Haifeng Wang

Laser repair of maraging steel components using dissimilar materials offers a promising route for performance restoration, but achieving compatible strength between the repair layer and substrate remains challenging. This study investigates laser melting deposition (LMD) of 17‐4PH stainless steel onto a 00Cr12Ni10MoTi (S03) substrate followed by solution treatments at 750, 900, and 1050 °C and aging at 490 °C. The solution temperature governs precipitate dissolution and recrystallization in the 17‐4PH layer and the microstructural stability of the S03 substrate, thereby determining strength matching and deformation compatibility. Insufficient solution treatment at 750 °C limits the strengthening response of the repair layer, whereas excessive solution treatment at 1050 °C induces pronounced grain coarsening in the S03 substrate. Among the investigated conditions, the 900 °C solution treatment provides the best overall balance between repair‐layer strengthening and substrate stability. Under the SA900 condition, nanoscale Cu‐rich precipitates effectively strengthen the 17‐4PH repair layer, while the S03 substrate retains adequate ductility and deformation compatibility. Consequently, tensile specimens fractured preferentially within the substrate rather than at the interface, demonstrating reliable strength overmatching and sound interfacial bonding. This work establishes a viable heat treatment strategy for achieving interfacial mechanical compatibility in dissimilar martensitic steel repairs via LMD.

Achieving robust and reliable ultra- to super-low friction combined with extremely low wear, which is applicable to industrial applications, has always been the pursuit of researchers. In this work, carboxylated graphene quantum dots (CGQDs) were synthesized for dissolution into polyether-modified silicone oil (PESO). The results indicate that CGQDs demonstrate exceptional solubility in PESO, which can be attributed to the favorable charge–transfer interaction between CGQDs and PESO molecules. Tribological tests indicate that the addition of CGQDs to PESO could result in a robust and reliable superior lubrication effect for steel tribopairs under a wide range of testing conditions, with the lowest friction coefficient being approximately 0.02. The investigation of the wear scars indicates that CGQDs can effectively embed into friction contacts due to their ultrasmall size, allowing them to interact effectively with the steel surface through their carboxy groups and therefore forming an in-situ robust CGQDs-based lubricant film. The generated CGQDs-based lubricant film could not only effectively passivate the direct asperity contacts of tribopairs but also provide a shearable path due to its desirable lamellar characteristics. The findings of this work are expected to provide a novel reliable strategy to achieve ultra- to super-lubrication for industrial applications.

The CoCrNi medium‐entropy alloy (MEA) is recognized for its high strength and ductility; however, its wear resistance is limited in harsh environments. While traditional powder‐pack boronizing enhances wear resistance, it requires prolonged high‐temperature treatments (900–1000 °C for 6–8 h), leading to thermal deformation and restricting scalability for large components. High‐energy lasers present a promising solution by enabling rapid, localized melting with a confined heat‐affected zone of 2 mm. This study presents a novel laser boronizing functional strategy for CoCrNi MEA that uses prefabricated boron layers (400–1600 μm) to create dual‐phase CrB and (Co,Ni) ₃ B coatings with a dendritic structure. The CoCrNi‐800B coating (800 μm boron layer) showed optimal performance: a hardness of 23.5 GPa, an elastic modulus of 258 GPa, a 96% reduction in wear rate in aqueous environments, and a 40% reduction in the friction coefficient. Tribofilm analysis revealed the formation of self‐lubricating B ₂ O ₃ /H ₃ BO ₃ layers at the friction interface, effectively reducing friction and wear. This ultrafast laser boronizing method (1–5 min, 60 times faster than conventional methods) minimizes thermal deformation while enabling localized boronizing of large components like bearings. This strategy lays the groundwork for the development of wear‐resistant materials for offshore wind power and hydropower applications.

In this study, a duplex lightweight steel with the compositions of Fe-30Mn-9Al-1C-1V-5Ni (wt.%) was designed, and its microstructure and mechanical properties were analyzed after simple rolling and heat treatment. The microstructure of duplex lightweight steel consists of austenite and B2 phases, with the dual-nanoprecipitation of L′1₂ type long-range ordered domains and VC carbides within the austenite. The steel exhibits an ultra-high strength-ductility combination, with a yield strength of 1316 ± 16 MPa, a tensile strength of 1458 ± 11 MPa, and a total elongation of 11.7 ± 1.2%. Its high strength is primarily attributed to hetero-deformation induced (HDI) strengthening, solid solution strengthening, and precipitation strengthening. Meanwhile, the substantial dislocation accumulation in both austenite and B2 phases, coupled with the HDI hardening from intense heterogeneous deformation near grain/phase boundaries, collectively confers the steel with excellent ductility.

To simultaneously enhance the strength and toughness of 18Ni (200) steel, the aging parameters (temperature and time) are systematically investigated to optimize the microstructure and mechanical properties. The results indicate that the steel aged at 550 °C exhibits optimum yield strength and ductility compared with that at 530 and 580 °C for the same duration. At 550 °C, strength decreases but ductility and Charpy impact energy increase with increasing time and the steel aged at 550 °C for 4 h shows an excellent combination of strength and toughness (exhibiting 1531.5 MPa yield strength and 80.2 J impact energy). With prolonged aging time and elevated aging temperature, the specimens exhibit decreased dislocation density alongside progressive coarsening of precipitates and reverted austenite. The aging process employed in this study simultaneously preserves elevated dislocation density, high precipitate density, and substantial reverted austenite content, while concurrently suppressing coarsening of precipitates and reverted austenite. Crucially, such microstructural optimization facilitates the synergistic effects of precipitation, dislocation, and grain boundary strengthening, combined with a high‐volume fraction of austenite, achieving an exceptional strength‐toughness balance in maraging steel.

The achievement of a superlubricity state with vanishing friction and negligible wear has important applications in minimizing energy dissipation and prolonging the service life of moving mechanical systems. However, the search for a superlubricious oil system applicable to industrial fields remains a big challenge. We demonstrate in this work for the first time that precisely employing polyether modification for silicone oil molecules could induce direct superlubricity and superlow wear for engineering steel tribopairs. Superlubricity originates as the polyether-modified silicone oil could effectively employ the polyether functional group to interact with the friction surfaces, during which a complex tribochemical reaction process could be induced under the catalytic role of friction, where an organic lubricious film mainly composed of carbon, silicon and oxygen elements could be induced to be in-situ formed, which could not only effectively passivate the friction surfaces but also enable the superlubric sliding by virtue of its easy-to-shear nature. Furthermore, iron oxides and chromium oxides could also be confirmed distributed within the tribofilm, desirable for increasing the load-bearing capability of tribofilm and the toughness. Thus, remarkable superlubricity of 0.01 without a running-in combined with superlow wear has been realized at the same time. The results of this work show high promise in promoting the industrial use of oil superlubricity and revolutionizing the development of mechanical systems.

The biological materials evolved in nature generally exhibit interpenetrating network structures, which may offer useful inspiration for the architectural design of wear-resistant composites. Here, a strategy for designing self-lubricating medium entropy alloy (MEA) composites with high strength and excellent anti-wear performance was proposed through quasi-continuously networked in-situ carbides and graphene nanosheets. The discontinuous coating of graphene on the MEA powder surface inhibits continuous metallurgy bonding of the MEA powders during sintering, generating the typical quasi-continuously networked architecture. A good combination of mechanical properties with high fracture strength over 2 GPa and large compressive plasticity over 30% benefits from metallurgy bonding that prevents crack initiation and extension. The wear rate of an order of 10^-6 m³N^-1m^-1 ascribing to an amorphous-crystalline nanocomposite surface, tribo-film induced by graphene, as well as the gradient worn subsurface during friction was achieved by the MEA composite, which is an order of magnitude lower than the unreinforced MEA matrix.

A new heat treatment process, presolid solution and cyclic solution treatment followed by aging treatment, is proposed to simultaneously increase the content of reversed austenite and precipitates in maraging steel. The optimized process significantly reduces the martensite block size from 798 to 705 nm, while increasing the content of reversed austenite from 18.2% to 29.6% and precipitates from 0.0328% to 0.0523%, compared to traditional methods. The cyclic solution treatment promotes multiple nondiffusive shear martensite transformations which increase the dislocation density and retained austenite, acting as nucleation sites for precipitates and reversed austenite, and also accelerating element partitioning during aging treatment. The multiscale microstructure, including high‐density dislocation laths martensite, reversed austenite, and Ni ₃ Ti precipitates, contributes to achieving high yield strength (1193 MPa) and reasonable ductility (8.0%). This is mainly attributed to precipitation strengthening, the transformation‐induced plasticity effect (TRIP) of reversed austenite during tensile testing, and the toughening effect of refined martensite lath.