Application of laser ultrasonics to monitor microstructure evolution in Inconel 718 superalloy

Abstract

Abstract. Laser ultrasonics for metallurgy is an innovative sensor dedicated to the measurement of microstructure evolution during thermomechanical processing. In this technique, broadband ultrasound pulses are generated and detected with lasers. The properties of the ultrasounds are then related to the characteristics of the microstructure. Ultrasound attenuation is primary originated by the scattering at grain boundaries and its frequency dependence can be related to the grain size. The present work aims to introduce this technology as an exciting tool for metallurgists. As an illustration of its capability, the evolution of the grain size during isothermal annealing from a fine grained structure is in-situ monitored in an Inconel 718 superalloy. Laser ultrasonic measurements are compared with ex-situ metallography observations. Indication of heterogeneous grain growth is observed, correlated to the dissolution of δ-phase particles present in the initial structure. This preliminary study illustrates the potential of this new technique to monitor microstructure evolution in more complex scenarios including recrystallization during simulation of hot forging processes.

In-situ monitoring of phase transformation in Ti-6Al-6V-2Sn using laser ultrasonics

“…For the ultrasonic attenuation determination, the ultrasonic echoes were cut out with Hanning windows of a width of 0.45µs (red boxes), centred over the first two longitudinal echoes, see inlay fig.4 [29]. The other reflections of the signal are due to different propagation modes and this evaluation is restricted to longitudinal echoes only.…”