Metal-Matrix Composites

Nickel-Titanium-Graphite-based metal matrix composites (MMC) with in situ formed titanium carbide (TiC), as well as graphite (C) reinforcement in the nickel (Ni) metal matrix, were processed using mechanical alloying (MA) and spark plasma sintering (SPS). The objective of this study is to synthesize the Ni-Ti-C composites by altering the carbon to titanium ratio and characterize to study its effects on mechanical and tribological behavior as compared with SPS processed pure nickel. Results indicated that these composites exhibit refined microstructure and the homogeneously distributed titanium carbide reinforcement in the nickel matrix. Moreover, by tailoring the carbon to titanium ratio in these composites, an additional graphitic phase is engineered into the microstructure. The steady-state coefficient of friction is obtained for pure nickel and Ni-Ti-C composites. The Ni-Ti-C composites exhibited increment in microhardness, as well as a significant improvement in the tribological behavior as compared to pure nickel.

In this brief review, I have classified MAX phase-based composites according to connectivity patterns. In type-I composites, MAX phases act as reinforcement in metal, ceramic, or polymer matrix composites to form 3-0 composites. In these composites, metal or ceramic or polymer forms the main matrix and the MAX phases are dispersed in the structure as reinforcements. In type-II composites, MAX phase particulates are bonded via a 3D network of metallic channel which cement the structure to form 3-0 composites. In type-III composites, MAX and metal for interpenetrating network with 3-3 connectivity. In type-IV composites, the MAX phase matrix can be also reinforced with ceramic additives to form composites with 0-3 connectivity. MAX phases can be oriented in different matrices to form 3-0 composites (Type-V). Composites with multiple layers of metal-MAX and metal can be designed with 3-0 connectivity (Type-VI). By reviewing the literature, the manufacturing method and properties of these different types of composites have been summarized. In addition, a case study has been presented to engineer the surface of Ti₃AlC₂ particles by etching. It is hypothesized that these engineered particles can be used for manufacturing next-generation MAX phase-based composites.

This paper presents the results of a recent study on the effectiveness of the stir casting technique using the method of mixed salt route method and the subsequent joining of the in situ titanium diboride particulate reinforced aluminum alloy metal matrix composites using the technique of friction stir butt welding. A bimetallic flame-hardened friction stir welding tool with a threaded titanium probe and having different shoulder geometries were used for this novel research study. The variation in process parameters to include tool shoulder geometry, tool rotational speed, and welding speed does exert an influence on mechanical properties of the welded composite sample to include ultimate tensile strength, elongation, and microhardness. A noticeable change in the grain morphology coupled with refinement and near-uniform redistribution of the reinforcing particulates was observed using the titanium weld probe for all of the experiments. Microstructural characterization studies were conducted using a high-resolution scanning electron microscope and X-ray diffraction analysis. A statistical model and appropriate optimization technique were used to evaluate and/or interpret the mechanical response of the friction-stir welded joint. A substantial improvement in properties of the joint was observed in comparison with the base metal.

The influence of variations in the titanium carbide (TiC) content employed during spark plasma sintering (SPS) of nickel–titanium carbide (Ni-TiC) composites on its microstructure and mechanical properties has been investigated systematically. Mechanical alloying (MA) uses a technique of cold welding and repetitive fracturing of composite powder to make homogenous alloys powder. The SPS consolidates alloy powder into dense samples using joule heating at a lower temperature. Mechanical alloying was performed using a planetary high energy ball mill with 400 rpm and ball to powder ratio 15:1 for 24 h. Bulk Ni-TiC composites (with TiC content varying from 5 to 25 wt.%) consolidated via mechanical alloying followed by SPS at 65 MPa pressure and 900 °C temperature. All consolidated Ni-TiC samples exhibit significant improvement in microhardness, compression strength, and grain size due to the addition of titanium carbide (TiC) particles. The grain size of Ni reduces to approx. 40 nm from approx. 55 nm. The microhardness increases from 294 to 483 HV by increasing the weight percentage of TiC from 5 to 25.

Magnesium alloy-based in-situ processed composite [RZ5/10 wt.% TiB₂] was synthesized using self-propagating high-temperature synthesis route and its tribological behavior was investigated for the purpose of applications in the aerospace industry. The wear behavior of both magnesium alloy (RZ5) and magnesium alloy-based composite [RZ5/10 wt.% TiB₂] was studied using pin-on-disc wear testing apparatus. The wear characteristics were analysed under different loading conditions of 10, 20 and 30 N, and for sliding distance of 1000, 2000 and 3000 m. A significant improvement in the wear resistance was observed by the addition of titanium diboride (TiB₂) reinforcement to the RZ5 magnesium alloy matrix. It is concluded that with an increase in the applied load, the wear loss reveals a noticeable increase with a corresponding decrease in the coefficient of friction. Moreover, with an increase in sliding distance, both wear loss and coefficient of friction were observed to increase. The morphology of the worn surface of the magnesium alloy-based metal matrix composite [RZ5/10 wt.% TiB₂] at the different operating conditions was examined using an optical profilometer and a field emission scanning electron microscope.

We describe the synthesis and optical properties of ligand-modified gold nanoparticles in solution and grown on stainless-steel wool filters. Their efficiency with regard to heavy metal uptake from water found at or near DOE facilities was also tested. Two different sequestration technologies for heavy metals were developed based on the surface functionalization of gold nanoparticles with either citrate or L-cysteine. Citrate-capped gold nanoparticles in solution show a greater heavy metal loading capacity than L-cysteine-functionalized gold nanoparticles. It was also found that the citrate-capped gold nanoparticles have a greater sensitivity for copper (II) than zinc (II) ions. L-cysteine-capped gold nanoparticles are more sensitive toward gradual uptake of zinc (II) ions making them valuable for sensing and sequestration applications. L-cysteine-capped gold nanoparticle stainless-steel wool filters are also efficient at the uptake of heavy metal ions. The nanomaterial-treated stainless-steel wool filters are advantageous because they serve as inactive supports allowing efficient flow of the contaminated water and can be easily replaced after heavy metal uptake. They are also comparable to nanomaterials free in solution with regard to the effectiveness of remediation of contaminated water resources.

The multi-walled carbon nanotubes (CNT) and graphene nanoplatelet (GNP) reinforced nickel matrix nanocomposites (Ni-GNP) have been processed via dry ball milling followed by a spark plasma sintering (SPS) process. The CNT and GNP content in these nanocomposites has been varied from 0.5 to 2 wt/% in order to study their effect on the microstructure and mechanical behavior of these composites. Ni-CNT/GNP powder is milled for six hours to investigate the effect on the microstructure, grain size, and the dispersion of CNT/GNP in the nickel matrix. Ni-CNT/GNP nanocomposites exhibited improvement in microhardness and mechanical performance in comparison with pure nickel. This improvement in Ni-CNT/GNP nanocomposites is primarily attributed to the uniform dispersion of reinforcement within the nickel matrix, refined grain size, and strong nickel CNT/GNP interfacial bonding, which effectively transfers stress during tensile deformation.

Copper–chromium alloys are a class of high-strength high-conductivity copper alloys. However, limited by the copper–chromium (Cu–Cr) phase diagram, the strength of copper–chromium (Cu–Cr) alloys by precipitation-hardening has reached a certain limit. Suitable nanoparticles incorporating into copper–chromium (Cu–Cr) alloys, i.e., nano-treating, are expected to modify the aging behavior and further improve their properties. In this study, copper–chromium (Cu–Cr) alloy containing tungsten (W) nanoparticles was cast. The aging behavior of the nano-treated Cu-Cr and Cu–Cr counterparts is assessed. Tungsten (W) nanoparticles accelerate the precipitation, leading to a significant reduction in the peak aging time. Besides, the microhardness of the nano-treated copper–chromium (Cu–Cr) is increased over Cu–Cr after 45-min aging. Cold rolling can further enhance the microhardness of the nano-treated copper–chromium (Cu–Cr). Moreover, the nano-treated sample exhibits a much improved thermal stability. Thus, nano-treating the copper–chromium (Cu–Cr) alloy by tungsten (W) nanoparticles is promising to break the limits of current copper–chromium (Cu–Cr) alloys.

Considerable efforts have been made to manufacture metal matrix composites (MMCs) in the solid state to enhance the mechanical properties by adding various volume fractions of alumina powder to achieve higher homogeneity of ceramic particles in the matrix. Here, we present the fine scale microstructure, interfacial characteristics and mechanical properties of the copper-alumina composite. The fine scale microstructure was characterized by transmission electron microscopy (TEM) to study the nature of oxide precipitates formed during internal oxidation of copper–aluminum alloy. We used nanoindentation to obtain the hardness and modulus of the composite and demonstrated that the enhancement of strength mostly stems from the nanocrystalline oxide particles. Furthermore, we observed that the elastic modulus of the composite is 15% greater that of the commercially pure copper. The improvement in modulus is shown to be associated with the formation of nanocrystalline coper oxide (Cu₂O) or copper–oxygen (Cu–O) clusters in copper matrix.

The application of graphene nanoplatelets (GNPs) and multi-walled carbon nanotubes (MWCNTs) as a thin interlayer between the faying surfaces of carbon steel (AISI-1008) joints and its effect on the microstructure and mechanical properties of the welded joints has been reported here. The resistance spot welding (RSW) technique has been utilised to entrap the nanoparticles in the weld nugget. Single lap shear tests were performed to get an insight into the weld strength of the bare, graphene nanoplatelets, and multi-walled carbon nanotubes interlayered samples, and ~49% and ~45% enhancements, respectively, were reported. Fracture surface morphology depicted that a combination of both brittle and ductile fractures was the major causes of failure. A detailed microstructural study was performed using light microscopy, scanning electron microscopy, transmission electron microscopy, X-ray diffraction, and Raman spectroscopy for both cases. The increase in the weld strength and hardness of the nanocomposite formed at the weld nugget was attributed to grain refinement and numerous strengthening mechanisms.

In this research paper, the physical properties, mechanical properties and microstructural characteristics of 3 mol% Yttria-Stabilized-Zirconia (3YSZ) matrix reinforced with 10 volume percent of alumina (Al₂O₃) are presented and briefly discussed. The composites were developed using the techniques of conventional sintering [1600 ℃, 5 ℃/min and held for 6 h] and microwave sintering [1600 ℃, 25 ℃/min and held for 1 h] under pressure-less condition. The sintered powders were subsequently compacted using a uniaxial cold isostatic press at a pressure of 200 MPa. The relative density, average grain size, microhardness and fracture toughness of both the conventional sintered samples and microwave sintered samples were determined and found to be [conventional sintered: density: 98.16 ± 0.15, grain size: 600 nm, microhardness: 16.81 ± 0.7 GPa and fracture toughness: 4.9 MPa m^0.5) and [microwave sintered density:99.29 ± 0.10, grain size: 421 nm, microhardness: 19.65 ± 0.5 GPa and fracture toughness: 5.2 MPa m^0.5], while the thermal conductivity was determined to be 2.3 W/mK for the conventional sintered sample and 2.6 W/mK for the microwave sintered sample. A near uniform microstructure was observed for both the conventional sintered and microwave sintered samples. The microwave sintered samples were observed to have superior properties when compared one-on-one with the conventional sintered counterpart. This study provides useful information specific to the development of a material for use as a thermal barrier coating and for its selection and use in dental applications.

A high performance infrared (HPIR) system was developed and demonstrated for the infrared absorption analysis of uranium-235 and uranium-238 isotopes in uranium hexafluoride gas samples. The method takes advantage of the recent commercial availability of quantum cascade lasers (QCL) and has required the use of advanced statistical data analysis, as well as materials selection due to the chemical reactivity of uranium hexafluoride gas. Sweeping the QCL over the spectral range and sampling via a high-rate analog-to-digital converter provided 0.0005 cm⁻¹ spectral resolution, allowing for high-precision measurements of the isotopic peak shift. A data analysis method was developed using principal component analysis to predict the isotope weight percent content of uranium-235. The HPIR precision, accuracy, and error were evaluated for a wide range of isotopic ratio samples (0.287–93.7 weight percent uranium-235), and the results were compared to the International Target Values (ITVs) set forth by the International Atomic Energy Agency (IAEA) for nondestructive and destructive analytical techniques used in safeguards verification under the Treaty on the Non-proliferation of Nuclear Weapons. The method meets or surpasses the IAEA ITVs for nondestructive analysis of samples with isotopic content of depleted to highly enriched. The results also demonstrated the capability of the HPIR system to correctly predict the uranium-235 weight percent content of a mislabeled sample whose isotopic distribution was validated by mass spectroscopic measurements. The HPIR measurement is nondestructive and, thus, allows for confirmatory analyses of the exact sample at a designated IAEA laboratory if higher resolution or a certified analysis is needed.

Composite metal foam (CMF) is a novel lightweight metal matrix composite material with lightweight, high strength to density ratio and high energy absorption capabilities. The material can be made out of many different metals, alloys, and combinations, e.g. aluminum, steel, titanium, etc. For example, it can be made 100% out of steel, but, due to its porosities, it will weigh as light as aluminum. CMF is made of closely packed metallic hollow spheres with a metallic matrix that fills the empty spaces in between spheres. In every combination of the spheres and matrix materials, the final product weight will be ~30–35% of the weight of the parent material; the rest would be the air trapped inside its porosities. In this study, a scaled-down version of the torch fire experiments specified in 49 Code of Federal Regulation (CFR) Part 179, Appendix B was developed to provide initial data on evaluating the thermal protection performance of steel-steel composite metal foam (S-S CMF) in the torch fire conditions. S-S CMF panels of 30 × 30 cm dimensions are manufactured and tested to evaluate their survivability when exposed to a 30-minute torch fire condition of high velocity jet fire with a gas temperature of 1204°C in accordance with 49 CFR Part 179. Testing was performed to characterize the jet burner gas temperature and velocity flow field, and a calibration fire test was conducted using steel only as required by the test specification. The assembly was tested in duplicate in two consecutive simulated torch fire exposures as specified in 49 CFR Part 179, Appendix B. Based on the experimental results, a 15 mm thick steel-steel composite metal foam tested as novel insulation system met the acceptance criteria for the simulated torch fire testing and is expected to pass when tested at a full size of 122 × 122 cm dimensions. The main factor for fire resistance and thermal protection performance of S-S CMF is attributed to the large air content in the material.

The primary objective of this paper is to present and discuss the appropriateness of using the stir casting process as a viable approach for the fabrication of an in situ aluminum alloy-based metal matrix composite (MMC). The exothermic chemical reaction that occurs between the K₂TiF₆ and KBF₄ salts is responsible for the formation and presence of the reinforcing titanium diboride (TiB₂) particles in the melted aluminum–copper alloy. Presence of these particles exerts an influence on hardness, tensile strength, and even ductility of the engineered composite material. With the help of X-ray diffraction (XRD) and field emission scanning electron microscopy (FE-SEM), both the chosen aluminum alloy and the synthesized aluminum alloy composite material were characterized to facilitate a better understanding of the intrinsic morphological details and/or intrinsic features to include the size, morphology, and distribution of the TiB₂ reinforcement in the aluminum alloy metal matrix. For purposes of enhancing the mechanical properties of the chosen Al-4.5 pct. Cu alloy and the Al-4.5 wt.pct Cu/xTiB₂ composite a T6 heat treatment sequence was used and test results of the heat treated alloy compared with results obtained for the as-cast counterpart.

An assessment of nucleation and growth mechanism of tin and cobalt over graphene oxide (GO) substrate is performed using the cyclic voltammetry (CV) and chronoamperometry (CA) techniques. The CV tests revealed that deposition of tin and cobalt on GO is an irreversible and diffusion-controlled process. From the CA tests, it was deduced that the deposition process involved the formation of adatom layer at the substrate-electrolyte interface prior to nucleation and growth. Proton reduction reaction over the deposited metal nuclei also took place simultaneously with three-dimensional diffusion-controlled nucleation and growth. While the deposition mechanism for both metals exhibits similarity, the kinetic parameters like nucleation rate constant (A) and number density of active nucleation sites (N₀) varied tremendously for both metals. Application of classical and atomistic theory of nucleation revealed that the Gibb’s free energy required for the formation of critical nucleus for Sn and Co deposition was comparable to room temperature thermal energy and the size of supercritical nucleus is one atom. This meant that under the experimental conditions of deposition, every Sn and Co atom that deposited over GO is a supercritical nucleus that can grow irreversibly.

An analytical technique for measuring both total protium (H) and total deuterium (D) in a gas mixture containing protium (H₂), deuterium (D₂), and hydrogen-deuterium (HD) has been developed. This technique uses a micro-gas chromatograph (uGC) with two molecular sieve columns each with thermal conductivity detectors. The carrier gas for one column is deuterium and the second column uses protium as the carrier gas. Laboratory tests have shown that, when used in this configuration, the micro-gas chromatograph can measure both total protium and total deuterium each with a detection and quantification limit of less than 20 ppm. This is a low-cost technology that can be used to provide rapid results (less than 1 min), that are comparable with analytical results from very expensive, high resolution low mass, magnetic sector mass spectrometers.

Multifunctional iron oxide–gold composite nanostructures with tailored “hot-spot” nano-gap junctions have been produced via a multi-seed-mediated approach and investigated for analyte detection. Tunable nano-gap “hotspot” junctions based on gold nanospheres were rationally created on iron oxide surface and evaluated for surface-enhanced Raman scattering (SERS) enhancement studies for a model reporter analyte, 4-mercaptophenol. Surface-enhanced Raman scattering studies show a three-time enhancement effect for composite gold–iron oxide nanoparticles when compared with gold nanostructures. These enhancements are attributed to the presence of the “hot-spot” junctions and nano-gaps obtained from both: (a) multi-seed-mediated approach that generates larger decoration of iron oxide with plasmonic nanoparticles and (b) aggregated assemblies formed due to the key magnetic iron oxide nanostructures.