Microstructure and mechanical properties of spark plasma sintered titanium‐added copper/reduced graphene oxide composites

Copper matrix composites were fabricated through mixing fixed amount of reduced graphene oxide and the different amounts of titanium. The dried copper/titanium/reduced graphene oxide mixture powders were firstly obtained by the wet‐mixing process, and then the spark plasma sintering process realized their faster densification. In the as‐sintered bulk composites, the layered reduced graphene oxide network, uniform titanium particles and copper‐titanium solid solution are observed in copper matrix. Investigations on mechanical properties show that the as‐prepared bulk composites exhibit the hardness and compressive yield strength compared with single reduced graphene oxide added composites. Increased titanium addition resulted into higher hardness and strength. The relevant formation and failure mechanisms of the composites and their influence on mechanical properties were discussed.     

Effect of fabrication process on the microstructure and dynamic compressive properties of SiCp/Al composites fabricated by spark plasma sintering

The effect of fabrication process on the microstructure and dynamic properties of SiC_p/Al composites was studied in this paper. Pure Al matrix composites reinforced with 20 vol.% SiC particles were fabricated by spark plasma sintering, and the pre-blended powders were prepared by two different processes. One was to mix the powders in conical flask by using a mechanical stirrer, and the other was the mechanical alloying process by using a planetary ball mill. The sintering temperature was also explored. The conventional split Hopkinson pressure bar was used to test the dynamic properties of these composites. The results show that the sintering temperature significantly affects the consolidation of the composites. The composites, which have not been fully densified, have very loose microstructure and poor mechanical properties. Mechanical alloying process can improve the microstructure and mechanical properties of the composites. These composites are rate dependent, their strengths increase with increasing strain rates.     

Effect of pore structure on mechanical properties of porous TiAl

Based on two sets of TiAl powder, two kinds of porous TiAl were separately fabricated by powder metallurgical route including four stages. The porous TiAl with single pore structure (SPS) was prepared using pre-alloyed TiAl powder prior mechanical ball milling. Another porous TiAl with composite pore structure (CPS) was manufactured depending on composite mixture of Ti/Al elemental powders. The sintering was achieved at much lower temperature for the pre-alloyed power than for the elemental composite mixture. Compressive mechanical tests indicate that much higher mechanical strength can be obtained for SPS than for CPS at the same porosity. It was suggested that the difference of mechanical properties is ascribed to the variety of the compressive deformation process.     

Mechanical properties of nanostructured Mg–5 wt%Al–x wt%AlN composite synthesized from Mg chips

In the present investigation, Mg chips are recycled to produce nanostructured Mg–5wt%Al reinforced with 1, 2 and 5 wt% nanosized AlN particulates by mechanical milling (MM). Each batch of composite mixture was milled for different milling durations to produce different degrees of grain refinement. The mechanical properties such as tensile strength, ductility and hardness with respect to the effect of grain refinement, in other words, milling duration were studied. It was found that grain size played an important role in controlling ductility of the composites.     

Utilizing Low‐Cost Eggshell Particles to Enhance the Mechanical Response of Mg–2.5Zn Magnesium Alloy Matrix

The search for lightweight high‐performance materials is growing exponentially primarily due to ever‐increasing stricter environmental regulations and stringent service conditions. To cater to these requirements, the use of low‐cost reinforcements has been explored in the Mg matrix to develop Economically Conscious Magnesium (ECo–Mg) composites. In this study, eggshell particles (3, 5, and 7 wt%) reinforced Mg–Zn composites are synthesized using blend‐press‐sinter powder metallurgy technique. The results reveal that the addition of eggshell particles enhances microhardness, thermal stability, damping, and yield strength with an inappreciable change in the density. In particular, Mg2.5Zn7ES composite do not ignite till ≈750 °C. The overall combination of properties exhibited by Mg–Zn–ES composites exceeds many of currently used commercial alloys in the transportation sector. An attempt is made, in this study, to interrelate microstructure and properties and to study the viability of compression and ignition properties with a comparison to commercially used Mg alloys.

     

Mechanical alloying process and mechanical properties of Cu–SiCp composite

Abstract

A composite of copper powder and SiC particle reinforcement was prepared by mechanical ball milling and subsequent sintering. Proper choice of processing parameters ensured a homogenous distribution of SiC particles in the copper matrix. Microstructure, powder morphology and mechanical properties of the composite were investigated as a function of milling time. With increasing milling time, the dentritic copper powder became flattened, which subsequently became spherical shaped. Mechanical properties of the composites change with the distribution of SiC.     

Grinding behavior of WO3, NiO,Fe2O3 by ultrasonic milling parameters control and preparation of nanocomposite powder

Tungsten-based alloys have been widely applied in various industries due to their excellent mechanical properties. Tungsten-based alloys have a high sintering temperature due to the high melting point of tungsten, so the coarse particles negatively affect the mechanical properties of the alloy. This problem can be solved by increasing the densification by reducing the sintering temperature and time by adding nanoparticles with high surface energy. Herein, we fabricated nanoparticle-sized metal oxides by ultrasonic milling to minimize the influx of impurities to improve the densification of tungsten alloys. The main parameters of the ultrasonic milling experiments were ball density and ball layer. Metal oxides prepared by ultrasonic milling showed an average particle size distribution of less than 200 nm, and metal composite powders prepared through subsequent hydrogen reduction also showed nanoparticle size distributions. We believe that this approach will enable the production of improved sintered tungsten-based alloys.     

The dynamic properties of SiCp/Al composites fabricated by spark plasma sintering with powders prepared by mechanical alloying process

The dynamic compressive properties of SiC particle reinforced pure Al matrix composites, fabricated by spark plasma sintering technique with mixture powders prepared by mechanical alloying process, were tested in this paper. Two different average SiC particle sizes of 12 μm and 45 μm were adopted, and the compressive tests of these composites at strain rates ranging from 800/s to 5200/s were conducted by split Hopkinson pressure bar. The damage mechanism of the SiC_p/Al composites was analyzed through the microstructural observations and high-precision density measurements. Results show that the dynamic properties and damage accumulation of these composites are significantly affected by the particle distribution, size, particle cracking, particle/matrix interface debonding and adiabatic heat softening. The composites containing smaller SiC particles exhibit higher flow stress, lower strain rate sensitivity, and less damage at high strain rate deformation.     

Effect of size and shape of metal particles to improve hardness and electrical properties of carbon nanotube reinforced copper and copper alloy composites

Utilizing the extra-ordinary properties of carbon nanotube (CNT) in metal matrix composite (MMC) for macroscopic applications is still a big challenge for science and technology. Very few successful attempts have been made for commercial applications due to the difficulties incorporating CNTs in metals with up-scalable processes. CNT reinforced copper and copper alloy (bronze) composites have been fabricated by well-established hot-press sintering method of powder metallurgy. The parameters of CNT–metal powder mixing and hot-press sintering have been optimized and the matrix materials of the mixed powders and composites have been evaluated. However, the effect of shape and size of metal particles as well as selection of carbon nanotubes has significant influence on the mechanical and electrical properties of the composites. The hardness of copper matrix composite has improved up to 47% compared to that of pure copper, while the electrical conductivity of bronze composite has improved up to 20% compared to that of the pure alloy. Thus carbon nanotube can improve the mechanical properties of highly-conductive low-strength copper metals, whereas in low-conductivity high-strength copper alloys the electrical conductivity can be improved.     

Fabrication of polystyrene/agave particle biocomposites using compression molding technique: evaluation of flammability,biodegradability, mechanical and thermal behaviour

Polystyrene (PS) composites reinforced with ungrafted and acrylonitrile (AN) grafted agave particles (AgP) have been prepared with 10–30% particle content by weight using compression molding technique. The composite specimens thus prepared were subjected to the evaluation of mechanical, chemical, flammability and biodegradability properties. PS composites with 20% particle loading exhibited optimum mechanical properties. AN grafted AgP/PS composites exhibited higher mechanical strength as compared to ungrafted AgP/PS composites. Further AN grafted AgP/PS composites exhibited better thermal properties and biodegradability as compared to PS matrix. Addition of fire retardant fillers such as magnesium hydroxide (Mg(OH) $_{2})$ and zinc borate lowered burning rate of PS composites considerably. Scanning electron microscopy (SEM) of tensile fracture surfaces of AN grafted AgP/PS composites showed better particle/matrix adhesion.     

Properties enhancement using oil palm shell nanoparticles of fibers reinforced polyester hybrid composites

Oil palm shell (OPS) nanoparticles were utilized as filler in fibers reinforced polyester hybrid composites. The OPS nanoparticles were successfully produced from the raw OPS using high-energy ball milling process. Fundamental properties including morphology, crystalline size, and particle size of the OPS nanoparticles were determined. Tri-layer natural fiber reinforcement (kenaf–coconut–kenaf fiber mat) polyester hybrid composites were prepared by hand lay-up techniques. The influences of the OPS nanoparticles loading in the natural fibers reinforced polyester hybrid composites were determined by analyzing physical, mechanical, morphological, and thermal properties of the composites. Results showed that the incorporation of the OPS nanoparticles into the hybrid composites enhanced the composite properties. Further, the natural fibers reinforced polyester hybrid composite had the highest physical, mechanical, morphological, and thermal characteristics at 3 wt.% OPS nanoparticles loading.     

Nano-AlN particle reinforced Mg composites: microstructural and mechanical properties

In this study, nano-AlN particles were introduced into pure Mg matrix through the powder metallurgy technique incorporating microwave assisted two-directional sintering followed by hot extrusion. The effect of varying volume fraction of nano-AlN addition on the microstructural and mechanical properties of pure Mg was investigated. Microstructural characterisation revealed marginal grain refinement due to the fairly uniform distribution of AlN nano-particulates. X-ray diffraction results indicated basal texture weakening in Mg/0·2AlN composite. Tensile property measurements revealed an overall increase in strength properties and ductility. Among the developed composites, Mg/0·8AlN displayed superior strength (～30% improvement) and Mg/0·2AlN showed enhanced ductility (～80% enhancement). Under compressive loading, the developed Mg/AlN nanocomposite formulations exhibited improved strength properties without significant effect on compressibility.     

Synthesis of Aluminium-Cementite Metal Matrix Composite by Mechanical Alloying

Cementite powder was prepared from elemental iron and graphite powder by mechanical alloying (MA) in a specially built dual-drive planetary mill. The phase evolution, particle-size distribution, and morphology of particles were studied during 40 hours grinding period. X-ray diffraction (XRD) shows formation of cementite and other iron carbides along with elemental iron after milling, whereas after annealing only cementite is present. Initially particle size increases with milling due to ductility of iron powder and then reduces with further milling.

Al-cementite composite was synthesized by mixing cementite with Al powders, and then by hot pressing or cold compaction and sintering. XRD analysis of Al-Fe₃C composite shows Fe₃C, FeAl, Al, and other iron carbides along with Al₄C₃ after sintering. Scanning electron microscope (SEM) micrograph of hot-pressed samples shows excellent compatibilility between Al matrix and cementite particles.     

Influence of Mg Addition on Graphite Particle Distribution in the Al Alloy Matrix Composites

Al alloy matrix composites reinforced with copper-coated graphite particle have been prepared by melt stirring process in this work. The effect of the addition of Mg on distribution of the graphite particles has been investigated. Scanning electron microscopy (SEM) was used to observe the micro-morphology of Al alloy matrix composites reinforced with graphite particles. Meanwhile, the content of graphite was analyzed in the different position of casting by dissolution method and the mechanical properties of the composites were detected. The results show that the content of graphite increase with increasing Mg content; the graphite particles distribute uniformly in the particle reinforced metal matrix composites (PMMC) with 0.6 wt pct Mg; however, the agglomeration of the graphite particles is observed obviously in the matrix when Mg content is more than 1.0 wt pct. In addition, the proper Mg addition amount is beneficial to enhance the mechanical properties of the graphite particles reinforced Al alloy matrix composites and the abrasion resistance of the materials due to a reduce friction coefficient.     

Preparation and mechanical properties of SiC-reinforced Al6061 composite by mechanical alloying

In this paper, an Al6061–10 wt% SiC composite was prepared using the mechanical alloying route. The morphology and the structure of the prepared powder, which change with milling time, were evaluated using scanning electron microscopy (SEM) and X-ray diffraction (XRD) techniques, respectively. Moreover, the relationships among the stages of mechanical alloying (MA), relative density and hardness of both pressed and hot extruded materials were investigated. The morphological evolutions showed that relatively equiaxed powders could be synthesized after 9 h of milling. The evolution of relative density and hardness with milling time is due to the morphological and microstructural changes imposed on the composite powder. High-relative densities are typical of the hot extruded samples. The effect of mechanical alloying process on hardness is more significant compared to reinforcement particles. The aging behaviors of the mechanically alloyed, commercially mixed and unreinforced Al6061 were compared. The results showed that MA composites exhibit no aging-hardenability.     

Formation of magnesium nanocomposite via mechanical milling

Nanocomposite Mg5wt%Al has been synthesized via mechanochemical milling of elemental Mg, Al and Ti powders with polyethylene–glycol. TiH₂ phase was formed through the reaction between Ti and polyethylene–glycol during the milling as well as the sintering processes. Formation of ultra-fine particles of a few nanometer in size was observed within the matrix grains. The formation of TiH₂ particles is hypothesized to occur through two stages. In the first stage, Ti is supersaturated in the Mg matrix during high energy milling while polyethylene–glycol decomposes to react with Mg as well as Ti which is not solid solute in the Mg matrix. In the second stage during sintering, the hydrogen and Ti released from the Mg react with each other, thus forming nanoparticles. As a result of the nanoparticles, the nanocomposite manifests improved yield strength and ductility in comparison to it counterpart.     

Preparation and properties of polypropylene reinforced by smectite

Toluene solutions of hydrophobic smectite (SAN) and polypropylene (PP) were mixed thoroughly. Trimethylsilylated SAN was also used to examine the effects of the surface modification. In both the smectites, the resulting mixtures were transparent but the stacked layer structures were retained, with expansion of the interlayer distance from 2.26 nm to 5 nm. The PP containing the fine SAN filler particles was prepared after removal of toluene, followed by mixing with the PP to produce a 3 wt% SAN content. The SAN particles were more finely dispersed in the resulting composites than was achieved by conventional mechanical mixing, but the mechanical properties were not improved remarkably. The trimethylsilylation conferred no favourable effect on the mechanical properties of the composite.     

Fabrication of ultrafine grained FeCrAl-0.6 wt.% ZrC alloys with enhanced mechanical properties by spark plasma sintering

Low mechanical strength, especially at high temperatures, is the key problem that limit the application of FeCrAl alloys as the accident tolerance fuel (ATF) cladding materials. Dispersion strengthening by carbide nanoparticles is an effective way to improve mechanical properties at high temperatures. In this work, an ultrafine grained FeCrAl-0.6 wt.% ZrC alloys with excellent mechanical properties were fabricated successfully by mechanical milling and spark plasma sintering. The effect of milling speed on powder characteristics, microstructure and mechanical properties of FeCrAl alloys were investigated. The particle size of the powders increase significantly after milling at 400 rpm, while it has a lower oxygen content. Increasing the milling speed decreased the resultant grain size and improved relative density. Transmission electron microscope (TEM) demonstrated the nano ZrC particles uniformly distributed in the matrix at higher milling speed, which effectively promotes grain refinement and dispersion strengthening. The results of mechanical properties show that the tensile strength, percentage elongation and hardness of FeCrAl-0.6 wt.% ZrC alloys at room temperature (RT) reached up to 1.05 GPa, 349.86 HV and 12.1%, respectively, after milling at 400 rpm. It is worth noting that the FeCrAl-0.6 wt.% ZrC alloy also exhibited a good high-temperature strength more than 110 MPa at 800 ℃, which is about 55.4% and 24.7% higher than previously reported FeCrAl-0.5 wt.% ZrC and FeCrAl-1.0 wt.% ZrC alloys, but the plasticity is reduced. The results demonstrated that the excellent mechanical properties were not only attributed to the dispersion strengthen by nanosized ZrC, a good interface bonding between Fe matrix and nanosized ZrC, but also the ultra-fine grained structure induced by the milling process.     

Processing and Performance of Alumina Fiber Reinforced Alumina Composites

Processing of alumina fiber-reinforced alumina matrix composites by hot-pressing was described. The mechanical properties of the composites fabricated by different sintering conditions including temperature and pressure have been investigated. The results indicated that the higher sintering temperature and pressure corresponded to the higher bulk density and higher maximum strength of the composite, whereas the pseudo-ductility of the composite was lower. The preliminary results of the composite with monazite-coated fibers showed that maximum strength could be improved up to 35% compared with the noncoated fiber composite in the same sintering condition. Moreover, the fracture behavior of the composite changed from completely brittle fracture to non-brittle fracture under the suitable sintering conditions. SEM observation of the fracture surface indicated that the coating worked as a protective barrier and avoided sintering of the fibers together even at high temperature and pressure during densification process.     

Si 含量对放电等离子烧结原位Nb/ Nb5Si3复合材料显微结构的影响

Nb/ Nb₅Si₃ 是一种新型的高温结构复合材料, 为了降低该材料的制备成本并有效控制材料的显微结构, 本文作者以Nb、Si 粉末为原料, 采用放电等离子烧结(SPS) 技术原位合成了近理论密度的Nb/ Nb₅Si₃ 复合材料, 着重研究了Si 含量对Nb/ Nb₅Si₃ 复合材料显微结构的影响。结果表明: 制备的复合材料由合成的Nb₅Si₃和均匀分布的Nb 颗粒组成; 在原子分数为6 %～20 %Si 范围内, 随着Si 含量增加, 复合材料中Nb₅Si₃ 数量增加, Nb 颗粒尺寸减小, 复合材料的致密性和硬度提高。