Localized detection of phase transition in tungsten by laser ultrasonics

Abstract

We demonstrated a method for localized, furnace-free detection of the onsets of melting and ablation in polycrystalline tungsten using nanosecond laser ultrasonics. Pulsed laserinduced melting is characterized by a delay in the arrival of the shear wave with increasing laser peak intensity. Pulse-laser induced ablation was characterized by pronounced increase of the amplitude of the signal associated with the arrival of longitudinal acoustic wave. Both phenomena are attributed to a change in character of the ultrasonic source. The described technique suggests a new spatially resolved method for detection of metal-to-melt phase transition in refractory metals.