Study On Spallation Of Surface Layer Of Metal Materials Under Femtosecond Laser Loading

Femtosecond laser is used in various processing fields and scientific research due to its characteristics of ultra-short pulse,ultra-high energy density and super impact pressure.Nickel-titanium shape memory alloy is widely used in medical,aerospace and deep sea industries due to its unique properties.The interaction process between femtosecond laser and Nitinol alloy is very complicated.In this paper,the damage layer cracks on the surface of Nitinol alloy under femtosecond laser loading are studied,and the influence of high temperature and high pressure environment on the layer cracks and deformation of Nitinol alloy is deeply discussed.The evolution process of layer crack damage is discussed from the perspective of thermodynamics,and the process of femtosecond laser loading of Nitinol alloy with different thickness is simulated by using the method of experiment and numerical simulation.The crack behavior of Nitinol alloy under femtosecond laser loading was studied.The research results obtained in this paper can provide data and experience accumulation for the study of Nitinol alloy microstructure crack under femtosecond laser loading,and can also provide data and method reference for Nitinol alloy metal in aviation military field and its industrial processing.In this paper,the process of femtosecond laser impinging on nickel-titanium surface is simulated by the method of two-temperature equation and molecular dynamics.Mainly done the following aspects of work:(1)various theoretical models describing the interaction between ultrafafer laser and material are summarized,and the inducement of the layer cracking phenomenon on the target surface under laser shock is briefly summarized.The double temperature model,potential function and the research method and theory of molecular dynamics simulation are explained in detail.(2)the s.i.nisimov classic two-temperature equation was used to explore the micro-thermal effect system of shape memory alloy under femtosecond laser loading,and the micro-thermal effect properties of shape memory metal NiTi alloy were studied from the aspects of pulse width condition,energy density and equilibrium temperature of electronic lattice system by using the finite difference method.The electron-lattice equilibrium temperature pairs obtained by treating the ion and electron temperature in the material respectively provide a better loading temperature for the molecular dynamics simulation.(3)the use of TTM obtained by electronic-lattice equilibrium temperature as temperature input,potential function,with Niti alloy by femtosecond laser under the load of Niti alloy of molecular dynamics simulation and experiment,analyzes the micro cavity nucleation under the phenomenon such as growth,experiment the macro spallation experiment compared with the past,the study of alloy surface crack mechanism analysis has a good guiding role.