Evaluation of Mechanical Properties and Structure of Al-1100 Composite Reinforced with ZrO<Subscript>2</Subscript> Nanoparticles via Accumulative Roll-Bonding

In this study, aluminum metal matrix composites reinforced with ZrO₂ nano-particles in volume fraction of 0.5, 0.75 and 1 % were manufactured through accumulative roll bonding (ARB) process. The results of composite microstructure indicated excellent ZrO₂ particle distribution in the Al matrix after 10 cycles of ARB process. The X-ray diffraction results also showed that nanostructured Al/ZrO₂ nano-particles composite with the average crystallite size of 48.6 nm was successfully achieved after 10 cycles of ARB process. The tensile tests were conducted on the ARBed strips. The tensile strength increased 2.15 times more than the initial value. The elongation dropped abruptly at the first cycle, and then increased slightly. The SEM images observations from the fracture surface showed that after 10 cycles of ARB process the fracture was almost shear fracture mode with fine and stretched pores.     

Development of Wear-Resistant Cu-10Cr-3Ag Electrical Contacts with Nano-Al<Subscript>2</Subscript>O<Subscript>3</Subscript> Dispersion by Mechanical Alloying and High Pressure Sintering

Cu-10Cr-3Ag (wt pct) alloy with nanocrystalline Al₂O₃ dispersion was prepared by mechanical alloying and consolidated by high pressure sintering at different temperatures. Characterization by X-ray diffraction and scanning electron microscopy or transmission electron microscopy shows the formation of nanocrystalline matrix grains of about 40 nm after 25 hours of milling with nanometric (<20 nm) Al₂O₃ particles dispersed in it. After consolidation by high pressure sintering (8 GPa at 400 °C to 800 °C), the dispersoids retain their ultrafine size and uniform distribution, while the alloyed matrix undergoes significant grain growth. The hardness and wear resistance of the pellets increase significantly with the addition of nano-Al₂O₃ particles. The electrical conductivity of the pellets without and with nano-Al₂O₃ dispersion is about 30 pct IACS (international annealing copper standard) and 25 pct IACS, respectively. Thus, mechanical alloying followed by high pressure sintering seems a potential route for developing nano-Al₂O₃ dispersed Cu-Cr-Ag alloy for heavy duty electrical contact.     

Microstructural Evolution and Mechanical Properties of Nanointermetallic Phase Dispersed Al<Subscript>65</Subscript>Cu<Subscript>20</Subscript>Ti<Subscript>15</Subscript> Amorphous Matrix Composite Synthesized by Mechanical Alloying and Hot Isostatic Pressing

The structure and mechanical properties of nanocrystalline intermetallic phase dispersed amorphous matrix composite prepared by hot isostatic pressing (HIP) of mechanically alloyed Al₆₅Cu₂₀Ti₁₅ amorphous powder in the temperature range 573 K to 873 K (300 °C to 600 °C) with 1.2 GPa pressure were studied. Phase identification by X-ray diffraction (XRD) and microstructural investigation by transmission electron microscopy confirmed that sintering in this temperature range led to partial crystallization of the amorphous powder. The microstructures of the consolidated composites were found to have nanocrystalline intermetallic precipitates of Al₅CuTi₂, Al₃Ti, AlCu, Al₂Cu, and Al₄Cu₉ dispersed in amorphous matrix. An optimum combination of density (3.73 Mg/m³), hardness (8.96 GPa), compressive strength (1650 MPa), shear strength (850 MPa), and Young’s modulus (182 GPa) were obtained in the composite hot isostatically pressed (“hipped”) at 773 K (500 °C). Furthermore, these results were compared with those from earlier studies based on conventional sintering (CCS), high pressure sintering (HPS), and pulse plasma sintering (PPS). HIP appears to be the most preferred process for achieving an optimum combination of density and mechanical properties in amorphous-nanocrystalline intermetallic composites at temperatures ≤773 K (500 °C), while HPS is most suited for bulk amorphous alloys. Both density and volume fraction of intermetallic dispersoids were found to influence the mechanical properties of the composites.     

Mechanical properties and bond strength of bimetallic AA1050/AA5083 laminates fabricated by warm-accumulative roll bonding

Accumulative roll bonding (ARB) is one of the most promising methods for the industrial production of bimetal sheet materials. In this study, ARB process has been used to combine aluminium alloys 1050 and 5083 sheets to produce a bimetal AA1050/AA5083 composite laminate. Materials with 2, 4, 8, 16 and 32 layers were roll bonded as alternate layers at 300°C for 5?min before each cycle. In this study, the microstructure and mechanical properties of composite laminates have been studied versus number of layers by tensile and peel testing. Moreover, the fracture surfaces of samples after the tensile test have been studied during various number of composite layers by scanning electron microscopy (SEM). Results showed that the tensile strength and tensile toughness improved by the number of layers. Also, the peeling strength among the layers and elongation decreased in the samples with less than 8 layers and improved by increasing the number of composite layers considerably. Also, SEM results revealed that the depth of dimples in the fracture surface decreased by increasing the number of layers.     

Microtexture Development of Niobium in a Multilayered Ti/Al/Nb Composite Produced by Accumulative Roll Bonding

Multilayered Ti/Al/Nb composites were produced by the accumulative roll bonding (ARB) process utilizing pure Ti, Al, and Nb element sheets. Up to four cycles of ARB were applied to the composites. The microstructure and texture evolution on the Nb phase were studied by X-ray diffraction (XRD), transmission electron microscopy, scanning electron microscopy, and electron backscattered diffraction. Nb and Ti layers necked and fractured as the number of ARB passes increased. After four ARB cycles, a nearly homogeneous distribution of Nb and Ti layers in Al matrix was achieved. As-received Nb sheet exhibited a fully lamellar structure and had a strong cold-rolling texture. After subjecting to ARB, slight grain refining was observed and the high-angle boundary fraction was increased. The intensity of the α-fiber was weakened, while that of the γ-fiber was strengthened during ARB. The texture evolution was attributed to partial recrystallization during the ARB process as a result of adiabatic heating.     

Processing,microstructure, and mechanical properties of cast <Emphasis Type="Italic">in-Situ</Emphasis> Al(Mg,Mn)-Al<Subscript>2</Subscript>O<Subscript>3</Subscript>(MnO<Subscript>2</Subscript>) composite

Cast particulate composites, containing in-situ generated reinforcing particles of alumina, have been developed by solidification of slurry obtained by dispersion of externally added manganese dioxide particles (MnO₂) in molten aluminum, and alumina is formed by reaction of manganese dioxide with molten aluminum. The chemical reaction also releases manganese into molten aluminum. Magnesium is added to the melt in order to help wetting of alumina particles by molten aluminum and to retain the particles inside the melt. The present work aims to understand the influence of key parameters such as processing temperature, time, and the amount of MnO₂ particles added on the microstructure and mechanical properties of the resulting cast in-situ composites. The sequence of addition of MnO₂ particles and magnesium has significant influence on the microstructure and mechanical properties. Increasing processing temperature and time increases the extent of reduction of MnO₂ particles, generating more alumina particles as well as releasing more manganese to the matrix alloy. Alumina helps to nucleate finer and sometimes blocky MnAl₆ in the matrix of the composite and thereby results in relatively higher ductility and increased strength in the composite as compared to the base alloy of similar composition. Even in the presence of relatively higher porosity of 8 to 9 vol pct, one observes a percent elongation not below 7 to 8 pct, which is considerably higher than those observed in cast Al(Mg)-Al₂O₃ composite synthesized by externally added alumina particles.     

Deformation and failure of Zr<Subscript>57</Subscript>Nb<Subscript>5</Subscript>Al<Subscript>10</Subscript>Cu<Subscript>15.4</Subscript>Ni<Subscript>12.6</Subscript>/W particle composites under quasi-static and dynamic compression

We have investigated the mechanical behavior of a composite material consisting of a Zr₅₇Nb₅Al₁₀Cu_15.4Ni_12.6 metallic glass matrix with 60 vol pct tungsten particles under uniaxial compression over a range of strain rates from 10⁻⁴ to 10⁴ s⁻¹. In contrast to the behavior of single-phase metallic glasses, the failure strength of the composite increases with increasing strain rate. The composite shows substantially greater plastic deformation than the unreinforced glass under both quasi-static and dynamic loading. Under quasi-static loading, the composite specimens do not fail even at nominal plastic strains in excess of 30 pct. Under dynamic loading, fracture of the composite specimens is induced by shear bands at plastic strains of approximately 20 to 30 pct. We observed evidence of shear localization in the composite on two distinct length scales. Multiple shear bands with thicknesses less than 1 μm form under both quasi-static and dynamic loading. The large plastic deformation developed in the composite specimens is due to the ability of the tungsten particles both to initiate these shear bands and to restrict their propagation. In addition, the dynamic specimens also show shear bands with thicknesses on the order of 50 μm; the tungsten particles inside these shear bands are extensively deformed. We propose that thermal softening of the tungsten particles results in a lowered constraint for shear band development, leading to earlier failure under dynamic loading.     

Improvement in the Shape Memory Response of Ti<Subscript>50.5</Subscript>Ni<Subscript>24.5</Subscript>Pd<Subscript>25</Subscript> High-Temperature Shape Memory Alloy with Scandium Microalloying

A Ti_50.5Ni_24.5Pd₂₅ high-temperature shape memory alloy (HTSMA) is microalloyed with 0.5 at. pct scandium (Sc) to enhance its shape-memory characteristics, in particular, dimensional stability under repeated thermomechanical cycles. For both Ti_50.5Ni_24.5Pd₂₅ and the Sc-alloyed material, differential scanning calorimetry is conducted for multiple cycles to characterize cyclic stability of the transformation temperatures. The microstructure is evaluated using electron microscopy, X-ray diffractometry, and wavelength dispersive spectroscopy. Isobaric thermal cycling experiments are used to determine transformation temperatures, dimensional stability, and work output as a function of stress. The Sc-doped alloy displays more stable shape memory response with smaller irrecoverable strain and narrower thermal hysteresis than the baseline ternary alloy. This improvement in performance is attributed to the solid solution hardening effect of Sc.     

Diffusion bonding of Si<Subscript>3</Subscript>N<Subscript>4</Subscript>-TiN composite with nickel-based interlayers

The diffusion bonding of a Si₃N₄-TiN composite with Ni, INVAR (Fe-Ni alloy), and IN600 (Ni-Cr-Fe alloy) interlayers has been investigated between 1100 °C and 1350 °C, under argon or nitrogen atmosphere. For the chosen bonding conditions, the Si₃N₄ phase of the composite reacts with the interlayer phase, leading to the release of silicon and nitrogen, whereas the TiN phase remains stable. The bonding mechanisms with nickel and INVAR (Ni-Fe alloy) interlayers are rather similar. Released silicon diffuses into the reaction layer and into the interlayer, forming a solid solution, whereas the released nitrogen remains gaseous. The bonding rate depends then on the elimination rate of nitrogen from the reaction interface. The thermal stability of these joints is very high up to 1100 °C. However, the interfacial porosity and the internal stresses created by the high nitrogen pressure are pernicious for the mechanical strength. The bonding mechanism with IN600 (Ni-Fe-Cr alloy) interlayer is rather different. The released nitrogen can form nitrides with interlayer elements (Cr, Al). Released silicon diffuses into the reaction layer and forms silicides. The joint porosity is less significant for the IN600 interlayer, which suggests a good mechanical strength. However, the formation of silicide is pernicious, because of the brittleness of these phases.     

Analysis of Strain Rate Sensitivity of Ultrafine-Grained AA1050 by Stress Relaxation Test

Commercially pure aluminum sheets, AA 1050, are processed by accumulative roll bonding (ARB) up to eight cycles to achieve ultrafine-grained (UFG) aluminum as primary material for mechanical testing. Optical microscopy and electron backscattering diffraction analysis are used for microstructural analysis of the processed sheets. Strain rate sensitivity (m-value) of the specimens is measured over a wide range of strain rates by stress relaxation test under plane strain compression. It is shown that the flow stress activation volume is reduced by decrease of the grain size. This reduction which follows a linear relation for UFG specimens, is thought to enhance the required effective (or thermal) component of flow stress. This results in increase of the m-value with the number of ARB cycles. Strain rate sensitivity is also obtained as a monotonic function of strain rate. The results show that this parameter increases monotonically by decrease of the strain rate, in particular for specimens processed by more ARB cycles. This increase is mainly linked to enhanced grain boundary sliding as a competing mechanism of deformation acting besides the common dislocation glide at low strain rate deformation of UFGed aluminum. Recovery of the internal (athermal) component of flow stress during the relaxation of these specimens seems also to cause further increase of the m-value by decrease of the strain rate.     

Fatigue crack growth in a particulate TiB<Subscript>2</Subscript>-reinforced powder metallurgy iron-based composite

Fatigue crack growth behavior has been examined in a particulate titanium diboride (TiB₂)-reinforced iron-based composite that had been produced via a mechanical alloying process. Comparison with equivalent unreinforced material indicated that fatigue crack growth resistance in the composite was superior to monolithic matrix material in the near-threshold regime. The composite exhibited relatively low crack closure levels at threshold, indicative of a high intrinsic (effective) threshold growth resistance compared to the unreinforced iron. The lower closure levels of the composite were consistent with reduced fracture surface asperity sizes, attributable to the reinforcement particles limiting the effective slip distance for stage I-type facet formation. The observed shielding behavior was rationalized in terms of recent finite-element analysis of crack closure in relation to the size of crack wake asperities and the crack-tip plastic zone. The different intrinsic fatigue thresholds of the composite and unreinforced iron were closely consistent with the influences of stiffness and yield strength on cyclic crack-tip opening displacements. Cracks in the composite were generally seen to avoid direct crack-tip-particle interaction.     

Effect of ARB Cycle Number and Second Phase Content on Mechanical properties and Microstructure of Pb–Ag Composite

A solid state method has been found for manufacturing of lead–silver composites for use as anodes in electrowinning production. Mechanical properties and microstructure of composite were characterized via peeling, tensile and microhardness tests, and scanning electron microscopy, transmission electron microscopy and fractography. Based on the peeling test results, maximum bond strength was achieved in the presence of 0.125 wt% of Ag (1.8 N/mm). Best mechanical properties were achieved in the Pb–0.5 wt% Ag composite after 10 ARB cycles by the enhanced tensile strength rising up to 50%, yield strength up to 170%, shear strength up to 63% and hardness up to 2.6 times higher, and the strain decreasing to 68% lower. These advanced properties led to higher stiffness and considerable enhancements in dimensional stability of the anodes and they improved creep characteristics. The advanced properties of the processed Pb–Ag composite anodes could be introduced as certification for slower anode failure, upkeep, surcharge and capital expenditure of industries with essential lead anode requirement.     

Abnormal Ductility Increase of Commercial Purity Al During Accumulative Roll Bonding

In this paper, sheets of commercial purity Al were fabricated by the accumulative roll-bonding (ARB) method up to six cycles. To increase the shear deformation, no lubricant was used during the ARB processing and the samples were carried out for ARB processing without any preheat treatment. One interesting finding is that the ductility and strength both increased during the first several cycles of ARB processing. It is proposed that the initial rolling texture might play an important part in the subsequent ARB processing since the original Al sheets for ARB processing have not been subjected to any annealing. The microstructures of the specimens after each ARB cycle were investigated by transmission electron microscopy and correlated with the mechanical properties.     

Enhancing physical and mechanical properties of Mg using nanosized Al<Subscript>2</Subscript>O<Subscript>3</Subscript> particulates as reinforcement

A magnesium-based composite with 1.1 volume percentage of nanosized Al₂O₃ particulates reinforcement was fabricated using an innovative disintegrated melt deposition technique followed by hot extrusion. Al₂O₃ particulates with an equivalent size of 50 nm were used as reinforcement. Microstructural characterization of the materials revealed grain refinement of magnesium matrix due to incorporation, retention, and uniform distribution of reinforcement. Physical properties characterization revealed that the addition of nano-Al₂O₃ particulates as reinforcement improves the dimensional stability of pure magnesium. Mechanical properties characterization revealed that the presence of nano-Al₂O₃ particulates as reinforcement leads to a significant increase in microhardness, dynamic elastic modulus, 0.2 pct yield strength (YS), ultimate tensile strength (UTS), and ductility of pure magnesium. The results revealed that the combined tensile properties of these materials are superior when compared to Mg reinforced with much higher volume percentage of SiC. An attempt is made in the present study to correlate the effect of nano-Al₂O₃ particulates as reinforcement with the microstructural, physical, and mechanical properties of magnesium.     

Crystallization Behavior and Microstructure of Silica-Free 5K<Subscript>2</Subscript>O-45CaO-50P<Subscript>2</Subscript>O<Subscript>5</Subscript> Bioglass

The crystallization behavior and microstructure of silica-free 5K₂O-45CaO-50P₂O₅ (KCP) bioglass have been studied using differential thermal analysis (DTA), X-ray diffraction (XRD), scanning election microscopy (SEM), transmission electron microscopy (TEM), and selected area electron diffraction (SAED). The activation energy for the KCP bioglass crystallization is found to be 337.4 kJ/mol using a nonisothermal method. The crystalline phases of the glass surface determined by XRD are KCa(PO₃)₃, 4CaO·3P₂O₅, and β-Ca(PO₃)₂ when the KCP bioglass is crystallized at 903 K for 4 hours. The crystalline phase of the powder samples determined by XRD is β-Ca(PO₃)₂ when silica-free KCP glasses crystallized at 873 to 1073 K for 8 hours. Crystallization starts at the surface of the KCP bioglass and then proceeds toward the interior of the glass matrix. The morphology of β-Ca(PO₃)₂ is a fibrillar shape 20 to 180 nm in length and 17 to 20 nm in diameter, with an aspect ratio ranging from 1.0 to 10.6.     

Synthesis and Characterization of Microwave Absorbing SrFe<Subscript>12</Subscript>O<Subscript>19</Subscript>/ZnFe<Subscript>2</Subscript>O<Subscript>4</Subscript> Nanocomposite

Zinc ferrite and strontium hexaferrite; SrFe₁₂O₁₉/ZnFe₂O₄ (SrFe_11.6Zn_0.4O₁₉) nanoparticles having super paramagnetic nature were synthesized by simultaneous co-precipitation of iron, zinc and strontium chloride salts using 5 M sodium hydroxide solution. The resulting precursors were heat treated (HT) at 850, 950 and 1150°C for 4 h in nitrogen atmosphere. The hysteresis loops showed an increase in saturation magnetization from 1.040 to 58.938 emu/g with increasing HT temperatures. The ‘as-synthesized’ particles have size in the range of 20–25 nm with spherical and needle shapes. Further, these spherical and needle shaped nanoparticles tend to change their morphology to hexagonal plate shape with increase in HT temperatures. The effect of such a systematic morphological transformation of nanoparticles on dielectric (complex permittivity and permeability) and microwave absorption properties were estimated in X band (8.2–12.2 GHz). The maximum reflection loss of the composite reaches −26.51 dB (more than 99% power attenuation) at 10.636 GHz which suits its application in RADAR absorbing materials.     

Modification of Cast Al-Mg<Subscript>2</Subscript>Si Metal Matrix Composite by Li

The effects of both Li modification and cooling rate on the microstructure and tensile properties of an in-situ prepared Al-15 pct Mg₂Si composite were investigated. Adding 0.3 pct Li reduced the average size of Mg₂Si primary particles from ~30 to ~6 μm. The effect of cooling rate was investigated by the use of a mold with different section thicknesses from 3 to 9 mm. The results show a refinement of primary particle size as a result of both Li additions and cooling rate increases, and their effects are additive. Similarly, both effects increased ultimate tensile stress (UTS) and elongation values. The thin sections show somewhat unexpectedly low and scattered tensile results attributed to the casting defects observed in fracture surfaces. The Li-modified alloy displays serrated yielding behavior that is not fully explained here. The refinement by Li and enhanced cooling rate is explained in terms of an analogy with the effect of Sr and cooling rate in Al-Si alloys, and is ultimately attributed to the effect of the alkali and alkaline earth metals deactivating oxide double films (bifilms) suspended in Al melts as favored substrates for intermetallics.     

Effects of Annealing and Pressure on Devitrification and Mechanical Properties of Amorphous Al<Subscript>87</Subscript>Ni<Subscript>7</Subscript>Gd<Subscript>6</Subscript>

Annealing studies at different temperatures, as well as those conducted with 940 MPa hydrostatic pressure, were conducted on amorphous ribbons of Al₈₇Ni₇Gd₆. The studies were performed to investigate the evolution of structure under different conditions and to particularly examine the effects of superimposed hydrostatic pressure during annealing. This amorphous alloy devitrifies at low temperatures via the precipitation of nano-crystalline α-Al particles. The effects of these various exposures on the amount of devitrification have been quantified using a variety of analytical techniques (i.e., X-ray diffraction (XRD), differential scanning calorimetry (DSC), and transmission electron microscopy (TEM)). In addition, the effects of devitrification on the mechanical properties have been quantified using microhardness indentation and uniaxial tension tests. This article is based on a presentation given in the symposium entitled “Bulk Metallic Glasses IV,” which occurred February 25–March 1, 2007 during the TMS Annual Meeting in Orlando, Florida under the auspices of the TMS/ASM Mechanical Behavior of Materials Committee.

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Microstructure and Properties of Fe<Subscript>3</Subscript>Al-Fe<Subscript>3</Subscript>AlC<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript> Composite Prepared by Reactive Liquid Processing

A Fe₃Al-Fe₃AlC _x composite was prepared using reactive liquid processing (RLP) through controlled mixture of carbon steel and aluminum in the liquid state. The microstructure and phases of the composite were assessed using X-ray diffraction, scanning electron microscopy, energy-dispersive X-ray spectroscopy, optical microscopy, and differential scanning calorimetry. In addition, the density, hardness, microhardness, and elastic modulus were evaluated. The Fe₃Al-Fe₃AlC _x composite consisted of 65 vol pct Fe₃Al and 35 vol pct Fe₃AlC _x (κ). The κ phase contained 10.62 at. pct C, resulting in the stoichiometry Fe₃AlC_0.475. The elastic modulus of the Fe₃Al-Fe₃AlC_0.475 composite followed the rule of mixtures. The RLP technique was shown to be capable of producing Fe₃Al-Fe₃AlC_0.475 with a microstructure and properties similar to those achieved using other processing techniques reported in the literature.     

Synthesis,Characterization and Mechanical Properties of AA7075 Based MMCs Reinforced with TiB<Subscript>2</Subscript> Particles Processed Through Ultrasound Assisted In-Situ Casting Technique

AA7075/TiB₂ composites have been synthesized through both in situ salt-melt reaction method and ultrasound assisted in situ process. Microstructural studies reveals that ultrasound assisted in situ method improves the dispersion of TiB₂ particles and reduces the porosity level. Moreover, the ultrasonic treatment refines the reinforcement particle size along with improvement in particle dispersion. The mechanical property assessment confirms that ultrasonic treatment improves the mechanical properties of composite. The hardness of the AA7075 alloy is increased from 55 H_V to 74 H_V by the addition of 5% TiB₂ particles and it further increased to 82 H_V by ultrasonic treatment. A similar trend is also observed when weight percentage of particles increases to 7.5%. Addition of 5% in situ TiB₂ particles increases the ultimate tensile strength of AA7075 alloy by 60 MPa and it is further enhanced by 80 MPa upon ultrasound assisted process. Composites have shown a small reduction in ductility when compared to un-reinforced alloy, though 81% ductility of matrix alloy has been retained. Similar trend has been observed in composites fabricated using ultrasonic assisted casting.