Abstract
A wide range of microstructures was generated using various thermomechanical processing sequences in Ti-6A1-4V Rotating Electrode Process (REP) powder compacts of low contaminant content. Low cycle fatigue results were found to be superior to those in higher contaminant compacts tested in a previous program. All microstructural groups showed fatigue strengths equivalent to those found in wrought alloy, with the beta-annealed condition being lowest as expected. Alpha + beta work and solution treatment resulted in an excellent fatigue strength of 875 MN/m2 (127 ksi) at 105 cycles; 85 pct of the UTS. In the five conditions tested, the fatigue strength increased with increasing tensile strength, decreasing grain size, and increasing volume fraction of low aspect ratio primary alpha. Most crack initiation sites were observed at the specimen surface. Only alpha + beta worked and solution-treated material exhibited subsurface initiations, none of which was associated with any defect or with a lower fatigue life. Although compacts contained some tungsten particles, in no case were they associated with crack initiation sites, indicating that they were innocuous in the conditions evaluated.
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