With the rapid developments of marine resource exploitation,mounts of marine engineering equipment are settled on the ocean.When it is not possible to move the damaged equipment into a dry dock,welding operations must...With the rapid developments of marine resource exploitation,mounts of marine engineering equipment are settled on the ocean.When it is not possible to move the damaged equipment into a dry dock,welding operations must be performed in underwater environments.The underwater laser welding/cladding technique is a promising and advanced technique which could be widely applied to the maintenance of the damaged equipment.The present review paper aims to present a critical analysis and engineering overview of the underwater laser welding/cladding technique.First,we elaborated recent advances and key issues of drainage nozzles all over the world.Next,we presented the underwater laser processing and microstructural-mechanical behavior of repaired marine materials.Then,the newly developed powder-feeding based and wire-feeding based underwater laser direct metal deposition techniques were reviewed.The differences between the convection,conduction,and the metallurgical kinetics in the melt pools during underwater laser direct metal deposition and in-air laser direct metal deposition were illustrated.After that,several challenges that need to be overcame to achieve the full potential of the underwater laser welding/cladding technique are proposed.Finally,suggestions for future directions to aid the development of underwater laser welding/cladding technology and underwater metallurgical theory are provided.The present review will not only enrich the knowledge in the underwater repair technology,but also provide important guidance for the potential applications of the technology on the marine engineering.展开更多
Direct laser metal deposition was used for preparing blocks of steel 12CrNi2 using four different laser powers under two different deposition environments including atmospheric environment and Ar-protected chamber.The...Direct laser metal deposition was used for preparing blocks of steel 12CrNi2 using four different laser powers under two different deposition environments including atmospheric environment and Ar-protected chamber.The results showed that microstructures and mechanical properties were significantly affected by different laser powers.Increasing laser power and deposition in Ar chamber will lead to a decrease in the quantity and size of the voids,which brings more elongation to the samples.Bainitic microstructure was replaced by Widmanstatten ferrite and pearlite,and the amount of proeutectoid ferrite increased with increasing laser power.Moreover,microstructures of previous layers were completely altered in high laser power.Excessive heat accumulation by using high heat input can produce equiaxed ferritic grains with the pearlites in previously deposited layers.Hardness of deposited samples increased from the bottom layer toward the top layer.By using a diode laser with a spot diameter size of 2 mm,the 900-W laser power is suitable for producing crack-and void-free samples.However,post-deposition heat treatment is necessary for obtaining homogeneous desired microstructure and grain size in the manufactured samples.展开更多
Direct laser metal deposition is a kind of advanced rapid manufacturing technology, which can produce near net shape parts by depositing metal powders layer by layer. This study demonstrates fabrication, the anisotrop...Direct laser metal deposition is a kind of advanced rapid manufacturing technology, which can produce near net shape parts by depositing metal powders layer by layer. This study demonstrates fabrication, the anisotropy of mechanical properties and hardness of a graded steel. The characteristics of constituent phases, microstructure, mechanical anisotropy, and microhardness were investigated using electron backscatter diffraction, optical microscopy, tensile test machine, and microhardness tester. It was found that the graded steel is dense and free of cracks. The crystal structures of the as-built samples evolved in three grades from fcc structures to fcc ＋ bcc structures and then to bcc ＋ fcc structures. Samples in x and z directions showed obvious mechanical anisotropy. The samples machined in x direction showed higher strength and lower elongation than those machined in z direction due to the presence of lack-of-fusion pores and the higher metallurgical bonding between layers in the x direction. The microhardness of the as-built samples increased along the cross section from the substrate （159.7 HV） to the top surface （545.4 HV）.展开更多
增材制造是融合材料科学、机械自动化及信息技术的先进制造技术,在近30年的发展中,发挥着越来越重要的作用。激光金属沉积(Laser metal deposition,LMD)是基于定向能量沉积(Directed energy deposition,DED)的一种增材制造技术,在近年...增材制造是融合材料科学、机械自动化及信息技术的先进制造技术,在近30年的发展中,发挥着越来越重要的作用。激光金属沉积(Laser metal deposition,LMD)是基于定向能量沉积(Directed energy deposition,DED)的一种增材制造技术,在近年来受到广泛关注和研究。阐述了LMD技术的基本工作原理及系统组成,重点介绍LMD技术国内外研究进展及应用现状,列举了一些基于LMD的工艺技术开发及装备研发制造,指出了LMD技术在成形效率和成形精度、工艺稳定性及性能一致性等方面的不足。最后,总结了LMD技术未来的5个发展趋势:材料体系集约化、工艺参数系统化、成形过程高效化、设备集成智能化和应用领域广泛化。展开更多
基金Supported by National Basic Scientific Research Project(Grant No.JCKY2017110B001)Jiangsu Provincial Postgraduate Research&Practice Innovation Program of China(Grant No.KYCX20_0080)。
文摘With the rapid developments of marine resource exploitation,mounts of marine engineering equipment are settled on the ocean.When it is not possible to move the damaged equipment into a dry dock,welding operations must be performed in underwater environments.The underwater laser welding/cladding technique is a promising and advanced technique which could be widely applied to the maintenance of the damaged equipment.The present review paper aims to present a critical analysis and engineering overview of the underwater laser welding/cladding technique.First,we elaborated recent advances and key issues of drainage nozzles all over the world.Next,we presented the underwater laser processing and microstructural-mechanical behavior of repaired marine materials.Then,the newly developed powder-feeding based and wire-feeding based underwater laser direct metal deposition techniques were reviewed.The differences between the convection,conduction,and the metallurgical kinetics in the melt pools during underwater laser direct metal deposition and in-air laser direct metal deposition were illustrated.After that,several challenges that need to be overcame to achieve the full potential of the underwater laser welding/cladding technique are proposed.Finally,suggestions for future directions to aid the development of underwater laser welding/cladding technology and underwater metallurgical theory are provided.The present review will not only enrich the knowledge in the underwater repair technology,but also provide important guidance for the potential applications of the technology on the marine engineering.
基金This work was financially supported by the National Key Research and Development Program of China(No.2016 YFB1100203).
文摘Direct laser metal deposition was used for preparing blocks of steel 12CrNi2 using four different laser powers under two different deposition environments including atmospheric environment and Ar-protected chamber.The results showed that microstructures and mechanical properties were significantly affected by different laser powers.Increasing laser power and deposition in Ar chamber will lead to a decrease in the quantity and size of the voids,which brings more elongation to the samples.Bainitic microstructure was replaced by Widmanstatten ferrite and pearlite,and the amount of proeutectoid ferrite increased with increasing laser power.Moreover,microstructures of previous layers were completely altered in high laser power.Excessive heat accumulation by using high heat input can produce equiaxed ferritic grains with the pearlites in previously deposited layers.Hardness of deposited samples increased from the bottom layer toward the top layer.By using a diode laser with a spot diameter size of 2 mm,the 900-W laser power is suitable for producing crack-and void-free samples.However,post-deposition heat treatment is necessary for obtaining homogeneous desired microstructure and grain size in the manufactured samples.
基金financially supported by the National Key Research and Development Program of China (Grant Nos. 2016YFB1100204 and 2013ZX06002-002)the Shenyang Science and Technology Funded Project (Grant Nos. 17-29-2-00, Y17-1-031 and Z17-2-002)Financial support by the Youth Foundation of School of Stomatology, China Medical University (Grant No. K101593-17-05)
文摘Direct laser metal deposition is a kind of advanced rapid manufacturing technology, which can produce near net shape parts by depositing metal powders layer by layer. This study demonstrates fabrication, the anisotropy of mechanical properties and hardness of a graded steel. The characteristics of constituent phases, microstructure, mechanical anisotropy, and microhardness were investigated using electron backscatter diffraction, optical microscopy, tensile test machine, and microhardness tester. It was found that the graded steel is dense and free of cracks. The crystal structures of the as-built samples evolved in three grades from fcc structures to fcc ＋ bcc structures and then to bcc ＋ fcc structures. Samples in x and z directions showed obvious mechanical anisotropy. The samples machined in x direction showed higher strength and lower elongation than those machined in z direction due to the presence of lack-of-fusion pores and the higher metallurgical bonding between layers in the x direction. The microhardness of the as-built samples increased along the cross section from the substrate （159.7 HV） to the top surface （545.4 HV）.
文摘增材制造是融合材料科学、机械自动化及信息技术的先进制造技术,在近30年的发展中,发挥着越来越重要的作用。激光金属沉积(Laser metal deposition,LMD)是基于定向能量沉积(Directed energy deposition,DED)的一种增材制造技术,在近年来受到广泛关注和研究。阐述了LMD技术的基本工作原理及系统组成,重点介绍LMD技术国内外研究进展及应用现状,列举了一些基于LMD的工艺技术开发及装备研发制造,指出了LMD技术在成形效率和成形精度、工艺稳定性及性能一致性等方面的不足。最后,总结了LMD技术未来的5个发展趋势:材料体系集约化、工艺参数系统化、成形过程高效化、设备集成智能化和应用领域广泛化。
