铁基粉末冶金合金的高周和超高周弯曲疲劳行为

High and Ultra-high Cycle Bending Fatigue Behaviors of Iron-Based Powder Metallurgy Alloy

通过在基粉中添加430L不锈钢粉的形式引入铬元素,采用粉末冶金工艺制备Fe-1.65Ni-1.4Cu-1Cr-0.5Mo-0.6C铁基合金,并进行了硬化和回火热处理,研究了该合金在105～108循环周次下的弯曲疲劳行为。结果表明:试验合金的高周和超高周弯曲疲劳曲线是连续下降的,没有出现疲劳平台;疲劳断口的裂纹为多源萌生,在高应力幅作用下裂纹在试验合金表面和次表面的缺陷处萌生,在低应力幅作用下裂纹主要在试验合金内部缺陷处萌生;裂纹扩展区有明显的疲劳辉纹特征,与低应力幅作用下的相比,在高应力幅作用下的疲劳辉纹间距较大,裂纹扩展速率较快;瞬断区主要由解理面和小韧窝组成,与高应力幅作用下的相比,在低应力幅作用下的解理面增多,韧窝数量减少,脆性断裂的特征更加明显。

The chromium element was introduced by adding 430 Lstainless steel powder to base powder.Fe-1.65 Ni-1.4 Cu-1 Cr-0.5 Mo-0.6 Ciron-based alloy was prepared by powder metallurgy,and then was treated by hardening and tempering heat treatment.The bending fatigue behaviors of the alloy under 105-108 cycles were studied.The results show that the high and ultra-high cycle bending fatigue curve of the tested alloy exhibited a continually falling trend,and there was no fatigue platform.The cracks on fatigue fracture initiated from multiple sources.The cracks initiated at the defects in surface and sub-surface of the tested alloy under high stress amplitude,and initiated at inner faults of the tested steel under low stress amplitude.Crack propagation region had an obvious fatigue striation feature.Under high stress amplitude,the striation space in crack propagation region was relatively big,indicating that the crack growth rate was high,compared with that under low stress amplitude.The rapid fracture region was composed of cleavage planes and small dimples.There were more cleavage planes and fewer dimples in rapid fracture region under low stress amplitude than those under high stress amplitude,indicating that the brittle fracture was more obvious.