摘要
根据热模拟实验结果和动态材料模型建立了Ti-46Al-8Nb合金的热加工图,确定了合理的热加工工艺制度,并采用包套轧制方法制备了Ti Al合金板材,考察了轧制高铌Ti Al合金的组织演变规律及流变软化机制。结果表明,在低应变时加工图中只存在2个失稳区,当应变增加到0.4时,在1250℃、0.006 s^-1附近位置也出现了失稳;在1200℃、1 s^-1和1150~1200℃、0.01 s^-1附近存在典型的动态再结晶区域。最终结合应变速率敏感系数的分析,选择在1150~1200℃、0.01~0.03 s^-1,每道次变形量约为18%的条件下进行复合包套轧制,获得厚度约为0.85 mm、变形均匀无裂纹缺陷的板材,其热轧组织局域流变软化严重,存在明显的轧制变形带,但整体组织均匀性较好。Ti-46Al-8Nb合金在热轧过程中的流变软化以γ相的动态再结晶以及热-力作用下L(α/γ)层片组织的相变分解为主,其中再结晶过程主要是通过位错塞积诱导亚晶界形成进而完成小角度晶界向大角度晶界的转化,L(α/γ)→γ+α+B2/β和α→γ转变是片层团分解的主要途径。此外,大量普通机械孪晶以及孪晶片层的出现,也可以显著提高热轧Ti Al合金的组织均匀性。
TiAl alloys are considered attractive structural materials because of their low density,excellent high-temperature strength,and oxidation resistance.However,their intrinsic characteristics,including low-temperature brittleness,poor workability,and narrow processing window,restrict their wide use in industrial applications.Various hot-work processes are conducted to enhance the inherent ductility of TiAl alloys,especially hot-pack rolling.In this work,the hot processing maps at different strains were developed based on isothermal compression tests and dynamic material model(DMM).The optimum hotworking parameters were selected and a crack free Ti-46Al-8Nb(atomic fraction,%)sheet was directly fabricated by hot pack rolling from ingot.Moreover,microstructure evolution and hot deformation behavior of the as-rolled alloys were investigated.The processing maps showed two typical dynamic recrystallization(DRX)domains which would facilitate the hot-work process,of which the temperature was at1200℃,strain rates was 1 s^-1with a peak efficiency of power dissipation of 0.38 and temperature of1150~1200℃,strain rate of 0.01 s^-1with a peak efficiency of power dissipation of 0.45.The instable-area temperature was 1100~1200℃and strain rate was 0.06~1 s^-1at low strain,which was expanded to low strain rate with the increasing strain.As the strain increased to 0.4,the region with the temperature of1250℃and strain rate of 0.006 s^-1always became instable.The Ti-46Al-8Nb alloy sheet with thickness of 0.85 mm was produced within processing windows of 1150~1200℃,0.01~0.03 s^-1with engineering strain 18%per pass.The produced sheet showed uniform microstructure as a whole,though the local flow softening and deformation bands were inevitable.Furthermore,the main softening mechanism of Ti-46Al-8Nb alloy was DRX which began with the pile-up of dislocations,the formation of sub-boundaries and mechanical twins.Then the substructures would rearrange to inducing the formation of DRXed grains with the cumulative reduction increasing.The phase transitions of Lamellae(α/γ)→γ+α+B2/βandα→γduring hot-pack rolling combining with the growth of DRXed grains were simultaneously a main softening mechanism.The formations of plentiful mechanical twinning and twin lamellae also contributed to the uniformity of as-rolled microstructure.
作者
李天瑞
刘国怀
于少霞
王文娟
张风奕
彭全义
王昭东
LI Tianrui;LIU Guohuai;YU Shaoxia;WANG Wenjuan;ZHANG Fengyi;PENG Quanyi;WANG Zhaodong(State Key Laboratory of Rolling and Automation,Northeastern University,Shenyang 110819,China;School of Materials Science and Engineering,Northeastern University,Shenyang 110819,China)
出处
《金属学报》
SCIE
EI
CAS
CSCD
北大核心
2020年第8期1091-1102,共12页
Acta Metallurgica Sinica
基金
国家重点研发计划项目No.2016YFB0301200
国家自然科学基金项目Nos.51504060和51301140
中央高校基本科研业务费项目No.N160713001。
