钛及钛合金具有优良的高温力学性能和耐腐蚀性能，在航空航天、海洋工程和船舶制造等领域的需求日益增长。获得成分准确、均匀以及无夹杂的钛锭是后续生产优质钛材的前提。电子束冷床炉熔炼（EBCHM）可生产大尺寸钛锭且易于去除其中的高低密度夹杂，被认为是生产优质纯钛锭的先进工艺，但该工艺要用于钛合金铸锭制备还需解决熔炼过程中的高饱和蒸气压元素挥发以及夹杂控制问题。本论文从理论上重点研究合金元素的挥发损失规律、高低密度夹杂的迁移去除规律以及α夹杂（氮化钛）的溶解去除规律，为EB炉生产优质钛合金铸锭提供理论指导。首先使用有限元软件耦合模拟了冷床中流场和温度场以及夹杂物粒子在冷床中的迁移过程。模拟结果表明，熔体温度随熔炼功率增加而升高，随熔炼速率增加而降低。冷床中熔体除了往冷床出口流动外，还存在Marangoni对流导致的横向速度分量，从而使得熔体从冷床中心流向冷床边缘。低密度夹杂主要在熔体表面运动，并且向冷床边缘迁移而被凝壳捕获或者被直接烧蚀；高密度夹杂在进入冷床后几乎立即沉积到冷床底部的凝壳中；而中等密度的夹杂沿熔体流线在冷床内大范围运动。根据热力学理论和传质理论建立了合金组元的挥发动力学模型，并结合流场模拟结果研究了熔炼工艺参数对铸锭成分的影响。计算结果表明，存在一个临界温度（约2200K）。当熔炼温度低于该温度时，界面反应为挥发控制环节；而高于该临界温度时，熔体中的扩散传质和界面反应均成为控制环节。计算了Ti-Al-V合金熔炼过程中Al和V元素的含量随原始配料成分以及工艺参数的变化规律，最终实现了Ti-6Al-4V目标成分铸锭的制备。建立了夹杂的扩散溶解模型，研究了夹杂在冷床内的扩散溶解过程。在溶解过程中，夹杂的溶解速率基本上不随时间变化。溶解速率随温度升高而增加，随夹杂尺寸增加而略有下降。在温度为2100K-2300K时，夹杂溶解速率在-之间。夹杂在冷床中的滞留时间在100s以上，熔炼速率增加时，滞留时间减少。从计算结果来看，目前使用的熔炼参数完全能够溶解常见的夹杂。
Titanium and titanium alloys have increasing applications in aerospace, marine and ship industry due to their superior high temperature mechanical property and well corrosion resistance. The clean and homogeneous titanium ingots with accurate composition are the important basis for producing high quality titanium parts. Electron beam cold hearth melting (EBCHM) is thought as an advanced melting process for pure titanium especially, considering that it is easily to remove high and low density inclusions in titanium melt due to the higher heating temperature, at the same time, this process can easily produce titanium ingots or slab with large size. However, some problems must be solved for EBCHM process to be applied for titanium alloys, especially the evaporation of alloying elements with high saturated evaporation pressure and the inclusions control. So this thesis will focus on the evaporation of alloying elements, the migrating of high and low density inclusions as well as the dissolution mechanism of inclusions (Ti-N) with medium density close to titanium.The coupled flow, heat transfer and the migrating of inclusions in the cold hearth were simulated using finite element software. The results show that the temperature of the melt increases with the increase of melting power and decreases with the increase of melting rate. There exists Marangoni flow in the cold hearth, which drives the melt move toward the hearth edge. Low density inclusions mainly move on the melt surface and toward the hearth edge. These inclusions will be captured by the shell or be burned directly. High density inclusions will drop to the bottom instantly after flowing into the hearth. The neutral density inclusions will flow along the stream line and moves in a wide range. The evaporation model of alloying elements was established based on thermodynamic and mass transfer theory. The effect of melting parameters on the composition of ingots was studied using this model and combining the simulation results of flow field. The results show that there is a critical temperature (about 2200K) in the melting process of EB furnace. The reaction on the interface is the control stage when melting temperature is lower than the critical temperature. When melting temperature is higher than the critical temperature, both interface reaction and mass transfer in the melt become control stages. The effect of melting parameters on the concentration of aluminum and vanadium in the melting process of Ti-Al-V alloy was analyzed. The Ti-6Al-4V was prepared, and the composition is close to the target composition. The resolving model of inclusions was established. The resolving process of inclusions was analyzed. In the resolving process, the resolving rate of inclusions almost won’t change with time. The resolving rate increases with the increase of temperature and slightly decreases with the increase of inclusion size. When the temperature increases from 2100K to 2300K, the resolving rate increases from -. The residual time of inclusions in the cold hearth is greater than 100s, which decreases with the increase of melting rate. The calculating results show that current melting parameters can remove common inclusions completely.
