First-principles electronic transport properties of Ti and Ti-6Al-4V for modeling ultrashort-pulse laser ablation

Abstract

Predictive modeling of ultrashort-pulse laser ablation requires temperature-dependent material parameters derived from the electronic structure, namely the electronic thermal conductivity, electron-phonon coupling, and heat capacity. These parameters are well documented for elemental metals but remain sparsely documented for alloys, apart from application-relevant exceptions such as stainless steels. The technologically important titanium alloy Ti-6Al-4V is a prominent example, which is still modeled using elemental-titanium values. We compute the electronic transport of hcp Ti and Ti-6Al-4V from first principles, using the Kubo-Greenwood formalism within the Korringa-Kohn-Rostoker coherent-potential-approximation framework, treating chemical and thermal disorder on equal footing. For elemental Ti, the calculated electrical resistivity agrees with independent electron-phonon calculations and experiment and also reproduces the high-temperature saturation near the Mott-Ioffe-Regel limit. Under electron-phonon nonequilibrium, the electronic thermal conductivity saturates and then decreases with electronic temperature, reaching a maximum of about 2.97 k W m − 1 K − 1 in Ti but only 0.47 k W m − 1 K − 1 in Ti-6Al-4V, a factor of 6.4 lower. In two-temperature-model simulations the alloy and elemental parameter sets yield peak lattice temperatures differing by only about 1.4%, because reduced electron-phonon coupling and thermal conductivity offset each other, consistent with reported experimental ablation thresholds that differ by about 3%, well within their measurement uncertainties. This compensation is strongest for subpicosecond pulses and weakens across the 1 to 10 ps crossover toward longer-pulse behavior. Replacing the first-principles thermal conductivity with the low-temperature Drude limit shifts the peak lattice temperature by up to 19%, showing that the functional form of the transport model is even more important than the elemental versus alloy distinction for predictive accuracy.