Fatigue Damage Detection in SLM-Formed Alloy Layers Based on Nonlinear Ultrasonic Technology

Abstract

Utilizing the ultrasonic nonlinear coefficient, the fatigue damage state of specimens can be accurately determined. This study rapidly assessed the fatigue damage of selective laser melting(SLM) GH4169 nickel-based alloy layers through higher harmonic detection techniques. Results showed that obvious second harmonics were detected when the frequency increased to 10MPa, and the second harmonics formed an amplitude lower than the fundamental wave. Compared with the initial specimen, the amplitude signal was more obvious in the specimen after 20,000 fatigue tests. There were equiaxed crystals, fusion lines, and columnar crystals in the samples, and many columnar crystals were arranged in regular directions. After the fatigue test, there were many fatigue cracks in the substrate, and the second harmonic amplitude also increased significantly. With the extension of the fatigue period, the β/β0 ratio increased. Different from test point 1, the ultrasonic nonlinear coefficients at point 2 and point 3 only showed a small increase trend relative to the fatigue cycle number. The research has a good theoretical support value for improving the fatigue damage detection accuracy of laser melting samples.

Keywords

• nonlinear ultrasonic| selective laser melting| fatigue damage| fatigue cycle| second harmonic