经a+β两相区变形及退火后的TB6钛合金模锻件低倍组织局部区域显现出了粗晶缺陷.通过热模拟试验,结合微拉伸及扫描电镜(Scanning electron microscope,SEM)、背散射电子衍射仪(Electron black-scattered diffraction,EBSD)等微观分析手段,分析对比低倍组织中粗、细晶区的显微特点及力学性能,探讨低倍粗晶形成机理,提出低倍粗晶显现的工艺判据并建立预测模型.结果表明,低倍粗晶主要分布在变形温度低且变形程度大的金属剧烈流动区域,与细晶材料相比,粗晶使得屈服强度降低,但伸长率和抗拉强度提高.经两相区加热后,锻件转运过程中表面温度降低,温降导致表面区域温度不均,在大变形速率下,表面圆弧区域软化程度差别较大,易发生部分动态再结晶,产生晶界角较大的动态再结晶晶粒(β相).退火后,该动态再结晶晶粒通过晶界迁移实现对周边产生的晶界角较小的静态再结晶晶粒的吞并,形成粗晶.变形温度(T)越低,变形量越大且不超过临界值时,低倍粗晶越容易显现.建立T与εf间的量化关系;以εf为判据,通过二次开发建立有限元子程序,实现锻件低倍粗晶分布的可视化预测.
Mechanism for the Macrostructure Coarse Grain of TB6 Titanium Alloy Die Forging and Its Prediction
The local area of macrostructure of TB6 titanium alloy die forging shows the flaw of coarse grain after deformation and annealing in two-phase region.By means of thermal modeling test,optical microscope(OM),micro-tensile tests and scanning electron microscope(SEM),electron black-scattered diffraction(EBSD),the microstructure characteristics and mechanical properties of"the area of macrostructure coarse grain"and"the area of macrostructure fine grain"are analyzed and compared,the formation mechanism of macrostructure coarse grain is discussed,the process condition criterion of the appearance of the macrostructure coarse grain is put forward and the prediction model is established.The results reveal that the macrostructure coarse grain is mainly distributed in the area of violent metal flow with low deformation temperature and large deformation degree.Compared with fine-grained materials,coarse-grained materials reduce the yield strength,but increase the elongation and tensile strength.After heating in the two-phase zone,the surface deformation temperature of the forging decreases during transportation,which leads to uneven temperature in the surface area.At large deformation rate,the softening degree of surface arc region is quite different,and partial dynamic recrystallization is easy to occur,resulting in dynamic recrystallized grains with large grain boundary angle(β phase).After annealing,the dynamic recrystallized grains merge the static recrystallized grains with small grain boundary angle around through grain boundary migration to form coarse grains.With the deformation temperature(T)decreases and the strain(ε)increases,the macrostructure coarse grains appear more easily when the strain(ε)does not exceed the critical value.The relationship between εf and T is expressed quantitatively;Taking εf as the criterion,the finite element subroutine is established through secondary development,and the visual prediction of macrostructure coarse grain of forging is realized.
TB6 titanium alloymacrostructure coarse grainformation mechanismrecrystallizationvisualisation model
NETL
NSTL
万方数据
