TC18大型锻棒冲击韧性的横纵向差异研究

Study on the difference of the transverse and longitudinalimpact toughness of TC18 large-scale forging rods

摘要:

本文针对TC18合金大型锻棒冲击韧性的横纵向差异及其内在原因进行了系统研究。夏比冲击实验显示,锻棒头部、中部和尾部三处C-L试样的冲击韧性均高于C-R试样。示波冲击实验发现,抵抗裂纹萌生的能力是决定合金冲击韧性的关键因素,C-L试样的裂纹萌生功明显大于C-R试样。断裂形貌分析表明,裂纹以微孔聚集方式萌生,主要起源于试样缺口附近的强硬相界面处(如晶界α相)。C-L样品中微观组织的拉长方向和开裂方向平行,但和微孔萌生后聚集生长的方向垂直,裂纹不易生长至临界尺寸进行纵深扩展,因而消耗的裂纹萌生功较高,表现出较好的冲击韧性；相反,C-R样品的初生α相(包括晶界α相)和裂纹萌生的方向相同,裂纹容易顺着强硬相界面直接生长至临界尺寸而失稳扩展,从而导致较低的冲击韧性。

Abstract:

The difference of the transverse and longitudinal impact toughness of TC18 large-scale forging rods and its microstructural relationships have been systematically investigated in this study. Two types of impact samples, i.e., the C-L ones and the C-R ones, were machined from the head, middle and tail positions of the forging rods for Charpy impact testing. It is found that the impact toughness of the C-L samples is always higher than that of the C-R samples. The instrumented impact test further reveals that the ability to resist crack initiation is a key factor affecting impact toughness, whilst crack initiation energy of the C-L samples is significantly greater than that of the CR samples. Meanwhile, impact fracture observation manifests that cracks initiate in the form of micro-void coalescence, and mainly originate from the strong-hard phase (such as the α-phase of the grain boundary) near the notch of the samples. For the C-L samples, the elongated direction of the forging microstructure is parallel to the fracture direction, while it is perpendicular to the propagation direction after the micro-void initiation. The crack is thus difficult to grow to the critical size for unstable propagation, which results in the high consumed energy for crack initiation; for the C-R siblings, however, the elongated direction of the primary α-phase including grain boundary α-phase is parallel to the direction of crack initiation, and the cracks easily grow directly to the critical size along the strong-hard phase for unstable propagation, which causes a lower impact toughness in the samples.