Research On Nondestructive Testing Technology Of Selective Laser Melted Titanium Alloy Components

Titanium alloy parts have the advantages of high strength,high corrosion resistance,high heat resistance and so on.It has a broad development prospect in aerospace,medical devices,automobile industry and other fields.With the development of laser technology,selective laser melting(SLM)has become an effective method for forming titanium alloy with high efficiency and quality.Turbulence in the molten pool and other factors will lead to different types of defects in SLM forming titanium alloy parts.Some defects are too small or concentrated,which brings difficulties to the detection and statistics.In this paper,the nondestructive testing method for internal defects of SLM titanium alloy parts is studied.The types,sizes,morphologies and common locations of potential metallurgical defects in SLM titanium alloy parts were analyzed.The formation mechanism of defects such as pores,cracks and inclusions was clarified.Based on Industrial CT detection technology,the relevant detection parameters and procedures for different types of defects were standardized,The main research contents and achievements are as follows:(1)Performance research and verification of industrial CT system.The main influencing factors of industrial CT system performance are analyzed theoretically,and the influence of different detection parameters on CT imaging quality is expounded,which lays a theoretical foundation for the standard selection of subsequent detection parameters;This paper analyzes the possible sources of uncertainty in CT detection,establishes the mathematical model of CT uncertainty evaluation,determines the uncertainty of industrial CT selected in this experiment,and reveals the main sources of uncertainty in CT system.The results show that the main source of uncertainty in CT detection is scanning indication error,which is within the allowable range;The density resolution and spatial resolution of the industrial CT were measured to ensure that the system performance of the industrial CT can meet the requirements of SLM titanium alloy parts detection technology.(2)Experimental study on defect detection of SLM titanium alloy parts.The typical defect types and their causes in SLM titanium alloy were systematically studied;The influence of various detection parameters of CT system on the image quality of defect CT is analyzed;The internal defect detection technology of SLM titanium alloy parts by CT was developed.The results show that the improvement of density resolution is beneficial to improve the image contrast to distinguish small-size defects or materials with similar density,but limited by the rated power of the X-ray tube,the improvement of density resolution will lead to the decline of spatial resolution,which is generally suitable for the detection of inclusions and small-size pore defects in SLM titanium alloy parts;The improvement of spatial resolution is conducive to the display of defect details,but limited by the detection limit of detector and the rated power of ray tube,the improvement of spatial resolution will cause the decline of density resolution,which is generally suitable for the detection of crack defects and general size pore defects in SLM titanium alloy parts.(3)Research on the influence of forming precision of the internal hole structure of SLM titanium alloy on the forming process.The test technology for the forming accuracy of the internal hole structure of SLM titanium alloy parts was developed,and the influence of the inclination on the forming accuracy of the internal hole structure of SLM titanium alloy parts was studied.Industrial CT was used to observe the internal structure of the part,and a reverse three-dimensional model was established,which was imported into the Poly Works software for fitting and comparison with the design model,so as to detect the deviation degree and surface quality of the internal hole structure overhanging surface of the part.The results show that the inclination has a great influence on the forming accuracy of the internal hole structure of SLM titanium alloy parts;When the inclination increases to 50 ° The results show that the deviation of the surface of the inner hole structure of SLM titanium alloy parts becomes smaller and the printing quality is improved obviously;However,when the inclination continues to increase,the deviation degree of the inner hole structure of SLM titanium alloy parts becomes larger and the printing quality decreases obviously.(4)SLM titanium alloy parts nondestructive testing rules.The detection steps and corresponding CT detection parameters of typical defects of SLM titanium alloy parts are summarized.The sample information table,detection demand table,CT parameter selection table and other tables are formulated.The evaluation rule table is formulated according to the defect detection results of SLM titanium alloy parts,which is convenient for relevant laboratory personnel to grade the tested SLM titanium alloy parts.