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

Abstract

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.

Keywords: Ceramics; Composites; High-temperature; MXenes; Mechanical; Metals; Nanomaterials.

Fig. 1

2D MXenes wide array of possible compositions, and impressive mechanical, electrical, and high-temperature properties. a MXenes can be comprised of transition metals of groups 3–6 of the periodic table with carbon or nitrogen and are surrounded by mixed surface groups, of which are commonly –O, –F, –(OH), and –Cl. b MXenes have shown the highest mechanical stiffness of all solution processable nanomaterials [9, 21]. c Ti₃C₂T_x MXenes have shown exceptionally high electrical conductivity depending on the synthesis and fabrication techniques [41]. d Ti₃C₂T_x MXenes have shown phase transitions to its highly stable TiC_y form at temperatures ranging from 700–1000 °C [40]

Fig. 2

MXenes metal matrix composites, processing and improved mechanical and tribological properties. a A schematic representing the MXene single-flake assembly and mixture with metal particles followed by densification to fabricate bulk metal matrix composite. b Strengthening efficiency of different nanoparticles and nanoflakes addition into Al matrices showing few-layer delaminated Ti₃C₂T_x flakes can improve the tensile strength over its pure Al matrix with a lower volume fraction than that of other common nano-reinforcement materials [44]. c MXenes can also be included into lower melting point metals in their molten phase, where sonication assists the homogenous dispersion of MXene flakes into the molten metal [48]. d Ti₃C₂T_x MXene flakes in a Cu matrix have shown a reduction of the coefficient of friction of two times over a pure Cu matrix [49]

Fig. 3

MXenes ceramic matrix composites using matrices such as Al₂O₃ and ZnO. a XRD patterns of Al₂O₃ and Al₂O₃—2 wt% Ti₃C₂T_x powder mixtures before sintering [58]. b SEM micrographs of Al₂O₃—2 wt%Ti₃C₂T_x composite prepared by sintering at 1500 °C [58]. c High-resolution TEM image of Al₂O₃—2wt% Ti₃C₂T_x with selected area electron diffraction (SAED) of the sintered MXene indicating TiC formation. Bottom inset shows the presence of graphitic carbon at the grain boundaries of the resulting TiC and alumina matrix [59]. d Schematic illustration showing (d) the grain boundary of ZnO–Ti₃C₂T_x nanocomposites [60] and (e) the fabrication process via cold sintering [60]. f, g SEM images of cols sintered pure ZnO and ZnO—1wt% Ti₃C₂T_x composite [60]. h TEM image of a cold sintered ZnO—1wt%Ti₃C₂T_x show the presence of MXene 2D flakes at ZnO grain boundaries. Top inset shows energy dispersive x-ray spectroscopy of ZnO—1wt%Ti₃C₂T_x where Zn is shown in red and Ti is shown in cyan indicating MXenes at the grain boundaries [60]. i Densities and relative densities of ZnO–Ti₃C₂T_x nanocomposites cold sintered at 300 °C for 1 h [60]

Fig. 4

Future applications of MXene metal and ceramic composites. a, b MXenes can be utilized as reinforcement materials in single-flake form (a) or be converted to lamellar TiC_y in metals under high-temperature applications (b). c, d Some of these high-temperature applications may require strong mechanical properties such as aircraft turbines (c) or low friction applications such as automotive engine cylinders (d). e, f MXenes’ 2D nature can be utilized to wrap ceramic grains (e) to undergo phase transformation to strong and conductive chemically bonded intergranular reinforcement materials (f). g, h The application of MXenes toward strong-intergranular bonding can provide use for MXenes as ultra-high temperature ceramic materials for aerospace re-entry cones (g) or rocket nozzles (h). In panels a, b, e, and f schematics, the size of MXene flakes versus the matrix grains are not proportional for the sake of visual clarity