Research On Surface Repair Technology Of Hyperbaric Underwater Laser Cladding

This paper proposed a "hyperbaric underwater laser cladding surface repair technology" that can be used for underwater emergency repair against the background of marine emergency repair,and launched systematic process experiments and formability verification.According to the form of materials,laser cladding can be divided into laser powder feeding cladding and laser wire feeding cladding.Firstly,a laser powder feeding cladding test system was built to explore the effects of laser power,scanning rate,powder feeding rate and the gas flow rate on the forming quality of cladding layer,and the defects such as deformities,pores,depressions and oxidation phenomena in the experiment were analyzed.And then,the experimental system of laser wire feeding cladding was built to explore the effects of laser power,defocusing amount,wire feeding rate,scanning rate,laser-wire distance and wire feeding angle on the formation of cladding layer.The laser powder feeding cladding as well as the laser wire feeding cladding were compared and analyzed while the result showed that the laser wire feeding cladding has the advantages in stable forming quality,controllability,reliability and high efficiency compared with the laser powder feeding cladding.The optimal parameters obtained by orthogonal experiment of laser wire feeding cladding are as follows:front wire feeding method,laser power is 3kW,defocusing amount is+50mm,scanning rate is 600mm/min,wire feeding rate is 1.6m/min,wire feeding angle is 45°,laser-wire distance is 0?(+4)mm.It was found that the liquid bridge transition is more conducive to the formation of the cladding layer than the droplet transition by analyzing the behavior of molten pool with the welding camera.In order to meet the repair requirements of 3D space of underwater structures,the experiments of multi-layer and multi-pass laser cladding were carried out,and the effects of lap ratio as well as different scanning paths on the forming quality of stacking layer were explored.The experimental results showed that:the cladding layer which had the best forming quality and the highest degree of metallurgical combination could be obtained when the lap ratio was 40%,the lifting height was 0.8mm,and the route was orthogonal lap path.The experimental verification of laser wire feeding cladding in pressure environment was carried out through the high-pressure welding experiment cabin which can simulate the water depth and pressure environment.It proved that the laser wire feeding cladding process had good adaptability under high pressure environment,and the cladding layer was well formed.A comprehensive performance test on the laser wire feeding cladding layer under optimized parameters was carried out,and the test result showed that:the macroscopic appearance of the cladding layer was good with out any obvious defects inside;the cladding layer was mainly composed of bainite and martensite with the clear grain boundaries,dense and uniform structure and small grain size;the first cladding metal showed a tempering trend;the tensile properties and mechanical properties meet the standards;the horizontal and vertical hardness of the cladding layer had little difference,and the internal hardness distribution was uniform;the hardness of the first additive part was lower than that of the second additive part.The research work in this paper showed that:compared with laser powder feeding cladding,laser wire feeding cladding had higher efficiency and technological adaptability,better forming quality of cladding layer and comprehensive performance.Hyperbaric underwater laser cladding surface repair technology can meet the maintenance application requirements of the actual underwater environment.