Short Fatigue Crack Initiation and Propagation in Ti-6A1-4V with Short-bar and Lamellar Microstructures

摘要

Long-focus microscopy and scanning electron microscopy (SEM) were used to investigate short fatigue crack initiation and propagation in Ti-6A1-4V alloy with two kinds of microstructures:short-bar and lamellar. Short crack (SC) growth rates in the two microstructures were measured and compared with long crack at three load ratios. For the lamellar microstructure,SC initiation and propagation are strongly affected by slip band and grain boundary, however they exhibit less microstructure-sensitivity for short-bar microstructure. SC propagates with higher da/ dN than long cracks at the same △K in both microstructures, but only in the lamellar microstructure SC can propagate below the long crack threshold △Kth,. Finally crack-microstructure interactions and crack closure level are discussed to explain the anomalous crack growth rates.