应变波形对Inconel 625合金低周疲劳性能的影响

在650℃以及拉压对称三角波(TR)、慢拉快压锯齿波(ST)和快拉慢压锯齿波(FT)3种应变波形下对Inconel625合金进行了低周疲劳实验,研究了合金在不同应变波形下的低周疲劳变形与断裂行为。结果表明:3种应变波形加载条件下,合金在0.3%～0.7%的外加总应变幅下均呈现循环硬化,其中在ST下的循环应力幅最高;采用锯齿波形时,由于拉伸蠕变分量和压缩蠕变分量的引入造成合金的疲劳寿命缩短;此外,合金的循环应力和应变之间呈现单斜率线性关系,且其塑性应变幅与弹性应变幅和疲劳寿命之间亦呈线性关系。利用扫描电子显微镜对Inconel625合金在3种加载波形下的低周疲劳断口形貌进行观察,结果表明,Inconel 625合金的疲劳裂纹萌生和扩展均是以穿晶方式进行的。

Effect of Strain Waveform on Low-Cycle Fatigue Properties of Inconel 625 Alloy

The low-cycle fatigue tests for the Inconel 625 alloy were performed at 650°C under three strain waveforms including triangular waveform as well as two sawtooth waveforms with slow-tension followed by fast-compression and fast-tension followed by slow-compression. And the low cycle fatigue deformation and fracture behaviors of the alloy under different strain waveforms were investigated. The experimental results show that the Inconel 625 alloy exhibits the cyclic hardening at the different waveforms and applied total strain amplitudes from 0.3% to 0.7%. When two sawtooth waveforms are adopted, the fatigue life of the alloy will shorten due to the introduction of either tensile or compressive creep strain component, In addition, the relation between the plastic or elastic strain amplitudes and fatigue life as well as between the cyclic stress amplitude and plastic strain amplitude exhibits a single slope linear behavior. The observations on the fatigue fracture surfaces reveal that under three strain waveforms used in this investigation, the fatigue cracks initiate and propagate in a transgranular mode.