TC18合金大型锻棒冲击韧性的横纵向差异研究

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3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化相界面处(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,裂纹容易顺着强化相界面生长至临界尺寸而失稳扩展,从而导致较低的冲击韧性。

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

The difference between the transverse and longitudinal impact toughness of TC18 alloy large-scale forging rods and its microstructural relationships were investigated.Two types of impact samples,i.e.,C-L and C-R,were machined from the head,middle and tail positions of the forging rods for Charpy impact testing.The results show 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 the impact toughness,whilst crack initiation energy of the C-L samples is significantly greater than that of the C-R 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 grain boundaryα-phase)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 primaryα-phase including grain boundaryα-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.