表面再结晶层对DZ4定向凝固合金低周疲劳性能影响

Effect of Recrystallization on Low-Cycle Fatigue Behavior of DZ4 Directionally-Solidified Superalloy

针对DZ4定向凝固合金表面再结晶层对材料性能的影响进行了低周疲劳实验研究,并通过岛津SEM伺服疲劳试验机进行表面裂纹实时观察跟踪。研究结果表明,表面再结晶层的存在对材料性能明显产生负面作用,低周疲劳寿命大大降低。不同喷丸强度试件在相同的高温退火条件下形成的再结晶具有不同的再结晶形态,高喷丸强度再结晶更加完全,晶界清晰平直,晶粒有长大的趋势。表层再结晶形态也对疲劳寿命的降低程度以及疲劳微裂纹萌生寿命和裂纹密度有较大的影响。较高喷丸强度形成的再结晶层的试件疲劳寿命降低较少,表面微裂纹萌生较晚,裂纹密度也很低。低喷丸强度试件表面微裂纹大量萌生,密度非常高。再结晶层的晶界开裂是导致表面微裂纹大量萌生的根源,从而导致疲劳寿命大幅度降低。

Low cycle fatigue failure was investigated on DZ4 directionally-solidified nickel-base superalloy at room temperature. Real-time SEM surface observation was employed. Experiment result reveals that its surface recrystallization layer strongly influences the material performance. All specimens were prepared under condition of shot peening and high temperature annealing, different shot peening pressure specimens have different recrystallization state. High shot penning pressure specimens have clear and straight grain boundaries and the grain size appears to be larger. Recrystallization state seems not only affect the fatigue life, but also the crack initiation pattern and crack initiation life. High shot peening pressure specimens have higher fatigue life comparing to low shot peening pressure specimens, although it is almost half lower as the virgin one. have much lower fatigue life, and SEM Real-time observation reveals that channeling crack initiated at the early stage of fatigue life. High shot peening pressure specimens have higher fatigue life comparing to low shot peening pressure specimens, although it＇ s almost half lower as the virgin one, and the crack density is also much smaller. Crack initiation life is much longer than those of low shot peening pressure. Low shot peening pressure specimens seems not fully recrystallized,Since the grain boundaries are much fragile which is responsible for high density microcrack initiation, and finally leads to the failure.