Cr_(2)AlC,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 p...Cr_(2)AlC,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 Cr_(2)AlC 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℃ to address the real-time phase transformation for Cr_(2)AlC coating.The results demonstrated that increas-ing the temperature from 25 to 370℃ led to the structural transformation from amorphous Cr-Al-C to the crystalline Cr_(2)Al interphases.However,the high-purity Cr_(2)AlC MAX phase was distinctly formed at 500℃,accompanied by the diminished amorphous feature.With the further increase of temperature to 650℃,the decomposition of Cr_(2)AlC to Cr_(7)C_(3)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 observa-tions not only provide fundamental insight into the phase formation mechanism for high-purity Cr_(2)AlC 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.展开更多
Due to the excellent corrosion resistance and high irradiation damage resistance,Ti 2AlC MAX phase is considered as a candidate for applications as corrosion resistant and irradiation resistant protective coating.MAX ...Due to the excellent corrosion resistance and high irradiation damage resistance,Ti 2AlC MAX phase is considered as a candidate for applications as corrosion resistant and irradiation resistant protective coating.MAX phase coatings can be fabricated through firstly depositing a coating containing the three elements M,A,and X close to stoichiometry of the MAX phases using physical vapor deposition,followed by heat treatment in vacuum.In this work,Ti-Al-C coating was prepared on austenitic stainless steels by reactive DC magnetron sputtering with a compound Ti （50）Al （50） target,and CH4 used as the reactive gas.It was found that the as-deposited coating is mainly composed of Ti 3AlC antiperovskite phase with supersaturated solid solution of Al.Additionally,the ratio of Ti/Al remained the same as that of the target composition.Nevertheless,a thicker thermally grown Ti 2AlC MAX phase coating was obtained after being annealed at 800℃ in vacuum for 1 h.Meanwhile,the ratio of Ti/Al became close to stoichiometry of Ti 2AlC MAX phases.It can be understood that owing to the higher activity of Al,it diffused quickly into the substrate during annealing,and then more stable Ti 2AlC MAX phases transformed from the Ti 3AlC antiperovskite phase.展开更多
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, Al...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, Al_(2)O_(3), the novel ternary nano-layered M_(n+1)AX_(n)(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). Ti_(2)AlC, as the representative of the MAX phase, was interestingly introduced into the magnesium matrix. Layered Ti_(2)AlC 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 Ti_(2)AlC-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 Ti_(3)SiC_(2)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.展开更多
MAX phases are gaining attention as precursors of two-dimensional MXenes that are intensively pursued in applications for electrochemical energy storage.Here,we report the preparation of V_(2)SnC MAX phase by the molt...MAX phases are gaining attention as precursors of two-dimensional MXenes that are intensively pursued in applications for electrochemical energy storage.Here,we report the preparation of V_(2)SnC MAX phase by the molten salt method.V_(2)SnC is investigated as a lithium storage anode,showing a high gravimetric capacity of 490 mAh g−1 and volumetric capacity of 570 mAh cm^(−3) as well as superior rate performance of 95 mAh g^(−1)(110 mAh cm^(−3))at 50 C,surpassing the ever-reported performance of MAX phase anodes.Sup-ported by operando X-ray diffraction and density functional theory,a charge storage mechanism with dual redox reaction is proposed with a Sn-Li(de)alloying reaction that occurs at the edge sites of V_(2)SnC particles where Sn atoms are exposed to the electrolyte followed by a redox reaction that occurs at V_(2)C layers with Li.This study offers promise of using MAX phases with M-site and A-site elements that are redox active as high-rate lithium storage materials.展开更多
The MAX phases are a group of layered ternary,quaternary,or quinary compounds with characteristics of both metals and ceramics.Over recent decades,the synthesis of bulk MAX phase parts for wider engineering applicatio...The MAX phases are a group of layered ternary,quaternary,or quinary compounds with characteristics of both metals and ceramics.Over recent decades,the synthesis of bulk MAX phase parts for wider engineering applications has gained increasing attention in aerospace,nuclear,and defence industries.The recent adoption of additive manufacturing(AM)technologies in MAX phase fabrication is a step forward in this field.This work overviews the recent progress in additive manufacturing(AM)of bulk MAX phases along with the achieved geometric features,microstructures,and properties after briefing the conventional powder sintering methods of fabricating MAX phase components.Critical challenges associated with these innovative AM-based methods,including,poor AM processability,low MAX phase purity,and insufficient geometric accuracy of the final parts,are also discussed.Accordingly,outlooks for the immediate future in this area are discussed based on the optimization of present fabrication routes and the potential of other AM technologies.展开更多
Herein,a novel kind of high-entropy MAX phases,(Mo_(0.25)Cr_(0.25)Ti_(0.25)V_(0.25))_(3)AlC_(2)powders were success-fully synthesized by a newly proposed two-step solid state reaction process.The oxidation experiments...Herein,a novel kind of high-entropy MAX phases,(Mo_(0.25)Cr_(0.25)Ti_(0.25)V_(0.25))_(3)AlC_(2)powders were success-fully synthesized by a newly proposed two-step solid state reaction process.The oxidation experiments demonstrate that the oxidation products of Al_(2)Mo_(3)O_(12) and rutile TiO 2 are formed at about 600 and 800℃,respectively.Besides,the dielectric and electromagnetic(EM)wave absorption properties of(Mo_(0.25)Cr_(0.25)Ti_(0.25)V_(0.25))_(3)AlC_(2)powders and those after oxidation at different temperatures were also exam-ined.The results show that the as-synthesized(Mo_(0.25)Cr_(0.25)Ti_(0.25)V_(0.25))_(3)AlC_(2)powders possess excellent EM wave absorption performances with the minimum reflection loss(RL)of-45.80 dB(at 1.7 mm thickness)and the maximum effective absorption bandwidth(E AB)of 3.6 GHz(at 1.5 mm thickness).After oxidation at 400-800℃,due to the coupling of conductivity loss and polarization loss,(Mo_(0.25)Cr_(0.25)Ti_(0.25)V_(0.25))_(3)AlC_(2)powders can retain good EM wave absorption properties in a certain frequency range.In this paper,the effects of oxidation on EM wave absorption properties of high-entropy MAX phases were systematically investigated for the first time.This work manifests that high-entropy MAX phases are promising EM wave absorbing candidates and can maintain good EM wave absorption performances after oxidation.展开更多
Medium-or high-entropy materials have great potential for applications due to their diverse compo-sitions and unexpected physicochemical properties.Herein,a novel medium-entropy(TiVNb)_(2)AlC was synthesized via hot p...Medium-or high-entropy materials have great potential for applications due to their diverse compo-sitions and unexpected physicochemical properties.Herein,a novel medium-entropy(TiVNb)_(2)AlC was synthesized via hot pressing at 1400℃from three individual M_(2)AlC(M=Ti,V,Nb)MAX phases.The microstructure of(TiVNb)_(2)AlC was characterized from the microscale to the atomic scale by scanning electron microscope microscopy(SEM),scanning transmission electron microscopy(STEM),and energy dispersive spectroscopy(EDS).The results showed that Ti,V,and Nb atoms were fully solid-soluble in the M-sites of the M_(2)AlC MAX phase.Compared with three individual MAX phases,the thermal conduc-tivity of(TiVNb)_(2)AlC was reduced greatly in the temperature range of 293-1473 K,and its mechanical properties(including Young’s modulus,Vickers hardness,and bending strength)were all increased due to the solid solution strengthening and electronic mechanism.展开更多
Defects engineering is an effective strategy for manipulating electromagnetic parameters and enhancing electromagnetic wave(EMW)absorption capacity.However,the relationship between them is not clear,especially in soli...Defects engineering is an effective strategy for manipulating electromagnetic parameters and enhancing electromagnetic wave(EMW)absorption capacity.However,the relationship between them is not clear,especially in solid solution structures.In this work,a series of(Cr_(1-x)V_(x))_(2)AlC MAX phase solid solutions with layered structure were prepared via tuning the ratio of Cr and V to explore their EMW absorption performance.The experimental results indicated that the doping of V atoms at the M-site could effectively regulate its impedance matching and EMW absorption properties by introducing appropriate numbers of defects in the crystal,such as twin boundaries,dislocations and lattice distortions.Among them,if Cr:V=3:1,Cr_(1.5)V_(0.5)AlC,as radar absorption materials,could reach a strong reflection loss of-51.8 dB at the frequency of 12.8 GHz under an ultra-thin thickness of 1.3 mm.The reflection loss value could attain-10 dB in a wide frequency range of 2.7-18 GHz and thickness range of 1-5 mm.In addition,after high temperature and acid-alkali immersion treatment,this sample still had good EMW absorption capability,and the effective absorption bandwidth was enhanced from 2.3 to 2.6 GHz after concentrated acid immersion or 3.1 GHz after concentrated alkali immersion.This work has great reference significance for the research and development of high-performance MAX-based EMW absorption materials in harsh environments.展开更多
The solid solution of (Cr2-xMnx)GaC with magnetic properties was synthesized by pressureless sintering.The composition,morphology,and magnetic properties of products were characterized by X-ray diffraction (XRD),scann...The solid solution of (Cr2-xMnx)GaC with magnetic properties was synthesized by pressureless sintering.The composition,morphology,and magnetic properties of products were characterized by X-ray diffraction (XRD),scanning electron microscopy (SEM),transmission electron microscopy (TEM),and vibrating sample magnetometer (VSM).The experimental results indicate that the solid solubility of Mn is related to the value of x,which reaches the maximum at x=0.4 and the characteristic peaks shift effect is most obvious.After the solution treatments,the samples of (Cr2-xMnx)GaC still presents the layered structure of MAX phase,and the lattice parameter has decreased slightly.By characterizing the magnetic properties of (Cr2-xMnx)GaC,the successful doping of Mn atoms was confirmed,and the intensity of magnetism was positively correlated with the doping amounts of Mn.展开更多
The interesting hybrid properties of ceramics and metals induced by unique nano-laminated structures make the M_(n+1)AX n(MAX)phase attractive as a potential protective coating for vital structural compo-nents in hars...The interesting hybrid properties of ceramics and metals induced by unique nano-laminated structures make the M_(n+1)AX n(MAX)phase attractive as a potential protective coating for vital structural compo-nents 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 V_(2)AlC and Cr_(2)AlC MAX phase coatings,the Ti_(2)AlC coating displayed a higher phase-forming tempera-ture accompanied by a lack of any intermediate phases before the appearance of the Ti_(2)AlC MAX phase.The results of the first-principle calculations correlated with the experience in which Ti_(2)AlC 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 Cr_(2)C,V_(2)C etc.,as well as their application as protective coat-ings in temperature-related harsh environments.展开更多
321 phases are an atypical series of MAX phases,in which A=As/P,with superior elastic properties,fea-turing in the MA-triangular-prism bilayers in the crystal structure.Until now,besides Nb 3 As 2 C,the pure phases of...321 phases are an atypical series of MAX phases,in which A=As/P,with superior elastic properties,fea-turing in the MA-triangular-prism bilayers in the crystal structure.Until now,besides Nb 3 As 2 C,the pure phases of the other 321 compounds have not been realized,hampering the study of their intrinsic prop-erties.Here,molten-salt sintering(MSS)and solid-state synthesis(SSS)were applied to synthesize As/P-containing 321 phases and 211 phases.Analyzing the phase composition of the end-product via multiple-phase Rietveld refinement,we found that MSS can effectively improve the purity of P-containing MAX phases,with the phase content up to 99%in Nb_(3)P_(2)C and 75.4(5)%in Nb 2 PC.In contrast,MSS performed poorly on As-containing MAX phases,only 8.9(4)%for Nb 3 As 2 C and 64(2)%for Nb 2 AsC,as opposed to the pure phases obtained by SSS.The experimental analyses combined with first-principles calculations reveal that the dominant formation route of Nb_(3)P_(2)C is through NbP+Nb+C→Nb_(3)P_(2)C.Moreover,we found that the benefits of MSS on P-containing MAX phases are on the facilitation of three consid-ered chemical reaction routes,especially on Nb 2 PC+NbP→Nb_(3)P_(2)C.Furthermore,the intrinsic physical properties and Fermi surface topology of two 321 phases consisting of electron,hole,and open orbits are revealed theoretically and experimentally,in which the electron carriers are dominant in electrical trans-port.The feasible synthesis methods and the formation mechanism are instructive to obtain high-purity As/P-containing MAX phases and explore new MAX phases.Meanwhile,the intrinsic physical properties will give great support for future applications on 321 phases.展开更多
MXenes,drawn from MAX phases,are special two-dimensional substances with numerous advantages in nonlinear optics,specifically in giant and ultrashort pulsed-laser applications.Ti_(3)C_(2)T_(x)and Ti_(2)CT_(x)nanosheet...MXenes,drawn from MAX phases,are special two-dimensional substances with numerous advantages in nonlinear optics,specifically in giant and ultrashort pulsed-laser applications.Ti_(3)C_(2)T_(x)and Ti_(2)CT_(x)nanosheets however rapidly deteriorate under ambient conditions,limiting their applications.This paper demonstrates how excellent modulation depth of one of the MAX phase compounds vanadium zinc carbide(V_2ZnC)makes it a brilliant saturable absorber(SA)in passively Q-switched all-fiber pulsed lasers,integrated such that a 16.73-μm V_(2)ZnC-polyvinyl alcohol(PVA)thin film acts as SA in the laser.Saturable and non-saturable absorptions were found to be 13.2%and 10.47%,while saturation optical intensity and modulation depth were 6.25 k W/cm^(2)and 12.43%,respectively,illustrating the optical nonlinearity.The superiority of MAX-PVA,fabricated in four distinct ratios,was demonstrated by the fact that it self-starts a giant pulsed laser at pump power as low as 22.5 mW and firmly accomplished 120.6 kHz repetition rate with a pulse width of 2.08μs.It is a fine SA for the use of pulsed-laser production using all-fiber laser due to fabrication simplicity and great optical,thermophysical,and mechanical qualities.展开更多
First-principles computation on the basis of density functional theory(DFT) is executed with the CASTEP code to explore the structural, elastic, and electronic properties along with Debye temperature and theoretical V...First-principles computation on the basis of density functional theory(DFT) is executed with the CASTEP code to explore the structural, elastic, and electronic properties along with Debye temperature and theoretical Vickers’ hardness of newly discovered ordered MAX phase carbide Mo2TiAlC2. The computed structural parameters are very reasonable compared with the experimental results. The mechanical stability is verified by using the computed elastic constants. The brittleness of the compound is indicated by both the Poisson’s and Pugh’s ratios. The new MAX phase is capable of resisting the pressure and tension and also has the clear directional bonding between atoms. The compound shows significant elastic anisotropy. The Debye temperature estimated from elastic moduli(B, G) is found to be 413.6 K. The electronic structure indicates that the bonding nature of Mo2TiAlC2is a mixture of covalent and metallic with few ionic characters. The electron charge density map shows a strong directional Mo–C–Mo covalent bonding associated with a relatively weak Ti–C bond.The calculated Fermi surface is due to the low-dispersive Mo 4d-like bands, which makes the compound a conductive one.The hardness of the compound is also evaluated and a high value of 9.01 GPa is an indication of its strong covalent bonding.展开更多
MAX phase ceramics is a large family of nanolaminate carbides and nitrides,which integrates the advantages of both metals and ceramics,in general,the distinct chemical inertness of ceramics and excellent physical prop...MAX phase ceramics is a large family of nanolaminate carbides and nitrides,which integrates the advantages of both metals and ceramics,in general,the distinct chemical inertness of ceramics and excellent physical properties like metals.Meanwhile,the rich chemical and structural diversity of the MAXs endows them with broad space for property regulation.Especially,a much higher self-lubricity,as well as wear resistance,than that of traditional alloys and ceramics,has been observed in MAXs at elevated temperatures in recent decades,which manifests a great application potential and sparks tremendous research interest.Aiming at establishing a correlation among structure,chemical composition,working conditions,and the tribological behaviors of MAXs,this work overviews the recent progress in their high-temperature(HT)tribological properties,accompanied by advances in synthesis and structure analysis.HT tribological-specific behaviors,including the stress responses and damage mechanism,oxidation mechanism,and wear mechanism,are discussed.Whereafter,the tribological behaviors along with factors related to the tribological working conditions are discussed.Accordingly,outlooks of MAX phase ceramics for future HT solid lubricants are given based on the optimization of present mechanical properties and processing technologies.展开更多
MAX phases and corresponding 2 D derivative MXenes have attracted considerable interests due to not only their fascinating mechanical,physical and chemical properties but also their unique atomically laminated structu...MAX phases and corresponding 2 D derivative MXenes have attracted considerable interests due to not only their fascinating mechanical,physical and chemical properties but also their unique atomically laminated structures.As the most important way to tailor the materials properties,the structural defects in MAX phases and MXenes have been extensively investigated but lack of systematic survey although six reviews and two books in this field have been published.To make the defect-engineering based materials design and exploration more efficient and targeted,this paper provides a review of the recent progress on the nature of different-dimensional structural defects and their influence on the properties,in the hope of facilitating the conversion of established experiment and simulation results into practical guideline for optimizing defects in a broad range of demand-oriented materials development in the future.Also,unsolved issues on the structural defects of these scientifically and technologically important materials are also highlighted for the future study.展开更多
Ternary layered MAX phase materials have excellent corrosion and oxidation resistance.However,their applications are limited by low hardness yet poor crack resistance,due to weak M–A metallic bonding and poor crack r...Ternary layered MAX phase materials have excellent corrosion and oxidation resistance.However,their applications are limited by low hardness yet poor crack resistance,due to weak M–A metallic bonding and poor crack resistance stemming from their extremely high plastic anisotropy with ultrahigh c/a ratio(>4).In this work,we demonstrate significant improvements in both hardness and crack resistance when the grain size of MAX phases is reduced to nanoscale.Nanocrystalline Cr_(2)AlC MAX coatings with grain size ranging from 0 to 100 nm were successfully fabricated using a controllable PVD-based twostep bottom-up strategy.Remarkable improvements are achieved in both hardness and toughness,with hardness(15.5 GPa)/record-high strength(8.53 GPa)and toughness/plasticity peaking at a grain size of 15.8 nm near the critical value.Such unusual hardening-toughening effect at nanoscale stems from homogeneous deformation mode transitions with synchronous Hall–Petch hardening.Transmission electron microscopic observations proved that both pyramidal and prismatic slip,which are unlikely to operate at microcrystalline regime at room temperature,are completely active at nanocrystalline regime,unlocking the key c-axial plasticity.As grain size further decreases approaching the critical value,a dynamic grain refinement-induced secondary sub-shear banding mechanism is triggered,which further extends the homogeneous deformation stage.These findings provide a simple route to fabricate advanced MAX phase corrosion-protection coatings with superior mechanical properties for extreme condition applications.展开更多
MAX-phase ceramics combine metallic and ceramic characteristics,while their two-dimensional(2D)derivatives,MXenes,have shown great potential as reinforcements for high-temperature structural applications.Leveraging th...MAX-phase ceramics combine metallic and ceramic characteristics,while their two-dimensional(2D)derivatives,MXenes,have shown great potential as reinforcements for high-temperature structural applications.Leveraging the structural similarity between MXenes and their MAX-phase precursors,Ti_(3)C_(2)T_(x)was incorporated into two 211-type MAX ceramics,Cr_(2)AlC and Ta_(2)AlC,to investigate its effects on mechanical properties and strengthening mechanisms.The addition of MXene improved both flexural strength and fracture toughness.The optimal enhancement was observed at 2 wt%forCr_(2)AlC(22%strength increase)and 4 wt%for Ta_(2)AlC(33%strength increase).Microstructural analysis revealed partial solid solution and TiC_(y)formation inCr_(2)AlC,while Ta_(2)AlC exhibited complete solid solution behavior.ensity functional theory(DFT)calculations confirmed that Ti ion diffusion into Ta_(2)AlC was energetically more favorable due to weaker Ta–Al bonding and larger interlayer spacing.A multi-mechanismΔσmodel was used to decouple the strengthening contributions from solid solution,grain refinement,dislocation density,and load transfer.InCr_(2)AlC,grain refinement and second-phase strengthening dominated,whereas in Ta_(2)AlC,solid solution and grain refinement prevailed.Theoretical predictions matched well with experimental data after incorporating a correction term into the shear-lag model.These findings provide insights into MXene-induced strengthening in layered ceramics and offer guidance for designing high-performance,damage-tolerant MAX-phase materials.展开更多
Due to their high-entropy effects,the high-entropy(HE)MAX-phase materials improve the comprehen-sive performance of MAX phases,opening up more possibilities for practical engineering applications.However,it is still c...Due to their high-entropy effects,the high-entropy(HE)MAX-phase materials improve the comprehen-sive performance of MAX phases,opening up more possibilities for practical engineering applications.However,it is still challenging to obtain S-containing high-entropy MAX phases because of the high volatilization behavior of sulfur,suffering from issues such as high reaction temperature and long re-action time of traditional synthesis methods.This paper proposes a novel process named as liquid metal assistant self-propagating high-temperature synthesis(LMA-SHS)for efficient synthesis of high-purity S-containing high-entropy MAX-phase materials.Low-melting-point metal(Sn or In)has been introduced into the raw mixture and melted into a liquid phase during the early stage of the SHS reaction.By serv-ing as a“binder”between transition metal atoms of the M-site due to the negative mixing enthalpy,this liquid phase can accelerate mass and heat transfer during the SHS process,ensuring a uniform solid solution of each element and realizing the synthesis of high-purity(TiNbVZr)_(2)SC in an extremely short time.The synthesis method for high-entropy MAX-phase materials developed in this study,i.e.,LMA-SHS,showing very short reaction time,low energy consumption,high yield,and low cost,has the promise to be a general energy-and resource-efficient route towards high-purity HE materials.展开更多
High-entropy nanolaminated materials, referred to as MAX phases, have exceptional potential in various fields, including physics, mechanics, and energy storage, owing to their diverse compositions and outstanding prop...High-entropy nanolaminated materials, referred to as MAX phases, have exceptional potential in various fields, including physics, mechanics, and energy storage, owing to their diverse compositions and outstanding properties. However, synthesizing stable high-entropy phases presents significant challenges because of the considerable differences in the physical and chemical properties of complex elements. In this study, we added low-melting-point metal tin (Sn) as an additive to facilitate the formation of solid solutions. The cohesion energy and formation enthalpy of the Sn-containing system are negative, which maintains the thermodynamic stability of the system, and the incorporation of Sn decreases the mixing enthalpy of the target high-entropy MAX phase and inhibits the formation of competing phases. The addition of Sn increases the lattice parameter and improves the structural stability by increasing the lattice distortion of octahedral M6X and prism M6A, which facilitates the successful synthesis of single-phase high-entropy MAX bulk materials. In addition, the high-entropy MAX phases with added Sn retain good mechanical and physical properties. This study provides a novel approach for the synthesis and application of high-entropy MAX phase materials, which has the potential to contribute to advancements in multiple technological fields.展开更多
To explore the MAX phase with experimental value over a wider range,a data-driven machine learning(ML)model was trained to rapidly predict the stability of MAX phases via a random forest classifier(RFC),support vector...To explore the MAX phase with experimental value over a wider range,a data-driven machine learning(ML)model was trained to rapidly predict the stability of MAX phases via a random forest classifier(RFC),support vector machine(SVM),and gradient boosting tree(GBT),where the deemed significant descriptors were compiled from the literature and the stability of 1804 combinations of MAX phases was collected.Using this well-trained model,190 new MAX phases were screened from 4347 MAX phases,150 of which met the criteria for thermodynamic and intrinsic stability on the basis of first-principles calculations.Additionally,with the help of the ML model,the mean number of valence electrons and the valence electron deviation are the two most critical factors influencing stability.Additionally,one of these predicted MAX phases,Ti_(2)SnN,was experimentally synthesized through Lewis acid substitution reactions at 750℃,with interesting A-site deintercalation and self-extrusion.First-principles calculations revealed that Ti_(2)SnN has lower elastic properties,higher damage tolerance and fracture toughness,and a higher coefficient of thermal expansion(CTE).展开更多
基金supported by the financial support of the National Science Fund for Distinguished Young Scholars of China(No.52025014)the National Natural Science Foundation of China(Nos.52101109 and 52171090)+1 种基金the Zhejiang Provincial Natural Science Foundation of China(No.LD24E010003 and LZJWY23E090001)the Natural Science Foundation of Ningbo(Nos.2023J410).
文摘Cr_(2)AlC,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 Cr_(2)AlC 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℃ to address the real-time phase transformation for Cr_(2)AlC coating.The results demonstrated that increas-ing the temperature from 25 to 370℃ led to the structural transformation from amorphous Cr-Al-C to the crystalline Cr_(2)Al interphases.However,the high-purity Cr_(2)AlC MAX phase was distinctly formed at 500℃,accompanied by the diminished amorphous feature.With the further increase of temperature to 650℃,the decomposition of Cr_(2)AlC to Cr_(7)C_(3)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 observa-tions not only provide fundamental insight into the phase formation mechanism for high-purity Cr_(2)AlC 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.
基金supported by the National Natural Science Foundation of China (Grant No.51522106 and Grant No.51401229)the National Science and Technology Major Project of China (Grant No.2015ZX06004-001)the Ningbo Municipal Natural Science Foundation (Grant No.2014A610013)
文摘Due to the excellent corrosion resistance and high irradiation damage resistance,Ti 2AlC MAX phase is considered as a candidate for applications as corrosion resistant and irradiation resistant protective coating.MAX phase coatings can be fabricated through firstly depositing a coating containing the three elements M,A,and X close to stoichiometry of the MAX phases using physical vapor deposition,followed by heat treatment in vacuum.In this work,Ti-Al-C coating was prepared on austenitic stainless steels by reactive DC magnetron sputtering with a compound Ti （50）Al （50） target,and CH4 used as the reactive gas.It was found that the as-deposited coating is mainly composed of Ti 3AlC antiperovskite phase with supersaturated solid solution of Al.Additionally,the ratio of Ti/Al remained the same as that of the target composition.Nevertheless,a thicker thermally grown Ti 2AlC MAX phase coating was obtained after being annealed at 800℃ in vacuum for 1 h.Meanwhile,the ratio of Ti/Al became close to stoichiometry of Ti 2AlC MAX phases.It can be understood that owing to the higher activity of Al,it diffused quickly into the substrate during annealing,and then more stable Ti 2AlC MAX phases transformed from the Ti 3AlC antiperovskite phase.
基金supported by the National Natural Science Foundation of China (No. 52175284, 52130509 and 52075543)the State Key Lab of Advanced Metmals and Materials (2021-ZD08)。
文摘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, Al_(2)O_(3), the novel ternary nano-layered M_(n+1)AX_(n)(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). Ti_(2)AlC, as the representative of the MAX phase, was interestingly introduced into the magnesium matrix. Layered Ti_(2)AlC 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 Ti_(2)AlC-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 Ti_(3)SiC_(2)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.
基金supported by the National Natural Science Foundation of China(Grants No.51902215,91426304,21671195,21805295,51902320,51902319,21875271,and U2004212)the China Postdoctoral Science Foundation(Grant No.2020M680082)+7 种基金the International Partnership Program of Chinese Academy of Sciences(Grants 174433KYSB20190019)the Leading Innovative and Entrepreneur Team Introduction Program of Zhejiang(Grant No.2019R01003)the Ningbo top-talent team program for financial supportsupport from the Swedish Government Strategic Research Area in Materials Science on Functional Materials at Link?ping University(Faculty Grant SFO Mat LiU No.200900971)support of the electron microscopy laboratory in Link?ping(Grant KAW 2015.0043)an Academy Fellow Grant(P.E.,2020.0196)the Swedish Foundation for Strategic Research(SSF)through project funding(EM16-0004)a Research Infrastructure Fellow Grant(RIF 14-0074)。
文摘MAX phases are gaining attention as precursors of two-dimensional MXenes that are intensively pursued in applications for electrochemical energy storage.Here,we report the preparation of V_(2)SnC MAX phase by the molten salt method.V_(2)SnC is investigated as a lithium storage anode,showing a high gravimetric capacity of 490 mAh g−1 and volumetric capacity of 570 mAh cm^(−3) as well as superior rate performance of 95 mAh g^(−1)(110 mAh cm^(−3))at 50 C,surpassing the ever-reported performance of MAX phase anodes.Sup-ported by operando X-ray diffraction and density functional theory,a charge storage mechanism with dual redox reaction is proposed with a Sn-Li(de)alloying reaction that occurs at the edge sites of V_(2)SnC particles where Sn atoms are exposed to the electrolyte followed by a redox reaction that occurs at V_(2)C layers with Li.This study offers promise of using MAX phases with M-site and A-site elements that are redox active as high-rate lithium storage materials.
基金financially supported by the ARC Discovery Project for funding support(No.DP210103162)。
文摘The MAX phases are a group of layered ternary,quaternary,or quinary compounds with characteristics of both metals and ceramics.Over recent decades,the synthesis of bulk MAX phase parts for wider engineering applications has gained increasing attention in aerospace,nuclear,and defence industries.The recent adoption of additive manufacturing(AM)technologies in MAX phase fabrication is a step forward in this field.This work overviews the recent progress in additive manufacturing(AM)of bulk MAX phases along with the achieved geometric features,microstructures,and properties after briefing the conventional powder sintering methods of fabricating MAX phase components.Critical challenges associated with these innovative AM-based methods,including,poor AM processability,low MAX phase purity,and insufficient geometric accuracy of the final parts,are also discussed.Accordingly,outlooks for the immediate future in this area are discussed based on the optimization of present fabrication routes and the potential of other AM technologies.
基金This work was financially supported by the Major Basic Re-search Projects of Shandong Natural Science Foundation(No.ZR2018ZB0104)the Science and Technology Development Project of Shandong Province(Nos.2016GGX102003,2017GGX20105)the Natural Science Foundation of Shandong Province(No.ZR2017BEM032).
文摘Herein,a novel kind of high-entropy MAX phases,(Mo_(0.25)Cr_(0.25)Ti_(0.25)V_(0.25))_(3)AlC_(2)powders were success-fully synthesized by a newly proposed two-step solid state reaction process.The oxidation experiments demonstrate that the oxidation products of Al_(2)Mo_(3)O_(12) and rutile TiO 2 are formed at about 600 and 800℃,respectively.Besides,the dielectric and electromagnetic(EM)wave absorption properties of(Mo_(0.25)Cr_(0.25)Ti_(0.25)V_(0.25))_(3)AlC_(2)powders and those after oxidation at different temperatures were also exam-ined.The results show that the as-synthesized(Mo_(0.25)Cr_(0.25)Ti_(0.25)V_(0.25))_(3)AlC_(2)powders possess excellent EM wave absorption performances with the minimum reflection loss(RL)of-45.80 dB(at 1.7 mm thickness)and the maximum effective absorption bandwidth(E AB)of 3.6 GHz(at 1.5 mm thickness).After oxidation at 400-800℃,due to the coupling of conductivity loss and polarization loss,(Mo_(0.25)Cr_(0.25)Ti_(0.25)V_(0.25))_(3)AlC_(2)powders can retain good EM wave absorption properties in a certain frequency range.In this paper,the effects of oxidation on EM wave absorption properties of high-entropy MAX phases were systematically investigated for the first time.This work manifests that high-entropy MAX phases are promising EM wave absorbing candidates and can maintain good EM wave absorption performances after oxidation.
基金This work was supported by the National Natural Science Foun-dation of China(Grant No.52071318)and the Fund of Science and Technology on Advanced Functional Composites Laboratory(Grant No.6142906210305).
文摘Medium-or high-entropy materials have great potential for applications due to their diverse compo-sitions and unexpected physicochemical properties.Herein,a novel medium-entropy(TiVNb)_(2)AlC was synthesized via hot pressing at 1400℃from three individual M_(2)AlC(M=Ti,V,Nb)MAX phases.The microstructure of(TiVNb)_(2)AlC was characterized from the microscale to the atomic scale by scanning electron microscope microscopy(SEM),scanning transmission electron microscopy(STEM),and energy dispersive spectroscopy(EDS).The results showed that Ti,V,and Nb atoms were fully solid-soluble in the M-sites of the M_(2)AlC MAX phase.Compared with three individual MAX phases,the thermal conduc-tivity of(TiVNb)_(2)AlC was reduced greatly in the temperature range of 293-1473 K,and its mechanical properties(including Young’s modulus,Vickers hardness,and bending strength)were all increased due to the solid solution strengthening and electronic mechanism.
基金financially supported by the National Natural Science Foundation of China(Nos.52275187 and 52202364)Natural Science Foundation of Henan(No.232300421135)+1 种基金Fundamental Research Funds for the Universities of Henan Province(No.NSFRF200101)Henan Postdoctoral Foundation(No.202101035)。
文摘Defects engineering is an effective strategy for manipulating electromagnetic parameters and enhancing electromagnetic wave(EMW)absorption capacity.However,the relationship between them is not clear,especially in solid solution structures.In this work,a series of(Cr_(1-x)V_(x))_(2)AlC MAX phase solid solutions with layered structure were prepared via tuning the ratio of Cr and V to explore their EMW absorption performance.The experimental results indicated that the doping of V atoms at the M-site could effectively regulate its impedance matching and EMW absorption properties by introducing appropriate numbers of defects in the crystal,such as twin boundaries,dislocations and lattice distortions.Among them,if Cr:V=3:1,Cr_(1.5)V_(0.5)AlC,as radar absorption materials,could reach a strong reflection loss of-51.8 dB at the frequency of 12.8 GHz under an ultra-thin thickness of 1.3 mm.The reflection loss value could attain-10 dB in a wide frequency range of 2.7-18 GHz and thickness range of 1-5 mm.In addition,after high temperature and acid-alkali immersion treatment,this sample still had good EMW absorption capability,and the effective absorption bandwidth was enhanced from 2.3 to 2.6 GHz after concentrated acid immersion or 3.1 GHz after concentrated alkali immersion.This work has great reference significance for the research and development of high-performance MAX-based EMW absorption materials in harsh environments.
基金the Foundation for Hubei Provincial Key Laboratory of Green Materials for Light Industry(No.201710A15)。
文摘The solid solution of (Cr2-xMnx)GaC with magnetic properties was synthesized by pressureless sintering.The composition,morphology,and magnetic properties of products were characterized by X-ray diffraction (XRD),scanning electron microscopy (SEM),transmission electron microscopy (TEM),and vibrating sample magnetometer (VSM).The experimental results indicate that the solid solubility of Mn is related to the value of x,which reaches the maximum at x=0.4 and the characteristic peaks shift effect is most obvious.After the solution treatments,the samples of (Cr2-xMnx)GaC still presents the layered structure of MAX phase,and the lattice parameter has decreased slightly.By characterizing the magnetic properties of (Cr2-xMnx)GaC,the successful doping of Mn atoms was confirmed,and the intensity of magnetism was positively correlated with the doping amounts of Mn.
基金financially supported by the National Natural Science Foundation of China (Nos.52025014,52171090,52101109,U22A20111).
文摘The interesting hybrid properties of ceramics and metals induced by unique nano-laminated structures make the M_(n+1)AX n(MAX)phase attractive as a potential protective coating for vital structural compo-nents 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 V_(2)AlC and Cr_(2)AlC MAX phase coatings,the Ti_(2)AlC coating displayed a higher phase-forming tempera-ture accompanied by a lack of any intermediate phases before the appearance of the Ti_(2)AlC MAX phase.The results of the first-principle calculations correlated with the experience in which Ti_(2)AlC 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 Cr_(2)C,V_(2)C etc.,as well as their application as protective coat-ings in temperature-related harsh environments.
基金supported by the National Science Foundation for Young Scientists of China(No.51902055)the Natural Science Foundation of Fujian Province(Nos.2021J011077,2021J05224,and 2020J01898).
文摘321 phases are an atypical series of MAX phases,in which A=As/P,with superior elastic properties,fea-turing in the MA-triangular-prism bilayers in the crystal structure.Until now,besides Nb 3 As 2 C,the pure phases of the other 321 compounds have not been realized,hampering the study of their intrinsic prop-erties.Here,molten-salt sintering(MSS)and solid-state synthesis(SSS)were applied to synthesize As/P-containing 321 phases and 211 phases.Analyzing the phase composition of the end-product via multiple-phase Rietveld refinement,we found that MSS can effectively improve the purity of P-containing MAX phases,with the phase content up to 99%in Nb_(3)P_(2)C and 75.4(5)%in Nb 2 PC.In contrast,MSS performed poorly on As-containing MAX phases,only 8.9(4)%for Nb 3 As 2 C and 64(2)%for Nb 2 AsC,as opposed to the pure phases obtained by SSS.The experimental analyses combined with first-principles calculations reveal that the dominant formation route of Nb_(3)P_(2)C is through NbP+Nb+C→Nb_(3)P_(2)C.Moreover,we found that the benefits of MSS on P-containing MAX phases are on the facilitation of three consid-ered chemical reaction routes,especially on Nb 2 PC+NbP→Nb_(3)P_(2)C.Furthermore,the intrinsic physical properties and Fermi surface topology of two 321 phases consisting of electron,hole,and open orbits are revealed theoretically and experimentally,in which the electron carriers are dominant in electrical trans-port.The feasible synthesis methods and the formation mechanism are instructive to obtain high-purity As/P-containing MAX phases and explore new MAX phases.Meanwhile,the intrinsic physical properties will give great support for future applications on 321 phases.
基金supported by the Ministry of Higher under Fundamental Research Grant Scheme(No.FRGS/1/2020/TK0/UTM/02/46)Nippon Sheet Glass Grant(No.R.K130000.7343.4B818)。
文摘MXenes,drawn from MAX phases,are special two-dimensional substances with numerous advantages in nonlinear optics,specifically in giant and ultrashort pulsed-laser applications.Ti_(3)C_(2)T_(x)and Ti_(2)CT_(x)nanosheets however rapidly deteriorate under ambient conditions,limiting their applications.This paper demonstrates how excellent modulation depth of one of the MAX phase compounds vanadium zinc carbide(V_2ZnC)makes it a brilliant saturable absorber(SA)in passively Q-switched all-fiber pulsed lasers,integrated such that a 16.73-μm V_(2)ZnC-polyvinyl alcohol(PVA)thin film acts as SA in the laser.Saturable and non-saturable absorptions were found to be 13.2%and 10.47%,while saturation optical intensity and modulation depth were 6.25 k W/cm^(2)and 12.43%,respectively,illustrating the optical nonlinearity.The superiority of MAX-PVA,fabricated in four distinct ratios,was demonstrated by the fact that it self-starts a giant pulsed laser at pump power as low as 22.5 mW and firmly accomplished 120.6 kHz repetition rate with a pulse width of 2.08μs.It is a fine SA for the use of pulsed-laser production using all-fiber laser due to fabrication simplicity and great optical,thermophysical,and mechanical qualities.
文摘First-principles computation on the basis of density functional theory(DFT) is executed with the CASTEP code to explore the structural, elastic, and electronic properties along with Debye temperature and theoretical Vickers’ hardness of newly discovered ordered MAX phase carbide Mo2TiAlC2. The computed structural parameters are very reasonable compared with the experimental results. The mechanical stability is verified by using the computed elastic constants. The brittleness of the compound is indicated by both the Poisson’s and Pugh’s ratios. The new MAX phase is capable of resisting the pressure and tension and also has the clear directional bonding between atoms. The compound shows significant elastic anisotropy. The Debye temperature estimated from elastic moduli(B, G) is found to be 413.6 K. The electronic structure indicates that the bonding nature of Mo2TiAlC2is a mixture of covalent and metallic with few ionic characters. The electron charge density map shows a strong directional Mo–C–Mo covalent bonding associated with a relatively weak Ti–C bond.The calculated Fermi surface is due to the low-dispersive Mo 4d-like bands, which makes the compound a conductive one.The hardness of the compound is also evaluated and a high value of 9.01 GPa is an indication of its strong covalent bonding.
基金National Natural Science Foundation ofChina,Grant/Award Number:52275212Fundamental Research Funds for theCentral Universities,Grant/Award Number:D5000230047the"Special Lubrication and Sealing forAerospace"Shaanxi Provincial Scienceand Technology Innovation Team,Grant/Award Number:2024RS-CXTD-63。
文摘MAX phase ceramics is a large family of nanolaminate carbides and nitrides,which integrates the advantages of both metals and ceramics,in general,the distinct chemical inertness of ceramics and excellent physical properties like metals.Meanwhile,the rich chemical and structural diversity of the MAXs endows them with broad space for property regulation.Especially,a much higher self-lubricity,as well as wear resistance,than that of traditional alloys and ceramics,has been observed in MAXs at elevated temperatures in recent decades,which manifests a great application potential and sparks tremendous research interest.Aiming at establishing a correlation among structure,chemical composition,working conditions,and the tribological behaviors of MAXs,this work overviews the recent progress in their high-temperature(HT)tribological properties,accompanied by advances in synthesis and structure analysis.HT tribological-specific behaviors,including the stress responses and damage mechanism,oxidation mechanism,and wear mechanism,are discussed.Whereafter,the tribological behaviors along with factors related to the tribological working conditions are discussed.Accordingly,outlooks of MAX phase ceramics for future HT solid lubricants are given based on the optimization of present mechanical properties and processing technologies.
文摘MAX phases and corresponding 2 D derivative MXenes have attracted considerable interests due to not only their fascinating mechanical,physical and chemical properties but also their unique atomically laminated structures.As the most important way to tailor the materials properties,the structural defects in MAX phases and MXenes have been extensively investigated but lack of systematic survey although six reviews and two books in this field have been published.To make the defect-engineering based materials design and exploration more efficient and targeted,this paper provides a review of the recent progress on the nature of different-dimensional structural defects and their influence on the properties,in the hope of facilitating the conversion of established experiment and simulation results into practical guideline for optimizing defects in a broad range of demand-oriented materials development in the future.Also,unsolved issues on the structural defects of these scientifically and technologically important materials are also highlighted for the future study.
基金supported by the National Sci-ence Fund for Distinguished Young Scholars of China(No.52025014)the National Natural Science Foundation of China(Nos.U22A20111 and 52171090)the Natural Science Foundation of Zhe-jiang Province(No.LD24E010003).
文摘Ternary layered MAX phase materials have excellent corrosion and oxidation resistance.However,their applications are limited by low hardness yet poor crack resistance,due to weak M–A metallic bonding and poor crack resistance stemming from their extremely high plastic anisotropy with ultrahigh c/a ratio(>4).In this work,we demonstrate significant improvements in both hardness and crack resistance when the grain size of MAX phases is reduced to nanoscale.Nanocrystalline Cr_(2)AlC MAX coatings with grain size ranging from 0 to 100 nm were successfully fabricated using a controllable PVD-based twostep bottom-up strategy.Remarkable improvements are achieved in both hardness and toughness,with hardness(15.5 GPa)/record-high strength(8.53 GPa)and toughness/plasticity peaking at a grain size of 15.8 nm near the critical value.Such unusual hardening-toughening effect at nanoscale stems from homogeneous deformation mode transitions with synchronous Hall–Petch hardening.Transmission electron microscopic observations proved that both pyramidal and prismatic slip,which are unlikely to operate at microcrystalline regime at room temperature,are completely active at nanocrystalline regime,unlocking the key c-axial plasticity.As grain size further decreases approaching the critical value,a dynamic grain refinement-induced secondary sub-shear banding mechanism is triggered,which further extends the homogeneous deformation stage.These findings provide a simple route to fabricate advanced MAX phase corrosion-protection coatings with superior mechanical properties for extreme condition applications.
基金the financial supports from the Natural Science Foundation of Jiangsu Province for Youths(No.BK20230948)the National Natural Science Foundation of China(Nos.11872171 and 52472090).
文摘MAX-phase ceramics combine metallic and ceramic characteristics,while their two-dimensional(2D)derivatives,MXenes,have shown great potential as reinforcements for high-temperature structural applications.Leveraging the structural similarity between MXenes and their MAX-phase precursors,Ti_(3)C_(2)T_(x)was incorporated into two 211-type MAX ceramics,Cr_(2)AlC and Ta_(2)AlC,to investigate its effects on mechanical properties and strengthening mechanisms.The addition of MXene improved both flexural strength and fracture toughness.The optimal enhancement was observed at 2 wt%forCr_(2)AlC(22%strength increase)and 4 wt%for Ta_(2)AlC(33%strength increase).Microstructural analysis revealed partial solid solution and TiC_(y)formation inCr_(2)AlC,while Ta_(2)AlC exhibited complete solid solution behavior.ensity functional theory(DFT)calculations confirmed that Ti ion diffusion into Ta_(2)AlC was energetically more favorable due to weaker Ta–Al bonding and larger interlayer spacing.A multi-mechanismΔσmodel was used to decouple the strengthening contributions from solid solution,grain refinement,dislocation density,and load transfer.InCr_(2)AlC,grain refinement and second-phase strengthening dominated,whereas in Ta_(2)AlC,solid solution and grain refinement prevailed.Theoretical predictions matched well with experimental data after incorporating a correction term into the shear-lag model.These findings provide insights into MXene-induced strengthening in layered ceramics and offer guidance for designing high-performance,damage-tolerant MAX-phase materials.
基金supported by the Shanghai Local Capacity Building Program(No.23010500700)the Project of Shanghai Municipal Science and Technology Commission(No.22DZ2291100)the Qinglan Project of Jiangsu Province,and the Open Project of Jiangsu Provincial Key Laboratory of Eco-Environmental Materials.
文摘Due to their high-entropy effects,the high-entropy(HE)MAX-phase materials improve the comprehen-sive performance of MAX phases,opening up more possibilities for practical engineering applications.However,it is still challenging to obtain S-containing high-entropy MAX phases because of the high volatilization behavior of sulfur,suffering from issues such as high reaction temperature and long re-action time of traditional synthesis methods.This paper proposes a novel process named as liquid metal assistant self-propagating high-temperature synthesis(LMA-SHS)for efficient synthesis of high-purity S-containing high-entropy MAX-phase materials.Low-melting-point metal(Sn or In)has been introduced into the raw mixture and melted into a liquid phase during the early stage of the SHS reaction.By serv-ing as a“binder”between transition metal atoms of the M-site due to the negative mixing enthalpy,this liquid phase can accelerate mass and heat transfer during the SHS process,ensuring a uniform solid solution of each element and realizing the synthesis of high-purity(TiNbVZr)_(2)SC in an extremely short time.The synthesis method for high-entropy MAX-phase materials developed in this study,i.e.,LMA-SHS,showing very short reaction time,low energy consumption,high yield,and low cost,has the promise to be a general energy-and resource-efficient route towards high-purity HE materials.
基金supported by the National Natural Sciences Foundation of China(Nos.52072311 and 52472079)Sichuan Science and Technology Program(2025YFHZ0082).
文摘High-entropy nanolaminated materials, referred to as MAX phases, have exceptional potential in various fields, including physics, mechanics, and energy storage, owing to their diverse compositions and outstanding properties. However, synthesizing stable high-entropy phases presents significant challenges because of the considerable differences in the physical and chemical properties of complex elements. In this study, we added low-melting-point metal tin (Sn) as an additive to facilitate the formation of solid solutions. The cohesion energy and formation enthalpy of the Sn-containing system are negative, which maintains the thermodynamic stability of the system, and the incorporation of Sn decreases the mixing enthalpy of the target high-entropy MAX phase and inhibits the formation of competing phases. The addition of Sn increases the lattice parameter and improves the structural stability by increasing the lattice distortion of octahedral M6X and prism M6A, which facilitates the successful synthesis of single-phase high-entropy MAX bulk materials. In addition, the high-entropy MAX phases with added Sn retain good mechanical and physical properties. This study provides a novel approach for the synthesis and application of high-entropy MAX phase materials, which has the potential to contribute to advancements in multiple technological fields.
基金supported by the National Natural Science Foundation of China(No.51972080).
文摘To explore the MAX phase with experimental value over a wider range,a data-driven machine learning(ML)model was trained to rapidly predict the stability of MAX phases via a random forest classifier(RFC),support vector machine(SVM),and gradient boosting tree(GBT),where the deemed significant descriptors were compiled from the literature and the stability of 1804 combinations of MAX phases was collected.Using this well-trained model,190 new MAX phases were screened from 4347 MAX phases,150 of which met the criteria for thermodynamic and intrinsic stability on the basis of first-principles calculations.Additionally,with the help of the ML model,the mean number of valence electrons and the valence electron deviation are the two most critical factors influencing stability.Additionally,one of these predicted MAX phases,Ti_(2)SnN,was experimentally synthesized through Lewis acid substitution reactions at 750℃,with interesting A-site deintercalation and self-extrusion.First-principles calculations revealed that Ti_(2)SnN has lower elastic properties,higher damage tolerance and fracture toughness,and a higher coefficient of thermal expansion(CTE).
