PSI - Issue 19

Lloyd Hackel et al. / Procedia Structural Integrity 19 (2019) 452–462 Valentin LOURY--MALHERBE/ Structural Integrity Procedia 00 (2019) 000–000

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with one more sequence of annealing plus laser peening and represented this as Process A ′ and treated additional samples with yet one more sequence represented as Process A ″” . As exposure times grow longer systematic drop off in performance was observed. However, it is significant that compared to the fatigue life of the AM material after 50 hours exposure to 600 ° C (57,925 cycles), the Process A ″ samples exposed for 350 hours lasted for 391,037 cycles, that is 670% improvement. We are investigating if the improvement continues with further iterations.

Figure 7. Fatigue test results for AM In718 samples treated with increasing iterations of LP+TME retained best performance following 50 hours exposure in air oven to 600oC. Samples were tested at 683 MPa loading, 86% of yield stress. Sample with LP(A”) exposed for 350 hours is 2.3 times better than AM with no exposure and 5 times better than AM sample with 50 hours exposure. Process A′ has one more sequence of annealing plus laser peening compared to Process A (Peen/Anneal/Peen/Anneal/Peen) and Process A″ has one more sequence compared to Process A.

In addition to fatigue testing, hardness measurements were made of peened and unpeened areas of the AM samples with the surprising result that the LP+TME samples show a significant increase in hardness of HRC 32-41 for a treated sample vs 14-16 for the unpeened. An increase in hardness due to microstructure changes would also increase yield strength is investigating and would expect to correlate with increased fatigue strength. This is being investigated in more detail.