微量B和C对TiAl合金铸锭缩孔缩松的影响

采用真空感应磁悬浮熔炼合金、重力浇注入室温石墨模具的方法,分别制备了Ti-47Al-2Cr-2Nb,Ti-47Al-2Cr-2Nb-0.8B和Ti-47Al-2Cr-2Nb-0.1C 3种名义成分的铸锭.对铸锭进行成分分析并利用体视显微镜和扫描电子显微镜对铸锭的铸造收缩缺陷和组织进行分析.结果表明:Ti-47Al-2Cr-2Nb合金铸锭有很强的柱状晶生长趋势,在轴线附近区域形成分散的缩松;加入0.8%B(原子分数)后,铸锭的组织得到细化,并削弱了柱状晶生长趋势,收缩缺陷分布集中以大缩孔方式存在,显微缩松的密度和尺寸均降低.添加0.1%C(原子分数)后,铸锭的组织和缩孔缩松与Ti-47Al-2Cr-2Nb比均无明显变化.

Influence of boron and carbon on the shrinkage defects of TiAl alloys

Alloys whose nominal compositions were Ti-47Al-2Cr-2Nb, Ti-47Al-2Cr-2Nb-0.8B and Ti-47Al-2Cr-2Nb-0.1C were vacuum induction skull melted. Ingots were produced by pouring the molten alloys into a room-temperature graphite mold. Chemical compositions of ingots obtained were analyzed respectively. Microstructure as well as shrinkage cavity and porosity were also investigated with stereo microscope and scanning electron microscope (SEM). The results indicate that Ti-47Al-2Cr-2Nb alloy shows an intense columnar-growth tendency, and shrinkage porosity distributes dispersedly in the center zone around axis of ingot. Microstructure is refined and the columnar-growth tendency is weaken with the addition of 0.8% boron (atomic fraction). Shrinkage porosity becomes more concentrated to form a cavity in the center zone of ingots, and the density and size of micro porosity also decrease. However, the addition of 0.1% carbon (atomic fraction) doesn-t result in any apparent effects in terms of shrinkage porosity or microstructure compared to ingots without any additive.