Shanghai Photonics Corporation has made progress in laser welding of structural materials (Ni-28W-6Cr alloy) for new-generation molten salt reactors

Recently, Yang Shanglu, a researcher at the Laser Intelligent Manufacturing Technology Research and Development Center of 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. 

The research team applied the high power fiber laser welding technology to Ni-28W-6Cr alloy for the first time, and analyzed the dynamic cracking behavior characteristics of the laser welding hot crack by using high speed camera technology, and clarified the cracking mechanism. 

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 "was 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. However, due to the high alloying level of the alloy, it has a very high sensitivity to welding hot cracks, which poses a great 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. The work laid a foundation for the control of Ni-28W-6Cr alloy laser welding hot crack, the realization of alloy defect free laser welding, and promote the construction of a new generation of molten salt reactor.

This work is supported by the National Natural Science Foundation Youth Fund and the National Key Research and Development Program.

Figure 1: (a) Dynamic cracking behavior of Ni-28W-6Cr alloy during laser welding; (b) microstructure of Ni-28W-6Cr alloy during laser welding.

Figure 2 EBSD analysis results of Ni-28W-6Cr alloy laser welding hot crack: (a) solidification crack, (b) liquefaction crack.

Source: Shanghai Institute of Optics and Fine Mechanics, Chinese Academy of Sciences