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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 1,369 records · Page 76
All sourcesNASA NTRSDOE OSTI
DOE OSTI2016

Study of chloride ion transport of composite by using cement and starch as a binder

This study presents the chemical bonding and the structural properties of composites from accelerator chloride test migration (ACTM). The volume fractions between binder (cement and starch) and charcoal in composites are 20:80 and 60:40. The effect of the binder to the chemical composition, chemical bonding, and structural properties before and after chloride ion passing through the composites was determined by X-ray fluorescence (XRF), by Fourier transform infra-red (FTIR), and x-ray diffraction (XRD), respectively. From the XRD data, XRF data, and the FTIR data shows the amount of chemical composition, the type of binding, and the structure of composites are depending on the type of binder. The amount of chloride migration using starch as binder is higher than that of cement as a binder due to the density effects.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2025

Enhancing Thermal Transport in Polymeric Composites Via Engineered Noncovalent Filler–Polymer Interactions

Understanding thermal transport mechanisms in polymeric composites allows us to expand the boundaries of thermal conductivity in them, either increasing it for more efficient heat dissipation or decreasing it for better thermal insulation. But, these mechanisms are not fully understood. Systematic experimental investigations remain limited. Practical strategies to tune the interfacial thermal resistance (ITR) between fillers and polymers and the thermal conductivity of composites remain elusive. Here, we studied the thermal transport in representative polymer composites, using polyethylene (PE) or polyaniline (PANI) as matrices and graphite as fillers. PANI, with aromatic rings in its backbone, interacts with graphite through strong noncovalent π–π stacking interactions, whereas PE lacks such interactions. We can then quantify how π–π stacking interactions between graphite and polymers enhance thermal transport in composites. PE/graphite and PANI/graphite composites with the same 1.5% filler volume fractions show a ∼22.82% and ∼34.85% enhancement in thermal conductivity compared to pure polymers, respectively. Calculated ITRs in PE/graphite and PANI/graphite are ~6 x 10 -8 m 2 KW -1 and ~1 x 10 -8 m 2 KW -1 , respectively, highlighting how π–π stacking interactions reduce ITR. Molecular dynamics (MD) simulations suggest that π–π stacking interactions between PANI chains and graphite surfaces enhance alignment of PANI's aromatic rings with graphite surfaces. This allows more carbon atoms from PANI chains to interact with graphite surfaces at a shorter distance compared to PE chains. Finally, our work indicates that tuning the π–π stacking interactions between polymers and fillers is an effective approach to reduce the ITR and enhance the thermal conductivity of composites.

atoms↗
DOE OSTI2022

Understanding the Elastic, Plastic, and Damage Features in Fracturing of Self-reinforced Thermoplastic Composites via Non-destructive Digital Imaging Correlation

This work demonstrated the utilization of non-destructive Digital Imaging Correlation (DIC) method to characterize the elastic, plastic, and damage features during the Mode I intra-laminar fracturing process of self-reinforced thermoplastic composites by using a self-reinforced polypropylene (PP) composite as an example. The DIC results clearly showed the development of huge plastic zone (PZ) and non-negligible Fracture Process Zone (FPZ) in front of the notch tip during the fracturing process, and the geometries and sizes of the foregoing zones at the peak load were further quantified. Such an interesting fracturing behavior of self-reinforced thermoplastic composites is way different from brittle materials (e.g., glass, acrylic, etc.), ductile materials (e.g., aluminum, steel, etc.), and even quasi-brittle materials (e.g., concrete, nanoparticle-reinforced composites, tough ceramics, wood, cement, carbon/glass fiber-reinforced polymers, etc.). Thus, understanding the elastic, plastic, and damage features is the first step before better characterizing the material fracture properties of self-reinforced thermoplastic composites through new analytical methods and computational modeling. These efforts are of utmost importance for wide applications of self-reinforced thermoplastic composites in various engineering fields in the future.

Lightweight Composites, Self-reinforced Thermoplas↗
DOE OSTI2022

Improving the damage tolerance of Si 3 N 4 by forming laminate composites with refractory metals

The objective of this research was to demonstrate that the damage tolerance of Si 3 N 4 could be significantly improved by forming laminate composites with refractory metals, providing materials that undergo graceful failure, rather than the fast-fracture mechanism exhibited by monolithic Si 3 N 4 . A damage tolerant Si 3 N 4 could be used as a ring material in an all-ceramic bearing, decreasing the chance for catastrophic failure if the ring is stressed in tension during operation. The technical approach formed a laminate composite material using alternating Si 3 N 4 -metallic layers, with both outer layers being Si 3 N 4 to take advantage of its greater wear resistance, chemical stability, and thermal stability. The metallic layers are designed to arrest any cracks in the outer layers, thus producing a toughened Si 3 N 4 and avoiding the catastrophic failure behavior exhibited by monolithic ceramics. The laminate composites were fabricated using a combination of tape-casting Si 3 N 4 and metals from slurries, as well as metal foils, followed by hot pressing at 1500°C. The metallic materials employed were chromium, titanium, and tantalum. Analysis confirmed that the interfaces were well formed, and the laminates with chromium and titanium formed intermetallic compounds more readily than the composites with tantalum. The Si 3 N 4 -Ta laminates demonstrated crack deflection and bridging behavior during failure and flexural strength of 800–900 MPa. The hardness and elastic modulus of Si 3 N 4 -Ta laminates measured by nanoindentation were similar to those reported in literature. The hardness across the interface of the Si 3 N 4 -Ta composite varied according to the composition of the interface, which displayed a profile indicative of a diffusion bond.

36 MATERIALS SCIENCE↗
NASA NTRSDate not supplied

Composite Technologies for Science Missions

ASTROLAB, Lunar Geophysical Network, Mars Icebreaker and Mars PLACER Net missions propose use of various types of vehicles – such as rovers, landers and flying probes - to accomplish their scientific objectives. Although designs for such vehicles are myriad, many structural components can be made using composite manufacturing technologies. Composite materials are also myriad, by nature, but carbon fiber reinforced polymers (CFRP) in particular are sought after for their high specific strength and specific stiffness. CFRP components could be especially beneficial in vehicle designs for Moon or Mars missions due to their nearly negligible coefficient of thermal expansion (CTE). CTE is a critical design characteristics in environments where significant thermal swings are prevalent, such as those of atmosphere-less Moon and Mars.MSFC/EM42 houses several relevant composites technologies. Strong and rigid struts can be filament-wound. Shells and platforms can be laid-up using automated fiber placement (for repeatability) or by hand (for small features). Monolithic structures can even be designed to reduce part count and therefore reduce the risk of joint failures. Composites are also tailorable, allowing the incorporation of different material types or formats through the thickness of a part. This includes materials which shield from radiation or electrostatic discharge. Finally, the rigidity of composite parts minimizes overall vibration and compliance within a design.Additionally, missions such as Triton Ocean World Surveyor anticipate use of traditional, metallic fuel tanks. Composite overwrapped pressure vessels (COPVs) are suitable for use in this application as well. The Triton mission even cites a concern for heat retention, for which CFRP also offers improved characteristics over traditional metallic tanks.

Lightweight↗
DOE OSTI2022

BETO 2021 Peer Review - 1.3.2.001 - Algae Biomass Composition

Addressing critical improvements in biomass productivity and associated biochemical composition is a priority for the economic and sustainable commercial development of biofuels and bioproducts from algae. Capitalizing on pathways that integrate engineering approaches with fundamental biochemistry of photosynthetic organisms will lead to a better understanding of the complex nexus of algae growth rates, productivity and composition. This project focuses on identifying the critical factors for economic development of fuel and bioproduct technologies. Algal compositional characteristics form the foundation of robust economic and business models. This project supports that foundation by developing and validating accurate compositional methods and disseminating them to the greater community. Simultaneously, we build a deep understanding of the dynamic biochemical composition and carbon allocation for biomass value and conversion yields. A co-product portfolio developed under this project demonstrated a 30% increase in intrinsic value. Additionally, an integrated pipeline of molecular diversity mapping for product discovery with quantitative demonstration across species was deployed over the BETO algae program. The advances made here are highly relevant to BETO's multi-year program targets of reducing costs and integrating dynamic biomass composition with conversion processes to provide options for bioproducts, all leveraging the molecular diversity of algae.

algal compositional characteristics↗
DOE OSTI2012

Induction Consolidation of Thermoplastic Composites Using Smart Susceptors

This project has focused on the area of energy efficient consolidation and molding of fiber reinforced thermoplastic composite components as an energy efficient alternative to the conventional processing methods such as autoclave processing. The expanding application of composite materials in wind energy, automotive, and aerospace provides an attractive energy efficiency target for process development. The intent is to have this efficient processing along with the recyclable thermoplastic materials ready for large scale application before these high production volume levels are reached. Therefore, the process can be implemented in a timely manner to realize the maximum economic, energy, and environmental efficiencies. Under this project an increased understanding of the use of induction heating with smart susceptors applied to consolidation of thermoplastic has been achieved. This was done by the establishment of processing equipment and tooling and the subsequent demonstration of this fabrication technology by consolidating/molding of entry level components for each of the participating industrial segments, wind energy, aerospace, and automotive. This understanding adds to the nation's capability to affordably manufacture high quality lightweight high performance components from advanced recyclable composite materials in a lean and energy efficient manner. The use of induction heating with smart susceptors is a precisely controlled low energy method for the consolidation and molding of thermoplastic composites. The smart susceptor provides intrinsic thermal control based on the interaction with the magnetic field from the induction coil thereby producing highly repeatable processing. The low energy usage is enabled by the fact that only the smart susceptor surface of the tool is heated, not the entire tool. Therefore much less mass is heated resulting in significantly less required energy to consolidate/mold the desired composite components. This energy efficiency results in potential energy savings of {approx}75% as compared to autoclave processing in aerospace, {approx}63% as compared to compression molding in automotive, and {approx}42% energy savings as compared to convectively heated tools in wind energy. The ability to make parts in a rapid and controlled manner provides significant economic advantages for each of the industrial segments. These attributes were demonstrated during the processing of the demonstration components on this project.

32 ENERGY CONSERVATION, CONSUMPTION, AND UTILIZATI↗
DOE OSTI2022

A review of the fabrication methods and mechanical behavior of continuous thermoplastic polymer fiber–thermoplastic polymer matrix composites

Abstract Thermoplastic polymer fiber–thermoplastic polymer matrix composites (PPCs or PRFPs), often recognized as self‐reinforced or single polymer composites, are potential candidates for future advanced polymer composites because of various advantages ( e.g., recyclability, formability, low‐cost, ultra‐lightweight, environmental friendliness, etc.). The manufacturability and mechanical behavior of these composites compared to conventional carbon‐/glass‐/aramid‐fiber‐reinforced polymers is of great interest to the composites community, but there are a limited number of studies in this area. To this end, this paper reviewed fabrication methods with different processing parameters and mechanical behavior of uni‐/multi‐directional thermoplastic PPCs featuring continuous thermoplastic polymer fibers from limited data in the literature. It was shown that most specific behaviors (normalized by density) of these materials in various loading conditions (e.g., quasi‐static tension/shear/flexure, tension‐tension fatigue, and out‐of‐plane impacting, etc.) are comparable to or better than glass‐/aramid‐fiber‐reinforced polymers. Particularly, the specific ductility in the foregoing conditions outperforms all the carbon‐/glass‐/aramid‐fiber‐reinforced polymers. Thermoplastic PPCs with remarkable performance can be achieved through several uncomplicated methods (e.g., film stacking, hot compaction, powder and solution impregnations, matrix infusion and injection molding, additive manufacturing, etc.), which have some similarities to the methods used for carbon‐/glass‐/aramid‐fiber‐reinforced polymers. Moreover, several opportunities and challenging problems of thermoplastic PPCs were summarized at the end of this review paper. Efficient solutions may require countless efforts in the composites community to further strengthen the performance and understanding of thermoplastic PPCs for wide applications in various engineering fields in the future.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Functional group effect of chemically modified microcrystalline methyl cellulose on thermoplastic polyurethane composites

Microcrystalline cellulose (MCC) is a promising bio-based filler for lightweight yet mechanically high-performance eco-polymer composites because of its low density and high biocompatibility. However, intermolecular hydrogen bonding among MCC is stronger than the polymer–filler interactions, which deteriorate the mechanical properties of the composites. Herein, we investigated the effects of functional groups on the mechanical properties of composites by scrutinizing chemically modified microcrystalline methyl cellulose (m-MMC) with three different substitution levels of hydroxyl group to hydroxypropyl (HP) group: no-, low-, and high-level substitution (HP-0, HP-low, and HP-high). The degree of HP substitution of m-MMC was quantitatively measured by CP/MAS NMR analysis. The relatively bulky HP groups interrupted the filler–filler intermolecular interactions and reduced the crystallinity and density of m-MMC, as evident from X-ray diffractometer and pycnometer data, respectively. For scalable production of the composites, the m-MMC were compounded with thermoplastic polyurethane (TPU) by a twin-screw extruder at concentrations between 0.5 and 10 wt%. Despite its low filler concentration, the toughness of m-MMC/TPU composites was remarkably enhanced, up to 28% (229.2 to 294.4 MJ/m 3 ) at 0.5 wt% loading of HP-low, owing to the enhanced polymer–filler interactions. In conclusion, the fundamental understanding on structure–property relationships will provide insights for designing of mechanically robust yet eco-friendly polymer composites.

composites↗
DOE OSTI2019

Lightweight TiC–(Fe–Al) ceramic–metal composites made in situ by pressureless melt infiltration

Lightweight ceramic–metal (cermet) composites combine stiffness and hardness with fracture toughness and ductility. TiC and Al are ideal pairs among lightweight cermet composites because of their relatively high strength-to-weight ratios, but these materials are difficult to process in solid state or with Al melt infiltration without making an aluminum carbide phase, which is detrimental to mechanical properties. Here, Fe is added to a TiC powder preform to reduce the activity of Al with TiC during Al melt infiltration and to aid in pressing TiC preforms, making a lightweight TiC–(Fe–Al) composite while avoiding other, unwanted phases. The composites are made by first pressing TiC powder mixed with Fe followed by Al melt infiltration; the result is a composite with high TiC content in a two-phase matrix, both of which are Fe–Al-based. The composite has low density, low porosity, high hardness, no detectable Al 4 C 3 phase with X-ray diffraction and retains shape well during infiltration.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Sustainable Use of Coffee Husks For Reinforcing Polyethylene Composites

The utilization of the coffee husk fiber (CHF) from the coffee industry as a reinforcing filler in the preparation of a cost-effective thermoplastic based composite was explored in this study. The chemical composition and thermal properties of the CHF were investigated and compared with those of wood fiber (WF). CHF proved to be mainly composed of cellulose, hemicellulose and lignin, and exhibited similar thermal behavior to WF. High density polyethylene (HDPE) composites with CHF loadings of from 40 to 70% were prepared using melt processing and extrusion. The processing properties, mechanical behavior, water absorption and thermal performance of these composites were investigated. The effect of maleated polyethylene (MAPE) used as a coupling agent on the composite was explored. The experimental results showed that increasing the CHF loading in the HDPE matrix resulted in an increase in the modulus and thermal properties of the composites, but resulted in poor water resistance. The addition of a 4% MAPE significantly improved the interfacial behavior of the hydrophilic lignocellulosic fiber and the hydrophobic polymer matrix.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Fiber from DDGS and Corn Grain as Alternative Fillers in Polymer Composites with High Density Polyethylene from Bio-based and Petroleum Sources

The steady increase in production of corn based ethanol fuel has dramatically increased the supply of its major co-product known as distiller’s dried grain with solubles (DDGS). Large amount of DDGS and corn flour are used as an animal feed. The elusieve process can separate DDGS or corn flour into two fractions: DDGS fraction with enhanced protein and oil content or corn flour fraction with high starch content, and hull fiber. This study investigated the feasibility of using fiber from DDGS and corn grain as alternative fillers to wood fiber in high density polyethylene (HDPE) composites made with two different sources of polymers. Two fiber loading rates of 30 and 50% were evaluated for fiber from DDGS, corn, and oak wood (control) to assess changes in various physical and mechanical properties of the composite materials. Two HDPE polymers, a bio-based HDPE made from sugarcane (Braskem), and a petroleum based HDPE (Marlex) were also compared as substrates. The biobased polymer composites with DDGS and corn fibers showed significantly lower water absorption than the Marlex composite samples. The Braskem composite with 30% DDGS fiber loading showed the highest impact resistance (80 J/m) among all the samples. The flexural properties showed no significant difference between the two HDPE composites.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Enhanced Interfacial Adhesion and Characterisation of Recycled Natural Fibre-Filled Biodegradable Green Composites

The structural, thermal, mechanical, and biodegradable properties of composite materials made from polylactide (PLA) and agricultural residues (arrowroot (Maranta arundinacea) fibre, AF) were evaluated. Melt blended glycidyl methacrylate-grafted polylactide (PLA-g-GMA) and coupling agent-treated arrowroot fibre (TAF) formed the PLA-g-GMA/TAF composite, which had better properties than the PLA/AF composite. The water resistance of the PLA-g-GMA/TAF composite was greater than that of the PLA/AF composite; the release of PLA in water from the PLA/AF and PLA-g-GMA/TAF composites indicated good biological activity. The PLA-g-GMA/TAF material had better mechanical properties than PLA/AF. This behaviour was attributed to better compatibility between the grafted polymer and TAF. The results indicated that the T{sub g} of PLA was increased by the addition of fibre, which may have improved the heat resistance of PLA. Furthermore, the mass losses following burial in soil compost indicated that both materials were biodegradable, especially at high levels of AF or TAF substitution.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Synthesis and Performance Evaluation of Unsaturated Polyester Blends of Resins and Its Application on Non-woven/Fabric Jute Fibers Reinforced Composites

The present study focuses on the generation of eco-friendly value added product by utilizing bio-based material as reinforced and matrix phase. Processing of soy and alkyd resin as matrix was carried out by utilization of soy flour and Ricinodendron heudelotii oil, followed essential modification in few inferior properties of soy flour resin by blending with alkyd resin. Separate sets of resin were prepared by maintaining 0%, 5% and 10% of alkyd resin in 100 g of soy flour resin respectively in each set to attain a comparative study on performance of prepared sets of resin blend. Subsequently, performance evaluation of polyester blends was evaluated by processing with non-woven/fabric jute fibers reinforced composites. The blend of R. heudelotii oil based alkyd and soy-flour resin in processing of composites was the noval approach of the study. The resins blend were characterized by FT–IR, viscosity and zeta potential measurements while thermo-mechanical analyses, water absorbancy and surface analyses were performed in composites. Significant increases noticed in the viscosity of blend, the blend containing 10% alkyd resin is two times more viscous compared to soy-flour resin. Furthermore, improvement in properties including water absorption, thermo-mechanical properties and better fiber-matrix interfacial adhesion of the composite could be observed. Higher glass transition temperature T{sub g} value i.e. 126.8 °C obtained for composites with 10% blend as matrix might emphasizes on increase of the degree of cross linking provided by the α-eleostearic fatty acid chain moiety. The enhancements in properties indicate extending opportunities for fiber-reinforced composites in several industries including building material, furniture, aerospace, nano etc.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Modified Magnetic and Electrical Properties of Perovskite-Spinel Multiferroic Composites

Multiferroic composite samples (1 − x) Bi{sub 0.9}Pr{sub 0.1}FeO{sub 3}–xNi{sub 0.5}Co{sub 0.5}Fe{sub 2}O{sub 4} for x = 0, 0.1, 0.2, 0.3, and 1.0 were synthesized by sol-gel auto-combustion method. Detailed investigations were made on the structural, magnetic, and electrical properties of these composites. The X-ray diffraction (XRD) patterns confirm the co-existence of perovskite BPFO and spinel ferrite NCFO without any impurity phase. The average particle size of BPFO and NCFO nanoparticles is nearly equal to 110 nm and 35 nm respectively which are confirmed by XRD and transmission electron microscopy (TEM) analysis. Structural and surface morphology are studied by scanning electron microscopy (SEM). The dielectric properties of the composites are also studied at room temperature. The saturation and remnant magnetization are found to increase with increase in NCFO weight percentage in the composites. The saturation magnetization (Ms) values are 3.38 emu/g, 8.65 emu/g, and 13.87 emu/g and coercivity (Hc) values are 936.52 Oe, 1058.12 Oe, and 1046.77 Oe for BPFO-NCFO 1, 2, and 3 composite samples respectively. The incorporation of BPFO and NCFO enhances the multiferroic properties in the present composite materials which are quite promising for applications point of view.

36 MATERIALS SCIENCE↗
DOE OSTI2017

Relationship Between the Integrity of Lubricating Film and the Tribological Behavior on TiAl-Ag Self-Lubricating Composites

To explore the relationship between the integrity of the lubricating film and the tribological behavior of a metal matrix self-lubricating composite, the friction and wear experiments of TiAl-Ag self-lubricating composites were carried out with a ball-on-disk configuration. Besides, an approximate model was developed for analyzing the relationship based on Blau’s theory. The research results suggest that the friction and wear behavior of the TiAl-Ag self-lubricating composites changes in accordance with the formation conditions of the Ag-rich lubricating film. Specifically, the friction coefficients and wear rates of the TiAl-Ag self-lubricating composites decreased from high levels at full composite–counterface ball contact to low levels at full-film lubrication. Hence, the integrity of the lubricating film is a possible criterion for the self-lubricating property of the self-lubricating composites.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Electron Backscattered Diffraction Study of Pulse Electrodeposited Cu-Y{sub 2}O{sub 3} Composite Coating

The current investigation is an effort of correlating the grain growth, crystallographic orientation and second-phase Y{sub 2}O{sub 3} particles to the mechanical properties of the electrodeposited pure copper (Cu) and Cu-Y{sub 2}O{sub 3} coatings. Energy-dispersive spectrum and elemental mapping confirm the codeposition of Y{sub 2}O{sub 3} in the composite coating matrix, which indeed justifies the composite (Cu-Y{sub 2}O{sub 3}) coating. Both pure Cu and Cu-Y{sub 2}O{sub 3} coatings have (101) preferred orientation; however, the volume fraction is found comparatively lower in composite coating. Both microstructural and textural characterization through electron backscattered diffraction technique show significant grain refinement in case of Cu-Y{sub 2}O{sub 3} composite coating compared to pure Cu coating, and prominent 〈011〉 fiber texture is observed in case of pure Cu coating compared to composite coating. By the addition of second-phase Y{sub 2}O{sub 3} in the matrix, the 〈011〉 fiber texture is disintegrated and concentrated at ϕ{sub 1} = 37°, ϕ = 45°, ϕ{sub 2} = 0°. Despite lower volume fraction of 〈011〉 fiber texture, better mechanical properties (hardness and wear resistance) of the composite coating compared to pure Cu coating can be attributed to finer grain size, higher misorientation angle and incorporation of second-phase Y{sub 2}O{sub 3} particles.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Microstructure and Mechanical Properties of Mg{sub 2}Si/AZ91 Composites In Situ Synthesized by Using Silica Fume as the Si Source

Microstructure and mechanical properties of in situ Mg{sub 2}Si/AZ91 composites fabricated using silica fume as the Si source were investigated. The composites contained α-Mg, network Mg{sub 17}Al{sub 12}, lamellar Mg{sub 17}Al{sub 12}, coarse polygonal Mg{sub 2}Si and needle-type Mg{sub 2}Si. Mischmetal modification eliminated the coarse polygonal Mg{sub 2}Si and resulted in a decreased amount of lamellar Mg{sub 17}Al{sub 12} and refined matrix grain size. Solution and aging treatment made the network Mg{sub 17}Al{sub 12} transform into lamellar Mg{sub 17}Al{sub 12}. As the volume fraction of Mg{sub 2}Si increased, the matrix grain size decreased, the amount of Mg{sub 17}Al{sub 12} increased, and more Mg{sub 17}Al{sub 12} precipitated in grain interiors as a result of the increased Al/Mg ratio caused by increasing the amount of Mg{sub 2}Si. The tensile strength and elastic modulus were much higher for the modified composites than for the unmodified one and increased by both increasing the volume fraction of Mg{sub 2}Si and performing aging treatment. The composites failed in a quasi-cleavage fracture mode, and coarse polygonal Mg{sub 2}Si phases were responsible for the lowest ductility of the unmodified composite. The highest UTS of 291.55 MPa obtained is much higher than those reported so far by using fly ash as the Si source, indicating that silica fume is more suitable as the Si source to synthesize Mg{sub 2}Si/AZ91 composites.

36 MATERIALS SCIENCE↗