The Study on the Physical Mechanism of Asymmetric Thermal History Effects in LIBS Response of Nickel Alloys

Abstract

Laser-induced breakdown spectroscopy (LIBS) holds significant potential for online monitoring in material thermal processing due to its rapid and in-situ analysis capabilities. However, drastic temperature changes during additive manufacturing and heat treatment can significantly affect signal stability and analysis reliability. Although existing studies have addressed temperature effects, the underlying mechanisms, especially the irreversible behaviors related to solid-state phase transitions, remain unclear. This study focuses on a nickel-based additive manufacturing alloy and systematically investigates the evolution of LIBS performance parameters (spectral intensity, plasma parameters, signal-to-noise ratio(SNR), and relative standard deviation(RSD) during the complete temperature rise and fall process. The results indicate that the LIBS response exhibits significant irreversibility and thermal history effects: during the temperature rise phase, various parameters change asynchronously, and an anomalous phenomenon occurs where the signal-to-noise ratio peaks and the relative standard deviation reaches its maximum at the phase transition point of 850 ℃; during the temperature fall phase, the parameters show non-monotonic changes, and all indicators synchronously reach their optimal values at 300 ℃. Based on surface layer evolution and phase transition dynamics, a three-stage physical model is established, revealing that supercooling and delayed transformation during solid-state phase transitions and cooling processes are the key mechanisms driving the evolution of LIBS signals. This study demonstrates that LIBS can serve as a highly sensitive in-situ probe for monitoring phase transition dynamics and provides new insights into understanding the thermal matrix effects of LIBS.