Shanghai Optical Machinery Institute has made progress in laser welding of structural materials for new-generation molten salt reactors

Recently, the team of Yang Shanglu, a researcher at the Laser Intelligent Manufacturing Technology Research and Development Center of the Shanghai Institute of Optics and Fine Mechanics, Chinese Academy of Sciences, has made new progress in laser welding of the fourth-generation reactor-molten salt reactor structural material Ni-28W-6Cr nickel-based superalloy.

In this study, the high power fiber laser welding technology was applied to Ni-28W-6Cr alloy for the first time, and the dynamic cracking behavior of the alloy was analyzed by high speed imaging technology, and the cracking mechanism was elucidated. The relevant research results are summarized as Dynamic laser welding hot cracking behavior and mechanism of new structural material Ni-28W-6Cr alloy for molten salt reactor is published in the Journal of Materials Research and Technology.

Ni-28W-6Cr high temperature nickel base alloy is a new structural material designed for the new generation of high temperature molten salt reactor (> 850℃) in China, which has excellent high temperature resistance and corrosion resistance to molten salt. Due to the high alloying level of the alloy, it has a very high sensitivity to welding hot cracks, which poses a threat to the service safety of welded joints and structures. In order to improve the laser welding quality of Ni-28W-6Cr alloy and promote the application of nuclear energy engineering, it is urgent to study the cracking behavior and influencing factors of Ni-28W-6Cr high temperature nickel base alloy laser welding, and solve the problem of laser cracking by elucidating the cracking mechanism.

The dynamic crack behavior of Ni-28W-6Cr alloy laser welding was analyzed by using a 10,000-watt laser processing unit combined with high-speed imaging technology, and the relationship between the type, number, size, propagation behavior and laser power of the hot crack was obtained. The influencing factors of hot crack initiation and propagation (laser process parameters, element segregation, precipitated phase and stress, etc.) were clarified, and the mechanism of hot crack cracking in laser welding was elucidated. This work lays a foundation for controlling the hot crack of Ni-28W-6Cr alloy laser welding, realizing the defect free laser welding and promoting the construction of a new generation of molten salt reactor.

The research work is supported by the National Natural Science Foundation Youth Science Fund Project and the national key research and development Plan.

(a) Dynamic cracking behavior of Ni-28W-6Cr alloy during laser welding; (b) microstructure of Ni-28W-6Cr alloy during laser welding.

EBSD analysis results of Ni-28W-6Cr alloy laser welding hot crack: (a) solidification crack, (b) liquefaction crack.

Source: OFweek