Simulation of materials erosion and lifetime under intense radiation heat sources

Ghadeer H Al-Malkawi, Purdue University

Abstract

The purpose of the present study was to investigate the energy transport through target materials irradiated by ultrashort laser pulses, which is characterized by the extremely high power density. The heat transfer and the ablation of the irradiated target were described numerically by the two-dimensional two-temperature model with temperature and phase dependent thermophysical properties of the electron and the lattice subsystems such as the heat capacity, the thermal conductivity, and the density. Based on the characteristics of the ultrashort laser heating two ablation mechanisms were used to estimate the ablation depth and the corresponding ablated mass and volume: the normal evaporation and phase explosion mechanisms. The impact of the total energy, spot size, reflectivity, and the electron-phonon coupling factor on the thermal evolution and the crater shape and size was investigated. Different models of temperature dependent electron-phonon coupling and electron heat capacity based on the calculation of the electronic structure of the density of state and other models based on the electron-electron and electron-lattice collision rate of copper irradiated by femtosecond laser pulse were used to investigate the temporal and spatial thermal evolution and the corresponding ablation as well. Due to the unique properties of the irradiation by ultrashort laser pulse with minimum heat-affected zone in target materials which makes it a promise choice for many applications, the coating was chosen as one of these applications by studying the double-layer irradiation by femtosecond laser where the first layer was the gold and the substrates were copper and aluminum. The impact of the thermal properties of the substrate on the thermal response of the first layer was investigated by analyzing the temporal and spatial electron and lattice temperature. Moreover some experiments were performed in order to validate the simulation results. In these experiments a set of copper target were prepared and irradiated by several energies of femtosecond laser pulses. The effect of crater depth on the number of pulses was studied by shooting various number of laser pulses at different spots and measuring the produced crater depths. The post irradiated samples were evaluated quantitatively and qualitatively by using the Atomic Force Microscope and the Scanning Electron Microscope respectively. Finally, a comparison between the experimental results and the simulation results was presented.

Degree

Ph.D.

Advisors

Hassanein, Purdue University.

Subject Area

Landscape architecture|Nuclear engineering

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