Analysis of microstructural facet fatigue failure in ultra-fine grained powder metallurgy Ti-6Al-4V produced through hydrogen sintering

•HSPT processing produces Ti-6Al-4V with thick GB α in all conditions.•GB α can form a long α grain with a single orientation, acts a super lamella.•Microstructural facets at fatigue failure sites are identified as grain boundary α.•Long effective slip length in GB α limits fatigue life.•Reducing prior β grain size reduces GB α slip length, may improve fatigue life.