I agree that the labeling is odd in the photo. I tend to believe the actual slow, but ever progressing fracture surface is in the forefront of the photo, out of focus. The "clean" fracture area does look brittle to me, the final break, so to speak. IMO, this part is a nickel-base alloy, an Inconel or Hastalloy type material. Normally a part like this would be investment cast to a near net shape and subsequently machined as required to final desired tolerances. I am sure vibration played a big role in this component failure besides whatever the configuration and how it got to be that way. I am sure oil was slowly seeping from this fracture into the cavity and one wonders how long and how much was there before the final event took place.
It has been silent as to the progress of the failure investigation, no updates from the ASTB since December 23. It makes one wonder about progress being made in going through the total failure progression scenario, identifying the true root cause or causes.