C/C composites， with low density， high specific strength， stable high-temperature mechanical properties and excellent thermal shock resistance， are one of the candidate materials for core components under extreme conditions such as hypersonic vehicle thermal protection systems and solid rocket motor nozzles. However， C/C composites are prone to oxidation above 400 ℃ and suffer from poor ablation resistance over 2000 ℃. Conventional single coating or matrix modification methods have limited protective effects， seriously restricting their long-term service reliability in extreme environments. Based on the “coating-matrix integration” modification idea， ceramic phases can be synergistically distributed inside and on the surface of C/C matrix to form an integrated matrix-surface protection structure， breaking through the performance bottleneck of traditional single modification technologies. This paper systematically reviews current thermal protection technologies for C/C composites， summarizes the preparation process， thermal protection performance and mechanism of coating-matrix integrated modified C/C composites， analyses existing research bottlenecks and future directions， and provides ideas for the design and application of ultra-high temperature and long-life carbon-based composites.

Mesophase pitch-based carbon fibers （MPCF） possess excellent properties， such as high modulus and high thermal conductivity， making them key strategic materials for national defense security and advanced equipment development. However， their oxidation behavior in high-temperature aerobic environments remains poorly understood. This study investigates the oxidation behaviors and the evolution of mechanical and thermal properties of two types of MPCF， namely split-structured （CF-A） and round-structured （CF-B）， in both carbonized （1600 ℃） and graphitized （3000 ℃） states. The results show that CF-A-1600 exhibits preferential core oxidation during the 600 ℃ oxidation process， leading to a tensile strength retention of only 34.93%， which is lower than that of CF-B-1600 （51.79%）. Conversely， the CF-A-3000 achieves tensile strength retention of 79.64% and thermal conductivity retention of 94.36%， respectively， higher than those of CF-B-3000 （77.46% and 90.93%）. For carbonized MPCF， the oxidation behavior is dominated by diffusion-controlled reactions， where structural morphology plays a decisive role， and CF-B fibers exhibit superior oxidation resistance. For graphitized MPCF， oxidation behavior is governed by chemical-controlled reactions， in which intrinsic crystallite activity becomes dominant. For comparison， CF-A fibers show superior performance due to their better-developed crystallites and consequently higher oxidation activation energy. This study reveals the coupled mechanism between structural morphology and intrinsic crystallite activity of MPCF， providing a theoretical reference for reliability assessment and material optimization design of MPCF and their composites in extreme thermal service conditions.

To address the strength-ductility trade-off dilemma of high-oxygen powder metallurgy （PM） titanium alloys， two types of near-α titanium alloys （880-PE1 and 880-PE2） with α/β_t composite lamellar microstructure and oxygen mass fraction of 0.36% are fabricated via the combination of sintering and hot extrusion process. The crystal size and morphological characteristics are analyzed by scanning electron microscopy （SEM） and transmission electron microscopy （TEM）. The crystallographic orientation features are examined through X-ray diffraction （XRD） macro-texture and electron backscatter diffraction （EBSD） micro-texture analysis. The relationships between microstructure and mechanical properties and deformation mechanisms are studied by combining room-temperature tensile tests and dislocation bright-field imaging observations. The results show that the 880-PE1 specimen exhibits no obvious micro-texture. Cracks initiate at grain boundaries of α phases during plastic deformation， resulting in a low elongation to fracture of only 8.9%. The 880-PE2 specimen develops a micro-texture with the 〈0001〉 direction of α grains aligned parallel to the extrusion direction. This unique micro-texture can effectively activate pyramidal 〈c+a〉 dislocations， which move via wavy slip and give rise to an extraordinary increase in work-hardening rate. Additionally， lamellar distortion and grain-boundary deformation compatibility are effectively promoted， and the initiation of intergranular cracks is suppressed simultaneously. Ultimate tensile strength of the 880-PE2 specimen reaches 1070 MPa，and the elongation to fracture increases to 22.0%， achieving synergistic improvement of strength–ductility.

Lithium ceramics （e.g.，Li₄SiO₄，Li₂TiO₃），as core tritium breeder materials， possess high lithium density， excellent thermal stability， and irradiation resistance. Traditional manufacturing methods such as extrusion-spheronization and melt-spraying face challenges including poor particle size uniformity， low crush load，and structural simplicity. As an advanced manufacturing technology， 3D printing offers innovative solutions for the precision forming of lithium-based tritium breeding ceramics in nuclear fusion reactors. Vat photopolymerization-based 3D printing enables the integrated fabrication of complex tritium breeding units （e.g.， honeycomb structures， porous frameworks），significantly improving structural precision， mechanical properties， and tritium release efficiency. This article systematically reviews the material properties， powder preparation processes， and limitations of conventional forming techniques for lithium ceramics， with a focus on the technical advantages and application prospects of vat photopolymerization 3D printing in achieving "structure-property synergy" manufacturing， as well as the multi-precursor-based generative shaping and material-forming method. Finally， future research directions are also proposed to address current technical challenges.

As modern high-end manufacturing increasingly trends towards miniaturization and multifunctionality， achieving high-quality joining of dissimilar materials has encountered severe technical bottlenecks. Addressing this challenge， nano-multilayer films have emerged as a highly promising technological pathway for realizing low-temperature， highly reliable bonding， owing to their pronounced size effects and high-density interfacial structures. This review focuses on immiscible nano-multilayer films of the Cu/X （X=W， V， Mo， Ta， Nb） refractory metal systems， systematically elucidating the thermal stability evolution mechanisms governed by interfacial microstructures， as well as the intrinsic mechanisms that modulate mechanical properties and irradiation responses. Furthermore， it summarizes the recent research progress on their applications as high-performance brazing fillers or interlayers in brazing and diffusion bonding， highlighting their critical roles in mitigating residual stress in joints and suppressing the formation of brittle intermetallic compounds. Finally， it points out that future research should focus on the multi-scale computational modeling of spatial interfacial transport mechanisms and interfacial evolution mechanisms under multi-field coupling. Overcoming the high-temperature thermal stability bottleneck of this system is also identified as a key direction to advance its engineering applications.

Laser cladding uses a high-energy laser to rapidly melt cladding materials with the substrate surface， forming a metallurgically bonded coating upon solidification. It is a key technology for producing high-performance surface coatings and remanufacturing metallic components. Recently， laser cladding has evolved from a surface coating technique into a comprehensive process integrating coating fabrication， repair of damaged parts， and additive manufacturing， showing great potential in new material development. This review first elaborates the metallurgical characteristics of laser cladding metals， then highlights process innovations in four directions： high efficiency， hybridization， specialization， and intellectualization. It further addresses the role of laser cladding in material development and fabrication， systematically reviewing research progress on conventional alloys， high-entropy alloys， amorphous alloys， metal matrix composites， and functionally graded materials， and summarizing their strengthening mechanisms and typical applications. However， challenges remain for laser cladding fabricating materials， including incomplete non-equilibrium solidification theories， lack of quantitative process-microstructure-property models， and inadequate monitoring and evaluation techniques. Future efforts should prioritize data-driven intelligent optimization， novel material system design， extreme-environment adaptability， and integration of multi-energy-field hybrid processes and combined process chains.

Friction stir welding and its derived solid-state additive manufacturing technologies stand as one of the effective approaches to avoid melting defects and achieve the fabrication of high-performance lightweight alloy components. However，the friction stir welding and solid-state additive manufacturing processes involve complex thermo-mechanical-fluid-microstructure couplings，posing significant challenges to traditional trial-and-error methods for process optimization. The emergence of machine learning provides a transformative solution for process understanding and intelligent control in this field. This paper presents a systematic review of machine learning applications in friction stir welding and additive friction stir deposition. It categorizes and elaborates on the current research status and data processing strategies in aspects such as performance prediction，defect detection，and in-situ control. Addressing the limitations of purely data-driven models，it focuses on investigating different fusion paradigms of physics-informed machine learning and their cutting-edge applications. Finally， it points out that future research should concentrate on further developing generalizable prediction models，achieving real-time closed-loop intelligent control，and integrating active learning for autonomous process exploration，aiming to provide references for advancing these technologies toward intelligent and high-performance development.

Titanium/steel （Ti/Fe） dissimilar metal composite components can fully utilize the advantages of titanium alloys， such as high specific strength， excellent corrosion resistance， and high-temperature stability， while also incorporating the benefits of steel， including high stiffness， low cost， and good machinability. However， the substantial differences in physical and chemical properties between Ti and Fe pose major challenges for the welding of titanium/steel dissimilar metal composites. Due to the advantages of good formability， strong adaptability， and high efficiency， fusion welding joints have garnered significant attention in the field of joining titanium/steel dissimilar metals in recent years. This paper systematically reviews the research progress of laser welding， arc welding， electron beam welding， and other processes， analyses the effects of different fusion welding processes， interlayers， and metallurgical products on the microstructure and properties of joints， and reveals the intrinsic relationship between process-microstructure-properties. Based on this analysis， the existing problems and future research directions of titanium/steel welding technique are summarized， such as the process improvement can not avoid the problems of intermetallic compounds， the limitations of single metal interlayer， and the complexity of composite interlayer scheme. The future research directions， such as metal high entropy alloying， machine learning aided design， and multi-process coordination are proposed to provide technical and theoretical support for the breakthrough of titanium/steel high-quality welding technique and speed up the engineering application process of titanium/steel composite components.

Fiber reinforced polymer （FRP） composites offer advantages such as lightweight construction， high specific strength， fatigue resistance， and corrosion resistance， making them widely applicable in aerospace， rail transit， and other sectors. However， internal damage that occurs during service is often concealed， posing potential safety risks. The advent of intelligent composite materials presents a promising approach for integrated structural health monitoring while enhancing mechanical properties. This paper introduces the preparation methods for carbon nanotube （CNT） reinforced FRP composites. Building on this foundation， the current state of research regarding CNT applications for structural health monitoring of composite materials is reviewed. This research can be categorized into two main areas： health monitoring using embedded carbon nanotube sensors in basic mechanical specimens and engineering components， and the self-monitoring technology of composite materials. The self-monitoring technology is further divided into two methods： resin matrix modification and fiber grafting. Finally， the challenges of CNT-modified FRP composites in industrial applications and sensor monitoring stability in multi-field coupling environments are reviewed， and the development direction of ‘structure-function’ integration of reinforcement system and health monitoring technology is prospected， so as to promote the key step of intelligent composite materials to industrial scale production.

China’s medium- and long-term space science development program clearly puts forward the major tasks of rapidly promoting deep space exploration and accelerating the construction of a space power. The increasingly complex and extreme thermal environment in space imposes more stringent requirements on spacecraft thermal control systems. Conventional thermal control materials exhibit limited and static thermoregulatory properties， failing to meet evolving performance demands. In contrast， smart thermal control materials can dynamically modulate their physical characteristics in response to external stimuli， thereby enabling smart regulation of spacecraft heat dissipation and insulation capabilities， and significantly improving the precision and energy efficiency of thermal management systems. As a result， smart thermal control technology has emerged as a critical development direction for next-generation spacecraft thermal control systems. This review systematically outlines the research progress of typical smart thermal control materials， including thermochromic and electrochromic materials， their applications in space missions and the key challenges in this field. To enable the widespread application of smart thermal control coatings， future research work should be carried out in the AI-assisted material design， low-cost fabrication， failure analysis and life prediction under space environments， and system integration. These endeavors are of great significance for driving innovation in aerospace thermal control technology， accelerating the iterative upgrading of thermal management systems， and supporting the steady progression of national space strategy.

With the rapid development of next-generation vehicles such as electric vertical take-off and landing （eVTOL） aircraft and electric vehicles （EVs）， there is an urgent demand for efficient energy storage systems that combine high energy density with lightweight characteristics. Multifunctional structural batteries （MSBs）， as a disruptive technology integrating energy storage and structural support， merge these two functions into a single component， thereby offering a novel approach to system-level weight reduction， space optimization， and functional integration. This review outlines the fundamental concepts of MSBs and surveys the primary technical pathways， focusing on two core integration strategies： embedded （physical integration） and intrinsic （chemical fusion） architectures. It provides an in-depth examination of key enabling technologies， including the optimization and modification of carbon fiber electrodes， the development of structural electrolytes， and interface engineering strategies. Recent advances in enhancing electromechanical performance through surface modification and composite-phase construction are summarized. Furthermore， novel structural designs and manufacturing processes are introduced， along with evaluation frameworks based on electromechanical coupling theory and multifunctional efficiency metrics. The review concludes by discussing the persistent challenges in the field. Although further fundamental researchs and technical breakthroughs are required for practical application， MSBs demonstrate significant potential to revolutionize conventional design paradigms.

MXene quantum dots （MQDs），with their excellent photovoltaic and surface-active properties，have shown good potential for application in multidisciplinary fields. In this paper，we systematically discuss MXene quantum dots （MQDs） from four dimensions： preparation process，application scenarios，technological bottlenecks and development paths. The process characteristics and applicability of top-down stripping and bottom-up synthesis are compared and analyzed. The innovative applications in the fields of energy storage and conversion，biosensing and molecular detection，precision medical intervention，environmental governance and information encryption are also discussed. In the future，machine learning-enabled reverse material design will accelerate the development of functionalized MQDs，defect engineering modulation and core-shell heterostructure construction are expected to break through the bottleneck of light absorption，the development of degradable bioelectronic devices will expand the boundaries of clinical applications，and the establishment of a standardized toxicity assessment system is a key prerequisite for medical translation. With the in-depth integration of the materials genome project and flexible electronics technology，MQDs are expected to catalyse subversive technological changes in the fields of intelligent sensing systems，individualized diagnostic and therapeutic devices，and human-machine interaction interfaces，and ultimately build a whole industry chain innovation ecology from basic materials innovation to terminal system integration.

TiAl alloys have become key materials for weight reduction and performance enhancement in aero-engines due to their low density， excellent high-temperature strength， and oxidation resistance. However， their room-temperature brittleness and low damage tolerance have long constrained their engineering applications. This paper systematically reviews the development history of TiAl alloys since the 1970s， covering the evolution of material characteristics， major scientific research programs， and progress in engineering applications. Through successive fundamental research projects， the United States and Europe have systematically addressed critical scientific issues such as casting processes， microstructural control， and property evaluation， laying the foundation for the application of GEnx engine blades. Since the 12th Five-Year Plan period， through systematic development under national science and technology programs such as the National Basic Research Program and the National Key Research and Development Program， China has overcome key technological bottlenecks， including the independent development of high-Nb alloy systems and the near-net shaping of full-scale blades， thereby establishing a complete full-chain technological system. Although TiAl alloy design has now evolved to the third generation， achieving fine-grained microstructures and compatibility with conventional forging， persistent challenges include low room-temperature ductility， high sensitivity of fatigue life to micro-defects and stress concentrations， high fatigue crack growth rate， and high creep elastic elongation. Furthermore， this paper identifies a series of critical challenges facing TiAl alloys from the perspectives of manufacturing processes and engineering service. Addressing these issues will lay the foundation for the reliable application of TiAl alloys in high thrust-to-weight ratio aero-engines.

Discontinuously reinforced titanium matrix composites （DRTMCs） exhibit outstanding properties including light weight， heat resistance， high strength， corrosion resistance， and deformability， holding immense promise for applications in aerospace， marine engineering， and biomedical fields，etc. This work systematically reviews the fabrication，processing，and typical properties and applications of DRTMCs. In terms of fabrication， the advantages and limitations of melting casting， powder metallurgy， and additive manufacturing in densification， reinforcement management， and forming scale are analyzed， and reinforcement architecture design with its strength-ductility synergy mechanisms is elaborated. In terms of processing， the influence of reinforcement alignment and matrix recrystallization during hot working on mechanical properties is discussed， along with constraints in cold deformation such as reinforcement fracture and shear band formation. Challenges in welding and machining arising from reinforcement introduction are identified， and advances in joint strengthening strategies and energy-field-assisted machining are reviewed. Regarding applications， typical properties of DRTMCs are summarized， and industrial cases， including hot-formed large-scale components， cold-formed precision sheets and wires， and near-net-shape powder metallurgy parts， are presented. Finally， key future research directions are proposed， encompassing multi-scale biomimetic architecture design， iterative upgrading of in-situ synthesis processes， deep development of additive manufacturing， synergistic control of cold/hot deformation and heat treatment， innovation in joining and machining technologies， and advancement toward industrial-scale application.

Elastocaloric cooling technology， which relies on the crystal structural phase transformation of Ni-Ti-based shape memory alloys， offers advantages such as high efficiency， energy saving， and environmental friendliness. These advantages establish it as a promising alternative to conventional vapor-compression refrigeration. Large adiabatic temperature changes， high material coefficient of performance， excellent fatigue resistance， and a wide operating temperature window are critical indicators of elastocaloric performance， attaining all of these simultaneously remains challenging. This bottleneck has constrained the practical development of the technology. This review systematically introduces the intrinsic relationships and research progress among the manufacturing processes， microstructures， phase transformations， and elastocaloric properties of Ni-Ti-based shape memory alloys. Firstly， it compares conventional and additive manufacturing processes， analyzing their effects on material microstructures and performance. Secondly， from the perspective of substructural features such as grain morphology， precipitates， and twins， it discusses the mechanism by which the microstructure regulates both the thermoelastic martensitic transformation and the defect-induced strain glass transition. Subsequently， the review elaborates on the primary controlling parameters of the elastocaloric effect across different phase transformation pathways， and summarizes technical approaches to enhance overall cooling performance. Finally， this review outlines future research directions： coordinating thermoelastic martensitic transformation and strain glass transition through process innovation and novel alloy design to achieve synergistic optimization of elastocaloric properties； and combining structural design to further enhance heat transfer efficiency， reduce driving energy consumption， and improve adaptability to operating conditions.

Metal-fiber reinforced resin matrix composites formed by combining metals with fiber reinforced polymers（FRP） represent a new generation of lightweight， multifunctional materials demonstrating significant application potential in aerospace， new energy vehicles， and high-end equipment manufacturing. The interfacial bonding state of this composite is the core factor determining its superior mechanical properties. However， issues such as insufficient wettability between metal and resin matrix， weak chemical bonding interactions， high thermal residual stresses due to differing thermal expansion coefficients， and interfacial debonding failure under thermo-mechanical coupled loads severely limit stress transfer efficiency between cross-scale heterogeneous materials and compromise long-term structural reliability. Interface modification techniques， such as metal surface treatment and functional layer introduction， can significantly enhance the interface bonding strength， stress transfer efficiency， and durability between metals and FRP composites， thereby optimizing the overall performance of composite structures. This paper systematically reviews key technologies and research progress in metal-FRP interface modification and outlines future development trends.

Electrochemical testing techniques，featuring high sensitivity，in-situ real-time monitoring，and multi-scale analysis，have become a core tool for studying corrosion mechanisms and evaluating protective performance of materials. This paper reviews the classification and recent advances of electrochemical testing methods. The characteristics and applicable conditions of traditional and localized electrochemical techniques are analyzed and compared. The role of multi-technique coupling and artificial intelligence data analysis in testing complex corrosion systems and elucidating mechanisms are discussed. The application of electrochemical techniques from the perspectives of corrosion behavior and mechanism research， protective performance evaluation， and online corrosion monitoring are systematically summarized. Finally， it points out that the development of electrochemical testing techniques lies not only in the popularization of single techniques but also in prioritizing the advancement of multi-technique coupling and high-spatiotemporal-resolution in-situ electrochemical characterization， enabling in-depth analysis from the extraction of intrinsic interfacial reaction parameters to the comprehensive understanding of corrosion mechanisms. On this basis，data-driven approaches and intelligent algorithms are integrated to establish quantitative correlations between electrochemical responses and the service life of materials. Furthermore，integrated and lightweight intelligent monitoring systems enable real-time assessment and lifetime prediction under complex engineering conditions，thereby promoting the transition of corrosion electrochemical testing from laboratory-based mechanistic studies to full-life-cycle safety management of engineering materials.

The aircraft landing gear endures complex loads and harsh service environments over extended periods， making it susceptible to various forms of damage. Remanufacturing technology provides an efficient means of repairing such damage and restoring performance， playing a vital role in ensuring flight safety. Focusing on the enhancement of overall performance， the design of both structure and materials has undergone continuous iterations and optimization. Traditional fixed landing gear gradually evolves into lightweight， high-strength retractable systems， while material design philosophies shift from static strength-based approaches toward multi-objective optimization that simultaneously considers damage tolerance， fatigue life， and maintainability. This paper reviews the types， materials， structural composition， typical damage mechanisms， and remanufacturing technologies of aircraft landing gear， emphasizes the typical failure modes and damage mechanisms encountered during service， and systematically summarizes key technological aspects of the remanufacturing process， including precise non-destructive testing and damage assessment， high-energy beam repair and surface strengthening techniques， as well as dimensional restoration and precision assembly repair processes. Furthermore， it highlights future trends such as the application of advanced high-performance materials， intelligent manufacturing technologies， and green remanufacturing processes. This review provides theoretical foundations and technical references for the engineering application and systematic development of aircraft landing gear remanufacturing technologies.

The Bauschinger effect is a classical phenomenon in which metallic materials exhibit a significant reduction in yield stress upon reverse loading after preloading. This review systematically summarizes research advances over the past two decades in microscopic physical mechanisms， responses of advanced materials， constitutive modeling， and engineering control strategies related to the Bauschinger effect. At the microscopic scale， multiscale experimental characterizations have revealed the asymmetric evolution of defect structures （e.g.， dislocation dipoles， dislocation cells， and twin boundaries） under cyclic loading， with such behavior observed in both high stacking-fault-energy metals （such as Al and its alloys， Fe） and low stacking-fault-energy metals （such as brass and austenitic stainless steels）， establishing a quantitative correlation between macroscopic back stress and microscopic defect structures. At the mesoscopic scale， cross-scale coupling of discrete dislocation dynamics and crystal plasticity finite element methods has elucidated the non-local characteristics of back stress and the nature of its heterogeneous intergranular distribution. This review discusses the Bauschinger effect in conventional metals such as aluminum alloys and steel， and focuses on the unique Bauschinger effect behaviors arising from multi-mechanism synergy in high-entropy alloys， magnesium alloys， nanostructured metals， and shape memory alloys. On this basis， the evolution of back stress models from empirical formulas to dislocation-density-based physically-based constitutive models is reviewed， along with constitutive modeling approaches that account for microstructural heterogeneity within the crystal plasticity framework. Furthermore， application strategies of the Bauschinger effect in material forming， fatigue evaluation， and performance-oriented design are summarized， reflecting a shift from passive avoidance to active utilization. Finally， future directions are discussed， including extreme environmental effects， high-throughput effect mapping， multi-physics field coupling， and cross-scale integrated computational platforms.

The creep behavior of the third-generation single crystal superalloy DD9 at 1100 ℃/137 MPa is investigated using high-throughput scanning electron microscopy（SEM） and transmission electron microscopy（TEM）. The results show that the average creep rupture life of the alloy under this condition is 260 h. During the creep process，the γ' strengthening phase exhibits a gradual evolution from an initial cuboidal shape to directional coarsening， rafting， and eventually to local derafting at the later stage of creep. The composition difference between the dendrite core and the interdendritic regions is an important factor affecting the microstructural evolution of the DD9 alloy. The dislocation evolution during creep is characterized by initial dislocation motion mainly within the γ matrix channels， the formation of dense dislocation networks at the γ/γ' interfaces during secondary creep， the shearing of the γ' strengthening phase by dislocation pairs during tertiary creep， and a further increase in the number of dislocations shearing into the γ' phase at the fracture stage.

Ultra-thin metal plate welding presents several formidable challenges， including a high susceptibility to deformation， difficulties in precisely controlling weld depth， and significant fluctuations in joint performance. Traditional welding methods frequently fall short in overcoming these obstacles to achieve high-quality welds. To overcome the limitations inherent in conventional welding processes， the constrained tungsten inert gas （TIG） arc welding technique is adopted. A comprehensive and comparative analysis is conducted on the weld quality and performance of three ultra-thin metals： 304 stainless steel， 5052 aluminum alloy， and T2 copper. Through in-depth metallurgical analysis， the microstructure of the welds is thoroughly examined. Moreover， laser confocal microscopy is utilized to quantitatively characterize the weld morphology and surface roughness. Tensile tests and the four-point probe method are employed to assess the mechanical properties and electrical conductivity of the welds， respectively. The results demonstrate that the constrained TIG arc welding process successfully achieve stable welding for all three ultra-thin metal materials， yielding well-formed welds with relatively excellent mechanical properties. A comparative analysis of the tensile strength of the welded joints reveal that the tensile strength of 304 stainless steel welds can reach 90% of that of the base material， while the tensile strengths of 5052 aluminum alloy and T2 copper welds are approximately 50% of the base material’s. Metallurgical examination show no obvious defects in the welds of 304 stainless steel and T2 copper， but minor undercutting is detected in the 5052 aluminum alloy welds. Conductivity tests indicate only a slight increase in weld resistivity compared to the base material， which still satisfies application requirements. The constrained TIG arc welding process exhibits significant advantages in ultra-thin metal plate welding， with the resulting weld quality and performance effectively meeting the needs of practical applications. This validates the promising application prospects of this process in ultra-thin plate welding and offers theoretical guidance for its practical implementation.

With the swift advancement of fourth-generation nuclear reactors and small modular reactors， the operating conditions for nuclear fuel elements， including temperature and irradiation environment， have become increasingly harsh， which in turn places higher demands on the performance of brazing materials. To promote the high-quality and self-sufficient development of nuclear-grade Ni-based brazing paste， a comprehensive and systematic investigation is carried out on the fundamental characteristics of imported nuclear-grade Ni-Cr-P brazing pastes.The findings reveal that the brazing paste contains 12.7 % （mass fraction， the same below）of a binder that decomposes or volatilizes at temperatures below 300 ℃. The residual amounts of nitrogen， oxygen， and sulfur are less than 0.015%， and the residual amount of carbon is less than 0.055%. The filler powders are spherical particles within the mesh size range of 120-230， composed of a Ni₃P-type compound and a Ni-based solid solution. The filler composition is Ni-13Cr-10.5P， and it has a hardness of（626±23）HV_0.3.When using this paste to braze nuclear-grade 304L stainless steel， the joints mainly consist of a Fe-Ni-Cr solid solution and a Ni₂P-type compound. At room temperature， the joints demonstrate a tensile shear strength of（226±14） MPa and a compressive shear strength of（184±10） MPa. However， the tensile shear strength drops to （130±5） MPa at 350 ℃. All fractures occur within the seam area and exhibit a brittle fracture mode. Under a stress ratio of 0.1 and a stress amplitude of 0.45F _max， the joint shows a fatigue life exceeding 10⁶ cycles.

The application of low heat input and a high cooling rate in the high-speed laser directed energy deposition （HL-DED） process proves advantageous in mitigating the unfavorable residual stresses， deformation， and crystalline grain size issues that are typically induced by conventional laser directed energy deposition （CL-DED）. Nevertheless， a comprehensive understanding of the thermo-mechanical behaviors in both CL-DED and HL-DED processes remains elusive. In this study， a fully-coupled thermo-mechanical model for laser directed energy deposition （L-DED） is developed and experimentally validated. This model takes into account the effects of solid-liquid phase change and the evolution of the gas-liquid interface. A systematic investigation is conducted to explore the influence mechanisms of HL-DED and CL-DED strategies on the geometries of the melt track and heat-affected zone （HAZ）， as well as on temperatures， stresses， and deformations.Under the combined influence of stress relaxation and the melting effect， the residual stresses in the melt track and the substrate phase transformation zone （PTZ） are predominantly determined by thermal contraction during the cooling stage and the constraint imposed by the substrate. The thermal contraction-induced tensile stresses in the melt track and substrate PTZ give rise to a bow-string effect， causing the substrate to warp towards the melt track.Compared with the CL-DED strategy， the temperature field generated by the HL-DED strategy exhibits a lower gradient along the track direction but higher gradients along the transverse and vertical directions. Additionally， the cooling rates during the solidification and phase transformation stages are significantly elevated under the HL-DED strategy. Although the HL-DED strategy leads to higher residual stresses in the melt track and substrate PTZ， along with a more uneven residual stress distribution in the substrate， it results in lower transient stress in the melt track， lower residual stress in the non-PTZ， and significantly reduced substrate deformation.

Focusing on the irradiation service demands of key structural materials in the nuclear power sector， this research delves into the evolution of mechanical properties in 316L stainless steel produced vialaser additive manufacturing when subjected to 3.5 MeV iron ion irradiation. The samples are fabricated using two distinct laser additive manufacturing processes： selective laser melting（SLM） and directed energy deposition（DED）. Subsequently， a comprehensive pre-irradiation analysis is conducted， encompassing microstructural examination， X-ray diffraction（XRD）， and nanoindentation tests under varying doses of iron ion irradiation.Microstructural observations revealed that the SLM samples exhibit fine cellular austenite structures， whereas the DED samples display coarse columnar grains with some ferrite precipitation. XRD analysis demonstrate that both sample types retain austenite as the predominant phase before and after irradiation， with no phase transformation detected， thus indicating their excellent phase stability. The nanoindentation results show that the hardness of the SLM samples increases from 2.81 GPa to 4.33 GPa， representing an approximate 54% rise. In contrast， the hardness of the DED samples rises from 2.70 GPa to 4.10 GPa， equating to an approximate 52% increase. Notably， the DED samples exhibit only a limited hardness improvement （approximately 7.6%） within the dose range of 1-10 dpa， suggesting an earlier onset of hardening saturation. By integrating the analysis with the strain gradient plasticity model， the differences in irradiation hardening under varying doses are clarified.