Al4C3 Phase Research Articles

Production of cast materials based on Cr<sub>2</sub>AlC MAX phase by SHS metallurgy using coupled chemical reaction

It is known that materials based on MAX phases have great potential for aerospace, automotive and industrial applications due to a unique combination of features offered by both metals and ceramics with high mechanical, chemical, thermal and electrical properties. This paper provides the results obtained by the SHS metallurgy of Cr–Al–C materials with different ratios between the MAX-Cr 2 AlC phase, carbides and chromium aluminides. Experiments were carried out in a 3-liter SHS reactor at an initial pressure of inert gas (Ar) of 5 MPa. The synthesis process was carried out based on coupled chemical reactions: weakly exothermic (heat acceptor) – Cr 2 O 3 /3Al/C and strongly exothermic (heat donor) – 3CaO 2 /2Al. The obtained experimental results have a good correlation with previously performed thermodynamic calculations. It is shown that varying the composition of the initial mixtures can significantly influence the calculated and experimental synthesis parameters as well as the phase composition and microstructure of final products. The paper establishes optimal conditions for material synthesis providing a maximum output of the Cr 2 AlC MAX phase in the ingot composition. A determining factor influencing the Cr 2 AlC content in the final product is the time of liquid phase presence under synthesis conditions. It is shown that the maximum content of the Cr2AlC MAX phase and the target product yield is achieved at the highly exothermic additive (3CaO 2 /2Al) content of 30 % in the initial mixture.

Application of a novel method for fabrication of graphene reinforced aluminum matrix nanocomposites: Synthesis, microstructure, and mechanical properties

In this study, the graphene reinforced aluminium matrix nanocomposite is fabricated through the combination of high energy ball milling (HEBM) and molecular level mixing (MLM) processes followed by spark plasma sintering (SPS) method. FTIR, XRD and FESEM analyses revealed that Cu/RGO nanocomposite was well synthesized by the MLM method with a uniform distribution of Cu nanoparticles on RGO surface. XRD and Raman spectroscopy showed that no Al4C3 phase was formed during the manufacturing process, but Al2Cu fine particles precipitated during the SPS treatment which were smaller in size and more uniform in distribution when RGO was used as reinforcement according to TEM analysis. Grain refinement of the nanocomposites was also investigated in the presence of RGO by EBSD method. The results showed that with increasing RGO content from 0 to 1 wt %, the coarse grained microstructure changed to bimodal microstructure. In addition, the mean grain size decreased from 3.9 to 1.6 μm, and dislocation density increased significantly with the increased RGO content. The SPS process also resulted in a nearly fully dense nanocomposite with a relative density higher than 99%. The investigation of mechanical properties of the sintered nanocomposite indicated an improvement of 79, 49 and 44% of yield strength, ultimate strength, and Vickers hardness, respectively, for only 1 wt % graphene containing nanocomposite in comparison to the unreinforced Al–4Cu alloy.

Microstructure of novel SiCp/Al-Si-Mg composites fabricated by high pressure sintering

Three kinds of SiCp/Al-Si-Mg composites, containing 20%, 40% and 60% volume fraction of silicon carbide particles (SiCp) were respectively sintered at high cubic anvil pressure, using SiC powders prepackaged by aluminum. Then microstructures of the composites were investigated, and the influences of pressure, sintering temperature and volume fraction of SiCp on the microstructures were analyzed. Results show that the composites own homogeneous microstructures, high density and few porosities. In the composites, SiCp and Al matrix were bounded to each other tightly and few agglomeration of SiCp or aluminum was observed. With the volume fraction of SiCp increased, the pinning effect of the reinforcement on the Al matrix is enhanced. With the sintering temperature and pressure increased, densities of the samples are also increased. Energy Dispersive Spectrometer (EDS) and X-ray diffraction (XRD) results show that there are transition layers and Al4C3 phases formed at the interface between SiCp and Al matrix when fabricated under pressure of 3.0GPa and temperature of 620 °C.

The interfacial structure of Al/Al4C3 in graphene/Al composites prepared by selective laser melting: First-principles and experimental

Abstract The graphene (Gr) reacted with Al, and the Al4C3 phase was precipitated during selective laser melting (SLM). The interfacial structure of Al/Al4C3 was calculated by the first principle. The degree mismatch between Al (1 1 1) and Al4C3 (0 0 0 1) interface was lowest. Al (1 1 1)/Al4C3 (0 0 0 1) interface models with different stacking sequences (top-site, center-site, and hollow-site) of different terminations (Al-termination and C-termination) were established. C-termination-center-sited interface has largest work of adhesion, and interfacial energy of this model is lower than that of α-Al/Al melt (0.15 J/m2), so that α-Al nucleus tend to form on the C-termination-center-sited Al4C3 (0 0 0 1). Al-C covalent bonds and Al-Al metallic bonds are formed across interface, which increased interfacial bonding strength.

Interfacial zone surrounding the diamond in reaction bonded diamond/SiC composites: Interphase structure and formation mechanism

Diamond/SiC composites have attracted considerable research interests due to their outstanding properties sought for a wide range of applications. Among a few techniques used for the fabrication of diamond/SiC composites, molten Si infiltration is an approach highly favored due to its cost-effectiveness and process flexibility. This study critically evaluated the interfacial zone surrounding the diamond in a reaction bonded (RB) diamond/SiC composite. XRD suggests that the composite consists of diamond, α-SiC, β-SiC, Si, and graphite. TEM reveals that a thin layer of graphite surrounds the diamond grain and it appears to form through a process of diamond graphitization and amorphous carbon transformation during the fabrication. In addition, a carbon dissolution and saturation process is proposed as a predominant mechanism for the formation of nano-crystalline SiC near the interface as well as the defects inside the SiC grits. A minor Al4C3 phase is occasionally detected near the interface region.

Revealing the Nuclei Formation in Carbon-Inoculated Mg-3%Al Alloys Containing Trace Fe.

In this study, Fe-bearing Mg-3%Al alloys were inoculated by combining carbon with or without Ca. Both processes can significantly refine the grain size of Mg-3%Al alloys. The highest refining efficiency can be obtained by carbon combined with Ca. The synergistic grain refining efficiency can be attributed to the constitutional undercooling produced by the addition of Ca. Two kinds of carbon-containing nuclei with duplex-phase particles and cluster particles were observed in the carbon-inoculated alloys. A thermodynamic model was established to disclose the formation mechanisms of the duplex-phase particles and Al4C3 cluster particles. This thermodynamic model is based on the change of Gibbs free energy for the formation of these two kinds of particles. The calculated results show that these two particles can form spontaneously, since the change of Gibbs free energy is negative. However, the Gibbs free change of the duplex-phase particle is more negative than the Al4C3 cluster particle. This indicates that the adsorption process is more spontaneous than the cluster process, and tiny Al4C3 particles are preferred to form duplex-phase particle, rather than gathering to form an Al4C3 cluster particle. In addition, the addition of Ca can reduce the interfacial energy between the Al4C3 phase and the Al–Fe phase and promote the formation of duplex-phase particles.

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 hard to process in solid state or with Al melt infiltration without making an aluminum carbide phase, which is detrimental to mechanical properties. In this research, 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 Al4C3 phase with X-ray diffraction and retains shape well during infiltration.

Microstructural Characteristics and Mechanical Properties of CNT/Ni Coated CNT–Dispersed Al Alloys Produced by High Energy Ball Milling and Hot Extrusion

The effect of dispersion of carbon nanotubes (CNT) and Ni coated CNT in Al alloy (AA) on the evolution of microstructure and resultant mechanical properties are investigated. Al alloy (Al–4.4Cu–0.5Mg), Al alloy–CNT (AC) and Al alloy–Ni coated CNT (ANC) composites were produced from elemental powders by mechanical milling (MM) followed by hot extrusion. Unlike CNT–containing Al or Al alloy milled powders, Al4C3 phase formed during milling of ANC powder. The formation of Al4C3 is due to the dissolution of Ni present on CNT surface in Al alloy during MM, thereby, creating defects on CNT that promoted Al4C3 formation. AC and ANC samples exhibited larger size and lower number density of θ′ precipitates when compared to AA. The larger size of θ′ precipitates is due to the presence of ultra–fine grains, reduced quenched–in vacancies and higher dislocation density that promoted the nucleation resulting in enhanced precipitation and growth kinetics. The strengths of AC and ANC samples are higher when compared to CNT-free AA, and ANC exhibited highest yield strength of 567 MPa. However, the ductility of ANC sample is not improved due to the presence of Al7Cu4Ni phase, which promoted crack initiation.

Influence of rolling temperature on the interfaces and mechanical performance of graphene-reinforced aluminum-matrix composites

To study the influence of rolling on the interfaces and mechanical performance of graphene-reinforced Al-matrix composites, a rolling method was used to process them. Using scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), Raman spectroscopy, and tensile testing, this study analyzed the micromorphology, interfaces, and mechanical performance of the composites before and after rolling. The experimental results demonstrates that the composites after hot rolling has uniform structures with strong interfacial bonding. With an increase in rolling temperature, the tensile strength and elastic modulus of the composites gradually increase. However, when the rolling temperature is higher than 500°C, granular and rod-like Al4C3 phases are observed at the interfaces and the mechanical performance of the composites is degraded. When the rolling temperature is 480°C, the composites show the optimal comprehensive mechanical performance, with a tensile strength and elastic modulus of 403.3 MPa and 77.6 GPa, respectively, which represent increases of 31.6% and 36.9%, respectively, compared with the corresponding values prior to rolling.

Effect of Na3AlF6 Addition and Surface Modification of SiCp on the Microstructure and Mechanical Properties of SiCp/Al Composites

Al-matrix composites reinforced with 56.5 vol% SiC were prepared by powder metallurgy with different amounts of additives and surface modifications of SiCp. The crystalline phase, morphology, elements on the surface of SiCp and the interface between SiCp and Al were characterized by XRD, SEM, EDS and EPMA. The results show that it is favorable for the reaction between TiO2-C on the surface of SiCp and Al at the SiCp-Al interface at 1 050 °C. Besides, the process of Na3AlF6 melting, dissolving and then contacting with Al2O3 formed the NaF-AlF3-Al2O3 system, which generated OAlF2−, promoting the dessolution of Al2O3 film on the surface of Al powder. Na3AlF6 meets the needs of chemical reaction in TiO2-C-Al system at the SiCp-Al interface in the way of offering more molten Al. After 0.75 wt% Na3AlF6 was added into raw materials, the whole TiO2-C film and most SiO2 film were destroyed and the interfacial bonding between SiCp and Al was keeping good, in which no obvious void and crack were observed. Meanwhile, no brittle Al4C3 phase formed in the system. At this time, the flexure strength and density of samples presented optimal values, reaching up to 106.5 MPa and 90.77% respectively.

Microstructure, and Mechanical and Wear Properties of Grp/AZ91 Magnesium Matrix Composites.

Based on semi-solid mixing technology, two kinds of as-cast Grp (Graphite particles)/AZ91 composites with different Grp volume fractions (5 vol %, 10 vol %) were prepared; these are called 5 vol % Grp/AZ91 composites and 10 vol % Grp/AZ91 composites, respectively. In order to eliminate casting defects, refine grains, and improve mechanical properties, thermal deformation analysis of these composites was conducted. The effect of the addition of Grp and thermal deformation on the microstructure, mechanical properties, and wear resistance of AZ91 composite was explored. The results showed that after 5 vol % Grp was added into the as-cast AZ91 alloy, Mg17Al12 phases were no longer precipitated reticularly along the grain boundary, and Al4C3 phases were formed inside the composite. With the increase in the volume fraction of Grp, the grains of the AZ91 composites were steadily refined. With the increase of forging pass, the grain size of 5% Grp/AZ91 composites decreased first, and then increased. Additionally, the Grp size decreased gradually. There was little change in the yield strength, and the tensile strength and elongation were improved to a certain extent. After forging and extrusion of 5% Grp/AZ91 composites once, the grain size and Grp size were further reduced, and the yield strength, tensile strength, and elongation were increased by 23%, 30%, and 65%, respectively, compared with the composite after forging. With the increase of the number of forging passes before extrusion, the grain size decreased little by little, while the Grp size remained unchanged. The average yield strength, tensile strength, and elongation of the composites after forging and extrusion six times were increased by 3%, 3%, and 23%, respectively, compared with the composite after forging and extrusion once. The wear rate and friction coefficient of the 5% Grp/AZ91 composites decreased after forging once, and the wear mechanism was mainly due to ploughing wear. By comparison, the wear rate and friction coefficient of the 5% Grp/AZ91 composites increased in the extrusion state, and the main wear mechanism was from wedge formation and micro-cutting wear.

Enhanced load transfer by designing mechanical interfacial bonding in carbon nanotube reinforced aluminum composites

The interfacial native oxide layer always acts as barriers preventing effective interfacial bonding and load transfer in carbon nanotube reinforced aluminum (CNT/Al) composites. In this work, annealing-controlled reaction between the interfacial native oxide layer and Mg element was attempted to improve interfacial bonding in CNT/AlMg composite, and mechanical interfacial bonding featured with direct CNT-Al contact and well-reserved CNTs was achieved in the 1 h annealed composite. For the 2 h annealed composite, chemical interfacial bonding featured with interfacial aluminum carbide (Al4C3) was established due to progressive interfacial reaction. Further tensile tests and numerical analysis revealed that, owing to barrier-free load path and increased interfacial friction stress, the mechanical interfacial bonding significantly enhanced CNT load transfer effect from 30.9 MPa to 59.4 MPa, which was close to shear-lag model prediction of 59.9 MPa. While, the chemical interfacial bonding led to a combined strengthening effect of 58.8 MPa from CNT-Al4C3 hybrid as a comprised outcome of Al4C3 strengthening and CNT damage. Thus, the design of mechanical interfacial bonding should be a superior strategy for improving interfacial bonding and enhancing mechanical performance in CNT/Al composites, considering its effective protection of CNT structure integrity and suppressed formation of hydrolysable Al4C3 phase.

Evolution of Multiwalled Carbon Nanotubes and Related Nanostructures during the Formation of Alumomatrix Composite Materials

Composite materials based on AMg2 aluminum alloy reinforced by additions of 0.05 wt % multiwalled carbon nanotubes (MWCNTs) or Al/MWCNT hybrid nanostructures have been obtained by powder metallurgy techniques. The evolution of MWCNTs and Al/MWCNT hybrid nanostructures at various stages of powder composite material formation has been studied by Raman spectroscopy. It is established that Al/MWCNT hybrid filler is subjected to lower damage and less favors the formation of Al4C3 phase during isothermal consolidation stage as compared to the case of nonmodified MWNTs.

Titanium dioxide protection against Al4C3 formation during fabrication of aluminum-TiO2 coated MWCNT composite

Aluminum and aluminum alloys have been very useful in the industry, mainly in the transport sector. So, is important to improve their mechanical properties to increase their applications. Carbon nanotubes (CNTs) could be an excellent reinforcing phase for metal matrix composites, specifically for composites with aluminum or aluminum alloy matrix. However, CNTs dispersion, wettability, and interaction with the matrix must be improved, without damaging their structure. In this work, multi-walled CNTs (MWCNTs) were coated by the sol-gel process with a titanium oxide (TiO2) layer with three different thickness and calcined at two different temperatures: 500 °C and 750 °C. The resultant powder was mixed by electrostatic adsorption method with aluminum powder and cold compacted. To simulate high temperature processing, the compacted disks were pressureless heated at 850 °C, aiming to check the effect of TiO2 in protecting the MWCNT when in contact with melted Al. The TiO2 coated MWCNT samples were characterized by a range of analytical techniques including Field-Emission Gun Scanning Electron Microscopy (FEG-SEM), X-ray diffraction (XRD), Z-Potential, Brunauer–Emmett–Teller (BET), Energy Dispersive X-Ray Spectroscopy (EDS) and Raman Spectroscopy (RS). The effect of the TiO2 layer as a protective barrier on the MWCNT against the Al4C3 formation during the heating process and the hardness of the Al/MWCNT (coated and uncoated) composite were studied. The results show that the MWCNT were successful coverage by a uniform amorphous TiO2 layer. After calcination at 500 °C and 750 °C, the layer was completely crystallized into a TiO2 film, with reduced surface area and pore volume. Electrostatic adsorption between TiO2 covered MWCNT and Al powders in aqueous suspension was found to disperse the reinforcing phase prior to consolidation. On the heat-treated discs, the formation of Al4C3 phase was observed to occur only for uncoated MWCNT samples, showing that the TiO2 layer effectively protected the nanotubes in presence of melted Al. The microhardness of the heated samples was increased up to 26% when reinforced with MWCNT and up to 46% when reinforced with TiO2 coated MWCNT, compared with pure aluminum.

A Study of the Materials Removal Mechanism of Grinding-Aided Electrochemical Discharge Machining of Metal Matrix Composites

In order to research the workpiece materials removal mechanism of Grinding-assisted Electro-chemical Discharge Machining(G-ECDM) of Metal Matrix Composites (MMCs), a good deal of single pulse experiments has been performed in this paper. The crater volume, convex edge, debris, machined surface of G-ECDM have been taken into considerationand it turns out to be that the grinding effect removes the convex edge of the Electro-chemical Discharge Machining (ECDM) crater during the machining of MMCs, the result show that the material removal rate (MRR) of G-ECDM is much higher than that of ECDM and Electrical Discharge Machining (EDM). When compared to the normal ECDM process, it is found that though the Al4C3 phase can be detected in this ECDM condition, no Al4C3 are observed in the processed surface, which indicates a better surface quality. The reason of this phenomenonhas been analyzed theoretically and experimentally. Based on these results, mechanism of the G-ECDM of MMCs was disclosed in this study.

The Research of Reinforced Cu-SiCp/ZA40 and Cu-SiCp/AZ91D Metal Matrix Composites’ Mechanisms

In this paper, the strengthening mechanism of the SiCp on two different kinds of metal matrix composites was studied by adding SiCp with a diameter of 4 micron in AZ91D alloy and ZA40 alloy. The study found that the strengthening mechanism was the dispersion strengthening when 0.5-1.5%Wt SiCp was added into ZA40 zinc alloy. In order to solve the wettability of the ZA40 and the SiCp, Cu layer was coated on the surface of SiCp. When Cu-SiCp was added into the ZA40 alloy, α-Al phase blocked by Cu-SiCp at the stage of solidification and crystallization. Therefore, the α-dendrite in the crystalline tissue was decreased and the grain was refined, and the strength of the alloy was improved significantly. SiCp was added to the AZ91D composite, the strengthening mechanism was solid solution strengthening when the adding amount was less than 10%Wt. The SiCp reacted with β-Mg17Al12, generated new Al4C3 phase and strengthened phase Mg2Si, formed Mg-Al solid solution. The formation of Al4C3 played a key role in grain refined and the formation of Mg2Si replaced the harmful divorced eutectic β-Mg17Al12 phase in the material that improved the strength and hardness of the alloy. When SiCp adding amount was more than 10%Wt, in order to alleviate the agglomeration and the wettability of the SiCp and the liquid AZ91D, a Cu layer was coated on SiCp surface, the strengthening mechanisms were both solid solution strengthening and dispersion strengthening.

Effect of the Thermomechanical Treatment Conditions on the Consolidation, the Structure, and the Mechanical Properties of Bulk Al–Mg–C Nanocomposites

The effect of the conditions of sintering under pressure (temperature, pressure) of mechanically synthesized Al–Mg–C nanocomposite powders on consolidation and the evolution of the structure–phase composition has been studied. The data on the mechanical properties of the prepared bulk nanocomposites are presented. It is found that the hardening of the material results from the joint action of the contributions of the nanostructuring of the matrix material, precipitation hardening due to the precipitation of the Al4C3 phase, and precipitation hardening with nanocrystalline graphite particles; i.e., the hardening obeys the Hall–Petch and Orowan mechanisms. The specific strength of the samples is dependent on the consolidation temperature and the graphite content in a charge and varies within the range 15.7–24.5 km.

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.

Development of the Properties of Al/SiC Nano-Composite Fabricated by Stir Cast Method by Means of Coating SiC Particles with Al

Due to the excellent properties of Al-SiC nanocomposite like high strength to weight ratio, excellent corrosion and erosion resistance, it has attracted a great attention of the automotive, military and aerospace industries. Stir casting is one of the desired techniques in order to fabricate this kind of composites. As the SiC particles in the Al melt do not have a desired wettability so there would be a high possibility of occurring the pernicious chemical reactions at the Al-Si interface. In this study, in order to get over these problems, SiC particles were coated by aluminum. To do so, SiC particles with the various volume fractions ranging from 0% to 5% were added to the circulating melted aluminum mixture. Then, microstructure of the composite were evaluated using the scanning electron microscopy (SEM). Moreover, X-ray diffraction (XRD) analysis was employed to evaluate the composites composition. The XRD results revealed that Al4C3 phase (as a pernicious phase) was not detected. In addition, the SEM images depicted a homogenous distribution of the coated SiC nanoparticles in the Al matrix. The results of the mechanical tests revealed that, the tensile strength and stiffness of the specimens consisting of the coated SiC particles were higher than that of the specimen consisting the uncoated SiC particles.

Microstructure and tensile properties of 5083 Al matrix composites reinforced with graphene oxide and graphene nanoplates prepared by pressure infiltration method

In the present work, 5083Al matrix composites reinforced with graphene oxide (GO) and graphene nanoplates (GNPs) have been prepared by the pressure infiltration method. Regardless of the graphene types, no peaks of Al4C3 phase have been detected by the XRD analysis. However, needle-like Al4C3 phase has been observed in the GO/5083Al and the GNPs/5083Al composites, while the content of the Al4C3 phase in the GNPs/5083Al composite was much lower. Furthermore, the segregation of Mg element at the surface of the GNPs has been found in the GNPs/5083Al composite, implying the inhibition effect of Mg element on the formation of the Al4C3 phase. It has been found that the yield strength of the composites was slightly improved by the addition of the GO and GNPs, and the GNPs/5083Al composite demonstrated 14% increment in the tensile strength. Meanwhile, the pulling-out of the GO and GNPs have been observed.