Cr2AlC MAX Phase Research Articles

Exploring the potential application of Cr2AlC MAX phase as an emerging electrocatalyst for overall water splitting

Exploring the potential application of Cr2AlC MAX phase as an emerging electrocatalyst for overall water splitting

Synthesis and characterization of chromium aluminum carbide MAX phases (CrxAlCx-1) for potential biomedical applications.

MAX phases, characterized as nanolaminates of ternary carbides/nitrides structure, possess a unique combination of ceramic and metallic properties, rendering them pivotal in materials research. In this study, chromium aluminum carbide ternary compounds, Cr2AlC (211), Cr3AlC2 (312), and Cr4AlC3 (413) were successfully synthesized with high purity using a facile and cost-effective sol-gel method. Structural, morphological, and chemical characterization of the synthesized phases was conducted to understand the effects of composition changes and explore potential applications. Comprehensive characterization techniques including XRD for crystalline structure elucidations, SEM for morphological analysis, EDX for chemical composition, Raman spectroscopy for elucidation of vibrational modes, XPS to analyze elemental composition and surface chemistry, and FTIR spectroscopy to ensure the functional groups analysis, were performed. X-ray diffraction analysis indicated the high purity of the synthesized Cr2AlC phase as well as other ternary compounds Cr3AlC2 and Cr4AlC3, suggesting its suitability as a precursor for MXenes production. Additionally, the antimicrobial activity against Candida albicans and biocompatibility assessments against Escherichia coli (E. coli), Staphylococcus aureus (S. aureus), and HepG2 cell line were investigated. The results demonstrated significant antifungal activity of the synthesized phases against Candida albicans and negligible impact on the viability of E. coli and S. aureus. Interestingly, lower concentrations of Cr2AlC MAX phase induced cytotoxicity in HepG2 cells by triggering intercellular oxidative stress, while Cr3AlC2 and Cr4AlC3 exhibited lower cytotoxicity compared to Cr2AlC, highlighting their potential in biomedical applications.

Unveiling the diffusion pathways under high-temperature oxidation of Cr2AlC MAX phase via nanoscale analysis

The MAX phase chromium aluminium carbide (Cr2AlC) is a potential candidate for high-temperature structural and energy applications due to the unique combination of properties, including excellent oxidation and corrosion resistance in harsh environmental conditions. In this work, the oxidation behaviour of bulk Cr2AlC was studied at temperatures of 1000 °C and 1200 °C in humid synthetic air, mimicking a realistic application environment. An α-Al2O3 scale forms at both temperatures, consisting of both inward and outward-growing layers, with a continuous Cr7C3 layer beneath the oxide. A special focus was put on employing atom probe tomography (APT) to analyse the oxide and carbide layers at the nanoscale. Decomposition of Cr2AlC to Cr7C3 is the main source (>70%) of aluminium needed for the oxide scale formation, while Al depletion in the underlying MAX phase remains marginal (<1 at%), exhibiting a pattern different from the common high-temperature oxidation of alloys. Al diffusion to the oxide scale proceeds predominantly through grain boundaries (GBs) in Cr2AlC and through the bulk in Cr7C3. Ionic diffusion through GBs of the large-grained inner alumina layer seems to be the rate-limiting step for the oxide scale growth, resulting in the apparent parabolic oxidation kinetics. No segregation of Cr, C or any impurities, which could affect ionic transport, was found at these alumina GBs by APT, rendering the results of this study as characteristic of a pure Cr2AlC oxidation.

Manufacturing of High Purity Cr2AlC MAX Phase Material and Its Characterization

AbstractPresent study discusses about a technique for producing high-purity Cr2AlC MAX phase materials and gaining insight into their thermal behavior for high-temperature applications. The research conducted involved synthesizing a pure layered ternary carbide Cr2AlC MAX phase material by mixing powders of Chromium, Aluminum, and Carbon and then subjecting them to two-step pressureless sintering process in argon atmosphere. First step involves the annealing of ball-milled mixture at 750 °C for 2 h followed by the second step in which the annealed mixture is subjected to heat-treatment at 1350 °C for 2 h. Analysis using XRD and Raman techniques revealed that the synthesized product consists of Cr2AlC phase, without any impurities. SEM studies confirmed that the Cr2AlC had a layered topography, while EPMA analysis indicated that the atomic percentage of Cr, Al, and C was consistent with the XRD phase analysis. XPS investigations confirmed the presence of Cr-C bonds representing Mn+1Xn of the MAX phase material. TG-DSC results showed an approximately 2% increase in weight. The Cr2AlC phase exhibited an endothermic pattern below 725 °C, an exothermic pattern above it, and did not decompose up to 1400 °C in vacuum environment. High-temperature XRD analysis at various temperatures also confirmed no formation of Al2O3 or CrO impurity compounds.

Phase formation mechanism of Cr2AlC MAX phase coating: In-situ TEM characterization and atomic-scale calculations

Cr2AlC, a representative MAX phase, gains increasing attention for the excellent oxidation tolerance and corrosion resistance used in harsh high temperature and strong radiation environments. However, the lack of the phase formation mechanism has become the key bottleneck to the practical applications for Cr2AlC synthesis with high purity at low temperatures. In this work, we fabricated the amorphous Cr–Al–C coating by a hybrid magnetron sputtering/cathodic arc deposition technique, in which the in-situ heating transmission electron microscopy (TEM) was conducted in a temperature range of 25–650 °C to address the real-time phase transformation for Cr2AlC coating. The results demonstrated that increasing the temperature from 25 to 370 °C led to the structural transformation from amorphous Cr–Al–C to the crystalline Cr2Al interphases. However, the high-purity Cr2AlC MAX phase was distinctly formed at 500 °C, accompanied by the diminished amorphous feature. With the further increase of temperature to 650 °C, the decomposition of Cr2AlC to Cr7C3 impurities was observed. Similar phase evolution was also evidenced by the Ab-initio molecular dynamics calculations, where the bond energy of Cr–Cr, Cr–Al, and Cr–C played the key role in the formed crystalline stability during the heating process. The observations not only provide fundamental insight into the phase formation mechanism for high-purity Cr2AlC coatings but also offer a promising strategy to manipulate the advanced MAX phase materials with high tolerance to high-temperature oxidation and heavy ion radiations.

Atomic force microscopy and transmission electron microscopy identification of deformation twinning in the Cr2AlC MAX phase

Elementary deformation mechanisms have been investigated in a single-crystalline Cr2AlC MAX phase. Plastic deformation has been induced at room temperature by spherical nanoindentation, with a crystal orientation chosen to minimize basal slip and to promote local crystal reorientation. The combination of Atomic Force Microscopy (AFM) surface observation, Transmission Electron Microscopy (TEM) characterization and Automated Crystal Orientation Mapping (ACOM) in a same region has provided a full 3D characterization of the deformation microstructure. Localized and isolated deformation twins have been identified below the indents. The whole microstructure consists in interactions between dislocations and {112¯4} twin variants. The TEM analysis also revealed activation of a 13〈112¯0〉{1¯103} slip system never reported before in a MAX phase.

Microstructural and compositional design of Cr2AlC MAX phases and their impact on oxidation resistance

The oxidation of MAX phases has largely been investigated, but the effect of secondary phases and microstructure is still unclear. We report on the effect of reactive and non-reactive sintering, and starting powders, on the microstructure, phase formation, and chemical composition of Cr2AlC MAX phases. The grain sizes are shown to be sensitive to both the processing method and the starting powders. Secondary phases were observed mostly in reactively sintered samples as Cr7C3 and AlCr2 were identified, and Al contents varied between 24.4 and 28.0 at%. Finally, the oxidation behavior of the produced MAX phases was evaluated after 60 and 120 min at 1100 °C. The Al content, the average grain size of the as-sintered samples, and the presence of secondary phases affected the decomposition of the MAX phase into Cr-carbides in the vicinity of the oxide scale and the composition of the oxide scale, respectively.

High-performance Cr2AlC MAX phase coatings for ATF application: Interface design and oxidation mechanism

Surface-modified Zr-based alloy (ZIRLO) claddings with advanced ceramic coatings are increasingly required for accident-tolerant fuel (ATF) systems in light-water reactors. Cr2AlC MAX phase coatings are promising for this purpose owing to their remarkable properties combining radiation/oxidation/corrosion resistance. However they are suffering from weak interface compatibility to ZIRLO substrate and poor structural densities for long-term services. Herein, we fabricated densely high-purity Cr2AlC MAX phase coatings with uniquely designed Cr/CrCx interfacial layers. The oxidation behavior of the coatings was focused under steam environments at 1000–1200 °C. Results showed that Cr2AlC coatings exhibited an oxidation mass gain of 8.9 mg/cm2 and an oxide thickness of 680 nm after oxidation at 1200 °C for 30 min, which were about 10% and 0.5% of ZIRLO substrate, respectively. Based on microstructural evolutions, the embedded interfacial layers significantly suppressed the rapid diffusion of Al in Cr2AlC coatings to the substrate and the premature delamination of oxidized coatings. Particularly, the formed oxides were identified as dense yet pure α-Al2O3, which endowed the protection against further oxidation and excellent resistance to high-temperature steam corrosion.

Temperature-adaptive lubrication of Ag doped Cr2AlC nanocomposite coatings

Self-lubricating nanocomposite carbides and nitrides coatings that enable to exhibit both low friction coefficient (CoF) and high wear resistance over a wide temperature range, are in high demand for mechanical components used in aerospace and marine systems. In this work, we developed high-purity Ag-doped Cr2AlC (Ag–Cr2AlC) nanocomposite coatings using a facile arc/sputter deposition technique followed by annealing. Compared to typical nanocrystalline Cr2AlC MAX phase coatings, the incorporation of Ag resulted in a unique nanocomposite structure, where Ag encapsulates elongated Cr2AlC nanograins. The dry sliding wear of this material was evaluated using the ball-on-disc method, with an Al2O3 ball as the counter body, at temperature ranging from 25 °C to 700 °C. Interestingly, Ag dopants contributed to a significant reduction in COF and wear rate at temperatures below 500 °C, while the synergistic effect of the Ag distributed at grain boundaries and the outermost oxides of Cr2O3 and Al2O3 generated during friction dominated the excellent self-lubrication at 500–700 °C. Notably, the Ag–Cr2AlC coatings promoted the in-situ formation of gradient bilayer oxides, consisting of a loosely coarse-grained inner layer and a densely refine-grained outmost layer. The combination of unique gradient oxides and a combined nanocomposite matrix allows the coating to accommodate plastic strains without extended cracks or localized brittle fracture.

Stoichiometric Cr2AlC MAX phase coatings deposited by HPPMS from composite targets using industrial deposition technology

Compositionally-graded Cr2AlC coatings were deposited from composite targets with Al concentration gradients along the long-axis of the targets, ranging from 20.0 to 30.0 at.%, in an industrial plant. Stoichiometric Cr2AlC coatings deposited by HPPMS with a peak-power density of 217 W/cm2 and at substrate bias potential of −100 V require an Al concentration in the target of 30.0 at.% to compensate for the Al-loss induced by preferential re-sputtering and thermally induced desorption at these deposition conditions. The HPPMS deposition of a stoichiometric Cr2AlC coating at floating potential can be attained from a target segment containing 26.4 at.% of Al. Hence, during synthesis at 560 °C in an industrial deposition system with two-fold rotation significant deviations between target and coating composition were observed. It was demonstrated that these ion energy and power density induced reductions in Al concentration can be compensated for by utilizing Al-rich composite targets.

Laser surface texturing and numerical simulation of heat flux on Cr2AlC MAX phase heat exchangers

The energetic worldwide emergency demands a significant drop in fossil energy to renewable energies as part of the sustainable solutions for global energy consumption. MAX phase materials, such as Cr2AlC, are potential candidates for heat exchanger applications due to their excellent oxidation and corrosion resistance, good thermal shock response and relatively high thermal conductivity. This study uses laser surface texturing (LST) technology to design plate heat exchanger patterns on the Cr2AlC MAX phase. Furthermore, performing numerical simulations on textured plate models under molten salt conduction and convection conditions, accessing temperature gradient and heat transfer behaviour were conducted on Cr2AlC, as well as on 316 L stainless steel and alumina for comparison. As a result, combined microtextures with a corrugated surface and spaced V-shape channels were obtained using LST in a single step. The parametric study indicated that the optimal channels (groves) were found for 25 W in air and 20 s laser conditions, with approximately 145 µm width and 340 µm depth. Furthermore, the numerical simulation showed that ceramics materials present better heat transfer conditions than 316 L stainless steel, where Cr2AlC and alumina only differ in 1.9% heat flux. In addition, the corrugated surface plate with 2.6% width of the total thickness increases heat transfer by 9.8%.

On the determination of the thermal shock parameter of MAX phases: A combined experimental-computational study

Thermal shock resistance is one of the performance-defining properties for applications where extreme temperature gradients are required. The thermal shock resistance of a material can be described by means of the thermal shock parameter RT. Here, the thermo-mechanical properties required for the calculation of RT are quantum-mechanically predicted, experimentally determined, and compared for Ti3AlC2 and Cr2AlC MAX phases. The coatings are synthesized utilizing direct current magnetron sputtering without additional heating, followed by vacuum annealing. It is shown that the RT of both Ti3AlC2 and Cr2AlC obtained via simulations are in good agreement with the experimentally obtained ones. Comparing the MAX phase coatings, both experiments and simulations indicate superior thermal shock behavior of Ti3AlC2 compared to Cr2AlC, attributed primarily to the larger linear coefficient of thermal expansion of Cr2AlC. The results presented herein underline the potential of ab initio calculations for predicting the thermal shock behavior of ionically-covalently bonded materials.

Point defects and hydrogen-permeation behavior of MAX phase Cr2AlC coating by first-principles studies

Point defects and hydrogen-permeation behavior of MAX phase Cr2AlC coating by first-principles studies

The effect of milling time and heat treatment on the synthesis of the Cr2AlC MAX phase

ABSTRACT Synthesis of the Cr2AlC MAX phase was investigated by mechanical alloying. Cr, Al, and C powders were milled and heat treated at temperature range of 500–1300°C for 1 h. X-ray diffraction and differential thermal analysis were used to study the reaction mechanisms and a scanning electron microscope was used to observe the microstructures. The Cr7C3 and Cr–Al compounds were formed by reactions among the initial elements. These compounds transformed to the Cr2AlC phase by increasing the temperature. The maximum amount of Cr2AlC phase was equal to 97.23 wt.%, which was related to the sample with 45 h of ball milling and subsequent heat treatment at temperature of 700°C. DTA results showed a major exothermic peak at about 685°C, which represents the formation of the Cr2AlC . This indicates that most conversions are completed in a single stage, below the temperature of 800°C.

In situ Coating and Hot Corrosion Behavior of Cr2AlC MAX Phase

In situ Coating and Hot Corrosion Behavior of Cr2AlC MAX Phase

Alumina scale buckling during high temperature oxidation of Cr2AlC MAX Phase

Single-crystal and fine-grained polycrystalline samples of Cr2AlC were oxidized under dry air flow at temperature in the 1000–1400 °C range during 100 h. A continuous alumina layer forms on top of the Cr2AlC surface whereas a Cr7C3 sublayer also appears. In-lab characterization of oxidized Cr2AlC samples shows strong damaging at the free surface, resulting from the buckling of the alumina scale. In-situ X-ray diffraction measurements under synchrotron radiations were performed to measure the lattice strain during the first hours of oxidation process and further calculate the internal stress in the Al2O3 layers. Alumina layers undergo tensile stress during isothermal oxidation, showing that the buckling of the alumina scale does not result from the oxide growth. Such a tensile stress likely results from the Cr2AlC to Cr7C3 phase transformation. During cooling, the tensile stress decreases down to compressive values, due to the thermal expansion coefficient mismatch between the film and the substrate, leading to buckling of the alumina layer. It is demonstrated that the dimensions of the buckles cannot be explained either by gas pressure or by the magnitude of the internal compressive stress in the alumina scale after cooling. The discrepancy between the experimental maximum deflection and the one predicted by the elastic theory can only be explained by a significant plastic deformation occurring in the alumina scale.

Catalytic activation of hydrogen peroxide by Cr2AlC MAX phase under ultrasound waves for a treatment of water contaminated with organic pollutants.

This study aims to investigate the sonocatalytic activation of hydrogen peroxide (H2O2) using Cr2AlC MAX phase prepared by the reactive sintering process. The hexagonal structure of the crystalline MAX phase was confirmed by X-ray diffraction. Moreover, the compacted layered structure of the MAX phase was observed via scanning electron microscopy and high-resolution transmission electron microscopy. Under the desired operating conditions, Cr2AlC MAX phase (0.75g/L) showed suitable potential to activate H2O2 (1mmol/L) under sonication, thereby allowing a considerable removal efficiency for various organic pollutants, including dimethyl phthalate (69.1%), rifampin (94.5%), hydroxychloroquine (100%), and acid blue 7 (91.5%) with initial concentration of 15mg/L within 120min of treatment. Kinetic analysis proved that the degradation reaction followed pseudo-first-order kinetics. Scavenging tests demonstrated that hydroxyl radicals and singlet oxygen were effective species during degradation. Furthermore, a probable mechanism for dimethyl phthalate degradation was suggested according to gas chromatography-mass spectroscopy and nuclear magnetic resonance analyses. The obtained results confirmed the capability of the triple Cr2AlC/H2O2/US process as a promising method for treating contaminated water.

Mode-locked operation in thulium-holmium doped fiber laser based on Cr2AlC MAX phase SA coated arc-shaped fiber

Mode-locked operation in thulium-holmium doped fiber laser based on Cr2AlC MAX phase SA coated arc-shaped fiber

Ion irradiation induced softening in Cr2AlC MAX phase

MAX phases have exhibited excellent irradiation resistance regarding structure stability, but limited knowledge is available on the irradiation induced change in the mechanical performance of MAX phases. In this work, Cr2AlC single crystal samples were irradiated with 6 MeV C ions, and smaples’ mechanical properties were measured by micropillar compression test and nanoindentation technique. After irradiation, new slip traces are activated, which means the deformation behavior changed by irradiation. More important is that both the yield strength and Young’s modulus decrease gradually with the increasing irradiation doses up to 0.098 dpa, suggesting a significant radiation softening effect but not the radiation hardening effect which is very popular in other materials. This radiation softening effect is possible the result of the irradiation-induecd vacancies, which is supported by the DFT calculation. These results indicate that MAX phases like Cr2AlC have an excellent irradiation tolerance regarding mechanical properties and is a new class of promising candidate material for the advanced nuclear systems.

Mechanical properties of SPS-processed Cr2AlC MAX phase with different impurity contents

Mechanical properties of SPS-processed Cr2AlC MAX phase with different impurity contents