Formation Mechanism of New Grains in Dynamic Recrystallizaion based on Local Orientation Analysis

为了阐明动态再结晶过程中新晶粒的形成机理，结合显微组织演变和晶界分析，研究了γ-TiAl、Ni和Cu在压缩动态再结晶过程中织构的形成。压缩试验在不同的温度和真应变率进行;相应的Zener-Hollomon参数lnZ的对数值范围从12.2到31.7。织构的形成行为因变形条件和材料种类的不同而不同，在低Z变形条件下，动态再结晶主要通过应变诱导晶界迁移生成新晶粒的过程进行。在这种情况下，γ-TiAl与镍和铜的织构形成行为不同，在γ-TiAl中织构明显发展（最大极密度PMAX= 10），而在镍和铜中没有织构形成（PMAX ≤ 2）。纹理格式的差异 ...更多信息 可以得出结论，在晶界迁移过程中孪晶形成频率的差异导致了这种现象。也就是说，再结晶晶粒朝向压缩稳定取向（γ-TiAl中的{032}）改变它们的取向，并且当孪晶几乎不发生时，以该取向为主要成分的织构急剧发展，而当孪晶非常频繁地发生时，如在镍和铜中，不发展织构。动态再结晶是通过晶界附近新晶粒的形核和长大进行的，晶界附近的变形严重且不均匀。在这种情况下，在每种材料中没有发现织构形成的显著差异;可以肯定地观察到具有在稳定压缩取向中或附近的主要成分的织构，尽管其不尖锐（PMAX=3-4）。PMAX的值和孪生频率都随着lnZ的值而变化，但是在它们的变化中没有观察到任何不连续的偏移。这表明，随着lnZ的增加，织构形成的行为逐渐从低Z条件下的高Z条件下的变化，取决于动态再结晶，晶界的隆起和新晶粒的形核和生长的两个过程的比例。少

In order to clarify the mechanism of new grain formation in dynamic recrystallization, the texture formation in γ-TiAl, nickel and copper during dynamic recrystallization (DRX) in compression was studied in relation to the microstructural evolution and grain boundary analysis. Compression tests were conducted at various temperatures and true strain rates ; the corresponding logarithmic value of Zener-Hollomon parameter lnZ ranged from 12.2 to 31.7. The behavior of texture formation was different, depending on the deformation conditions and the kind of materials.In low Z deformation conditions, DRX proceeded mainly through the process in which new grains are generated by strain induced migration of grain boundaries. In this case, the behavior of texture formation was different in γ-TiAl and in nickel and copper, texture developed sharply in γ-TiAl (the maximum pole density PMAX= 10) but it was not formed in nickel and copper (PMAX less than or equal 2). The difference in texture formati … More on was concluded to arise from the difference in the frequency of twin formation during grain boundary migration. That is, recrystallized grains change their orientation towards the stable orienctation for compression ({032) in γ-TiAl) and the texture, having this orientation as a main component develops, sharply when twinning scarcely occurs, while no texture develops when twinning occurs very frequently as in nickel and copper.In high Z deformation conditions, DRX proceeded through the nucleation and growth of new grains in the vicinity of grain boundaries where the deformation occurred severely and inhomogeneously. In this case, no notable difference in texture formation was found in each material ; the texture having a main component in or near the stable orientation for compression could certainly be observed though it was not sharp (PMAX=3-4).Both the value of PMAX and the frequency of twinning changed with the value of lnZ, but any discontinuous shift was not observed in their variation. This indicates that, with increasing lnZ, the behavior of texture formation changes gradually from that for low Z conditions to that for high Z conditions, depending on the proportion of the two processes of DRX, the bulging of grain boundaries and the nucleation and growth of new grains. Less