Development of the high-strength ductile ferritic alloys via regulating the intragranular and grain boundary precipitation of G-phase

Authors：Yang, Mujin; Huang, Chao; Han, Jiajia^*; Wu, Haichen^*; Zhao, Yilu; Yang, Tao; Jin, Shenbao; Wang, Chenglei; Li, Zhou; Shu, Ruiying; Wang, Cuiping; Lu, Huanming; Sha, Gang^*; Liu, Xingjun^*

Source：JOURNAL OF MATERIALS SCIENCE & TECHNOLOGY, 2023, 136: 180-199.

DOI：10.1016/j.jmst.2022.07.029

• G-phase
• Precipitation strengthening
• Grain boundary segregation
• Nano-precipitates

A typical G-phase strengthened ferritic model alloy (1Ti:Fe-20Cr-3Ni-1Ti-3Si, wt.%) has been carefully studied using both advanced experimental (EBSD, TEM and APT) and theoretical (DFT) techniques. During the classic "solid solution and aging " process, the superfine (Fe, Ni)(2)TiSi-L2(1) particles densely precipitate within the ferritic grain and subsequently transform into the (Ni, Fe)(16)Ti6Si7-G phase. In the meanwhile, the elemental segregation at grain boundaries and the resulting precipitation of a large amount of the (Ni, Fe)(16)Ti6Si7-G phase are also observed. These nanoscale microstructural evolutions result in a remarkable increase in hardness (10 0-30 0 HV) and severe embrittlement. When the "cold rolling and aging " process is used, the brittle fracture is effectively suppressed without loss of nano-precipitation strengthening effect. Superhigh yield strength of 1700 MPa with 4% elongation at break is achieved. This key improvement in mechanical properties is mainly attributed to the pre -cold rolling process which effectively avoids the dense precipitation of the G-phase at the grain boundary. These findings could shed light on the further exploration of the precipitation site via optimal processing strategies.

• Institution
  TEST; 南京理工大学; 中国科学院; 厦门大学; test; 中国科学院宁波材料技术与工程研究所