Study On Nondestructive Testing Of Defects In Inconel 718 Components Manufactured By Selective Laser Melting

Selective Laser Melting(SLM)is one of the most important additive manufacturing technologies for metal materials.Inconel 718 material has high yield strength at high temperature,good plasticity and good microstructure stability.Through the repeated scanning,melting and solidification process of Inconel 718 powders by the laser source,customized design,development and production of parts can be realized,and rapid manufacturing can be achieved.At present,SLM technology has been widely used in the processing of high-temperature components with complex structures in aerospace,national defense equipment and power equipment.The results show that the defects of SLM parts,such as cracks and pores,affect the performance of the parts seriously.Because the structure and defect characteristics of SLM parts are different from those of traditional metal parts,it is impossible to use the traditional defect detection method of metal parts.Therefore,it is imperative to explore the defect detection method of SLM parts by selective laser melting.Laser ultrasonic technology is a nondestructive testing technology with nondestructive and noncontact characteristics.At the same time,it has two major technical advantages of high sensitivity(sub-optical nanometer order)and high nondestructive testing frequency bandwidth(GHz),which can meet the unique inspection requirements of SLM products.The main contents of this paper are as follows:(1)The laser ultrasonic finite element simulation model of Inconel 718 specimens was established using COMSOL Multiphysics 5.5 software,and the simulation results were compared with or without defects.It was obtained that the through-hole defects had a reduction effect on the peak of the transverse wave echo after the transmission effect.And the crack defect has an enhancement effect on the surface wave echo peak after the reflection effect.(2)The finite element simulation models of through-hole and crack defects were established respectively,and the process of ultrasonic wave excited by laser in Inconel 718,the encounter and interaction process of ultrasonic wave and material defect were numerically simulated.The size and location of the defect can be evaluated by observing the change of the peak value at a specific position in the simulated ultrasonic echo waveform.(3)The Inconel 718 specimens with different defect parameters were experimentally tested by using the laser ultrasonic testing platform.By analyzing the ultrasonic waveforms measured in the experiment,the influence laws of radius and depth on the flaw detection of through hole and the influence laws of width and depth on the flaw detection of crack were obtained.In this paper,through hole defects and crack defects of Inconel 718 parts are studied from two parts of finite element numerical simulation and experiment.The conclusions laid a foundation for the practical application of laser ultrasonic defect detection.