难变形Ti_(2)AlNb基合金梯度挤压工艺数值模拟和试验研究

采用梯度挤压工艺方案,并利用有限元仿真和试验相结合的方法,对Ti_(2)AlNb基合金的成形过程进行了系统研究。利用DEFORM软件分析了其成形过程中的载荷、应力、应变分布和金属流动行为,并结合Lode系数和应力三轴度对变形区的变形类型和应力状态进行了分析和表征。在RZU200HF液压机上进行了5A06铝合金物理网格试验和Ti_(2)AlNb基合金梯度挤压试验。结果表明,在Ti_(2)AlNb基合金梯度挤压成形过程中,塑性变形区的应力状态出现“三向压”和“一拉两压”情况。应变状态为压应力状态下的压缩类应变与伸长类应变。在坯料内部纵截面上,等效应变值从中心沿径向呈现上升梯度分布,应变梯度系数最大约为0.94。物理网格变化情况与数值模拟试验中基本一致,表层等效应变的理论计算值和网格试验值分别为4.06和4.27,验证了有限元模拟的有效性,且成功制备出Ti_(2)AlNb基合金成形件,为进一步制备高强塑性钛合金提供了参考依据。

The growth mechanism of the basic magnesium chloride whisker

Based on the theoretical model of anion coordination polyhedron growth units, the growth mechanism of the basic magnesium chloride whisker was discussed in this paper.It was found that the basic magnesium chloride whisker habits were related to the different environments in which anion coordination polyhedra grew. The growth units of basic magnesium chloride whiskers are [Mg - (OH) 4]2 -and [Mg - Cl 4]2 -. The growth process is the incorporation process of growth units. Growth units will have different incorporations and orientations caused by different system characters or heating. Furthermore, the formation mechanism of basic magnesium chloride whiskers was also interpreted using anion coordination polyhedron growth units.