Wednesday  |  Phipps  |  03:10 PM–03:30 PM

#13285, Fatigue Response of Additively Manufactured Ti6Al4V

Additively manufactured (AM) Ti6Al4V offers a solution to aerospace supply chain shortages for newer and aging aircraft caused by declining manufacturing capabilities in the United States. Implementation of AM-produced components has lagged due to reduced fatigue life of Ti6Al4V AM compared to wrought counterparts. Previous experimental work examining constant stress ratio fatigue behavior has shown laser powder bed fusion Ti6Al4V to exhibit earlier fatigue crack initiation and lower fatigue crack growth rates while wrought Ti6Al4V required orders of magnitude more cycles for crack nucleation followed by faster fatigue crack growth. These observations provide motivation of the current work to investigate near crack tip strain fields to improve understanding of the role that microstructural differences of AM and wrought specimens play in fatigue crack growth. The wrought condition is compared against AM specimens subjected to the following heat treatments which are intended to achieve a bi-modal material structure. The heat treatments used are: 1) heating to 1020° C for 0.5 hours, furnace cooled to 700° C for 2 hours followed by rapid argon cooling and 2) applying a sawtooth heating pattern, 875°C to 975°C for 12 hours, and 3) a constant 925° C heat treatment for 12 hours. After heat treatment, specimen surfaces are polished and a fine speckle pattern is applied. Specimens are subjected to fatigue loading at 10Hz with a constant ΔK=20 MPa√m achieved through load shedding. Periodically, experiments are interrupted and high magnification optical microscope images are captured over a region of interest to gain insight into the evolution of the processes zone in front of the crack tip. The strain evolution maps are superimposed on electron backscatter diffraction grain maps to assess fatigue crack progression through each microstructure. This experiment methodology will assess if AM microstructure fatigue characteristics can be improved through aggressive heat treatments.

Roger Beal   University of Utah
Owen Kingstedt   University of Utah