Mn+1AXn Phases Research Articles

Topotactic transformations in Hf-Al-C MAX phase compounds: Synthesis and characterization of nanolaminated Hf2AlC, Hf3AlC2 and Hf5Al2C3

The synthesis of high-purity Mn+1AXn (MAX) phase ceramics in the Hf-Al-C ternary system from near-stoichiometric feedstock powder mixtures has been exceptionally challenging due to the rapid concurrent formation of persistent, ultrafine HfC impurities. This work synthesized ceramics containing the nanolaminated Hf5Al2C3 ‘superstructure’, showing that it comprises alternating Hf2AlC and Hf3AlC2 atomic stackings. For the first time, the Hf5Al2C3 complex structure was associated with the topotactic transformation of Hf2AlC into Hf3AlC2, which is observed upon heating the powder compact to temperatures higher than 1500 °C; moreover, an inverse decomposition reaction of Hf3AlC2 into Hf2AlC was observed as result of further heating the powder compact to temperatures exceeding 1600 °C. The crystal structure and lattice parameters of the Hf5Al2C3 ‘superstructure’ were determined. MAX phase ceramics containing up to 40–45 wt% Hf3AlC2/Hf2AlC were produced with HfC as the main competing phase. The hardness and damage tolerance of these MAX phase ceramics were also evaluated.

Thermo-lp: A computational tool to evaluate reaction thermodynamics for synthesizing Mn+1AXn (MAX) phases based on linear programming optimization method

Thermo-lp (Thermodynamics-Linear Programing) is a computational program written in C and Python for evaluating the thermodynamic formability of MAX phases at the finite temperature, including configurational, electronic, and vibrational entropies. The program uses the phonon density of states (PDOS) and electron density of states (EDOS) as the main inputs to obtain the Gibbs free energy in a temperature range from 0 K to 2000 K for each crystal structure in the self-contained structural and thermodynamic data pool. Thermo-lp offers a highly reliable evaluation of the overall thermodynamic stability of a target MAX phase with respect to many competing impurities using linear programing optimization algorithm. Thermo-lp program is also capable to simultaneously compose and optimize the synthetic pathways for the target MAX phase due to the implementation of constrained linear programing procedure. The capabilities of Thermo-lp program are demonstrated using the quaternary Cr2TiAlC2 o-MAX compound as the typical example by successfully predicting the thermodynamically most feasible synthetic route, and the most likely impurities at 1724 K for the annealing temperature. Program summaryProgram Title: Thermo-lpCPC Library link to program files:https://doi.org/10.17632/ykdpvcr8by.1Developer's repository link:https://gitlab.com/FxhLn/thermo-lp.gitLicensing provisions: MITProgramming language: C and PythonNature of problem: Evaluating the thermodynamic formability of a MAX phase and finding the most competing impurities associated with a specific synthetic pathway among many possible decomposition reactions requires an efficient and reliable searching algorithm within a large structural data pool.Solution method: Using phonon density of states and electron density of states as the main input data to calculate the finite-temperature corrections to Gibbs free energy. Utilizing the advanced linear programing optimization procedure to evaluate the overall thermodynamic formability of MAX phase with respect to competing impurities based on a self-built thermodynamic data pool.

MAX phase forming mechanism of M–Al–C (M = Ti, V, Cr) coatings: In-situ X-ray diffraction and first-principle calculations

• The phase evolution of MAX phases dependent on temperature were clarified using in-situ XRD. • First-principle calculations correlated with the experience revealed the phase forming mechanism. • The relationship between phase composition and mechanical properties was established. • This study provided a deeper understanding to guide the preparation of high-purity MAX phase coatings. The interesting hybrid properties of ceramics and metals induced by unique nano-laminated structures make the Mn+1AXn (MAX) phase attractive as a potential protective coating for vital structural components in harsh systems. However, an extremely narrow phase-forming region makes it difficult to prepare MAX phase coatings with high purity, which is required to obtain coatings with high-temperature anti-oxidation capabilities. This work describes the dependence of the phase evolution in deposited M–Al–C (M = Ti, V, Cr) coatings as a function on temperature using in-situ X-ray diffraction analysis. Compared to V2AlC and Cr2AlC MAX phase coatings, the Ti2AlC coating displayed a higher phase-forming temperature accompanied by a lack of any intermediate phases before the appearance of the Ti2AlC MAX phase. The results of the first-principle calculations correlated with the experience in which Ti2AlC exhibited the largest formation energy and density of states. The effect of the phase compositions of these three MAX phase coatings on mechanical properties were also investigated using ex-situ Vickers and nano-indenter tests, demonstrating the improved mechanical properties with good stability at high temperatures. These findings provide a deeper understanding of the phase-forming mechanism of MAX phase coatings to guide the preparation of high-purity MAX phase coatings and the optimization of MAX phase coatings with expected intermediate phases such as Cr2C, V2C etc., as well as their application as protective coatings in temperature-related harsh environments.

Synthesis and in situ sulfidation of molybdenum carbide MXene using fluorine-free etchant for electrocatalytic hydrogen evolution reactions

Synthesizing MXenes from Mn+1AXn (MAX) phases using hazardous hydrogen fluoride is a common and effective method. However, fluorine termination on the basal planes and edges of the resulting MXenes is undesirable for the electrocatalytic hydrogen evolution reaction (HER), while oxygen (O), hydroxyl (OH), and sulfur (S) termination favors this reaction. Herein, we unveil a simple fluorine-free exfoliation and two-step vulcanization method for synthesizing molybdenum sulfide-modified molybdenum carbide (MoS2/Mo2CTx MXene, T = OH, O, S) for the HER in alkaline medium. Microwave-assisted hydrothermal treatment of the MAX phase (Mo3AlC2) with sodium hydroxide-sodium sulfide as an etching solution and thioacetamide as a source of sulfide ions enabled the selective dissolution of the aluminum (Al) layer and sulfidation of the surface Mo atoms to form amorphous MoS2. Thus, the vulcanization of Mo2CTx MXene resulted in the formation of MoS2/Mo2CTx MXene. The MoS2 formed on the surface of Mo2CTx provided enhanced stability by preventing oxidation. MoS2/Mo2CTx exhibited enhanced electrocatalytic activity toward the HER, mainly due to the O, OH, and amorphous MoS2 functionalities. The MoS2 sites on the surface exhibited an overpotential of 110 ± 7 mV at a current density of 10 mA cm−2 as a result of enhanced charge transfer and mass transfer. Thus, the sulfidation method demonstrated herein is capable of producing amorphous MoS2 structures on Mo2CTx MXene, which could be applied for the surface modification of other molybdenum-based nanomaterials or electrocatalysts to improve stability and enhance electrocatalytic activity.

A review of novel ternary nano-layered MAX phases reinforced AZ91D magnesium composite

In recent decades, the demand for lightweight and high specific strength materials brings about the development of magnesium matrix composites. Different from some traditional binary ceramic particles, such as SiC, Al2O3, the novel ternary nano-layered Mn+1AXn (MAX) phase carbide or nitride ceramics exhibit metal-like properties and self-lubricate capacity (where “M” is an early transition metal, “A” belongs to the group A element, “X” is C or/and N, and n = 1–3). Ti2AlC, as the representative of the MAX phase, was interestingly introduced into the magnesium matrix. Layered Ti2AlC MAX phased reinforced AZ91D magnesium composites manufactured through the stir casting exhibit sufficient deformation capacity due to unique deformation behaviors of MAX, namely delamination and the formation of kinking band. Further, the Ti2AlC-AZ91D composites exhibit a distinctive characteristic in strengthening mechanism, damping mechanism and tribological capacity due to the other special properties of MAX phase, such as self-lubricated property. Accordingly, to give a comprehensive understanding, we overviewed the fabrication process, microstructural characterization, mechanical properties, damping property and tribological capacity on these composites. In order to understand the A-site effect in MAX phase on the microstructure, we introduced another representative Ti3SiC2 MAX phase to explain the interfacial evolution. In addition, due to the high aspect ratio of MAX, MAX particles could be orientationally regulated in Mg matrix by plastic deformation such as hot extrusion. Herein, we discussed the anisotropic mechanical and physical properties of the textured composites produced by hot extrusion. Moreover, the potential applications and future development trends of MAX phases reinforced magnesium matrix composites were also given and prospected.

Phase orientation improved the corrosion resistance and conductivity of Cr2AlC coatings for metal bipolar plates

In view of the Mn+1AXn (MAX) phase coatings benefiting the adaptive passivation film for good corrosion resistance and high electronic density of states for excellent electrical conductivity, here, we reported the Cr2AlC MAX phase coatings with different preferred orientations by a homemade technique consisting of vacuum arc and magnetron sputtering. The dependence of surface and interface microstructural evolution upon the corrosion and electrochemical properties of deposited coating was focused. Results showed that all the Cr2AlC coatings with different phase orientations greatly improved the performance of stainless steel (SS) 316 L substrate. Specifically, the lowest value of interface contact resistance (ICR) reached to 3.16 mΩ cm2 and the lowest corrosion current density was 2 × 10−2 μA cm−2, which were much better than those of bare SS316L. The combined studies of electrochemical properties and theoretical calculations demonstrated that the Cr2AlC coatings with preferred (103) orientation were easier to form oxide passivation film on their surface to increase the corrosion resistance.

Tribo-Surface Variation Caused by Ti2AlC and Ti3AlC2 Particles-Containing Lubricant under Cyclic Impact Loading

Mn+1AXn (MAX) phase materials present an attractive potential for friction reduction and wear resistance applications due to the ternary layered structure. This work was done to investigate how the combination of Ti2AlC and Ti3AlC2 MAX phase particles with zinc dialkyl dithiophosp (ZDDP) additives in the lubricant affected the tribo-surface by means of a reciprocating test rig with cyclic impact loading. The results indicated that the friction and wear properties of Ti3AlC2-containing lubricant were better than those of Ti2AlC-containing lubricant. The distinctive microstructure of worn surface caused by the Ti3AlC2 particles was characterized by the uniform distribution of many fine scratches, while the other was distributed with more peeling pits by the Ti2AlC particles. The tribo-chemical reaction of ZDDP involving Ti3AlC2 particles promoted a larger regional distribution of the tribofilm and the generation of short-chain phosphates. The synergistic effect of Ti3AlC2 particles and ZDDP additives led to excellent tribological properties.

Near-room temperature ferromagnetic behavior of single-atom-thick 2D iron in nanolaminated ternary MAX phases

Mn+1AXn (MAX) phases' nanolaminated ternary carbides or nitrides possess a unique crystal structure in which single-atom-thick “A” sublayers are interleaved by alternative stacking of a “Mn+1Xn” sublayer; these materials have been investigated as promising high-safety structural materials for industrial applications because of their laminated structure and metal and ceramic properties. However, limited of A-site elements in the definition of Mn+1AXn phases, it is a huge challenge for designing nanolaminated ferromagnetic materials with single-atom-thick two-dimensional iron layers occupying the A layers in the Mn+1AXn phases. Here, we report three new ternary magnetic Mn+1AXn phases (Ta2FeC, Ti2FeN, and Nb2FeC) with A sublayers of single-atom-thick two-dimensional iron through an isomorphous replacement reaction of Mn+1AXn precursors (Ta2AlC, Ti2AlN, and Nb2AlC) with a Lewis acid salts (FeCl2). All these Mn+1AXn phases exhibit ferromagnetic behavior. The Curie temperatures of the Ta2FeC and Nb2FeC Mn+1AXn phases are 281 and 291 K, respectively, i.e., close to room temperature. The saturation magnetization of these ternary magnetic MAX phases is almost two orders of magnitude higher than V2(Sn,Fe)C, whose A-site is partially substituted by Fe. Theoretical calculations on magnetic orderings of spin moments of Fe atoms in these nanolaminated magnetic Mn+1AXn phases reveal that the magnetism can be mainly ascribed to an intralayer exchange interaction of the two-dimensional Fe atomic layers. Owing to the richness in composition of Mn+1AXn phases, our work provides a large imaginary space for constructing functional single-atom-thick two-dimensional layers in materials using these nanolaminated templates.

High-throughput reaction engineering to assess the oxidation stability of MAX phases

The resistance to oxidizing environments exhibited by some Mn+1AXn (MAX) phases stems from the formation of stable and protective oxide layers at high operating temperatures. The MAX phases are hexagonally arranged layered nitrides or carbides with general formula Mn+1AXn, n = 1, 2, 3, where M is early transition elements, A is A block elements, and X is C/N. Previous attempts to model and assess oxide phase stability in these systems has been limited in scope due to higher computational costs. To address the issue, we developed a machine-learning driven high-throughput framework for the fast assessment of phase stability and oxygen reactivity of 211 chemistry MAX phase M2AX. The proposed scheme combines a sure independence screening sparsifying operator-based machine-learning model in combination with grand-canonical linear programming to assess temperature-dependent Gibbs free energies, reaction products, and elemental chemical activity during the oxidation of MAX phases. The thermodynamic stability, and chemical activity of constituent elements of Ti2AlC with respect to oxygen were fully assessed to understand the high-temperature oxidation behavior. The predictions are in good agreement with oxidation experiments performed on Ti2AlC. We were also able to explain the metastability of Ti2SiC, which could not be synthesized experimentally due to higher stability of competing phases. For generality of the proposed approach, we discuss the oxidation mechanism of Cr2AlC. The insights of oxidation behavior will enable more efficient design and accelerated discovery of MAX phases with maintained performance in oxidizing environments at high temperatures.

Covalent Surface Alteration of MXenes and Its Effect on Superconductivity

Surface functional groups such as F, O, and OH attached to MXenes have a profound impact on the electronic properties. Generally, MXenes are synthesized by the aqueous acidic etching of the MAX phase, and these functional groups are inherently incorporated during the synthesis. Recently, covalent surface modification of MXene has been demonstrated at low temperature using molten inorganic salts.

Butane Dry Reforming Catalyzed by Cobalt Oxide Supported on Ti2 AlC MAX Phase.

MAX (Mn+1AXn) phases are layered carbides or nitrides with a high thermal and mechanical bulk stability. Recently, it was shown that their surface structure can be modified to form a thin non‐stoichiometric oxide layer, which can catalyze the oxidative dehydrogenation of butane. Here, the use of a Ti2AlC MAX phase as a support for cobalt oxide was explored for the dry reforming of butane with CO2, comparing this new catalyst to more traditional materials. The catalyst was active and selective to synthesis gas. Although the surface structure changed during the reaction, the activity remained stable. Under the same conditions, a titania‐supported cobalt oxide catalyst gave low activity and stability due to the agglomeration of cobalt oxide particles. The Co3O4/Al2O3 catalyst was active, but the acidic surface led to a faster deactivation. The less acidic surface of the Ti2AlC was better at inhibiting coke formation. Thanks to their thermal stability and acid‐base properties, MAX phases are promising supports for CO2 conversion reactions.

Screen the elastic and thermodynamic properties of MAX solid solution using DFT procedue: Case study on (Ti1-xVx)2AlC

As one of Mn+1AXn (MAX) family, where M is an early transition metal, A is an A-group element, and X is either C or N and n = 1, 2, and 3, Ti2AlC is a promising candidate material for nuclear energy industry due to its unique features such as elastically stiff, good electrical conductivity, high thermal conductivity and excellent resistance to high temperature oxidation and corrosion. However, the mechanical and thermal properties of Ti2AlC compound are expected to be improved. For the first time, the effect of V content on the structural, elastic, electronic and thermodynamic properties of the (Ti1-xVx)2AlC (x = 0, 0.25, 0.50, 0.75 and 1.00) solid solutions was examined systematically and their compression behavior under 50 GPa was studied using density functional theory (DFT). The optimized lattice constants agree well with the experimental values and decrease with the increase of V content. The (Ti1-xVx)2AlC solid solutions are compressible along both a and c directions in the pressure range of 0–50 GPa. Calculated elastic constants verified mechanical stability under 50 GPa. The constant C44, directly related to the valence electron concentration, is found to increase with increasing V content. The bulk modulus, shear modulus, Young's modulus and Vickers hardness are found to reach a significant maximum value respectively when V content is 75%, and the reason is studied. The shear anisotropy factors show that (Ti1-xVx)2AlC compounds containing Ti and V are more anisotropic than Ti2AlC, and they have a tendency towards improved ductility. The metallic behaviors of (Ti1-xVx)2AlC solid solutions are confirmed by analyzing the electronic band structures and density of states. The thermal properties imply that the (Ti0.25V0.75)2AlC is expected to be more thermally conductive due to its highest Debye temperature of 771K of the five compounds. In addition, the bulk modulus, shear modulus, Young's modulus and Debye temperature increase with the increase of pressure under 50 GPa. The results reveal that the mechanical properties of Ti2AlC are improved much better than the thermal properties by the inclusion of V. Especially, the (Ti0.25V0.75)2AlC MAX phase in (Ti1-xVx)2AlC solid solutions is probably the most suitable candidate material for mechanical and thermal applications at high temperature.

Diffusion-controlled intercalation approach to synthesize the Ti2AlC MAX phase coatings at low temperature of 550 °C

Mn+1AXn (MAX) phase materials have unique nano-laminated structures and exhibit interesting hybrid properties with ceramics and metals. However, high synthesis temperatures, e.g. typically ≥700 °C for Ti2AlC coatings, are the key barriers to their wide application on various substrates. In this study, Ti2AlC MAX phase coatings were firstly fabricated by annealing the pre-designed α-TiC0.65/Al multilayer coatings at temperatures as low as 550 °C till now, which is the lowest synthesis temperature compared to already-reported literatures. Different with the common used short-time annealing (1–3 h), noted that the long-time annealing from 15 h to 400 h was particularly conducted based on the sluggish diffusion kinetics at lower temperature. Moreover, the dependence of structural evolution upon annealing proposed that Al diffusion-controlled intercalation process played the key factor to reduce the the formation temperature of Ti2AlC MAX phase. The results provide a strategy to fabricate high-quality Ti2AlC MAX phase coatings at 550 °C for wide application of temperature-sensitive substrates.

Anisotropic swelling and microcracking of neutron irradiated Ti3AlC2–Ti5Al2C3 materials

Mn+1AXn (MAX) phase materials based on Ti–Al–C have been irradiated at 400°C (673K) with fission neutrons to a fluence of 2×1025n/m2 (E>0.1MeV), corresponding to ~2 displacements per atom (dpa). We report preliminary results of microcracking in the Al-containing MAX phase, which contained the phases Ti3AlC2 and Ti5Al2C3. Equibiaxial ring-on-ring tests of irradiated coupons showed that samples retained 10% of pre-irradiated strength. Volumetric swelling of up to 4% was observed. Phase analysis and microscopy suggest that anisotropic lattice parameter swelling caused microcracking. Variants of titanium aluminum carbide may be unsuitable materials for irradiation at light water reactor-relevant temperatures.

Tribological behavior of selected Mn + 1AXn phase thin films on silicon substrates

In the last years, Mn+1AXn (MAX) phases came into the focus of functional thin film research. Potential fields of application for MAX phases are structural materials for high temperatures, tribological protective coatings, electrical contacts in aggressive environments, and as sensing materials in sensor technology.This paper focuses on the tribological behavior of Ti3SiC2, Ti2AlN and Cr2AlC phase thin films against a counterpart bearing steel 1.3505. The MAX films are deposited by magnetron sputtering of elemental multilayers and a rapid thermal annealing synthesis. The formation of the MAX phases is investigated by X-ray diffraction and transmission electron microscopy. The reciprocating micro-tribological sliding against steel balls, scanning electron microscopy and energy dispersive X-ray spectroscopy revealed an adhesive wear mechanism for Cr2AlC and Ti2AlN with friction coefficients in the range of 0.30 to 0.70 and 0.15 to 0.50, respectively. The best friction and wear behavior were observed for Ti3SiC2 with a friction coefficient in the range of 0.15 to 0.25. Furthermore, for all MAX phases, hypotheses for the wear mechanisms are formulated.

A genomic approach to the stability, elastic, and electronic properties of the MAX phases

In this study, we report a comprehensive assessment on the elastic and electronic properties of 792 possible MAX (Mn+1AXn) phases with n = 1–4 using ab initio methods. These crystals are then screened based on their elastic and thermodynamic stability resulting in a large database of 665 viable crystals. All the experimentally verified MAX phases passed the screening. Various correlations among and between them are fully explored. In particular, the key elements in the interdependence between the elastic properties together with mechanical parameter derived from them and the electronic structure are identified. Detailed analysis of various correlation plots shows that there is a clear correspondence between bulk modulus K and total bond order density (TBOD). Calculations show a marked difference between the carbides and nitrides. This database is also used to test the efficacy of data mining algorithms for materials genome. We further identified several thermodynamically stable new MAX phases with unusual mechanical parameters that have never been synthesized in the laboratory or theoretically investigated. The complete database on the elastic and electronic structure together with the mechanical parameters for these 665 MAX phases compounds are included in the Supplementary Materials and fully accessible.

Ab initio study of irradiation tolerance for different Mn+1AXn phases: Ti3SiC2 and Ti3AlC2

Layered ternary Mn+1AXn (MAX) materials are recently proposed to be promising candidates for future fission and fusion programmes because of their unique properties inherited from both ceramics and metals. However, different Mn+1AXn materials demonstrate different behaviors when exposed to energetic neutron or ion irradiations. Based on first-principles calculations, we have investigated the irradiation tolerance of two typical Mn+1AXn materials: Ti3SiC2 and Ti3AlC2 from two aspects. First, we make a detailed analysis on the interatomic bonding characters, which are believed to be responsible for the resistance to radiation-induced amorphization. Second, the formation energies of various intrinsic and antisite defects in these two compounds are calculated in order to elucidate their amorphization mechanism. Our results show that the absence of orbitals overlap of Al-C in Ti3AlC2 renders it more resistant to amorphization compared to Ti3SiC2. In addition, the antisite defects AlTi(1) and AlTi(2) in Ti3AlC2 have much lower formation energies compared to SiTi(1) and SiTi(2) in Ti3SiC2, which implies that the replacement of Ti with Al is easier than Si, thus providing an alternative way to accommodate the defects resulted from irradiation damage cascades. These results indicate that Ti3AlC2 is more irradiation tolerant than Ti3SiC2, in accordance with experimental observations. Our results have profound implications for the choice of appropriate MAX phase with best performance to be used in next reaction reactors.

High-temperature neutron diffraction and first-principles study of temperature-dependent crystal structures and atomic vibrations in Ti3AlC2, Ti2AlC, and Ti5Al2C3

Herein we report on the thermal expansions and temperature-dependent crystal structures of select ternary carbide Mn+1AXn (MAX) phases in the Ti–Al–C phase diagram in the 100−1000 °C temperature range. A bulk sample containing 38(±1) wt. % Ti5Al2C3 (“523”), 32(±1) wt. % Ti2AlC (“211”), 18(±1) wt. % Ti3AlC2 (“312”), and 12(±1) wt. % (Ti0.5Al0.5)Al is studied by Rietveld analysis of high-temperature neutron diffraction data. We also report on the same for a single-phase sample of Ti3AlC2 for comparison. The thermal expansions of all the MAX phases studied are higher in the c direction than in the a direction. The bulk expansion coefficients—9.3(±0.1)×10−6 K−1 for Ti5Al2C3, 9.2(±0.1) ×10−6 K−1 for Ti2AlC, and 9.0(±0.1)×10−6 K−1 for Ti3AlC2—are comparable within one standard deviation of each other. In Ti5Al2C3, the dimensions of the Ti–C octahedra for the 211-like and 312-like regions are comparable to the Ti–C octahedra in Ti2AlC and Ti3AlC2, respectively. The isotropic mean-squared atomic displacement parameters are highest for the Al atoms in all three phases, and the values predicted from first-principles phonon calculations agree well with those measured.

Material properties and machining performance of hybrid Ti2AlN bulk material for micro electrical discharge machining

Mn+1AXn (MAX) phases are a family of nanolaminated compounds that possess unique combination of typical ceramic properties and typical metallic properties. As a member of MAX phase, Ti2AlN bulk materials are attractive for some high-temperature applications. The synthesis, characteristics and machining performance of hybrid Ti2AlN bulk materials were focused on in this work. The bulk samples mainly consisting of Ti2AlN MAX phase with density close to theoretic one were synthesized by a spark plasma sintering method. Scanning electron microscopy results indicate homogenous distribution of Ti2AlN grains in the samples. Micro-hardness values are almost constant under different loads (6–6.5 GPa). A machining test was carried out to compare the effect of material properties on micro-electrical discharge machining (micro-EDM) performance for Ti2AlN bulk samples and Ti6242 alloy. The machining performance of the Ti2AlN sample is better than that of the Ti6242 alloy. The inherent mechanism was discussed by considering their electrical and thermal conductivity.

Substrate orientation effects on the nucleation and growth of the Mn+1AXn phase Ti2AlC

The Mn+1AXn (MAX) phases are ternary compounds comprising alternating layers of a transition metal carbide or nitride and a third “A-group” element. The effect of substrate orientation on the growth of Ti2AlC MAX phase films was investigated by studying pulsed cathodic arc deposited samples grown on sapphire cut along the (0001), (101¯0), and (11¯02) crystallographic planes. Characterization of these samples was by x-ray diffraction, atomic force microscopy, and cross-sectional transmission electron microscopy. On the (101¯0) substrate, tilted (101¯8) growth of Ti2AlC was found, such that the TiC octahedra of the MAX phase structure have the same orientation as a spontaneously formed epitaxial TiC sublayer, preserving the typical TiC–Ti2AlC epitaxial relationship and confirming the importance of this relationship in determining MAX phase film orientation. An additional component of Ti2AlC with tilted fiber texture was observed in this sample; tilted fiber texture, or axiotaxy, has not previously been seen in MAX phase films.