真空铜模吸铸三元Ti-44Al-6Nb合金凝固组织演化研究

Study on Solidification Microstructure Evolution of Ternary Ti-44Al-6Nb Alloy Prepared by Cu-mold Vacuum Suction Casting

采用真空非自耗电弧炉和铜模真空吸铸设备分别制备了三元Ti-44Al-6Nb合金钮扣铸锭和真空吸铸棒状试样(φ5 mm×90 mm),借助扫描电镜和能谱及X射线衍射仪分别研究了合金铸态和吸铸凝固组织的形貌、成分以及相组成,同时利用Thermo-Calc软件计算了Ti-Al-6Nb合金变温截面相图并预测了凝固路径。结果表明:通过相图及铸态凝固组织特征分析,初生相为β相,凝固路径为单一β相的凝固,铸态组织均匀化,白色β型偏析呈条状分布,未观察到明显的凝固偏析;真空铜模吸铸急冷区凝固组织均匀、细化且无凝固偏析,而在糊状区呈现出明显的枝晶形貌且具有典型的包晶凝固特征,这表明随着冷却速率的降低,凝固路径由单一β相凝固转变为包晶凝固。

The ternary Ti-44Al-6Nb alloy button ingot and vacuum-suction rod sample(φ5 mm×90 mm) were prepared by non-self-consuming vacuum arc furnace and Cu-mold vacuum suction casting equipment, respectively. The morphology,composition and phase composition of the as-cast and suction-cast solidification structures were studied by means of scanning electron microscopy, energy dispersive spectroscope and X-ray diffraction, respectively. Meanwhile, the phase diagram of variable temperature section of Ti-Al-6Nb alloy was calculated by Thermo-Calc software and the solidification path was predicted. The results indicate that through the analysis of phase diagram and the characteristics of as-cast solidification structure, the primary phase is β phase, the solidification path is the solidification of single β-phase, the as-cast microstructure is homogenized, and white β-segregation is strip distributed and the solidification segregation is unobserved. The solidification structure of vacuum copper mold die suction casting in quenching zone is uniform, refined and without solidification segregation. In the paste region, the dendrite morphology is obvious and has typical characteristics of peritectic solidification.It shows that the solidification path is changed from single β-phase to peritectic solidification with the decrease of cooling rate.