Research On Nanosecond Laser Ablation Characteristics And Microstructure Detection Of TC4 Titanium Alloy Based On Laser Ultrasound

In order to understand the morphology of the ablation pit and the mechanism of its generation,as well as the characteristics of the two-phase composition of the TC4 titanium alloy by the attenuation characteristics of the laser ultrasonic echo.In this paper,a method based on laser ultrasound is used to study the physical process of laser point source excitation in TC4 titanium al oy.In this thesis,TC 4 titanium alloy is firstly subjected to laser ablation at different temperatures and with different pulse times.The Hi RO X K H-8700 microscope is used to obtain the ablation pit depth,morphology and other information,combined with the existing laser ablation process model to analyze the effects of different parameters on ablation.The relationship between ablation pit,diameter and different pulsed laser parameters is established,and a material removal coeffic ient is proposed to characterize the phase explosion process during ablation.The results show that the number of pulses does not affect the process of phase explosion and plasma shielding in laser ablation;Increasing ambient temperature will reduce the ablation depth and material removal coefficient,and the ambient temperature will enhance the effect of plasma shielding.Increasing laser energy will significa ntly affect the pit morphology of the material.After formulating different heat treatment processes for TC4 titanium alloy samples,different heat treatment structures were obtained.Then TC 4 titanium alloy was detected by laser-excited ultrasonic method.Optical microscopy and electron scanning microscopy(SEM)were used to obtain material structure information,and ultrasonic echo attenuation information was obtained through signa l processing,and the relationship between the titanium alloy microstructure and ultrasonic attenuation was established.Using the obtained important parameter of acoustic attenuation to characterize the phase and ? phase ratios.The results show that the ? phase in TC4 titanium alloy has a significant effect on the ultrasonic attenuation compared with?.Ultrasonic time-domain attenuation has better characterization ability for TC4 titanium alloy samples under air c ooling,and ultrasonic frequency-domain attenuation has better characterization effect for water-cooled samples.