强相变织构形成原理及形变、再结晶对变体选择的影响机制

Phase transformation is an important way to be used for controlling structures and properties of materials. Texture exists extensively in the products under various processing routines and renders a polycrystalline material the property of its single crystal counterpart, thus can increase its property significantly. Phase transformation generally weakens texture, but it can induce strong texture under the help of heavy plastic deformation. As strong transformation texture cannot be produced by a combination of deformation and recrystallization processes with respect to its type and intensity, therefore, it establishes a new way to increase strongly materials properties by utilizing the intrinsic properties of materials to the largest extent. This research proposal aims to investigate the formation mechanisms of strong transformation textures in three kinds of materials with different orientation relationship, different transformation types and different transformation temperature ranges, namely pure iron, pure titanium and high manganese steel by exploring the formation rules of strong transformation texture and the controlling factors for strong variant selection, by revealing the special role of recrystallization for strong transformation texture formation and the mode of microstructure evolution, by understanding the interaction rules among deformation, recrystallization and transformation and the change of controlling factors for variant selection. The objectives are to establish, on the one hand, a generalized theory of the formation of strong transformation texture in deferent types of transformations, and, on the other hand, to set up a solid fundamental to develop a new generation of electrical steels with high magnetic properties, titanium sheets with deep drawing ability and high manganese steels with high combination of strength and plasticity with all possessing strong transformation textures.

相变是调控材料组织、性能的重要途径。织构广泛存在于材料各种制备过程并使多晶材料最大程度展示其单晶的本征特性，进而可显著提高材料性能。相变一般弱化织构，强塑性变形作用下的相变却可强化织构。强相变织构多具有形变、再结晶工艺组合无法得到的织构类型或织构强度，因而又构成一种显著提高材料性能并最大程度利用材料最佳方向性能的途径。本项目通过对三类具有不同取向关系、不同相变类型、不同相变温度范围的材料（纯铁、纯钛、高锰钢）中出现强相变织构的研究，探索强相变织构的形成规律、强变体选择过程的控制因素，揭示再结晶对强相变织构形成的特殊作用及微观组织演变模式，澄清强相变织构形成时形变、再结晶、相变之间的交互作用规律和变体选择控制因素的转换条件。在理论上建立不同类型相变的强相变织构形成的共性理论，在应用上为开发新一代利用强相变织构提高磁性的电工钢、提高冲压性能的钛板材和提高强塑积的高锰TRIP钢而奠定理论基础。

固态相变常遵循特定的取向关系，晶体的高对称性造成相变时多变体出现并弱化相变织构，但变形可导致强变体选择，进而强化相变织构；加热相变又使再结晶成为相变织构新的影响因素。本项目选取具有不同类型和不同取向关系的相变的电工钢、高锰TRIP钢和钛合金，揭示、分析、归纳了各类相变织构形成原理和强化相变织构的变体选择规律。在理论上建立强相变织构形成理论，在应用上提升合金的磁学性能或力学性能。.结果表明，形变是强相变织构出现的必要条件，但对不同类型相变织构影响机制不同。高锰钢动态相变中，取向因子和变形功控制相变织构和变体选择；扩散型相变中，形变保障了再结晶织构，为相变准备特殊取向种子；表面效应诱发相变时，弹性模量及界面能各向异性成为新的控制因素。在全相变型电工钢及钛合金中显著出现的表面效应诱发相变织构明显不同于形变再结晶织构，也区别于低相变加热温度下的遗传型相变织构。利用Mn元素挥发的真空退火处理诱发了部分相变型相变织构并在加热过程形成，这区别于冷却中形成的全相变型相变织构，并伴随化学成分变化，在高硅电工钢中形成了极强的{100}织构，在高锰钢表层则完全保留了轧制织构且对应等轴晶组织。三种材料中调控出的相变织构都伴随性能提升，电工钢中强{100}织构显著提升了磁性能，纯钛板中强{11-20}织构显著提升了强度，但降低了塑性，高锰TRIP钢板表层形成{111}和{112}<110>织构高强度铁素体与心部奥氏体组成三明治结构，显著提升了屈服强度和冲压性能。再结晶晶粒尺寸控制着遗传型相变织构向表面效应诱发型相变织构的转变，细晶有利于前者，粗晶有利于后者。低牌号电工钢中粗大{100}柱状晶组织的相变被显著抑制，晶界不是优先形核地点，晶内相变显著受周围压缩或膨胀应力阻碍，少量相变组织内含大量∑1变体和∑3特殊界面；前者是弹性模量各向异性的作用，后者对应变体与未相变的粗大柱状晶之间的取向差，是低能界面的作用结果。依据柱状晶相变被抑制的现象提出高温亚稳铁素体轧制强化{100}织构新工艺。