Microstructural effects on the rotating bending fatigue behavior of Ti–6Al–4V produced via laser powder bed fusion with novel heat treatments

• Published in: International journal of fatigue 2024-08, Vol.185, p.108362, Article 108362
• Main Authors: Derimow, Nicholas, Benzing, Jake T., Newton, David, Beamer, Chad, Lu, Ping, DelRio, Frank W., Moser, Newell, Kafka, Orion L., Fishel, Ryan, Koepke, Lucas, Hadley, Chris, Hrabe, Nik
• Format: Article
• Language: English
• Subjects: Additive manufacturing; Heat treatment; Laser powder bed fusion; Rotating bending fatigue; Ti–6Al–4V
• ISSN: 0142-1123
• DOI: 10.1016/j.ijfatigue.2024.108362

The rotating bending fatigue (RBF) behavior (fully reversed, R = −1) of additively manufactured (AM) Ti–6Al–4V alloy produced via laser powder bed fusion (PBF-L) was investigated with respect to different microstructures achieved through novel heat treatments. The investigation herein seeks to elucidate the effect of microstructure by controlling variables that can affect fatigue behavior in Ti–6Al–4V, such as chemistry, porosity, and surface roughness. In order to control these variables, different hot isostatic pressing (HIP) treatments at 800 °C, 920 °C, and 1050 °C with a 920 °C temper were applied to three sets of Ti–6Al–4V cylinders that originated from the same PBF-L build, such that there were 30 tests per condition. After HIP treatment, the specimens were machined and tested. The highest runout stress was achieved after sub-β transus HIP at 800 °C for 2 h at 200 MPa of pressure. A significant drop in fatigue strength was attributed to large prior-β grains and grain boundary α resulting from super-β transus HIP treated specimens. For the sub-β transus HIP specimens, differences in fatigue strength were attributed to α lath thickness, relative dislocation density, and dislocation boundary strengthening. •HIP treatments with cooling rates of 100 °C/min resulted in high fatigue strength.•The sub-β transus HIP suppressed the deleterious continuous grain boundary α.•The sub-β transus HIP treatments retained the as-built, small prior-β grain size.•All HIP conditions are comparable in fatigue strength with wrought Ti–6Al–4V.