MAX Phase Research Articles

Synthesis, microstructure and micro-mechanical characterization of metal (Nb, Ti) – MAX phase (Ti2AlC) nanolaminates

We utilize elevated temperature physical vapor deposition (PVD) techniques to design metal/MAX multilayered nanocomposite thin films with alternating nanoscale metallic (Nb, Ti) and MAX phase (Ti2AlC) layer thicknesses. These metal/MAX nanolaminate architectures attempt to exploit a unique hierarchical topology – as interfaces between the layers are expected to be in direct competition with the internal interfaces within the MAX layers, to drive their tunable macroscopic mechanical behavior. Two metal/MAX nanolaminates – Nb/Ti2AlC and Ti/Ti2AlC – were deposited. The Nb/Ti2AlC metal/MAX system showed highly diffused layer interfaces with distinct Ti – rich and Nb–Al – rich layers, with the presence of MAX phase alongside TiC and other Ti–Al and Nb–Al intermetallic phases. The Nb/Ti2AlC system possessed a layered architecture, though the MAX phases were not found to be continuously present in each alternating layer. The second Ti/Ti2AlC system showed a non-lamellar nanocomposite microstructure and the formation of mixed Tin+1AlCn phases (a mix of n = 1, 2), and no indication of layering. Diffusion occurring between the metal/MAX layers in both cases, likely due to the elevated temperatures during the deposition process, is speculated as the likely cause of these resultant microstructures. The mechanical properties of both systems were evaluated using micromechanical (nanoindentation and micro-pillar compression) techniques, which demonstrated high strengths for both systems (Nb system: yield and instability strengths of 4.88 ± 0.1 GPa and 5.57 ± 0.03 GPa, Ti system: yield and instability strength of 5.61 ± 0.28 GPa and 6.21 ± 0.25 GPa). This work highlights the promising mechanical properties of metal/MAX multilayered depositions and summarizes the challenges in PVD synthesis of metal/MAX multilayered nanolaminates.

Synthesis of Ti1‐xWx Solid Solution MAX Phases and Derived MXenes for Sodium‐Ion Battery Anodes

AbstractA distinguishing feature of MAX phases and their MXene derivatives is their remarkable chemical diversity. This diversity, coupled with the 2D nature of MXenes, positions them as outstanding candidates for a wide range of electrochemical applications. Chemical disorder introduced by a solid solution can improve electrochemical behavior. Up to now, adding considerable amount of tungsten (W) in MAX phase and MXenes solid solutions, which can enhance electrochemical performance, proved challenging. In this study, the synthesis of M site Ti1‐xWx solid solution MAX phases are reported. The 211‐type (Ti1‐xWx)2AlC exhibits a disordered solid solution, whereas the 312‐type (Ti1‐xWx)3AlC2 displays a near‐ordered structure, resembling o‐MAX, with W atoms preferentially occupying the outer planes. Solid‐solution MXenes, Ti2.4W0.6C2Tz, and Ti1.6W0.4CTz, are synthesized via selective etching of high‐purity MAX powder precursors containing 20% W. These MXenes are evaluated as sodium‐ion battery anodes, with Ti1.6W0.4CTz showing exceptional capacity, outperforming existing multilayer MXene chemistries. This work not only demonstrates the successful integration of W in meaningful quantities into a double transition metal solid solution MAX phase, but also paves the way for the development of cost‐effective MXenes containing W. Such advancements significantly widen their application spectrum by fine‐tuning their physical, electronic, mechanical, electrochemical, and catalytic properties.

First-principles study of electronic, mechanical, and optical properties of M3GaB2 (M = Ti, Hf) MAX phases

Integrating ceramic and metallic properties in MAX phases makes them highly desirable for diverse technological applications. In this study, through first-principles density functional theory (DFT), we investigated the physical properties of two new 312 MAX compounds, M3GaB2 (M = Ti, Hf). Chemical stability is confirmed via formation energy assessment, while mechanical stability is established by determining elastic stiffness constants. A thorough analysis of mechanical behaviors includes bulk modulus, shear modulus, Young's modulus, and hardness parameters. M3GaB2 demonstrates elastic constants and moduli closely aligned with other 312 carbides. Understanding the electronic band structure and density of states (DOS) sheds light on metallic properties, with anisotropy in electrical conductivity clarified through energy dispersion analysis. Investigation of photon interaction with titled compounds, including dielectric constants (real and imaginary parts), refractive index, absorption coefficient, photoconductivity, reflectivity, and energy loss function, has been carried out. The potential of M3GaB2 borides as a coating to reduce solar is evaluated based on the reflectivity spectra. These findings deepen our understanding of material properties and suggest diverse applications for M3GaB2 in various technological domains.

Solid solution of zirconium on the M-site in Ti2AlC MAX phase coatings: Synthesis, structure and mechanical properties

Ti2AlC MAX phase is considered an ideal candidate for surface protective coatings in harsh environments due to its excellent resistance to oxidation and corrosion, yet poor mechanical properties are a key bottleneck for practical applications. In this work, taking the conception of solid solution, high-purity and high-hardness (Ti, Zr)2AlC coatings were synthesized on Ti-6Al-4V substrates using a multiple-target magnetron sputtering technique combined with subsequent annealing. The as-deposited Ti-Zr-Al-C coating was partially crystalline containing TiAlx phase, and MAX phases formed after annealing at 750 °C for 90 min. Comprehensive X-ray diffraction and high-resolution TEM analysis identified the formation of solid solution (Ti0.9Zr0.1)2AlC. The incorporation of Zr reduced the surface roughness and grain size of the coatings due to the increased nucleation sites and the suppressed atomic diffusion. Comparing with pristine Ti2AlC coating, the hardness of the (Ti0.9Zr0.1)2AlC coating was enhanced by 30 % from 12.8 GPa to 16.6 GPa. This enhancement can be ascribed to the synergistic strengthening from solid solution and grain refinement. However, fracture toughness slightly deteriorated in the (Ti0.9Zr0.1)2AlC coating due to the preferential crack path along the refined-grain boundaries.

Process Optimization for the Synthesis of V2AlC MAX Phase to Enhance Sustainable Production

Process Optimization for the Synthesis of V2AlC MAX Phase to Enhance Sustainable Production

Spontaneous growth of Sn whisker on the hot-dipping Al[sbnd]Sn alloy coating on Fe-Cr-B cast steel

Although the MAX phase solid solutions and spontaneous growth of Sn whiskers had been reported widely, the study on the spontaneous growth of whisker at room temperature on the MAB phase was very rare. In our previous work, the periodic layered structure consisted of alternatively arranged Cr-Al-B MAB phase and FeAl3 was formed during the hot-dip aluminizing of Fe-Cr-B cast steel. Herein, the Cr-(Al, Sn)-B MAB phase solid solution was prepared by HDA of Fe-Cr-B cast steel in a AlSn alloy melt and subsequently thermal diffusion treatment. Sn atoms in the Al melt could partially occupy the positions of Al atoms in the Cr-Al-B MAB phase by A-site replacement approach, which resulted in the formation of the Cr-(Al, Sn)-B MAB phase solid solution. Subsequently, spontaneous growth of β-Sn whisker occurred on the Cr-(Al, Sn)-B MAB phase solid solution at room temperature. The original Sn source was the pure Sn phase among the grains of Cr-(Al, Sn)-B MAB phase solid solution. The mass transport pathway for maintaining the spontaneous growth of Sn whiskers was: pure Sn among the grains of Cr-Al-B MAB phase→ Cr-(Al, Sn)-B MAB phase→ SnO2 → Sn whisker. The spontaneous growth of Sn whisker in the air resulted in the deep grooves covered on the surface of whisker, while, growth in the vacuum resulted in the prism structure at the bottom of whisker. The spontaneous growth of Sn whisker could grow from both the bottom and the tip. The findings will expand the family of MAB phase and help well understand the growth mechanism of Sn whisker.

Electromagnetic characterization of MAX phase and MXene in Ti–Al–C ternary system

The present paper set out to investigate the synthesis and electromagnetic characterization of Ti3AlC2 MAX phase and Ti3C2Tx MXene in Ti–Al–C ternary system. In this regard, Ti3AlC2 MAX phase was synthesized using mechanical milling process of TiC, Al, and Ti powder mixtures based on 2TiC–Al–Ti + xAl (x = 0, 0.25, 0.5, 0.75 and 1). The HF acidic etching was also employed to synthesize the Ti3C2Tx MXene. Structural and electromagnetic characterizations of the prepared samples were conducted using X-ray diffraction (XRD), scanning electron microscopy (SEM) and vector network analyzer. The obtained results point to the impossibility of the formation of Ti3AlC2 single-phase structure in stoichiometric system. In other word, development of the Ti3AlC2 single-phase structure is only possible in non-stoichiometric 2TiC–2Al–Ti system. The minimum reflection losses of the prepared Ti3AlC2 MAX phase was estimated to be around −30.73 dB at the matching frequency of 15.25 GHz. The results further revealed that the etching time affects electromagnetic behavior of the MXene. That is, an increase in the etching time brings about a change in the reflection loss (RL) from −24.17 to −5.69 dB within the frequency range of 1–18 GHz.

Synthesis of glucose‐derived MAX phases and investigation on the phase evolution behavior

AbstractThe family of MAX phases and their two‐dimensional derivative MXenes attract significant attention due to their unparalleled properties. Synthesis of MAX phases and MXene from biomass sources is important to expand their biology‐related applications, while it remains a challenge. The present work explores the possibility to synthesize MAX phases and subsequently derive MXenes by using biomass precursor. Ti3AlC2 MAX phase was synthesized by using glucose as the carbon source in molten salt. The conversion behavior from glucose to Ti3AlC2 was investigated, and the conversion rate of carbon from glucose reached to 70.4% by optimizing the reaction conditions. The as‐obtained Ti3AlC2 can be derived into Ti3C2Tx MXene and MXene quantum dots by common chemical treatments, which provides possibility for biomass‐derived nanolaminates applying in biological applications such as biological catalysis, bioinstrumentation, and biological tracking.

Effect of MAX phase Ti2SnC content on microstructure, mechanical properties, and friction behavior of iron-based self-lubricating composites

This work focuses on developing novel iron-based self-lubricating composites reinforced with Ti2SnC MAX phase produced by powder metallurgy. Two amounts of Ti2SnC (5 and 10 vol%) and the addition of 10 vol% graphite were evaluated. The microstructure revealed a partial reaction between the matrix and the Ti2SnC, exhibiting a degree of dissociation in the presence of graphite, leading to the precipitation of carbides. The addition of the MAX phase significantly improved the hardness and compression strength. The dry coefficient of friction was around 0.12 for Fe + 5Ti2SnC + 10Gr, showing a remarkable reduction in wear rate up to 85 % compared to pure iron. The results demonstrate a synergistic effect between the MAX phase and graphite, enhancing tribological performance and wear resistance.

Effect of M-site element on the interaction of M2AlC and Ag and the induced properties of Ag/M2AlC composites

The deintercalation of weakly bonded A element affects the microstructure and properties of MAX phases and their reinforced composites. In this work, the effect of M-site element on the interaction of Al-containing M2AlC (M = V, Cr) phase and Ag, and the induced properties of Ag/M2AlC electrical contact materials (ECMs) were investigated. Though Ag and Al are soluble to each other and can form intermetallics, the variation of M element significantly affected the vacancy formation of Al, and thereby the interfacial reaction of Ag/M2AlC. The difficult formation of Al vacancy in V2AlC contributed to no obvious interfacial reaction in Ag/V2AlC. But the easy deintercalation of Al atoms in Cr2AlC led to their massive replacement by Ag, which generated Ag nano-twins and Cr3C2 with the same crystallographic relationship in one original Cr2AlC, and Cr7C3 and Ag3Al as well. Due to the distinct interactions, the resistivities of Ag/V2AlC and Ag/Cr2AlC increased by roughly 1 and 5 times after sintering, respectively. The low resistivity and proper hardness of the sintered Ag/V2AlC, which were very close to those of the “all-purpose” commercial Ag/CdO, contributed to its superior arc erosion resistance.

Molten fluoride salt-assisted synthesis of titanium carbide (Ti2C) MXene and its application for 2 µm mode-locking in a thulium-doped fiber laser

Titanium carbide (Ti2C), a new two-dimensional material named MXenes, has attracted interest due to its potential applications in numerous fields. Of the many unique characteristics of Ti2C MXene, its nonlinear properties are attractive for optoelectronic applications, specifically for ultrafast laser generation. In this work, a Ti2C MXene was fabricated by etching a MAX phase precursor titanium aluminum carbide (Ti2AlC) using a mixture of lithium fluoride and hydrochloric acid, eliminating the risk of using the harmful hydrofluoric acid. The Ti2C MXene was prepared in solution form and then dropped onto a reduced core diameter of tapered fiber before being used as a saturable absorber (SA). The SA device was inserted into a thulium-doped fiber laser to generate stable mode-locked pulses at a center wavelength of 1951 nm with a pulse width of 1.67 ps. The mode-locked laser was highly stable when tested over time, with peak optical power fluctuations of as little as 0.005 dB measured. The results show that the Ti2C MXene exhibit outstanding performance for ultrafast laser generation.

Investigation of the stability and physical properties of the newly synthesized Ta2AC (A=Co and Ni) MAX phases from first principles

Recently, the MAX phase compounds Ta2NiC and Ta2CoC have been successfully synthesized. In order to theoretically explore their properties, we conducted first-principles calculations based on density functional theory to investigate the structural stability, elastic anisotropy, mechanical behavior, electronic, and thermodynamic properties of these MAX phases. Our results reveal that the calculated structural parameters agree well with the experimental data. The MAX phases under investigation have been observed to exhibit thermodynamic, dynamic, and mechanical stability. Their electrical conductivity primarily originates from the d states of Ta, Ni, and Co at the Fermi level. They are ductile, elastically anisotropic, and demonstrate favorable machinability. The thermal parameters obtained from our calculations were compared with the reported values of a well-established material commonly used in thermal barrier coatings (TBCs). It has been concluded that the newly synthesized MAX phases Ta2NiC and Ta2CoC are potential thermal barrier coating materials.

Enhanced oxidation resistance in Ti3AlC2 via selective self-healing

Ti3AlC2 is anticipated to be used in high temperature fields owing to its excellent dual characteristics of metal and ceramic. However, a critical challenge arises from the inevitable formation of pores within bulk Ti3AlC2 during the sintering process, which are detrimental to its oxidation resistance performance. Herein, the high temperature self-healing and selective oxidation characteristics of Ti3AlC2 are combined, and the selective self-healing of Ti3AlC2 is realized by controlling the pre-oxidation atmosphere, i.e., the pores are effectively filled with α-Al2O3. As a result, the oxidation resistance of Ti3AlC2 was significantly enhanced by 860 times. This method provides a simple and economical way to improve the high-temperature oxidation resistance of Al-containing MAX phase materials represented by Ti3AlC2.

Enhanced properties of multi‐element soluted (Nb0.8Ti0.05Zr0.05Mo0.05M0.05)4AlC3 (M = Hf, Ta) ceramics

AbstractRecently multielements solid solution has shown significant improvement to the mechanical properties of parent MAX phases. Therefore, in this work, five elements with different radii were incorporated to check the effect on properties of MAX phases. (Nb0.8Ti0.05Zr0.05Mo0.05Hf0.05)4AlC3 (MAXHf) and (Nb0.8Ti0.05Zr0.05Mo0.05Ta0.05)4AlC3 (MAXTa) ceramics were successfully synthesized using the spark plasma sintering technique. The microstructure and elemental map analysis results further confirmed that the five transition metals were successfully solid soluted at the M‐sites of the hexagonal M4AlC3 unit cell. The mean elemental compositions for M‐site elements were achieved as Nb0.85Ti0.052Zr0.035Mo0.027Hf0.036 and Nb0.847Ti0.051Zr0.043Mo0.025Ta0.033 for MAXHf and MAXTa ceramics, respectively. The electrical and thermal conductivities of multielement solid solution MAX phases were decreased compared to pure Nb4AlC3. However, Mechanical properties were significantly increased with the solid solution of five transition metals. The fracture toughness, flexural strength, compressive strength and Vickers hardness (10 N) of MAXHf and MAXTa ceramics were achieved as 8.87 MPa m1/2, 448 MPa, 867 MPa, 6.5 GPa and 10.36 MPa m1/2, 557 MPa, 1039 MPa, 8.2 GPa, respectively. The enhanced mechanical properties suggest the effectiveness of the solid solution strengthening effect and provide new opportunities to further tailor the mechanical properties of the MAX phase ceramics.

Regulating the mechanical anisotropy of Mo2AC MAX phases through interlayer control

The structural editing protocol for layered carbides (MAX phases) has been proven to be an effective means of expanding the MAX family. Therefore, this study employs first-principles calculations to manipulate the mechanical anisotropy of Mo2AC MAX phase by regulating the interlayer (A = Fe, Co, Ni, Cu, Zn, Ga, Ge, As, Se). By manipulating the A layer, the anisotropy of Young's modulus can alternate among spindle, funnel, and shuttle shapes, while the shear modulus can similarly transition among these forms. This method can adjust anisotropy indices AU from 0.13 to as high as 3.4 and Ashear from 1.15 % to 25.37 %. Besides, electronic calculations indicate that the interlayers of Mo2AC (A = metal) possess a large number of free electrons along the XY plane, while the electrons in Mo2AsC and Mo2SeC are distributed along the Z-axis. Consequently, Mo2AsC and Mo2SeC exhibit good ductility and are suitable for mechanical processing. This work lays a solid foundation for the manipulation of mechanical anisotropy in practical engineering applications through the regulation of the interlayer in the Mo2AC MAX phase.

Photoexcited charge carrier dynamics and electronic properties of two-dimensional MXene, Nb2CT x

Two-dimensional, 2D, niobium carbide MXene, Nb2CT x , has attracted attention due to its extraordinarily high photothermal conversion efficiency that has applications ranging from medicine, for tumor ablation, to solar energy conversion. Here, we characterize its electronic properties and investigate the ultrafast dynamics of its photoexcitations with a goal of shedding light onto the origins of its unique properties. Through density functional theory, DFT, calculations, we find that Nb2CT x is metallic, with a small but finite DOS at the Fermi level for all experimentally relevant terminations that can be achieved using HF or molten salt etching of the parent MAX phase, including –OH, –O, –F, –Cl, –Br, –I. In agreement with this prediction, THz spectroscopy reveals an intrinsic long-range conductivity of ∼60 Ω−1 cm−1, with significant charge carrier localization and a charge carrier density (∼1020 cm−3) comparable to Mo-based MXenes. Excitation with 800 nm pulses results in a rapid enhancement in photoconductivity, which decays to less than 25% of its peak value within several picoseconds, underlying efficient photothermal conversion. At the same time, a small fraction of photoinjected excess carriers persists for hundreds of picoseconds, and can potentially be utilized in photocatalysis or other energy conversion applications.

Molybdenum gallium carbide coated D-shape fiber for nanosecond dark pulse generation in erbium-doped fiber laser

Molybdenum gallium carbide (Mo2Ga2C), a material belongs to MAX phase group, has garnered significant interest in a wide range of scientific field, including material science, engineering, and laser physics. It is chemically and structurally promising since it exhibits a low shear modulus, superconducting behaviour, and high mechanical stability. Here, we prepared a saturable absorber (SA) based on Mo2Ga2C coated D-shape fiber using solution casting technique. It exhibits outstanding saturable absorption of 7.2%, allowing it to generate dark pulse laser in an erbium-doped fiber laser cavity. We analyzed the laser’s performance and obtained a dark pulse with a pulse energy, peak power, and average output power of 3.9 nJ, 27.5 mW, and 7.3 mW, respectively. This foundational work may introduce a new material as an alternative SA device in fiber laser cavity.

Performance improvement of polyethersulfone membranes with Ti3AlCN MAX phase in the treatment of organic and inorganic pollutants

In this work, the hydrophobic polyethersulfone (PES) membrane was modified by incorporating Ti3AlCN MAX phase. Synthesis of Ti3AlCN MAX phase was performed using the reactive sintering method. The scanning electron microscopy (SEM) images showed a 3D compressed layered morphology for the synthesized MAX phase. The Ti3AlCN MAX phase was added to the casting solution, and the mixed-matrix membranes were fabricated by the non-solvent induced phase inversion method. The performance and antifouling features of bare and modified membranes were explored by pure water flux, flux recovery ratio (FRR), and fouling resistance parameters. Through the modification of membranes by introducing the Ti3AlCN MAX phase, the enhancement of these features was observed, in which the membrane containing 1 wt% of MAX phase showed 17.7 L/m2.h.bar of permeability and 98.6% for FRR. Also, the separation efficiency of all membranes was evaluated by rejecting organic and inorganic pollutants. The Ti3AlCN MAX membranes could reject 96%, 95%, and 88% of reactive blue 50, Rose Bengal, and azithromycin antibiotics, respectively, as well as 98%, 80%, 86%, and 36% of Pb2+, As5+, Na2SO4, and NaCl, respectively. Finally, the outcomes indicated the Ti3AlCN MAX phase was an excellent and efficient novel additive for modifying the PES membrane.

Advances of MAX phases: Synthesis, characterizations and challenges

AbstractMAX phases and their MXene compounds have received significant attention owing to their extensive potential applications. The quality and purity of the MAX phase guarantee the desired quality of the MXene product, which is essential for a variety of applications, including energy storage, catalysis, and electrical devices. Due to the purity, quality, complex structure, and unavailable commercial pure MAX powders, it is frequently required to have sophisticated synthesis and characterization techniques for the expected MAX products. Many researchers entering this field seek a comprehensive approach to the synthesis and characterization of MAX phases. Despite this, a significant portion of existing reviews have overlooked the synthesis and characterization methods specific to MAX phases, particularly when addressing MXenes. Consequently, this review aims to offer a thorough overview of the various synthesis methods and characterization techniques that are often required for MAX phases. In this review, various synthesis techniques, including their advantages and disadvantages, have also been discussed. Characterization techniques, especially x‐ray diffraction (XRD), were found to be quite critical for new researchers. However, the integration of other techniques such as scanning electron microscopy, transmission electron microscopy, x‐ray photoelectron spectroscopy, and infrared analysis enhances and complements the findings obtained through XRD. The review also underscores the challenges associated with MAX phase synthesis and proposes potential solutions, emphasizing the assessment of their suitability across a broad spectrum of applications. Overall, this review serves as a comprehensive resource and guide for researchers engaged in the exploration and application of MAX phases, emphasizing the essential techniques of synthesis and characterization in harnessing their massive potential.

Erosion behaviors and mechanisms of Ti3AlC2 material under arc discharge in various mixed atmospheres

The present study establishes an experimental platform for investigating arc erosion and explores the erosion characteristics of Ti3AlC2 material under a voltage of 10 kV in SF6/N2, SF6/CO2, and N2/CO2 environments. Our findings reveal that the arc energy and duration exhibit a gradual increase in the sequence of SF6/N2, SF6/CO2, and N2/CO2, while the breakdown strength decreases. Scanning electron microscopy (SEM) and a three-dimensional laser confocal microscope were employed to observe uneven erosion morphology. Additionally, high-speed camera footage captures the arc bending and drifting phenomenon caused by Rayleigh-Taylor instability between the arc and gas. X-ray diffraction (XRD), Raman spectroscopy, and X-ray photoelectron spectroscopy (XPS) analysis were utilized to characterize the composition of eroded surfaces. Erosion models were proposed for each mixed atmosphere along with comprehensive discussions on their underlying mechanisms. This work expands the application scope of MAX phase materials while providing a theoretical foundation for designing electrical contact materials.