Study Of The Fracture Failure Behavior And Microstructure Evolution Of Tungsten Under Laser Shock Loading

Tungsten is widely used in military defense,aerospace,nuclear industry,and other essential fields because of its high strength,high density,good corrosion resistance,electrical and thermal conductivity,and other excellent physical and mechanical properties.The design of existing tungsten materials is mainly based on its quasi-static performance requirements.Still,tungsten usually faces extreme conditions such as high temperature,high pressure,and high strain rate in the service environment.The dynamic damage behavior,deformation mechanism,and microstructure evolution of pure tungsten under a high strain rate are essential for the design and application of tungsten materials.Therefore,in this paper,the fracture failure behavior of tungsten at high strain rates and its fracture mechanism are systematically studied by using the laser shock loading technique combined with the laser velocimetry system,and the microstructure evolution and deformation mechanism of tungsten at high strain rates are explored.The main conclusions obtained are as follows.（1）The spall strength was positively affected by the strain rates,which increased from 0.97 to 5.86 GPa when the tensile strain rate increased from5.88×10⁵ to 1.68×10⁶ s^-1and the laser energy of sintered tungsten increased from～30 J to～130 J.Correspondingly,the damage rate of materials also increased with the strain rate.（2）The primary fracture mechanism of pure tungsten at a high strain rate is still dominated by intergranular cleavage,accompanied by transgranular cleavage.As the strain rate increases,the percentage of transgranular cleavage mode increases for both sintered and melting tungsten,resulting in a positive sense of the spall strength to strain rate.And transgranular cleavage is caused by parallel screw dislocations emitted from the crack tip lead to.In the cross-section,many through-crystal cracks appear in the sintered tungsten at～130 J,and transgranular cracks appear in the melting tungsten at～30 J,with significant secondary spallation at～130 J.（3）For sintered tungsten,dislocations slip is still the main deformation mechanism at～30 J.Twinning,recrystallization nucleation,and growth begin to occur in sintered tungsten at～130 J,and dislocations slip and twinning deformation compete with each other.For melting tungsten,the dislocations slip is still the main deformation mechanism at～30 J;there are obvious traces of shock melting caused by adiabatic temperature rise at the pores of the melting tungsten,a small number of recrystallization an twinning features exist at the spall plane at～130 J,and secondary spallation dominates at high strain rates.（4）The presence of intergranular pores in the sintered tungsten reflects and weakens the shock waves,making the sintered tungsten less susceptible to secondary spallation while subjecting the vicinity of the pores to continuous shock loading.As a result,many dislocations and dislocations tangle are formed around the holes,and the rapid increase of adiabatic temperature rise and deformation storage energy makes the recrystallization start to nucleate and grow.As the shock wave decays with the sample thickness,the degree of recrystallization decreases from the shock surface to the spall plane.