Al Phase Research Articles

Static recrystallization and grain growth behaviour of Al0.3CoCrFeNi high entropy alloy

Single phase Al0.3CoCrFeNi (Al0.3) FCC high entropy alloy (HEA) synthesized through arc melting was subjected to cold rolling and subsequent annealing to study its recrystallization and grain growth behaviour. For the as-cast alloy, only partial recrystallization was achieved after cold deformation followed by annealing at 800 and 900 °C, which was attributed to the pining effect of AlNi rich precipitates formed during annealing. The activation energy of static recrystallization (549 kJ/mol) for the as-cast Al0.3 HEA was significantly higher than that of conventional alloys due to the distorted lattice, sluggish diffusion and most importantly the interaction of AlNi rich precipitates with the recrystallization. Homogenization heat treatment on Al0.3 HEA increased the static recrystallization kinetics and was associated with the lower volume fraction of precipitates formed during annealing. An increased grain growth exponent (n ≈ 5) and activation energy (583 kJ/mol) compared with conventional alloys, particularly at low annealing temperatures, was observed for the Al0.3 HEA mainly due to the pinning effect of AlNi rich precipitates. Finally, through investigating the mechanical performance of the alloy after annealing in the precipitation-free (1050 and 1000 °C) and precipitation-containing (900 °C) temperature ranges, the relative contributions for grain boundary and precipitation strengthening were estimated for the annealed Al0.3 HEA.

The coarsening behavior of γ′-Ni3(Ti, Al) phase in a precipitation strengthened Fe-based alloy

The γ′-Ni3(Ti, Al) phase is an important strengthening phase of Fe-based alloys and nickel-based superalloys, its coarsening behavior is very important for the strengthening effects. In this study, the precipitation behavior of γ′-Ni3(Ti, Al) phase in a thermally aged precipitation strengthened Fe-based alloy was evaluated during aging at 700 °C and 750 °C for different time using transmission electron microscopy (TEM) and atom probe tomography (APT). The results show that, the homogeneously distributed spherical γ′-Ni3(Ti, Al) particles with L12 structure which coherent with the matrix can be observed in all the aged samples. The size of the precipitate increases, while the number density of the precipitate decreases with aging temperature and time increasing. The volume fraction of γ′ particle is one key factor that influences the strength of bulk sample. During the process of γ′ particle growth, the partition ratios of Ni, Al and Ti between precipitates and matrix decrease with the aging temperature increasing significantly, while increase with aging time prolonging slightly. The Ti/Al ratio decrease with the aging time prolonging and aging temperature decreasing significantly. Based on the experiment results, the coarsening behavior of γ′ phase and their strengthening effects are discussed, which are expected to contribute to the design of Fe-based alloy compositions with improved mechanical properties.

Influence of Aerospace Standard Surface Pretreatment on the Intermetallic Phases and CeCC of 2024-T3 Al-Cu Alloy

A standard three-step surface pretreatment employed in the aerospace sector for Al alloys have been investigated prior to the generation of cerium conversion coatings (CeCC) on aluminium-copper alloy 2024. Two pretreatments were analysed, one without final acid etching (Pretreatment 1) and another with this step (Pretreatment 2). Both pretreatments affect the alloy intermetallic phases, playing a key role in the development of the CeCC, and also in the susceptibility to localised corrosion in NaCl medium. Scanning electron microscopy coupled with energy-dispersive X-ray analysis (SEM-EDX) revealed that after Pretreatment 2, Al(Cu,Mg) phases were partially or totally removed through dealloying with their subsequent copper enrichment. Conversely, none of these intermetallic phases were affected when the final acid step was not employed (Pretreatment 1). Meanwhile, Al-Cu-Fe-Mn-(Si) phases, the other major Al–Cu alloys intermetallics, suffers minor changes through the whole pretreatments chain. The protective efficiency of CeCC was evaluated using electrochemical techniques based on linear polarisation (LP) and electrochemical impedance spectroscopy (EIS). Samples with CeCC deposited after the Pretreatment 1 gave higher polarisation resistance and impedance module than CeCC deposited after Pretreatment 2. SEM-EDX and X-ray photoelectron spectroscopy analysis (XPS) indicate that the main factors explaining the corrosion resistance of the coatings is the existence of Al(Cu,Mg) intermetallics in the surface of the alloy, which promote the deposition of a cerium-based coating rich in Ce4+ compounds. These Al(Cu,Mg) intermetallics were kept in the 2024 alloy when acid etching was not employed (Pretreatment 1).

Rhodium influence on the microstructure and oxidation behaviour of aluminide coatings deposited on pure nickel and nickel based superalloy

Abstract The rhodium 0,5 μm thick layer was deposited on pure nickel and CMSX 4 Ni-based superalloy using the electroplating method. The rhodium coated substrates were aluminized by the CVD method. Oxidation resistance of nonmodified and rhodium modified coatings deposited both on nickel and CMSX 4 superalloy was compared. The triple-layer structure of rhodium modified coatings deposited on pure nickel was found. The β-(Ni,Rh)Al, rhodium doped γ'-Ni3Al and rhodium doped γ-Ni(Al) phases were the main components of the coatings on pure nickel. Two layers – additive and interdiffusion ones were identified in coatings deposited on CMSX 4 superalloy. TEM, SEM and XRD analysis revealed that β-(Ni,Rh)Al phase was the main component of the additive layer. Moreover Topologically Closed-Pack σ phases containing refractory elements in the β-(Ni,Rh)Al matrix of the interdiffusion layer were found. The rhodium modified aluminide coatings have better oxidation resistance than the nonmodified ones both on the pure nickel and CMSX 4 superalloy.

Influence of temperature cycles on strength and microstructure of spray-deposited Si–Al CE9F alloy

This paper investigates the effects of temperature cycles between −55 °C and 125 °C (the temperature range for intended space application) on the strength and microstructure of spray deposited Si–Al CE9F alloy. After 500 cycles, the strength is significantly improved of 9% (i.e., 26 MPa). Moreover the Weibull modulus also undergoes a significant increase. Microstructure characterizations by XRD, SEM, EBSD and DSC evidence recovery and recrystallization processes in the Al phase, and subgrain development at grain boundaries in the Si phase, leading to lower crystallite size. A Hall–Petch dependence of mean strength to average crystallite size in Si is proposed as strengthening mechanism.

Influences of mechanical activation and heating rate on reaction processes in combustion synthesis of NiAl-Al2O3 composites

This paper investigates the combustion synthesis of NiAl-Al2O3 composites by the heating of Ni, NiO and Al powder mixture from 20 °C to 1300 °C. The influence of mechanical activation (without and with 1 h) and heating rate (20 °C/min and 40 °C/min) on thermal events in combustion synthesis process are investigated. Thermal events are assessed by Differential Thermal Analysis (DTA), X-Ray Diffractometry (XRD) and Scanning Electron Microscopy (SEM). By heating the sample without mechanical activation, exothermic reaction of NiO reduction by Al and Ni-Al intermetallic phases (Al3Ni, Al3Ni2, AlNi and AlNi3) production happened in the presence of molten Al at 870 °C as one DTA peak. Mechanical activation causes occurrence of these reactions more separately at lower temperatures (590 °C and 630 °C). By decrement in the heating rate, these reactions happened in a more dispersed way at lower temperatures (590 °C and 630 °C). The reaction temperature for nickel aluminides formation in the presence of eutectic melt of AlNi3-Al is constant regardless of heating rate in mechanically activated powder. A seven-stage mechanism for reactions in a mechanically activated sample at a heating rate of 40 °C/min is proposed. Initially, by heating of the powder, an exothermic reaction between nickel oxide and aluminum and also nickel and aluminum occurs at 590 °C in solid state. NiO is consumed totally and Al2O3 is produced from the nickel oxide reduction by aluminum. Nickel aluminide phases are formed from reactions between aluminum and primary nickel and also from aluminum and nickel formed by aluminothermic reduction of nickel oxide. With continuation of heating process, Al-Al3Ni eutectic transition happens at 630 °C and results in the liquid phase formation. Presence of the molten phase accelerates the exothermic nickel aluminides formation reactions. Aluminum is consumed totally in this stage and more intermetallic phases are developed. By increasing the temperature, diffusion is enhanced. The remaining Al3Ni melts at 856 °C. This small amount of molten phase slightly enhances exothermic reactions between nickel aluminides and leads the system towards the equilibrium phase. After this event, reactions progresses gradually. The nickel core shrinks by the diffusion progressively and the whole nickel aluminides system undergoes a gradual evolution towards the NiAl equilibrium phase.

Processing and Mechanical Properties of Dual-Carbide (B4C, SiC), Dual-Metallic Phases (Al, Si) Infiltrated Composites

Abstract This work is on processing and studying of toughening property of indentation fracture composites. By applying reactive melt infiltration method infiltrated composites were prepared where different Si-Al compositions and as-pressed porous boron carbide were used at various infiltration temperatures. In which the process became feasible within the experimental constrains of this task. Polished sections of infiltrated composites were examined by quantitative methods with standards for the volumetric fractions of B4C, Si, Al, and SiC crystalline phases; and the element distribution in the phases were investigated by SEM/EDS, represented through ternary phase diagram. The distribution of ductile aluminium and brittle phases could determine the means of toughening mechanism and further discussed the de-bonding of interphases.

Microstructural Evolution of Reaction Layer of 1.5 GPa Boron Steel Hot-Dipped in Al-7wt%Ni-6wt%Si Alloy

The constituents, distribution, and characteristics of the phases formed on the coating layer of boron steel hot-dipped in Al-7wt%Ni-6wt%Si were evaluated in detail. In particular, the microstructure and phase constitution of the reaction layer were characterized. Moreover, the microstructural evolution mechanism of the phase was presented with reference to the (Al-7wt%Ni-6wt%Si)-xFe from the pseudo-binary phase diagram. The solidification layer consisted mainly of Al, Al3Ni, and Si phases. Reaction layers were formed in the order of Al9FeNi(Τ), Fe4Al13(θ), and Fe2Al5(η) from the solidification layer side. In addition, the κ (Fe3AlC) layer was formed at the Fe2Al5(η)/steel interface. From pseudo-binary phase diagram analysis, it was found that Fe4Al13(θ) can form when the Fe concentration is over 2.63 wt% in the 690 °C Al-7wt%Ni-6wt%Si molten metal. When the concentration of Fe increased to 10.0–29.0 wt%, isothermal solidification occurred in the Fe4Al13(θ) and Al9FeNi(Τ) phases simultaneously. Moreover, given that the T phase does not dissolve Si, it was discharged, and the Si phase was formed around the Al9FeNi(T) phase. The Fe2Al5(η) phase was formed by a diffusion reaction between Fe4Al13(θ) and steel, not a dissolution reaction. Moreover, Al2Fe3Si3(τ1) was formed at the Fe4Al13(θ)-Fe2Al5(η) interface by discharging Si from Fe4Al13(θ) without Si solubility. Furthermore, the Fe3AlC(κ) layer was formed by carbon accumulation that discharged in the Fe2Al5(η) region transformed from steel to Fe2Al5(η). The twin regions in the Fe4Al13(θ) and Fe2Al5(η) grain were due to the strains caused by the lattice transformation in the constrained state, wherein the phases are present between the Al9FeNi(Τ) layer and steel.

Patterns of the Formation of Antimicrobial Micro/Nanocomposites during the Oxidation of Bimetallic Al/Zn Nanoparticles

Porous composites of different phase composition are synthesized via oxidation in a water–ethanol mixture of bimetallic Al/Zn nanoparticles obtained through a joint electrical explosion of aluminum and zinc wires in an argon atmosphere. It is found that the oxidation of aluminum and the formation of boehmite nanosheets proceed in solutions containing 7‒20 wt % of water. At water contents over 20 wt %, the almost complete oxidation of aluminum is followed by the onset of zinc oxidation, resulting in the formation of composites containing boehmite nanosheets and hexagonal plates enriched with zinc oxide. Composites synthesized in this way display high antimicrobial activity against bacteria, due mainly to the release of Zn2+ ions into the solution. The greatest antimicrobial activity is observed in composites that simultaneously contain AlOOH, Al, ZnO, and Zn phases. The strong migration of Zn2+ ion is due to the structure of these composites, in which the active zinc surface grows as a result of the availability of ZnO plates located between the boehmite nanosheets. The boehmite nanosheets ensure stability of the composite structure and electrostatic interaction with bacteria.

Embedded-atom potential for Ni-Al alloy

We construct a new embedded-atom potential for Ni-Al system. The lattice constants, cohesive energies, elastic constants, vacancy formation energies, stacking fault energies and equations of state of Ni and Al are included in the fitting process of potentials for pure Ni and pure Al. The cross-interaction potential is fitted to the lattice constants, cohesive energies, elastic constants of Ni3Al and NiAl and the energies of (100) APB and (111) SISF of Ni3Al. The potential accurately reproduces the various physical properties of Ni, Al, Ni3Al and NiAl phases. The results of the new embedded-atom potential and other embedded-atom potentials are compared and discussed in detail.

Precipitation of η-Ni3(Ti, Al) Phase at Grain Boundaries in an Austenitic Precipitation-Strengthened Stainless Steel

The precipitation of the η-Ni3(Ti, Al) phase at grain boundaries in austenitic stainless steels significantly affects grain-boundary-related properties of the bulk material. In this study, the precipitation behavior of the η-Ni3(Ti, Al) phase in a thermally aged austenitic precipitation-strengthened stainless steel was evaluated during aging at 750 °C for 0.5 to 64 hours using scanning electron microscopy, transmission electron microscopy, and atom probe tomography. A higher number of plate-like η-Ni3(Ti, Al) phase particles precipitated at the grain boundaries with increasing aging time, and grew into the grain interior until the entire grain was occupied by this phase. The η phase had a {0001}η//{111}γ, $$ \langle 11\bar{2}0\rangle_{{{\upeta }}} $$ //〈110〉γ semi-coherent orientation relationship with the matrix, and contained many stacking faults. Ni- and Ti-rich layers alternated periodically between adjacent stacking faults in the η phase. Al segregated at stacking faults and the interface between the η phase and matrix. The partition coefficients of Ni, Al, and Si between the η precipitates and matrix decreased with increased aging time; however, the partition coefficient of Ti did not change significantly. The partition coefficients of the other elements increased with increasing aging time. The Ti:Al ratio of the η phase significantly increased with increasing aging time. Based on the experimental results, the precipitation and growth behaviors of η-Ni3(Ti, Al) phase precipitated at grain boundaries were discussed, which are expected to contribute to the design of austenitic stainless steel compositions with improved mechanical properties.

Phase-pure τ-MnAlC produced by mechanical alloying and a one-step annealing route

Phase-pure τ-MnAlC powder has been synthesized using mechanical alloying followed by a single annealing step. Mechanical alloying from the elemental constituents resulted in 100 wt.% nanocrystalline β-Mn(Al) phase. Complete β-Mn(Al) to τ-MnAlC phase transformation – via the high-temperature ε-phase – was obtained through annealing and quenching of the as-milled powder. The influence of the quenching rate (3.5–100 °C/s) is discussed in detail. Powder synchrotron X-ray and neutron diffraction data was used to confirm phase-purity, and to determine the magnetic moments of Mn. A coercivity of 0.15 T was obtained for the as-synthesized τ-MnAlC, significantly higher than previously reported values for τ-MnAlC synthesized with a one-step route. A systematic study utilizing cryomilling was attempted to further increase the coercivity.

Effect of processing routes on structure-property correlationship of ADC 12 Al alloy

The present work focuses primarily on the effect of processing routes on structure-property correlationship of ADC 12 Al alloy. Both conventional processing (Gravity cast and pressure die cast) and Semi Solid processing techniques (cooling slope and Rheo-Pressure Die Cast; RPDC) were attempted to bring out the correlationship between their microstructures and mechanical properties of ADC 12 Al alloy. Gravity cast experiment was done on ingots of ADC12 Al melted in an resistance furnace and poured at temperature 585 °C in a copper mould. In the Pressure Die-Casting process, ingots of ADC12 Al alloy were melted in an resistance furnace and the liquid metal was poured in the mould of the pressure die casting system. Semi-solid metal processing was carried out using cooling slope experiments in a developed in-house set up and effect of rheocasting on the semi solid microstructure was studied. Rheo pressure die cast experiments were carried out in an integrated set-up of cooling slope and pressure die-cast system. The obtained result of gravity cast material reveals dendritic morphology of primary Al phase and elongated eutectic phase; upon using pressure in a pressure die cast system, the structure of primary Al phase changes to large size dendrites along with rosette shaped morphology. The cooling slope technique to generate semi-solid structure yields nearly globular and fine grains; whereas the rheo pressure die casting experiments reveal nearly globular shape primary Al exhibit that distribute relatively uniformly in the matrix compared to the all three above the processing routes. From The best mechanical properties are also obtained in Rheo-pressure die cast system with tensile strength (223 MPa), elongation (6.5%), and hardness (87 VH) compared to all other processing routes. Explanations of fracture micro mechanisms are supplement to the investigation.

Phase stability of single phase Al0.12CrNiFeCo high entropy alloy upon irradiation

Phase stability of NiCoFeCr and Al0.12NiCoFeCr single phase high entropy alloys (HEAs) was studied under 3 MeV Ni2+ irradiation at 500 °C to a fluence of 1 × 1017/cm2 reaching a peak dose of ~100 displacements per atom (dpa). Transmission electron microscopy (TEM) diffraction pattern and scanning transmission electron microscopy-energy dispersive X-Ray spectroscopy (STEM-EDS) were utilized to detect any second phases that formed in the irradiated regions of the specimens. While the single phase of NiCoFeCr alloy has remained stable under the irradiation, the phase in Al0.12NiCoFeCr alloy decomposed into FCC matrix phase, and Ni3Al type nanoprecipitates with L12 ordered structure. On the other hand, in Al0.12NiCoFeCr alloy, the non-irradiated region of the TEM specimen (annealed for 10 h at 500 °C) and the as-cast alloy annealed for 490 h at 500 °C exhibited no such precipitates similar to those observed in the irradiated region. Based upon the thermodynamic stability of these alloys, we propose that radiation-enhanced diffusion under the irradiation accelerated the formation of the Ni3Al type equilibrium phase. Our study clearly demonstrates that the phase stability of HEAs under irradiation should be considered as one of the deciding factors in the materials design and selection for nuclear applications.

First-principles study of thermophysical properties of interaction layer products in U-Mo/Al dispersion fuel

Thermophysical properties of interaction layer (IL) formed in U-Mo/Al dispersion fuel are important for the evaluation of its impact on the fuel performance. Binary and ternary phases observed in the IL, however, are not well studied yet. Recently we predicted the thermophysical properties of the binary U-Al compounds in U-Al system using density functional theory (DFT) calculations. In this paper, we investigated the structural, elastic, electronic, vibrational and thermodynamic properties of the ternary U-Mo-Al compounds formed in IL, including (U0.75,Mo0.25)Al3, U6Mo4Al43 and UMo2Al20, using DFT calculations. The polycrystalline aggregate properties of these compounds were obtained from the predicted single crystal elastic constants. The calculated electronic density of states confirm that all of the compounds exhibit typical metallic behavior with the majority states at the Fermi level dominated by U 5f electrons. Using quasi-harmonic approximation, we predicted the thermodynamic properties of these compounds by including both electronic and lattice contributions. We also investigated the effect of density on the thermodynamic properties of (U0.75,Mo0.25)Al3 phase. The current results are expected to be helpful to the modeling of the fuel performance of U-Mo/Al dispersion fuel and the thermodynamic modeling of the ternary U-Mo-Al system.

The synthesis of NiCrAlHf powders with mechanical alloying method for thermal sprayed coating

NiCrAl is a material commonly used for coating in order to increase corrosion or oxidation resistance of materials applied at high temperatures. The addition of hafnium (Hf) as reactive elements to NiCrAl coating are found to prolong the life of the industrial gas turbine blade and increase its performance. NiCrAlHf powders used as the base material were mixed using planetary mill device for 36 hours with a speed of 25 Hz or 1500 rpm. Characterization of NiCrAlHf powder was investigated before and after milling process using Scanning Electron Microscopy (SEM) and X-ray diffraction (XRD). The results showed that the synthesized powders were agglomerated. The obtained particle size of 9.64 µm, 19.97 µm, 39.27 µm, 19.93 µm, and 22.8 µm was observed before milling process, after 9, 18, 27, and 36 hours milling process, resepectively. The phase formed on the synthesized NiCrAlHf powder after 36 hours milling process included Ni and Cr with crystallite size of Ni 25.4 nm and Cr 8.8 nm calculated by Scherrer method. In addition the peak profile of the Al phase gets more amorphous after 27 hours.

Effect of micro-groove on microstructure and performance of MAO ceramic coating fabricated on the surface of aluminum alloy

Micro-arc oxidation (MAO) ceramic coatings on the surface of aluminum alloy substrates with and without micro-groove have been successfully fabricated in the Na2SiO3-NaOH-EDTA-2Na solution. Microstructure characterization indicated that the micro-grooves on substrate surface could increase the content of α-Al2O3, γ-Al2O3 and 3Al2O3·2SiO2 phases and reduce the content of Al phase in the ceramic coating due to the sharp corner effect. EDS and XPS analysis showed that the content of Al and Si on the near outer surface of MAO coating on grooved substrate was more than that on non-grooved substrate. Meanwhile, MAO ceramic coating on micro-grooved substrate exhibited the faster growth rate in the initial stage of oxidation and the lower growth rate in the later oxidation. The final MAO coating showed the bigger micro pores and thicker oxidation film compared with that on the non-grooved substrate. Furthermore, the surface micro grooving pretreatment could dramatically improve the wear resistance and hardness of MAO coating, and the highest hardness of ceramic coatings of grooved substrate was around 1715 HV, which could be attributed to their special trapezoidal micro-groove structure.

Molecular Dynamics Study on Adhesion of Various Ni/Al Interface for Ni-Plated Aluminum Alloys

As a fundamental study on the adhesion of Ni-plating on aluminum alloys, various molecular dynamics simulations are performed on Ni/Al infinite laminate structure under tension, by changing mixing concentration of Ni and Al at the interface. The adhesion shows the highest at the perfect (001) Ni/Al interface while it decreases with the rate of random mixing in Ni/Al phases (10%, 30% and 50% substitution in each phase). Especially the 50% substitution in Al phase remarkably decreases the adhesion compare to the same substitution in Ni phase. The (111) interface shows weaker adhesion than (001) for perfect Ni/Al interface, and the substitution doesn’t largely affect to the adhesion reduction as the (001) interface. The (001) interfaces are always ruptured in brittle manner near the interface in Al side, and few Ni atoms are observed on the fracture surface. The (111) interfaces shows shear-lip breakage by void formation and growth in Al side further away from the interface. We obtained simple conclusion that the Ni/Al interface is inherently strong and the delamination never takes place at the interface, since the surface energy and elastic coefficients of Ni is much larger than Al. The large reduction of adhesion by atom mixing in the (001) interfaces can be explained with the initial misfit at the interface while it doesn’t largely affect to the close-packed (111) interface. Assuming various phenomena in real Ni-plating, we also performed simulations with Ni3Al and NiAl interlayer, (001)–(110) surfaces combination; and all results in the same story above mentioned. Finally, we performed calculations on Ni–P system, and revealed that the surface energy of amorphous Ni–P is close to that of Al. Thus interfacial delamination can be occurred between the amorphous Ni–P plating and aluminum base.

Contrasting mechanical behavior in precipitation hardenable AlXCoCrFeNi high entropy alloy microstructures: Single phase FCC vs. dual phase FCC-BCC

AlxCoCrFeNi is a prominent high entropy alloy system with varying crystal structure from FCC to BCC depending on aluminum content. The mechanical behavior of Al0.7CoCrFeNi with dual phase FCC+BCC microstructure has been compared with that of single phase FCC Al0.3CoCrFeNi. Both quasi-static and dynamic strain rate regimes were investigated. Hypo-eutectic Al0.7CoCrFeNi showed much higher strength due to fine lamellar microstructure with a large number of FCC-BCC interphase boundaries. But this also leads to lower strain rate sensitivity due to the long-range nature of these interfaces, overcoming them is indifferent with temperature elevation to assist slip, thus making them athermal barriers. Both these precipitation hardenable alloys were aged to induce precipitation of ordered L12 in the FCC phase. This coherent nano-scale L12 precipitate caused a significant increase in the yield strength of both single-phase and dual phase structures while reducing the strain rate sensitivity (SRS) only slightly. L12 precipitation in FCC matrix greatly enhanced twinning during dynamic deformation. Large-scale deformation twins were observed in coarse Al0.3CoCrFeNi FCC and FCC + L12 microstructures. The scale of deformation twins was much smaller in the dual phase Al0.7CoCrFeNi whose refined lamellae width retarded twinning. The lamellar structures, nevertheless, had higher work hardening due to their higher dislocation density storage capability.

Study on Texture Evolution and Shear Behavior of an Al/Ni/Cu Composite

The microstructure, texture, and mechanical properties of the Al/Ni/Cu composite during various accumulative roll bonding (ARB) cycles were studied using optical microscopy, scanning electron microscopy, x-ray diffraction, shear punch test, and hardness test. In addition, ImageJ software and Rietveld software were used in order to study microstructure and dislocation density variations, respectively. It was found that Ni and Cu layers were fractured and distributed in the Al matrix due to differences in their mechanical properties. Fracture and distribution of Cu and Ni particles after cycle five led to the alteration of the composite structure from a layered to a particle-reinforced structure. ARB process leads to the formation of strong orientation along the β-fiber and also to pronounced copper and dillamore components in both Al and Cu phases. Furthermore, the shear yield stress and ultimate shear strength of the composite increased as the ARB process advanced; however, shear elongation presented a non-uniform variation. Investigation of the fracture surfaces revealed that the mechanical properties of the composite are affected not only by the strain hardening of the Cu layer, but also by the structural change in the composite during the initial ARB cycles. During the last stages of the process, however, changes in mechanical properties were mostly governed by reinforcement particles serving as strain concentration zones and the strain hardening of the Al matrix.