TC19合金铸锭中Zr、Mo元素的宏观偏析行为  

Macrosegregation of Zr and Mo in TC19 Titanium Alloy Ingot

作　　者：朱绍祥 王清江[1,2] 刘建荣 陈志勇[2] ZHU Shaoxiang;WANG Qingjiang;LIU Jianrong;CHEN Zhiyong(School of Materials Science and Engineering,University of Science and Technology of China,Shenyang 110016,China;Shi-changxu Innovation Center for Advanced Materials,Institute of Metal Research,Chinese Academy of Sciences,Shenyang 110016,China)

机构地区：[1]中国科学技术大学材料科学与工程学院,沈阳110016 [2]中国科学院金属研究所师昌绪先进材料创新中心,沈阳110016

出　　处：《金属学报》2024年第7期869-880,共12页Acta Metallurgica Sinica

基　　金：国家科技重大专项项目No.J2019-VI-0005-0119。

摘　　要：为了提高航空发动机转动件用高温钛合金铸锭的成分均匀性,本工作研究了真空自耗电弧熔炼(VAR) TC19 (Ti-6Al-2Sn-4Zr-6Mo,质量分数,%)合金工业化铸锭中合金元素的宏观偏析行为,运用定向凝固技术分析了合金元素的偏析机制。结果表明,Al、Sn元素无明显宏观偏析,Zr、Mo元素存在宏观偏析。Zr元素在铸锭中心等轴晶区含量低,顶部冒口区含量高;Mo元素分布与Zr的分布趋势相反。Zr、Mo元素偏析与铸锭凝固组织相对应。凝固速率差异是造成Zr、Mo元素宏观偏析的主要原因;表面细晶区和柱状晶区由于较快的凝固速率,元素来不及再分配,基本保留液相的均匀成分;铸锭心部等轴晶区由于其较低的凝固速率和温度梯度,固/液界面呈平面或胞状,有利于元素在固/液界面充分再分配,使得凝固分配系数小于1的正偏析元素Zr在液相中的浓度大于固相,随凝固过程沿铸锭心部向冒口方向逐渐增加;凝固分配系数大于1的负偏析元素Mo在液相中的浓度小于固相,沿铸锭心部向冒口方向逐渐减少。液固两相的密度差造成等轴晶沉降及浮力促进了元素的宏观偏析。电磁搅拌产生的Lorentz力是熔池流动的主要驱动力,使熔池产生环轴向流场,与浮力产生的密度流和自感Lorentz力产生的环流相互作用,可降低溶质元素宏观偏析。Theα+βtitanium alloy TC19(Ti-6Al-2Sn-4Zr-6Mo,mass fraction,%)has shown great application potential in aerospace because of its superior moderate-temperature mechanical properties.The bulk composition of this alloy contains Al,Sn,Zr,and Mo,which are the main alloying elements in the field of high-temperature titanium alloys.Compared with Ti,Al and Sn,which are characterized by lower melting points and densities,can be easily volatilized during vacuum arc remelting(VAR).In addition,Zr has a higher density,and Mo has a higher melting point and density compared with Ti.Therefore,controlling the chemical homogeneity either in the macro-or micro-scale for industrial-scale titanium alloy ingot with complex compositions is challenging.In this study,the macrosegregation behavior and mechanism of Zr and Mo were investigated systematically in a TC19 industrial-scale ingot(f720 mm×1160 mm)by using a directional solidification technology where samples were solidified under a constant-temperature gradient of approximately 200o C/cm and a wide range of withdrawal rates(solidification rate)from 3 mm/h to 150 mm/h.Result shows an evident macrosegregation of Zr and Mo,which is primarily attributed to the difference in the solidification rate during solidification.Zr as the negative segregation element was pushed to the front of the solid-liquid interface continuously,whereas Mo as the positive segregation element was enriched in the solid phase at the solid-liquid interface.Consequently,the content of Zr is relatively lower at the center equiaxed crystal zone but higher at the top casting riser in the TC19 industrialscale ingot.However,Mo exhibits the opposite trend in comparison with Zr.The degree of element segregation decreased with the increase of the solidification rate.Moreover,the“crystal rain”caused by the density difference between liquid and solid phases as well as buoyancy would promote the macrosegregation in industrial-scale ingots.The Lorentz force arising from electromagnetic stirring is the main driving forc

关 键 词：TC19合金 真空自耗电弧熔炼 宏观偏析 定向凝固 电磁搅拌 

分 类 号：TG146.2[一般工业技术—材料科学与工程]