Internal Defects Detection And The Effect Of Defects On Mechanical Properties In Additive Manufacturing

The internal defects of additive parts have an obvious influence on the mechanical properties of materials,however,the parameter setting before ultrasonic testing,the display of defects after testing and the mechanism of internal defects on the mechanical properties are not perfect.In order to detect the internal defects of additive manufacturing more accurately and clearly,and at the same time reveal the mechanism of the influence of large internal defects on mechanical properties.Therefore,ultrasonic inspection is used as the main method of nondestructive testing for laser deposited TA15 titanium alloys by in this paper,with the following four main parts:The acoustic properties and ultrasonic parameters of the material can be detected by prefabricating the same horizontal through hole defects.The results indicate that the forged samples have higher sound velocities than laser deposited samples,and there is little difference between the detection directions;the sound velocity of the laser deposited samples is higher than that of the double-annealed samples,and at the same time they all show the characteristics that the sound velocity in the X direction is higher than that in the Z direction,and the amplitude curve of the defects have a good correspondence with the speed of sound velocity;after analyzing the structure characteristics,it is found that the attenuation degree of ultrasonic propagation inside the deposited part is higher than that of the forged part,and the longitudinal wave sound velocity increases with the increase of the length-width ratio of lath shape a phase,and the attenuation coefficient shows the opposite law.Using the results of sound velocity detection,three-dimensional reconstruction of the flatbottomed hole defect inside the laser-deposited TA15 titanium alloy longitudinal wave sound velocity detection comparison test block is used to obtain effective information of the defect,and the reconstruction is based on Matlab R2018a software.The results indicate that the algorithm allows a preliminary three-dimensional reconstruction of the flat-bottom hole defects,and the calibration results are verified to be within an acceptable error range.Influence of internal defects on fatigue performance is based on artificial prefabrication of internal hole defects,comparison of high cycle fatigue tests at high and low levels of stress by comparison with artificially defect-free specimens.The results indicate that the presence of artificial defects can significantly reduce fatigue life,so much so that the reduction at the same stress level is more than 95%,and the crack propagation zone is similar to the brittle fracture characteristics,which is a plane perpendicular to the load direction,and the transient fracture zones all show the characteristics of ductile fracture.The association between ultrasonic sound speed and performance was investigated using different microstructure samples as the test objects.The results indicate that the microhardness and longitudinal wave sound velocity will change under different heat treatment systems,and the two show an approximately linear decreasing relationship;as heat treatment does not change the strength of TA15 titanium alloy significantly,the correlation between tensile strength and sound velocity is not obvious.