Kinetics and Dynamics of Phase Transformations in Metals Under Action of Ultra-Short High-Power Laser Pulses

Abstract

Additional information is available at the end of the chapter http://dx.doi.org/10.5772/50731 IntroductionAction of super-power and ultra-short laser pulses on highly absorbing condensed media is investigated in the past two decades [1] - [5]. The urgency of this problem is primarily determined by a variety of practical applications of pulsed laser irradiation. In a short period of time scientists have mastered such operations as ablation of elemental materials by femtosecond lasers (100 fs) [6], femtosecond nanostructuring [7], generation of metallic nanoparticles and nanostructures by laser ablation of massive targets by 40 fs and 2ps pulses [8], etc.The use of super-power G~10 12 ÷10 15 W/cm 2 and ultra-short τL≈10 -12 ÷10 -15 s laser pulses for dimensional processing of materials, such as cutting of various materials by picofemtosecond laser pulses [9], micro-drilling by a femtosecond laser [10 ], surface etching of metals (Al, Cu, Mo, Ni) and semiconductors (Si) [11], is accompanied by realization of unique physical conditions. In particular, the duration of action becomes comparable with the characteristic times of thermalization and phase transitions in matter. This leads to the need to address complex fundamental problems, including the heating of the material and the kinetics of phase transitions in a strong deviation from local thermodynamic equilibrium.It should be noted that the majority of laser technologies is associated with the beginning of phase transformations in the material. In particular, the action of pico -femtosecond laser pulses of high intensity on solid targets is one of the ways to create individual particles with unique characteristics, or to form their streams, consisting of a cluster, liquid or solid fragments of the target. The formation of the particle flux in the pulsed laser ablation is observed for a wide range of materials: metals, semiconductors and insulators. The Laser Pulses -Theory, Technology, and Applications 220 possibility of usage of laser ablation products in practical applications was the impetus for a number of experimental and theoretical studies [12], aimed at studying the conditions and mechanisms of formation of particles of nano -and micro-sizes during the laser exposure.The accumulation of knowledge of the experimental nature in the first place in this dynamic field leads not only to the variety of practical applications of pulsed laser action, but also to a number of issues of independent physical interest.T h e m a i n f e a t u r e s o f u l t r a s h o r t a c t i o n o n m e t a l s a r e a s s o c i a t e d w i t h h i g h s p e e d a n d voluminous nature of the energy release of the laser pulse. The high rate of heating of a condensed medium is associated with rapid phase transformations of matter, characterized by the transfer of superheated phase boundaries of high-power fluxes of mass and energy. Overheated metastable states at the interface are characterized by temperatures, whose values can be hundreds of degrees higher than the equilibrium val...

3D Model of Heat Flow during Diffusional Phase Transformations

“…Additionally, tsteps = 70, a = 1, and k q = 20 were assumed. The results obtained can be directly related to the data presented in the literature [ 38 ].…”

Equations of state of the molten and crystalline phases of aluminum with deep entry into metastable regions

“…In the problem of mathematical modeling of metal ablation by ultrashort high-power laser pulses using continuum hydrodynamic models, the choice of the equation of state plays an important role. The difficulties associated with the choice and construction of EOS are determined by the specifics of the action of femtosecond laser radiation on solid targets [31,32]. The hydrodynamic models used are developed on the basis of fundamental knowledge of the physics of nonequilibrium processes, which allows them to most fully cover the basic mechanisms of ablation.…”

The approximate kinetic analysis of strong condensation

“…and z c u are the molecular and hydrodynamic velocities 1 , 2 v kT m = is the molecular thermal velocity corresponding to local temperature T. 1 Strictly speaking, the concept of hydrodynamic velocity cannot be applied to the Knudsen layer, so parameter  u can be described as a second (along with ε) ellipsoid parameter. According to (21), the boundary of Knudsen layer demonstrates 1…”

“…This kind of problems arise is study of many processes. When we apply laser methods for material treatment, it is crucial to know the laws of evaporation process (thermal laser ablation from the target surface) and condensation process (for expanding vapor cloud interacting with the target) [1]. The power industry faces the risks of accidental situations caused by rapid contact between volumes of cold liquid and hot vapor.…”