Application of IR Thermography methods to fatigue life prediction of additively manufactured IN625 alloy

In this study, the rapid fatigue assessment of additively manufactured IN625, through the utilization of infrared thermography (IRT), is examined. A comparative analysis is conducted considering both temperature-based (initial rise slope and steady temperature) and energy-based (Q-parameter from cooling curve and Φ parameter) methods. In addition, various fitting strategies reported in literature are implemented. Cyclic stepped tests on a single specimen were carried out for four material conditions resulting from heat treatments: Stress Relief, Annealing, Direct Aging, and Solution+Aging. Across thermal indexes and fitting algorithms, variability was limited. IRT fatigue predictions showed a reasonable, albeit incomplete, correlation with conventional tests. The methods were sensitive to variations as a function of HT, confirming their potential usefulness as screening tools. The estimated fatigue stress limits approximately corresponded to actual lives between 1E6 and 2E6 cycles, while in conventional fatigue tests, conducted up to 2E7 cycles, some failures occurred even at lower stress levels. This may be attributed to the role of defects in AM materials, which may increase the likelihood of fracture initiation and propagation. Consequently, the accuracy of IR thermography when applied to AM may be affected by a slight bias in the presence of defects.