Grain Refinement and Strengthening Mechanisms of In-situ Follow-up Hammering-Assisted Wire Arc Additive Manufacturing for Hydraulic Turbine Blade Repairing

Authors：Xiong, Xiaochen; Qin, Xunpeng^*; Hua, Lin; Wan, Gang; Wei, Shilong; Ni, Mao; Hu, Zeqi^*

Source：Metals and Materials International, 2023, 29(6): 1796-1814.

DOI：10.1007/s12540-022-01335-0

• Hydraulic turbine blade repairing
• In-situ follow-up hammering
• Wire arc additive manufacturing
• Grain refinement
• Strengthening mechanism

An in-situ follow-up hammering-assisted (FH) wire arc additive manufacturing (WAAM) process is proposed for hydraulic turbine blade repairing. With different hammering intervention temperatures above the austenite recrystallization temperature (Tre-gamma), the influence and mechanism of the process on the grain size of prior austenite grains and room-temperature martensite, as well as the texture of 0Cr13Ni5Mo deposited layers are systematically studied. The OM, SEM and EBSD are used for characterization. The repairing layer of large-sized blade is dominated with the coarse columnar grains with several millimeters in length, and the grain size is rated as grade 0. After the FH process, the prior austenite grains are significantly refined to grade 8. As the hammering temperature increases, the recrystallized austenite grains gradually grow and coarsen owing to the higher ambient temperature. FH at 950 celcius, a temperature slightly higher than the Tre-gamma can achieve the austenite grains with excellent grain refinement effect. Meanwhile, thanks to microstructure inheritance, the room-temperature martensitic is also refined from 4.69 to 2.47 mu m, and the typical < 100 > fibre texture content in the deposited layer is obviously reduced with the texture intensity reduced from 6.68 to 2.95. Furthermore, the yield strength is increased by about 200 MPa. The main strengthening mechanisms are grain refinement strengthening and dislocation strengthening, and the contributions to the yield strength are 96.1 MPa and 79 MPa respectively. Additionally, the FH process is also expected to simultaneously improve the formability of the blade repaired layer.

• Institution
  武汉理工大学