扭转预变形对定向凝固DZ4合金低周疲劳寿命的影响

Influence of Torsional Pre-deformation on the Low Cycle Fatigue Life of Directionally Solidified Superalloy DZ4

对定向凝固DZ4合金进行扭转预变形和热处理后的高温低周疲劳寿命与断裂行为进行测试与研究,分析不同的扭转变形程度、变形速率等对低周疲劳寿命和再结晶的影响,研究沿晶特征区的形成机制。结果表明,定向凝固DZ4合金在扭转预变形和热处理后其低周疲劳寿命急剧下降,分析发现与塑性变形区产生的再结晶组织有关。再结晶区与基体变形不协调导致在再结晶与基体界面处出现损伤和裂纹,裂纹沿再结晶晶界扩展形成沿晶特征区,使高温低周疲劳寿命下降,且疲劳寿命随着再结晶深度的增大而急剧降低。扭转预变形程度较小时,低周疲劳断口上的沿晶特征区的深度与断面沿再结晶区扩展的深度一致;扭转预变形程度较大时,沿晶特征区的深度相对较小。另外,应变速率增大,加剧了不协调变形,再结晶具有局部化倾向,且再结晶程度增加,使高温低周疲劳寿命下降更严重。

The low cycle fatigue （LCF） life and fracture behavior of directionally solidified superalloy DZ4 after torsional pre-deformation and heat treatment was tested and studied. The influence of different pre-deformation extents and rates on LCF life and recrystallization was analyzed. The formation mechanism of intergranular area was investigated. The results show that LCF life of directionally solidified superalloy DZ4 decreases rapidly after torsional pre-deformation and heat treatment, which is related to recrystallization texture in plastically deforming area. Cracks and damages are found on the interface of the recrystallization and the matrix caused by their inharmonious deformation, and the cracks propagate along the recrystallization boundary to form intergranular area, resulting in the decrease of LCF life. Meanwhile the life is decreased sharply with the increase of the recrystallization depth. The depth of intergranular area is in accord with the recrystallization depth when the pre-deformation is small; while when the pre-deformation is larger, the depth of intergranular area is relatively smaller. Besides, the increase of strain rate aggravates inharmonious deformation, and makes recrystaUization localize, which cause more serious decrease of LCF.