2 and 3.5 vol%, respectively. Fractographic analysis determined a ductile fracture behavior with deep-equiaxed dimples for the annealed and FSPed alloy. The facture surface of the nanocomposites revealed a combined ductile–brittle fracture mode with finer dimples. The mechanism of the fatigue fracture and the role of nano-metric inclusions were elaborated.