近α型钛合金长时高温暴露过程中显微组织演变及其对热稳定性的影响

研究了近α型钛合金TG6经α+β两相区热加工的盘锻件在600℃长时暴露过程中的显微组织演变及其对热稳定性的影响。结果表明:经600℃/100h和600℃/300h长时高温暴露后,TG6钛合金的室温拉伸强度略有提高,其增幅在5%左右,而其拉伸塑性显著降低,塑性保持率小于50%,拉伸断口趋于平直化,且存在梯田状台阶和二次裂纹等,表现为显著的解理断裂特征。在600℃高温长时暴露过程中,TG6钛合金中的显微组织变化主要有在基体组织中的共格有序α2相析出及硅化物析出。随着高温暴露时间的延长,TG6钛合金的显微组织逐渐趋于稳定,拉伸性能的变化也相应趋缓。α2相析出促进了拉伸变形时位错滑移的平面化及变形不均匀,是热稳定性下降的主要原因;而硅化物析出协同促进位错滑移集中化,是热稳定性下降的次要因素。

Microstructural Evolution of Near-α Titanium Alloy during Long-Term High Temperature Exposure and its Influence on Thermal Stability

Microstructural evolution of a near-α titanium alloy TG6 disc forging processed in α+β phase field during long-term high temperature exposure and its influence on the thermal stability were studied. The results show that the room temperature tensile strength increased about 5% and the ductility reduced remarkably lower than 50% after 600℃/100h or 300h exposed for TG6 titanium alloy, and the fracture surface has a tendency of flat, terrace-like steps and secondary crack which showed an obvious cleavage fracture characteristic. During long-term exposure under 600℃ environment, the microstructural change is precipitation of the coherent ordered α_2 phase and silicide. The microstructure and the tensile properties tend to be stable with increasing the exposure time. The precipitation of α_2 phase is the main reason for the great loss of ductility during high temperature long-term exposure because the precipitated α_2 may promote planar slip and inhomogeneous deformation while tensile deformation. The precipitation of silicide may promote the intensity of slip and is the minor reason for the ductility loss.