The effect of notch depth on J-integral and critical fracture load in plates made of functionally graded aluminum–silicone carbide composite with U-notches under bending

The present paper deals with the effect of notch depth on J-integral and critical fracture load in a plate made of functionally graded aluminum–silicone carbide composite (Al–SiC) with U-notch under bending. The weight fraction of SiC particles varies from 0% to 20% through the specimen width. Using three criteria namely mean stress (MS), point stress (PS), and averaged strain-energy density (ASED), the critical fracture load has been predicted and its variation with respect to the notch depth has been studied. A comparison of the J-integral between functionally graded and homogeneous Al–SiC composite were made, where the notch tip in the functionally graded material is situated in a layer with same mechanical properties as the homogeneous composite. The results indicated that in the case where the notch scene is toward brittleness increment the critical J-integral in functionally graded material (FGM) is larger than that of in homogeneous material with the same mechanical properties at the notch tip. Therefore, FGM is more convenient than homogeneous material against fracture.     

Development of Al 6063–TiB2 in situ composites

In situ TiB₂ reinforced Al 6063 composites have been successfully synthesized through the chemical reaction between Al–10%Ti and Al–3%B master alloys in the Al 6063 alloy using liquid metallurgy route. The amount of TiB₂ formed in the composite is estimated using gravimetric analysis. Mechanical properties in terms of microhardness, ultimate tensile strength and modulus of elasticity have been improved by 21%, 47% and 65% respectively in comparison with matrix alloy. Further, ductility in terms of percentage elongation of the composites was found to increase by about 368% when compared with the matrix alloy. The improvement in ductility may be associated with the grain refinement of the composite with an increase in the content of Al–3%B master alloy.     

Effect of cell shape anisotropy on the compressive behavior of closed-cell aluminum foams

The closed-cell Al–Si foams have been prepared by molten body transitional foaming process using TiH₂ foaming agent. The cell shape anisotropy ratio of specimens with various relative densities was measured. The quasi-static compressive behavior of Al–Si foams in both longitudinal and transverse directions were investigated. The results show that Al–Si foam loaded in the transverse direction exhibits a lower stress drop ratio. The relationship between plastic collapse stress ratio and cell shape anisotropy is in accordance with Gibson and Ashby model. The plastic collapse stress and the energy absorption property of Al–Si foams increase following power law relationship with relative density. Moreover, Al–Si foams exhibit higher plastic collapse stress and the energy absorption property in the longitudinal direction than that in the transverse direction.     

Structure and electrical properties of ZnO doped barium-metaphosphate glasses

The zinc–barium–metaphosphate glasses (ZBP) with composition of (50 − x)BaO–xZnO–50P₂O₅; (0 ≤ x ≤ 50 mol %), have been successfully prepared. The influences of the amount of ZnO on the structure, physical and chemical properties, and crystallization behavior of the glasses were investigated using Fourier transform infrared spectroscopy (FT-IR), differential scanning calorimetry (DSC), X-ray diffraction and energy dispersive X-ray techniques (XRD/EDX). The density and the glass transition temperature (T_g) of glass were measured using Archimedes' method and differential thermal analysis (DTA). The FTIR analysis revealed a shortening of the phosphate chains by the shift of (P–O–P)_as band to higher wave number owing to the substitution ZnO of BaO. The amount of ZnO was further increased, [ZnO4] tetrahedra were formed and ZnO acted as a glass network former, integrating the phosphate glass network. The density, chemical stability and the activation energy of crystallization of the glasses increased with the amount of ZnO, whereas the glass transition temperature decreased. The dc- and ac-conductivity were measured. The results obtained from ac-conductivity reveals that the values of σ(ω) increases on increasing frequency and it is also increases on increasing the ZnO content level. The dc-conductivity of all the glasses increases with an increase in temperature. The dielectric permittivity (?′) and loss factor (?″) were calculated in the frequency range of 50 Hz–1 MHz. The dipolar relaxation occurred between 10⁵–10⁶ Hz. Finally, the dielectric strength (Δ?) and the relaxation time (τ) were estimated.     

Compressive and impression creep behavior of a cast Mg–Al–Zn–Si alloy

Creep behavior of an Mg–6Al–1Zn–0.7Si cast alloy was investigated by compression and impression creep test methods in order to evaluate the correspondence of impression creep results and creep mechanisms with conventional compression test. All creep tests were carried out in the temperature range 423–523 K and under normal stresses in the range 50–300 MPa for the compression creep and 150–650 MPa for impression creep tests. The microstructure of the AZ61–0.7Si alloy consists of β-Mg₁₇Al₁₂ and Mg₂Si intermetallic phases in the α-Mg matrix. The softening of the former at high temperatures is compensated by the strengthening effect of the latter, which acts as a barrier opposing recovery processes. The impression results were in good agreement with those of the conventional compressive creep tests. The creep behavior can be divided into two stress regimes, with a change from the low-stress regime to the high-stress regime occurring, depending on the test temperature, around 0.009 < (σ/G) < 0.015 and 0.021 < (σ_imp/G) < 0.033 for the compressive and impression creep tests, respectively. Based on the steady-state power-law creep relationship, the stress exponents of about 4–5 and 10–12 were obtained at low and high stresses, respectively. The low-stress regime activation energies of about 90 kJ mol⁻¹, which are close to that for dislocation pipe diffusion in the Mg, and stress exponents in the range of 4–5 suggest that the operative creep mechanism is pipe-diffusion-controlled dislocation viscous glide. This behavior is in contrast to the high-stress regime, in which the stress exponents of 10–12 and activation energies of about 141 kJ mol⁻¹ are indicative of a dislocation climb mechanism similar to those noted in dispersion strengthening mechanisms.     

Effects of deposition and annealing conditions on the defects in the Al/glass composites of TFT specimens

Al/glass specimens are prepared following the orthogonal table of five-level six-factorial (L₂₅(5⁶)) design. The governing factors for the preparation of the specimens are deposition conditions, annealing temperature and annealing time. Defects, including hillocks and nanovoids, are found to be created during the annealing process. The threshold value of the annealing stress (σ _an ) required for the incipience of hillocks is thus determined. The stress change parameter, σ _f –σ _an (σ _f :internal stress after annealing), is a positive value that increases linearly with σ _an . The density of hillocks increases linearly with (σ _f –σ _an ) when the value of the stress change parameter is beyond the critical value (130 MPa). Nanovoids are produced even in specimens without hillocks. The wedge angle that forms in a specimen after wet etching linearly decreases with decreasing (σ _f –σ _an ). A high wedge angle lowers the hillock density at the wedge slope. The electrical resistance of the gate layer linearly increases with increasing product value (R*) of the mean size (area) and the density of nanovoids. R* increases nonlinearly with increasing (σ _f –σ _an ).     

Constitutive equations for elevated temperature flow stress of Ti–6Al–4V alloy considering the effect of strain

In order to study the workability of Ti–6Al–4V alloy, the experimental stress–strain data from isothermal hot compression tests, in a wide range of temperatures (800–1050 °C) and strain rates (0.0005–1 s⁻¹), were used to develop the constitutive equation of different phase regimes (α + β and β phase). The effects of temperature and strain rate on deformation behaviors a represented by Zener–Holloman parameter in an exponent-type equation. The influence of strain was incorporated in constitutive analysis by considering the effect of strain on material constants. Correlation coefficient (R) and average absolute relative error (AARE) were introduced to verify the validity of the constitutive equation. The values of R and AARE were 0.997% and 9.057% respectively, which indicated that the developed constitutive equation (considering the compensation of strain) could predict flow stress of Ti–6Al–4V alloy with good correlation and generalization.     

Effect of A-site cation size on magnetic and charge-ordering properties of Ln0.5Sr0.5Mn0.9Cu0.1O3 (Ln = La,Pr, Nd,or Ho)

The structural, magnetic, and electrical properties of Ln_0.5Sr_0.5Mn_0.9Cu_0.1O₃ (Ln = La, Pr, Nd, or Ho) perovskite manganites have been investigated to explore the influence of A-site cation radius (〈r_A〉) and the A-site cation size-disorder (σ²) on the various interdependent phenomena such as ferromagnetism (FM), phase separation (PS), and charge ordering (CO). The temperature dependence magnetization (M–T) curve of La-based sample shows four distinct points at ∼269 K, 255 K, 200 K, and 148 K corresponding to strong FM, cluster glass (CG), weak FM, and charged ordered antiferromagnetic (COAFM) transitions, respectively. Our investigation shows that Neel temperatures (T_N) increases, whereas Curie (T_C) and irreversibility temperatures (T_irr) decrease with decreasing 〈r_A〉, i.e., with increasing σ². Furthermore, the value of the magnetization decreases and resistivity increases with decreasing 〈r_A〉. All samples exhibit insulating behavior in the temperature range 77–300 K and above 110 K the electronic conduction mechanism has been described within the framework of the variable range hopping (VRH) model.     

Fabrication,characterization and wear corrosion testing of bioactive hydroxyapatite/nano-TiO2 composite coatings on anodic Ti–6Al–4V substrate for biomedical applications

This study elucidated structure and mechanical properties of the electroplated hydroxyapatite/nano-TiO₂ composite coatings on Ti–6Al–4V alloy. Their effect on the corrosion and wear corrosion resistance in Hanks’ solution was examined as well. The anodizing process was performed on Ti–6Al–4V alloy surface to enhance the adhesion of these composite coatings on Ti alloy. Anodizing treatment was then conducted at 10 V at room temperature with different times of 40, 50, 60, 120 and 180 min. Experimental results indicate that the hardness of Ti–6Al–4V alloy was increased due to the anodizing treatment, capable of improving the adhesion of electroplated calcium phosphate coating in addition to the electroplated hydroxyapatite/nano-TiO₂ composite coatings. Additionally, the coatings on anodic substrate exhibited a higher uniformity and Ca/P ratio and thickness than that on nonanodized substrate. The nano-TiO₂ particles could be co-deposited on the Ti–6Al–4V alloys and capable of reinforcing the hydroxyapatite coating, subsequently increasing the hardness and refining the structure. Moreover, the corrosion and wear corrosion resistance of the electroplated hydroxyapatite/nano-TiO₂ composite coatings were also improved significantly when increasing the duration of anodizing alloy substrates.     

Aluminium-free glass polyalkenoate cements: ion release and in vitro antibacterial efficacy

Glass polyalkenoate cements (GPCs) have exhibited potential as bone cements. This study investigates the effect of substituting TiO₂ for SiO₂ in the glass phase and the subsequent effect on cement rheology, mechanical properties, ion release and antibacterial properties. Glass characterization revealed a reduction in glass transition temperature (T _g ) from 685 to 669 °C with the addition of 6 mol % TiO₂ (AT-2). Magic angle spinning nuclear magnetic resonance (MAS-NMR) revealed a shift from ?81 ppm to ?76pmm when comparing a Control glass to AT-2, indicating de-polymerization of the Si network. The incorporation of TiO₂ also increased the working time (T _w ) from 19 to 61 s and setting time (T _s ) from 70 to 427 s. The maximum compressive strength (σ _c ) increased from 64 to 85 MPa. Ion release studies determined that the addition of Ti to the glass reduced the release of zinc, calcium and strontium ions, with low concentrations of titanium being released. Antibacterial testing in E. coli resulted in greater bactericidal effects when tested in aqueous broth for both titanium containing cements.     

Interfacial microstructure and shear strength of Ti–6Al–4V/TiAl laminate composite sheet fabricated by hot packed rolling

A two layer Ti–6Al–4V(wt.%)/Ti–43Al–9V–Y(at.%) laminate composite sheet with a uniform interfacial microstructure and no discernible defects at the interfaces has been prepared by hot-pack rolling, and its interfacial microstructure and shear strength were characterized. Characterization of the interfacial microstructure shows that there was an interfacial region of uniform thickness of about 250 μm which consisted of two layers: Layer I on the TiAl side which was 80 μm thick and Layer II on the Ti–6Al–4V side which was 170 μm thick. The microstructure of Layer I consisted of massive γ phases, needlelike γ phases and B2 phase matrix, while the microstructure of Layer II consisted of α₂ phase. The microstructure of the interfacial region is the result of the interdiffusion of Ti element from Ti–6Al–4V alloy layer into the TiAl alloy layer and Al element from the TiAl alloy layer into the Ti–6Al–4V alloy layer. The shear strength measurement demonstrated that the bonding strength between the TiAl alloy and Ti–6Al–4V alloy layers in the laminate composite sheet was very high. This means that the quality of the interfacial bonding between the two layers achieved by the multi-path rolling is high, and the interface between the layers is very effective in transferring loading, causing significantly improved toughness and plasticity of the TiAl/Ti–6Al–4V laminate composite sheet.     

Analysis of workability behavior of Al–SiC P/M composites using backpropagation neural network model and statistical technique

This paper presents an artificial neural network (ANN) model for predicting and analyzing the workability behavior during cold upsetting of sintered Al–SiC powder metallurgy (P/M) metal matrix composites (MMCs) under triaxial stress state condition which is the multifaceted technological concept, depending upon the ductility of the material and the process parameters. The input parameters of the ANN model are the preform density, the particle size, the percentage of reinforcement and the applied load. The output parameters of the model are the axial stress, the hoop stress, the axial strain, the hoop strain, the instantaneous strain hardening index, and the instantaneous strength coefficient. This model is a feed forward backpropagation neural network and is trained and tested with pairs of input/output data. A very good performance of the neural network, in terms of good agreement with the experimental data has been achieved. As a secondary objective, quantitative and statistical analyses were performed in order to evaluate the effect of the process parameters on the workability and the plastic deformation behavior of the composites.     

Interfacial reactions and wetting in Al–Mg/oxide ceramic interpenetrating composites made by a pressureless infiltration technique

The present paper considers the microstructures of Al–Mg/oxide ceramic interpenetrating composites made by a pressureless infiltration technique. The composites were produced using an Al–10 wt.% Mg alloy with two oxide ceramic foams, spinel (MgAl₂O₄) and mullite (Al₆Si₂O₁₃), at 915 °C in a flowing N₂ atmosphere. Full infiltration of the aluminium alloy into the ceramic preform has been achieved with good bonding between the metal and ceramic phases. The composites were characterised by a range of techniques and compared with those for alumina from the literature. It has been found that the metal–ceramic interface of the composite consisted of an oxide layer near the ceramic phase and a nitride layer from Mg₃N₂ to AlN near the metal phase. The improvement of Al wetting and adhesion on the oxide ceramics by the addition of Mg and in the presence of N₂ was studied by a sessile drop technique to clarify which compound that formed at the interface contributed to the spontaneous infiltration.     

Hydrogen absorption/desorption properties of Li–Al–N–H composite

Li₃AlH₆ and LiNH₂ at a 1:3 molar ratio were mechanically milled to yield a Li–Al–N–H composite. The hydrogen storage properties of the composite were studied using thermogravimetry, differential scanning calorimetry, mass spectrometry, and X-ray diffraction. Addition of LiNH₂ lowered the decomposition temperature of Li₃AlH₆. The Li–Al–N–H composite began to release hydrogen at around 110 °C, which was 90 °C lower than the initial desorption temperature of Li₃AlH₆. About 7.46 wt% of hydrogen was released from the composite after heating from room temperature to 500 °C. A total hydrogen desorption capacity of 8.15 wt% was obtained after accounting for hydrogen released in the ball-milling process. The resulting dehydrogenated composite absorbed 3.56 wt% of hydrogen at 400 °C under a hydrogen pressure of 110 bar. The hydrogen absorption capacity and kinetic properties of the Li–Al–N–H composite significantly improved when CeF₃ was added to the composite. A maximum hydrogen absorption capacity of 4.8 wt% was reached when the composite was doped with 2 mol% CeF₃.     

Formation of Al3Ti/Mg composite by powder metallurgy of Mg–Al–Ti system

An in situ titanium trialuminide (Al₃Ti)-particle-reinforced magnesium matrix composite has been successfully fabricated by the powder metallurgy of a Mg–Al–Ti system. The reaction processes and formation mechanism for synthesizing the composite were studied by differential scanning calorimetry (DSC), x-ray diffractometry (XRD), scanning electron microscopy (SEM) and energy-dispersive x-ray spectroscopy (EDS). Al₃Ti particles are found to be synthesized in situ in the Mg alloy matrix. During the reaction sintering of the Mg–Al–Ti system, Al₃Ti particles are formed through the reaction of liquid Al with as-dissolved Ti around the Ti particles. The formed intermetallic particles accumulate at the original sites of the Ti particles. As sintering time increases, the accumulated intermetallic particles disperse and reach a relatively homogeneous distribution in the matrix. It is found that the reaction process of the Mg–Al–Ti system is almost the same as that of the Al–Ti system. Mg also acts as a catalytic agent and a diluent in the reactions and shifts the reactions of Al and Ti to lower temperatures. An additional amount of Al is required for eliminating residual Ti and solid-solution strengthening of the Mg matrix.     

Tensile behavior of glass/epoxy laminates at varying strain rates and temperatures

In the present work tensile tests at different strain rates and temperatures were performed in glass fiber reinforced polymer (GFRP). It is observed that such kind of composite presents an elasto–viscoplastic behavior – the rate dependency only occurs for loading levels above a given elasticity limit. Strain rate strongly affects the ultimate tensile strength (σ_u) and the modulus of elasticity is almost insensitive to it while temperature only influences the modulus. Analytical expressions to predict the modulus of elasticity and (σ_u) as a function of the temperature and strain rate are proposed and compared with experimental data showing a reasonable agreement.     

Influence of equal channel angular extrusion processing parameters on the microstructure and mechanical properties of Mg–Al–Y–Zn alloy

An as-cast Mg–Al–Y–Zn alloy was successfully processed by equal channel angular extrusion (ECAE) in the temperature range of 225–400 °C, and the influences of processing temperature on the microstructure and mechanical properties were investigated. The use of back pressure during one-pass ECAE of Mg–Al–Y–Zn alloy was favorable for eliminating the undeformed area in the billet. At the processing temperature below 250 °C, the microstructures were characterized by unrecrystallised structure and the precipitated phase Mg₁₇Al₁₂ was elongated along the extrusion direction. With increasing processing temperature to 350 °C, a large number of recrystallised grains were obtained. Increasing processing temperature promoted workability but led to decrease in the strength of Mg–Al–Y–Zn alloy. Then billets of as-cast Mg–Al–Y–Zn alloy were extruded at different numbers of ECAE passes. It was found that the microstructure was effectively refined by ECAE and mechanical properties were improved with numbers of ECAE passes increasing from one-pass to four passes. However, strengths decreased slightly after five passes though the grain size decreased considerably.     

Effect of room-temperature aging on shape memory characteristics of Ti–10Nb–10Zr–11Ta (at.%) alloy

In this study, the effect of room-temperature (RT) aging on the shape memory characteristics of the Ti–10Nb–10Zr–11Ta (at.%) alloy was investigated by tensile tests. Ingots were prepared using the arc melting method and then cold-rolled at a reduction of up to 95%. After cold-rolling, the plates were solution-treated at 1173 K for 1.8 ks, followed by aging at RT and temperatures up to ∼573 K for various periods of times. Superior superelasticity was observed at RT in the solution-treated specimen. The critical stress for inducing martensitic transformation (σ_SIM), tensile strength, and critical stress for slip (σ_S) of specimens aged at RT increased with increasing aging time up to 60 days, showing no noticeable changes with further increases in the aging time. On the other hand, in the specimens aged at 373 K, 423 K, and 473 K for 3.6 ks, the values of σ_SIM and the tensile strength increased with increasing aging temperature, while the specimen aged at 573 K exhibited mature fractures. There were little change in σ_SIM and σ_S of the specimen that was solution-treated followed by aging at 373 K for 3.6 ks during RT aging. This result indicated that aging at 373 K resulted in good resistance against the effect of RT aging.     

Study of transport properties and conduction mechanism of pure and composite resorcinol formaldehyde aerogel doped with Co-ferrite

A series of resorcinol formaldehyde aerogels (RF aerogels) composite with nanoparticles of CoFe₂O₄ have been prepared by sol–gel method. Four samples of pure RF aerogels were prepared at different concentrations of Na₂CO₃ as catalyst (0.02, 0.025, 0.03, and 0.04 wt.%) and four samples of composite RF aerogels were prepared at different concentration of doped CoFe₂O₄ (0.075, 0.1, 0.125, and 0.15 wt.%; Na₂CO₃ concentration = 0.03 wt.%). DC electrical conductivity as a function of temperature was studied in the temperature range 25 °C–200 °C for all samples. AC electrical conductivity and dielectric properties were determined using RLC Bridge in the frequency range 100 Hz–1 MHz at different temperature (25–200 °C). The pore size of the samples was determined using positron annihilation lifetime spectroscopy (PALS). RF aerogels are found to exhibit a semiconducting behavior and characterized by two transition temperatures T₁ and T₂. Also σ_DC increases with increase of Co-ferrite contents. Pure RF aerogels posses a very low dielectric constant, where the lowest value of ?′ is ∼4 times as that of air. ?′ decreases with increase of frequency, and increases with increase of temperature. Large overlapping polaron (OLP) is found to be the preferred conduction mechanism in these materials. The results of PALS show that there are two types of pore size in these samples; the first ranges from 1.9 to 2.5 nm, while the second ranges from 3.2 to 5.3 nm.