TiAl基合金非平衡凝固过程中的相选择及凝固特征  

PHASE SELECTION AND THE SOLIDIFICATION CHARACTERISTICS OF TiAl BASE ALLOYS IN THE NONEQUILIBRIUM SOLIDIFICATION

作　　者：胡锐[1] 柳翊[1] 张铁邦[1] 寇宏超[1] 李金山[1] 

机构地区：[1]西北工业大学凝固技术国家重点实验室,西安710072

出　　处：《金属学报》2013年第11期1295-1302,共8页Acta Metallurgica Sinica

基　　金：国家重点基础研究发展计划资助项目2011CB605503~~

摘　　要：通过研究TiAl合金中不同Al含量和不同β相稳定元素含量的变化,分析了Al含量和β相稳定元素对TiAl合金初生相选择与凝固特征的影响.结果表明,单一β相凝固的TiAl基合金含Al量低,结晶温度范围窄,凝固组织均匀细化.采用背散射法(BSE)观察并分析了不同过冷度下铸造TiAl基合金非平衡凝固的枝晶形貌,运用经典竞争形核理论研究了Ti48Al2Cr2Nb(原子分数,%)包晶合金非平衡凝固中β相与α相的形核与过冷度的关系,并计算了Ti48Al2Cr2Nb合金深过冷凝固中的β相(bcc)和α相(hcp)的临界形校功及稳态形核率,结果表明,在约15 K/s的冷速下,Ti48Al2Cr2Nb合金在所能达到的过冷度((?)370 K)范围内凝固时,β相始终为领先相优先形核.以过包晶凝固的TiAl基合金,其Al含量高,结晶温度范围窄,凝固枝晶细小,趋向逐层凝固,可减少并消除糊状凝固所造成的疏松和热裂趋势.β相稳定元素对凝固路径的影响取决于其Al当量,并可使TiAl合金的凝固路径从过包晶凝固转变为亚包晶凝固;过多的Al含量将导致铸造TiAl合金凝固组织中存在过多γ相,从而影响合金的强度和塑性.The Al content and the β stabilizers in TiAl base alloys were investigated,which have an important effect on the solidification characteristics and phase selection.TiAl base alloys with single β-solidifying have the characteristics of low Al content and narrow crystallization temperature range. It is attributed to forming a homogeneous fine-grained microstructure. Dendrite morphology in TiAl base alloys is investigated by SEM-BSE in the nonequilibrium solidification conditions. The relationships between undercooling and nucleation of two phases are investigated systematically by using the classical nucleation theory in the undercooled Ti48Al2Cr2Nb （atomic fraction, %） peritectic alloy. By calculating the interfacial critical nucleation work and steady state nucleation rates of β phase （bcc） and α phase （hcp）, it is obtained that β phase is always prior to nucleate from the Ti48Al2Cr2Nb undercooled melts at the cooling rate about 15 K/s in the achieved undercooling range. Due to narrow crystallization temperature range, microstructures of TiAl base alloys with high Al content as the hyper-peritectic solidification path take on the gradual solidification style and finer dendrite morphology. It is conducive to reducing and eliminating shrinkage porosity and hot cracking caused by mushy solidification. The β stabilizers have an important effect on solidification path depending on its Al equivalent and will change the solidification path of TiAl alloy from hyper--peritectic solidification to hypo-peritectic solidification. The overmuch Al content in TiAl base alloys leads to the formation of large number of massive γ phase impacting on strength and ductility of alloys.

关 键 词：TIAL基合金 非平衡凝固 相选择 过冷 初生相 

分 类 号：TG146.2[一般工业技术—材料科学与工程]