Effective lubrication is essential for mitigating friction and wear in mechanical systems, particularly in high-temperature, oxygen-containing environments where friction-induced energy dissipation and material degradation critically affect operational efficiency and safety. Traditional low-shear strength materials often suffer severe wear or even failure under such harsh conditions, making robust high-temperature lubrication a pressing need and key challenge in materials research. Here, we present recent advances in tailoring Ta(Zr)B2 films for superior high-temperature lubrication, guided by an unconventional design principle: first constructing materials with exceptional strength to withstand wear at elevated temperatures, and subsequently creating lubricity via operando tribochemical reactions at the contacting surface. Magnetron-sputtered Ta(Zr)B2 solid solution films exhibit enhanced mechanical and chemical stability compared with the recently deposited high-strength TaB2 film, exhibiting outstanding anti-wear ability with low wear rates of 1.0 × 10-5 - 1.7 × 10-5 mm3/N m. Moreover, tribochemically generated weak-shear products (B2O3 and Ta2O5) provide effective lubrication, yielding low friction coefficients (0.2 - 0.3) at 773 K. These findings offer a roadmap for solving the classic lubricity-durability tradeoff and developing a new class of transition-metal diboride protective films for demanding applications under high-temperature and oxygen-containing conditions.

TaCN/NbCN multilayers with varying modulation periods, as well as TaCN and NbCN monolayers, were prepared on Si substrates using magnetron sputtering. Detailed investigation about the microstructure, mechanical and tribological properties of the multilayer films was conducted, focusing specifically on the effects of modulation periods. The results reveal that TaCN/NbCN multilayers exhibited the face centered cubic structure with a (111) preferred orientation. Notably, the hardness and fracture toughness of multilayer films increase with increase of the modulation periods. When the modulation periods reached 30 nm, the hardness and fracture toughness of the TaCN/NbCN multilayers reached the maximum values of 42.88 +/- 0.87 GPa and 2.9 +/- 0.088 MPa m(1/2), respectively. This strengthening effect can be attributed to the synergistic action of the modulus difference and the alternating stress field. Furthermore, the multilayer had the lowest wear rate (1.68 x 10(-7) mm(3)/N & sdot;m) and coefficient of friction (similar to 0.19). The lower coefficient of friction observed in multilayer films could be attributed to the formation of TM2O3 during the friction process, which enhanced the self-lubricating properties of the film.

ABSTRACT Transition metal diborides (TMB 2 ) possess excellent properties but suffer from rapid oxidation at elevated temperatures, severely limiting their applications. Here, we demonstrate crystal orientation engineering as an effective strategy to enhance oxidation resistance while retaining intrinsic characteristics. The polycrystalline TaB 2 films with strong (001) and (100) preferred orientations were synthesized via substrate‐bias‐controlled deposition. Air annealing revealed that (001)‐oriented TaB 2 films exhibit significantly improved oxidation resistance over (100)‐oriented films. First‐principles calculations show that the TaB 2 (001) surface has higher oxygen adsorption energy and a larger diffusion barrier, attributed to the alternating boron–metal layer stacking along [001]. Moreover, (001)‐oriented films maintain higher hardness and shear strength at both room temperature and 600°C. These findings establish orientation control as a promising pathway to simultaneously optimize oxidation resistance and mechanical robustness in TMB 2 , offering guidance for the design of protective coatings for high‐temperature applications.

Transition metal diboride (TMB2) films are attractive for high-temperature applications, yet their oxidation resistance is constrained by porous, unstable oxide scales. Aluminum doping improves this by forming dense, adherent Al2O3, which enhances oxide layer integrity and restrict oxygen ingress. However, the influence of Al concentration remains insufficiently understood. Here, we investigate the oxidation behavior of Hf1-xAlxB2 +/-delta films (x = 0-0.69) combined with first-principles calculations to clarify how Al content regulates phase evolution and oxygen transport. Oxidation resistance shows a non-monotonic dependence on Al content, peaking at x = 0.60, where annealing at 800 degrees C for 8 h produces an ultrathin oxide scale of 79.1 +/- 14 nm. To reveal the atomicscale origin, structural models of Hf1-yAlyB2 (y = 0-0.750) were constructed. The calculations show that for y >= 0.500, oxygen adsorbs at Al-containing hollow sites, which promotes the nucleation of a dense alumina layer. At y = 0.625, the oxygen diffusion barrier reaches a maximum of 12.21 eV, effectively suppressing inward oxygen transport. Appropriate Al incorporation stabilizes the oxide scale and increases the oxygen diffusion barrier, significantly improving oxidation resistance. This experimental-computational evidence provides a mechanistic basis for composition-driven optimization of next-generation oxidation-resistant TMB2 films.

Friction and wear in load-bearing metallic systems cause substantial energy loss and material degradation, whereas conventional oil lubrication increasingly relies on environmentally regulated additive chemistries. Catalytic formation of carbon tribofilms from oil enabled by Pt has emerged as a promising additive-free approach, yet its long-term effectiveness is fundamentally limited by the mechanical softness and rapid wear of Pt. Here, we report a thermodynamics-guided structural–lubricating hierarchical self-assembly strategy that intrinsically integrates mechanical robustness with catalytic lubrication in Zr–Hf–Nb–Ta–Mo–Pt high-entropy alloys (HEAs). Through enthalpy engineering, Pt incorporation induces spinodal decomposition, enabling the primary self-assembly of Mo-/Pt-enriched amorphous nano-multilayers with controllable crystalline medium-range order (MRO) and well-defined thickness ratios (lMo:lPt = 1:1, 1:1.5, and 1:2.5). The optimized nanomultilayer (lMo:lPt = 1:1.5) exhibits a high density of heterogeneous interfaces and an increased population of crystalline MRO motifs, which effectively suppresses shear localization and provides a mechanically stable platform that preserves Pt catalytic activity. During oil-lubricated sliding, gradual exposure of Pt-enriched sublayers continuously drives a secondary tribochemical self-assembly, forming a dynamically regenerated bilayered tribofilm consisting of a lubricating graphene-like/amorphous carbon top layer and a sacrificial Nb-/Ta-oxide-enriched bottom layer. Consequently, such a Pt-containing HEA system delivers an ultralow friction coefficient of ∼0.02 and an exceptionally low wear rate of 1.997 × 10−7 mm3 (N m)−1 maintained over 80,000 cycles, far outperforming the Pt-free counterpart. This work establishes structural–lubricating hierarchical self-assembly as a general paradigm for the design of additive-free metallic materials with durable solid–liquid lubrication.

To combat microbiologically influenced corrosion of titanium alloy components in extreme marine environments, a NbTiZrCrCu high-entropy film was developed via magnetron sputtering. The sputtering bias voltage was adjusted to optimize the microstructure, thereby enhancing mechanical properties and corrosion performance in 3.5 wt% NaCl solution. The NbTiZrCrCu film deposited at a bias voltage of -150 V exhibited a nanostructured high-entropy metallic glass, yielding a high hardness (similar to 23.7 GPa). This hierarchical structure resulted in significantly higher impedance and a lower current density (i(corr) similar to 6.45 x 10(-8) Acm(-2)). Mott-Schottky analysis revealed that the passive film exhibited n-type semiconductor characteristics, and the nanostructure promoted the formation of a more stable passive film. XPS and Pourbaix diagrams confirmed the presence of metallic Cu-0 and the chromium-rich oxides (Cr2O3, CuCrO2), which collectively contributed to the enhanced density and stability of the passive film. Furthermore, the incorporation of Cu endowed the NbTiZrCrCu high-entropy metallic glass films with significant antibacterial activity, thus mitigating microbiologically influenced corrosion and providing effective protection for marine equipment.

Transition metal diborides (TMB2) possess excellent properties but suffer from rapid oxidation at elevated temperatures, severely limiting their applications. Here, we demonstrate crystal orientation engineering as an effective strategy to enhance oxidation resistance while retaining intrinsic characteristics. The polycrystalline TaB2 films with strong (001) and (100) preferred orientations were synthesized via substrate-bias-controlled deposition. Air annealing revealed that (001)-oriented TaB2 films exhibit significantly improved oxidation resistance over (100)-oriented films. First-principles calculations show that the TaB2(001) surface has higher oxygen adsorption energy and a larger diffusion barrier, attributed to the alternating boron-metal layer stacking along [001]. Moreover, (001)-oriented films maintain higher hardness and shear strength at both room temperature and 600 degrees C. These findings establish orientation control as a promising pathway to simultaneously optimize oxidation resistance and mechanical robustness in TMB2, offering guidance for the design of protective coatings for high-temperature applications.

Architectured lamellar structures with flat interfaces in transition-metal carbide or nitride (TMC(N))/metal nano-multilayers have been extensively utilized for toughness enhancement, a perpetual pursuit in engineering applications. Recently, lithosphere-inspired architecture with a wavy pattern has provided a new avenue for further improving toughness via triggering a higher rate of mechanical energy dissipation than that of the flat lamellar pattern. Herein, the self-assembled TaC/TiNi lithosphere-inspired nano-multilayer architecture (wavy type) has been prepared by activating the Stranski-Krastanov (SK) growth mode and inducing solid-state dewetting during periodic layered deposition. The novel wavy TaC/TiNi lithosphere-inspired nano-multilayer demonstrates extraordinary fracture toughness, which can be attributed to the following mechanisms: (1) the wavy lamellar structure facilitates efficient stress transfer, thereby promoting uniform strain distribution and enabling extensive plastic co-deformation; (2) crack deflection along the wavy interlamellar interfaces between TaC and TiNi nanolayers extends crack propagation paths and increases energy dissipation. Our study reveals that the lithosphere-inspired nano-multilayer architecture can act as a design route for the construction of TMC(N)/metal nano-multilayers with exceptional damage tolerance

Continuous SiC fiber-reinforced Ti3Al（SiCf/Ti3Al） composite combines the advantages of high damage tolerance and ease of forming for Ti3Al matrix and high-strength for SiC fibers. It is an ideal candidate material for lightweight， high-strength， and high-temperature resistant fasteners in the aerospace field. However，complex residual stresses are inevitably introduced during the thread machining process of SiCf/Ti3Al composites. Therefore，analyzing the residual stresses in the threaded regions of SiCf/Ti3Al composites is of great significance for enhancing the service safety and reliability of fasteners. Given the complex geometric structures of the threaded regions in turned SiCf/Ti3Al composites and the close relationship between their stress distribution and core diameter， the characterization and analysis of stress are challenged by the intricate thread profile and limited dimensions. Residual stress measurements and analyses are conducted on the thread crest and radial cross-sections of the threads using side-inclined X-ray diffraction and nanoindentation method，respectively. The results show that the thread crest is in a state of compressive stress after turning. When the core diameter increases from 3.0 mm to 4.0 mm，the compressive stress increases from 387.6 MPa to 540.6 MPa. The radial cross-sections of the thread are also under compressive stress. As the core diameter increases from 3.0 mm to 4.0 mm，the compressive stress at the same location 100 μm from the thread crest increases from 326.9 MPa to 430.8 MPa. Furthermore， the compressive stress decreases with increasing distance from the thread crest.

The high directional alignment of continuous CNT fiber (CNTf) consisting of numerous carbon nanotubes (CNTs) makes it a potential reinforcement to construct novel CNTf reinforced Cu matrix (CNTf/Cu) composite. However, the interfacial properties between CNTf and Cu matrix can be severely deteriorated by contaminating O adsorbed on the surface of pristine CNTf. It is revealed that for CNTf/Cu composite, only similar to 16 nm-thickness Cu2O interfacial reaction layer (RL) is formed at CNTf/Cu interface; meanwhile, the excess contaminating O induces the amorphization of CNTs nearby CNTf/Cu interface, ultimately resulting in low tensile strength of similar to 301 MPa that is only similar to 69.8 % of the value calculated by rule of mixture (ROM). Notably, the introduction of highly oxygen-active Ti interlayer between Cu matrix and CNTf can sufficiently consume the surface contaminating O of CNTf to avoid the amorphization of CNTs and self-assemble in situ to form a similar to 170 nm-thickness TiO2 interface-modified layer, which enables its tensile strength to increase to similar to 417 MPa reaching similar to 91.9 % of the value calculated by ROM due to significantly improved interface strength. Moreover, self-assembling TiO2 interface-modified layer increases the thermal conductivity and electrical conductivity from similar to 350.8 W/m.K and similar to 5.08 x 10(7) S m(-1) in CNTf/Cu composite to similar to 377 W/m.K and similar to 5.39 x 10(7) S m(-1) in CNTf/Ti/Cu composite, respectively.

Ta-Si-C coatings with Si content varying from 2.7 to 30.8 at.% were synthesized by magnetron co-sputtering. Their microstructure, tribological properties and corrosion performance were investigated. The coatings exhibited two distinct structural forms: a Ta(C, Si) solid solution for the lower silicon contents (2.7 and 5.6 at.% Si) and a Ta(C, Si)/a-C:Si nanocomposite for higher Si content (13.7, 20.8 and 30.8 at.% Si). Notably, the Ta(C, Si) solid solution at 5.6 at.% Si demonstrated the highest hardness of 44 +/- 2.7 GPa, resulting from the solid solution strengthening. Furthermore, this solid solution also demonstrated the lowest wear rate (1.21x10- 6 mm3N- 1m- 1), due to its superior hardness and H3/E2 ratio. Additionally, the coating with 5.6 at.% Si displayed the most outstanding corrosion resistance, attributed to its higher crystalline quality and denser structure, which effectively prevented the permeation of corrosive media through the coating to the substrate.

The Mo-Ag-Si solid solution film was prepared using magnetron sputtering to enhance hardness and toughness while reducing friction and wear. Compared with the pure MoSi2 film, the Mo-Ag-Si solid solution film exhibited a 25.69 % increase in hardness, a 5.17 % increase in the H/E ratio, and a 33.33 % boost in the H3/E2 ratio. Tribological tests revealed that Ag atoms formed a self-lubricating AgMoxOy phase, reducing the friction coefficient to 0.09 and the wear rate to 3.89 x 10-7 mm3 /N & sdot;m over 565 m. First-principle calculations indicate that the Mo-Ag-Si solid solution film exhibited better mechanical and tribological properties than the pure MoSi2 film. These findings provide another approach for developing reliable MoSi2 films with high performance.

Tool protective films operate under extreme service conditions, requiring exceptional hardness. Transition metal diborides (TMB2), with strong covalent TM–B and B–B bonds, are promising candidates, but achieving superhardness while preserving their simple binary structure remains challenging. Here, we use HfB2 as a model system to reveal how boron vacancy filling and in-plane compressive stress synergistically enhance hardness, through combined experimental synthesis and first-principles calculations. (001)-oriented HfB2 thin films were fabricated, including sub-stoichiometric HfB2−x, stoichiometric HfB2, and stoichiometric HfB2 under compressive stress. Nanoindentation shows the hardness increases from 33.0 ± 1.1 GPa in HfB1.90 to 40.5 ± 0.4 GPa in stoichiometric HfB2, and further to 45.7 ± 1.1 GPa under −3.67 GPa stress. Calculations reveal that vacancy filling increases the number of load-bearing bonds and strengthens B–B bonding via charge accumulation, while compressive stress shortens B–B bonds to further enhance their strength. These findings clarify the atomic-scale mechanisms of vacancy and stress engineering in TMB2, and propose a simple, scalable pathway to superhard protective films without alloying or doping, addressing a long-standing challenge in coatings for extreme environments.

The superb fracture toughness endowed by abundant deformation modes enables CrMnFeCoNi (Cantor) high- entropy alloy to be an ideal modulating layer for constructing nanomultilayer films for simultaneous strengthening and toughening. However, the lack of a comprehensive understanding of the deformation behavior of Cantor nanolayers in nanomultilayer film systems obscures the development of high-performance Cantor-based nanomultilayer films. In this work, the nanocrystalline Cantor film and bcc-Nb/fcc-Cantor nanomultilayer film were fabricated by magnetron sputtering technology, and their mechanical properties and deformation behaviors were investigated via nanoindentation and transmission electron microscopy. It is found that the plastic deformation of the nanocrystalline Cantor film is mainly carried by both grain growth and localized amorphization during indentation, which can be attributed to its intrinsically high lattice resistance and the presence of high- density grain boundaries. When the Nb nanolayers were inserted onto the Cantor nanolayers to form bcc-Nb/fccCantor a nanomultilayer structure, its hardness increased to similar to 9.6GPa, which is 1.4 times higher than that calculated from the rule of mixture. The confinement effect of adjacent Nb nanolayers prevents grain growth in the Cantor nanolayers and promotes their complete amorphization transition in the deformed regions. However, the Cantor nanolayer on the outermost surface exhibits higher mobility, leading to the aggregation of high- density stacking faults induced by indentation. In addition, severe co-deformability occurs in the region directly below the nanoindentation tip subjected to large compressive stress, while the intermixing of Cantor and Nb nanolayers appeared in the edge region of the indentation through severe cross-slips under the combined effect of compressive and shear stresses. These results are important for understanding the deformation modes of Cantor nanolayers in nanomultilayered structure, and the findings provide new insights for developing high strength-ductility Cantor-based nanomultilayer films.

Equal-period modulated metal/ceramic multilayers have shown promise in enhancing the toughness of ceramic thin films. However, this toughness enhancement typically comes at the sacrifice of hardness, limiting their potential applications. To tackle this issue, this study designed and fabricated two gradient-structured multilayer variations using Ta/TaB2: one with a higher ceramic layer fraction near the surface (M2) and the other with a converse structure (M3). A conventional equal modulation period Ta/TaB2 multilayer film (M1) served as a reference. M2 exhibited superior performance, with a 30% hardness increase and significant toughness enhancement compared to M1. Conversely, M3 experienced failure due to excessive thermal stress from its unique gradient structure. Finite element simulations revealed that M2's structure could alleviate in-plane stress and enhance loading uniformity, thus enhancing the film's toughness. These findings suggest that a well-designed gradient structure holds promise for concurrently improving the hardness and toughness of metal/ceramic multilayer films. Gradient structure solves the hardness-toughness trade-off dilemma. image

Molybdenum disulfide (MoS2) exhibits excellent lubrication capacity rooted in its layered structure, but it suffers significant structural and functional deterioration due to oxidation in ambient environments, limiting its applications. Concerted efforts are focused on enhancing the antioxidation ability of MoS2, but challenges remain. This work conceptualizes and demonstrates a contrarian design of MoS2-based film via metal incorporation and oxidation based on consideration of key fundamental principles of thermodynamics, chemistry, and physical mechanics. A three-pronged process finds a metal of negative mixing enthalpy with Mo to induce amorphization of film, leading to structural densification and suppression of abrasive metal oxides that are harmful to lubrication, promotes, rather than impedes, oxidation in a top layer to enhance wear resistance and allow friction activated lamellar structure, and seeks low stacking fault energy for easy sliding in the lamellar structure to ensure superb low-shear lubrication. A screening of selected transition metals identifies niobium (Nb) as the promising choice; ensuing experiments synthesize amorphous MoS2-Nb (a-MoS2-Nb) film with superior tribological benchmarks. The present design strategy regulates the morphology and composition of the film to achieve the concurrent low-friction and low-wear functionality, opening a fresh path to making versatile lamellar structured lubricants for wide use in diverse environments.

To acquire excellent mechanical properties in ceramic/metal nano-multilayers, it is necessary to reasonably regulate the thickness of the metal nanolayer and interface configurations between ceramic and metal nanolayers. Herein, TiC/Ti nano-multilayers have been fabricated by magnetron sputtering technology, and face- centered cubic (fcc) Ti and hexagonal close-packed (hcp) Ti nanolayers could be obtained when Ti sublayer thickness is about 1.5 and 8 nm, respectively. The formation of fcc-TiC(111)/fcc-Ti(111) coherent interface achieves synergistic enhancement of hardness (38.8 GPa) and fracture toughness (3.26 MPa m1/2), while the appearance of fcc-TiC(111)/hcp-Ti(002) coherent interface significantly deteriorates hardness (20.8 GPa) and fracture toughness (2.11 MPa m1/2). The superior fracture toughness of the fcc-TiC(111)/fcc-Ti(111) nanomultilayer originates from an excellent crack-arresting capability owing to a large elastic modulus mismatch between fcc-TiC and fcc-Ti nanolayers and a small periodicity of elastic modulus variation. Moreover, the higher fracture strength of the fcc-TiC(111)/fcc-Ti(111) nano-multilayer results from a little stiffness loss owing to the introduction of thin Ti nanolayers as compared to the fcc-TiC(111)/hcp-Ti(002) nano-multilayer. In addition, the simultaneous improvement of hardness and fracture toughness brings about superb wear resistance for the fccTiC(111)/fcc-Ti(111) nano-multilayer. During the friction process, the preferential oxidation of Ti nanolayers in fcc-TiC(111)/fcc-Ti(111) nano-multilayer preserves the curved graphene nanosheets from severe tribo-oxidation, which is conducive to decreasing the coefficient of friction.

Transition metal nitride (TMN) films are well-known for high hardness, excellent chemical stability, and outstanding wear resistance. However, despite the widespread use as protective materials, inherent brittleness and typical hydrophilicity limit the broader application. This study overcomes these limitations through the synergistic doping of rare earth element Y and soft ductile metal Ag. By fixing the Y content at 1.90 at.% and regulating the Ag content, Zr-Y-Ag-N solid solution film containing 1.68 at.% Ag was formed, with the hardness increased to 30.3 GPa, representing a 46 % increase compared to pure ZrN film (20.7 GPa). The formation of Y2O3 and Ag2O on the surface increased the contact angle from 85 degrees to 127 degrees, significantly enhancing hydrophobicity. During the friction process, multiple lubricating phases (ZrO2, Y2O3, and Ag2O) reduced the friction coefficient to 0.077, and the film demonstrated excellent wear resistance, with a wear rate of only 4.61 x 10-7 mm3/(Nm). Electrochemical testing confirmed that the synergistic doping of Y and Ag significantly improved corrosion resistance by optimizing the microstructure to be dense and enhancing hydrophobicity. This study realizes the integration of hardness, lubricity, wear resistance, and corrosion resistance in TMN films by introducing solute Y and Ag atoms, providing an effective strategy for demanding green tribology applications.

Molybdenum disulfide (MoS 2 ) exhibits excellent lubrication capacity rooted in its layered structure, but it suffers significant structural and functional deterioration due to oxidation in ambient environments, limiting its applications. Concerted efforts are focused on enhancing the antioxidation ability of MoS 2 , but challenges remain. This work conceptualizes and demonstrates a contrarian design of MoS 2 ‐based film via metal incorporation and oxidation based on consideration of key fundamental principles of thermodynamics, chemistry, and physical mechanics. A three‐pronged process finds a metal of negative mixing enthalpy with Mo to induce amorphization of film, leading to structural densification and suppression of abrasive metal oxides that are harmful to lubrication, promotes, rather than impedes, oxidation in a top layer to enhance wear resistance and allow friction activated lamellar structure, and seeks low stacking fault energy for easy sliding in the lamellar structure to ensure superb low‐shear lubrication. A screening of selected transition metals identifies niobium (Nb) as the promising choice; ensuing experiments synthesize amorphous MoS 2 ‐Nb (a‐MoS 2 ‐Nb) film with superior tribological benchmarks. The present design strategy regulates the morphology and composition of the film to achieve the concurrent low‐friction and low‐wear functionality, opening a fresh path to making versatile lamellar structured lubricants for wide use in diverse environments.