Microstructure and Phase Transformation of a Niobium-rich TiAl-based Alloy Containing Boron and Carbon  

作　　者：Ziyong Chen Xianglin Su Zhilei Xiang Zuoren Nie 

机构地区：[1]College of Materials Science and Engineering,Beijing University of Technology,Beijing 100124,China

出　　处：《Journal of Materials Science & Technology》2012年第5期453-460,共8页材料科学技术（英文版）

基　　金：supported by the highrank talents program of Beijing University of Technology (No. J500900120081);the high-rank talents program of Beijing Municipal Education Commission (No.00900054R8002)

摘　　要：Microstructure and phase transformation of Ti46Al8Nb0.5B0.2C alloy have been investigated.X-ray diffraction （XRD）,optical microscopy （OM）,scanning electron microscopy （SEM） and transmission electron microscopy （TEM） results show that as-cast and hot isostatic pressing （HIP） alloy mainly composed of γ and α 2 phase have fully lamellar microstructure with point-like or ribbon-like TiB 2 distributing in lamellar colony or at grain boundary.The mean size of lamellar colony is about 150 and 450 μm for as-cast and HIP alloy,respectively.The lamellar spacing is about 550 and 600 nm for as-cast and HIP alloy,respectively.It has been found that cooling rates and quenching temperatures have significant effect on phase transformation of Ti46Al8Nb0.5B0.2C alloy.When the alloy is treated at 1380℃ for 1 h and cooled from α domain,water cooling leads to complete α → α 2 transformation,oil cooling leads to predominant α → α 2 and part α → γ m transformation,air cooling leads to α → α ＋ γ p2 →L（α ＋ γ） →L（α 2 ＋ γ） transformation,and furnace cooling leads to α → α ＋ γ p3 →L（α ＋ γ） →L（α 2 ＋ γ） transformation.However,when the alloy is treated at 1400℃ for 1 h and cooled from α domain,water cooling leads to predominant α → α 2 and part α → α ＋ γ p4 → γ m transformation,oil cooling leads to α → α ＋ γ p5 → γ m transformation,air cooling leads to α → α ＋ γ p6 →L（α ＋ γ） →L（α 2 ＋ γ） transformation,and furnace cooling leads to α → α ＋ γ p7 →L（α ＋ γ） →L（α 2 ＋ γ） transformation.Microstructural evolution of the alloy during various heat treatments has been examined and the phase transformation mechanisms have been elucidated.Based on the experimental observation,schematic CCT diagrams for the alloy have been given.Microstructure and phase transformation of Ti46Al8Nb0.5B0.2C alloy have been investigated.X-ray diffraction （XRD）,optical microscopy （OM）,scanning electron microscopy （SEM） and transmission electron microscopy （TEM） results show that as-cast and hot isostatic pressing （HIP） alloy mainly composed of γ and α 2 phase have fully lamellar microstructure with point-like or ribbon-like TiB 2 distributing in lamellar colony or at grain boundary.The mean size of lamellar colony is about 150 and 450 μm for as-cast and HIP alloy,respectively.The lamellar spacing is about 550 and 600 nm for as-cast and HIP alloy,respectively.It has been found that cooling rates and quenching temperatures have significant effect on phase transformation of Ti46Al8Nb0.5B0.2C alloy.When the alloy is treated at 1380℃ for 1 h and cooled from α domain,water cooling leads to complete α → α 2 transformation,oil cooling leads to predominant α → α 2 and part α → γ m transformation,air cooling leads to α → α ＋ γ p2 →L（α ＋ γ） →L（α 2 ＋ γ） transformation,and furnace cooling leads to α → α ＋ γ p3 →L（α ＋ γ） →L（α 2 ＋ γ） transformation.However,when the alloy is treated at 1400℃ for 1 h and cooled from α domain,water cooling leads to predominant α → α 2 and part α → α ＋ γ p4 → γ m transformation,oil cooling leads to α → α ＋ γ p5 → γ m transformation,air cooling leads to α → α ＋ γ p6 →L（α ＋ γ） →L（α 2 ＋ γ） transformation,and furnace cooling leads to α → α ＋ γ p7 →L（α ＋ γ） →L（α 2 ＋ γ） transformation.Microstructural evolution of the alloy during various heat treatments has been examined and the phase transformation mechanisms have been elucidated.Based on the experimental observation,schematic CCT diagrams for the alloy have been given.

关 键 词：TiAl-based alloys Heat treatment MICROSTRUCTURE Phase transformation 

分 类 号：TG146.2[一般工业技术—材料科学与工程] TG111.5[金属学及工艺—金属材料]