Study On Laser Ablation Mechanism Of Al₃BC/Al Composites

With the advantages of concentrated energy and long transmission distance,high strike accuracy and fast response time,strong resistance to electromagnetic interference and high cost-efficiency ratio,laser weapons have attracted Western military powers to carry out research on laser weapons,and have entered the actual combat stage.It can be predicted that laser weapons are likely to become the dominant force to occupy the future battlefield,and even change the mode and pattern of future war.With the increasing investment in laser weapon research by various military powers,we should strengthen the research in the field of laser protection.Based on the current development of high energy laser protection materials and the study of the interaction mechanism between laser and materials,a new laser protection material,Al₃BC/Al composites,is proposed in this paper.Firstly,the laser protection properties of Al₃BC/Al composites with a variety mass fractions were prepared and studied.Then the laser protective coating of Al₃BC/Al composites with 15%Al₃BC content was prepared by HVAF.The phase structure,microstructure and properties of the coating were analyzed.The optimal spraying process parameters were determined by orthogonal test results.Finally,pure Al coating and Al₃BC/Al composites coating were prepared using the optimal parameters determined by orthogonal test.The laser protection effect of Al₃BC/Al composite coating was analyzed with Al coating as the control.Experimental results show that:（1）The reflectance of 15-Al and 25-Al block samples is similar to that of pure Al,and the thermal conductivity is lower than that of pure Al sample.After the ablation,there are different regions in the block sample,which are named as the ablation center area,the heat affected zone and the unaffected zone.The sample with low volume fraction（15-Al,25-Al）has a higher ablative failure threshold,but when a certain limit is broken,the ablative failure is more serious than that of the sample with high volume fraction（50-Al）.By analyzing the phase structure and microstructure of the sample before and after ablation,it is concluded that Al₃BC will react at high temperature and form two new phases,B₄C and Al₄C₃.（2）The main phases of the coating are Al,Al₃BC,a small amount of B₄C and Al₂O₃,and the coating is complete without cracks.The coating showed a typical lamellar structure composed of flat particles,with a maximum porosity of 2.84%and a minimum porosity of0.44%.The maximum hardness of the coating section is 115.9 HV,and the minimum is 92.36HV,which is higher than that of the substrate.The minimum surface roughness of the coating is 5.964μm,and the maximum surface roughness is 30.511μm.The highest laser reflectance of the coating is 36.85%,which is lower than that of the bulk material,but still satisfies the characteristics of high reflectance.（3）The optimal parameters were determined by orthogonal test:spraying distance of 250mm,transverse movement speed of 1000 mm/s,powder feeding capacity of 6 r/min.The pure Al and Al₃BC/Al composites coatings were prepared with these parameters,and the ablation tests were carried out.At the laser energy density of 1500 W/cm²,the Al coating in the ablation center has been burned through for 5 s,and the Al₃BC/Al composites coating has been burned through for 10 s.The oxidation range of Al₃BC/Al composites coating is still smaller than that of Al coating after the ablation of the two coatings for 15 s.The mass ablation rate of the composite coating after laser irradiation is small,which is only 0.037 g/s at 15 s ablation time,which is 59.78%lower than that of Al coating.Al₃BC/Al composite coating has better laser ablation resistance.