Ti2AlC MAX Phase Research Articles

Synthesis of Ti3alc2 Max Phase Under Vacuum, its Structural Characterisation and Using for Ti3c2tx Mxene Preparation

Synthesis of Ti3alc2 Max Phase Under Vacuum, its Structural Characterisation and Using for Ti3c2tx Mxene Preparation

Microstructure, mechanical and electrochemical properties of Ti3AlC2 coatings prepared by filtered cathode vacuum arc technology

Ti3AlC2 MAX phases have attracted increasing attention due to their unique properties. However, high synthesis temperatures of Ti3AlC2 bulk materials limit their further development. In this work, Ti3AlC2 coatings were prepared by a two-step method with filtered cathode vacuum arc (FCVA) deposition at room temperature and annealing at 800 °C for 1 h. The structure and properties of coatings were investigated. The results showed that the formation of Ti3AlC2 phase in the annealed coating depended on the C2H2 flow rate during deposition. At low C2H2 flow rates (≤ 9 sccm), almost no Ti3AlC2 phase was formed. As the C2H2 flow rate increased, the annealed coatings mainly exhibited Ti3AlC2 phases, the texture of which transformed from (104) to (105) planes. Meantime, the hardness of Ti3AlC2 coatings continuously increased to a maximum of 20.7 GPa, and the corrosion resistance first increased and then decreased with the increase of C2H2 flow rate.

Role of Ti3AlC2 MAX phase on characteristics of in-situ synthesized TiAl intermetallics. Part II: Phase evolution

In this research, the 2nd part of a series of papers on the processing and characterization of TiAl–Ti3AlC2 composites, the phase evolution during the manufacturing process was investigated by X-ray diffraction (XRD) analysis and Rietveld refinement method. Metallic Ti and Al powders with different amounts of previously-synthesized Ti3AlC2 additives (10, 15, 20, 25 and 30 wt%) were ball-milled and densified by spark plasma sintering (SPS) under 40 MPa for 7 min at 900 °C. Before the sintering process, XRD test verified that the powder mixtures contained metallic Ti and Al as well as Ti3AlC2 and TiC (lateral phase synthesized with Ti3AlC2) phases. In the sintered composites, the in-situ synthesis of TiAl and Ti3Al intermetallics as well as the presence of Ti3AlC2 and the formation and Ti2AlC MAX phases were disclosed. The weight percentage of each phase in the final composition of the samples and the crystallite size of different phases were calculated by the Rietveld refinement method based on the XRD patterns. The size of Ti3AlC2 crystallites in sintered samples was compared with the crystallite size of synthesized Ti3AlC2 powder.

MXsorption of mercury: Exceptional reductive behavior of titanium carbide/carbonitride MXenes

Two-dimensional (2D) transition metal carbides and nitrides (MXenes) have drawn considerable attention for application in the field of environmental remediation. In this study, we report the simultaneous reductive–adsorption behavior of Ti3CNTx for toxic metal ion Hg2+ ion in the aqueous phase. 2D Ti3CNTx and Ti3C2Tx MXene nanosheets were synthesized by exfoliation of Ti3AlCN and Ti3AlC2 MAX phases, respectively. Various characteristics analysis confirmed the successful fabrication of MAX phases and their exfoliation into MXenes. The fabricated MXene nanosheets were used to investigate their Hg2+ removal, Hg2+ intercalation, and surface interaction mechanism efficiencies. Both MXenes were found to adsorb and reduce a large amount of Hg2+. Analytical techniques such as X-ray powder diffraction, field emission transmission electron microscopy, zeta-potential analyses, and X-ray photoelectron spectroscopy were used to investigate the material characteristics and structural changes after uptake of Hg2+. The quantitative investigation confirmed the interaction of bimetal and hydroxyl groups with Hg2+ using electrostatic interactions and adsorption-coupled reduction. In addition, both MXenes exhibited extraordinary Hg ion removal capabilities in terms of fast kinetics with an excellent distribution coefficient (KdHg) up to 1.36 × 10+9. Based on batch adsorption results, Ti3C2Tx and Ti3CNTx exhibited removal capacities of 5473.13 and 4606.04 mg/g, respectively, for Hg2+, which are higher than those of previous Hg adsorbents.

Influence of selective laser treatment on thermal stability of Ti3AlC2 and Ti3AlC2/Cu powders

Commercial Ti3AlC2 MAX phase powder and Ti3AlC2/Cu powder blends were used to obtain bulk materials using selective laser sintering/melting technique. In the present work, the influence of laser line energy on the stability of Ti3AlC2 composition was investigated. The structure of MAX phases was better maintained in composites with copper addition, forming a metal matrix composite with a copper matrix and Ti3AlC2 inclusions.

An Investigation on Substitution of Ag Atoms for Al or Ti Atoms in the Ti2AlC MAX Phase Ceramic Based on First-Principles Calculations.

The present work introduced first-principles calculation to explore the substitution behavior of Ag atoms for Al or Ti atoms in the Ti2AlC MAX phase ceramic. The effect of Ag substitution on supercell parameter, bonding characteristic, and stability of the Ti2AlC was investigated. The results show that for the substitution of Ag for Al, the Al-Ti bond was replaced by a weaker Ti-Ag bond, decreasing the stability of the Ti2AlC. However, the electrical conductivity of the Ti2AlC was enhanced after the substitution because of the contribution of Ag 4d orbital electrons toward the density of states (DOS) at the Fermi level coupled with the filling of Ti d orbital electrons. For the substitution of Ag for Ti, new bonds, such as Ag-Al bond, Ag-C bond, Al-Al bond, Ti-Ti anti-bond, and C-C anti-bond were generated in the Ti2AlC. The Ti-Ti anti-bond was strengthened as well as the number of C-C anti-bond was increased with increasing the substitution ratio of Ag for Ti. Similar to the substitution of Ag for Al, the stability of the Ti2AlC also decreased because the original Al-Ti bond became weaker as well as the Ti-Ti and C-C anti-bonds were generated during the substitution of Ag for Ti. Comparing with the loss of Ti d orbital electrons, Ag 4d orbits contributed more electrons to the DOS at the Fermi level, improving the electrical conductivity of the Ti2AlC after substitution. Based on the calculation, the substitution limit of Ag for Al or Ti was determined. At last, the substitution behavior of Ag for Al or Ti was compared to discriminate that Ag atoms would tend to preferentially substitute for Ti atoms in Ti2AlC. The current work provides a new perspective to understand intrinsic structural characteristic and lattice stability of the Ti2AlC MAX phase ceramic.

Electrical Conductivity Enhancement and Electronic Applications of 2D Ti3C2Tx MXene Materials

AbstractIn the past 10 years, MXene (transition metal carbides, nitrides, and carbonitrides), a 2D nanomaterial, has become one of the research hotspots with its hydrophilic ends, solution machinability, and excellent electronic, mechanical, and optical characteristics. Herein, recent progress on Ti3C2Tx MXene materials is reviewed, analyzed, and evaluated with highlights on their electrical performances and applications. The progress on electrical conductivity enhancement of Ti3C2Tx MXene is carefully reviewed from a number of aspects in Ti3AlC2 MAX phase precursor, synthesis methods, delamination treatment, removal of delamination compounds, surface terminations, thin‐film deposition methods, and storage environment and time. Finally, a summary is provided and the challenges are discussed to further enhance the electrical conductivity.

Abstract 11474: Ti 3 C 2 T x MXene Nanosheets for Immunomodulation and Prevention of Allograft Vasculopathy

Allograft vasculopathy is an aggressive form of accelerated atherosclerosis that manifests uniquely in transplanted hearts, lungs and kidneys. Activated blood vessel endothelial cells (ECs) stimulate alloreactive CD4 + and CD8 + T-lymphocytes to result in sustained inflammation. MXenes, an emerging class of transition metal carbides, have recently been shown to have unique immunomodulatory properties that may be leveraged to treat allograft vasculopathy. In this study, we present the synthesis, characterization and application of novel two-dimensional titanium carbide MXene (Ti 3 C 2 T x ) nanosheets for immunomodulation. MXene nanosheets (MNSs) were selectively etched from bulky Ti 3 AlC 2 MAX phase using hydrofluoric acid. The resultant MNSs are 2 to 5 μm in size and are surface modified with carboxyl, hydroxyl and amine functional groups for biological interactions. Using an in vitro co-culture system, we found that MNSs interact with activated human ECs to reduce activation and pro-inflammatory Th1 polarization of allogeneic CD4 + lymphocytes. Mechanistically, we showed that treatment with MNSs significantly decreased expression of the co-stimulatory molecule CD86 and altered the ratio of endothelial surface co-stimulatory to co-inhibitory molecules. Furthermore, when applied in an in vivo rat model of allograft vasculopathy, treatment with MNSs reduced lymphocyte infiltration and preserved medial smooth muscle cell integrity within transplanted vessel segments. Taken together, these findings suggest that these novel MNSs have potential as an effective treatment to prevent allograft vasculopathy.

Water-dispersible Ti3C2Tz MXene nanosheets by molten salt etching

SummaryMolten-salt etching of Ti3AlC2 MAX phase offers a promising route to produce 2D Ti3C2Tz (MXene) nanosheets without hazardous HF. However, molten-salt etching results in MXene clays that are not water dispersible, thus preventing further processing. This occurs because molten-salt etching results in a lack of -OH terminal groups rendering the MXene clay hydrophobic. Here, we demonstrate a method that produces water-dispersible Ti3C2Tz nanosheets using molten salt (SnF2) to etch. In molten salt etching, SnF2 diffuses between the layers to form AlF3 and Sn as byproducts, separating the layers. The stable, aqueous Ti3C2Tz dispersion yields a ζ potential of −31.7 mV, because of -OH terminal groups introduced by KOH washing. X-ray diffraction and electron microscopy confirm the formation of Ti3C2Tz etched clay with substantial d-spacing as compared with clay etched with HF. This work is the first to use molten salt etching to successfully prepare colloidally stable aqueous dispersions of Ti3C2Tz nanosheets.

An optimized method for synthesizing phase-pure Ti3AlC2 MAX-phase through spark plasma sintering

So far many attempts have been made to synthesize phase-pure Ti3AlC2 MAX-phase. But still the challenge posed by the presence of TiC and Ti-Al based intermetallic transient impurity phases in the final product is a persisting problem. Spark plasma sintering (SPS) technique has been the most successful method to decrease the impurity content of the final product. Even so, synthesis of phase-pure Ti3AlC2 MAX-phase, without any TiC and Ti-Al based intermetallic impurities, has not been achieved and reported in literature with substantial evidences. Further, high purity Ti3AlC2 MAX-phase synthesized using SPS technique has shown lack of phase and microstructural stability above 1350°C temperature. In this work, we have reported an optimized method for producing phase-pure Ti3AlC2 MAX-phase (having more than 99 % purity) using commercial grade Ti, Al and C elemental powders through SPS technique. The final product also showed very good high temperature stability up to 1500°C under flowing Argon inert atmosphere.

Microstructure, properties and fracture mechanism of MAX phase Ti3AlC2 ceramics with Si doping via Ti–Al–C system by powder metallurgy

The key problems restricting the wide development of Ti3AlC2 material are the low hardness and strength. In this paper, MAX phase Ti3(Al,Si)C2 solid solutions with different Si doping were successfully synthesized using an in-situ reaction of Ti–Al–C system by powder metallurgy route. The phase structures and microstructures of the as-synthesized Ti3(Al,Si)C2 solid solutions were analyzed, the mechanical properties were tested, and the fracture surface morphologies were characterized. The results show that doping Si can prevent the lath-like structure of MAX phase from coarsening. When doping 0.2 mol Si, the as-synthesized Ti3Al1.0Si0.2C2 sample offers fine microstructure and has excellent performance. Its Vickers hardness, flexural strength and the fracture toughness are 5.52 GPa, 546 MPa, 7.51 MPa m1/2, respectively. The fracture mode is transgranular cleavage fracture. During propagation, the main crack deflects and branches obviously. The crack extends in a zigzag like path, accompanied by transgranular fracture. When suffering external force, the particular layered structure of Ti3(Al,Si)C2 can absorbs and dissipates more energy through hybrid deformation modes such as extrusion, kink, fold, interlaminar separation and tearing. With this complex and mixed fracture mode, the crack propagation were effectively prevented, and its flexural strength and fracture toughness were enhanced.

Nonlinear absorption property investigation into MAX phase Ti2AlC at 1.9 μm

An experimental and theoretical investigation into the nonlinear absorption properties of MAX phase Ti2AlC was conducted at 1900 nm wavelength. First, the nonlinear absorption coefficient measurement of Ti2AlC was carried out using an open-aperture (OA) Z-scan technique. This measurement revealed that the nonlinear absorption coefficient of Ti2AlC was ∼(-24.13×103) cm2/GW at 1900 nm. Subsequently, the energy band structure of the Ti2AlC was calculated through density functional theory (DFT) calculation. This calculation confirmed that Ti2AlC had a metallic band structure implying an ultrawide absorption bandwidth. Finally, the feasibility of fabricating an all-fiberized device of a saturable absorber (SA) using Ti2AlC was conducted with a side-polished fiber platform. The SA was successfully used for the generation of femtosecond soliton pulses with features of 17.91 MHz repetition rate, 4.3-nm bandwidth, and ∼960 fs pulse width at 1922 nm. To the best of authors’ knowledge, this is the first demonstration of the use of a MAX phase-based SA for femtosecond mode-locking in the 1.9 μm spectral region.

Role of Ti3AlC2 MAX phase on characteristics of in-situ synthesized TiAl intermetallics. Part I: sintering and densification

Five TiAl–Ti3AlC2 composite samples containing (10, 15, 20, 25 and 30 wt% Ti3AlC2 MAX phase) were prepared by spark plasma sintering technique at 900 °C for 7 min under 40 MPa. For this purpose, metallic titanium and aluminum powders (aiming at the in-situ formation of the TiAl matrix phase) were ball-milled with predetermined contents of Ti3AlC2 MAX phase, which already was synthesized using the same metallic powders as well as graphite flakes. Displacement-time-temperature variations during the heating and sintering steps, displacement rate versus temperature, displacement rate versus time, and densification behavior were studied. Two sharp changes were detected in the diagrams: the first one, ~16 min after the start of the heating process due to the melting of Al, and the second one, after ~35 min because of the sintering progression and the applied final pressure. The highest relative densities were measured for the samples doped with 20 and 25 wt% Ti3AlC2 additives. More Ti3AlC2 addition resulted in decreased relative density because of the agglomeration of MAX phase particles.

The performance of Ti2C MXene and Ti2AlC MAX Phase as saturable absorbers for passively mode-locked fiber laser

This research provides feasibility investigations of Ti2C MXene and Ti2AlC MAX Phase materials to be used as saturable absorbers (SAs). The fabrication procedure for both SAs has been described in this paper, where both laser parameters of Ti2C MXene and Ti2AlC MAX Phase were compared in detail. Ti2C MXene deposited tapered fiber has a modulation depth of 4.7% and saturation intensity of 0.98 MW/cm2, whereas Ti2AlC MAX Phase deposited tapered fiber has corresponding values of 3.27%, 0.86 MW/cm2, respectively. The findings shows that Ti2C MXene can provide a stable mode-locked operation with pulse width of 1.655 ps and optical bandwidth of 2.57 nm at a center wavelength of 1933.82 nm. Similarly, the Ti2AlC MAX Phase produced the corresponding values of 1.382 ps, 2.75 nm, and 1894.54 nm, respectively. Additionally, Ti2C MXene appeared to be a better candidate based on a higher signal-to-noise ratio (SNR) value of 70 dB as compared to that of Ti2AlC MAX Phase at 66 dB when operating in a thulium-holmium doped fiber laser (THDFL). The Ti2C MXene and Ti2AlC MAX Phase based SAs have significant potential for photonics applications in the “eye-safe” region.

A new MAX phases-based electroconductive coating for high-temperature oxidizing environment

In the paper, results of variations of structure, oxidation resistance, and electrical conductivity of novel MAX-phase composite coating are presented. The characteristics of highly dense Ti-Al-C composite bulks and vacuum-arc deposited 6 μm thick coatings before and after heating at 600 °C in air for 1000 h were compared. High electrical conductivity (σ = 1.3·106 S/m) of the highly resistant toward oxidation (Δm/S = 0.07 mg/cm2) Ti-Al-C coating was preserved after long-term heating in air. It was found that the specimen surface layers of MAX-phases Ti3AlC2 and Ti2AlC based bulks and chromium-containing Crofer 22APU steel became semiconductors because of high-temperature long-term oxidation (at 600 °C). The vacuum-arc deposited Ti-Al-C composite coating revealed high oxidation resistance and electrical conductivity along with good mechanical characteristics, namely nanohardness H(10mN) = 9.5 ± 1.5 GPa, and Young’s modulus E = 190 ± 10 GPa, which make it very promising for interconnects of solid oxide fuel cells (SOFCs).

A New High-Temperature Durable Absorber Material Solution through a Spinel-Type High Solar Absorptivity Coating on Ti2AlC MAX Phase Material.

Enhancing the operating temperature of concentrating solar power systems is a promising way to obtain higher system efficiency and thus enhance their competitiveness. One major barrier is the unavailability of suitable solar absorber materials for operation at higher temperatures. In this work, we report on a new high-temperature absorber material by combining Ti2AlC MAX phase material and iron–cobalt–chromite spinel coating/paint. This durable material solution exhibits excellent performance, passing the thermal stability test in an open-air environment at a temperature of 1250 °C for 400 h and at 1300 °C for 200 h. The results show that the black spinel coating can offer a stable high solar absorptivity in the range of 0.877–0.894 throughout the 600 h test under high temperatures. These solar absorptivity values are even 1.6–3.3% higher than that for the sintered SiC ceramic that is a widely used solar absorber material. Divergence of solar absorptivity during these relatively long testing periods is less than 1.1%, indicating remarkable stability of the absorber material. Furthermore, considering the simple application process of the coating/painting utilizing a brush followed by curing at relatively low temperatures (room temperature, 95 and 260 °C in sequence), this absorber material shows the potential for large-scale, high-temperature solar thermal applications.

High-Energy Mechanical Grinding to Produce Cr2AlC and Ti2AlC Max Phases

High-Energy Mechanical Grinding to Produce Cr2AlC and Ti2AlC Max Phases

Effects of A-site atoms in Ti2AlC and Ti3SiC2 MAX phases reinforced Mg composites: Interfacial structure and mechanical properties

AZ91D magnesium composites reinforced by Ti3SiC2 MAX phase were fabricated by the stir casting technique. Tensile tests reveal that the reinforced effects of Ti3SiC2 and Ti2AlC on Mg matrix are different. Unlike Ti2AlC-AZ91D composite for which Ti2AlC delamination happens during the fracture, Ti3SiC2-AZ91D composite fractures by interfacial debonding mechanisms. Transmission electron microscopy characterization shows that few nanometric Mg grains form in the vicinity of Ti3SiC2 particles, while huge amount of nanometric Mg grains form along with Ti2AlC particles. Elements mapping confirms that Al atoms of Ti2AlC diffuse into Mg matrix. In contrast, no outward diffusion of Si of Ti3SiC2 is observed. This outcome points out that it is possible to regulate the mechanical properties of their relevant Mg composite through adjusting the content of Al and Si in MAX phases, such as Ti3SiAlC2 solid solution.

Corrosion mechanism of Ti2AlC MAX phase coatings under the synergistic effects of water vapor and solid NaCl at 600 °C

The corrosion behavior of Ti2AlC MAX phase coatings coated on 1Cr11Ni2W2MoV substrates in NaCl deposit in water vapor at 600 °C has been fully investigated. The results demonstrated that the substrates underwent serious corrosion, but the coatings performed better. The mass gain per unit area of coatings was less than 1/6 of substrates, because of the formed compact and uniform corrosion scale. Such dense corrosion scale was composed of NaxTiyOz fine grains with the size of 11 ± 0.4 nm and amorphous Al2O3 phases which self-healed the generated defects during corrosion, benefiting from the novel layered structure of MAX phase.

Sputtering and Characterization of MAX‐Phase Forming Cr–Al–C and Ti–Al–C Coatings and Their Application on γ‐Based Titanium Aluminides

MAX‐phases are of increasing interest as coating material for high temperature applications due to their unique metallic as well as ceramic properties. Herein, the deposition of Cr2AlC and Ti3AlC2 or Ti2AlC MAX‐phase forming coatings by magnetron sputtering is demonstrated. Using pure elemental targets, the manufacturing with a coating thickness of above 7 μm is established. The MAX‐phase forming coatings are characterized by high‐temperature X‐ray diffraction (HT‐XRD) measurements and provide a good oxidation behavior due to the development of protective thermally grown oxide layers. The performance of the MAX‐phases is strongly depended on the substrate material and the accompanying interdiffusion processes. Therefore, the Ti–Al–C coating is favored for TiAl alloys due to the thermodynamic stability of the Ti2AlC MAX phase in particular in the presence of the γ‐TiAl phase. An excellent oxidation behavior is confirmed up to 300 h at 850 °C due to the development of an alumina layer above a homogenous Ti2AlC phase coating. The Cr2AlC MAX‐phase coating degrades after 100 h at 800 °C due to interdiffusion processes between coating and substrate and the accompanying development of carbides and nitride phases. Nevertheless, the oxidation resistance of the Cr–Al–C‐coated TiAl alloy is given by the formation of the Ti2AlC MAX‐phase.