The Research On The Defect Detection And Evaluation Of Laser Deposition Parts

Inevitably there are defects in the interior of laser-deposited parts,and in order to ensure its reliability,the defect detection are particularly important.In this paper,as for the internal defects of laser-deposited parts,ultrasonic detection method that based on the knowledge of the influence of its microstructure on ultrasound detection,is used to study the enhanced recognition of tiny and low-contrast defects and the attenuation of ultrasonic waves in different detection directions.Firstly,the acoustic properties of laser deposited TA15 titanium alloy were studied.It is found that the coarse ?-columnar crystals and the ?-layers accumulated at the grain boundaries are the main factors causing the attenuation of ultrasonic scattering,and combined with the reflection and scattering of the defect itself,therefore,they cause difficulty in the identification of weak and small defects in laser-deposited parts when ultrasonically detecting.Then,based on the discrete wavelet transform,an algorithm is proposed to enhance the tiny and low-contrast defects in the ultrasonic images of laser deposited TA15 alloys,in which the Penalized soft threshold is used to denoise the high-frequency detail information of defects and the Gamma transform is enhance the contrast of low-frequency information of defects.After the algorithm is enhanced,the tiny and low-contrast defects in the C-scan image are obviously enhanced.The research results show that,the proposed algorithm has a better ability of tiny and low-contrast defect enhancement compared with those from the Gaussian filtering and fuzzy set enhancement theories.And the metallographic phase was confirmed that the defect image processed by the algorithm has no distortion in the size and distribution of the defect.Finally,the through holes were prefabricated on the laser deposition test block,and the ultrasonic attenuation test in different detection directions was carried out.The difference in the degree of ultrasonic attenuation and the difference in sound velocity in different detection directions are mainly studied.The experimental data shows that under the same ultrasonic detection parameters,the ultrasonic detection along the detection direction perpendicular to the laser deposition direction is more ultrasonically attenuated than the detection direction parallel to the laser deposition direction,and the ultrasonic sound velocity is small in this direction,which is the embodiment of its acoustic anisotropy.