Interfacial Al4C3 Research Articles

Regulating microstructure of Al matrix composites with nanocarbon architecture design towards prominent strength-ductility combination

Evading the strength-ductility trade-off is essential for engineering application of metal matrix composites. Herein, we propose a novel strategy to achieve the prominent strength-ductility combination of nanocarbon-Al composites. The strategy makes use of the nanocarbon architecture design via longitudinally unfolding the multi-walled carbon nanotubes (CNTs) into graphene nanoribbons (GNRs). It was found that the nano-sized intragranular and interfacial Al4C3 (length: 64±23 nm) easily formed in GNR/Al via the “heterogeneous nucleation-growth” pattern, which is contrary to the submicron-sized epitaxial Al4C3 (length: 133±39 nm) in CNT/Al. Detailed characterizations reveal the specific orientation relationships between Al4C3 and Al in GNR/Al, which benefits the robust interfacial bonding. The intragranular Al4C3 and intergranular GNR with large aspect ratio effectively increase the dislocation storage and hence working hardening ability, which leads to the strength-ductility synergy of GNR/Al. Meanwhile, the GNR anchored by dense interfacial Al4C3 introduces extra toughening effect by crack bridging, blunting and deflection.

Architecting micron SiC particles on diamond surface to improve thermal conductivity and stability of Al/diamond composites

In this paper, a new method to synthesize micron silicon carbide (SiC) particles on the diamond surface at low temperature was proposed, namely, the micron SiC particles had been synthesized by aluminum-silicon (Al-Si) mixed powders and vacuum annealing technology. Continuity and formation mechanism of the SiC particles were studied. The continuity of the SiC particles is affected by annealing temperature and the mass fraction of silicon (Si) in Al-Si mixed powders. When the mass fraction of Si in Al-Si powders is 70 wt.% and the annealing temperature is 800°C, SiC particles with a continuous structure can be synthesized. Aluminum carbide (Al4C3) as the indispensable intermediate phase plays a crucial role in promoting the formation of SiC particles at low temperature. The Al/diamond composite with high thermal conductivity of 711 W·m−1·K−1 was obtained by introducing SiC particles with a continuous structure. Meantime, the continuous SiC layer effectively inhibited the formation of Al4C3 at the interface of the composite, and only 0.5 wt.% of Al4C3 was detected by gas chromatography. This study provides a novel practical way for surface coating engineering on diamond particles, which can be used to improve thermal conductivity and inhibit the interfacial Al4C3 of Al/diamond composites.

Formation of the orientation relationship-dependent interfacial carbide in Al matrix composite affected by architectured carbon nanotube

In-situ formed carbides at interface can enhance the interfacial bonding and load-transfer effect in nanocarbon/Al composites, but always sacrifice the structure integrity of reinforcement, inevitably degrading the strengthening efficiency. To alleviate such limitation, a novel hybrid leaf-like carbon nanotube (CNT)-graphene nanoribbon (GNR), architectured via partially longitudinal unzipping of multi-walled CNT (UZCNT), was adopted to reinforce Al matrix composites. Results show that the prominent mechanical properties of UZCNT/Al over CNT/Al were achieved, which originates from the in-situ formed interfacial Al4C3 together with the well-retained integrity of UZCNT. The regulated interfacial reaction between UZCNT and Al generates dense nano-sized Al4C3 (diameter: 14–19 nm, length: 36–82 nm), rather than its submicron-sized counterpart (diameter: 26–37 nm, length: 111–186 nm) with low number density which forms in unmodified CNT/Al composites. Systematic analysis indicates that the interfacial Al4C3 in UZCNT/Al forms via “nucleation-growth” pattern, contrary to the predominant epitaxial growth of Al4C3 in CNT/Al. It is revealed that UZCNT can stimulate Al4C3 nucleation via reducing the nucleation energy barrier and increasing the number of nucleation sites. Meanwhile, finite active C atoms and low-defective inner walls in UZCNT retard the fast growth of Al4C3 after nucleation. Such “nucleation-growth” pattern renders the formation of high number-density nano-sized Al4C3 at GNR margin in UZCNT/Al. Atomic-scale characterizations demonstrate that the coherent/semi-coherent Al4C3-Al interfaces in UZCNT/Al preferentially exhibit specific orientation relationships, most of which are reproducible by the edge-to-edge matching model. The present work is supposed to provide important insights on interfacial carbide formation in nanocarbon/metal composites.

Design of high-performance Al4C3/Al matrix composites for electric conductor

Increased strength of Al matrix composites (AMCs) with a high electrical conductivity are in demand to replace copper conductors. In this study, a high-performance Al4C3/Al composite was synthesized in situ via the high-energy densification of uniform graphene oxide (GO)/Al powder combination; GO was completely transformed to monocrystalline Al4C3 nanorod structures, robustly bridging across the Al grain boundary. The formation mechanism of interfacial Al4C3 was illustrated by high-resolution transmission electron microscope observations. The Al4C3 nanorods were homogeneously dispersed and possessed an intimate and faceted interface with the matrix, resulting in the enhanced tensile strength of Al. Moreover, the Al4C3/Al composite retained the required electrical conductivity similar to that of pure Al, in addition to the stable interface at elevated temperatures and long-term service reliability in moist environment. The findings of this study will be significant in providing the basis of designing novel heat-resistant AMCs in electrical applications.

Strengthening effect induced by interfacial reaction in graphene nanoplatelets reinforced aluminum matrix composites

GNPs/Al composites with the different volume fractions of GNPs (0.3, 0.6, 0.9 and 1.2 vol %) were successfully fabricated by spark plasma sintering. Microscopy observation indicated that interfacial Al4C3 phases take on nano-rod or granulate with a mean diameter of ∼30 nm. Nano-sized Al4C3 phases are uniformly distributed and intimately contacted with GNPs. The interfacial bonding state between GNPs and Al matrix changes from mechanical bonding to strong chemical bonding, because Al4C3 phases are tightly locked into Al matrix forming an anchor effect. The strengthening effect induced by interfacial reaction in GNPs/Al composites was investigated according to grain refinement strengthening, Orowan strengthening, dislocation strengthening by CTE mismatch and load transfer. It is innovatively proposed that GNPs and nano-sized Al4C3 phase should be taken as a whole to discuss the strengthening effect in GNPs/Al composites. Load transfer in GNPs/Al composites is significantly affected by interfacial nano-sized Al4C3 phases. Due to the deformation strengthening of Al matrix during tension and the anchor effect of Al4C3 phase, load transfer calculated from the experimental value is one-to twofold higher than its theoretical maximum. This work can provide some meaningful suggests for revealing the strengthening behavior of GNPs reinforced metal matrix composites.

Microstructure and mechanical properties of graphene nanoplatelets reinforced Al matrix composites fabricated by spark plasma sintering

Abstract Graphene nanoplatelets reinforced aluminum matrix (GNPs/Al) composites were successfully fabricated by high-energy ball milling and spark plasma sintering. The microstructure and mechanical properties of the GNPs/Al composites were investigated. Microstructure and distribution of GNPs were analyzed with a scanning electron microscope (SEM), X-ray diffraction (XRD) and transmission electron microscope (TEM). Tensile properties and hardness were studied at room temperature. The GNPs/Al composites with the well-dispersed GNPs and good densification were fabricated, indicating this technology can effectively fabricate the GNPs/Al composites. The randomly distributed nano-rods Al4C3 was found in the GNPs/Al composites fabricated at 600 °C. The ultimate tensile strength, yield strength, elongation, as well as Vickers hardness of GNPs/Al composites increase with the increase of fabrication temperature. The GNPs/Al composites with nano-Al4C3 have a good balance between tensile strength and elongation, because the nano-sized Al4C3 phase helps to improve the interfacial bonding and mechanical properties of GNPs/Al composites. The GNPs/Al composites exhibit a ductile mode of failure, and GNPs pull-out was detected at the fracture surface. The strengthening mechanism of GNPs/Al composites was discussed according to the load transfer strengthening, Orowan strengthening and dislocations strengthening, and the interfacial Al4C3 phase plays a critical role in determining the load transfer efficiency of GNPs. This paper may render significant information for understanding the strengthening behaviors of GNPs reinforced metal matrix composites.

Effect of Processing Conditions on Bonding Strength at Al(Si)/Diamond Interfaces

Understanding thermos-physical properties of MMCs includes considering interfacial processes and interactions between the constituents in MMCs. In this context, interfacial bonding is of vital interest for a deeper understanding of composites. Neutron diffraction experiments on Al/diamond composites were performed and reconciled with their thermo-physical properties and quantification of interfacial carbides formation. To create different interfacial conditions both, the contact time during processing the MMCs by liquid metal infiltration and the nominal composition of the matrix were changed, thus creating different amounts of interfacial Al4C3 carbides. Neutron diffraction showed the increase in contact time and the addition of Si to Al both increase the bonding strength, although going with a significant decrease of the composite`s thermal conductivity.

Enhanced stability of the Diamond/Al composites by W coatings prepared by the magnetron sputtering method

In the present work, the effect of the W coatings prepared by the magnetron sputtering method on the stability of the thermal and mechanical properties of the Diamond/Al composites has been investigated. Due to the decomposition of the interfacial Al4C3 phase, the thermal conductivity and bending strength of the Diamond/Al composites without W coating were decreased 23% and 33%, respectively. However, the variation of the normalized thermal conductivity (NTC) of the Diamond/Al composites has been changed from polynomial to linear relationships after the W-coating treatment, indicating the enhancement of the thermal conductivity and the bending strength stability. Diamond/Al composite with 45 nm W coating demonstrated the best thermal and mechanical stability with slight decrement of 3% after 720 h heat-moisture treatment (HMT). Due to the decomposition of the Al4C3 phase and the corresponding weakened interfacial bonding, more “clean {111} planes” of the diamond particles were observed in the fracture surface of Diamond/Al composites without W coating after HMT. However, no significant difference was found in the fracture surface of the Diamond/Al composites with 45 nm and thicker W coatings before and after HMT. It is suggested that the continuous, stable and well bonded interfacial structure without the formation of the Al4C3 phase is the key for the improvement of the stability of the Diamond/Al composites.

Aluminum carbide hydrolysis induced degradation of thermal conductivity and tensile strength in diamond/aluminum composite

Diamond particles reinforced aluminum matrix (diamond/Al) composite is receiving great interests as a thermal management material due to its superior thermal conductivity and light weight. The diamond/Al composite is, however, incurring a problem of aluminum carbide (Al4C3) hydrolysis in the applications. Here we propose an accelerated hydrolytic ageing method to assess the reliability of diamond/Al composite in water environment. The diamond/Al composite specimens have been immersed in distilled water at room temperature up to 115 days. The microstructural characterization shows that water diffuses into the composite and reacts with the interfacial Al4C3 phase to generate Al(OH)3 and CH4. The concentration of the collected methane gas was measured by using a gas chromatograph technique to monitor the hydrolysis reaction. With prolonging soaking time from 5 to 115 days, the normalized methane concentration increases from 4 × 10−4 to 2 × 10−3, the thermal conductivity decreases from 467 to 347 W/mK, and the tensile strength decreases from 105 to 61 MPa. The property degradation is ascribed to the hydrolysis of Al4C3, which is harmful to the structural integrity of the diamond/Al composite. The finding provides guideline for the protection of diamond/Al composite components in service environments.

Solid-state interfacial reaction and load transfer efficiency in carbon nanotubes (CNTs)-reinforced aluminum matrix composites

Carbon nanotubes (CNTs)/aluminum (Al) composites with various interfacial reaction degrees were fabricated by powder metallurgy at sintering temperature range of 700–900 K (75–96% melting point of Al). Interfacial reaction product, aluminum carbide (Al4C3), was formed in Al matrix composites (AMCs) reinforced by homogeneously-dispersed CNTs. Microscopy observations revealed three types of temperature-dependent interfaces, i) clean CNT-Al interfaces without interfacial carbide, ii) CNT-Al4C3-Al interfaces for partially reacted CNTs with Al4C3 nanoparticles, and iii) Al4C3-Al interface for in-situ Al4C3 nanorods evolved from completely reacted CNTs. Interfacial Al4C3 on partially reacted CNTs led to significant improvement of interfacial strength and consequent enhancement of load transfer efficiency in AMCs, compared to those composites without carbide. The load transfer mechanism of CNTs in composites was confirmed by the pull-out phenomena during in-situ tensile tests. The role of interfacial carbide played in determining the load transfer efficiency of CNTs was discussed. This study may provide new insights into the interfacial phenomena and load transfer mechanism in CNT-reinforced metal matrix composites.

Nucleation and growth mechanisms of interfacial Al 4 C 3 in Al/diamond composites

Controlling the nucleation and growth of interfacial Al4C3 carbide to optimize interfacial microstructure is well accepted as a critical factor to improve thermal properties of Al/diamond composites. In this study, the nucleation and growth mechanisms of Al4C3 carbide have been studied. The inhomogeneous nucleation of Al4C3 is revealed on both diamond (100) and (111) surfaces ((100)D and (111)D surfaces). Al4C3 particles nucleate at (111)D facets on both (111)D and (100)D surfaces. Growth of Al4C3 particles is controlled by diffusion and Ostwald ripening. The proposed mechanisms well explain the observation of high density and small flower-like carbide on (100)D surface and less dense larger plate shape carbide on (111)D surface. The orientation relationship between diamond and Al4C3 was identified to be [11¯0]D//[21¯1¯0] Al4C3 and (111)D//(0003)Al4C3 on both diamond surfaces. Our results will provide guidance to the further improvement of properties of Al/diamond composites.

FEA evaluation of the Al4C3 formation effect on the Young’s modulus of carbon nanotube reinforced aluminum matrix composites

The effect on Young’s modulus of Al4C3 formation in the carbon nanotube (CNT)–Al interface, for Al matrix composites, was analyzed using Finite Elements Analysis (FEA) models, incorporating different CNT volume fractions and interfacial Al4C3 layers of various thicknesses. Reinforcements were modeled with and without the hemispherical end caps that characterize CNT. FEA estimations were compared to the Rule of Mixtures predictions. Results showed that the elastic modulus of the composites significantly rises as the CNT volume fraction increases, while the increase in the Al4C3 layer thickness provokes a slight increment in the Young’s modulus. This could be attributed to a combined reinforcement effect of the CNT and the interface. The inclusion of CNT with hemispherical end caps in the FEA model drops the estimated Young’s modulus. Finally, the results presented in this work demonstrated the importance of the model selection for analyzing the mechanical behavior of the composites.

Interfacial characterisation in Al–20 vol.-%SiCp explosively compacted composite

Al–20 vol.-%SiCp composite was prepared using direct explosive compaction. Interfacial characterisation of the composite was preformed using scanning electron microscopy, X-ray diffraction and transmission electron microscopy. The results showed that the interface seemed to be clean and no interfacial Al4C3 reaction product was generated along the interface between SiC particles and Al matrix. The results also showed a better bonding between SiC particles and Al matrix in the central region of the compact sample.

Interfaces of SiC fibres and Al-5% Mg developed under systematically varied processing conditions

Abstract In the present work, attention has been focused on the processing-dependent nature of the interface of SiC fibre-reinforced A1 matrix composites fabricated by pressurized liquid metal infiltration. To determine the effect of variation of the processing parameters on the interface formation. Tyranno continuous SiC fibres have been infiltrated with Al-5% Mg melt under a range of melt superheat and infiltration pressure conditions. During processing the major processing parameters of the pressurized infiltration were precisely monitored. Analytical transmission electron microscopy of the obtained interfaces was employed to study the nature and extent of the interfacial reactions. Oxygen pre-existing in the fibres results in the formation of an interfacial oxide layer. The chemical reaction between SiC and Al occurs by Al penetration, in situ SiC decomposition and Al4C3 formation. Surplus C and the reduced Si diffuse into the interfacial matrix, resulting in the formation of interfacial Si and/or Mg2Si and interfacial Al4C3 protruding into the matrix Mg in the melt preferentially penetrates into the fibres but does not cause any observable variation in the fibre structure. Increases in melt superheat and infiltration pressure intensify the interfacial reactions. It is also found that the extent of the interfacial reactions and interfacial binding can be significantly altered by the geometrical location of the interface in question.

Strengthening of Al/20 v/o TiC composites by isothermal heat treatment

A chemical potential gradient exists across the reinforcement/matrix interface of metal-matrix composites which serves as the basis for either diffusion or chemical reaction between the two components at high temperatures. While poor control of this reaction may degrade mechanical properties, it may also be employed to improve them. Such improvements as an increase in elastic modulus in the case of Al-Mg/SiC(p) are attributable to improved load transfer, due either to an interactive diffusion process at the interface or the 'keying' effect of interfacial Al4C3. A systematic study is presently undertaken of the effects of 600 C exposure on the microstructure and mechanical properties of Al/20 vol pct TiC; a reduction in tensile ductility is associated with an increase in strength and elastic modulus. 5 refs.