Evaluation of microstructure and mechanical properties of Al/Al2O3/SiC hybrid composite fabricated by accumulative roll bonding process

In this investigation, a new kind of metal matrix composites with a matrix of pure aluminum and hybrid reinforcement of Al₂O₃ and SiC particles was fabricated for the first time by anodizing followed by eight cycles accumulative roll bonding (ARB). The resulting microstructures and the corresponding mechanical properties of composites within different stages of ARB process were studied. It was found that with increasing the ARB cycles, alumina layers were fractured, resulting in homogenous distribution of Al₂O₃ particles in the aluminum matrix. Also, the distribution of SiC particles was improved and the porosity between particles and the matrix was decreased. It was observed that the tensile strength of composites improved by increasing the ARB passes, i.e. the tensile strength of the Al/1.6 vol.% Al₂O₃/1 vol.% SiC composite was measured to be about 3.1 times higher than as-received material. In addition, tensile strength of composites decreased by increasing volume fraction of SiC particles to more than 1 vol.%. Scanning electron microscopy (SEM) observation of fractured surfaces showed that the failure mechanism of broken hybrid composite was shear ductile rupture.     

Microstructure and mechanical properties of Al/Al2O3 MMC produced by anodising and cold roll bonding

Abstract

In the present paper, Al–Al₂O₃ composite strips are produced by the cold roll bonding process of anodised aluminium strips. This technique has the flexibility to control the volume fraction of metal matrix composites by varying the oxide layer thickness on the anodised aluminium strip. Microhardness, tensile strength and elongation of composite strips are investigated as a function of quantity of alumina and the applied production method. It is found that higher quantities of alumina improve microhardness and tensile strength, while the elongation value decreases negligibly. Furthermore, prerolling annealing is found to be the best method of producing this composite via the cold roll bonding process. Finally, it is found that both monolithic aluminium and aluminium/alumina composite exhibited a ductile fracture, having dimples and shear zones.     

Effect of heat treatment on mechanical properties of low alloy steel foams

Effect of heat treatment on compressive properties of low alloy steel foams (Fe–1.75 Ni–1.5 Cu–0.5 Mo–0.6 C) having porosities in the range of 47.4–71.5% with irregular pore shape, produced by the space holder-water leaching technique in powder metallurgy, was investigated. Low alloy steel powders were mixed with different amounts of space holder (carbamide), and then compacted at 200 MPa. Carbamide in the green compacts was removed by water leaching at room temperature. The green specimens were sintered at 1200 °C for 60 min in hydrogen atmosphere. Sintered compacts were heat treated by austenitizing at 850 °C for 30 min and then quenched at 70 °C in oil and tempered at 210 °C for 60 min. In this porosity range, compressive yield strengths of as-sintered and heat treated specimens were 28–122 MPa and 18–168 MPa, respectively. The resultant Young’s moduli of the as-sintered and heat treated specimens were 0.68–3.12 GPa and 0.47–3.47 GPa, respectively. The heat treatment enhanced the Young’s modulus and compressive yield strength of the foams having porosities in the range of 47.4–62.3%, as a consequence of matrix strengthening. However, the compressive yield stress and Young’s modulus of the heat treated foam having 71.5% porosity were lower than that of the as-sintered foam’s, as a result of cracks in the structure. The results were discussed in light of the structural findings.     

Effect of Al2O3 particles on mechanical properties of directionally solidified intermetallic Ti–46Al–2W–0.5Si alloy

The effect of Al₂O₃ particles on microhardness and room-temperature compression properties of directionally solidified (DS) intermetallic Ti–46Al–2W–0.5Si (at.%) alloy was studied. The ingots with various volume fractions of Al₂O₃ particles and mean ₂–₂ interlamellar spacings were prepared by directional solidification at constant growth rates ranging from 2.78×10⁻⁶ to 1.18×10⁻⁴ ms⁻¹ in alumina moulds. The ingots with constant volume fraction of Al₂O₃ particles and various mean interlamellar spacings were prepared by directional solidification at a growth rate of 1.18×10⁻⁴ ms⁻¹ and subsequent solution annealing followed by cooling at constant rates varying between 0.078 and 1.889 K s⁻¹. The mean ₂–₂ interlamellar spacing λ for both DS and heat-treated (HT) ingots decreased with increasing cooling rate according to the relationship λ∝ ^−0.46. In DS ingots, microhardness, ultimate compression strength, yield strength and plastic deformation to fracture increased with increasing cooling rate. In HT ingots, microhardness and yield strength increased and ultimate compression strength and plastic deformation to fracture decreased with increasing cooling rate. The yield stress increased with decreasing interlamellar spacing and increasing volume fraction of Al₂O₃ particles. A linear relationship between the Vickers microhardness and yield stress was found for both DS and HT ingots. A simple model including the effect of interlamellar spacing and increasing volume fraction of Al₂O₃ particles was proposed for the prediction of the yield stress.     

Microstructure and mechanical properties of aluminum alloy matrix composites reinforced with Fe-based metallic glass particles

Fe-based metallic glass (FMG) particles reinforced Al-2024 matrix composites were fabricated by using the powder metallurgy method successfully. Mechanical alloying result in nanostructured Al-2024 matrix with a grain size of about 30 nm together with a good distribution of the FMG particles in the Al matrix. The consolidation of the composites was performed at a temperature in the super-cooled liquid region of the FMG particles, where the FMG particles act as a soft liquid-like binder, resulting in composites with low or zero porosity. The microstructure and mechanical properties of the composites were investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and compression test. The yield and fracture strength of the composites are 403 MPa and 660 MPa, respectively, while retaining a considerable fracture deformation of about 12%. The strengthening mechanism is associated with the grain refinement of the matrix and uniform distribution of the FMG particles.     

Study of standard heat treatment on mechanical properties of Inconel 718 using ball indentation technique

The effect of standard heat treatment on the microstructure and mechanical properties of Ni–Fe base super-alloy, Inconel 718 was studied by optical microscopy and ball indentation technique (BIT) using small amount of specimen. In order to get good ductility, good formability, yield, tensile and creep rupture, as-received material was given the standard heat treatment, viz solution treatment at two temperatures 940 °C and 1040 °C for1 h and water quenched (WQ) followed by aging treatment at 720 °C for 8 h. and furnace cooling (FC). The BIT has revealed that the strengths for as-received material are maximum compared to other heat-treated materials. After solution treatment there has been a radical decline in strength. But the ageing causes a significant enhancement of strength. Optical microscopy studies supported the obtained BIT results. γ″-phase is the basic strengthening phase in 718 alloys.     

Microstructure and property characterization of Al-based composites reinforced with CuZrAl particles fabricated by mechanical alloying and spark plasma sintering

In the present work, CuZrAl metallic glass particles were synthesized by mechanical alloying method. High relative density Al-based composites (ABCs) reinforced with different volume fraction of CuZrAl particles have been fabricated by spark plasma sintering (SPS) technique. The microstructures, mechanical properties and corrosion resistance in seawater solution of the ABCs were investigated. The sintered products are all composed of fcc-Al, Al₃Zr and CuAl₂ phases. For CuZrAl addition, bright and network precipitates are clearly observed in the Al matrix. On account of the interdiffusion of Al and Cu atoms between matrix and reinforcement, the ABCs present the good interfacial bonding. Compared with SPS-ed pure Al bulk, ABCs possess the excellent mechanical properties. It is mainly ascribed to the second phase strengthening, continuously distributed precipitates, high relative density or bonding interface, and grain refinement strengthening. Thereinto, combined with a degree of plastic strain, the composite with 20?vol% CuZrAl reinforcement reveals the best micro-hardness (290?HV), and the highest yield strength and fracture strength of 408 and 459?MPa, respectively. Moreover, the ABCs bear the better pitting resistance with wide passive region in seawater solution.     

热处理对各向同性热解炭材料微观结构和力学性能的影响

对化学气相沉积法（CVD）制备的各向同性热解炭材料在不同温度下进行热处理，利用金相显微镜、扫描电镜、透射电镜、X射线衍射和显微激光喇曼光谱等表征手段及显微硬度实验、三点弯曲实验，研究了材料的微观结构和力学性能与热处理温度之间的关系。结果表明，随着热处理温度的提高，各向同性热解炭材料的石墨片层间距缩小，石墨化程度增加，晶粒尺寸增大，同时材料中的孔隙结构也发生了较大的变化。材料的显微硬度和弹性模量随热处理温度的升高而降低，抗弯强度在1750℃和2400℃之间没有变化，在2600℃时有显著的增加。     

Structural characterization and creep resistance of nano-silicon carbide reinforced Sn–1.0Ag–0.5Cu lead-free solder alloy

Nano-sized, non-reacting, non-coarsening SiC particles were successfully fabricated by high energy ball milling. Mechanically mixing was adopted to prepare SiC-particulate reinforced Sn–1.0Ag–0.5Cu (SAC105) composite solders. The effects of SiC addition on the melting behavior, microstructure and the corresponding creep properties were explored. It is found that the addition of 0.35–0.75 wt.% SiC nano-sized particles can effectively decrease the undercooling, while the melting temperature is sustained at the SAC(105) level, indicating that the novel composite solder is fit for existing soldering process. After the addition of 0.35% SiC nano-particles, a fine microstructure of Ag₃Sn and Cu₆Sn₅ IMCs with small spacing appeared in the β-Sn matrix. Moreover, the creep rate of the composite solder exhibited a consistently lower value than that of plain SAC(105) solder due to a second phase dispersion strengthening mechanism as well as a refinement of IMCs. Hence, the composite SAC(105)/0.35% SiC solder displayed a higher creep resistance (3.1 times) and fracture lifetime (3 times) than that of plain solder. However, this effectiveness is reduced when 0.75% SiC addition starts constricting the growth Ag₃Sn and Cu₆Sn₅ IMC and forming a weak interface with the enlarged β-Sn matrix.     

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.     

High velocity compaction of 0.9Al2O3/Cu composite powder

The 0.9Al₂O₃/Cu composite powder was compacted by high velocity compaction (HVC) technique and the effects of sintering temperature on density and mechanical properties such as tensile strength and hardness were studied. The results showed that with an increase in impact velocity the green density of the compacts significantly increased. At impact velocity of 9.40 m s⁻¹, the maximum green density of the compacts reached up to 8.460 g/cm³ (RD 96.8%). The green compacts were then sintered at different temperatures and it was found that with the increase in sintering temperature the sintered density and the mechanical properties also increased. At sintering temperature of 1080 °C, the compacts obtained the maximum relative sintered density of 98%, a tensile strength of 346 MPa and hardness of 71.1 HRB. Additionally with the increase in sintering temperature, the shrinkage along both axial and radial direction increased. The electrical conductivity of the samples was measured as 71% IACS.     

Preparation and mechanical properties of Al2O3 reinforced by submicrometer Co particles

Al2O3/Co composites were fabricated by vacuum hot-pressing a mixture of -Al2O3 powder and a fine cobalt powder. Submicron-sized cobalt particles were uniformly dispersed into the Al2O3 matrix, and the dispersed type was a more inter-/intragranular one with increases of cobalt content up to 40 wt% Co addition. The growth of cobalt particles occurred with increasing cobalt content. At 50 wt% Co addition, however, the growth as well as coalescence of cobalt particles occurred. The phases formed in the Al2O3/Co composites were f-Co(fcc), h-Co(hcp), -Al2O3, and a small amount of graphite. Significant improvements in bending strength (from 341 to 771 MPa) and fracture toughness (from 3.7 to 6.7 MPam1/2) of the Al2O3/40 wt% Co(23 vol% Co) composite compared to monolithic Al2O3 were achieved by dispersing submicron-sized Co particles into the Al2O3 matrix. The improvement in bending strength was attributed to the compressive thermal residual stress in the matrix Al2O3 induced by the mismatch of the coefficients of thermal expansion (CTE) between the matrix Al2O3 grains and cobalt particles during cooling from hot-pressing temperature. The fracture toughness of the composite was enhanced by crack bridging, crack deflection, and compressive thermal residual stress.     

Influence of SiC particles on mechanical properties of Mg based composite

AZ91 magnesium alloy reinforced with different sizes of SiC particulates has been fabricated using powder metallurgy route. Mechanical properties of the specimens have been studied. Yield and ultimate tensile stresses show a decrease with the increase in the size of SiC particulates. The influence of thermal shock between 400°C and 30°C on the mechanical properties was also investigated. The results show a decrease in yield stress and elongation to fracture with the number of thermal shock cycles.     

Effects of volume ratio on the microstructure and mechanical properties of particle reinforced magnesium matrix composite

In the present study, the AZ91 alloy reinforced by (submicron + micron) SiCp with four kind volume ratio was fabricated by the semisolid stirring casting technology. The influence of volume ratio between submicron and micron SiCp on the microstructure and mechanical properties of Mg matrix was investigated. Results show that the submicron SiCp is more conducive to grain refinement as compared with micron SiCp. With the increase of volume ratio, the submicron particle dense regions increase and the average grain size decreases. The yield strength of bimodal size SiCp/AZ91 composite is higher than monolithic micron SiCp/AZ91composite. Both Δσ_Hall–Petch and Δσ_CTE increase as the volume ratio changes from 0:10, 0.5:9.5, 1:9 to 1.5:8.5. Among the composite with different volume ratio, the S-1.5 + 10-8.5 composite has the best mechanical properties. The interface debonding is found at the interface of micron SiCp-Mg. As the increase of volume ratio, the phenomenon of interface debonding weakens and the amount of dimples increases.     

Effect of solidification on microstructures and mechanical properties of carbon nanotubes reinforced magnesium matrix composite

A novel approach was successfully developed to fabricate bulk carbon nanotubes (CNTs) reinforced Mg matrix composites. The distribution of CNTs in the composites depends on the solidification rate. When the solidification rate was low, CNTs were pushed ahead of the solidification front and will cluster along grain boundaries. When the solidification rate was high, CNTs were captured by the solidification front, so the CNTs remained inside the grain. Moreover, good interfacial bonding was achieved in the composite under high solidification rate. Meanwhile, compared with the matrix alloy, the ultimate tensile strength (UTS) and yield strength (YS) of the composite were significantly improved. The mechanical properties of the composite under higher solidification rate are better than composite under low solidification rate and the alloy. Moreover, most CNTs on the fracture surfaces were directly pulled out from the matrix. The Kelly–Tyson formula agreed well with the experimental tensile value in the composite under higher solidification rate, and the load-transfer efficiency is almost equal to 1.     

Effect of heat treatment on microstructure and mechanical properties of a new β high strength titanium alloy

Microstructure and mechanical properties of a new β high strength Ti–3.5Al–5Mo–6V–3Cr–2Sn–0.5Fe titanium alloy were investigated in this paper. Both the α/β and β solution treatment and subsequent aging at temperatures ranging from 440 °C to 560 °C for 8 h were introduced to investigate the relationship between microstructures and properties. Microstructure observation of α/β solution treatment plus aging condition shows that the grain size is only few microns due to the pinning effect of primary α phase. The β solution treatment leads to coarser β grain size and the least stable matrix. The size and volume fraction of secondary α are very sensitive to temperature and strongly affected the strength of the alloy. When solution treated at 775 °C plus aged at 440 °C, the smallest size (0.028 μm in width) of secondary α and greatest volume fraction (61%) of α resulted in the highest yield strength (1624 MPa). And the yield strength decreased by an average of 103 MPa with every increase of 40 °C due to the increase of volume fraction and decrease of the size of secondary α. In β solution treatment plus aging condition, tensile results shows that the strength if the alloy dramatically decreased by an average of 143 MPa for every increase of 40 °C because of larger size of secondary α phase than α/β solution treated plus aged condition.     

Microstructures and properties of Cu-10Sn oil bearings reinforced by Al2O3 nanoparticles

Using Sn and Cu-Al powders as raw materials, three oxide dispersion-strengthened (ODS) Cu-10Sn alloy powders with different Al₂O₃ mass content (0.42%, 0.85% and 1.68%, respectively) were prepared by mechanochemical synthesis combined with diffusion alloying method. The oil bearings were then fabricated by pressing and sintering. The effects of Al₂O₃ on microstructures and properties of the powders and the oil bearings were investigated. The results show that Al₂O₃ nanoparticles with sizes of about 5 nm are uniformly distributed in the ODS Cu powders. The content of Al₂O₃ nanoparticles has no effect on the distribution uniformity of tin during the diffusion process. And three ODS Cu-10Sn alloy powders with homogeneous tin distribution are prepared. However, the temperatures of forming liquid phases in the ODS Cu-10Sn alloys decrease with increasing Al₂O₃ content. This affects the sintering behaviors and mechanical properties of oil bearings. Increasing Al₂O₃ content also has a significant promoting effect on the precipitation of Sn-rich particles. In order to synergize the solid solution strengthening of tin and the dispersion strengthening of Al₂O₃ nanoparticles, the content of Al₂O₃ in the ODS Cu-10Sn alloys will not exceed 0.85%. The ODS Cu-10Sn oil bearings with 0.42% Al₂O₃ sintered at 900 °C have the best comprehensive properties, with uniform radial and axial shrinkage, oil content of 19.1%, radial crushing strength of 284 MPa and micro-hardness of 142 HV.     

Microstructures and mechanical properties of heat-resistant HPDC Mg-4Al-based alloys containing cheap misch metal

Mg-4Al-xCe/La-0.3Mn (Ce/La: mixture of Ce and La, x = 1, 2, 4 and 6 wt.%) alloys were prepared by high-pressure die-casting. The microstructures, mechanical properties and thermal stability were investigated. The cross-section of test bar could be divided into the fine skin region and the relatively coarse interior region. Two binary Al-(Ce, La) phases with the former being the dominant one, Al₁₁(Ce, La)₃ and Al₂(Ce, La), are mainly distributed along the dendrite boundaries, and La prefers to exist in Al₁₁(Ce, La)₃. The alloy with 4 wt.% Ce/La exhibits high tensile properties and good heat resistance until 200 °C, which were mainly attributed to the fine dendritic arm spacing and the main strengthening phase Al₁₁(Ce, La)₃, which is present in high volume fraction, and possesses fine rod-like morphology, network or “orderly stack” distribution and good thermal stability. The results of this research provide a basis for further investigation of the new low cost high-pressure die-cast Mg-Al-RE alloys designed to serve at temperature up to 200 °C.