Nominal vs Local Shot-Peening Effects on Fatigue Lifetime in Ti-6Al-2Sn-4Zr-6Mo at Elevated Temperature
AIR FORCE RESEARCH LAB WRIGHT-PATTERSON AFB OH MATERIALS AND MANUFACTURING DIRECTORATE
Pagination or Media Count:
A study is presented of elevated temperature fatigue lifetime variability in the shot-peened condition of the titanium alloy, Ti-6Al-2Sn-4Zr-6Mo. It is shown that failures separate into two distributions 1 governed by the nominal residual stress RS profile, promoting subsurface crack initiation and longer lifetimes and 2 life-limiting behavior that is controlled by localized material-shot-peening interaction. In the residual-stress-free condition, failures occurred predominantly by surface crack initiation at the microstructural scale, by crystallographic facet formation in one or a few a particles or colonies. This mechanism was mitigated under the nominal shot-peening SP RS profile, producing failures initiating from the subsurface region by crystallographic faceting spread over a significantly larger area than in the absence of RS. Although the microstructure-scale surface-crack initiation was suppressed, the life-limiting failures under SP continued to occur by surface initiation. but through an apparently larger crack initiation size by formation of a flat, noncrystallographic fracture.
- Fabrication Metallurgy