Patent Application
20250043392
Support provided by the Interdisciplinary Research Center for Hydrogen & Energy Storage (IRC-HES), at King Fahd University of Petroleum & Minerals (KFUPM), Dhahran, Saudi Arabia, is gratefully acknowledged.
The present disclosure is directed to an aluminum-based composite, particularly, to a method of making an aluminum-cubic boron nitride composite (Al-cBN).
The “background” description provided herein is to present the context of the disclosure generally. Work of the presently named inventors, to the extent it is described in this background section, as well as aspects of the description that may not otherwise qualify as prior art at the time of filing, are neither expressly nor impliedly admitted as prior art against the present invention.
Metal matrix composites (MMCs) with synergistic metallic and ceramic properties are valuable for applications that prioritize low cost, lightweight construction, and high strength as essential material design parameters. Among metals and alloys, aluminum (Al) has attracted attention in the manufacturing of composite materials owing to its beneficial characteristics, including ease of processing and lower density compared to alternatives like grey cast iron and steel, and is therefore used in the automobile, aerospace, and many other industries. Al-based MMCs are promising materials for aerospace (e.g., fuselage, wings, and supporting structures in aircraft) and automotive applications (such as pistons, connecting rods, engine blocks, brake rotors, current collectors, propeller shafts, and brake disks). Their utilization contributes to weight reduction, fuel consumption reduction, and improved performance in oxidizing environments.
Composite materials possess a unique combination of properties, with ceramic-reinforced Al composites facilitating the design and development of materials tailored to specific applications, resulting in efficiency improvement and superior emission control compared to individual component materials. Ceramic particles introduce increased density and elastic modulus to the resulting composites. The selection and quantity of reinforcement materials within the matrix, as well as the matrix's interaction with the reinforcement, play a critical role in realizing the desired properties and overall performance of the composite. Therefore, various fabrication processes and reinforcements, such as SiC, WC, B4C, Al2O3, AlN, and other ceramics, have been employed in the development of Al-MMCs.
The selection of fabrication techniques for metal matrix composites (MMCs) is influenced by various factors, including production cost, process efficiency, and desired product quality. Among the commercially utilized techniques, liquid infiltration, stir casting, and powder metallurgy have been employed to produce MMCs. However, the powder metallurgy processing technique is promising due to its stability to offer better control over interface kinetics. Furthermore, it involves lower processing temperatures than casting and provides improved control over the resulting microstructures (uniform and fine microstructures). This enables accurate net shaping and improved material utilization. The powder metallurgy technique also allows for shorter sintering durations. Sintered aluminum (Al) composites developed through powder metallurgy processes exhibit potential for applications in automobile and aerospace industries. These composites possess a high strength-to-weight ratio and leverage the specific gravity advantages of aluminum [Koli, D. K., G. Agnihotri, and R. Purohit, Advanced aluminum matrix composites: the critical need of automotive and aerospace engineering fields. Materials Today: Proceedings, 2015. 2(4-5): p. 3032-3041; and Bishop, D., et al., On enhancing the mechanical properties of aluminum P/M alloys. Materials Science and Engineering: A, 2000. 290(1-2): p. 16-24]. Spark plasma sintering (SPS) may be used to strengthen the composites. The SPS is a non-conventional sintering technique in which materials in the form of powders are subjected to a combination of heat (generated by applying a high direct current) and uniaxial pressure to form coherent bodies with reduced porosities, increased densities, and improved mechanical and electrochemical properties, owing to the fine grain boundaries of composites.
Metal matrix composites (MMCs) are potential candidates for replacing metallic alloys in aerospace, automobile, and security applications due to their desirable characteristics such as corrosion resistance, high wear resistance, and thermal resistance. However, it is essential to carefully consider the corrosion behavior of MMCs when selecting them for specific applications and environmental conditions. One significant challenge associated with MMCs is the impact of reinforcement particles on their corrosion resistance properties. Even minor changes can have a significant effect on the long-term stability of their properties. Pardo et al. investigated the effect of SiC particles (10-20 vol. %) on the corrosion behavior of A360 and A380 prepared via a pressure die casting process in a NaCl solution (1 to 3.5 wt. %) [Pardo, A., et al., Influence of reinforcement proportion and matrix composition on pitting corrosion behavior of cast aluminum matrix composites (A3xx. x/SiCp). Corrosion Science, 2005. 47(7): p. 1750-1764]. Singh et al. studied the influence of SiC particles on an Al—Cu alloy fabricated using the stir-casting technique to examine its pitting susceptibility in a marine environment [Singh, I., et al., Influence of SiC particles addition on the corrosion behavior of 2014 Al—Cu alloy in 3.5% NaCl solution. Corrosion Science, 2009. 51(2): p. 234-241].
Acevedo-Hurtado et al. reported that increasing the percentage of Al2O3 particles in an Al—Al2O3 MMC decreases the corrosion rate in an aerated 3.5 wt. % NaCl solution. This composite material was fabricated using a powder metallurgy process, in which Al-alloyed powder and Al2O3 particles were first blended. Subsequently, the resulting materials were hot-consolidated and extruded to form a billet with a circular cross-section [Acevedo-Hurtado, P. and P. Sundaram, Corrosion behavior of novel Al—Al2O3 composites in aerated 3.5% chloride solution. Journal of Materials Engineering and Performance, 2017. 26(1): p. 69-75]. Ananda Murthy et al. investigated the influence of the TiN content (2 to 6 wt. %) on Al 6061 in a chloride medium (0.1 to 1N NaCl) [Murthy, H. A., V. B. Raju, and C. Shivakumara, Effect of TiN particulate reinforcement on corrosive behavior of aluminum 6061 composites in chloride medium. Bulletin of Materials Science, 2013. 36(6): p. 1057-1066]. Sherif et al. reported that the presence of exfoliated graphite (1-3 wt. %) in pure Al increases its corrosion rate [Sherif, E.-S. M., et al., Effects of graphite on the corrosion behavior of aluminum-graphite composite in sodium chloride solutions. Int. J. Electrochem. Sci, 2011. 6: p. 1085-1099].
However, there are still challenges that need to be overcome to further advance the commercial applications of aluminum-based composites. The cost-effectiveness and performance ratio of aluminum-based composites play a crucial role in their widespread industrial adoption. Achieving an optimal balance of properties in aluminum-based composites for advanced applications remains a significant challenge that requires further development and efforts. By addressing these challenges, the industrial viability and potential applications of aluminum-based composites can be enhanced.
In view of the foregoing, it is one objective of the present disclosure to develop an aluminum-based composite that overcomes the limitations of the art. A second objective of the present disclosure is to describe a method of making an aluminum-cubic boron nitride (Al-cBN) composite. A third objective of the present disclosure is to describe a light weight material containing the Al-cBN composite.
In an exemplary embodiment, a method of making an aluminum-cubic boron nitride (Al-cBN) composite is described. The method includes mixing an aluminum powder and particles of cubic boron nitride (cBN) in a solvent and sonicating to form an Al-cBN mixture. The method further includes drying the Al-cBN mixture to form a dried mixture powder, and sintering by pressing and heating the dried mixture powder to form the Al-cBN composite in the form of a disc. In some embodiments, the aluminum powder has an average particle size of 10 to 100 micrometers (μm). In some embodiments, the cBN particles have an average particle size of from 10 to 100 m, and are uniformly dispersed throughout the Al-cBN composite.
In some embodiments, the aluminum powder has an average particle size of about 50 μm.
In some embodiments, the cBN particles have a cubic or octahedral shape and an average particle size of from 20 to 60 μm.
In some embodiments, the Al-cBN composite prepared by the method of the present disclosure has a network matrix of aluminum. In some embodiments, the cBN particles are uniformly dispersed throughout the network matrix of aluminum.
In some embodiments, the solvent is at least one alcohol selected from the group consisting of methanol, ethanol and propanol.
In some embodiments, a weight ratio of the aluminum powder to the cBN particles is in a range of from 100:1 to 5:1.
In an exemplary embodiment, the pressing is performed under a uniaxial pressure in a range of 30 to 70 megaPascals (MPa).
In some embodiments, the heating is performed at a temperature in a range of 500 to 600° C.
In some embodiments, during the sintering, the aluminum powder and the cBN particles in the dried mixture do not react.
In some embodiments, the Al-cBN composite has an average hardness in a range of 1 to 2 gigaPascals (GPa).
In some embodiments, the Al-cBN composite has an average elastic modulus in a range of 70 to 80 GPa.
In some embodiments, the Al-cBN composite has a density in a range of 2.5 to 2.7 grams per cubic centimeter (g/cm3).
In some embodiments, the Al-cBN composite has a densification in a range of 94 to 99% based on a density of the aluminum powder.
In an exemplary embodiment, a light weight material comprising the Al-cBN composite prepared by the method of present disclosure is described. A weight ratio of the aluminum powder to the cBN particles is about 9:1, and the cBN particles have an average particle size of from 20 to 60 μm.
In some embodiments, the light weight material has a density in a range of 2.55 to 2.65 g/cm3.
In some embodiments, the light weight material is at least part of a cutting tool, an abrasive tool, mold, die, break-ring, nozzle, glass forming tool, metal forming refractory tool, high temperature refractory shape, furnace vent, furnace stack, furnace fixture, generator component, reactor component, turbine component, engine component, vehicular component, aerospace component, ship, submarine component, aircraft component, weapon, or armor.
In some embodiments, the light weight material when exposed to a salt solution has a corrosion rate in a range of from 4 to 35 mils per year (mpy).
In some embodiments, the salt solution contains at least one salt selected from the group consisting of sodium chloride, potassium chloride, magnesium chloride, magnesium sulfate, calcium sulfate, calcium carbonate, and sodium bicarbonate.
In some embodiments, the salt is present in the salt solution at a concentration of 1 to 8% by weight.
In some embodiments, the light weight material has a corrosion current density (icorr) of 3 to 30 microamperes square centimeters (μA cm2) under a potential of −1.0 to 0 V (vs Ag/AgCl).
The foregoing general description of the illustrative present disclosure and the following The detailed description thereof are merely exemplary aspects of the teachings of this disclosure and are not restrictive.
A more complete appreciation of this disclosure and many of the attendant advantages thereof will be readily obtained as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings, wherein:
In the drawings, reference numerals designate identical or corresponding parts throughout the several views. Further, as used herein, the words “a,” “an,” and the like generally carry a meaning of “one or more,” unless stated otherwise.
Furthermore, the terms “approximately,” “approximate,” “about,” and similar terms generally refer to ranges that include the identified value within a margin of 20%, 10%, or preferably 5%, and any values therebetween.
Aspects of the present disclosure are directed to aluminum-cubic boron nitride (Al-cBN) composites with different reinforcement sizes made by via spark plasma sintering (SPS) while maintaining a constant weight percentage. The mechanical and electrochemical properties of the composites were investigated as a function of the cBN particle size.
At step 52, the method 50 includes mixing an aluminum powder and particles of cubic boron nitride (cBN) in a solvent and sonicating to form an Al-cBN mixture. In some embodiments, the aluminum powder has an average particle size of 10 to 100 micrometers (μm), preferably 20-80, preferably 30-60, preferably 40-50, preferably 50 m, as depicted in
Boron nitride occurs in a variety of forms, including as amorphous boron nitride, cubic boron nitride (cBN), hexagonal boron nitride (hBN), or as rhombohedral (rBN) or Wurtzeit (wBN) boron nitride allotropes. Boron nitride may also be in the form of nanotubes of substantially pure boron nitride. In the present disclosure, the boron nitride generally contains at least 90 wt. % cBN, preferably at least 95 wt. % cBN, preferably at least 99 wt. % cBN, or even more preferably at least 99.9 wt. % cBN. Other ranges are also possible.
At step 54, the method 50 includes drying the Al-cBN mixture to form a dried mixture powder. The Al-cBN mixture was dried to a temperature range of 60-100° C., preferably 70-90° C., preferably 80° C. for at least 4 hours, preferably at least 8 hours, preferably at least 12 hours, preferably at least 16 hours, preferably at least 20 hours, or even more preferably at least 24 hours, to allow for the evaporation of the solvent. Other ranges are also possible. In some embodiments, the temperature may be determined based on the choice of the solvent. The drying can be done by using heating appliances such as ovens, microwaves, autoclaves, hot plates, heating mantles and tapes, oil baths, salt baths, sand baths, air baths, hot-tube furnaces, and hot-air guns.
Referring to
At step 56, the method 50 includes sintering by pressing and heating the dried mixture powder to form the Al-cBN composite in the form of a disc. Sintering, which is also called “frittage,” is the process of forming a solid mass of material through heat and pressure without melting to the point of liquefaction. During the sintering process, the aluminum powder, and particles of cBN to fuse together to form a homogeneous material in which the cBN particles are dispersed in a matrix of the Al particles, with no chemical reaction taking place between the aluminum powder and the cBN particles. The sintering cycle is dependent on the geometry and the dimension aspect ratio of the pressed shape. Because of the possible hazards of reaction or ignition during sintering, sintering is performed under an inert media, for example, an argon atmosphere, to prevent any oxidation or surface reaction. It involves two stages—pressing the dried mixture followed by heating to form the Al-cBN composite.
During pressing, the dried mixture is pressed in a die, preferably a graphite die, to make a specific shape. The graphite die has a thickness of 10-30 mm, preferably 15-25 mm, preferably 20 mm. Other ranges are also possible. A uniaxial force was applied to the dried mixture in a range of 30 to 70 megaPascals (MPa), preferably 40-60 MPa, preferably 50 MPa. A holding time of 10-20 minutes, preferably 10 minutes, is sufficient, depending on the amount of dried mixture. Other ranges are also possible. The pressed sample is further heated at a rate of about 50-120° C./minute, preferably 60-100° C./minute, preferably 100° C./minute, to a final temperature in the range of 500-600° C., preferably 550° C., holding at the final temperature for 10-20 minutes, preferably 10 minutes, and then cooling to room temperature, to form the Al-cBN composite, where the cBN particles are uniformly dispersed throughout the Al-cBN composite. Other ranges are also possible. The Al-cBN composite thus obtained is in the form of a disk having the specific shape of the graphite die. In some embodiments, the disk of the Al-cBN composite has a thickness of 0.1 to 10 mm, preferably 0.15 to 5 mm, preferably 0.2 to 1 mm, or even more preferably about 0.35 mm, as depicted in
The crystalline structures of the Al-cBN composite may be characterized by X-ray diffraction (XRD). The XRD patterns are collected in a Rigaku MiniFlex diffractometer equipped with a Cu-Kα radiation source (λ=0.15416 nm) for a 20 range extending between 5 and 100°, preferably 15 and 80°, further preferably 30 and 60° at an angular rate of 0.005 to 0.04° s−1, preferably 0.01 to 0.03° s−1, or even preferably 0.02° s−1. In some embodiments, the Al-cBN composite has at least a first intense peak with a 2 theta (0) value in a range of 37 to 40°, preferably about 38.7°, as depicted in
Also referring to
Referring to
In some embodiments, the Al-cBN composite has an average elastic modulus in a range of 70 to 80 GPa, preferably 72 to 78 GPa, preferably 74 to 76 GPa, or even more preferably about 75 GPa, as depicted in
In some preferred embodiments, the Al-cBN composite has a density in a range of 2.5 to 2.7 grams per cubic centimeter (g/cm3), preferably 2.55 to 2.65 g/cm3, or even more preferably about 2.6 g/cm3. In some more preferred embodiments, the Al-cBN composite has a densification in a range of 94 to 99% based on a density of the aluminum powder, preferably 95 to 98%, or even more preferably 96 to 97% based on the density of the aluminum powder. Other ranges are also possible.
Electrochemical characterization may be performed using an electrochemical cell equipped with a three-electrode configuration. In some embodiments, graphite was used as the counter electrode, and a Ag/AgCl (sat. KCl) electrode was employed as a reference coupled with a potentiostat (1000E, Gamry, USA). In some embodiments, the Al-cBN composite may be used as the working electrode. The electrochemical analysis may be performed in a NaCl electrolyte having a concentration of 1 to 5 wt. %, or even more preferably about 3.5 wt. % by weight at room temperature (25±1° C.). The open-circuit potential (OCP) analysis may be performed for 0.5 to 3 hours, or even more preferably about 1 hour. Electrochemical impedance spectroscopy (EIS) tests may be performed at the corrosion potential (EOCP) and a frequency range of 100 kHz to 0.01 Hz with a potential perturbation of 1 to 10 mV (rms), or even more preferably about 5 mV (rms) at 0 V vs. OCP. In some embodiments, the cyclic potentiodynamic polarization (CPP) analysis may be scanned from −0.3 to +1.5 V against OCP at the scan rate of 1 to 10 mV/s, or even more preferably about 2.5 mV/s. Other ranges are also possible.
Referring to
Referring to
A light weight material, including the Al-cBN composite, prepared by the method of the present disclosure, is described. As used herein, the term “lightweight material”, generally refers to a type of material that exhibits low density or weight relative to its volume or size. In the present disclosure, the light weight material has a density in the range of 2.55 to 2.65 g/cm3, preferably 2.57 to 2.63 g/cm3, or even more preferably 2.59 to 2.61 g/cm3. Other ranges are also possible. Suitable examples of the light weight material is at least part of a cutting tool, an abrasive tool, mold, die, break-ring, nozzle, glass forming tool, metal forming refractory tool, high temperature refractory shape, furnace vent, furnace stack, furnace fixture, generator component, reactor component, turbine component, engine component, vehicular component, aerospace component, ship, submarine component, aircraft component, weapon, or armor. In an embodiment, the Al-cBN composite of the invention may be used to form a material such as a durable solid material, granule or powder. As a powder or granule (e.g. having grains ranging from 0.001 to 2 mm in average size (TEM) it may be incorporated into or onto an abrasive surface such as a surface or into a gaseous, liquid or solid composition for grinding, polishing, buffing, honing, cutting, drilling, sharpening, lapping, or sanding.
In the light weight material, the cubic boron nitride is crystalline. In some embodiments, other forms of boron nitride, such as amorphous form, hexagonal form, wurtzite form, and combinations thereof, may be present in the particles of the cubic boron nitride, with the major component being the boron nitride in the cubic phase. The cBN particles have an average particle size of 10 to 100 m, preferably 20-80, preferably 20 to 60 μm. The weight ratio of the aluminum powder to the cBN particles is in a range of from 100:1 to 5:1, preferably 90:1 to 5:1, preferably 80:1 to 5:1, preferably 70:1 to 5:1, preferably 60:1 to 5:1, preferably 50:1 to 5:1, preferably 40:1 to 5:1, preferably 30:1 to 5:1, preferably 20:1 to 5:1, preferably 10:1 to 5:1, preferably 9:1. The weight ratio of the aluminum powder to the cBN particles is about 9:1. Other ranges are also possible.
The light weight material including Al-cBN composite shows an increased resistance to corrosion. For example, the light weight material, including the Al-cBN composite, when exposed to a salt solution has a corrosion rate in a range of from 4 to 35 mils per year (mpy). The salt solution includes at least one salt selected from the group consisting of sodium chloride, potassium chloride, magnesium chloride, magnesium sulfate, calcium sulfate, calcium carbonate, and sodium bicarbonate. In an embodiment, the salt is present in the salt solution at a concentration of 1 to 8% by weight. The light weight material has a corrosion current density (icorr) of 3 to 30 microamperes square centimeters (μA cm2), preferably 8 to 25 pA cm2, preferably 13 to 20 pA cm2, or even more preferably about 17 pA cm2, under a potential of −1.0 to 0 V (vs Ag/AgCl). Other ranges are also possible.
A physical property of the light weight of the invention, including a mechanical, chemical or thermal property, may vary upward or downward by at least 1, 2, 3, 4, 5, 10, 15, 20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85, 90, 95 100% or more (or any intermediate value within this range) compared to an otherwise similar aluminum composite made without the cBN particles, or to an otherwise similar composite that is conventionally sintered not using SPS.
The composite of the present invention with a cBN particle size of, e.g., 20 μm strengthens the matrix owing to the better stress drive in the matrix and exhibits the improved average hardness (1.78 GPa), elastic modulus (76.1 GPa), and percentage of densification (98.1%).
As used herein, the term “stress drive,” or “stress distribution” generally refers to how stress is distributed or spread throughout a material under external loads or forces. In the present disclosure, the term “stress drive” may be determined by numerical simulations, e.g., finite element analysis; by experimental methods, e.g., strain gauges and/or stress-sensitive materials; and by any other suitable method known to those of skill in the art.
The corrosion behavior and resistance against pitting corrosion of pure Al and cBN-based composites were investigated in a 3.5 wt. % NaCl solution using electrochemical techniques, such as open circuit potential, electrochemical impedance spectroscopy, and cyclic potentiodynamic polarization analyses. Electrochemical studies revealed that among the analyzed samples, the composite with 20 m cBN particles exhibits an improved polarization resistance in addition to the lowest corrosion rate (4.533 mills per year) and a high resistance to pit formation in a corrosive environment.
The following examples demonstrate a method of making an aluminum-cubic boron nitride composite (Al-cBN) as described herein. The examples are provided solely for illustration and are not to be construed as limitations of the present disclosure, as many variations thereof are possible without departing from the spirit and scope of the present disclosure.
Pure Alfine powder (average particle size ˜50 m), 93% complexometric; CAS: 7429-90-5, Sigma-Aldrich) was used as a matrix for preparing the composites. cBN with average particle sizes of 20, 40, and 60 μm (Element Six, ABN800, USA) was used as a reinforcement. The weights of the compositions of each sample are listed in Table 1.
The samples were homogenized using an ultrasonic probe sonicator (Model VC 750, Sonics, 300 Johnny Bench Dr., Oklahoma City, OK, 73104, USA), using ethanol as the mixing medium. Next, ethanol was evaporated by heating the samples in an oven at 80° C. for 24 h. Finally, the powder mixtures were consolidated using the SPS apparatus (FCT System, HP D5, Germany), as depicted in
To facilitate the removal of the sample from the die and avoid the wear of the punches, a graphite sheet (thickness: 0.35 mm) was inserted between the graphite die and the powders. Additionally, the die was covered with a graphite blanket during sintering to minimize heat loss. The sintering temperature was measured using a pyrometer placed near the sample. To remove the graphite sheet and obtain a clean surface, the sintered samples were first ground using 60-grit SiC paper, followed by grinding on a diamond disk. The samples were ground and polished using an AutoMet 300 Buehler grinding machine for mechanical and microstructural investigations. Grinding was performed using diamond wheels with grit sizes ranging from 74 to 10 μm. Subsequently, the samples were polished using alumina (200 nm) suspension to attain a 0.25 μm surface finish. Following SPS and grinding, the densities of the sintered samples were measured via Archimedes' method using density determination equipment (Mettler Toledo), with deionized water as the immersion medium. A nanoindenter (iMicro, Nanomechanics, Oak Ridge, TN, USA) with a three-sided Berkovich tip was used to measure the hardness and elastic modulus. A maximum load of 100 mN was applied during the nanoindentation tests. The reported density, hardness, and elastic modulus values are the average of nine measurement values. To identify the phases, present in the sintered samples, a Rigaku MiniFlex X-ray diffractometer (manufactured by Rigaku, 3 Chome-9-12 Matsubaracho, Akishima, Tokyo 196-8666, Japan) was used with Cu Kα1 radiation (γ=0.15416 nm); it was operated at a tube current of 10 mA and an accelerating voltage of 30 kV. A field-emission scanning electron microscopy (FESEM) system (Lyra3, manufactured by Tescan Brno, Czech Republic) equipped with energy-dispersive X-ray spectroscopy (EDX) silicon drift detector (X-MaxN, Oxford Instruments, Tubney Wood, Abingdon, Oxfordshire, OX13 5QX, United Kingdom) operated at an accelerating voltage of 20 kV was used to characterize the microstructures of the sintered samples and powders. Electrochemical characterization was performed using an electrochemical cell with a three-electrode configuration. Herein, graphite was used as the counter electrode, and Ag/AgCl (sat. KCl) electrode was employed as a reference coupled with a potentiostat (1000E, Gamry, 734 Louis Dr, Warminster, Pennsylvania, 18974, United States). Pure Al and Al-cBN composite electrodes were used as the working electrodes. Each specimen was prepared for electrochemical measurements by soldering a copper wire to one end and then cold-mounted in resin. The samples were dried in the open air for 24 h at room temperature (25±1° C.). Before executing the test, the exposed area was ground using P1000 grit emery paper. The electrode was cleaned with deionized water and dried in dry air. The exposed surface area of each specimen was 1.12 cm2. Electrochemical analysis was performed in a 3.5 wt. % NaCl electrolyte at room temperature (25±1° C.). The open-circuit potential (OCP) analysis was performed for 1 h. Electrochemical impedance spectroscopy (EIS) tests were performed at the corrosion potential (EOCP) and a frequency range of 100 kHz to 0.01 Hz with a potential perturbation of 5 mV (rms) at 0 V vs. OCP. For cyclic potentiodynamic polarization (CPP) analysis, the potential was first forward scanned from −0.3 to +1.5 V against OCP at the scan rate of 2.5 mV/s. After that, the potential was reversed in the opposite direction from +1.5 to −0.3 V for the back scan at the same scan rate to complete the test.
The X-ray diffraction (XRD) patterns of pure Al and cBN powders, as depicted in
Referring to
The densification of the Al-cBN composite decreased as the reinforcement size increased due to the difference in consolidation and the presence of voids at the interface. Composites with finer particles have a relatively well-consolidated and denser microstructure, owing to the fine voids and the excess number of particles in the metallic matrix (maintaining a constant weight or volume percent of reinforcement). This result agrees with the FESEM micrographs (as depicted in
The hardness and elastic modulus increased with the addition of increased number of particles (i.e., finer reinforcement), imparting the strengthening effect to the metallic matrix. According to
cBN is known for its properties (similar to those of a diamond), such as high hardness, oxidation resistance, high thermal conductivity, and chemical inertness [McKie, A., et al., Mechanical properties of cBN-Al composite materials. Ceramics International, 2011. 37(1): p. 1-8; and Zhao, W., et al., Tribological performances of epoxy resin composite coatings using hexagonal boron nitride and cubic boron nitride nanoparticles as additives. Chemical Physics Letters, 2019. 732: p. 136646, each of which is incorporated herein by reference in its entirety]. The OCPs were recorded for pure Al and its composites with different particle sizes of cBN (20, 40, and 60 μm) in a 3.5 wt. % NaCl solution for 1 h. Referring to
The development of galvanic interactions between the cBN reinforcement particles and the Al matrix is an important factor that accelerates corrosion. In the schematic graph shown in
EIS measurements were performed to study the electrochemical behavior of cBN on the Al matrix toward pitting corrosion. The impedance response of Al-cBN composite in 3.5 wt. % NaCl is presented in the Nyquist plot in
An electrical equivalent circuit (EEC) is shown in
Generally, the value of Rp is lower for composite materials and increases as the percentage of reinforcement increases because of the formation of phase (such as carbide or intermetallic) at the matrix and reinforcement interface. The Rs were calculated from Nyquist plots for pure Al and Al-cBN composites. The values are listed in Table 2, which demonstrates that the cBN addition to the Al matrix increases the Rs to a certain level, which emphasizes good corrosion resistance properties. Moreover, in a corrosive environment, the cBN addition results in higher Rct values and lower CPE values [Kamel, M., et al., Electrodeposition of Ni—Co/nano Al2O3 composite coating on low carbon steel and its characterization. Int. J. Electrochem. Sci, 2020. 15: p. 6343-6358, which is incorporated herein by reference in its entirety].
Compared to the Nyquist plot, the Bode plot has the advantage of obtaining valuable information owing to its simultaneous analysis of impedance (Z) and phase angle (θ) with respect to frequency (f).
The corrosion potential (Ecorr), corrosion current density (icorr), pitting potential (Epit), corrosion rate (CR), and Tafel slopes (βa and βc) were obtained from the CPP curves. The specimens containing cBN particles show a more negative Ecorr, as listed in Table 3A and Table 3B, which further indicates the thermodynamic instability of the material in a corrosive environment with a high CR [Wang, X., et al., Corrosion behavior of Al2O3-reinforced graphene encapsulated Al composite coating fabricated by low pressure cold spraying. Surface and Coatings Technology, 2020. 386: p. 125486, which is incorporated herein by reference in its entirety]. However, the CR of Al-cBN composite with a particle size of 20 m is lower than that of pure Al. The Epit value became slightly negative by adding cBN particles into the Al matrix.
In cyclic polarization studies, when scanning toward positive potentials, a stable pit generally starts to grow when the potential reaches Epit where the current increases sharply from the passive current level. Both pure Al and cBN-based Al composite materials exhibit a positive hysteresis loop, which indicates the difficulty of preventing the initiation of pits. A larger positive hysteresis shows greater difficulty reestablishing the damaged layer [Liu, Y., et al., Understanding pitting corrosion behavior of AZ91 alloy and its MAO coating in 3.5% NaCl solution by cyclic potentiodynamic polarization. Journal of Magnesium and Alloys, 2022. 10(5): p. 1368-1380, which is incorporated herein by reference in its entirety]. The largest positive hysteresis loop is determined for the 40 m Al-cBN composite. The difference between the Epit and Ecorr values provides beneficial information regarding the tendency of the material to develop pits. A more significant difference between these values shows that the material is more resistant to pitting corrosion and further demonstrates the protection level of the material in a corrosive environment [Pardo, A., et al., Influence of reinforcement proportion and matrix composition on pitting corrosion behaviour of cast aluminium matrix composites (A3xx. x/SiCp). Corrosion Science, 2005. 47(7): p. 1750-1764, which is incorporated herein by reference in its entirety].
A favorable combination of properties is obtained for the composite with the cBN particle size of 20 μm, exhibiting densification, elastic modulus, and hardness values of 98.1% (2.65 g/cm3 density), 76.1 GPa, and 1.78 GPa, respectively, along with the lowest corrosion rate (4.533 mpy) at room temperature (Table 4). Additionally, the above observations show that a high degree of consolidation was achieved using fine-sized cBN particles with a constant weight (10 wt. % cBN and 90 wt. % Al) and volume percentage (12 vol. % cBN and 88 vol. % Al). Furthermore, mechanical and electrochemical properties improvements are expected to be beneficial for wear-resistant composite and lightweight applications (in the ground transportation industry), such as diesel engine piston crowns, connecting rods, and other components with optimal weight and cost efficiency [Chawla, N. and K. Chawla, Metal-matrix composites in ground transportation. JoM, 2006. 58(11): p. 67-70, which is incorporated herein by reference in its entirety]. Therefore, the as-developed Al-MMCs can endure high mechanical loads with good electrochemical resistance and save weight for potential automotive, aerospace, and other engineering applications [Koli, D. K., G. Agnihotri, and R. Purohit, Advanced aluminium matrix composites: the critical need of automotive and aerospace engineering fields. Materials Today: Proceedings, 2015. 2(4-5): p. 3032-3041, which is incorporated herein by reference in its entirety].
To conclude, Al-cBN composites were developed with different reinforcement particle sizes using SPS at a sintering temperature of 550° C. The microstructure, elastic modulus, density, hardness, and corrosion resistance of the Al-cBN composites were evaluated. With the increase in the cBN particle size, the properties mentioned above degraded, and a favorable combination of properties was obtained for the composite with 20 μm cBN particles. By maintaining a constant weight composition and reducing the particle size (i.e., increased number of particles in the matrix), reinforcement provides better strength and stress drive to the overall matrix, leading to an improvement in the mechanical and electrochemical performance. On the other hand, the presence of larger cBN particles in the Al matrix resulted in a higher corrosion rate due to galvanic interactions between the reinforcement particles and the matrix. Herein, the 20 μm Al-cBN composite exhibited an improved polarization resistance. Additionally, it possessed the lowest corrosion rate and a lower tendency for pit formation in a corrosive environment compared to the other tested samples. Therefore, the Al-cBN composite of the present disclosure exhibits a favorable and promising combination of mechanical and electrochemical properties and significant potential for industrial applications requiring lightweight materials.
Numerous modifications and variations of the present disclosure are possible in light of the above teachings. It is, therefore, to be understood that within the scope of the appended claims, the invention may be practiced otherwise than as specifically described herein.
