Study On Remote Laser-induced Breakdown Spectroscopy Of GH4169 Nickel-based Superalloy

Nickel-based superalloys are widely used in petrochemical,aviation,electric power,shipbuilding and other fields because of their excellent high temperature resistance,corrosion resistance,oxidation resistance and high strength mechanical properties.For this kind of functional material,in order to ensure its performance,the quality of the product must be strictly controlled.At present,the wet chemical analysis methods are often used to determine the composition of nickel-based superalloy.The pretreatment process of wet chemical analysis is complex and lengthy,which is only suitable for laboratory analysis.With the demand of green development,the important role of production process quality control has become increasingly prominent.As a remote and non-contact detection method,Laser-induced Breakdown Spectroscopy(LIBS)has been successfully applied to on-line detection of steel and aluminum.In the paper,based on the self-designed remote LIBS system,the composition analysis method of GH4169 nickel-based superalloy is studied in the laboratory,hoping to provide reference for the application of remote LIBS technology in the on-line analysis of nickel base superalloy.Firstly,the remote focusing characteristics of the LIBS system are analyzed.In this LIBS system,the laser focusing optical path and the plasma optical signal acquisition optical path are coaxial and independently focused.Through automatic focusing,the remote analysis of 1～8 m can be achieved.The results show that the detection range of plasma optical signal increases with the increase of the working distance of the system,which means that the system has lower requirements on the focusing accuracy.Meanwhile,the decrease of power density caused by the increase of the ablation spot size and the decrease of signal acquisition solid angle,make the signal strength decay in Inverse fourth power relationship with the increase of the working distance.Then,the LIBS system was used to analyze Ni,Cr,Mo,Nb,Ti and Al in GH4169 nickel-based superalloy under the optimized parameters of 5 m working distance,80 mJ laser energy,4 Hz laser frequency and 1.8 μs delay time.The goodness of fit of the standard curve of the internal standard method(0.9981～0.9997)is significantly improved compared with the method without internal standard(0.8766～0.9916),and the accuracy and precision are also significantly improved(RE for the method without internal standard is-9.9%～4.6%,RSD is 2.3%～8.7%;RE with internal standard method is-3.9%～0.4%,RSD is 1.4%～6.8%).The RE of the multiple linear regression method is-4.0%～2.6%,and the RSD is 2.9%～7.5%,which is also improved compared to the method without internal standard.For most elements,the internal standard method is better than the multiple linear regression method and the method without internal standard.Therefore,the paper chooses the internal standard method for remote LIBS analysis of GH4169 nickel-based superalloy.Finally,the paper verified the internal standard method.Experiments comparing LIBS internal standard method and XRF method found that although the precision of LIBS analysis is slightly inferior to XRF,the error can be effectively reduced by repeating multiple measurements.Moreover,compared to XRF,LIBS can be used for remote analysis and can detect light-weight elements such as H,Li,Be,and C.The experiment also studied the applicability of this method to other grades of nickel-based alloys.The results show that the accuracy and precision of this method are better for nickel-based alloys with different casting processes but similar compositions.In summary,the application of LIBS technology to remote online analysis of nickel-based superalloys has certain feasibility.