材料期刊网

研究了两种有代表性的粒子强化(氧化物弥散强化和γ′沉淀强化)镍基高温合金的循环蠕变和应力断裂行为。研究表明,在760℃和一定的循环载荷下,试验频率从0.05至6cycles/h变化时,循环蠕变速率随频率提高而下降,而断裂寿命则一般随频率增加而增加(但对于沉淀强化高温合金,在所采用的最高频率下,断裂寿命反而下降,这是由于频率使平面滑移程度增加的结果)。分析了在加载和卸载期间的塑性和滞弹性应变以及在循环蠕变中的位错结构。结果表明,在循环加载时所观察到的行为及明显的材料强化,并不是循环应变硬化效应所造成的,而是滞弹性应变效应的结果。这种滞弹性应变在加载期间被累积,而在卸载期间则被恢复。在滞弹性机构的基础上,导出了一个循环蠕变或蠕变疲劳交互作用减速因素的现象学模型,这一模型与实验所观察到的行为相符合。

The cyclic creep and stress rupture behaviour of two representative particle strengthcncd alloys, an oxide dispersion strengthened nickel-base alloy and a nickel-base supcralloy strengthened by γ' precipitates, has been studied. It was found that the minimum creep rate decreases with increasing frcquency and the rupture life generally increases with increasing frequency in the load cycled and the frequency range of 0.05-6 cycles/h at 760℃. For the supcraIloy strengthened by γ' precipitates, however, the rupture lives decreased at the highest frequencies used, apparently due to frequency induced increase in degree of planar slip.An analysis was made of the plastic and anelastic strains that occur during the on-load and off-load periods, and of dislocation structures during cyclic creep. The observed behaviour and thc apparent material strengthening during cyclic loading was found not to bc attributable to a cyclic strain hardening effect but rather to the effects of anclastic strain that is accumulated during the on-load period and recovered during the off-load period. Using a phenomenological model based on the anelastic mechanism, a cyclic creep deceleration or creep/fatigue deceleration factor was derived. It shows reasonable agreement with the expcrimentally observed behaviour.