| Metal additive manufacturing is an important branch in the field of additive manufacturing.Its preparation process can be divided into the following three steps:(1)The expected samples are modeled in 3D,and the model is divided into many layers with sample information along the deposition direction.(2)Layer-by-layer digital information is converted into sample composition information through program design and digital control.(3)Samples are manufactured layer by layer and piled up from bottom to top,and finally the sample is prepared.This technology has many advantages,such as high material utilization,needlessness of mould forming,high processing accuracy,high speed and high degree of freedom of preparation.Especially in metal sample composition design,it has incomparable advantages compared with traditional process.However,the preparation method is not yet mature,and further research is needed in the aspects of manufacturing mechanism,procedure setting and technological parameter.Cracks,spheroidization,shrinkage and other defects often exist in the samples prepared by this method,which seriously affect the performance of the workpiece and restrict the engineering application.The whole process tracking and testing from raw materials,preparation process through finished products is of great significance for improving and optimizing the quality of additive manufacturing products.Therefore,this paper summarizes the two major requirements of component detection and characterization technology in the field of metal additive manufacturing on the basis of a large number of literature research:(1)Rapid identification and review of metal powder raw material ingredients to quickly determine raw material batches and avoid the occurrence of mixtures.(2)The analysis of distribution of multi-element components in the larger analysis area of the finished workpiece to understand the homogeneity of sample composition and assist in determining the cause of defects,so as to guide the optimization of the manufacturing process.However,these are the needs that cannot be met with the existing technology.Laser-induced breakdown spectrometer(abbreviated as LIBS)has the characteristics of fast analysis speed,simultaneous analysis of multiple elements,unconstraint from sample status,small excitation light spot,and practicable analysis in harsh environment.It has great potential in the above analysis requirements.In this paper,firstly,a self-developed laser-induced breakdown spectrometer was used to study the quantitative analysis method of stainless steel powder materials for metal additives manufacturing.Based on the comparison of homogeneity,spectral signal intensity and stability of four sample preparation methods,die-pressing method was selected as the sample preparation method.Through the successive optimization of sample preparation mould,pressure and laser spectrum analysis conditions,the optimum preparation and analysis conditions were determined as follows:polyethylene mould,140 t of sample-making pressure;laser source pump lamp voltage 1.32 kV;Q-switching delaying 265?s;spot size 250?m;sample chamber was filled with high purity argon and atmospheric pressure 5900 pa;denudation mode was 5 times of denudation signal collection following 10 times of pre-denudation;The delay conditions were Fe,Ni,Cr,Si,Ti 0.3?s,Mo,Sn 0.6?s,Mn,Co,C,S 0.9?s,and W 1.2?s.Under the same conditions,calibration curves were drawn with a series of block stainless steel standard samples of matched components.The measurement of eight elements in stainless steel powders 316L and JY-Fe45A in the above method showed that the relative standard deviation of all the elements were approximately within 10%with a satisfaction of sensitivity.It can be seen that each element can reach the level of quantitative analysis.This method was simple to operate and had a low requirement on analysis environment.The time from ICP sample dissolution to the end of the test was reduced from hours to less than 10 minutes.The results showed that the powder direct quantitative analysis method established in this paper can be used as a rapid test method for powder raw materials of metal additive manufacturing.On the basis of the component gradient stainless steel sample prepared by laser cladding and multi-route powder feeding process,the element distribution quantitative analysis method of elements in a larger analysis area was attempted.The optimized LIBS analysis conditions were as follows:pumping lamp voltage 1.30 kV;Q-switching delaying 280?s;spot size 200 um;sample chamber filled with high purity argon,atmospheric pressure 6200 pa;denudation mode being 15 times of denudation signals collection after 0 pre-denudation.The calibration curve was drawn under the same conditions.Through fixed-point analysis and high-precision scanning analysis,the quantitative analysis of the composition distribution of large-scale samples was realized.Using this method,the quantitative information of the composition distribution of eight main elements in the deposition surface of 1~#and 2~#workpieces prepared by different powder feeding methods was obtained.Spark-OES and Spark-OPA were respectively used to compare the accuracy of fixed-point quantitative analysis and element distribution analysis.The results show that this method realizes the layer-by-layer analysis of additive manufacturing samples by virtue of high spatial resolution.The results of component distribution visually indicate that the powder feeding process of 2~#sample is more suitable for the preparation of component gradient samples,and the problems in the process of 1~#sample manufacturing are revealed.Based on the information of energy spectrum and composition distribution of scanning electron microscopy,the causes of repeated crack bands in two workpieces were analyzed and explained.The results show that the quantitative analysis method of element distribution established in this paper can be used as a means of quality evaluation for the samples made of metal additives. |
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