Synthesis,microstructure and mechanical properties of Al2O3 reinforced Ni3Al matrix composite

A new method to synthesize alumina reinforced Ni₃Al intermetallic matrix composites has been described. The powder mixture of nickel and aluminium was mechanically alloyed. The powder mixture was excessively heated during mechanical alloying and then exposed to atmosphere for oxidation. The oxidized powder mixture was transformed into alumina reinforced nickel aluminide matrix composite on subsequent pulse current processing. Alumina reinforcements were generated in the nickel aluminide matrix by in situ precipitation. The microstructure of the composite showed that the alumina reinforcements were 50–150 nm in size. The fine alumina reinforcements were homogeneously distributed in the matrix phase. The mechanical properties of the alumina reinforced nickel aluminide matrix composite fairly exceeded the nickel aluminide alloys. This novel synthesis approach allowed the rapid and facile production of high strength alumina reinforced Ni₃Al matrix composites.     

Microstructure and mechanical properties of an Al–Ni–Co intermetallics reinforced Al matrix composite

A new intermetallic particle reinforced metal matrix composite was produced from pure Al and 15 wt% Al₇₂Ni₁₂Co₁₆ quasicrystalline particles by stir-casting method, followed by hot-extrusion. Microstructural analysis of the as-cast composite shows that the Al₇₂Ni₁₂Co₁₆ quasicrystalline phase has transformed to the crystalline phase Al₉(Co, Ni)₂ and an eutectic structure has formed in the Al matrix during the casting process. The particle size of the Al₉(Co, Ni)₂ phase is much smaller than that of the original quasicrystalline particles. After extrusion, the composite has a more uniform distribution of the reinforcement particles and eutectic structure as well as a reduced porosity. Tensile tests indicate that the mechanical properties of the as-cast composite are improved over the matrix properties remarkably, except for the ductility. The strength and ductility of the composite can be improved by the hot-extrusion, while the elastic modulus can be slightly decreased.     

Effects of SiC,Al2O3, and ZrO2 particles on the LBMed characteristics of Al/SiC,Al/Al2O3, and Al/ZrO2 MMCs prepared by stir casting process

The effects of SiC, Al₂O₃, and ZrO₂ particles on the characteristics of Al/SiC, Al/Al₂O₃, and Al/ZrO₂ metal matrix composites (MMCs) have been studied in the present research work. The comparison of machining characteristics has been done to analyze the behavior of various reinforced particles with the variation of laser machining variables. The output characteristics such as dross height and kerf deviation have been investigated and compared with each MMCs. SEM and XRD have been used for the investigation of morphological changes in the structure and agglomeration of reinforced particles. The crack and recast layer formation has been examined in the specimens of higher quantity of reinforced particles. It was observed that the MMC material reinforced with SiC particles has shown different behavior as compared to other MMC materials.     

Effect of heat treatment on microstructure and interface of SiC particle reinforced 2124 Al matrix composite

The microstructure and interface between metal matrix and ceramic reinforcement of a composite play an important role in improving its properties. In the present investigation, the interface and intermetallic compound present in the samples were characterized to understand structural stability at an elevated temperature. Aluminum based 2124 alloy with 10 wt.% silicon carbide (SiC) particle reinforced composite was prepared through vortex method and the solid ingot was deformed by hot rolling for better particle distribution. Heat treatment of the composite was carried out at 575 °C with varying holding time from 1 to 48 h followed by water quenching. In this study, the microstructure and interface of the SiC particle reinforced Al based composites have been studied using optical microscopy, scanning electron microscopy (SEM) coupled with energy dispersive X-ray spectroscopy (EDS), electron probe micro-analyzer (EPMA) associated with wavelength dispersive spectroscopy (WDS) and transmission electron microscopy (TEM) to identify the precipitate and intermetallic phases that are formed during heat treatment. The SiC particles are uniformly distributed in the aluminum matrix. The microstructure analyses of Al–SiC composite after heat treatment reveal that a wide range of dispersed phases are formed at grain boundary and surrounding the SiC particles. The energy dispersive X-ray spectroscopy and wavelength dispersive spectroscopy analyses confirm that finely dispersed phases are CuAl₂ and CuMgAl₂ intermetallic and large spherical phases are Fe₂SiAl₈ or Al₁₅(Fe,Mn)₃Si. It is also observed that a continuous layer enriched with Cu and Mg of thickness 50–80 nm is formed at the interface in between Al and SiC particles. EDS analysis also confirms that Cu and Mg are segregated at the interface of the composite while no carbide is identified at the interface.     

Fabrication and microstructure of in situ toughened Al2O3/Fe3Al

Fe₃Al nano-particles and commercial purity Al₂O₃ powders were used as raw materials to fabricate in situ reinforced Al₂O₃/Fe₃Al nano/micro-composites. Densification and microstructure were studied. The Al₂O₃ matrix grains were characterized by platelet grains. The Fe₃Al particles inhibited the grain growth of Al₂O₃ grains and limited the densification of the composites. In Al₂O₃/Fe₃Al composites, the Fe₃Al particles were uniformly dispersed in the Al₂O₃ matrix. The major Fe₃Al micro-particles, about 1 μm in average size, existed at Al₂O₃ grain boundaries, and the Fe₃Al nano-particles were found embedded in the matrix grains. The grain size of the intragranular particles ranged from several to several hundred nanometers. The grain size and aspect ratio of Al₂O₃ platelet grains and distribution of intragranular Fe₃Al could be optimized by controlling the Fe₃Al contents and sintering process. The in situ formed Al₂O₃ platelet grains, as well as Fe₃Al dispersoids, were beneficial to the increase of the mechanical properties of alumina.     

Micro-yield property of sub-micron Al2O3 particle reinforced 2024 aluminum matrix composite

The microstructure and micro-yield strength of sub-micron Al₂O₃ particle reinforced 2024Al composites and the effect of the thermal-cold cycling treatment on the microstructure and properties were studied. The results show that the dislocations are rare in the microstructure of the sub-micron Al₂O_3p/2024Al composite in the squeeze casting condition. Aging and thermal-cold cycling treatment does not change this phenomenon. The Al₂O₃ particles are fine, so the thermal misfit between particles and the matrix is very small during the temperature change, resulting in decreased dislocations. The tiny and uniformly dispersed S′ precipitates and sub-micron particles can effectively pin dislocations, therefore, the micro-yield strength of the composite increases. Depending on the condition of the thermal-cold cycling treatment after aging, both the size and distribution of the S′ precipitates in the composite change, and they have great effect on the micro-yield strength of the composite.     

Crack growth resistance (R-curve) behaviour and thermo-physical properties of Al2O3 particle-reinforced AlN/Al matrix composites

Crack growth resistance behaviour and thermo-physical properties of Al₂O₃ particle-reinforced AlN/Al matrix composites have been studied as a function of AlN volume fraction as well as Al₂O₃ particle size. The fracture toughness of the composites decreased with increase in vol% AlN and decrease in Al₂O₃ particle size. All the composites exhibited R-curve behaviour which has been attributed to crack bridging by the intact metal ligaments behind the crack tip. The Young’s modulus of the composites increased with the vol% of AlN whereas the thermal diffusivity and coefficient of thermal expansion followed a reverse trend. The composites exhibited hysteresis in thermal expansion as a function of temperature and the hysteresis decreased with decrease in metal content of the composite.     

Characterization of the correlation between the interfaces and failure behaviors for particle reinforced Mg–Li composites

The interfacial microstructure of SiC_p or YAl_2p reinforced Mg–14Li–3Al matrix composites was comparatively characterized by scanning electron microscopy and electron probe microanalysis. A nanoindentation combined with scanning electron microscopy technique was used to characterize the interfacial mechanical properties between the reinforcements and matrix. The interfacial strength and failure behaviors for the composites were analyzed from the load–penetration curves and corresponding images. In situ tensile tests were used to observe the fracture and deformation processes with the aid of scanning electron microscopy. The results show that both the chemical and mechanical compatibilities between the YAl₂ particles and LA143 matrix are better than those between the SiC particles and LA143 matrix. The interfacial breakage load for the SiC/LA143 composite is lower than that for the YAl₂/LA143 composite because of the worse chemical and mechanical compatibilities between the ceramic particles and metal matrix. Interfacial breakage is the main failure mechanism for the SiC/LA143 composite, while the particle breakage and matrix crack are the main failure mechanism for the YAl₂/LA143 composite. These may be related to the stronger interfacial bonding between the intermetallic particles and metal matrix.     

Development of Al3Ti and Al3Zr intermetallic particulate reinforced aluminum alloy AA6061 in situ composites using friction stir processing

Aluminum rich intermetallic particles are potential reinforcements for discontinuously reinforced aluminum matrix composites (DRAMCs). The objective of the present work is to produce AA6061/Al₃Ti and AA6061/Al₃Zr composites using in situ casting technique and applying friction stir processing (FSP) to enhance the distribution and morphology of Al₃Ti and Al₃Zr particles. AA6061/Al₃Ti and AA6061/Al₃Zr DRAMCs were produced by the in situ reaction of inorganic salts K₂TiF₆ and K₂ZrF₆ with molten aluminum. The microstructure was observed using optical and scanning electron microscopy. AA6061/Al₃Ti DRAMC exhibited clusters of Al₃Ti particles while the segregation of needle shape Al₃Zr particles was observed in AA6061/Al₃Zr DRAMC. The prepared composites were subjected to FSP. Significant changes in the distribution and morphology of Al₃Ti and Al₃Zr particles were observed after FSP. The changes in microhardness and sliding wear behavior of AA6061/Al₃Ti and AA6061/Al₃Zr DRAMCs before and after FSP is detailed in this paper.     

Fatigue damage development in Al2O3/Al composite

Fatigue damage development in two aluminium matrix (Al7SiO.6Mg and Al5Si-3Cu1Mg) composites reinforced with discontinuous Al₂O₃ fibres has been monitored by means of acoustic emission (AE). The AE signals (RMS) recorded during the tests clearly exhibit three distinct stages which correspond to crack initiation, dominant crack formation and stable propagation. Generally speaking, the cracks initiated at a high load level form close together and a dominant crack forms easily. By contrast, at a low load, initiated cracks are widely separated and the formation of a dominant crack is difficult. If there are large defects in the composite, the first stage is absent, even at low load. In the first stage, little change in microstructure and modulus of the composite is observed; in the second, fibre fracture, interface debonding and matrix cracking occur and there are often sinusoidal cracks in the matrix; in the last stage, the principal characteristic is stable propagation of the dominant crack. The degradation of the elastic modulus of the composite in the last two stages is small.     

Deformation behaviour and microstructure of a 20% Al2O3 reinforced 6061 Al composite

Deformation and microstructural behaviours of a 20% (volume percent) particle reinforced 6061 Al matrix composite have been studied by torsion from 25 to 540°C with strain rates of 0.1, 1 and 5 s⁻¹. The logarithmic stress versus reciprocal temperature relationship exhibits two slopes indicating different deformation mechanisms. The 20% Al₂O₃/6061 Al composite shows a greater hardening behaviour than those of the 10% Al₂O₃/6061 Al composite and of the monolithic alloy. Above 250°C, TEM investigations reveal much smaller subgrain size and higher volume of non-cellular substructures, as well as dynamic recrystallization nuclei in the 20% Al₂O₃/6061 Al composite in comparison to those of the 10% Al₂O₃/6061 Al composite and matrix alloy the same test condition. The torsion fracture surface was studied and compared to the three point bending failure specimens.     

INFLUENCE OF PARTICLE SIZE AND VOLUME FRACTION ON DAMAGE AND FRACTURE IN Al–Al3 Ti COMPOSITES AND MICROMECHANICAL MODELLING USING THE GTN MODEL

Six different Al–Al₃ Ti composites were prepared via the powder metallurgy route. The size and volume fraction of Al₃ Ti particles was varied for a systematic investigation of fracture behaviour. The dominant failure mechanism in the composites is particle fracture and void growth starting from the broken particles. In comparison with the pure Al–matrix, an incorporation of Al₃ Ti particles reduces the crack initiation toughness and reduces the slope of the crack growth resistance curve. The inter-particle distance was found to be the main microstructural parameter controlling the slope of the crack growth resistance curve. The modified Gurson–Tvergaard–Needleman model (GTN model) was applied to one of the composites. The behaviour of tensile specimens could be successfully modelled, whereas the experimentally observed crack propagation in precracked single edge bend specimens [SE(B)] could not be simulated with the GTN model.     

Effect of MoSi2 and Nb reinforcements on mechanical properties of Al2O3 matrix composites

The room temperature mechanical properties of Al₂O₃ composites reinforced with 25 vol% of either MoSi₂ or Nb particulates were investigated. It was found that addition of Nb particles resulted in a reduction in the elastic modulus, but caused a significant increase in both flexural strength and fracture toughness. On the other hand, the addition of MoSi₂ particles resulted in only a marginal decrease in elastic modulus and marginal increase in both flexural strength and fracture toughness. The elastic modulus results were explained on the basis of Tsai - Halpin model. For both the composites, the increase in flexural strength was attributed to the grain refinement of the Al₂O₃ matrix as well as the load transfer to the reinforcement particles. The marginal increase in fracture toughness in Al₂O₃ / MoSi₂ composites was attributed to crack deflection, whereas the threefold increase in fracture toughness in Al₂O₃ / Nb composites was attributed to crack blunting and bridging.     

Analyses on fracture characteristics of SiCp-6061Al/6061Al composites extruded by different ratios

Two 6061 Al alloy matrix composites reinforced with rods that are themselves composites of the same Al alloy reinforced with a high volume fraction of SiC particles were studied. After vacuum pressure infiltration, one was hot extruded at a ratio of 10 : 1 and the other at a ratio of 60 : 1. The fracture characteristics of the two SiC_p-6061Al/6061Al composites were examined in detail. It was found that increasing the hot extrusion ratio of this kind of composite can improve the bonding between the SiC_p-6061Al bars and the 6061Al matrix. The strengths of the SiC_p-6061Al bars and the 6061Al matrix were considered to increase with increasing extrusion ratio. Thus, the SiC_p-6061Al/6061Al composite extruded at a ratio of 60 : 1 shows fracture characteristics which are different from the composite extruded at a ratio of 10 : 1. The former has a higher fracture toughness, and its crack opening displacement versus load curve indicates a higher elastic modulus and maximum load. After application of the maximum external load, there is a slow decrease with increasing crack opening displacement in the case of the 60 : 1 extruded composite, but the load can be maintained for wide crack opening displacement in the case of the 10 : 1 extruded composite.     

Fabrication of AA6061/Al2O3p composites from elemental and alloy powders

The tensile properties and microstructures of AA6061/Al₂O_3p composites fabricated by the pressureless infiltration method under a nitrogen atmosphere were examined. Since the spontaneous infiltration of molten metal into elemental powders bed as well as alloy powders bed occurred at 700°C for 1 hour under a nitrogen atmosphere, it was possible to fabricate 6061 Al matrix composite reinforced with Al₂O_3p irrespective of the type of metal powders. Both MgAl₂O₄ and MgO were formed at interfaces between Al₂O₃ and the matrix. In addition, MgAl₂O₄ was formed at within the matrix by in situ reaction during composite fabrication. Fine AlN was formed by in situ reaction in both composites. A significant strengthening in the composites occurred due to the formation ofin situ AlN particle and addition of Al₂O₃ particles, as compared to the commercial alloy, while tensile properties in the both elemental and alloy powders composites showed similar trend.     

Synergistic effects of TiC and graphene on the microstructure and tribological properties of Al2024 matrix composites

Al matrix composites have attracted significant attention of researchers in recent years due to their lightweight, excellent mechanical and tribological properties. In this study, an Al2024 matrix hybrid composite (AMHC) reinforced with both TiC nanoparticles and graphene nanoplatelets (GNPs) was produced via a route of powder metallurgy. And its microstructure, microhardness and tribological properties are compared with those of unreinforced Al2024 alloy matrix and Al2024 matrix composites reinforced with either only TiC or GNPs. It was found that the distribution of Al₂Cu, TiC nanoparticles and GNPs in the matrix and the wear resistance are significantly improved when introducing both TiC nanoparticles and the GNPs. The wear mechanisms change from the adhesion-dominant wear for Al2024 and the other singly reinforced composites into abrasive-dominant wear for the hybrid composite. The significantly improved wear resistance of the AMHC is attributed to the synergistic effects of reinforcing and self-lubricating of the TiC and GNPs.     

Formation of Al3Ti/Mg composite by powder metallurgy of Mg–Al–Ti system

An in situ titanium trialuminide (Al₃Ti)-particle-reinforced magnesium matrix composite has been successfully fabricated by the powder metallurgy of a Mg–Al–Ti system. The reaction processes and formation mechanism for synthesizing the composite were studied by differential scanning calorimetry (DSC), x-ray diffractometry (XRD), scanning electron microscopy (SEM) and energy-dispersive x-ray spectroscopy (EDS). Al₃Ti particles are found to be synthesized in situ in the Mg alloy matrix. During the reaction sintering of the Mg–Al–Ti system, Al₃Ti particles are formed through the reaction of liquid Al with as-dissolved Ti around the Ti particles. The formed intermetallic particles accumulate at the original sites of the Ti particles. As sintering time increases, the accumulated intermetallic particles disperse and reach a relatively homogeneous distribution in the matrix. It is found that the reaction process of the Mg–Al–Ti system is almost the same as that of the Al–Ti system. Mg also acts as a catalytic agent and a diluent in the reactions and shifts the reactions of Al and Ti to lower temperatures. An additional amount of Al is required for eliminating residual Ti and solid-solution strengthening of the Mg matrix.     

Microstructure and mechanical properties of Cr3C2 particulate reinforced Al2O3 matrix composites

Al₂O₃ matrix with three grades of Cr₃C₂ particle size (0.5, 1.5 and 7.5 m) composites were fabricated by a hot-pressing technique. Fully dense compacts with Cr₃C₂ content up to 40 vol % can be acquired at 1400 °C under 30 MPa pressure for 1 h. The flexural strength increases from 595 to 785 Mpa for fine Cr₃C₂ particle (0.5 m) reinforced Al₂O₃ matrix composites. The fracture strength is significantly dependent on the fracture modes of matrix (intergranular or transgranular). The transgranular fracture with a compressive residual stress gives a high fracture strength of composites. At the same time, the fracture toughness increases from 5.2 MPa m^1/2 (10 vol % Cr₃C₂) to 8.0 MPa m^1/2 (30 vol % Cr₃C₂) for the coarse Cr₃C₂ particle (7.5 n) reinforced Al₂O₃ matrix composites. The toughening effects of incorporating Cr₃C₂ particles into Al₂O₃ matrix originate from crack bridging and deflection. The electrical conductivity and the possibility of electrical discharge machining of these composites were also investigated.     

Sliding wear and solid particle erosion response of aluminium reinforced with tungsten carbide nanoparticles and aluminide particles

In the present effort, aluminium matrix composites (AMCs) were produced by the addition of submicron‐sized WC particles of low (up to 2.5 vol%) content into a melt of Al1050. Casting was assisted by the use of K₂TiF₆ as a wetting agent and mechanical stirring in order to limit particle clustering. Particle distribution was reasonably uniform comprising both clusters and isolated particles. Various different reinforcing particles' phases were identified, both in situ (Al‐W, Al‐Ti, and Al‐W‐Ti intermetallic phases) and ex situ (WC particles) of various morphologies shapes and sizes. Increase of the reinforcing particle content led to an increase of the tendency for clustering. The wear properties of the composite were examined by dry sliding wear. The worn surfaces and the produced debris were examined by SEM‐EDX, and an effort to correlate the wear response of the produced materials with the matrix and the reinforcing phase characteristics was attempted. In general, the increase of the reinforcing phase content led to an improvement of the sliding wear response. Solid particle erosion experiments were carried out for impact angles of 30°, 60°, and 90°. Τhe eroded surfaces were examined with SEM‐EDX, and possible erosion mechanisms were proposed based on morphological and other material characteristics. Intensive particle clustering seemed to deteriorate the erosion resistance of the systems. Medium concentrations of the reinforcing particles (1.0‐1.5 vol% WC) are proposed as a recipe for optimum sliding wear and solid particle erosion resistance behavior.     

Formation mechanism of in situ Al3Ti in Al matrix during hot pressing and subsequent friction stir processing

In situ Al₃Ti/Al composites were fabricated by a combination of vacuum hot pressing (VHP) and friction stir processing (FSP). The formation mechanism of the Al₃Ti and the effect of VHP and FSP parameters on the resultant microstructure and mechanical properties were investigated. The Al₃Ti formed due to the reactive diffusion between Al and Ti during VHP, and the number of Al₃Ti particles increased with increasing the temperature and holding time of the VHP. FSP not only induced the Al–Ti reaction, but also resulted in significant refining of the Al₃Ti, thereby creating a homogeneous distribution of Al₃Ti particles in the Al matrix. These microstructural changes led to significant improvement in the tensile properties of the in situ Al₃Ti/Al composite. However, the change trends of the tensile properties of the FSP samples were dependent on the extent of the Al–Ti reaction during VHP.