Investigation of the fatigue damage mechanism of Inconel 617 at elevated temperatures obtained by in situ SEM fatigue tests

In the present study, fatigue damage evolution of Inconel 617 at 600 degrees C and 700 degrees C was investigated by using an in situ scanning electron microscope (SEM) fatigue test. The fatigue crack initiation and propagation processes were directly observed and recorded online. Fractography and microstructure analyses were performed to further reveal the mechanism of high-temperature failure. Experimental results showed that Inconel 617 was not sensitive to an artificial notch even if the curvature reached approximately a hundred microns, and it was more vulnerable to intergranular fracture. This alloy showed multiple crack initiation and propagation behavior at high temperatures. Multiple crack initiation sites did not occur in the same planes, and the number of crack initiation sites increased with increasing environmental temperature. Intergranular cracking behavior was observed in the near surface region, and transgranular crack initiation and propagation were mainly observed in the interior. Coarsening and discrete M23C6-type carbides formed at grain boundaries were the main factors responsible for intergranular cracking. The twin boundary (TB) was directly observed as the crack initiation site, and it retarded crack propagation along the TB and changed the crack propagation mode.

Automated summary

Experimental results indicate that Inconel 617 is not sensitive to artificial notches, even with a curvature of approximately a hundred microns, and is more prone to intergranular fracture at high temperatures. Multiple crack initiation and propagation behaviors were observed, with increasing temperatures leading to more crack initiation sites. Intergranular cracking was found to be caused by the formation of coarsening and discrete M23C6-type carbides at grain boundaries, while twin boundary (TB) was identified as a crack initiation site that impeded crack propagation.