Laser Method for Thermal Diffusivity and Near-Infrared Absorptivity Measurements of a 310S Austenitic Stainless-Steel Block

This study develops and critically assesses a modified flash-laser method for estimating, in a single arrangement, the effective thermal diffusivity and the effective near-infrared laser absorptivity of a bulk (8-mm-thick) 310S austenitic stainless steel block. Samples were irradiated with a defocused, continuous-wave ytterbium fiber laser, while thermocouples monitored the rear-face temperature response. Thermal diffusivity was estimated by fitting the normalized transient temperature curves as a function of time, whereas absorptivity was calculated using a calorimetric approach based on the measured temperature rise and the delivered laser energy. The mean thermal diffusivity obtained from nine measurements was α = (2.6 ± 0.1) × 10−6 m2/s, with acceptable fitting quality and moderate replicate scatter. This value is approximately 25% lower than handbook values for austenitic stainless steels. Three-dimensional simulations show that beam non-uniformity, heat losses, and the finite response time of the contact thermocouple bias the one-dimensional estimate by a comparable amount; the diffusivity is therefore reported as an effective, configuration-specific value. The mean effective absorptivity at 1070 nm was A = 0.30 ± 0.04 (mean ± standard deviation; expanded uncertainty of a single determination ±0.05, dominated by the manually controlled irradiation time), with improved repeatability at fixed delivered energy. This value agrees well with reported calorimetric absorptivities for metallic alloys irradiated with near-infrared lasers. The results apply to ground surfaces near room temperature (rear-face temperatures below 60 °C), and the analysis identifies the improvements needed for the method to deliver intrinsic property values.