Fabrication and Mechanical Properties of Magnesium Alloy Composites Reinforced with TiC and Ti2AlC Particles

Herein we report on the fabrication and mechanical properties of Mg composites fabricated by pressureless melt infiltration of Mg and Mg alloys into porous preforms of TiC and Ti2AlC. The latter is a member of the MAX phases - viz. layered machinable ternary carbides and nitrides - some of which are relatively light and stiff. In this study, pure Mg and three, commercially available, aluminum-containing Mg alloys - AZ31, AZ61 and AZ91 - were used as matrices at a loading of ~ 50 vol.%. For the most part, increasing the Al content enhanced the elastic moduli, Vickers hardness values and yield and ultimate compressive strengths. Reducing the particle sizes of the TiC and Tisub>2AlC particulate reinforcements also had a large impact on the mechanical properties. At 1028±5 MPa, the ultimate compressive strength of a TiC-AZ61 composite, in which the TiC particle size distribution is Lorentzian and centered at, dc = 0.41±0.01 µm, was ~ 40% higher than that of the same composite with coarser TiC particles with bimodal size distributions centered around dc=1.6±0.1 µm, and 5.8±0.3 µm. In addition, the elastic modulus and Vickers hardness of the former composite were measured to be 174±5 GPa and 3.4±0.3 GPa, respectively. For the Ti2AlC reinforced composites, the best properties were obtained when AZ61 was reinforced with Ti2AlC particles with dc = 0.51±0.01 µm. The enhancements in elastic and mechanical properties are attributed to finer grained Mg-matrices, the presence of Al in the matrices which enhances the wetting of TiC and Ti2AlC by Mg to create a strong interface and finer reinforcement particle sizes. The latter two attributes, in turnlead to better mechanical interlocking. For the composites studied herein better elastic and mechanical properties, were obtained at the expense of damping. The TiC-reinforced Mg matrix composites despite their high mechanical properties, have very small energy dissipation capabilities. However, by using Ti2AlC, which inherently dissipates mechanical energy, it is possible to achieve higher damping while simultaneously enhancing the mechanical properties almost to the same levels as for the TiC reinforced composites. Using Mg alloys instead of pure Mg and reducing the reinforcement particle sizes also reduced the damping capabilities of these composites. There is a threshold stress below which the damping capacities of the Ti2AlC reinforced composites are comparable to those of their TiC reinforced counterparts. This was ascribed to the negligible damping of Ti2AlC below the threshold stress ( ~ 200 MPa). The Ti2AlC composites are slightly lighter and can be fabricated at lower temperature than comparable TiC composites; the former are also readily machinable but more expensive.Ph.D., Materials Science and Engineering -- Drexel University, 201

Highly Stable Nanolamellar MXene-derived Carbides by Phase Transformation of Ti3C2Tx and Mo2TiC2Tx MXenes

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Temperature-dependent mechanical properties of Tin+1CnO2 (n = 1, 2) MXene monolayers: a first-principles study

Two-dimensional (2D) transition metal carbides, carbonitrides, and nitrides (named as MXenes) have become of the fastest growing family of 2D materials in terms of compositions and their applications in different areas. One of the least explored properties of MXenes is their mechanical properties. While the basic elastic properties of MXenes have been studied by first-principles, the effects of temperature on the elastic properties have never been explored. In this study, we investigate temperature-dependent structural and mechanical properties of the titanium-containing MXenes (Tin+1CnO2 (n = 1, 2)) based on the first-principles calculations combined with quasi-harmonic approximation. The effective Young's modulus of a single layer of Ti2CO2 and Ti3C2O2 is calculated to be 565 and 482 GPa, respectively, at 0 K. By increasing temperature to 1000 K, Young's moduli of Ti2CO2 and Ti3C2O2 decrease to 469 GPa and 442 GPa, respectively, which indicates a larger reduction in stiffness in thinner MXenes at higher temperatures. Our calculations of the temperature-dependent bond strengths within MXenes showed that titanium and carbon atoms in Ti3C2O2 form stronger bonds than Ti2CO2 and atomic bonds in Ti2CO2 lose their stiffness more than Ti3C2O2 with increasing temperatures. The Debye temperature of these monolayers is also calculated to provide a comparison of the thermal conductivity between these monolayers, in which the results show that the Ti3C2O2 has a higher thermal conductivity than Ti2CO2. Our calculated electronic properties results of the monolayers are also shown that the electrical conductivity of the monolayers would not change with temperature. Our study extends MXenes applications to high-temperature applications, such as structural composite components and aerospace coatings

Nanoscale MXene Interlayer and Substrate Adhesion for Lubrication: A Density Functional Theory Study

Understanding the interlayer interaction at the nanoscale in two-dimensional (2D) transition metal carbides and nitrides (MXenes) is important to improve their exfoliation/delamination process and application in (nano)-tribology. The layer-substrate interaction is also essential in (nano)-tribology as effective solid lubricants should be resistant against peeling-off during rubbing. Previous computational studies considered MXenes' interlayer coupling with oversimplified, homogeneous terminations while neglecting the interaction with underlying substrates. In our study, Ti-based MXenes with both homogeneous and mixed terminations are modeled using density functional theory (DFT). An ad hoc modified dispersion correction scheme is used, capable of reproducing the results obtained from a higher level of theory. The nature of the interlayer interactions, comprising van der Waals, dipole-dipole, and hydrogen bonding, is discussed along with the effects of MXene sheet's thickness and C/N ratio. Our results demonstrate that terminations play a major role in regulating MXenes' interlayer and substrate adhesion to iron and iron oxide and, therefore, lubrication, which is also affected by an external load. Using graphene and MoS2 as established references, we verify that MXenes' tribological performance as solid lubricants can be significantly improved by avoiding -OH and -F terminations, which can be done by controlling terminations via post-synthesis processing

2D metal carbides and nitrides (MXenes) for energy storage

The family of 2D transition metal carbides, carbonitrides and nitrides (collectively referred to as MXenes) has expanded rapidly since the discovery of Ti3C2 in 2011. The materials reported so far always have surface terminations, such as hydroxyl, oxygen or fluorine, which impart hydrophilicity to their surfaces. About 20 different MXenes have been synthesized, and the structures and properties of dozens more have been theoretically predicted. The availability of solid solutions, the control of surface terminations and a recent discovery of multi-transition-metal layered MXenes offer the potential for synthesis of many new structures. The versatile chemistry of MXenes allows the tuning of properties for applications including energy storage, electromagnetic interference shielding, reinforcement for composites, water purification, gas- and biosensors, lubrication, and photo-, electro- and chemical catalysis. Attractive electronic, optical, plasmonic and thermoelectric properties have also been shown. In this Review, we present the synthesis, structure and properties of MXenes, as well as their energy storage and related applications, and an outlook for future research

2D MXenes: Tunable Mechanical and Tribological Properties

2D transition metal carbides, nitrides, and carbonitrides, known as MXenes, were discovered in 2011 and have grown to prominence in energy storage, catalysis, electromagnetic interference shielding, wireless communications, electronic, sensors, and environmental and biomedical applications. In addition to their high electrical conductivity and electrochemically active behavior, MXenes' mechanical properties, flexibility, and strong adhesion properties play crucial roles in almost all of these growing applications. Although these properties prove to be critical in MXenes' impressive performance, the mechanical and tribological understanding of MXenes, as well as their relation to the synthesis process, is yet to be fully explored. Here, a fundamental overview of MXenes' mechanical and tribological properties is provided and the effects of MXenes' compositions, synthesis, and processing steps on these properties are discussed. Additionally, a critical perspective of the compositional control of MXenes for innovative structural, low-friction, and low-wear performance in current and upcoming applications of MXenes is provided. It is established here that the fundamental understanding of MXenes' mechanical and tribological behavior is essential for their quickly growing applications

Perspectives of 2D MXene Tribology

The Large and Rapidly Growing Family of 2D Early Transition Metal Carbides, Nitrides, and Carbonitrides (MXenes) Raises Significant Interest in the Materials Science and Chemistry of Materials Communities. Discovered a Little More Than a Decade Ago, MXenes Have Already Demonstrated Outstanding Potential in Various Applications Ranging from Energy Storage to Biology and Medicine. the Past Two Years Have Witnessed Increased Experimental and Theoretical Efforts toward Studying MXenes\u27 Mechanical and Tribological Properties When Used as Lubricant Additives, Reinforcement Phases in Composites, or Solid Lubricant Coatings. Although Research on the Understanding of the Friction and Wear Performance of MXenes under Dry and Lubricated Conditions is Still in its Early Stages, It Has Experienced Rapid Growth Due to the Excellent Mechanical Properties and Chemical Reactivities Offered by MXenes that Make Them Adaptable to Being Combined with Other Materials, Thus Boosting their Tribological Performance. in This Perspective, the Most Promising Results in the Area of MXene Tribology Are Summarized, Future Important Problems to Be Pursued Further Are Outlined, and Methodological Recommendations that Could Be Useful for Experts as Well as Newcomers to MXenes Research, in Particular, to the Emerging Area of MXene Tribology, Are Provided

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2D transition metal carbides (MXenes) in metal and ceramic matrix composites

Two-dimensional transition metal carbides, nitrides, and carbonitrides (known as MXenes) have evolved as competitive materials and fillers for developing composites and hybrids for applications ranging from catalysis, energy storage, selective ion filtration, electromagnetic wave attenuation, and electronic/piezoelectric behavior. MXenes’ incorporation into metal matrix and ceramic matrix composites is a growing field with significant potential due to their impressive mechanical, electrical, and chemical behavior. With about 50 synthesized MXene compositions, the degree of control over their composition and structure paired with their high-temperature stability is unique in the field of 2D materials. As a result, MXenes offer a new avenue for application driven design of functional and structural composites with tailorable mechanical, electrical, and thermochemical properties. In this article, we review recent developments for use of MXenes in metal and ceramic composites and provide an outlook for future research in this field

Elastic properties of 2D Ti3C2Tx MXene monolayers and bilayers

Two-dimensional (2D) transition metal carbides and nitrides, known as MXenes, are a large class of materials that are finding numerous applications ranging from energy storage and electromagnetic interference shielding to water purification and antibacterial coatings. Yet, despite the fact thatmore than 20 different MXenes have been synthesized, the mechanical properties of a MXene monolayer have not been experimentally studied. We measured the elastic properties of monolayers and bilayers of the most important MXene material to date, Ti3C2Tx (Tx stands for surface termination).We developed amethod for preparingwell-strainedmembranes of Ti3C2Tx monolayers and bilayers, and performed their nanoindentation with the tip of an atomic force microscope to record the force-displacement curves. The effective Young’s modulus of a single layer of Ti3C2Tx was found to be 0.33 ± 0.03 TPa, which is the highest among the mean values reported in nanoindentation experiments for other solution-processed 2D materials, including graphene oxide. This work opens a pathway for investigating the mechanical properties of monolayers and bilayers of other MXenes and extends the already broad range of MXenes’ applications to structural composites, protective coatings, nanoresonators, and membranes that require materials with exceptional mechanical properties