Underwater wet laser cladding (UWLC) technology has considerable application potential for in situ repair of offshore engineering equipment. Moreover, multipass UWLC has notable practical application value and can ensure the efficiency of underwater repair processing. A multipass laser cladding layer with high forming quality that is formed in a complex underwater environment has notable application value. Herein, new results regarding the preparation of in situ multipass UWLC duplex stainless steel (DSS) coatings are reported. Multipass ER2209 UWLC coatings are successfully prepared in a completely wet environment. Laser-induced self-protection materials are used to counter and eliminate the effects of the water environment on the forming quality of the UWLC coatings. The results show that the numerous porosity defects on the cladding layer surface are attributed to effects such as laser-induced cavitation and water ionization. Effective use of laser-induced protective materials mitigates the detrimental effects of water intrusion. The rapid cooling effect of the underwater environment is counteracted by the heat input form the underwater multipass laser and the exothermic action of the protective material. Compared with ER2209 air laser cladding (ALC) coatings, the accumulation of dislocations at grain boundary slightly decreases the corrosion resistance of the ER2209 UWLC coatings. Multipass underwater cladding formation assisted by laser-induced protection materials offers valuable theoretical insights for in situ repair of underwater equipment.

Due to the influence of the water environment, it is a serious challenge to achieve high-quality and highperformance on-site restoration of the underwater equipment in the underwater environment. In this paper, TC4 was used as the modulation material to strengthen the Fe-based material by its better wettability with the Fe-based material and the TC4/316L composites with excellent properties was successfully prepared by the underwater laser directed energy deposition technology. And the effect of TC4 on the microstructure evolution, tribo-corrosion resistance and mechanical properties of the composite was studied. The result showed that with increase of TC4 content, the eutectic reaction occurred at the ferritic grain boundary to form Fe2Ti precipitates. And the grain size of the composite showed the tendency to decrease first and then increase due to the increase of solute elements at the solid/liquid interface and the influence of thermal conductivity. The addition of TC4 content also promoted the increase of microhardness and ultimate tensile strength of the composite, and the ultimate tensile strength increased from 492 MPa to 675 MPa. When the TC4 content was 10 wt%, the wear resistance of the composite was the best, and the wear rate was 8.65 x 10- 7mm3N- 1 m- 1. This research can open up a new idea for the design of underwater directed energy deposition materials, which is of great significance in the field of underwater restoration field.

It is challenging to obtain the underwater wet laser cladding layer with excellent properties while maintaining formability. In this paper, the method of using synchronous mechanical vibration assisted in the underwater wet laser cladding process of TiN/Fe-based cladding layer was introduced. The effect of mechanical vibration frequency on the dilution rate, microstructure, corrosion resistance, tribo-corrosion behavior of the cladding layer was studied. The result displayed that with increase of mechanical vibration frequency, the dilution effect of the substrate was obviously weakened and the phase changed from ferrite to ferrite and austenite, and TiN particles were evenly distributed. In addition, the grain size of the cladding layer showed a tendency to decrease first and then increase. When the mechanical vibration frequency was 400 Hz, the grain refinement phenomenon was the most obvious and the average grain size was 8.39 mu m. Based on the effect of dispersion strengthening and fine grain strengthening, the microhardness and wear resistance of the cladding layer assisted at 400 Hz were improved, and the wear rate was 1.17 x 10-15m3N-1 m-1. While the cladding layer assisted at 400 Hz exhibited better corrosion resistance by forming a dense passivation film. In addition, the mechanism of mechanical vibration on microstructure evolution and performance enhancement of the cladding layer was also analyzed. This study provided the theoretical support for the formability of the underwater laser wet cladding assisted by mechanical vibration.

Underwater wet laser cladding (UWLC) has gradually become a hotspot in the research on online repair technology. In this study, by adjusting the ratio of CaF2 and TiO2 in an assistive agent, CaTiO3 slag was formed at a ratio of 1:1 and uniformly covered the top of cladding layers. The slag isolated molten pools from the influence of water and reduced the generation of porosity and cracks. A cladding layer with good macro forming and ideal performance was successfully prepared. Among all samples, a cladding layer with a 1:1 ratio for the assistive agent comprised the smallest grain size under complete coverage protection of the liquid slag. Moreover, it exhibited the highest hardness and consequently the lowest wear rate, wear volume loss, and excellent friction resistance; it also had the best corrosion resistance. The cladding layer with a 1:1 ratio for the assistive agent had a self-corrosion current density of 0.9201 x 10(-7) A cm(-2), which is the lowest among the samples, indicating that it had the lowest corrosion rate. Furthermore, it had the highest corrosion potential of -0.196 V, implying that corrosion is least likely to occur. This research elucidates the protective mechanism of the ratio of CaF2 and TiO2 components in assistive agents on the macro formability of UWLC layers. It holds considerable reference value for designing protective methods for cladding layer molding in aqueous environments.

The friction and wear of bearing cages, sealing rings and other transmission components working in harsh environments such as high vacuum and heavy load directly affect the operational stability and safety reliability of the equipment. Therefore, it is vitally important to improve the tribological properties of machine components. In this paper, NiCrBSi alloy coating, NiCrBSi-30 wt% WS2 coating and double-layer NiCrBSi-30 wt% WS2 coating were prepared on 38CrMoAl steel by laser cladding. The results show that a metal sulfide layer is formed on the double-layer NiCrBSi-30 wt% WS2 coating compared to NiCrBSi-30 wt% WS2 coating. The NiCrBSi-30 wt% WS2 coating consists of gamma-(Ni,Fe) solid solution, (Fe,Ni)9S8, Cr7S8 and M7C3 phases. The metal sulfide layer consists of gamma-(Ni, Fe) solid solutions, Fe3S4, CrxSy and M7C3 phases. The double-layer NiCrBSi-30 wt% WS2 coating is 4 mm thicker than the NiCrBSi-30 wt% WS2 coating. The average microhardness values of NiCrBSi coating, NiCrBSiWS2 coating and double-layer NiCrBSi-WS2 coating are 412.6 +/- 15.2HV0.3, 383.9 +/- 14.5HV0.3, and 368.6 +/- 13.3HV0.3, respectively. The average coefficient of friction of the double-layer NiCrBSi-30 wt% WS2 coating is 0.29, which is 37 % and 14.7 % lower than that of the NiCrBSi coating (0.46) and the NiCrBSi-30 wt% WS2 coating (0.34), respectively. The wear rate of the double-layer NiCrBSi-30 wt% WS2 coating is 1.51 x 10-5 mm3/ (N & sdot;m), which is 47.6 % and 34.9 % lower than that of NiCrBSi coating (2.88 x 10-5 mm3/(N & sdot;m)) and NiCrBSi-30 wt% WS2 coating (2.32 x 10-5 mm3/(N & sdot;m)), respectively. Therefore, double-layer NiCrBSi-30 wt% WS2 coating has the best wear resistance and friction reduction performance at room temperature. A more continuous lubricating film was formed on the surface of the double-layer NiCrBSi-30 wt% WS2 coating, which explains its lowest coefficient of friction and wear rate.

Underwater wet laser cladding technology (UWLC) will play a crucial role in the emergency repair of marine engineering equipment. The existence of water environment makes the UWLC process face more challenges. Therefore, it is meaningful to develop materials suitable for underwater wet laser cladding. Considering the special demands of UWLC coatings for corrosion resistance, Ni, Cr and Nb elements with excellent corrosion resistance were selected as the main components. In this article, Ni80Cr20-x wt% Nb (x = 0, 10) coatings were successfully prepared by UWLC. The forming process of Ni80Cr20-x wt% Nb (x = 0, 10) coatings in water environment were studied. The corrosion resistance, corrosion morphology and elemental valence of Ni80Cr20-x wt% Nb (x = 0, 10) coatings were studied. The results shown that Ni80Cr20-x wt% Nb (x = 0, 10) coatings were well formed, with excellent metallurgical bonding between the coating and substrate. The addition of Nb element resulted in the transition of the single solid solution (FCC) into the dual-phase solid solution (FCC and Laves) of Ni80Cr20-10 wt% Nb UWLC coating. Furthermore, Ni80Cr20-10 wt% Nb UWLC coating exhibited higher self-etching potential, lower self-etching current density and higher critical point corrosion potential, indicating excellent anti-corrosion properties. The composition design of the underwater cladding coatings, which combined good formability and excellent corrosion resistance, has significant implications for improving of underwater repair quality.

An in situ TiC-enhanced NiTi 2 -based composite deposition layer was prepared by ultrasonic assisted underwater wet laser deposition. The evolution of the microstructure and interface state, and the friction properties in the air and brine solution environments of the deposition layer were analyzed and researched. The results demonstrated that the thermal and steady-state cavitation from ultrasound effects increase the total energy of the melt pool and promote mixing. The dilution rate of the ultrasonic assisted underwater laser deposition layer increases to 86.72 % compared with that of the underwater laser deposition layer (78.75 %). Ultrasonic reduced underwater laser deposition defects such as lack of fusion and weld slag, and enhanced the wettability between the deposition layer and substrate. The contact angle of the UWNT layer (24.40 degrees , in average) is smaller than the WNT layer (29.80 degrees , in average). Ultrasonic shortened the contact time between the deposition layer surface and the solution, which reduced the reaction of the Ni element with the brine solution. It also transformed the deposition layer from hypereutectoid microstructure to hypoeutectic microstructure and from planar interface to cellular interface. With the effect of the ultrasonic field, the elements in the deposition layer become more uniformly distributed and the secondary phases undergo spheroidization. In the ultrasonic assisted deposition layer, stressinduced FCC-Ti was discovered. Ultrasonic field also reduced the dispersion of the microhardness and increased the average microhardness to 863.3 +/- 45.1 HV 0.3 . Tribology properties show that ultrasonic field effectively improved the wear resistance and friction stability of the ultrasonic assisted deposition layer. The COF of the ultrasonic assisted deposition layer was less affected by the environment, with values of 0.25 and 0.24 observed in air and brine solution, respectively. Overall, the research results in this paper can provide a new insight to improve the surface properties of NiTi 2 -based alloy underwater laser deposition.

Underwater wet laser cladding technology (UWLC) offers advantages such as short repair cycles, low costs, and independence from drainage equipment, making it highly practical. The exceptional design flexibility of high entropy alloys, combined with the convenience of UWLC technology, presents significant application potential. To assess the feasibility of utilizing high entropy alloys (HEAs) in underwater wet laser cladding, (NiCrCoFe)100-xNbx (x = 0, 5, 10) coatings were prepared. This study investigates the effects of Nb addition on the formation characteristics and metallurgical process of (NiCrCoFe)100-xNbx HEA coatings. The results show that the addition of Nb promotes the efficient utilization of laser energy underwater by altering the melting latent heat of UWLC materials and enhancing the fluidity of the molten pool. Furthermore, the introduction of Nb element improves the corrosion resistance of the coatings and inhibits the expansion of corrosion pits. This study confirms the feasibility of utilizing high entropy alloys for underwater wet laser cladding and offers new ideas and methods for the underwater online repair of marine equipment.

MgLi alloys have a wide application in the lightweight structure materials on account of their ultra-light-weight, good machinability and high specific strength. However, the low strength, insufficient wear and corrosion resistances of MgLi alloys have become a critical problem that hinders their applications. In order to achieve excellent wear and corrosion properties, LC-Cu3Al, LC-Cu6Al and LC-Cu9Al coatings are designed and prepared on MgLi alloy substrates in this study. The phase structure, microstructure, hardness, wear and corrosion properties of CuAl alloy coatings are investigated in detail. The results show that a good metallurgical bond is achieved between the CuAl alloy coatings and the substrates. LC-Cu6Al coating's hardness, wear and corrosion properties are the best. Compared with the MgLi alloy substrate, the average hardness of LC-Cu6Al coating increases by 6.75 times, while the wear volume decreases by 88.32 % and the corrosion current density decreases by two orders of magnitude. The results suggest that using laser cladding CuAl alloy coatings is an excellent strategy to enhance the surface properties of MgLi alloy.

Underwater wet laser cladding technology has become one of the research hotspots in the marine engineering, but the existence of the water environment inevitably leads to process instability and defects. In this study, the nano-ZrO2 protective layer was used to increase the viscosity of the molten pool surface to resist the impact force generated by the high-speed water jet, and the underwater wet laser Fe-based cladding layer with good forming quality and desirable performance was successfully prepared. The nano-ZrO2 protective layer improved the formability of the cladding layer and guaranteed the depth of the melt pool, while reducing the depth of the heat affected zone. The addition of nano-ZrO2 particles reduced the average grain size of the cladding layer from 4.90 mu m to 3.66 mu m. In addition,the corrosion resistance of the cladding layer was greatly improved with the appli-cation of the nano-ZrO2 protective layer, with the evident passivation region of 0.74 V. The wear rate of the cladding layer with the nano-ZrO2 protective layer (0.64x10-15m3N-1m-1) was significantly lower than that of the substrate (9.01x10-15m3N-1m-1), and the excellent wear resistance of the cladding layer with nano-ZrO2 pro-tective layer benefited from the good carrying capacities and high microhardness of the microstructure with ZrO2 particles. This study reveals the strengthening mechanism of nano-ZrO2 protective layer on the Fe-based cladding layer, which can provide theoretical guidance for the development of the underwater laser cladding.

Underwater wet laser cladding technology as a new online repair technology, has a wide application prospect in the field of marine engineering. In this work, the underwater wet laser cladding layers of 316L stainless steel with in-situ Ni interlayer on EH40 were successfully manufactured using the underwater wet laser cladding technology. The effect of the in-situ Ni interlayer on the elemental distribution, microhardness, properties and interfacial characteristics of the underwater wet cladding layer was investigated. The in-situ Ni interlayer formed a diffusion buffer between the substrate and cladding layer to mitigate the Fe, Cr and C element diffusion and increased the Ni content in the cladding layer. The addition of the in-situ Ni interlayer promoted the formation of austenite. The wear resistance of the underwater wet laser cladding layer with in-situ Ni interlayer was higher than that of the in-air laser cladding layer, and the main wear mechanism was abrasive wear. In addition, the corrosion resistance of the underwater wet laser cladding layer was improved effectively by applying the in-situ Ni interlayer, and the corrosion resistance basically reached the same level with the in-air laser cladding layer. Thus, the in-situ Ni interlayer has guiding significance for the underwater wet laser cladding technology of Fe-based materials.

Underwater wet laser deposition is a technology of great importance for the online emergency repairs of underwater equipment. In this study, ultrasonic solid-liquid dual-phase conduction (USLC) was used to assist in the preparation of TiC in-situ reinforced Ti-based underwater wet laser deposition layer. The formation mechanism, microstructure, phase composition, microhardness, and tribology properties of the underwater deposition layer before and after the USLC were comprehensively analyzed and evaluated. The results indicated that the dilution rate of the USLC-assisted underwater laser deposition (U-ULD) layer increases to 71.72 % compared with that of the underwater laser deposition layer (49.04 %). The USLC treatment can promote the degassing process and reduce the porosity defects of underwater laser deposition by the transient cavitation effect. And the USLC treatment promoted the globularization and refinement of the TiC in-situ reinforced phase and caused the granular TiC in-situ reinforced phase in a discontinuous reticular distribution. The average microhardness of the U-ULD layer was 548.4 & PLUSMN; 15.5 HV0.3. The synergistic effects of the discontinuous reticular distribution of TiC particles and the abrasive chips of TiC and TiO2 significantly enhanced the friction properties of the U-ULD layer. The U-ULD layer had the lowest coefficient of friction, with an average coefficient of friction of 0.16. Noticeably, the friction mechanism of the U-ULD layer demonstrated the feasibility of USLC treatment to enhance the friction property of the underwater wet laser deposition. It can provide a new technique to improve the surface properties of titanium-based alloy underwater wet laser deposition.

The improvement of wear resistance has a profound effect on the far-ranging application of aluminum alloy. In this study, the Al-Cu-based in-situ reinforced composite coating was successfully manufactured on the AlSi10Mg substrate by laser cladding. The microstructure, microhardness and wear resistance under gradient loading (3 N, 6 N, 9 N, 12 N and 15 N) and thermal conditions (200 degrees C, 300 degrees C and 400 degrees C) of the composite coating were studied. The research results showed that the composite coating exhibited a gradient distributed microstructure due to the different diffusion degrees of Cu and Al atoms. The composite coating was mainly composed of Al4Cu9, Al7Cu4Ni and alpha-Al in the bottom, center and top area, respectively, and Al2Cu evenly distributed in each area. The microhardness showed gradient distribution owing to the gradient microstructure. Compared with the AlSi10Mg substrate, the composite coating possessed higher microhardness and better wear resistance contrib-uted by the gradient Al-Cu intermetallic compounds. At room temperature, the main wear mechanisms of the composite coating changed from abrasive wear to adhesive wear with the increase of loading condition. At high temperatures, the main wear mechanisms of the composite coating were adhesive wear and plastic flow. During the wear process, Al-Cu intermetallic compound was the key to improving the wear resistance and stabilizing the friction coefficient.