12吨级Ti80合金铸锭的成分均匀性及其偏析规律研究

随着海洋装备的大型化发展及其各项性能的提升，对高均匀超大规格钛合金铸锭的研发有了更加迫切的需求。本文利用MeltFlow模拟获得优化的熔炼工艺，制备出国内第一个12吨级Ti80合金铸锭，并完成2炉稳定性验证。成分检测结果表明，铸锭头、中、尾3点成分极差小于1000ppm，冒口17点成分极差小于3000ppm，成分均匀性与现行5吨级铸锭基本相当。分析冒口径向成分分布规律发现，Al、Nb和Mo元素呈现边部高、心部低，从边部到心部逐渐降低的趋势，而Zr元素的分布规律则与之相反。利用EDS对不同部位晶内和晶界的微区成分分析发现，Nb、Mo元素呈现晶内高、晶界低，而Al、Zr元素呈现晶内低、晶界高的分布规律。其中，Nb、Mo、Zr元素的宏、微观偏析规律基本一致，即随着凝固的进行，固相中Mo、Nb含量逐渐降低，Zr含量逐渐升高。然而，Al元素的宏、微观偏析规律正好相反，分析认为主要是由于Al元素的饱和蒸气压较高，与其他合金元素相比更容易挥发，在长时间、高真空熔炼和溶质再分配的共同作用下，铸锭中的宏、微观偏析规律出现不一致的现象。

Composition uniformity and segregation in 12 tons ingot of Ti80 alloy

With the large-scale development of marine equipment and the improvement of its performance, it is necessary to research and develop ultra-large sized titanium alloy ingots with high uniform composition. Based on the simulation results by MeltFlow, the 1st 12 tons ingot of Ti80 alloy is melted in Chinese and then was verified by two times. The chemical testing results show that the composition difference of the upper, middle and bottom of the ingot is less than 1000ppm, and the composition difference of the 17 positions of the riser is less than 3000ppm. Both of them are equivalent to that of the 5 tons ingot. Further, the macrosegregation at the riser was investigated and it is found that Al, Nb, Mo are enriched in the edge of the ingot and poor in the center of the ingot, whereas Zr has the opposite phenomenon. EDS was used to study the microsegregation between the grain boundary and interior. The results show that Nb and Mo are enriched within grain and poor at grain boundary. On the contrary, Al and Zr are enriched in grain boundary and poor within grain. The macro and micro segregation are consistent for Nb, Mo and Zr and opposite for Al. This is largely because the distribution of Nb, Mo and Zr is more largely depended on the solute redistribution at the solidification interface. By contrast, due to the highSsaturated vapor pressure at high temperature, Al is volatilized severe during the long time and high vacuum melting process and the solute redistribution at the solidification interface.