Mechanism and morphology evolution of the O phase transformation in Ti-22Al-25Nb alloy  

作　　者：Zong Yingying Wang Jiwei Shao Bin Tang Wei Shan Debin 

机构地区：[1]National Key Laboratory for Precision Hot Processing of Metals,Harbin Institute of Technology,Harbin,150001,China

出　　处：《Journal of Materials Science & Technology》2021年第30期97-106,共10页材料科学技术（英文版）

基　　金：the financial support from the National Natural Science Foundation of China under Grant No.52005129。

摘　　要：The phase transformation and microstructure in Ti-22Al-25Nb alloy are extremely complex.In this work,the morphology evolution of the O phase during the heating and cooling process was investigated by electron backscatter diffraction(EBSD)and first-principles calculations.The results show that the O→α_(2)phase transformation process during the heating process is as follows:spheroidization of the O phase occurs first,then theα_(2)phase nucleates in the spheroidized O phase,grows and replaces the O phase,completing the O→α_(2)phase transformation.In the meanwhile,the diffusion of Nb from Nb-poor O to Nb-rich B2 phases is a back-diffusion process.According to first-principles calculations,the driving force of the O→α_(2)phase transformation is the difference in the free energies of formation for the two phases(0.09 eV/atom).When the Nb content is greater than 15.625%,the lattice distortion of theα_(2)phase sharply increases,and the distortion energy drives the back-diffusion of Nb.During the cooling process,theα_(2)→O phase transformation is difficult and slow due to the difficult diffusion of Nb from the B2 toα_(2)phases.When holding for 60 min at 960℃,the coarseα_(2)phase gradually transforms to the O phase from the margin to the inside,forming a dispersed mixed structure of the O andα_(2)phases.During the B2→O transformation,the nucleation of the O phase induces a high stress region,in the range of approximately 200 nm.

关 键 词：Ti-22Al-25Nb alloy Phase transformation MICROSTRUCTURE O phase FIRST-PRINCIPLES 

分 类 号：V252[一般工业技术—材料科学与工程] TG146.23[航空宇航科学与技术—航空宇航制造工程]