Heat-treated Composites Research Articles

Microstructure and mechanical properties of cast in-situ TiAl matrix composites reinforced with (Ti,Nb)2AlC particles

The in-situ TiAl matrix composites with nominal compositions of Ti-44.5Al-8Nb-0.8Mo-0.1B-xC (at.%), where x is ranging from 1.4 to 4.8at.%, were prepared by casting. The microstructure of the as-cast composites consists of primary (Ti,Nb)2AlC particles distributed in the matrix composed of lamellar γ(TiAl)+α2(Ti3Al) and γ phase regions with a small amount of β/B2 phase. The chemical composition of some coarse carbides is not homogeneous and central regions enriched by C are identified to be (Ti,Nb)C phase. The mean aspect ratio of the primary carbide particles decreases and their volume fraction and shape factor increase with increasing content of C. A linear relationship is identified between the volume fraction of the carbide particles and average content of C in the composites. The heat treatments lead to the formation of fine secondary carbide particles within the matrix. The mean grain size of the as-cast composites increases during the heat treatments. The Vickers hardness, compression yield strength, Charpy impact value and dynamic fracture toughness of the heat-treated composites decrease with the increasing volume fraction of carbide particles. The brittle fracture behaviour of the in-situ composites includes crack deflection, delamination on the matrix-carbide interfaces and pull-out of the carbide particles from the γ matrix.

Interfacial characterisation and mechanical properties of heat treated non-woven kenaf fibre and its reinforced composites

This paper reports on the comprehensive characterisation of heat treated kenaf fibre (KF) and its composites. The kenaf fibres were modified by heating for 2.5–12.5 h inside a drying oven. Heat treatment produces an increase in the crystallinity index and fibre strength of KF. The highest value of KF strength was recorded by applying heat treatment of 10 h on KF. The heat treatment results in the partial removal of impurities/extractives on the KF surface which is detected by scanning electron microscopy and X-ray photoelectron spectroscopy. Atomic force microscopy results signify the decrease of roughness, the increase in peak area density and the increase of the adhesion force on the surface area of heat treated KF. The effect of the heat treatment in enhancing the interface bonding characteristics between the KF and unsaturated polyester matrix can be reflected by the interlaminar shear strength (ILSS) and dynamic mechanical analysis value of the composites. The flexural properties of the composites showed a similar trend to ILSS. However, the fracture toughness revealed contrasting results. Water absorption induced a drastic loss of the mechanical properties of the composites albeit better retention of properties was observed in the case of heat-treated KF composites.

Nano-scaled Ti5Si3 evolution and Strength Enhancement of titanium matrix composites with two-scale architecture via heat treatment

To further improve the mechanical properties of Ti5Si3 and TiBw reinforced Ti6Al4V ((Ti5Si3 + TiBw)/Ti6Al4V) composites with a two-scale network structure, heat treatments were carried out to adjust nano-scaled Ti5Si3 (n-Ti5Si3) particles and matrix characteristics. The fraction of Ti5Si3 particles in the vicinity of first-scale TiBw reinforcements decreases with increasing quenching temperatures. When the quenching temperature is elevated to 1200°C, the Ti5Si3 particles dissolve and re-solute into the matrix. Both the size and fraction of n-Ti5Si3 particles increase with increasing aging temperatures. The size of n-Ti5Si3 particles in the β phase can be refined from 400–500nm (as-sintered) to 10–60nm after heat treatments. The strength of the heat-treated composites was significantly enhanced through heat treatments, when compared with the composites with one-scale architecture and Ti6Al4V alloy. The room temperature compressive strength and high temperature (600°C) tensile strength can reach 2245MPa and 880MPa, respectively. This can be attributed to the heat treatments adjustment of n-Ti5Si3 particles, supersaturated martensite α' phase and two-scale network structure.

Effect of ZrO2 on microstructure and wear properties of Al2O3/Al–Si composites

This study has investigated the dry sliding wear behaviour of aluminium (Al)–silicon (Si) alloy matrix hybrid composites reinforced with nanosized alumina (Al2O3) and zirconia (ZrO2) in cast and heat-treated conditions. Dry sliding wear tests were performed on a pin-on-disc apparatus under a normal load of 10 N. Optical microscopy, X-ray diffraction and scanning electron microscopy examination were used to investigate the microstructures and tribological properties of the composites and the base alloy. For comparison of the wear behaviours of the samples, the wear constant (K) was measured based on the wear rate data. The lowest wear constant was observed in the heat-treated composite containing 2 wt.% zirconia, which shows a decrease of around 65% in comparison to the non-reinforced base alloy. It has been suggested that the wear process is controlled by nucleation and propagation of cracks; however, in the case of heat-treated composites, the fragmentation of layers decreases due to the spherical nature of silicon particles.

Nanoboron nitride-filled heat-treated wood polymer nanocomposites: Comparison of different multicriteria decision-making models to predict optimum properties of the nanocomposites

The aim of this study is to investigate the effects of nanoboron nitride on the physical, mechanical, morphological and thermal properties of heat-treated wood high-density polyethylene composites. Three different multicriteria decision-making models such as the technique for order preference by similarity to ideal solutions, multi-attribute utility theory and compromise programming were used to predict the nanocomposites having optimum properties. High-density polyethylene as a matrix, heat-treated wood (30%) as a reinforcement filler and nanoboron nitride (0.5%, 1% and 2%) for improving the thermal stability were used; the composites prepared were grounded in a single-screw extruder, and the test samples were prepared with injection molding. According to the results, both testing and multicriteria decision-making models showed that heat-treated wood polymer nanocomposites with 2% nanoboron nitride have the optimum properties. Multicriteria decision-making methods are thought to be useful tools for materials having the optimal properties. It can be said that this study will be a guide for future material selection studies.

Development of carboxylated multi-walled carbon nanotubes and bovine serum albumin reinforced hydroxyapatite for bone substitute applications

The similarity of the chemical composition of hydroxyapatite (HA) to the mineral phase of bone and their excellent biocompatibility meets the requirement of materials designed for bone repair and augmentation purposes. However, the application of HA in load-bearing devices is limited by its poor mechanical properties. Carbon nanotubes (CNTs), with their outstanding stiffness and strength, have good potential applications in tissue engineering. These properties, combined with their small size and large interfacial area, suggest that they may have great potential as a reinforcing agent for HA. The hydroxyapatite/multi-walled carbon nanotubes/bovine serum albumin (HA/MWCNTs-COOH/BSA) with particle size in the range 20 to 25 nm composites was successfully produced using precipitation technique. The compressive strength of heat-treated composites at 600 to 1000 °C is in the range between 27 and 37 MPa. The cytotoxic effect of the composites with different concentrations was evaluated by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay (MTT assay) against normal human colon fibroblast. The developed composites were found to be non-cytotoxic when treated to the human fibroblast cells and imply a proliferative effect on cells. The developed composites are possibly a good choice to use as non-toxic material for bone substitution at the level of the trabecular bone.

Effect of heat treatment on the mechanical and microstructural characterization of Mg-AZ91E/TiC composites

Mg-AZ91E/TiCp composite was fabricated using a spontaneous infiltration technique at 950 °C under an argon atmosphere. The composites produced have 37 vol.% of metal matrix and 63 vol.% of TiC-like reinforcement. The obtained composites were subsequently solution heat-treated at 413 °C during 24 h, cold water quenched, and subsequently artificially aged at 168 and 216 °C during 16 h in an argon atmosphere. Effect of heat treatment on the microstructure and mechanical properties was evaluated. Microstructural characterization was analyzed using different techniques such as X-ray diffraction (XRD) and scanning electron microscopy (SEM). Interface between matrix and reinforcement was examined using transmission electron microscopy (TEM), and mechanical properties were evaluated by measuring the elastic modulus and hardness. Mg, TiC, Al, and Mg17Al12 phases through XRD were detected. Meanwhile, using TEM analysis in heat-treated composites MgAl2O4, MgO, and Al2O3 were identified. The as-fabricated composite have elastic modulus and hardness of 162 GPa and 316 Hv, respectively. After solution heat treatment and aging at 168 °C during 12 h, the composites reaches values of 178 GPa and 362 Hv for the elastic modulus and hardness, respectively. Time of aging was correlated with measures of elastic modulus and hardness.

Microstructural characterization and mechanical properties of TiC/near-α Ti composite obtained at slow cooling rate

In this paper, microstructural characterization and mechanical properties of 10vol% TiC/Ti-6Al-3Sn-3.5Zr-0.4Mo-0.75Nb-0.35Si composite obtained at slow cooling rate has been discussed. Equiaxed or near-equiaxed α phase was formed in the composite when cooled from above the β-transus temperature at a cooling rate of 10°C/min. This is due to the fact that α precipitates can heterogeneously nucleate on TiC particles during the slow-cooling process. It was obtained that the lattice disregistry between TiC and α precipitates was only 3.8%, which corresponds to the crystallographic orientation relationship of [2-1-10]α//[011]TiC; (0001)α//(1-11)TiC. The tensile results showed that heat treatment improved UTS and elongation, simultaneously, below 700°C. The enhancement of UTS is mainly attributed to solid solution strengthening of C in matrix since about 5.5vol% TiC dissolved into matrix after heat treatment. The obvious increase in room-temperature elongation is because of the formation of equiaxed microstructure and the reduction in the sizes of spheroidised TiC particles. With the increase of temperature, the discrepancy in UTSs of the as-cast and heat-treated composites became small.

Properties of „In Situ” 7475 Alloy Matrix Composites Reinforced Al3Ti Intermetalic Compound Extruded in Semi-Solid State

Studies were conducted to improve the mechanical properties of composites based on 7475 aluminium alloy reinforced with Al3Ti particles fabricated by the “in situ” process. The first step involved “dissolving” of titanium in the liquid aluminium alloy and fabricating in this way composite materials with different content of the reinforcing phase (15-45wt%). A relationship between the composite hardness and content of the reinforcing phase was confirmed. The second step involved the improvement of cohesion between the reinforcing particles and composite matrix. By extrusion of samples in semi-solid state, an average increase in hardness by 15-20% relative to the unextruded composite was obtained. In the third step, the fabricated composite was subjected to a heat treatment corresponding to the state T6 in 7475 alloy, which raised the hardness by about 30%. Structure examinations carried out by means of optical microscopy and scanning electron microscopies as well as the results of hardness measurements were described. They enabled estimating the effect of the content of produced Al3Ti particles, and of the extrusion process in semi-solid state and heat treatment parameters on the composite properties. In compression test, the yield strength and compressive strength of the heat-treated composites were determined.

Applications of Fiber Reinforced Polymer Composites

Fueled by the need to surpass the limitations of conventional materials, recent years have seen a large increase in engineering applications of advanced fiber reinforced polymer (FRP) composite materials in many major industries, such as aerospace and defense, automotive, construction, marine, and oil and gas. FRP composites are very attractive for these applications due to their highly favorable material properties, including high strength-to-weight and stiffness-to-weight ratios, and corrosion resistance. Studies conducted to date have demonstrated the numerous advantages offered by FRP composites in various engineering applications. However, there are still a number of technical and implementation issues that need to be resolved prior to broader uptake of the application of FRP composites by some engineering communities such as civil construction. This special issue is aimed at disseminating the most recent advances and developments in this exciting field. A total of 17 paperswere submitted to the special issue and after a rigorous peer-review process six of themwere accepted to appear in the issue as original research articles. These six papers deal with a range of topics on the structural behavior of composite members/structures and mechanical properties and development of composite materials. The studies on the former investigate the dynamic behavior of composite FRP bridge systems and flexural behavior of previously damaged steel beams repaired with FRP. The studies on the latter are concerned with the development of ecoefficient engineered cementitious composites, mechanical properties of carbon fiber composites obtained using different molding techniques, and properties of high-density and ultra-high molecular weight polyethylene and heat-treated bamboo fiber composites. We hope that some of the most recent advances on the development and applications of FRP composites that have been disseminated in this special issue will be of interest to readers and contribute toward the advancement of research in the field.

High-Density Polyethylene and Heat-Treated Bamboo Fiber Composites: Nonisothermal Crystallization Properties

The effect of heat-treated bamboo fibers (BFs) on nonisothermal crystallization of high-density polyethylene (HDPE) was investigated using differential scanning calorimetry under nitrogen. The Avrami-Jeziorny model was used to fit the measured crystallization data of the HDPE/BF composites and to obtain the model parameters for the crystallization process. The heat flow curves of neat HDPE and HDPE/heat-treated BF composites showed similar trends. Their crystallization mostly occurred within a temperature range between 379 K and 399 K, where HDPE turned from the liquid phase into the crystalline phase. Values of the Avrami exponent (n) were in the range of 2.8~3.38. Lamellae of neat HDPE and their composites grew in a three-dimensional manner, which increased with increased heat-treatment temperature and could be attributed to the improved ability of heterogeneous nucleation and crystallization completeness. The values of the modified kinetic rate constant (KJ) first increased and then decreased with increased cooling rate because the supercooling was improved by the increased number of nucleating sites. Heat-treated BF and/or a coupling agent could act as a nucleator for the crystallization of HDPE.

Effect of heat treatment on the microstructure of C/C composites with different high textured pyrolytic carbon contents

C/C composites reinforced using carbon felt and 3 K carbon cloth laminated preforms were prepared by chemical vapor infiltration and samples taken from them were subsequently subjected to heat treatment at 2500 °C. The microstructures of the C/C composites were characterized by X-ray diffraction, polarized light microscopy and Raman spectroscopy. Results showed that the matrix of composites reinforced with carbon felt contained only high textured (HT) pyrolytic carbon, while those reinforced with the 3 K carbon cloth had a banded texture composed of isotropic, HT and medium textured (MT) pyrolytic carbon when moving from fibers to matrix, and the content of HT pyrolytic carbon was less than 50%. Regardless of the preform, both the as-prepared and heat-treated composites had a similar degree of graphitization. The L c value of the carbon felt-reinforced composites was higher than their counterparts both for the as-prepared and heat-treated samples. The L a values of the carbon fibers, MT and HT pyrolytic carbon increased after the heat treatment, and the L a value of the HT pyrolytic carbon had a much larger increase than that of the others. [New Carbon Materials 2014, 29(5): 369–373]

Mechanical and Tribological Characterization of Al-Mg2Si Composites After Yttrium Addition and Heat Treatment

In this study, the effect of heat treatment and yttrium additions on the microstructure, mechanical properties, and tribological behavior of Al-15% Mg2Si cast composites was investigated. The microstructural study revealed the presence of both primary and secondary Mg2Si phases in all composite specimens and also Y-containing intermetallics (Al2Y phases) at higher concentrations. It was also found that Y addition does not change the size and morphology of primary Mg2Si particles considerably, but the pseudo-eutectic Mg2Si changed from a flake-like morphology to fine fibrous or rod-like one. The results show that proper content of Y additions can reduce the amount of Mg2Si phase through dissolving it into the matrix, lead to the precipitation of Al2Y phase and improve the mechanical properties. Modified composites with 0.5% Y exhibited an ultimate tensile strength (UTS) of 290 MPa with an elongation of 4.3%. After exposing the composite to solution treatment at 520 °C for 4 h, the tensile strength of the composite continuously increased with the increase of Y content, and reached the maximum at 1% Y. The maximum UTS and elongation at room temperature for the heat-treated composites are 294 MPa and 7.4%, respectively. In the cast specimen, fracture surfaces are covered by packets with coarse steps, suggesting a brittle mode of failure. Modified composites with 0.5 wt.% Y contain several cracked particles together with a few decohered primary Mg2Si particles. In solution heat-treated state, dimples present at the fracture surface are rather coarse but homogenous, showing a semi-ductile mode of fracture. Wear test results showed that the wear resistance of all specimens increases with the addition of Y up to 0.3 wt.%. Scanning electron microscopic observations of the worn surfaces revealed that the dominant wear mechanism was abrasive wear accompanied by some delamination wear mode.

Fabrication and Characterization of SnO₂/Graphene Composites as High Capacity Anodes for Li-Ion Batteries.

Tin-oxide and graphene (TG) composites were fabricated using the Electrostatic Spray Deposition (ESD) technique, and tested as anode materials for Li-ion batteries. The electrochemical performance of the as-deposited TG composites were compared to heat-treated TG composites along with pure tin-oxide films. The heat-treated composites exhibited superior specific capacity and energy density than both the as-deposited TG composites and tin oxide samples. At the 70th cycle, the specific capacities of the as-deposited and post heat-treated samples were 534 and 737 mA·h/g, respectively, and the corresponding energy densities of the as-deposited and heat-treated composites were 1240 and 1760 W·h/kg, respectively. This improvement in the electrochemical performance of the TG composite anodes as compared to the pure tin oxide samples is attributed to the synergy between tin oxide and graphene, which increases the electrical conductivity of tin oxide and helps alleviate volumetric changes in tin-oxide during cycling.

Surface Energetic and Strength Characteristics of Heat-Treated Composites Based on Butadiene–Acrylonitrile Elastomer Modified with Carbon Black

An investigation was made of the effect of annealing and quenching on the interphase tension and strength of carbon-black-filled composites based on butadiene–acrylonitrile rubber with different nanoparticle contents. It was shown that the properties of filled blends depend non-additively on the carbon black concentration and heat treatment.

Preparation of Aluminum Metal Matrix Composite with Novel In situ Ceramic Composite Particulates, Developed from Waste Colliery Shale Material

A novel method is adapted to prepare an in situ ceramic composite from waste colliery shale (CS) material. Heat treatment of the shale material, in a plasma reactor and/or in a high temperature furnace at 1673 K (1400 °C) under high vacuum (10−6 Torr), has enabled in situ conversion of SiO2 to SiC in the vicinity of carbon and Al2O3 present in the shale material. The composite has the chemical constituents, SiC-Al2O3-C, as established by XRD/EDX analysis. Particle sizes of the composite range between 50 nm and 200 μm. The shape of the particles vary, presumably rod to spherical shape, distributed preferably in the region of grain boundaries. The CS composite so produced is added to aluminum melt to produce Al-CS composite (12 vol. pct). For comparison of properties, the aluminum metal matrix composite (AMCs) is made with Al2O3 particulates (15 vol. pct) with size <200 μm. The heat-treated Al-CS composite has shown better mechanical properties compared to the Al-Al2O3 composite. The ductility and toughness of the Al-CS composite are greater than that of the Al-Al2O3 composite. Fractographs revealed fine sheared dimples in the Al-CS composite, whereas the same of the Al-Al2O3 composite showed an appearance of cleavage-type facets. Abrasion and frictional behavior of both the composites have been compared. The findings lead to the conclusion that the in situ composite developed from the colliery shale waste material has a good future for its use in AMCs.

Chemically imaging the effects of the addition of nanofibrillated cellulose on the distribution of poly(acrylic acid) in poly(vinyl alcohol)

The distribution of poly(acrylic acid) (PAA) in model laminates of nanocellulose and poly(vinyl alcohol) (PVOH) was investigated by FTIR chemical imaging. The method was effective in spatially discerning the three components of the composite. PAA can potentially improve the performance of nanocellulose reinforced PVOH by not only crosslinking the PVOH matrix but also improving the adhesion between PVOH and nanocellulose by forming ester linkages with both of them. However, PAA was found to migrate out of the PVOH matrix and concentrate in the nanocellulose layer of the laminate. This led to a PAA-depleted region in the matrix near the nanocellulose layer, which would likely lead to a weak interphase and limited stress transfer between the fiber and matrix in the heat-treated composite. Methods for improving the distribution of the PAA need to be investigated to optimize performance. This is the first chemical imaging study of nanocellulose materials using synchrotron-based vibrational spectroscopy.

Thermal ageing on the microstructure and mechanical properties of Al–Cu–Mg alloy/bagasse ash particulate composites

Thermal ageing on the microstructure and mechanical properties of Al–Cu–Mg alloy/bagasse ash(BAp) particulate composites was investigated. The composites were produced by a double stir-casting method by varying bagasse ash from 2 to 10wt.%. After casting the samples were solution heat-treated at a temperature of 500°C in an electrically heated furnace, soaked for 3h at this temperature and then rapidly quenched in water and thermal aged at temperatures of 100, 200 and 300°C. The ageing characteristics of these grades of composites were evaluated using scanning electron microscopy (SEM), hardness and tensile test samples obtained from solution heat-treated composites samples subjected to the temperature conditions mentioned above. The results show that the uniform distribution of the bagasse ash particles in the microstructure of both the as-cast and age-hardened Al–Cu–Mg/BAp composites is the major factor responsible for the improvement in mechanical properties. The presence of the bagasse ash particles in the matrix alloy results in a much smaller grain size in the cast composites compared to the matrix alloy. The addition of bagasse ash particles to Al–Cu–Mg (A2009) does not alter the thermal ageing sequence, but it alters certain aspects of the precipitation reaction. Although thermal ageing is accelerated in the composites the presence of bagasse ash particles in A2009 reduces the peak temperatures.

Functional Carbonaceous Compound Assisted Assembling of SnO2@C Nanocomposite as a Lithium Storage Anode Material

Self-assembled SnO2@C nanocomposites were fabricated by a simple hydrothermal duel reaction process using glucose and potassium stannate. In this process, glucose acted as the carbon source for the production of a carbonaceous compound, which has active functional groups on its surface. At the same time, the acidic by-products from the dehydration of glucose lower the pH of the solution to facilitate the precipitation of SnO2 nanocrystals from potassium stannate. These two concurrently occurred chemical processes enable the creation of SnO2 nanocrystals decorated with the carbonaceous compound with active functional groups, thus allow self-assembling of these SnO2 nanocrystals into spherical aggregates of SnO2@C nanocomposites. The electrochemical performance of the SnO2@C nanocomposites created was evaluated as an anode material for lithium ion storage. The heat-treated composites exhibited a reversible lithium storage capacity of 300 mAh/g after 50 charge/discharge cycles.

Comparative study of EVA-Cloisite&lt;sup&gt;®&lt;/sup&gt; 20A and heat-treated EVA-Cloisite&lt;sup&gt;®&lt;/sup&gt; 20A on heavy-metal adsorption properties

Ethylene vinyl acetate (EVA)/ Cloisite® 20A (C20A) composite fabricated via the melt-blending method was used for the development of a heavy-metal adsorbent through acid and heat treatment. Heat-treated composites were produced at 400°C to 1 000°C in air and N2 atmospheres. The materials were characterised through TGA, FT-IR, contact angle and Zetasizer. Treating EVA/C20A composites with H2SO4 at 130°C reduced the contact angle from 99.73° to 30.40°. The acid-functionalised composite was tested for the removal of Pb2+ and an adsorption capacity of 49 mg·g-1 was recorded while the heat-treated composite exhibited an adsorption capacity of 153 mg·g-1.