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.     

Investigation on diffusion bonding of functionally graded WC–Co/Ni composite and stainless steel

A functionally graded WC–Co/Ni composite (FGWC) and 410 stainless steel (410ss) were successfully bonded by diffusion bonding. With the bonding temperature or holding time increasing, the tensile strength of the joints increased firstly and then decreased. The maximum tensile strength of the FGWC/410ss joints was 195 MPa bonded at 950 °C for 80 min. A diffusion layer was formed between the Ni layer and the 410ss as a result of the interdiffusion of Ni and Fe. The Ni layer could release the residual stresses of the FGWC/410ss joints. The fracture of the FGWC/410ss joints occurred in the Ni layer by the way of ductile fracture.     

Effect of nano-metal particles on the fracture toughness of metal–ceramic composite

A theoretical model is proposed to study the influence of nano-metal particles (NMPs) on the fracture toughness of metal–ceramic composites (MCC). In the framework of the model, the crack tip intersects the grain boundary of the NMPs. Stress concentration at crack tip initiates edge dislocations which makes a shielding effect on the crack and leads to fracture toughness of the MCC. The dependence of critical crack intensity factors on grain size of the NMPs was calculated. The calculation suggested that the existence of the NMPs lead to an increase of critical crack intensity factors by 14%.     

The ballistic performance of SiC–AA7075 functionally graded composite produced by powder metallurgy

The potential of silicon carbide reinforced Functionally Gradient Material (FGM) to be used as armor material was investigated under the impact of armor piercing projectile. For this purpose, the SiC–Aluminum Alloy (AA) 7075 functionally graded composite at different thicknesses was produced from the metallic and ceramic powders via powder metallurgy method. Before the ballistic testing, the precipitation hardening behavior of the samples was determined. And also, the microstructural characterizations of the samples were done with the aid of microscopy techniques. Next, the FGM samples were tested using armor piercing projectile to analyze their impact behavior. In the produced samples, some pore formation was detected. The ballistic experiments showed that the investigated FGMs (up to a thickness of 25 mm) did not withstand the impact of the projectile. At the tested samples, some major cracks and plug formation were detected at macrolevel while there were some microcracks, deformed and elongated grains in the regions near to the deformation zone of the samples.     

Synthesis and processing of ceramic–metal composites by reactive metal penetration

Molten aluminum reduces and penetrates silicate ceramics to produce a metal–ceramic composite which yields an Al₂O₃ skeleton infiltrated with a solidified Al–Si alloy. Penetration experiments have been used to study the influence of p(O₂), temperature and substrate composition on penetration kinetics and composite microstructure. The limiting kinetic step for Al penetration is the chemical reaction between Al and the ceramic. For dense substrates the maximum reaction rates are observed between 1000–1200°C and are independent of p(O₂). For porous substrates it is necessary to reach a critical temperature or p(O₂), before infiltration starts. Increasing the Si concentration in the molten Al results in the reduction of the reaction rates.     

Three-phase polymer–ceramic–metal composite for embedded capacitor applications

This paper addresses the materials and processes for printed wiring board compatible embedded capacitor using ceramic, polymer and metal. The Ca[(Li_1/3Nb_2/3)_0.8Ti_0.2]O_3?δ (CLNT)–epoxy–silver, three-phase composites were prepared by two step mixing and thermosetting technique. The dielectric properties of the three-phase composites were investigated in terms of volume fraction of silver, temperature and frequency. The dielectric properties of epoxy–CLNT composites were compared with theoretical predictions. The relative permittivity of the three-phase composites increased with silver loading. Addition of 0.28 volume fraction of silver increases the relative permittivity of epoxy–CLNT composites from 8 to 142 at 1 MHz. This composite is flexible and can be fabricated into various shapes with low processing temperature.     

Development of functionally graded Cu–Sn–Ni/Al2O3 composite for bearing applications and investigation of its mechanical and wear behavior

This study investigates the mechanical and tribological properties of a functionally graded Cu–Sn–Ni/Al₂O₃ metal matrix composite, synthesized using horizontal centrifugal casting technique with dimension Φ_out100?×?Φ_in85?×?100?mm. The microstructure was examined along radial distances at 1, 8, and 13?mm from outer periphery. Specimens were tested for tensile strength from outer (1–8?mm) and inner zone (9–15?mm) of the casting and fractured surfaces were subjected to fractographic analysis. Wear resistance of inner layer was experimented using pin-on-disc tribometer based on Taguchi’s L₂₇ orthogonal array using three variable process parameters, such as applied loads (10, 20, and 30?N), sliding velocities (1, 2, and 3?m/s), and distances (500, 1000, and 1500?m). Optimum parameters were determined for wear rate on “smaller-the-better” basis using signal-to-noise ratio. Analysis of variance predicted the effect of each influential parameter and their interactions. Results depict that wear rate increased with load and distance, forming phases such as Cu₃Sn, Ni₃Sn, Cu₆Sn₅, etc. Worn surfaces analysis using scanning electron microscope predicted the formation of mechanically mixed layers, showing a V-trend influence of velocity on wear. Thus, fabricated composite shows the replaceability of conventional leaded bearing materials with superior copper functionally graded composites having better wear characteristics.     

Assessment of Voigt and Mori–Tanaka models for vibration analysis of functionally graded plates

The small- and large-amplitude vibrations are presented for a functionally graded rectangular plate resting on a two-parameter (Pasternak-type) elastic foundation in thermal environments. Two kinds of micromechanics models, namely, Voigt (V) model and Mori–Tanaka (M–T) model, are considered. The motion equations are based on a higher order shear deformation plate theory that includes plate-foundation interaction. The thermal effects are also included and the material properties of functionally graded materials (FGMs) are assumed to be temperature-dependent. Two cases of the in-plane boundary conditions are considered. Initial stresses caused by thermal loads or in-plane edge loads are introduced. The accuracy of Voigt and Mori–Tanaka models for the vibration analysis of FGM plates is investigated. The comparison studies reveal that the difference between these two models is much less compared to the difference caused by different solution methodologies and plate theories. The results show that the difference of the fundamental frequencies between M–T and V solutions is very small, and the difference of the nonlinear to linear frequency ratios between M–T and V solutions may be negligible.     

Free vibration of Euler and Timoshenko functionally graded beams by Rayleigh–Ritz method

Present investigation is concerned with the free vibration analysis of functionally graded material (FGM) beams subjected to different sets of boundary conditions. The analysis is based on the classical and first order shear deformation beam theories. Material properties of the beam vary continuously in the thickness direction according to the power-law exponent form. Trial functions denoting the displacement components of the cross-sections of the beam are expressed in simple algebraic polynomial forms. The governing equations are obtained by means of Rayleigh–Ritz method. The objective is to study the effects of constituent volume fractions, slenderness ratios and the beam theories on the natural frequencies. To validate the present analysis, comparison studies are also carried out with the available results from the existing literature.     

Compressive properties of sandwiches with functionally graded rubber core and jute–epoxy skins

The compressive behaviour of a new class of sandwich composite made up of jute fiber reinforced epoxy skins and piece-wise linear fly ash reinforced functionally graded (FG) rubber core is investigated in flat-wise mode. FG samples are prepared using conventional casting technique. Presence of gradation is quantified physically by weight method. This paper addresses the effect of weight fraction of fly ash, core to thickness ratio (C/H) and orientation of jute on specific compressive modulus and strength. In each trial five replicates are tested with lower amount of fly ash below the upper skin of sandwich (rubber-up). Results of experimentation are subjected to statistical analysis of variance (ANOVA) to find the influential factor governing the compressive behaviour. Furthermore piece-wise linear gradation is modeled in finite element and strength values are compared with experimental results. Sandwich sample with fly ash content of 40%, C/H of 0·4 and orientations of 30°/60° registered better performance. Specific strength is observed to increase upto 30% filler content followed by stabilization. Finite element results for strength match very well with experimental ones.     

Active metal brazing of SiO_2–BN ceramic and Ti plate with Ag–Cu–Ti+BN composite filler

SiO_2–BN ceramic and Ti plate were joined by active brazing in vacuum with Ag–Cu–Ti+BN composite filler.The effect of BN content,brazing temperature and time on the microstructure and mechanical properties of the brazed joints was investigated.The results showed that a continuous Ti N–Ti B_2reaction layer formed adjacent to the SiO_2–BN ceramic,whose thickness played a key role in the bonding properties.Four Ti–Cu compound layers,Ti_2Cu,Ti_3Cu_4,Ti Cu_2and Ti Cu_4,were observed to border Ti substrate due to the strong affinity of Ti and Cu compared with Ag.The central part of the joint was composed of Ag matrix,over which some fine-grains distributed.The added BN particles reacted with Ti in the liquid filler to form fine Ti B whiskers and Ti N particles with low coefficients of thermal expansion(CTE),leading to the reduction of detrimental residual stress in the joint,and thus improving the joint strength.The maximum shear strength of 31 MPa was obtained when 3 wt%BN was added in the composite filler,which was 158%higher than that brazed with single Ag–Cu–Ti filler metal.The morphology and thickness of the reaction layer adjacent to the parent materials changed correspondingly with the increase of BN content,brazing temperature and holding time.Based on the correlation between the microstructural evolution and brazing parameters,the bonding mechanism of SiO_2–BN and Ti was discussed.     

In vitro and in vivo biocompatibility of graded hydroxyapatite–zirconia composite bioceramic

To obtain bioceramics with good osteoinductive ability and mechanical strength, graded hydroxyapatite–zirconia (HA–ZrO₂) composite bioceramics were prepared in this work. The biocompatibility of the bioceramics was investigated in vitro based on acute toxicity and cytotoxicity tests and hemolysis assay. Results showed the studied graded HA–ZrO₂ had little toxicity to mouse and L929 mouse fibroblasts. Also, hemolysis assay indicated a good blood compatibility of the bioceramics. Based on the results of in vitro tests, animal experiments were performed on white New Zealand rabbits by implantation into hip muscles and femur. It was found that the graded HA–ZrO₂ composite bioceramics exhibited superior osteoinductive ability, which may be a promising bioceramics implant.     

Mechanical behaviour of metal–matrix composite deposits

The electroplating technique is used for producing thin sheets of copper- or nickel-based composites containing different volume fractions of -alumina dispersions. The microhardness and tensile behaviour of such composites, in both the as-deposited and the annealed state, are characterized. The strengthening mechanism of electroplated composites is found to be a combination of Orowan-type strengthening and the Hall–Petch effect.     

Mechanical properties of nanocomposite metal–ceramic thin films

Thin film composites consisting of metallic nanocrystals embedded in an insulating host have been synthesized using alternating-target pulsed laser deposition of Ni and Al₂O₃ on silicon (100) substrate. The evaluation of structural quality of the thin film composites using high resolution transmission electron microscopy and scanning transmission electron microscopy with atomic number contrast has revealed the formation of a biphase system with thermodynamically driven segregation of Ni and alumina during pulsed laser deposition. The best hardness values of the thin film composites, measured using nanoindentation techniques, were found to be 20–30% larger than pure alumina films fabricated under identical conditions. Fracture toughness measurements of the composite showed slight toughening due to embedding of Ni nanoparticles.     

Preparation and characterisation of ceramic-faced metal–ceramic interpenetrating composites for impact applications

This article accesses the impact performance of ceramic-faced, metal–ceramic interpenetrating composites (IPCs) produced in situ from infiltrating ceramic foams with a molten aluminium–magnesium alloy. The approach had two variations, viz., the production of a metal bond between a ceramic front face and backing IPC and the creation of a ceramic bond. The impact performance of metal-bonded IPCs was evaluated using both split Hopkinson’s pressure bar (SHPB) and depth of penetration (DoP) techniques. With a 4-mm thick Al₂O₃ front face and an 8-mm thick IPC backing, the DoP was zero. In one case, a sample survived fundamentally intact with only spall damage to the dense Al₂O₃ front face. The resulting damage was thoroughly assessed using a range of techniques, including polarized light microscopy, scanning electron microscopy (SEM), 3D MicroCT and transmission electron microscopy (TEM). The metal phase deformed as a result of the formation of large numbers of dislocations, whilst the ceramic phase accommodated the deformation via localised cracking. Metal bridges across the cracks formed, increasing the damage tolerance of the IPCs. The metal bond between the ceramic front face and the IPC was also observed to withstand the impact of the armour piercing rounds without any sign of debonding occurring.     

Smart control of nonlinear vibrations of doubly curved functionally graded laminated composite shells under a thermal environment using 1–3 piezoelectric composites

This paper addresses the active control of geometrically nonlinear vibrations of doubly curved functionally graded (FG) laminated composite shells integrated with a patch of active constrained layer damping (ACLD) treatment under the thermal environment. Vertically/obliquely reinforced 1-3 piezoelectric composite (PZC) and active fiber composite (AFC) are used as the materials of the constraining layer of the ACLD treatment. Each layer of the substrate FG laminated composite shell is made of fiber-reinforced composite material in which the fibers are longitudinally aligned in the plane parallel to the top or bottom surface of the layer and the layer is assumed to be graded in the thickness direction by way of varying the fiber orientation angle across its thickness according to a power law. The novelty of the present work is that, unlike the traditional laminated composite shells, the FG laminated composite shells are constructed in such a way that the continuous variation of material properties and stresses across the thickness of the shell is achieved. The Golla-Hughes-McTavish (GHM) method has been implemented to model the constrained viscoelastic layer of the ACLD treatment in time domain. Based on the first-order shear deformation theory (FSDT), a finite element (FE) model has been developed to model the open-loop and closed-loop nonlinear dynamics of the overall FG laminated composite shell under a thermal environment. Both symmetric and asymmetric FG laminated composite doubly curved shells are considered for presenting the numerical results. The analysis suggests that the ACLD patch significantly improves the damping characteristics of the doubly curved FG laminated composite shells for suppressing their geometrically nonlinear transient vibrations. It is found that the performance of the ACLD patch with its constraining layer being made of the AFC material is significantly higher than that of the ACLD patch with vertically/obliquely reinforced 1-3 PZC constraining layer. The effects of variation of piezoelectric fiber orientation in both the obliquely reinforced 1-3 PZC and the AFC constraining layers on the control authority of the ACLD patch have also been investigated.     

Failure analysis of adhesively-bonded skin-to-stiffener joints: Metal–metal vs. composite–metal

The purpose of this research is to evaluate the performance of two adhesively bonded skin-to-stiffener connections: composite stiffener bonded to a Fiber Metal Laminate (FML) skin, representing a hybrid joint, and an Aluminium stiffener bonded to a FML skin, representative for a metal joint. The bonded joints were tested using Stiffener Pull-Off Tests (SPOT), which is a typical set-up used to simulate the structural behavior of full-scale components subject to out-of-plane loading, such as internal pressure of a fuselage or leading edge low pressure zone. In the hybrid joint, the damage initiates at the central noodle of the composite stiffener. Unstable delamination then propagates from the noodle to the tip of the stiffener foot, preferably through the stiffener foot plies (>90% of inter/intra-laminar failure) and, in limited areas, through the adhesive bond line (<10% of cohesive failure). In the metal joint, the failure starts at the tip of the stiffener foot at the adhesive bond line. Unstable debonding then propagates along the stiffeners foot. The complete failure occurs in the adhesive bond line (100% cohesive failure). The loads associated with >90% of inter/intra laminar failure of the composite stiffener (hybrid joint) are 40–60% lower than the ones associated with 100% cohesive failure (metal joint). This research identifies that in order to use the full capacity of adhesively bonded hybrid joints, the adhesion between carbon fibers of the composite laminate, ie intralaminar strength, must be improved. Otherwise, Aluminium stringers are still very competitive.     

Fabrication and characterization of functionally graded Al–SiC nanocomposite by using a novel multistep friction stir processing

Functionally graded materials are one of the most promising candidates among advanced materials. However, some challenges still exist in its fabrication methods. The current study aims to produce functionally-graded bulk Al–SiC nanocomposites by a novel multistep friction stir processing (FSP) for the first time. The SiC nanoparticles were packed into a groove on the 6061 aluminum plate and FSP was performed by using a tool with pin length of 6 mm. Subsequently, FSP was reapplied on another groove by using a tool with a shorter pin length of 3.2 mm. The desirable distribution of SiC nanoparticles in the matrix was confirmed by scanning electron and atomic force microscopes. The composition of graded sample was changed continuously from 18 to 0 wt% SiC along the thickness. Accordingly, the microhardness profile showed a maximum of 160 Hv in the enriched zone which is 3.2 times higher than the hardness of the particle-depleted zone. However, a constant hardness value of 135 Hv was obtained along the thickness of homogenous sample which is 15% lower than that of superficial layer in graded sample. Moreover, the hardness values were linearly correlated with the inverse of interparticle spacing.